Engineering Surface Architectures for Improved Durability in III-V Photocathodes.

GaInP ₂ has shown promise as the wide bandgap top junction in tandem absorber photoelectrochemical (PEC) water splitting devices. Among previously reported dual-junction PEC devices with a GaInP ₂ top cell, those with the highest performance incorporate an AlInP ₂ window layer (WL) to reduce surface recombination and a thin GaInP ₂ capping layer (CL) to protect the WL from corrosion in electrolytes. However, the stability of these III-V systems is limited, and durability continues to be a major challenge broadly in the field of PEC water splitting. This work provides a systematic investigation into the durability of GaInP ₂ systems, examining the impacts of the window layer and capping layer among single junction pn-GaInP ₂ photocathodes coated with an MoS ₂ catalytic and protective layer. The photocathode with both a CL and WL demonstrates the highest PEC performance and longest lifetime, producing a significant current for >125 h. In situ optical imaging and post-test characterization illustrate the progression of macroscopic degradation and chemical state. The surface architecture combining an MoS ₂ catalyst, CL, and WL can be translated to dual-junction PEC devices with GaInP ₂ or other III-V top junctions to enable more efficient and stable PEC systems.