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. 2023 Feb 14;8(8):7368–7377. doi: 10.1021/acsomega.2c05513

g-C3N4 Nanosheet Supported CuO Nanocomposites for the Electrochemical Carbon Dioxide Reduction Reaction

Chien-Lin Sung †, Ren-Hung Wang †, You-Cheng Shih †, Zhi-Ying Wu †, Samuel R Alvarado ‡, Yu-Hsu Chang †,*, Chia-Cheng Lin †,*
PMCID: PMC9979231  PMID: 36872995

Abstract

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We have prepared CuO-derived electrocatalysts on a graphitic carbon nitride (g-C3N4) nanosheet support for the electrochemical carbon dioxide reduction reaction (CO2RR). Highly monodisperse CuO nanocrystals made by a modified colloidal synthesis method serve as the precatalysts. We use a two-stage thermal treatment to address the active site blockage issues caused by the residual C18 capping agents. The results show that the thermal treatment effectively removed the capping agents and increased the electrochemical surface area. During the process, the residual oleylamine molecules incompletely reduced CuO to a Cu2O/Cu mixed phase in the first stage of thermal treatment, and the following treatment in forming gas at 200 °C completed the reduction to metallic Cu. The CuO-derived electrocatalysts show different selectivities over CH4 and C2H4, and this might be due to the synergistic effects of Cu-g-C3N4 catalyst–support interaction, varied particle sizes, dominant surface facets, and catalyst ensemble. The two-stage thermal treatment enables sufficient capping agent removal, catalyst phase control, and CO2RR product selection, and with precise controls of the experimental parameters, we believe that this will help to design and fabricate g-C3N4-supported catalyst systems with narrower product distribution.

Introduction

The utilization of sustainable energy to alleviate the current dependence on fossil fuel-based energy sources is one of the solutions to address the emerging global warming and climate change. The intermittent nature of renewable energy sources nevertheless hinders the development of related techniques. Measures such as smart grids,1 supercapacitors,2 and electrochemical small molecule activations have been taken to address the issues. The electrochemical CO2 reduction reaction (CO2RR) offers an alternative route for renewable energy conversion and storage.3 Among various CO2RR products, hydrocarbons are more desired in consideration of energy density. Metallic electrodes have been used for CO2RR, and Cu-based materials have especially drawn attention due to their unique catalytic performance for producing variable fuels.4,5

Efforts have been devoted to the development of Cu-based electrocatalysts to improve the CO2RR catalytic activity and selectivity, such as CO2RR with planar Cu,6−9 Cu foams,10 Cu2O-derived catalysts,11 CuO-derived nanoribbons,12 CuO-derived microspheres,13 CuO-derived nanowires,13,14 plasma-treated Cu electrodes,15 CuO-derived planar electrodes,16,17 CuO-derived Cu nanoparticles,18 CuO-derived three-dimensional (3D) structure,19 branched CuO/Cu2O-derived electrodes,20 and ZnO/Cu2O for the photocatalytic CO2RR.21 Mechanistic studies about the correlation between CO2RR selectivity and different possible pathways22 and theoretical work on Cu electrodes,23 Cu nanoparticles,24 and facet exposure effect on Cu-based electrocatalysts25,26 all combined reveal that the product selectivity of CO2RR in Cu-based materials is a convoluted situation.27 In addition to the intrinsic catalytic mechanistic factors, a study of CO2RR on Au opal electrodes demonstrates the effect of mass transport control.28 Effects of various parameters, such as particle grain size, mass transport, local pH, electrolyte, temperature and pressure, and surface facets, have been summarized in retrospective articles.5,29

The nature of the catalyst support can also influence product selectivity. Recent studies suggest that N-doped carbon supports can stabilize Cu in a Cu–N coordination environment during electrolysis and shows the product selectivity toward ethanol or other C2 products.30−36 Cu on N-doped carbon has also been used in thermal catalysis and shows enhanced stability,37 and there are reports utilizing N-doped carbon as a catalyst support for electrocatalysis.38−47 A theoretical study of Cu dimer on C2N predicts a favored product of C2H4.48 We hypothesize that the N-doped carbon support for CO2RR will stabilize the intermediate states of CO2 adsorbates and the catalysts, which leads to specific CO2RR products, owing to the coordination between the N and the d-orbitals of the metal atoms. In other words, the electron-donating capability of nitrogen atoms can direct the reaction to different pathways.

In this work, we seek to combine the capability of Cu-based catalysts to produce more reduced CO2RR products and add metal stabilization from the N-doped carbon support. Here, we prepare CuO on graphitic carbon nitride (g-C3N4) nanocomposites as the CO2RR catalysts. Most N-doped carbon supports do not possess evenly and periodically distributed nitrogen dopants. One of the advantages of the selection of g-C3N4 as the N-doped carbon support is the even distribution of N and C due to two-dimensional periodicity of g-C3N4.49 Nanocrystals of CuO were prepared, according to reported colloidal synthesis methods with minor modifications,50,51 in which oleylamine (OAm) and oleic acid (OA) were chosen as the capping agents and reductants,51 and OAm removal was achieved by thermal treatment of AuNPs at 180 °C overnight.52

Experimental Section

Materials

Copper(II) acetylacetonate (Cu(acac)2, 98%), oleylamine (80–90%), and oleic acid (85–88%) were purchased from Acros Organics. Dicyandiamide (DCDA, 99%) was purchased from Alfa Aesar. Sodium bicarbonate (NaHCO3, 100%) was purchased from Honeywell Fluka. Nafion 117 membrane and 5 wt % Nafion 117 solution (in a mixture of lower aliphatic alcohols and water) were purchased from Giant An Technology. Carbon fiber paper (AvCarb GDS22100) was purchased from HEPHAS Energy. Argon (99.99%), nitrogen (99.99%), carbon dioxide (>99%), and forming gas (5% H2 and 95% Ar) were purchased from Fung Ming Industrial. Ultrapure water (with a resistivity of 18.2 MΩ·cm) was generated with a Merck Direct-Q3 water purification system. Ferrocenecarboxylic acid (97%) was purchased from Nova Materials. All chemicals were used as received without further purification.

Synthesis of Cupric Oxide (CuO)

CuO nanoparticles were synthesized using a modified procedure involving the thermal decomposition of metal acetylacetonate in mixed organic solvents.27,29,34,53 Typically, 0.5 mmol of Cu(acac)2, 7.5 mL of oleylamine, and 0.16 mL of oleic acid were mixed in a 50 mL single neck round bottom flask equipped with a gas inlet adapter and a Teflon-coated stir bar. Degassing was performed by pumping out the system at room temperature, gradually increasing the temperature to 60 °C, and dwelling for an hour. After degassing, the system was refilled with Ar and heated to 100 °C with a heating ramp of 10 °C/min. After dwelling for 6 h, the reaction was stopped, and the products were isolated and purified with a precipitation and redispersion procedure.

