Atomic-scale engineering of Pt shells on chiral Au nanoparticles for enhanced oxygen reduction

Abstract

Spin selection in chiral nanocatalysts enabled by the chiral-induced spin polarization (CISS) effect has emerged as a promising strategy for boosting the performance of the oxygen reduction reaction (ORR). However, achieving atomic-scale control of catalytically active surfaces on chiral nanostructures remains challenging. Herein, we demonstrate an approach for the atomic-level engineering of Pt shells on chiral substrates to enhance ORR performance. Pt shells with controlled thicknesses are deposited on chiral Au nanoparticles through a combined protocol of cyclic underpotential deposition and galvanic replacement reaction. This strategy not only maximizes the atomic utilization efficiency of Pt but also preserves the chiral geometry of the substrate and its chiroptical activity. For the chiral Au@Pt nanocatalysts, a volcano-type relationship is observed between the Pt shell thickness and ORR performance. The chiral Au@Pt nanoparticles exhibit a capability of spin polarization due to the CISS-like effect and competitive ORR activities. This work establishes a route for fabricating catalytically active chiral nanocatalysts with CISS-like effects, thereby laying a foundation for the development of advanced spin-selective electrocatalysts.

Spin selection via chiral-induced spin polarization in chiral nanocatalysts represents a promising route to enhance oxygen reduction reaction activity. Here, the authors report a Pt shell number engineering strategy on chiral Au substrates to promote catalytic performance through spin polarization.

Introduction

Sustainable clean energy technologies, exemplified by fuel cells and metal-air batteries, have emerged as a crucial pathway for resolving contemporary environmental and energy challenges¹. However, the oxygen reduction reaction (ORR), a key cathodic reaction in such devices, is hampered by slow kinetics that impose significant limitations on overall energy conversion efficiency^2,3. Therefore, advancing the development of high-efficiency, stable ORR catalysts is of paramount priority^4,5. However, due to the inherent scaling relations among the adsorption energies of oxygen-containing intermediates, ORR exhibits a theoretical minimum overpotential of approximately 0.3–0.4 V⁴. Traditional catalyst design strategies are confined to working within this limit, primarily by modulating electronic structures and optimizing active sites^6,7. In recent years, the role of electron spin in catalytic reactions has attracted growing interest^8–11. The ORR initiates with triplet ground-state oxygen molecules and produces singlet-state products, proceeding through a four-electron transfer mechanism. In conventional materials, the populations of spin-up and spin-down electrons are balanced. To satisfy the spin-asymmetric electron transfer requirement of this reaction, extra energy is consumed for electron spin flipping. If the transport of electrons with a specific spin orientation can be promoted, a spin-polarized current can be generated, which in turn matches the spin dependence of the ORR⁹. Although numerous studies have validated the feasibility of spin manipulation using external magnetic fields⁸, the chiral-induced spin selectivity (CISS) effect provides an alternative approach for the control of electron spin.

The CISS effect refers to the phenomenon where the passage of electrons through a chiral structure couples their spin direction with linear momentum, resulting in spin-polarized transport^12–17. Spin selection in chiral nanocatalysts enabled by the CISS effect has emerged as a promising strategy for boosting the performance of oxygen electrocatalysis^18–26. Particularly, intrinsically chiral inorganic nanomaterials have risen as a compelling chiral platform^27–33, offering tremendous application potential in the fields of catalysis^34–37. Thus, we have recently proposed a supported catalyst strategy: intrinsically chiral Au nanoparticles (NPs) are utilized as spin-selected substrates to transfer spin-polarized electrons to highly active achiral catalysts anchored on their surfaces, where the latter undertakes the catalytic function³⁸. This strategy broadens the design scope for chiral nanocatalysts and enables further performance optimization through the integration of principles derived from traditional catalyst design. While catalytically active chiral materials such as Pt or Pd can be synthesized through a dedicated synthetic approach very recently^39–42, achieving atomic-scale control of catalytically active surfaces on chiral nanostructures with preserved chiroptical activities remains a challenge yet to be addressed.

Atomic-level control over nanocatalysts has emerged as one of the key research directions in catalysis, featuring substantial scientific research significance and application potential in diverse catalytic reactions^43,44. Although single-atom catalysts theoretically offer the highest atomic utilization, it is still quite difficult to effectively integrate them with chiral metallic supports due to the instability of chirality^22,44. In contrast, constructing atomically thin catalytic shells on metallic NPs presents a more viable alternative, which has been broadly used in the design of Pt-based catalysts for enhanced ORR^45–49. For instance, a Pt monolayer can be constructed on Au surfaces through a protocol of cyclic underpotential deposition (UPD) of Cu, followed by a galvanic replacement reaction (GRR) between Cu and Pt^46,50,51. Such control over atomic-level shells not only significantly enhances atomic utilization but also offers better stability of hybrid metallic catalysts^48,52,53. Furthermore, since the strength of the CISS effect in chiral materials is closely related to their structural chirality, a thin shell minimally perturbs the chiral structure of the substrate, thereby helping to preserve its capability toward spin polarization of electrons^22,38. Meanwhile, the chiroptical activities of chiral metallic NPs^54–59, characterized by circular dichroism (CD) spectroscopy, can also be well-preserved through the atomic-scale engineering of a thin Pt shell compared to other methods of creating chiral Pt structures^39,40,42. Thus, atomic-scale engineering of the Pt shells on chiral NPs represents an important step toward the development of advanced spin-selective electrocatalysts.

In this work, we report an atomic-level engineering strategy for Pt shells on intrinsic chiral substrates to boost ORR performance. Specifically, Pt shells with precisely controlled thicknesses were deposited on chiral Au NPs via a combined UPD and GRR protocol. This approach maximizes Pt atomic utilization, retains the substrate’s chiral geometry and corresponding strong chiroptical activity. For chiral Au@Pt nanocatalysts, a volcano-type correlation between Pt shell thickness and ORR performance was observed. Notably, they exhibited high spin polarization capability, attributed to the significant CISS-like effect. Compared with achiral counterparts and commercial 20% Pt/C catalysts, the chiral Au@Pt nanocatalysts showed competitive ORR activity, with mass and specific activities enhanced by 4.8-fold and 7.4-fold, respectively. This work not only shows a route to fabricate chiral nanocatalysts with precise control of active sites at the atomic level but also provides an important knowledge framework that guides the design of spin-selective electrocatalysts.

Results

Atomic-level engineering of Pt shells on chiral Au NPs

As it is widely demonstrated, a Pt monolayer can be constructed on Au surfaces through a protocol of cyclic UPD of Cu, followed by GRR between Cu and Pt(II) tetrachloride complex (Fig. 1a)⁵¹. Therefore, we first investigated the UPD process of Cu atoms on chiral Au vortex cube (VC) NPs to verify the feasibility of our proposed approach (Figs. 1b, c and S1). Chiral Au NPs with a structure of VC were prepared based on a seed-mediated chiral growth method using L/D-Cys (cysteine) as the chiral inducer (See details in Supplementary Information)⁶⁰. As shown in Fig. 1b, c, cyclic voltammetry (CV) scans of a glassy carbon electrode (GCE) coated with Au VC NPs in an electrolyte containing Cu²⁺ (CuSO₄) revealed two distinct reduction stages. A slight increase in cathodic current was observed around 0.45 V, which quickly saturated to form a saturated plateau. This indicates that a small amount of Cu deposition occurs at potentials positive to the equilibrium potential for Cu²⁺/Cu (E_Cu²⁺/Cu), confirming the UPD of Cu on Au VC NPs. As the potential was swept further negative beyond the equilibrium potential, a substantial reduction current appeared, corresponding to the bulk deposition of Cu. In contrast, a bare GCE in the same electrolyte only exhibited the latter bulk deposition process, confirming that Cu UPD does not occur on GCE (Fig. S1). This difference arises because the UPD process requires a stronger interaction between the deposited metal atoms and the substrate than between the deposited atoms themselves, a condition satisfied between Au and Cu atoms, but not between Cu and the GCE surface⁵¹.

