Unassisted PEC Water Splitting Using III–V Multijunction Photoabsorbers: Insights into the Degradation Mechanism

Despite the record solar-to-hydrogen efficiencies achieved by III–V semiconductor-based photoabsorbers, their lack of long-term stability during unassisted water splitting remains a major barrier to scalable solar hydrogen production. Here, we identify the degradation mechanism in Pt/TiO₂/III–V photocathodes, with catalyst detachment emerging as the primary initiator. Using a combination of front-contact potential measurements, nanoscale imaging, and elemental analysis of both the surface and electrolyte composition, we demonstrate that Pt detachment increases the HER overpotential, driving TiO₂into a thermodynamically unstable regime. This instability leads to TiO₂dissolution, which subsequently exposes the photoabsorber to cathodic corrosion. The degradation proceeds in a sequential cascade, independent of whether the device operates in a two- or three-electrode configuration, highlighting the critical role of local catalyst potential in governing corrosion. Based on this adhesion-driven degradation mechanism, we propose practical interface engineering strategies to enhance durability and advance PEC devices toward real-world implementation.