Synthesis of Graphitic Carbon Nitride (g-C3N4)

Graphitic carbon nitride was prepared by following a two-step synthesis process.54 Bulk carbon nitride was first synthesized by heating DCDA to 550 °C in air with a heating ramp of 2.3 °C/min and held for 4 h. After grinding, the yellow powder was re-heated to 500 °C in air with a heating ramp of 5 °C/min and a dwelling time of 2 h. The second heat treatment yielded the light yellow graphitic carbon nitride product.

Preparation of g-C3N4-Supported CuO

Ten milligrams of CuO was dispersed in 15 mL of hexane. After sonication, 100 mg of g-C3N4 was added to the solution, and the mixture was vigorously stirred for 2 h. After settling for 30 min, the clear upper layer and the solid were separated by decanting. The residual solvent in the product composite was removed under vacuum.

Thermal Treatment of g-C3N4-Supported CuO

The surface capping agents were removed by heating the composites at 200 °C under reduced pressure for 2 h.55 After being gradually cooled to room temperature, the system was refilled with forming gas, re-heated to 200 °C, and dwelled for another 2 h to yield the catalyst.37 Sample labeling and descriptions are summarized in Table S1.

Characterization

Powder X-ray diffraction (PXRD) data were recorded with a Bruker D8 Advance powder X-ray diffractometer with a Cu Kα radiation source (40 kV, 44 mA). Transmission electron microscopy (TEM) images were collected with a JEOL-JEM2100F. TEM samples were prepared by drop-casting on Ni TEM grids. Fourier transform infrared (FTIR) spectra were collected with a Thermo Nicolet 6700. Ultraviolet–visible (UV–vis) spectra were collected with an Agilent Cary 8454. N2 physisorption measurements were performed with a Micromeritics ASAP 2020. Samples were heated to 120 °C under N2 flow overnight prior to the physisorption measurements. X-ray photoelectron spectroscopy (XPS) spectra were acquired on a ULVAC PHI 5000 VersaProbe II instrument with a monochromatic Al X-ray source.

Working Electrode Preparation

Carbon fiber paper strips (1 cm × 3 cm) were used as the working electrodes. The catalyst inks were prepared by dispersing 10 mg of CuO or g-C3N4-supported CuO (containing 10 mg of CuO) in a solution of 0.5 mL of hexane, 0.5 mL of isopropyl alcohol, and 10 μL of Nafion 117 solution (5% in alcoholic solution). The inks were sonicated for 15 min before drop-casting. In each drop-casting addition, 50 μL of the ink was applied onto the strips in a 1 cm × 1 cm area and dried at 60 °C for 10 min. The drop casting–drying steps were repeated until a total CuO loading of 1 mg/cm2 was achieved.

Electrochemical Analysis

All electrochemical measurements were conducted with a Bio-Logic SP300 potentiostat/galvanostat with a built-in electrochemical impedance spectroscopy (EIS) analyzer. Reference electrodes (Ag/AgCl(sat.), Aubotech) were externally referenced to a solution of ferrocenecarboxylic acid in 0.2 M phosphate buffer at pH 7 (0.329 V vs Ag/AgCl(sat.)) prior to each set of experiments, and carbon rods (>99%, Nature World Company) were used as the auxiliary electrodes.

Data were collected using the Bio-Logic EC-Lab software package. All electrochemical measurements were conducted in custom two-compartmented H-cells. The main chamber held the working and reference electrodes in about 100 mL of 0.1 M NaHCO3 solution, while the second chamber held the counter electrode in about 20 mL of 0.1 M NaHCO3 solution. The two compartments were separated with a Nafion 117 membrane. Prior to each set of measurements, the electrolyte solutions were purged with Ar or CO2 for at least 30 min, and the solution was continuously purged during cyclic voltammetry (CV) measurements. Each electrochemical measurement was repeated at least three times. The uncompensated solution resistance (Ru) was measured with a high-frequency single-point impedance measurement at 100 kHz with a 20 mV amplitude near the open-circuit potential (OCP), and CV and controlled potential electrolysis measurements were corrected for IR drop at 85% through positive feedback using Bio-Logic EC-Lab software. All electrochemical data were presented vs reverse hydrogen electrode (RHE).

For working electrodes that had not been thermally treated, controlled potential experiments at −0.3 V vs RHE were performed in separate cells filled with Ar-sparged solutions to preactivate the CuO catalyst by reducing it to Cu.24,26 Electrochemically active surface area (ECSA) measurements were taken around the open-circuit potential with a 0.1 V window at scan rates ranging from 5 to 200 mV/s.

Product Analysis

Gas-phase products in the headspace after electrolysis were analyzed with a PerkinElmer Clarus 690 gas chromatograph, equipped with an integrated system of custom valves, column configuration, analytical methods, and thermal conductivity detectors (TCDs). The TCDs used Ar as both reference and carrier gas.

Liquid-phase products were analyzed using an Agilent 1260 Infinity II Quaternary Pump system, equipped with an Agilent Hi-Plex H analytical column. Liquid aliquots were taken from the working electrode chamber, and 10 μL of each liquid sample was injected into the sampling loop. The mobile phase was 5 mM H2SO4 aqueous solution with a flow rate of 0.6 mL per min. The temperature of the column was maintained at 50 °C. Products were detected using a UV–vis detector (1260 Infinity II variable wavelength detector) and a refractive index detector (1260 Infinity II refractive index detector).

Faradaic Efficiency Calculation

Faradaic efficiency (FE) of each product was calculated with the following equation

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where nx is the number of electrons involved in each reduction reaction; molesx is the moles of each product quantified by gas chromatography (GC) or high-performance liquid chromatography (HPLC); F is the Faraday constant, 96,485 C/mol; and Qtotal is the total charge passed in controlled potential electrolysis experiments (about 50C).

Results and Discussion

Synthesis and Characterizations of CuO-Derived Nanocomposites

The CuO nanocrystals were synthesized by a modified colloidal synthesis method, which employs the thermal decomposition of copper complexes in a mixture of oleylamine and oleic acid. As shown in Figure 1, the PXRD pattern of the as-synthesized CuO (as-syn CuO) matches well with that of the monoclinic CuO reference (JCPDS Card No. 48-1548) with a grain size of 3.2 nm determined by the Scherrer equation. The representative TEM image of CuO nanocrystals is shown in Figure 2a. Figure S2a shows the particle size distribution acquired from 200 particles, where the average particle size is 2.7 ± 0.2 nm. The selected area electron diffraction (SAED) (Figure 2b) confirms the crystal phase of CuO with the typical ring-like pattern characteristic of nanoparticles. A more detailed TEM image of slightly agglomerated CuO is shown in Figure S1a, and the high-resolution TEM (HRTEM) image (Figure S1b) shows the lattice fringe of CuO(111).

Figure 1.

Figure 1

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PXRD data of as-syn CuO, as-syn Cu2O/Cu, as-syn Cu, as-syn CuO/C3N4, as-syn Cu2O/Cu/C3N4, as-syn Cu/C3N4, and simulated reference patterns JCPDS: Cu (04-0836), Cu2O (75-1531), and CuO (48-1538).