Fig. 1. Atomic-level engineering of Pt shells on chiral Au NPs.

a Schematic illustration of the synthetic strategy from chiral Au VC to chiral Au@Pt VC with a tunable layer of Pt shell. Pt shells with precisely controlled thicknesses (1–10 atomic layers) were deposited on chiral Au VCs through a combined protocol of cyclic underpotential deposition (UPD) and galvanic replacement reaction (GRR). Au@Pt VC-nL represents a chiral Au@Pt VC with an n-layer of Pt shell. VC Vortex Cube. b CV curve of an Au L-VC modified GCE in an Ar-saturated 0.1 M H₂SO₄ solution containing 2.0 mM CuSO₄ at a scan rate of 50 mV s⁻¹. The CV curve shows two pairs of redox peaks (R₁-O₁ and R₂-O₂). The peak R₁ at 0.41 V is attributed to the Cu UPD process, and its corresponding oxidation peak appears at 0.56 V. Another cathode peak appears when the potential is lower than 0.2 V, which can be attributed to the reduction of bulk Cu, and its corresponding oxidation peak appears at 0.35 V. c CV curve of the Cu UPD region on the chiral Au VC NPs. d Open-circuit potential variation of Au L-VC NPs and GCE during the GRR of Pt. All measured results are presented without iR correction. Source data for this figure are provided as a Source Data file.

Based on the above findings, a potential of 0.4 V was selected for the UPD of Cu on chiral Au VC NPs. During deposition at this potential, the cathodic current decreased rapidly and stabilized, indicating that the UPD of Cu on the Au VC NPs was completed within a very short timeframe (Fig. S2). The subsequent GRR of Cu by Pt(II) tetrachloride complex is a spontaneous process, which can be monitored through the open-circuit potential (OCP)⁵¹. As the UPD-deposited Cu layer on the Au surface was galvanically replaced by Pt, the OCP gradually increased. Once the replacement was complete and the surface state stabilized, the OCP reached a steady value (Figs. 1d and S2). In this case, a monolayer of Pt shell was constructed on the surface of Au VC NPs to form chiral Au@Pt VC NPs. As schematically illustrated in Fig. 1a, by sequentially repeating the Cu UPD and GRR steps, Pt atomic layers can be deposited onto the surface of the chiral Au VC NPs in a controlled, layer-by-layer manner (VC-nL: n can be 1–10 atomic layers). Importantly, this approach allows to effectively preserves the original chiral nanostructure of the Au VC substrate.

Construction and characterization of chiral Au@Pt VC NPs

The geometric and compositional features of chiral Au and Au@Pt VC NPs were carefully characterized using SEM, TEM, STEM, and EDS mapping (Fig. 2). Both chiral Au and Au@Pt VC-5L (5 L: 5 atomic layers of Pt) NPs exhibit mirrored and twisted structures, whereas the racemic ones showed a concave but non-twisted morphology (Figs. 2a, b and S3). Importantly, after depositing 5 atomic layers of Pt, the underlying chiral structure remained virtually unchanged, indicating that the Pt shell replicated the original morphology of the chiral Au VC NPs (Figs. 2b and S4). Note that the chiral surfaces of VC NP can be attributed to the asymmetric growth of a set of high-index facets with opposite handedness, induced by chiral molecules. To determine the specific chiral facet of the chiral Au VC NPs, we analyzed high-magnification TEM images of the achiral Rac-Au VC NPs along the [100] zone axis. By measuring the interfacial angles between different facets and comparing them with constructed models, we identified these high-index facets of chiral VC NPs as {521} (Fig. S5)^61,62. Furthermore, aberration-corrected high-resolution TEM images confirmed the presence of the Pt layer on the surface of Au VC NPs (Figs. 2c and S6). A distinct atomic layer misaligned with the Au lattice was observed, with an average width of ~1.0 nm, consistent with the expected thickness of 5 Pt atomic layers (Figs. 2d and S6). STEM images and EDS elemental maps provided further confirmation of the multi-layer Pt atom distribution on the surface of chiral Au VC NPs, showing a thin outer shell composed of Pt atoms (Figs. 2e and S6–S8).

Fig. 2. Construction and characterization of chiral Au@Pt VC NPs with ~5 atomic layers of Pt shell.

a, b SEM images of (a) chiral Au VC NPs and (b) chiral Au@Pt VC-5L NPs (5L: 5 atomic layers). The insets show the geometric models. c TEM image of individual chiral Au@Pt VC-5L NPs. d High-resolution TEM image of the Au and atomic layered Pt area of chiral Au@Pt VC-5L NPs. This area is marked in (c). The insets are the fast Fourier transform (FFT) pattern of the selected Au domain as marked in the image. e HAADF-STEM image and corresponding EDS elemental maps (Au and Pt) of the local corner of chiral Au@Pt VC-5L NP. f The CV curves of chiral Au VC NPs and chiral Au@Pt VC-5L NPs. The peak areas of Pt-H_abs and Pt-H_des are observed and marked for chiral Au@Pt VC-5L NPs. The schematic diagram on the right illustrates the adsorption process of hydrogen on the surface of Pt in an alkaline electrolyte environment. g Comparison of the atomic percentage of Pt and Au of chiral Au@Pt VC-5L NPs obtained from the XPS and EDS measurements, respectively. h, i Experimental and simulated g-factor spectra of chiral Au VC NPs and Au@Pt VC-5L NPs. All measured results are presented without iR correction. Source data for this figure are provided as a Source Data file.

The presence of a Pt shell on the surfaces of chiral Au VC NPs can also be electrochemically characterized by hydrogen adsorption/desorption (Fig. 2f). Due to the strong hydrogen adsorption capability of Pt, the approximate loading of Pt can be assessed by the hydrogen adsorption/desorption peaks⁴⁹. As shown in Fig. 2f, CV scans of the samples in the potential range of 0.05–0.95 V (vs. reversible hydrogen electrode (RHE)) revealed that the pristine Au VC NPs exhibited only oxygen adsorption/desorption features at higher potentials. In contrast, after Pt deposition, distinct hydrogen adsorption/desorption peaks appeared in the range of 0.05–0.4 V. Since Au exhibits negligible hydrogen adsorption in this region, these features are exclusively attributed to Pt. Furthermore, the shift in the oxygen adsorption/desorption features originally belonging to Au suggests the formation of a dense, continuous Pt shell that fully encapsulates the Au core. The above conclusion is further supported by X-ray photoelectron spectroscopy (XPS) characterization of the chiral Au@Pt VC-5L NPs (Fig. S9). Considering that the typical probing depth of XPS ranges from 5 to 10 nm, this analytical technique primarily reflects the surface composition of the particles. The XPS results revealed a relatively high surface Pt atomic ratio of 15.4% (Fig. 2g). Based on the Pt shell thickness of ~1 nm measured via TEM and an assumed XPS probing depth of ~5.0 nm, the theoretically calculated surface Pt atomic ratio is approximately 20%. The good consistency between the experimental and theoretical values verifies the successful formation of a dense Pt shell with a thickness of ~5 atomic layers. In contrast, EDS analysis, which probes the entire particle volume, indicated a much lower overall Pt atomic ratio of only ~1.5% (Fig. 2g). Thus, our experimental findings demonstrated the effectiveness of our strategy in minimizing Pt usage while achieving full surface coverage on the chiral substrate.

Chiral Au NPs exhibit significantly enhanced optical chirality due to their strong light-matter interaction through localized surface plasmon resonance^63–67. In contrast, intrinsically chiral Pt-based NPs usually demonstrate weak chiroptical activity, a phenomenon rooted in their inherent poor response to light irradiation^38–42. In our case, as shown in the g-factor spectra, the chiroptical properties of the chiral Au VC NPs were nearly unaffected after the Pt coating, indicating that the Pt layer maximally preserves the intrinsic chiroptical response (Figs. 2h and S10). To gain more quantitative insights into the structure-property relationship, we further simulated the g-factor spectra as well as the near-field distributions of chiral Au and Au@Pt VC NPs with tunable Pt atomic layers by using the commercial COMSOL Multiphysics software (See details in Supplementary Information, Fig. S10). The g-factor slightly decreased as the thickness of the Pt shell increased in the range of 3–5 atomic layers (Figs. 2i and S10), which agrees well with our experimental observations. Furthermore, three-dimensional near-field simulations demonstrated that upon coating with the ultrathin Pt shell, the electromagnetic field intensity remained virtually unchanged and extended into the outer Pt layer (Fig. S10). Thus, our results demonstrate that this strategy not only maximizes the atomic utilization efficiency of Pt but also preserves the chiral geometry of the substrate as well as its chiroptical activity.

