Surface‐Structured Cocatalyst Foils Unraveling a Pathway to High‐Performance Solar Water Splitting

AbstractAn ideal catalytic interface for photoelectrodes that enables high efficiency and long‐term stability remains one of the keys to unlocking high‐performance solar water splitting. Here, fully decoupled catalytic interfaces realized using surface‐structured cocatalyst foils are demonstrated, allowing optimized photoabsorbers to be combined with high‐performance earth‐abundant cocatalysts. Since many earth‐abundant cocatalysts are deposited via solution‐based methods, deposition on chemical‐sensitive photoabsorbers is a significant challenge. By synthesizing cocatalyst foils prior to device fabrication, photoabsorbers are completely isolated from corrosive chemical environments and are provided with outstanding protection during operation. Si and GaAs photoelectrodes prepared using Ni‐based cocatalyst foils achieve excellent half‐cell efficiencies and generate stable photocurrents for over 5 days. Furthermore, a GaAs artificial leaf achieves a solar‐to‐hydrogen efficiency of 13.6% and maintains an efficiency of over 10% for longer than nine days, an accomplishment that has not been previously reported for an immersed solar water splitting system. These results, together with theoretical calculations of other photoelectrode systems, demonstrate that cocatalyst foils offer a very attractive method for fabricating high‐performance solar water splitting systems.