Figure 2.

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Representative TEM and SAED images of as-syn CuO (a, b) and TEM images of as-syn CuO/C3N4 (c) and as-syn Cu/C3N4 (d).

After the first stage of thermal treatment, the PXRD data of thermally treated catalyst under vacuum (labeled as as-syn Cu2O/Cu) reveals the presence of Cu2O and Cu. The residual oleylamine molecules enable the partial reduction of CuO to Cu2O/Cu at elevated temperatures. It has been reported that oleylamine can reduce Cu(II) precursors, and a higher reaction temperature leads to more reduced products.53 After the consequent heat treatment in forming gas, the PXRD data of the final product (labeled as as-syn Cu) shows the complete transformation to metallic Cu.

The FTIR spectrum of the mixture of oleylamine and oleic acid (Figure 3a) shows the broad N–H stretching vibration at around 3400 cm–1, asymmetric C–H stretching vibrations at 2918 and 2850 cm–1, C=C bending vibration at 1650 cm–1, C–H stretching vibration at 1550 cm–1, C–H bending vibrations at 1458 and 1400 cm–1, and C–C bending vibration at 700 cm–1. The FTIR spectrum of as-syn CuO (Figure 3b) shows the presence of the aforementioned peaks. The FTIR spectrum of as-syn Cu2O/Cu (Figure 3c) reveals that no significant characteristic peaks of oleylamine or oleic acid are detectable, and it confirms the successful removal of the ligands by thermal treatment under vacuum. The FTIR spectrum of as-syn Cu (Figure 3d) reveals the absence of those of oleylamine or oleic acid as well.

Figure 3.

Figure 3

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FTIR spectra of a mixture of oleylamine and oleic acid (a), as-syn CuO (b), as-syn CuO/Cu (c), and as-syn Cu (d).

Figure S3 shows the thermogravimetric analysis (TGA) thermogram of as-syn CuO. The first weight loss before 200 °C, ca. 9%, could be attributed to the removal of physisorbed water, and the weight loss between 200 to 350 °C, ca. 51%, could be assigned to the removal of organic content, i.e., oleylamine and oleic acid. Thermal treatment at this temperature in vacuum facilitates the evaporation of the capping agents.

We attempted to remove ligands by acid treatment (data not shown), as achieved in other colloidal syntheses with oleylamine ligands.55,56 However, the acidic environment induced problems of instability and corrosion of CuO, which resulted in blue-colored solutions.

Synthesis and Characterizations of g-C3N4 Support

The g-C3N4 nanosheets were prepared by a two-step synthesis method.54 In Figure S4, the PXRD diffraction patterns consist of reflections from the graphite structure and tri-s-triazine units, which have been documented in previous reports.49,57−59 The major peak at ca. 27° is indexed as (002), representing the interlayer separation of the graphitic material, and the broad peak at ca. 13° represents the in-plane packing of motif (100), which is equivalent to a d-spacing of 0.7 nm. The slight shift of the (002) peak of the g-C3N4 nanosheets toward a wider angle compared to the bulk g-C3N4 is possibly due to the reduced interplanar separation after the second thermal treatment.

The specific surface area of bulk g-C3N4 and g-C3N4 nanosheets was measured by nitrogen physisorption. The calculation based on the multipoint Brunauer–Emmett–Teller (BET) (Figure S5) shows the increase of specific surface area after the second thermal treatment, i.e., the increase from 19.79 ± 0.06 to 91.84 ± 0.53 m2/g.

Preparation of g-C3N4-Supported Nanocomposites

The g-C3N4-supported CuO nanocomposites were prepared by adding controlled amounts of g-C3N4 nanosheets to a suspension of CuO in hexane, followed by vigorous mixing, decanting, and drying in vacuum. Figure 2c shows the TEM of as-synthesized g-C3N4-supported CuO (as-syn CuO/C3N4). The CuO nanocrystals are well separated on the g-C3N4 support with a nominal loading of 9 wt %. The residual oleylamine and oleic acid might serve as a protective layer to prevent potential aggregation during the drying process, while the van der Waals force between the small CuO particles and g-C3N4 also contributes to maintain particle separation. The PXRD patterns of supported CuO nanocomposites at different stages of thermal treatment are shown in Figure 1. Similar to the unsupported CuO, thermal treatment of as-syn CuO/C3N4 first yields a mixture of Cu2O and Cu. XRD peaks of Cu2O were present in as-syn Cu2O/Cu/C3N4 but were not as intense as in the unsupported as-syn CuO. This might be due to the presence of more residual oleylamine, which has some reductive capability, on the g-C3N4 support. Additional thermal treatment with forming gas completes the conversion to Cu nanoparticles on g-C3N4 nanosheets (as-syn Cu/C3N4).

Energy-dispersive spectroscopy (EDS) elemental mapping was performed to investigate the CuO particle dispersion on g-C3N4 nanosheets. In Figure 4, the individual elemental mapping images and the superimposed image all reveal an even distribution of the CuO particles without noticeable agglomeration or phase segregation. Figure 2d shows the TEM of as-syn Cu/C3N4 after two-stage thermal treatment. After the removal of capping agents and thermal reduction in forming gas, more distinct particles appear near the edges of the folded structure with an average particle size of 6.0 ± 0.7 nm. The particle size distribution is shown in Figure S2b. The EDS mapping images, Figure 5c–e, of C, N, and Cu show no significant difference while the O signal intensity, Figure 5f, decreases slightly compared to that of the as-syn CuO/C3N4. The slightly weaker O signal intensity could be due to the formation of surface oxide, which is inevitable after the system is re-exposed to air.

Figure 4.

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TEM of as-syn CuO/C3N4 (a), superimposed TEM and EDS elemental mapping (b), and individual EDS elemental mapping images of Cu, C, N, and O (c–f); scale bar of 200 nm.

Figure 5.

Figure 5

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TEM of as-syn Cu/C3N4 (a), superimposed TEM and EDS elemental mapping (b), and individual EDS elemental mapping images of Cu, C, N, and O (c–f); scale bar of 200 nm.

Prereduction of Nonthermally Treated Samples

CV of as-syn CuO, Figure 6, shows two reduction peaks at around 0.4 and −0.1 V vs RHE, which are attributed to the Cu(II)/Cu(I) and Cu(I)/Cu(0) reduction couples, respectively,60 although the theoretical reduction potentials of both steps are slightly more positive.5 The convoluted oxidation peak might be due to a mix of Cu(0)/Cu(I) and Cu(I)/Cu(II) oxidation processes. To ensure that the catalysts were completely reduced to Cu, controlled potential pretreatments at −0.3 V vs RHE were performed. Chronoamperometry data, Figure S6, shows that the reduction completes within 10 minutes. The absence of the distinct oxidation–reduction features in the CVs of g-C3N4-supported composites might be due to the capacitance of the g-C3N4 matrix masking the peaks.