To further verify that the chiral Au@Pt VC NPs successfully retain the chiral surface structure of the parent Au VC NPs, we conducted experiments on the electrooxidation of L/D-DOPA (3,4-dihydroxyphenylalanine) enantiomers using chiral Au@Pt VC NPs as catalysts (Fig. S11). The electrocatalytic oxidation of enantiomers, including DOPA, glucose, tyrosine, and tryptophan, has been proven to be used as a benchmark reaction for assessing the enantioselectivity of chiral nanocatalysts due to their enantioselective interaction with enantiomers at interfaces^68–71. Thus, our results showed that L-Au VC NPs generated a larger oxidation current for D-DOPA, indicating that D-DOPA is more readily recognized on the L-Au VC NPs surface, and vice versa for D-Au VC NPs, which agrees with previous results^69–71. The enantioselectivity persisted even after depositing ~3 atomic layers of Pt (Fig. S11), showing that the deposited Pt atoms largely preserve the chiral surface features of the underlying Au VC NPs. We further extend our strategy to fabricate other catalytically active chiral surfaces, such as chiral Au@Pd VC NPs with a tunable atomic layer of Pd shell (Fig. S12). Moreover, the chiral substrate can be tailored by using other chiral Au NPs, for example, chiral Au rhombic dodecahedron (RD) NPs with a distinct chiral geometry and surface (Fig. S13). Overall, the above results strongly show the robustness and versatility of our strategy in achieving atomic-scale engineering of the catalytically active shells on chiral Au substrates.

ORR performances of Au@Pt L-VC-nL NPs with a tailored Pt shell

To investigate the impact of varying Pt shell thickness on the ORR catalytic activities, we prepared chiral Au@Pt VC-nL NPs with different numbers of Pt atomic layers (Fig. 3a). By comparing the Cu deposition current curves during UPD and the OCP changes during the GRR, it was observed that as the number of Pt layers increased, the cathodic current during Cu UPD gradually increased. Concurrently, the OCP during GRR also increased and eventually stabilized near 0.88 V (Fig. S14). Among the synthesized catalysts, chiral Au@Pt VC NPs with 1, 3, and 5 atomic layers of Pt shell were selected for XPS analysis to probe the influence of Pt thickness on their electronic structure (Fig. S15). The Au 4f spectra of chiral Au@Pt VC NPs exhibited two sets of peaks. The peaks with lower binding energy correspond to metallic Au, while the peaks with higher binding energy are assigned to oxidized Au species. The presence of oxidized Au species can be attributed to electron transfer from Au to Pt at the Au-Pt interfaces^51,53, which is not observed in the XPS spectra of chiral Au VC NPs (Fig. S16). We found that the proportion of oxidized Au decreased with increasing Pt layer thickness, indicating a reduction in the electron transfer from Au to Pt at the interface. We propose that when the Pt layer is thin, the Pt atoms adjacent to the Au core also serve as the outermost surface atoms. In this configuration, the surface Pt atoms feature numerous unsaturated coordination sites, which exert a strong attraction on electrons from the interior. As the Pt shell thickens, the electron-withdrawing effect at the interface gradually weakens. Additionally, the surface atomic ratios of Pt for Au@Pt VC-1L, Au@Pt VC-3L, and Au@Pt VC-5L NPs were calculated from the Au and Pt peak areas to be 3.4, 11.4, and 15.4%, respectively (Table S1). Thus, the presence of multi-layers of Pt atoms on chiral Au NPs can also be supported by the electrochemical data (Fig. S14) and XPS results (Fig. S15). While the atomic layer (1–10 L) construction of the Pt layer on chiral Au NPs might not be perfect due to the local curved surface of the chiral Au NPs, our experimental results still demonstrate the capability of tuning the atomic-scale Pt layer on chiral Au NPs with diverse thicknesses.

Fig. 3. The ORR performances of Au@Pt L-VC-nL NPs with a tailored Pt shell.

a Schematic illustration of the atomic-scale engineering of the Pt shells on chiral Au VC NPs through the integrated procedure of UPD and GRR. b LSV curves (upper and lower panels: ring and disk current density), c H₂O₂ selectivity, d Nyquist plots, and e Tafel plots in ORR measured by rotating ring-disk electrode (RRDE) using Au@Pt L-VC-nL NPs as catalysts, respectively. The LSV curves were measured in O₂-saturated 0.1 M KOH solution with a scan rate of 5 mV s⁻¹ at room temperature (25 ± 1 °C). f Comparison of specific activities and mass activities of Au@Pt L-VC-nL NPs with tailored Pt shells. All measured results are presented without iR correction. The error bars are obtained from at least 3 measurements that used different batches of catalysts. Source data for this figure are provided as a Source Data file.

Subsequently, we evaluated the ORR performance of the Au@Pt VC-nL NPs catalysts in alkaline conditions using a rotating ring-disk electrode setup (See details in Supplementary Information, Fig. 3b–f). A comparison of the ORR polarization curves revealed a significant enhancement in activity after depositing a single atomic layer of Pt on the L-Au VC NPs, indicating that the active sites had shifted from Au to Pt (Fig. 3b). Similar results of enhanced ORR performance after coating a Pt layer can also be observed under acidic conditions (Fig. S17), further confirming that Pt is the catalytically active site. The ORR activity continued to improve as the Pt layer number increased up to 3. However, a decline in performance was observed when the Pt layers increased to 5, and a more pronounced decrease occurred at 10 layers (Fig. 3b). A similar conclusion was also obtained after comparing the Tafel slopes among Au@Pt VC-nL NP with a tailorable Pt atomic layer as catalysts (Fig. 3e). Our results suggest that for this system, the optimal activity is achieved at approximately 3 Pt atomic layers. In contrast, the percentage of H₂O₂ generated, calculated from the RRDE data, consistently decreased with increasing Pt layers (Fig. 3c), indicating an enhancement in the four-electron selectivity of the ORR. Electrochemical impedance spectroscopy results further showed that the charge transfer resistance of the catalysts decreases with increased Pt layers (Fig. 3d). Although these electrochemical results collectively demonstrate the benefit of increasing Pt layers for ORR, the observed activity trend of initial enhancement followed by a decline reflects the combined effect of multiple competing factors. XPS results reveal that electrons transfer from Au to Pt across the interface, which enhances the electron density at Pt sites and downshifts the d-band center of Pt, consequently attenuating the adsorption energy of oxygen-containing intermediates^72,73. Pure Pt resides in the over-strong adsorption regime on the ORR activity volcano plot; such electronic modulation moderately weakens the adsorption strength, thereby boosting ORR catalytic activity. When the Pt shell is merely one atomic layer thick, the electronic effect of the Au core is prominent, leading to an excessive downshift of the d-band center that compromises O₂ adsorption. With the increase in the number of Pt atomic layers, the electronic influence of the Au core on the outermost active Pt layers attenuates, mitigating the modulation effect. At the optimal Pt thickness, the adsorption energy attains the most favorable value, which corresponds to the maximum ORR activity. Another critical factor is the evolution of the surface structure of chiral Au@Pt NPs as the number of Pt layers increases (Fig. S18). We propose that chiral surface atomic features (e.g., step sites and defects) are gradually smoothed with Pt deposition. They eventually form low-index facets with lower intrinsic activity, leading to low ORR catalytic activities. It is also observed that at 10 Pt layers deposited, larger Pt clusters started to form on the surface, which is probably because Pt preferentially deposits at reactive edges and step sites during GRR (Fig. S18). Similar volcano-type trends were also observed in other core-shell electrocatalysts with a thin Pt layer for ORR^74–76.

