Fig. 3.

Effect of electron deficient Cu nanoparticles on the catalytic performance. EDD stereograms of a Cu/PI and b Cu/C models. c Experimentally estimated work functions and band structures of Cu and PI components (left) and schematic diagram of rectifying contact of Cu and PI hybrid (right), resulting in electron rich (red) and deficient (blue) areas at their interface. The estimated work functions from UPS analysis d and X-ray photoelectron spectroscopy (XPS) Cu 2p spectra e of Cu/PI samples. f The calculated adsorption energies of N₂ molecules on pristine Cu (Cu) and electron-deficient Cu (Cu-0.04e⁻and Cu-0.06e⁻) surface. g The N₂-temperature programmed desorption (TPD) results of Cu/PI catalysts (spheres) and corresponding bare PI supports (circles). h The cyclic voltammograms (CVs) of Cu/PI electrodes (catalyst loading: 1 mg cm⁻²) at a scan rate of 5 mV s⁻¹ in Ar-saturated 0.1 M KOH. i The NH₃ yield rates and Faradaic efficiencies of Cu/PI electrodes at −0.3 V vs. RHE. Insets: f EDD stereograms of N₂ molecules on pristine Cu (Cu) and electron-deficient Cu (Cu-0.04e⁻and Cu-0.06e⁻) surface. h the deactivation mechanism of the HER process over electron deficient Cu nanoparticles in Cu/PI-300; i proposed electron localization at the Cu-PI boundaries