Figure 6.

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CVs of g-C3N4 (black), as-syn CuO (red), as-syn CuO/C3N4 (green), and as-syn Cu/C3N4 (blue) in Ar-sparged 0.1 M NaHCO3 solutions.

Effectiveness of Removal of Capping Agents

Figure S7a–c shows the CVs of the g-C3N4 nanosheets, as-syn CuO/C3N4, and as-syn Cu/C3N4. Figure S7d reveals the linear plot of capacitive currents of the non-Faradaic region, at 0.95 V vs RHE, with different scan rates of 5, 10, 25, 50, 100, 150, and 200 mV/s, and the slope of the plot leads to the estimated double-layer capacitance (Cdl) of each electrode. The Cdl serves as a quantitative evaluation of the electrochemically active surface areas because the direct measurement of surface active sites is not available. The Cdl of as-syn CuO/g-C3N4 is only slightly higher than those of g-C3N4 nanosheets. This could be attributed to the relatively small accessible surface area of ligand-capped CuO compared to the g-C3N4 nanosheets, which possess a specific surface area of 91.84 ± 0.53 m2/g. After thermal treatment, the Cdl increases by ca. 42%, suggesting that more surface active sites are available. Nevertheless, the particle size estimation based on PXRD and TEM reveals the particle growth after thermal treatment.

Electrochemical CO2RR Activity Measurements

CVs of carbon paper, g-C3N4 nanosheets, unsupported CuO, as-syn CuO/g-C3N4, and as-syn Cu/g-C3N4 are shown in Figure S8. The carbon paper and g-C3N4 nanosheets show no CO2RR activity, while the g-C3N4 support shows a larger current response at more negative potential. An earlier study suggests that low CO2RR activity is observed when only g-C3N4 nanosheets are present.61 CuO, as-syn CuO/C3N4, and as-syn Cu/C3N4 demonstrate CO2RR capability. Among the g-C3N4 supported catalysts, the as-syn Cu/C3N4 shows nearly double current response compared to as-syn CuO/C3N4. This increase could be attributed to the increase in surface active sites after capping agent removal, in agreement with the ECSA measurements.

Aside from specific activity, product selectivity is another measurement for evaluating catalyst performance. Figure 7 shows the CO2RR product distributions of controlled potential electrolysis experiments of different samples at −0.6, −0.8, −1.0, and −1.2 V vs RHE. The g-C3N4 support only produces H2 while others produce different amounts of H2/CO/C2H4/CH4. More reduced products are observed at more negative potentials, which is consistent with findings of electrochemical CO2RR by Cu-based catalysts in previous studies.62,63Figure 8 shows the comparison of Faradaic efficiency (FE) in different samples. The CuO, as-syn CuO/C3N4, and as-syn Cu/C3N4 show the FE of H2 ranging from 70–80% and the FEs of CO/CH4/C2H4 near 10%. For the production of CO, g-C3N4-supported catalysts show slightly more positive onset potential than CuO. The unsupported CuO shows the highest production of C2H4, while as-syn Cu/C3N4 has the highest production of CH4.

Figure 7.

Figure 7

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Electrochemical CO2RR activities presented in terms of FEs of H2/CO/C2H4/CH4: (a) g-C3N4, (b) as-syn CuO, (c) as-syn CuO/C3N4, and (d) as-syn Cu/C3N4.

Figure 8.

Figure 8

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Electrochemical CO2RR activity comparisons by products: (a) H2, (b) CO, (c) C2H4, and (d) CH4.

Several factors might contribute to the discrepancy between the electrochemical CO2RR performance of samples with or without g-C3N4 support. Carbon paper support has a specific surface area of about several m2 per gram, and the equivalent real surface area per 1 cm2 of geometric surface area of working electrodes is about 50 cm2.64 The 10 mg of g-C3N4 loadings has a total surface area of 9000 cm2, which is two orders of magnitude greater than the carbon paper support. In other words, the catalyst dispersion density on carbon paper is two orders of magnitude greater than that on g-C3N4/carbon paper.

This huge difference in dispersion density leads to different spatial separation of CuO particles. For the sample of CuO on carbon paper, the electrochemical prereduction causes particle aggregation, i.e., particle size growth. Surface reconstruction of Cu during electrolysis induces particle growth as well.65 Several recent reports also demonstrate similar effects on supported/unsupported Cu2O-derived catalysts and their effects on electrochemical CO2RR product selectivity.62,66,67 In an earlier report of Cu catalysts on a Si wafer, the authors attribute the difference between electrochemical CO2RR product selectivity of particles with various sizes to the number of atoms possessing under-coordinated facets.63 Computational studies suggest that product selectivity depends on the interaction between the intermediates and various facets.48,68−72 The growth of crystals leads to different facet populations, which affect the surface affinities toward different adsorbates/intermediates.

In addition to different facet populations, catalyst dispersion also affects the local mass transport of reactants/intermediates. In the case of high catalyst dispersion density, the less spatially separated active sites increase the probability of the readsorption of the intermediates, and the limited mass transport causes local depletion of proton supply. As a result, the C2 product is favored over C1 products when g-C3N4 is absent, and vice versa. A recent computational study suggests that Cu species can be stabilized in a C2N porous matrix due to the hybridization of Cu 3d orbitals and N 2p orbitals. This makes CH4 the favored electrochemical CO2RR product,48 which is consistent with our results from g-C3N4-supported specimens.

Ex Situ XPS Measurement of Selected Samples at Different Stages

XPS data of as-syn CuO/C3N4, as-syn Cu/C3N4, and post-CO2RR Cu/C3N4 were collected to serve as the complementary evidence to the oxidation states and chemical environments of Cu and C in the specimens. The C spectra (Figure S9) show a decrease of the relative peak intensity at ca. 284 eV (C–C) in as-syn Cu/C3N4 compared to as-syn CuO/C3N4. This confirms the successful removal of alkyl ligands, which is also observed by the FTIR measurement. The additional peak at ca. 291 eV (C=O) in post-CO2RR Cu/C3N4 reveals the residual carbonates from the electrolytes [CO3]2– and [HCO3]−.

The Cu spectra (Figure S10) show the transition from Cu(II) in CuO/C3N4 to Cu(0) in Cu/C3N4. In the XPS of CuO/C3N4, the satellite peaks at ca. 960 and 950 eV are characteristic peaks of Cu(II) species. These peaks are absent in the spectra of as-syn Cu/C3N4 and post-CO2RR Cu/C3N4, suggesting a reduced form of Cu. There is no noticeable difference in Cu XPS before and after electrolysis, implying no significant oxidation state change.

Conclusions

We have successfully prepared CuO-derived catalysts for the electrochemical CO2RR. A two-stage thermal treatment leads to the successful removal of the capping agents and reduction to Cu. An organic moiety removal is verified by FTIR and XPS measurements, and CV measurements also confirm the increase of electrochemically active surface area after thermal treatment.