To further assess the ORR performance of the chiral Au@Pt VC-nL NPs, we calculated the electrochemical surface area (ECSA) from the hydrogen adsorption/desorption region in the CV curves and determined the Pt mass loading through EDS (Fig. S19). The kinetic current density at 0.9 V (vs. RHE) was then normalized to the ECSA and the Pt mass to obtain the specific activity (SA) and mass activity (MA), respectively. Both MA and SA exhibited a volcano-shaped trend with increasing Pt layers, peaking at 3 layers, which is consistent with the prior conclusions (Fig. 3f). Notably, the SA calculated for the single-layer Pt catalyst was relatively high. This inaccuracy arises because the ECSA calculation uses the charge associated with a monolayer of hydrogen on polycrystalline Pt as the reference. The strong electronic influence of the Au substrate on the single Pt layer significantly alters its hydrogen adsorption behavior, making the derived ECSA unreliable. This effect diminishes as the Pt shell thickens, making the data for catalysts with 2 or more layers valid for comparison. We further performed CO stripping experiments to accurately determine the ECSA (particularly for chiral Au@Pt VC-1L NPs) for comparison (Fig. S20). CO strongly poisons Pt and is largely insensitive to the Au electronic effect, thus providing a more reliable ECSA. Our CO stripping results show that the ECSA increases only slightly with Pt layer number, without the dramatic variation seen in the H_upd data (Fig. S20). For Pt layers ≥2, both methods give similar ECSA values, also confirming that the H_upd method is reliable for thicker layers of Pt. Importantly, a volcano-type relationship between the Pt shell thickness and SA is also observed when using ECSA derived from the CO-stripping method. Similar volcano-type trends were also observed when using Au@Pt D-VC-nL and Rac-VC-nL NPs as catalysts for ORR (Figs. S21 and S22). To summarize, the observed volcano-type relationship between the Pt shell thickness and ORR performance can be attributed to the combined effect of the changes in electronic structure and atomic structure of Pt layers.

Spin polarization of chiral Au@Pt VC NPs

Beyond the regulation of ORR performance by the tailored Pt shell at the atomic scale, the role of chirality in this process is of particular interest. We previously demonstrated that chiral Au NPs exhibit CISS-like effects and can be used for the polarization of electron spin, which has also been reported by others^24,25,38. A comparison of samples with the same number of Pt layers but different handedness (L/D) reveals that the achiral Au@Pt Rac-VC-nL NPs exhibit significantly inferior ORR performance compared to their two chiral counterparts (Fig. S23). This underscores the non-negligible contribution of the CISS-like effect enabled by the chiral structure. Based on the optimization results from varying the Pt layers, we selected the catalyst with the optimal 3-layer Pt structure for further investigation. We employed magnetic conductive atomic force microscopy (mc-AFM) to quantify the capability of Au@Pt VC-3L NPs with different chirality in modulating the electron spins (Figs. 4 and S24). The AFM images show that the Au@Pt VC-3L NPs form a uniform and dense layer on the ITO substrate (Fig. 4a). Before measurement, a conductive AFM tip coated with CoCr was magnetized using a neodymium magnet. Current–voltage (I–V) curves were then recorded on different samples under an applied bias. The results demonstrate that for the Au@Pt L-VC-3L NPs sample, the measured current was significantly enhanced when the tip was magnetized with its magnetic moment pointing vertically upward. Conversely, when the tip magnetization was reversed, the current was strongly suppressed (Fig. 4b). The opposite relationship between magnetic field direction and current magnitude was observed for the Au@Pt D-VC-3L NPs sample (Fig. 4c). These experiments clearly prove that samples of different handedness selectively transmit electrons based on their spin orientation. In contrast, measurements on the achiral Au@Pt Rac-VC-3L NPs yielded similar current magnitudes regardless of the tip’s magnetization direction, confirming that only the chiral structure can modulate the electron spins through the CISS-like effect (Fig. 4d). It is worth noting that a current limit of ±5 nA was set during the tests to protect the AFM tip from melting under high current, which could degrade resolution. The spin-dependent anisotropy exhibited by the charge current can be characterized through a dissymmetry parameter g_c, defined by the relation:

$$gc=\left(I_{up}-I_{down}\right)/\left(I_{up}+I_{down}\right)\times 100\%$$ 1

Fig. 4. Spin polarization of monolayered chiral and racemic Au@Pt VC-3L NPs on an ITO substrate measured by magnetic conductive AFM (mc-AFM).

a Schematic illustration of the mc-AFM measurement of chiral Au@Pt VC-3L NPs on an ITO substrate. The red and blue spheres represent electrons with opposite spin directions. The arrow indicates the direction of the magnetic field (H) from the magnetic tip. On the right is the AFM image of the sample used in the test, clearly showing the monolayered structure of the chiral Au@Pt VC-3L NPs. b–d The averaged I−V curves of b Au@Pt L-VC-3L NPs, c Au@Pt D-VC-3L NPs, and d Au@Pt Rac-VC-3L NPs obtained from mc-AFM measurements. The tip is magnetized in the up and down directions, respectively. e Calculated g_c curves of chiral Au@Pt VC-3L NPs. Insets: Corresponding geometric models. The shadow region is the error bar that shows the standard deviations obtained from different locations and different samples for mc-AFM measurements. Source data for this figure are provided as a Source Data file.

Here, I_up and I_down denote the charge currents recorded under magnetizations aligned along the upward and downward directions, respectively. The g_c is closely correlated to the spin polarization (P_CISS) of chiral nanomaterials and has been widely adopted to characterize spin-filtering behaviors across diverse chiral material systems²⁶. Furthermore, calculation of the g_c revealed a high value of ~75% for chiral Au@Pt VC-3L NPs (Fig. 4e), indicating their strong spin-modulating capability. To ensure statistical reliability, over 50 I–V curves were randomly collected at different locations for each sample, and the average current was used for analysis (Fig. S24). We further compared the dissymmetry parameter g_c of chiral Au VC NPs and Au@Pt VC-nL (n = 1, 3, and 10) NPs on an ITO substrate measured by mc-AFM (Fig. S25). The g_c of Au L-VC NPs is ~70%, which is in line with other reports^38,77. Moreover, the g_c of Au@Pt L-VC-1L and Au@Pt L-VC-3L is very close to that of Au L-VC NPs, indicating the well-defined chiral geometry could maintain the CISS-like effect for the chiral Au@Pt VC NPs with an ultrathin Pt shell (1–3 layers). Notably, there may be a correlation between the thickness of the Pt shell (0–3 layers) and the g_c; however, we are not able to gain quantitative results because these changes in I–V curves are very subtle and the error bars of the data overlap (Fig. S25). In contrast, an obvious decrease in g_c (down to ~50%) for Au@Pt L-VC-10L (~ 2 nm), which could be attributed to the limited diffusion length of the Pt layer^78,79, the large spin-orbit coupling of Pt atoms, as well as the less well-defined chiral geometry due to the formation of small Pt islands at 10 layers. Thus, our experimental observations suggest that a thick Pt shell (~ 2 nm) would reduce the CISS effect of chiral Au@Pt VC NPs and may affect the ORR activities; however, we could not build a correlation between the spin polarization and ORR performance based on our current work.

Chiral Au@Pt VC NPs with a thin Pt shell for enhanced ORR performance

After experimentally demonstrating the CISS-like effect in the chiral Au@Pt VC NPs, we further investigated the enhanced ORR performance using chiral Au@Pt nanocatalysts compared to achiral ones and commercial Pt/C catalysts (Fig. 5). As it is anticipated, the chiral Au@Pt substrate could work as a spin selector by aligning the spin direction of electrons after they transfer to the Pt surfaces (Fig. 5a)³⁸. While the electrocatalytic performance is dependent on the surface structure of catalysts, the spin polarization of electrons induced by the chiral structure could also play an important role in oxygen electrocatalysis. First, with all other synthetic parameters carefully controlled, the facet structures induced by the two enantiomeric chiral molecules are expected to be similar, while the Rac-VC serves as a non‑chiral reference (Figs. S3 and S4). Afterwards, a multi-layer of Pt atoms was coated onto the chiral and achiral Au VC NPs using the same method. Thus, it is expected to have a very similar size and surface structure (high-index facets) for Au@Pt L/D-VC and Rac-VC NPs when using them for the ORR measurements. Second, under the above conditions, the observed activity difference between the enantiomorphic chiral catalysts and between each of them and the racemic reference can be reasonably attributed to the CISS effect. This attribution is further supported by a growing number of recent experimental studies^21–23,38. Also, the chiral Au and Au@Pt VC NPs show prominent spin polarization of electrons, as experimentally characterized by the mc-AFM measurements (Figs. 4, S24, and S25). Third, we further performed a comparative ORR experiment between the chiral Au VC NPs, their racemic counterpart, and the achiral Au RCO NPs (Fig. S26). The results show that the racemic VC sample, despite being achiral, exhibits slightly higher ORR activity than the achiral Au RCO. This modest enhancement can be attributed to differences in crystal or other morphological factors. Importantly, this facet‑induced enhancement is far less significant than the performance improvement imparted by chirality in our system. We also performed control experiments using other chiral and corresponding achiral NPs (AuAg alloy helical nanorods) as ORR catalysts, which further confirm the positive effect of chirality on ORR performance (Figs. S27 and S28). We believe this comparison provides strong evidence that the spin polarization of electrons induced by chiral structure is responsible for the improved ORR performance.

