Sandwich-nanostructured n-Cu2O/AuAg/p-Cu2O Photocathode with Highly Positive Onset Potential for Improved Water Reduction

A n-Cu2O layer formed a high-quality buried junction with p-Cu2O to increase the photovoltage and thus to shift the turn-on voltage positively. Mott−Schottky measurements confirmed that the improvement benefited from a thermodynamic shift of the flat-band potentials. The obtained extremely positive onset potential, 0.8 V (vs. RHE) in n-Cu2O/AuAg/p-Cu2O, is comparable with measurements from water-reduction catalysts. The AuAg alloy sandwiched between the homojunction of n-Cu2O and p-Cu2O improved the photocatalytic performance. This alloy both served as an electron relay and promoted electron-hole pair generation in nearby semiconductors; the charge transfer between n-Cu2O and p-Cu2O in the sandwich structure was measured with X-ray absorption spectra. Acting as a plasmonic photosensitizer, the alloy increased the efficiency of conversion of solar energy to electric current. The mechanism of plasmonic energy transfer involved a direct transfer of the plasmonic hot carriers; the interfacial Schottky barrier...