Sandwich-Nanostructured n-CuO/AuAg/p-CuO Photocathode with Highly Positive Onset Potential for Improved Water Reduction.

An n-CuO layer formed a high-quality buried junction with p-CuO to increase the photovoltage and thus to shift the turn-on voltage positively. Mott-Schottky measurements confirmed that the improvement benefited from a positive shift in flat-band potential. The obtained extremely positive onset potential, 0.8 V in n-CuO/AuAg/p-CuO, is comparable with measurements from water reduction catalysts. The AuAg alloy sandwiched between the homojunction of n-CuO and p-CuO 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-CuO and p-CuO in the sandwich structure was measured with X-ray absorption spectra. The proposed sandwich structure can be considered as a new direction for the design of efficient solar-related devices.