Fig. 5. Chiral Au@Pt VC NPs with a thin Pt shell for enhanced ORR performance.

a Schematic illustration of the chiral Au@Pt VC NPs with the integration of a catalytically active Pt shell with chiral Au NPs as an electron spin polarizer for driving the formation of H₂O rather than H₂O₂ during ORR. b LSV curves of disk electrodes and c The H₂O₂ selectivity in ORR measured by RRDE using different catalysts as marked. The LSV curves were measured in O₂-saturated 0.1 M KOH solution with a scan rate of 5 mV s⁻¹ at room temperature (25 ± 1 °C). d Tafel plots and e CV curves of chiral and achiral Au@Pt VC-3L NPs and commercial 20% Pt/C. f Comparison of specific activity and mass activity of the above catalysts. The error bars are obtained from at least 3 measurements that used different batches of catalysts. All measured results are presented without iR correction. Source data for this figure are provided as a Source Data file.

To demonstrate the practical potential of the design strategy involving chiral Pt-layer catalysts, we further compared them with a commercial 20% Pt/C catalyst (Fig. 5b). The results show that the chiral Au@Pt VC-3L NPs catalysts possess similar ORR activity, with their half-wave potential enhanced by ~34 mV compared to the achiral Au@Pt Rac-VC-3L NPs. Notably, even relative to the commercial Pt/C, the chiral Au@Pt VC-3L NPs exhibit a ~ 10 mV increase in half-wave potential (Fig. 5b). By regulating electron spin orientation through the CISS-like effect, the chiral Au@Pt-3L VC NPs effectively suppress the formation of the singlet-state product H₂O₂ (Fig. 5c). Although Pt itself already exhibits high four-electron selectivity, the chiral Au@Pt VC-3L NPs catalysts further reduce the H₂O₂ yield by ~2% compared to their achiral counterparts (Fig. 5c). As shown in Fig. 5d, the chiral Au@Pt-3L VC NPs also exhibit the smallest Tafel slope, which is in line with the above conclusion.

As previously mentioned, a major advantage of the thin Pt-shell catalyst design is the significant enhancement of Pt atomic utilization and the reduction in Pt usage. A comparison of CV curves confirms that the Pt loading in the Au@Pt VC-3L NPs is far lower than that in the 20% commercial Pt/C (Fig. 5e). Subsequently, the SA and MA of these catalysts were calculated using the current density at 0.9 V as the benchmark. The results show that both the SA and MA of the chiral Au@Pt VC-3L NPs catalysts are substantially higher than those of the achiral version. This benefit stems from the atomic-level Pt shell, which effectively preserves the chiral surface structure of the original Au VC NPs, thereby maximizing the spin polarization of the composite catalyst. Furthermore, compared to the commercial Pt/C catalyst, the SA and MA of our chiral catalyst are enhanced by factors of ~7.4 and ~4.8, respectively. We further evaluated the stability and performance of chiral Au@Pt VC-3L NPs and 20% commercial Pt/C as ORR catalysts (Fig. S29). After more than 5000 cycles, the ORR performance remained more than 95% of that of the initial tests for chiral Au@Pt VC-3L NPs, which is fourfold better than 20% commercial Pt/C, indicating stable electrocatalytic performance. While the stability of CISS-based chiral electrocatalysts has received relatively little attention, our results demonstrate that these chiral Au@Pt VC NPs employed as spin selectors exhibit good stability during long-term electrochemical tests. Overall, these results collectively demonstrate the practical application potential of the chiral Au@Pt NPs with a tailored ultrathin Pt shell as ORR catalysts. Moreover, considering the cost-effective chiral substrates in comparison to the chiral Au NPs used in this work, chiral Cu and MoS₂ substrates could be alternatives for practical applications in oxygen electrocatalysis^80,81, which inspires more systematic work.

In summary, we have developed an atomically precise deposition strategy based on a cyclic “UPD-GRR” process to fabricate ultrathin Pt shells on chiral substrates. Atomic-scale engineering of the Pt shell not only maximizes the atomic utilization efficiency of Pt but also accurately replicates and retains the chiral surface structure of the Au substrate. As a result, the as-prepared composite catalysts simultaneously exhibit competitive catalytic activity and robust chiroptical signals suitable for direct characterization, thereby offering an ideal platform for investigating the CISS effect. Electrochemical measurements further uncovered a “volcano-type” correlation, wherein the overall ORR performance first enhanced and subsequently diminished with the increase in Pt shell thickness. Among all the prepared samples, the Au@Pt VC-3L catalyst delivered the optimal ORR performance, with its MA and SA reaching ~4.8 and ~7.4 times those of commercial 20% Pt/C, respectively. This study establishes a crucial knowledge framework for the design of next-generation high-efficiency chiral electrocatalysts.

Methods

Chemicals and materials

Sodium borohydride (NaBH₄, 99%), L-ascorbic acid (AA, 99.9%), and potassium iodide (KI, >99%) were obtained from Sigma-Aldrich. Gold (III) chloride tetrahydrate (HAuCl₄·4H₂O, AR), potassium tetrachloroplatinate (II) (K₂PtCl₄, AR), sulfuric acid (H₂SO₄, GR), and potassium hydroxide (KOH, GR) were purchased from China National Medicines Corporation Ltd. Palladium (II) chloride (PdCl₂, 99%) was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Silver nitrate (AgNO₃, 99.9995% metals basis) was obtained from Alfa Aesar. Cetyltrimethylammonium bromide (CTAB, >98%), cetyltrimethylammonium chloride (CTAC, >95%), sodium oleate (NaOL, >97%), and cysteine hydrochloride monohydrate (L-Cys, D-Cys, >99%) were purchased from TCI. Copper dinitrate (Cu(NO₃)₂·3H₂O, >99%) and copper sulfate pentahydrate (CuSO₄·5H₂O, >99%) were purchased from Aladdin. Pt/C catalyst (20 wt.%) was purchased from Johnson Matthey. L/D-3,4-dihydroxyphenylalanine (L/D-DOPA) was purchased from Macklin Biochemical Co., Ltd. Cysteine-phenylalanine (L-CYP, D-CYP, >98%) and PBS solution (0.1 M, 500 mL) were purchased from Sangon Biotechnology. Nafion solution (D520) was purchased from E.I.Du Pont Company. The GCE was purchased from Tianjin Aida Hengsheng Technology Development Co., Ltd. All electrolytes should be prepared and used immediately, and any excess should be stored in a dark and dry place. All reagents were used as received without further purification. Millipore ultrapure water (18.2 MΩ resistivity) was used for all experiments.

Synthesis of Au seeds

Single-crystalline RCO was synthesized using a previously published seed-mediated growth method with slight modifications⁸². For the synthesis of single-crystalline Au NPs, colloidal Au seeds were first prepared by reducing HAuCl₄ with NaBH₄ in the presence of CTAC. Typically, 100 μL of 25 mM HAuCl₄ was mixed with 5 mL of 0.2 M CTAC solution and 4.9 mL of water. Then, 450 μL of ice-cold, freshly prepared 20 mM NaBH₄ was quickly injected into the mixture under magnetic stirring. The seed solution was stirred for 2 min and then left undisturbed for 1 h at 30 °C.

