Polyimide stabilized Cu2O photocathode for efficient PEC water reduction

Cuprous oxide (Cu 2 O) is a promising photocathode for photo-electrochemical hydrogen production. One of the main issues limiting the application of Cu 2 O is photo-corrosion in aqueous electrolyte during the PEC process. Herein, to improve the stability of Cu 2 O, for the first time, a soluble polymer polyimide (PI) was introduced as a protective layer using a facile spin-coating method. It was found that dense PI films effectively isolated Cu 2 O from the aqueous electrolyte and inhibited self-reduction and oxidation reactions of Cu 2 O as evidenced by XRD spectra. Compared with bare Cu 2 O, the photocurrent density and stability of modified Cu 2 O samples were increased with increasing the spin-coating amount of PI solutions. It was found that sample Cu 2 O/PI-200 showed the highest current density value of 1.8 mA/cm 2 at 0 V RHE after 1200 s without attenuation, which is 40 times higher than the bare Cu 2 O (0.04 mA/cm 2 at 0 V RHE ). Further enhancing the PI amount, such as sample Cu 2 O/PI-300, will lead to a very stable but lower current density (1.48 mA/cm 2 ) during the whole test duration. EIS measurements indicated that thicker PI films lead to larger charge transfer resistance and higher capacitance in the space charge layer. Therefore, there is an optimum amount of PI (Cu 2 O/PI-200) to balance the above two opposite effects and achieve the best PEC performance. This work provides a facile strategy to improve the PEC activity and stability of Cu 2 O, which may be extended to other systems with photo-corrosion problems, such as BiVO 4 or ZnO.