For the electrochemical CO2RR product selectivity of more reduced products, CuO shows the highest selectivity toward C2H4, while the g-C3N4-supported CuO catalysts yield more CH4. We attribute this selectivity discrepancy to three major possible factors: (1) the change of the surface dominant facets due to particle growth, (2) the ensemble effect induced by different catalyst loading densities, and (3) the hybridization and stabilization of the catalyst–support interaction. By precise control of the experimental parameters, we believe that this will enable the design and fabrication of catalyst systems with narrower product distribution of hydrocarbons over H2 or CO.

Acknowledgments

This work was supported by the Ministry of Science and Technology in Taiwan (MOST 109-2113-M-027-001-MY3) and (MOST 110-2113-M-027-008).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c05513.

  • g-C3N4 characterizations, TEMs, CVs, XPS, and ECSA measurements (PDF)

Author Contributions

§ C.-L.S. and R.-H.W. contributed equally to this work.

The authors declare no competing financial interest.

Supplementary Material

ao2c05513_si_001.pdf (661.4KB, pdf)

References

  1. Kakran S.; Chanana S. Smart operations of smart grids integrated with distributed generation: A review. Renewable Sustainable Energy Rev. 2018, 81, 524–535. 10.1016/j.rser.2017.07.045. [DOI] [Google Scholar]
  2. González A.; Goikolea E.; Barrena J. A.; Mysyk R. Review on supercapacitors: Technologies and materials. Renewable Sustainable Energy Rev. 2016, 58, 1189–1206. 10.1016/j.rser.2015.12.249. [DOI] [Google Scholar]
  3. De Luna P.; Hahn C.; Higgins D.; Jaffer S. A.; Jaramillo T. F.; Sargent E. H. What would it take for renewably powered electrosynthesis to displace petrochemical processes?. Science 2019, 364, eaav3506 10.1126/science.aav3506. [DOI] [PubMed] [Google Scholar]
  4. Li W.Electrocatalytic Reduction of CO2 to Small Organic Molecule Fuels on Metal Catalysts. In Advances in CO2 Conversion and Utilization; Hu Y. H., Ed.; American Chemical Society: Washington, DC, USA, 2010; pp 55–76. [Google Scholar]
  5. Nitopi S.; Bertheussen E.; Scott S. B.; Liu X.; Engstfeld A. K.; Horch S.; Seger B.; Stephens I. E. L.; Chan K.; Hahn C.; Nørskov J. K.; Jaramillo T. F.; Chorkendorff I. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Chem. Rev. 2019, 119, 7610–7672. 10.1021/acs.chemrev.8b00705. [DOI] [PubMed] [Google Scholar]
  6. Kuhl K. P.; Hatsukade T.; Cave E. R.; Abram D. N.; Kibsgaard J.; Jaramillo T. F. Electrocatalytic Conversion of Carbon Dioxide to Methane and Methanol on Transition Metal Surfaces. J. Am. Chem. Soc. 2014, 136, 14107–14113. 10.1021/ja505791r. [DOI] [PubMed] [Google Scholar]
  7. Kuhl K. P.; Cave E. R.; Abram D. N.; Jaramillo T. F. New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces. Energy Environ. Sci. 2012, 5, 7050–7059. 10.1039/c2ee21234j. [DOI] [Google Scholar]
  8. Terunuma Y.; Saitoh A.; Momose Y. Relationship between hydrocarbon production in the electrochemical reduction of CO2 and the characteristics of the Cu electrode. J. Electroanal. Chem. 1997, 434, 69–75. 10.1016/S0022-0728(97)00122-8. [DOI] [Google Scholar]
  9. Hori Y.; Murata A.; Takahashi R. Formation of Hydrocarbons in the Electrochemical Reduction of Carbon Dioxide at a Copper Electrode in Aqueous Solution. J. Chem. Soc., Faraday Trans. 1 1989, 85, 2309–2326. 10.1039/f19898502309. [DOI] [Google Scholar]
  10. Sen S.; Liu D.; Palmore G. T. R. Electrochemical Reduction of CO2 at Copper Nanofoams. ACS Catal. 2014, 4, 3091–3095. 10.1021/cs500522g. [DOI] [Google Scholar]
  11. Le M.; Ren M.; Zhang Z.; Sprunger P. T.; Kurtz R. L.; Flake J. C. Electrochemical Reduction of CO2 to CH3OH at Copper Oxide Surfaces. J. Electrochem. Soc. 2011, 158, E45–E49. 10.1149/1.3561636. [DOI] [Google Scholar]
  12. Ke F.-S.; Liu X.-C.; Wu J.; Sharma P. P.; Zhou Z.-Y.; Qiao J.; Zhou X.-D. Selective formation of C2 products from the electrochemical conversion of CO2 on CuO-derived copper electrodes comprised of nanoporous ribbon arrays. Catal. Today 2017, 288, 18–23. 10.1016/j.cattod.2016.10.001. [DOI] [Google Scholar]
  13. Li D.; Huang L.; Liu T.; Liu J.; Zhen L.; Wu J.; Feng Y. Electrochemical reduction of carbon dioxide to formate via nano-prism assembled CuO microspheres. Chemosphere 2019, 237, 124527 10.1016/j.chemosphere.2019.124527. [DOI] [PubMed] [Google Scholar]
  14. Ma M.; Djanashvili K.; Smith W. A. Selective Electrochemical Reduction of CO2 to CO on CuO-Derived Cu Nanowires. Phys. Chem. Chem. Phys. 2015, 17, 20861–20867. 10.1039/C5CP03559G. [DOI] [PubMed] [Google Scholar]
  15. Mistry H.; Varela A. S.; Bonifacio C. S.; Zegkinoglou I.; Sinev I.; Choi Y. W.; Kisslinger K.; Stach E. A.; Yang J. C.; Strasser P.; Cuenya B. R. Highly Selective Plasma-Activated Copper Catalysts for Carbon Dioxide Reduction to Ethylene. Nat. Commun. 2016, 7, 12123 10.1038/ncomms12123. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Li C. W.; Ciston J.; Kanan M. W. Electroreduction of carbon monoxide to liquid fuel on oxide-derived nanocrystalline copper. Nature 2014, 508, 504–507. 10.1038/nature13249. [DOI] [PubMed] [Google Scholar]