Synthesis of Au rhombicuboctahedron (RCO) nanoparticles (NPs)

For the Au RCO NPs growth solution, two vials labeled A and B containing the same composition were first prepared. The vials were then kept in a water bath set at 30 °C. For the synthesis of Au RCO: to both vials were added 5 mL of 0.2 M CTAC, 4.595 mL of water, 100 μL of 25 mM HAuCl₄ solution, and 30 μL of 1 mM KI in sequence. Finally, 220 μL of 40 mM AA was introduced to the vials for synthesis. The total volume of solution in each vial was set to 10.0 mL. Next, 55 μL of the Au seed solution was added to the growth solution in vial A with shaking until the solution color turned light red ( ~ 10 s). Then 55 μL of the solution in vial A was transferred to vial B with thorough mixing for ∼20 s. The solution in vial B was left undisturbed for 15 min at 30 °C for particle growth. The products were collected by centrifugation and re-dispersed in 1 mL of 1 mM CTAB for further use.

Synthesis of chiral Au vortex cube (VC) NPs

Chiral Au VC NPs were synthesized using a Cu²⁺-dominated seed-mediated chiral growth method that was developed by our group with slight modifications⁶⁰. Au VC NPs were prepared through the overgrowth of single-crystalline Au RCO in the presence of HAuCl₄, CTAB, AA, Cu(NO₃)₂, and L/D-Cys. In a typical procedure, 1 mL of single-crystalline Au RCO was first re-dispersed in 1 mL of 1 mM CTAB after being washed twice with water and used as seeds. The growth solution was prepared by sequentially adding H₂O (3.6 mL), HAuCl₄ (100 μL, 10 mM), and AA (475 μL, 0.10 M) into a CTAB (0.8 mL, 0.10 M) solution. After gently mixing the growth solution for 30 s, 20 μL of 0.10 mM L/D-Cys solution and 5 μL of 1 mM Cu(NO₃)₂ were added, followed by gentle mixing for 30 s. The growth of chiral Au NPs was initiated by adding 20 μL of Au RCO. The reactants were gently mixed for 30 s immediately after the addition of Au RCO and then left undisturbed at 30 °C for 2 h in a water bath. The obtained chiral Au VC NPs were centrifuged to remove unreacted reagents and were re-dispersed in a 1 mM CTAB solution for further characterization. The racemic (Rac) Au NPs were obtained by adding an equal amount of L-Cys and D-Cys. Achiral Au NPs were obtained in the absence of L/D-Cys without changing any other synthetic conditions. By using Cu²⁺ ions with different concentrations, chiral Au VC NPs with distinct geometric chirality and tunable optical chirality can be obtained.

Synthesis of chiral Au rhombic dodecahedron (RD) NPs

Chiral Au RD NPs were prepared through the overgrowth of single-crystalline Au RCO in the presence of HAuCl₄, CTAB, AA, and L/D-CYP⁶⁴. In a typical procedure, 1 mL of Au RCO was first re-dispersed in 1 mL of 1 mM CTAB after being washed twice with water and used as seeds. The growth solution was prepared by sequentially adding H₂O (3.116 mL), HAuCl₄ (100 μL, 10 mM), and AA (960 μL, 0.10 M) into a CTAB (0.8 mL, 0.10 M) solution. After gently mixing the growth solution for 30 s, 4 μL of 0.1 mM L/D-CYP solution was added, followed by a gentle mixing for 30 s. The growth of chiral Au RD NPs was initiated by adding 20 μL of Au seeds. The reactants were gently mixed for 30 s immediately after the addition of Au seeds and then left undisturbed at 30 °C for 2 h in a water bath. The obtained chiral Au RD NPs were centrifuged at 3000 rpm for 5 min to remove unreacted reagents and were re-dispersed in a CTAB (1 mL, 1 mM) solution for further use.

Synthesis of chiral Au@Pt VC-nL NPs

Chiral Au@Pt VC-nL NPs were prepared by the underpotential deposition (UPD) of monolayered Cu atoms on the surface of Au VC NPs, followed by a GRR with Pt ions. The reaction was performed using a three-electrode system, where a Pt wire served as the counter electrode and an Ag/AgCl electrode was used as the reference. The working electrode was prepared by drop-casting an ink containing pre-synthesized chiral Au VC NPs onto either a polished GCE (5 mm in diameter) or an ITO substrate (1 × 2 cm, with ink coverage over 0.5 × 2 cm). Specifically, 12 μL of the ink was applied to the GCE, and 40 μL was applied to the ITO substrate, followed by natural drying. The ink was prepared as follows: the synthesized chiral Au VC NPs were centrifuged and washed once with ultrapure water to remove excess CTAB, then dispersed in 1 mL of isopropanol containing 0.1% Nafion. The mixture was sonicated for 20 min to ensure homogeneous dispersion. Then, the three-electrode system was immersed in an Ar-saturated 0.1 M H₂SO₄ electrolyte containing 2 mM CuSO₄. A potential of 0.4 V vs. RHE was applied to induce the UPD of Cu atoms, resulting in the formation of Au@Cu VC NPs with a monolayer of Cu atoms. After being washed with water, the electrode was transferred into an Ar-saturated 0.1 M H₂SO₄ solution containing 5 mM K₂PtCl₄ and kept at OCP for 20 min to allow the GRR of Cu atoms by Pt atoms, yielding Au@Pt VC NPs with a monolayer Pt shell. The completion of the GRR was confirmed by monitoring the change in OCP. By repeating the Cu UPD and Pt replacement cycles, Au@Pt VC-nL NPs with any desired number of Pt layers (1–10 atomic layers in this work) could be obtained. The racemic structure can be prepared simply by replacing the L/D-Au VC NPs with Rac-Au VC NPs. Chiral Au@Pd VC-nL NPs were prepared following the same procedure except for the use of K₂PdCl₄ instead of K₂PtCl₄. Chiral Au@Pt RD-nL NPs were prepared following the same procedure except for the use of chiral Au RD NPs instead of chiral Au VC NPs.

Synthesis of Au nanorods (NRs)

Au NRs were prepared using a previously published seed-mediated overgrowth approach with slight modifications^83,84. In a typical procedure, Au seeds were obtained by reducing HAuCl₄ with NaBH₄ in the presence of CTAB as surfactant. 5.0 mL of 0.5 mM HAuCl₄ was first added to 5.0 mL of 0.2 M CTAB solution. After that, 1.0 mL of freshly prepared, ice-cold 6.0 mM NaBH₄ was quickly injected into the mixture under magnetic stirring (1200 rpm). The seed solution was stirred for a while (2 min) and then left undisturbed in a 30 °C water bath for 30 min before further use. To prepare the overgrowth solution, 7.0 g of CTAB and 1.234 g of NaOL were dissolved in 250 mL of water at 50 °C in a 1.0 L flask. The solution was cooled to 30 °C, and then 36.0 mL of 4.0 mM AgNO₃ was added. The mixture was kept undisturbed for 15 min at 30 °C, followed by the addition of 250 mL of 1.0 mM HAuCl₄ solution. The solution became colorless after being stirred at 700 rpm for 90 min, and 2.1 mL of HCl (12.1 M) was then added to the solution. After another 15 min of magnetic stirring at 400 rpm, 1.25 mL of 64.0 mM reducing agent (AA) was added. Then, 4.0 mL of seed solution was injected into the growth solution, and the mixture solution was stirred for another 30 s and then left undisturbed at 30 °C for 12 h. The Au NRs were collected by centrifugation at 7000 rpm for 20 min, followed by removal of the supernatant, and finally re-dispersed in 30.0 mL of 0.1 M CTAB for future use.

Synthesis of chiral AuAg helical nanorods (HNRs)

Chiral AuAg NRs were prepared by the chiral overgrowth of Au NRs in the presence of chiral molecules following a previously published protocol with minor modifications^85,86. Au NRs were centrifuged and redispersed in 0.1 M CTAB solution before use. In a typical procedure, the Au NRs were first incubated with 4.8 mL of CTAB (10 mM), 30 μL of L-Cys (10 mM), and 15 μL of 4-ATP (10 mM) in a 30 °C water bath for 3 h. Then AgNO₃ (3 mM), HAuCl₄ (3 mM), and AA (10 mM) were added to the solution one by one with gentle mixing in each step. After fully mixing the growth solution, the reaction solution was left undisturbed in a 70 °C water bath for 1 h. The obtained chiral AuAg NRs were washed with water twice through centrifugation/redispersion cycles and finally redispersed in 1.0 mL of CTAB aqueous solution (1 mM) for later use. The handedness of chiral AuAg NRs was controlled by using L-Cys (LH: left-handed) or D-Cys (RH: right-handed). The aspect ratio of AuAg NRs was tuned by using Au NRs with varying aspect ratios as seeds, as well as adjusting the amount of Au NRs that were added to the growth solution. The Ag/Au ratio in the alloy shell can also be adjusted by changing the amount of AgNO₃ (3 mM) and HAuCl₄ (3 mM) that was added to the growth solution while keeping the total amount of Ag and Au constant.

