In situ Observation of Electrodeposited Bimetallic p‐Si Micropillar Array Photocathode for Solar‐Driven Hydrogen Evolution

The integration of Earth‐abundant materials with light‐harvesting absorbers to create a high‐efficiency photocathode is a promising approach for solar‐driven water splitting. It is essential for such systems to provide a practical photocurrent response and overpotential for driving hydrogen production. Herein, electrodeposited Ni–M (M = Co, Fe, Mo) is investigated as a surface catalyst onto p‐type silicon micropillar arrays for solar‐driven hydrogen evolution, and the generation of catalytic active species by in situ and ex situ tracking methods is directly observed. The dynamic electronic and atomic structures of highly active surface catalysts are identified during photocatalysis in alkaline condition. Furthermore, the incorporation of high‐valence Mo species acts as a key promoter for triggering the in situ formation of active Ni 2+ species on the surface of alloys. These findings offer guidelines for the design and development of highly efficient catalytic photocathodes.