  17. Verdaguer-Casadevall A.; Li C. W.; Johansson T. P.; Scott S. B.; McKeown J. T.; Kumar M.; Stephens I. E. L.; Kanan M. W.; Chorkendorff I. Probing the Active Surface Sites for CO Reduction on Oxide-Derived Copper Electrocatalysts. J. Am. Chem. Soc. 2015, 137, 9808–9811. 10.1021/jacs.5b06227. [DOI] [PubMed] [Google Scholar]
  18. Feng X.; Jiang K.; Fan S.; Kanan M. W. A Direct Grain-Boundary-Activity Correlation for CO Electroreduction on Cu Nanoparticles. ACS Cent. Sci. 2016, 2, 169–174. 10.1021/acscentsci.6b00022. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Raciti D.; Wang Y.; Park J. H.; Wang C. Three-Dimensional Hierarchical Copper-Based Nanostructures as Advanced Electrocatalysts for CO2 Reduction. ACS Appl. Energy Mater. 2018, 1, 2392–2398. 10.1021/acsaem.8b00356. [DOI] [Google Scholar]
  20. Kim J.; Choi W.; Park J. W.; Kim C.; Kim M.; Song H. Branched Copper Oxide Nanoparticles Induce Highly Selective Ethylene Production by Electrochemical Carbon Dioxide Reduction. J. Am. Chem. Soc. 2019, 141, 6986–6994. 10.1021/jacs.9b00911. [DOI] [PubMed] [Google Scholar]
  21. Bae K.-L.; Kim J.; Lim C. K.; Nam K. M.; Song H. Colloidal zinc oxide-copper(I) oxide nanocatalysts for selective aqueous photocatalytic carbon dioxide conversion into methane. Nat. Commun. 2017, 8, 1156 10.1038/s41467-017-01165-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Schouten K. J. P.; Kwon Y.; van der Ham C. J. M.; Qin Z.; Koper M. T. M. A new mechanism for the selectivity to C1 and C2 species in the electrochemical reduction of carbon dioxide on copper electrodes. Chem. Sci. 2011, 2, 1902–1909. 10.1039/c1sc00277e. [DOI] [Google Scholar]
  23. Nie X.; Esopi M. R.; Janik M. J.; Asthagiri A. Selectivity of CO2 Reduction on Copper Electrodes: The Role of the Kinetics of Elementary Steps. Angew. Chem., Int. Ed. 2013, 52, 2459–2462. 10.1002/anie.201208320. [DOI] [PubMed] [Google Scholar]
  24. Dong H.; Li Y.; Jiang D.-E. First-Principles Insight into Electrocatalytic Reduction of CO2 to CH4 on a Copper Nanoparticle. J. Phys. Chem. C 2018, 122, 11392–11398. 10.1021/acs.jpcc.8b01928. [DOI] [Google Scholar]
  25. Keerthiga G.; Viswanathan B.; Chetty R. Electrochemical reduction of CO2 on electrodeposited Cu electrodes crystalline phase sensitivity on selectivity. Catal. Today 2015, 245, 68–73. 10.1016/j.cattod.2014.08.008. [DOI] [Google Scholar]
  26. Luo W.; Nie X.; Janik M. J.; Asthagiri A. Facet Dependence of CO2 Reduction Paths on Cu Electrodes. ACS Catal. 2016, 6, 219–229. 10.1021/acscatal.5b01967. [DOI] [Google Scholar]
  27. Bagger A.; Ju W.; Varela A. S.; Strasser P.; Rossmeisl J. Electrochemical CO2 Reduction: A Classification Problem. ChemPhysChem 2017, 18, 3266–3273. 10.1002/cphc.201700736. [DOI] [PubMed] [Google Scholar]
  28. Hall A. S.; Yoon Y.; Wuttig A.; Surendranath Y. Mesostructure-Induced Selectivity in CO2 Reduction Catalysis. J. Am. Chem. Soc. 2015, 137, 14834–14837. 10.1021/jacs.5b08259. [DOI] [PubMed] [Google Scholar]
  29. Raciti D.; Wang C. Recent Advances in CO2 Reduction Electrocatalysis on Copper. ACS Energy Lett. 2018, 3, 1545–1556. 10.1021/acsenergylett.8b00553. [DOI] [Google Scholar]
  30. Karapinar D.; Huan N. T.; Sahraie N. R.; Li J.; Wakerley D.; Touati N.; Zanna S.; Taverna D.; Tizei L. H. G.; Zitolo A.; Jaouen F.; Mougel V.; Fontecave M. Electroreduction of CO2 on Single-Site Copper-Nitrogen-Doped Carbon Material: Selective Formation of Ethanol and Reversible Restructuration of the Metal Sites. Angew. Chem., Int. Ed. 2019, 58, 15098–15103. 10.1002/anie.201907994. [DOI] [PubMed] [Google Scholar]
  31. Zhao K.; Liu Y.; Quan X.; Chen S.; Yu H. CO2 Electroreduction at Low Overpotential on Oxide-Derived Cu/Carbons Fabricated from Metal Organic Framework. ACS Appl. Mater. Interfaces 2017, 9, 5302–5311. 10.1021/acsami.6b15402. [DOI] [PubMed] [Google Scholar]
  32. Chen C.; Yan X.; Liu S.; Wu Y.; Wan Q.; Sun X.; Zhu Q.; Liu H.; Ma J.; Zheng L.; Wu H.; Han B. Highly Efficient Electroreduction of CO2 to C2+ Alcohols on Heterogeneous Dual Active Sites. Angew. Chem., Int. Ed. 2020, 59, 16459–16464. 10.1002/anie.202006847. [DOI] [PubMed] [Google Scholar]
  33. Wang H.; Tzeng Y.-K.; Ji Y.; Li Y.; Li J.; Zheng X.; Yang A.; Liu Y.; Gong Y.; Cai L.; Li Y.; Zhang X.; Chen W.; Liu B.; Lu H.; Melosh N. A.; Shen Z.-X.; Chan K.; Tan T.; Chu S.; Cui Y. Synergistic enhancement of electrocatalytic CO2 reduction to C2 oxygenates at nitrogen-doped nanodiamonds/Cu interface. Nat. Nanotechnol. 2020, 15, 131–137. 10.1038/s41565-019-0603-y. [DOI] [PubMed] [Google Scholar]
  34. Zarandi R. F.; Rezaei B.; Ghaziaskar H. S.; Ensafi A. A. Modification of Copper Electrode with Copper Nanoparticles@ Reduced Graphene Oxide-Nile Blue and Its Application in Electrochemical CO2 Conversion. Mater. Today Energy 2020, 18, 100507 10.1016/j.mtener.2020.100507. [DOI] [Google Scholar]
  35. Li Q.; Zhu W.; Fu J.; Zhang H.; Wu G.; Sun S. Controlled assembly of Cu nanoparticles on pyridinic-N rich graphene for electrochemical reduction of CO2 to ethylene. Nano Energy 2016, 24, 1–9. 10.1016/j.nanoen.2016.03.024. [DOI] [Google Scholar]