Physical characterizations

The optical extinction spectra of the NPs were measured on aqueous colloidal suspensions at room temperature using a Shimadzu UV-2600i spectrophotometer. Ensemble CD spectra were obtained using a JASCO J-1500 spectrometer with a 10 mm path-length quartz cell at 25 °C. Three scans were collected and averaged for each measurement with a bandwidth of 1.00 nm and at a rate of 100 nm/min. The morphologies and structures of the nanoparticles were characterized by scanning electron microscopy (SEM) using Zeiss Merlin Compact field emission scanning electron microscopes. The samples for SEM were dispersed in water and drop-dried on silicon wafers. Transmission electron microscopy (TEM) images were obtained with a JOEL JEM-2100 Plus and Talos F200X G2 transmission electron microscope operated at an accelerating voltage of 200 kV. High-resolution transmission electron microscopy images and EDX mapping/line-scan were performed using a 300 kV JEM-ARM300F2 spherical aberration-corrected transmission electron microscope. TEM and EDS investigations were also conducted using a Thermo Fisher Spectra 300 microscope equipped with double spherical-aberration-correctors, operated at 300 kV. All samples for TEM measurements were dispersed in water and drop-dried on 300 mesh Formvar/carbon-coated Cu grids. XPS was conducted using an EnvironESCA NAP-XPS spectrometer. The binding energies were calibrated to the C 1s line at 284.8 eV.

Calculation of anisotropy factor (g-factor) values

The g-factor represents the degree of asymmetry in the extinction of the circularly polarized light. It can be used as an index to evaluate the chiroptical activity of substances. Our g-factors were calculated by the following equation:

$$\mathrm{g}-\mathrm{factor}=CD\left(mdeg\right)/\left(32980\times Extinction\right)$$ 2

where the CD values and the extinction values were obtained from CD spectra and the corresponding UV–Vis spectra, respectively.

Preparation of electrolytes

All electrolytes were prepared using ultrapure deionized water and analytical-grade reagents. The 0.1 M KOH solution was made by dissolving the appropriate amount of potassium hydroxide in water and diluting to 1 L in a volumetric flask; to avoid silicate contamination, it was stored in a polyethylene (PE) volumetric flask at room temperature and replaced every three days with a fresh aliquot. The 0.1 M HClO₄ electrolyte was obtained by carefully diluting concentrated HClO₄ (70% w/w) with water (acid added to water, never the reverse) to a final volume of 1 L, and the solution was kept in an amber glass volumetric flask at room temperature, protected from light, and renewed every three days. The 0.1 M PBS (pH 7.4) buffer was purchased as a ready-to-use solution; after each use, the container was sealed and stored at room temperature, and the solution was replaced with fresh buffer every seven days. The pH of each freshly prepared electrolyte was measured at room temperature (25 ± 1 °C) using a calibrated pH meter (with a combined glass electrode) that was standardized with three buffer solutions (pH = 4.01, 7.00, and 10.01) before use. For each electrolyte, three independent aliquots were measured, and the results are expressed as the mean ± standard deviation. The measured pH values were 1.02 ± 0.02 for 0.1 M HClO₄, 12.98 ± 0.03 for 0.1 M KOH, and 7.41 ± 0.02 for the commercial 0.1 M PBS (nominal pH 7.4).

Calibration of the reference electrode

To calibrate the reference electrodes, a commercial polycrystalline Pt disk electrode was used as the working electrode. The Ag/AgCl (saturated KCl) reference electrode was calibrated in 0.1 M HClO₄ solution saturated with high-purity H₂, while the Hg/HgO reference electrode was calibrated in 0.1 M KOH solution saturated with H₂. Before each measurement, the Pt electrode was polished with alumina slurries, rinsed thoroughly with ultrapure water, and electrochemically cleaned by CV in the corresponding electrolyte. The OCP was then recorded against the reference electrode under continuous H₂ flow until a stable value was reached (typically within 5–10 min). Since the Pt surface in a H₂-saturated electrolyte establishes the equilibrium of the RHE, its potential is defined as 0 V versus RHE. Consequently, the potential of the reference electrode versus RHE was calculated as

$$E_{ref}\left(vs.RHE\right)=-E_{OCP}$$ 3

where $E_{OCP}$ is the measured potential versus that reference electrode. This calibration was performed daily before each set of electrochemical measurements to ensure accuracy. All potentials measured against the Ag/AgCl (saturated KCl) and Hg/HgO (1 M KOH) reference electrodes were converted to the RHE scale using the following equations at 25 °C:

$$\mathrm{E}\left(\mathrm{RHE}\right)=\mathrm{E}\left(\mathrm{Ag}/\mathrm{AgCl}\right)+0.197+0.059\times \mathrm{pH}$$ 4

$$\mathrm{E}\left(\mathrm{RHE}\right)=\mathrm{E}\left(\mathrm{Hg}/\mathrm{HgO}\right)+0.098+0.059\times \mathrm{pH}$$ 5

where E(_Ag/AgCl) and E(_Hg/HgO) are the experimentally measured potentials versus the respective reference electrodes, and pH refers to that of the working electrolyte. The values 0.197 and 0.098 V are the potentials of the Ag/AgCl (sat. KCl) and Hg/HgO (1 M KOH) electrodes versus the standard hydrogen electrode, respectively. While the equations above give an approximate conversion to the RHE scale, we adopted the OCP measurement as the actual reference in our experiments, since it directly reflects the true potential, including the liquid junction potential and other practical factors.

Evaluation of the catalytic activities of chiral Au and Au@Pt-3L VC NPs toward electrooxidation of L/D-DOPA enantiomers

The enantioselective catalytic activities of chiral Au and Au@Pt-3L VC NPs were evaluated using the electrooxidation of L/D-DOPA enantiomers. A conventional three-electrode test system was employed to evaluate the enantioselective catalytic activities of chiral VC NPs toward the electrooxidation of L/D-DOPA. Ag/AgCl (saturated KCl) electrode, platinum wire, and the GCE with a diameter of 5 mm were used as the reference electrode, counter electrode, and working electrode, respectively. To modify GCE with chiral VC NPs, 20 mL of NP dispersion was dropped on the surface of GCE and dried at room temperature. The mass of all catalytic materials was normalized for the test. The concentration of NP suspension was kept the same for different samples. Then, 5 mL of 0.2% Nafion solution was dispersed on the electrode and allowed to naturally dry. The differential pulse voltammogram (DPV) with 1 mM L-DOPA (D-DOPA) in 0.1 M PBS electrolyte was measured using a CHI 760E electrochemical workstation (Shanghai Chenhua, China). The DPV parameters were set to the scan rate of 4 mV s⁻¹, 50 mV pulse amplitude, 60 ms pulse width, 0.5 V initial potential, and 1.1 V final potential.

