Wittichenite semiconductor of CuBiS films for efficient hydrogen evolution from solar driven photoelectrochemical water splitting.

A highly efficient, low-cost and environmentally friendly photocathode with long-term stability is the goal of practical solar hydrogen evolution applications. Here, we found that the CuBiS film-based photocathode meets the abovementioned requirements. The CuBiS-based photocathode presents a remarkable onset potential over 0.9 V with excellent photoelectrochemical current densities (~7 mA/cm under 0 V) and appreciable 10-hour long-term stability in neutral water solutions. This high onset potential of the CuBiS-based photocathode directly results in a good unbiased operating photocurrent of ~1.6 mA/cm assisted by the BiVO photoanode. A tandem device of CuBiS-BiVO with an unbiased solar-to-hydrogen conversion efficiency of 2.04% is presented. This tandem device also presents high stability over 20 hours. Ultimately, a 5 × 5 cm large CuBiS-BiVO tandem device module is fabricated for standalone overall solar water splitting with a long-term stability of 60 hours.