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CIGS (Cu(In,Ga)(S,Se)₂) is a promising photocathode material owing to its high absorption coefficient, adjustable band gap and suitable band edge for the hydrogen evolution reaction (HER). However, most CIGS photocathodes suffer from instability for applications in a wide range of pH conditions and require rare-earth metal HER catalysts to achieve a high performance. Thus, improving the durability of the CIGS photocathode and developing a cost-effective non-noble metal catalyst are critical issues in the photoelectrochemical (PEC) application of this promising photocathode material. Herein, we catalyze the CIGS photocathode with Ni-Mo as a non-noble metal to enhance the PEC efficiency and employ atomically grown TiO₂ to passivate the CdS/CIGS to improve the stability. Our Ni-Mo alloy exhibits the best HER catalytic activity among reported earth-abundant HER catalysts in wide pH conditions. The Ni-Mo/CdS/CIGS photocathode yields an onset potential of 0.5 V (vs RHE) and a short circuit photocurrent density as high as ~ 25 mA/cm². Furthermore, the TiO₂ passivation effectively prevents the photocorrosion of CdS and the dissolution of the Mo back contact, which are main causes of the photocathode degradation. The optimized Ni-Mo/TiO₂/CdS/CIGS photocathode produces a stable photocurrent density for 100 minutes. This work presents a very useful method to improve the efficiency and durability of CIGS photocathodes with an earth-abundant metal catalyst which completely replaces Pt.
PMID: 30134016 [PubMed - as supplied by publisher]