  36. Wang X.; Wang Z.; de Arquer F. P. G.; Dinh C.-T.; Ozden A.; Li Y. C.; Nam D.-H.; Li J.; Liu Y.-S.; Wicks J.; Chen Z.; Chi M.; Chen B.; Wang Y.; Tam J.; Howe J. Y.; Proppe A.; Todorović P.; Li F.; Zhuang T.-T.; Gabardo C. M.; Kirmani A. R.; McCallum C.; Hung S.-F.; Lum Y.; Luo M.; Min Y.; Xu A.; O’Brien C. P.; Stephen B.; Sun B.; Ip A. H.; Richter L. J.; Kelley S. O.; Sinton D.; Sargent E. H. Efficient electrically powered CO2-to-ethanol via suppression of deoxygenation. Nat. Energy 2020, 5, 478–486. 10.1038/s41560-020-0607-8. [DOI] [Google Scholar]
  37. Bulushev D. A.; Chuvilin A. L.; Sobolev V. I.; Stolyarova S. G.; Shubin Y. V.; Asanov I. P.; Ishchenko A. V.; Magnani G.; Riccò M.; Okotrub A. V.; Bulusheva L. G. Copper on carbon materials: stabilization by nitrogen doping. J. Mater. Chem. A 2017, 5, 10574–10583. 10.1039/C7TA02282D. [DOI] [Google Scholar]
  38. Liu Z.; Cao J.; Wu B.; Qian L.; Guan A.; Yang C.; Lv X.; Zhang L.; Zheng G. Surface Energy Tuning on Cu/NC Catalysts for CO Electroreduction. ACS Catal. 2022, 12, 12555–12562. 10.1021/acscatal.2c02261. [DOI] [Google Scholar]
  39. Zhang J.; Guo Y.; Shang B.; Fan T.; Lian X.; Huang P.; Dong Y.; Chen Z.; Yi X. Unveiling the Synergistic Effect between Graphitic Carbon Nitride and Cu2O toward CO2 Electroreduction to C2H4. ChemSusChem 2021, 14, 929–937. 10.1002/cssc.202002427. [DOI] [PubMed] [Google Scholar]
  40. Li H.; Cao S.; Sun H.; Lu Y.; Zhang Y.; Lu X.; Zeng J.; Yan Z. CuNCN derived Cu-based/CxNy catalysts for highly selective CO2 electroreduction to hydrocarbons. Appl. Catal., B 2023, 320, 121948 10.1016/j.apcatb.2022.121948. [DOI] [Google Scholar]
  41. Pan Y.; Li H.; Xiong J.; Yu Y.; Du H.; Li S.; Wu Z.; Li S.; Lai J.; Wang L. Protecting the state of Cu clusters and nanoconfinement engineering over hollow mesoporous carbon spheres for electrocatalytical C-C coupling. Appl. Catal., B 2022, 306, 121111 10.1016/j.apcatb.2022.121111. [DOI] [Google Scholar]
  42. Zhao S.; Tang Z.; Guo S.; Han M.; Zhu C.; Zhou Y.; Bai L.; Gao J.; Huang H.; Li Y.; Liu Y.; Kang Z. Enhanced Activity for CO2 Electroreduction on a Highly Active and Stable Ternary Au-CDots-C3N4 Electrocatalyst. ACS Catal. 2018, 8, 188–197. 10.1021/acscatal.7b01551. [DOI] [Google Scholar]
  43. Woyessa G. W.; dela Cruz J.-a. B.; Rameez M.; Hung C.-H. Nanocomposite catalyst of graphitic carbon nitride and Cu/Fe mixed metal oxide for electrochemical CO2 reduction to CO. Appl. Catal., B 2021, 291, 120052 10.1016/j.apcatb.2021.120052. [DOI] [Google Scholar]
  44. Zhang L.; Mao F.; Zheng L. R.; Wang H. F.; Yang X. H.; Yang H. G. Tuning Metal Catalyst with Metal–C3N4 Interaction for Efficient CO2 Electroreduction. ACS Catal. 2018, 8, 11035–11041. 10.1021/acscatal.8b03789. [DOI] [Google Scholar]
  45. Jiao Y.; Zheng Y.; Chen P.; Jaroniec M.; Qiao S.-Z. Molecular Scaffolding Strategy with Synergistic Active Centers To Facilitate Electrocatalytic CO2 Reduction to Hydrocarbon/Alcohol. J. Am. Chem. Soc. 2017, 139, 18093–18100. 10.1021/jacs.7b10817. [DOI] [PubMed] [Google Scholar]
  46. Fu S.; Liu X.; Ran J.; Jiao Y.; Qiao S.-Z. CO2 reduction by single copper atom supported on g-C3N4 with asymmetrical active sites. Appl. Surf. Sci. 2021, 540, 148293 10.1016/j.apsusc.2020.148293. [DOI] [Google Scholar]
  47. Lin W.; Chen H.; Li Z.; Sasaki K.; Yao S.; Zhang Z.; Li J.; Fu J. A Cu2O-derived Polymeric Carbon Nitride Heterostructured Catalyst for the Electrochemical Reduction of Carbon Dioxide to Ethylene. ChemSusChem 2021, 14, 3190–3197. 10.1002/cssc.202100659. [DOI] [PubMed] [Google Scholar]
  48. Zhao J.; Zhao J.; Li F.; Chen Z. Copper Dimer Supported on A C2N Layer as an Efficient Electrocatalyst for Co2 Reduction Reaction: A Computational Study. J. Phys. Chem. C 2018, 122, 19712–19721. 10.1021/acs.jpcc.8b06494. [DOI] [Google Scholar]
  49. Thomas A.; Fischer A.; Goettmann F.; Antonietti M.; Müller J.-O.; Schlögl R.; Carlsson J. M. Graphitic Carbon Nitride Materials: Variation of Structure and Morphology and Their Use as Metal-Free Catalysts. J. Mater. Chem. 2008, 18, 4893–4908. 10.1039/b800274f. [DOI] [Google Scholar]
  50. Mourdikoudis S.; Liz-Marzán L. M. Oleylamine in Nanoparticle Synthesis. Chem. Mater. 2013, 25, 1465–1476. 10.1021/cm4000476. [DOI] [Google Scholar]
  51. Zhang J.; Fang J. A General Strategy for Preparation of Pt 3d-Transition Metal (Co, Fe, Ni) Nanocubes. J. Am. Chem. Soc. 2009, 131, 18543–18547. 10.1021/ja908245r. [DOI] [PubMed] [Google Scholar]
  52. Zhu W.; Michalsky R.; Metin Ö.; Lv H.; Guo S.; Wright C. J.; Sun X.; Peterson A. A.; Sun S. Monodisperse Au Nanoparticles for Selective Electrocatalytic Reduction of CO2 to CO. J. Am. Chem. Soc. 2013, 135, 16833–16836. 10.1021/ja409445p. [DOI] [PubMed] [Google Scholar]
  53. Liu X. W.; Geng B. Y.; Du Q. B.; Ma J. Z.; Liu X. M. Temperature-Controlled Self-Assembled Synthesis of CuO,Cu2O and Cu Nanoparticles through a Single-Precursor Route. Mater. Sci. Eng.: A 2007, 448, 7–14. 10.1016/j.msea.2006.08.104. [DOI] [Google Scholar]
  54. Niu P.; Zhang L.; Liu G.; Cheng H. M. Graphene-Like Carbon Nitride Nanosheets for Improved Photocatalytic Activities. Adv. Funct. Mater. 2012, 22, 4763–4770. 10.1002/adfm.201200922. [DOI] [Google Scholar]