Electrochemical characterization of oxygen reduction reactions (ORR)

The electrochemical measurements for the ORR were conducted using a standard three-electrode system. A carbon rod and an Hg/HgO (0.1 M KOH) electrode were used as the counter and reference electrodes, respectively. Depending on the measurement requirements, the catalyst was loaded onto either a glassy carbon disk electrode with a platinum ring (disk diameter 6 mm, geometric area ca. 0.283 cm²) or a bare GCE (diameter 5 mm, geometric area ca. 0.196 cm²) as the working electrode. Electrochemical data were recorded at room temperature (25 ± 1 °C) on a CHI-760e electrochemical workstation. The potential was measured versus a Hg/HgO reference electrode and then calibrated with reference to a standard RHE. During the test, the working electrode was installed on the rotating ring-disk electrode (RRDE, DC-DSRROTATOR, PHYCHEMI) device to ensure the stability of the test conditions. Linear sweep voltammetry (LSV) was performed in an O₂-saturated 0.1 M KOH solution (saturated by purging O₂ for at least 20 min before testing). The disk potential was scanned from 1.1 to 0.2 V (vs. RHE) at a scan rate of 5 mV s⁻¹, while the Pt ring was held at a constant potential of 1.3 V (vs. RHE) to oxidize the generated H₂O₂. During the ORR measurements, the rotating RRDE rotation rate was set at 1600 rpm. All measured results are presented without iR correction. CV was carried out in an Ar-saturated 0.1 M KOH solution within a potential range of 0.95 to 0.05 V (vs. RHE) at a scan rate of 50 mV s⁻¹. For electrochemical tests performed in acidic media, the only modifications required are the substitution of the electrolyte with 0.1 M HClO₄ and the replacement of the reference electrode with an Ag/AgCl (saturated KCl) electrode, while all other experimental parameters remain unchanged. The equations used to calculate n (the apparent number of electrons transferred during ORR) are the following:

$$n=\frac{4I_D}{I_D+I_R/N}$$ 6

where I_D is the current at the disk, I_R is the current at the ring, and N (calculated value is 0.37) is the RRDE collection efficiency.

The ECSA is calculated using the hydrogen underpotential deposition (H_upd) peaks of Pt. The specific formula is as follows:

$$ECSA=\frac{Q_{H-upd}}{q_H}$$ 7

Where $Q_{H-upd}$ is the charge associated with the hydrogen under potential deposition peaks, obtained by integrating the H_upd peaks in the CV curves. $q_H$ is the charge required for a monolayer of hydrogen adsorption on Pt, typically taken as 210 μC·cm⁻². MA and SA are critical metrics to evaluate catalyst performance. Their calculations are based on the following formulas:

$$MA=\frac{J}{m_{active}}$$ 8

$$SA=\frac{J}{ECSA}$$ 9

Where $J$ is the measured current density, and $m_{active}$ is the mass of the active component. In this system, the catalytic activity is considered to originate solely from Pt. The mass of Pt in the catalyst was calculated from the charge associated with the underpotential deposition of copper, on the assumption that the GRR proceeds to completion, given a sufficiently long reaction time, ensuring a thorough exchange between Pt and Cu. The specific formula used for the calculation is as follows:

$${n_{Pt}=n}_{Cu}=\frac{Q_{Cu-upd}}{2\cdot F}$$ 10

$$m_{active}=m_{Pt}=n_{Pt}\cdot M_{Pt}$$ 11

Where $n_{Pt}$ and $n_{Cu}$ are the molar amounts of Cu and Pt, respectively;$Q_{Cu-upd}$ is the charge passed during Cu UPD; $m_{Pt}$ is the mass of Pt on the catalyst; $M_{Pt}$ is the molar mass of Pt, and F is the Faraday constant. For example, to calculate Au@Pt L-VC-3L NPs loading on electrode: Q_Cu-upd was calculated from the UPD curve, and the specific values (m_Pt) are listed in Table S2.

$$m_{Pt}=n_{Pt}\cdot M_{Pt}=\frac{Q_{Cu-upd}\cdot M_{Pt}}{2\cdot F}=\frac{0.424\times {10}^{-3}\mathrm{C}\times 195.08\mathrm{g}/\mathrm{mol}}{2\times 96485\mathrm{C}/\mathrm{mol}}\approx 0.429\mathrm{\mu }\mathrm{g}$$ 12

Magnetic conductive-probe atomic force microscopy (mc-AFM) measurement

To avoid measurement artifacts caused by nanoparticle stacking, we employed an interfacial assembly approach for mc-AFM sample preparation to ensure that most Au VC NPs are monodispersed. Briefly, the as‑prepared Au VC NPs were centrifuged and then dispersed in 10 mL of ethanol containing 1% PVP (MW = 55,000). After sonication for 2 h, the NPs were centrifuged and washed twice with ethanol to remove excess PVP. The resulting NPs were redispersed in 5 mL of dichloromethane, followed by the addition of 5 mL of ultrapure water. Vigorous shaking was applied to transfer the Au VC NPs from the dichloromethane phase to the aqueous phase. The mixture could stand for 5 min for complete phase separation. Subsequently, 2 mL of n‑hexane was added, leading to the formation of an Au film at the n‑hexane/water interface. Most of the upper n‑hexane layer was removed using a pipette, and the remaining n‑hexane was left to evaporate naturally. The interfacial Au film was then transferred onto an ITO substrate, yielding a monolayer of well‑dispersed Au VC NPs for subsequent measurements. The Dimension ICON atomic force microscope system was used to carry out the mc-AFM measurements. I–V curves were acquired using a magnetic Pt-coated Cr tip (Multi75E-G, Budget Sensors) with a nominal spring constant of 3 N m⁻¹. The tips are pre-magnetized in the up and down directions with a permanent magnet: place the probe between two magnets at a distance of 6 mm for magnetization, with each magnet having a strength of 5680 Gs and a magnetization time of 20 min. I–V curves were measured in the voltage range of −1 to 1 V with a frequency of 0.5 Hz. To prevent the tip from melting due to excessive current, which would degrade resolution and measurement accuracy, the current was limited to a maximum of 5 nA. For each sample, over 100 data points were collected, and the final I–V curve was obtained by averaging 40 randomly selected traces. The spin-dependent anisotropy of the charge current is quantified by a dissymmetry parameter g_c, which is defined as: g_c = (I_up−I_down)/(I_up+I_down) × 100%, where I_up and I_down correspond to the measured currents when the magnetization direction is up or down. The g_c is highly correlated to the spin polarization (P_CISS) of chiral nanomaterials and has been used to probe the spin-filtering properties of various types of chiral materials.

Numerical simulations

The extinction and g-factor spectra of the synthesized chiral Au VC NPs, both with and without Pt coating, were numerically simulated using the commercial COMSOL Multiphysics software. The geometric models of chiral Au NPs were constructed based on orientation-dependent SEM images. The detailed geometrical parameters of chiral Au VC NPs were also extracted from the corresponding TEM images. The Pt coating was approximated by constructing a multi-layer transition boundary condition on the surface of the Au VC NPs. The final geometrical model has a side length of ~120 nm for the Au VC NPs. The dielectric permittivity tabulated by Johnson and Christy was used for Au and Pt⁸⁷. The chiral NPs were immersed in a water environment with a refractive index of 1.33, and the simulation mesh sizes were set as follows: a minimum mesh size of 1.6 nm for the particles and a mesh size ranging from 2 to 60 nm for the water region. The scattered-field formalism in COMSOL was employed for the simulations, with the background optical field configured as circularly polarized plane-wave incidence. A Perfectly Matched Layer was applied around the simulation system to absorb the scattered field and suppress reflection interference. The scattering cross-section was calculated via the built-in interface in COMSOL, determined by integrating the Poynting vectors of the scattered field over the chiral NPs region. The extinction spectra for left/right-handed circularly polarized light excitation were obtained separately as σ_L and σ_R, so the unpolarized extinction equation: σ = (σ_L + σ_R)/2, and the g-factor spectra can be obtained using the equation: g-factor = (σ_L−σ_R)/σ.

Author contributions

Q.Z., L.S., Z.W., and B.Z. conceived and designed the experiments. Z.W., B.Z., J.D., and Y.T. performed the synthesis, analysis, simulations, and measurements. Z.W., L.S., and Q.Z. co-wrote the paper. Q.Z. and L.S. supervised the entire study. All the authors contributed to the final version of the manuscript.

Peer review

Peer review information

Nature Communications thanks Jin Huang and the other anonymous reviewer(s) for their contribution to the peer review of this work. A peer review file is available.

Funding

Q.Z. discloses support for National Natural Science Foundation of China [grant number 22472119 and 22174104] and the Fundamental Research Funds for the Central Universities [grant number 2042026kf0048]. L.S. discloses support for National Natural Science Foundation of China [grant number 22405195], the Basic Research Program of Jiangsu [grant number BK20240448], and the Natural Science Foundation of Hubei [grant number 2025AFB642]. Z.W., B.Z., J.D., and Y.T. declare no relevant funding.

Data availability

The data that support the findings of this study are available in the main text and Supplementary Information. Source data are provided with this paper.

Competing interests

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at https://doi.org/10.1038/s41467-026-76426-2.