  55. Li D.; Wang C.; Tripkovic D.; Sun S.; Markovic N. M.; Stamenkovic V. R. Surfactant Removal for Colloidal Nanoparticles from Solution Synthesis: The Effect on Catalytic Performance. ACS Catal. 2012, 2, 1358–1362. 10.1021/cs300219j. [DOI] [Google Scholar]
  56. Lee Y. H.; Lee G.; Shim J. H.; Hwang S.; Kwak J.; Lee K.; Song H.; Park J. T. Monodisperse PtRu Nanoalloy on Carbon as a High-Performance DMFC Catalyst. Chem. Mater. 2006, 18, 4209–4211. 10.1021/cm052881k. [DOI] [Google Scholar]
  57. Yan S. C.; Li Z. S.; Zou Z. G. Photodegradation Performance of g-C3N4 Fabricated by Directly Heating Melamine. Langmuir 2009, 25, 10397–10401. 10.1021/la900923z. [DOI] [PubMed] [Google Scholar]
  58. Wang X.; Chen X.; Thomas A.; Fu X.; Antonietti M. Metal-Containing Carbon Nitride Compounds: A New Functional Organic-Metal Hybrid Material. Adv. Mater. 2009, 21, 1609–1612. 10.1002/adma.200802627. [DOI] [Google Scholar]
  59. Sun B.-w.; Yu H.-y.; Yang Y.-j.; Li H.-j.; Zhai C.-y.; Qian D.-J.; Chen M. New complete assignment of X-ray powder diffraction patterns in graphitic carbon nitride using discrete Fourier transform and direct experimental evidence. Phys. Chem. Chem. Phys. 2017, 19, 26072–26084. 10.1039/C7CP05242A. [DOI] [PubMed] [Google Scholar]
  60. Kulkarni R.; Kunwar S.; Mandavkar R.; Jeong J.-H.; Lee J. Hydrogen Peroxide Detection by Super-Porous Hybrid CuO/Pt NP Platform: Improved Sensitivity and Selectivity. Nanomaterials 2020, 10, 2034 10.3390/nano10102034. [DOI] [PMC free article] [PubMed] [Google Scholar]
  61. Lu X.; Tan T. H.; Ng Y. H.; Amal R. Highly Selective and Stable Reduction of CO2 to CO by a Graphitic Carbon Nitride/Carbon Nanotube Composite Electrocatalyst. Chem. - Eur. J. 2016, 22, 11991–11996. 10.1002/chem.201601674. [DOI] [PubMed] [Google Scholar]
  62. Kim D.; Kley C. S.; Li Y.; Yang P. Copper Nanoparticle Ensembles for Selective Electroreduction of CO2 to C2–C3 Products. Proc. Natl. Acad. Sci. U.S.A. 2017, 114, 10560–11056. 10.1073/pnas.1711493114. [DOI] [PMC free article] [PubMed] [Google Scholar]
  63. Reske R.; Mistry H.; Behafarid F.; Cuenya B. R.; Strasser P. Particle Size Effects in the Catalytic Electroreduction of CO2 on Cu Nanoparticles. J. Am. Chem. Soc. 2014, 136, 6978–6986. 10.1021/ja500328k. [DOI] [PubMed] [Google Scholar]
  64. Singh A. K.; Yasri N.; Karan K.; Roberts E. P. L. Electrocatalytic Activity of Functionalized Carbon Paper Electrodes and Their Correlation to the Fermi Level Derived from Raman Spectra. ACS Appl. Energy Mater. 2019, 2, 2324–2336. 10.1021/acsaem.9b00180. [DOI] [Google Scholar]
  65. Lee S. H.; Lin J. C.; Farmand M.; Landers A. T.; Feaster J. T.; Acosta J. E. A.; Beeman J. W.; Ye Y.; Yano J.; Mehta A.; Davis R. C.; Jaramillo T. F.; Hahn C.; Drisdell W. S. Oxidation State and Surface Reconstruction of Cu under CO2 Reduction Conditions from in Situ X-Ray Characterization. J. Am. Chem. Soc. 2021, 143, 588–592. 10.1021/jacs.0c10017. [DOI] [PubMed] [Google Scholar]
  66. Möller T.; Scholten F.; Thanh T. N.; Sinev I.; Timoshenko J.; Wang X.; Jovanov Z.; Gliech M.; Cuenya B. R.; Varela A. S.; Strasser P. Electrocatalytic CO2 reduction on CuOx nanocubes: Tracking the evolution of chemical state, geometric structure, and catalytic selectivity using operando spectroscopy. Angew. Chem., Int. Ed. 2020, 59, 17974–17983. 10.1002/anie.202007136. [DOI] [PMC free article] [PubMed] [Google Scholar]
  67. Wang X.; Varela A. S.; Bergmann A.; Kühl S.; Strasser P. Catalyst Particle Density Controls Hydrocarbon Product Selectivity in CO2 Electroreduction on CuOx. ChemSusChem 2017, 10, 4642–4649. 10.1002/cssc.201701179. [DOI] [PubMed] [Google Scholar]
  68. Peterson A. A.; Abild-Pedersen F.; Studt F.; Rossmeisl J.; Nørskov J. K. How Copper Catalyzes the Electroreduction of Carbon Dioxide into Hydrocarbon Fuels. Energy Environ. Sci. 2010, 3, 1311–1315. 10.1039/c0ee00071j. [DOI] [Google Scholar]
  69. Zhang H.; Chang X.; Chen J. G.; Goddard W. A. III; Xu B.; Cheng M. J.; Lu Q. Computational and experimental demonstrations of one-pot tandem catalysis for electrochemical carbon dioxide reduction to methane. Nat. Commun. 2019, 10, 3340 10.1038/s41467-019-11292-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  70. Mangione G.; Huang J.; Buonsanti R.; Corminboeuf C. Dual-Facet Mechanism in Copper Nanocubes for Electrochemical CO2 Reduction into Ethylene. J. Phys. Chem. Lett. 2019, 10, 4259–4265. 10.1021/acs.jpclett.9b01471. [DOI] [PubMed] [Google Scholar]
  71. Todorova T. K.; Schreiber M. W.; Fontecave M. Mechanistic Understanding of CO2 Reduction Reaction (CO2RR) Toward Multicarbon Products by Heterogeneous Copper-Based Catalysts. ACS Catal. 2020, 10, 1754–1768. 10.1021/acscatal.9b04746. [DOI] [Google Scholar]
  72. Chang C.-C.; Ku M.-S. Role of High-Index Facet Cu(711) Surface in Controlling the C2 Selectivity for CO2 Reduction Reaction - A DFT Study. J. Phys. Chem. C 2021, 125, 10919–10925. 10.1021/acs.jpcc.1c00297. [DOI] [Google Scholar]

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