Tunable Electrodeposition of Ni Electrocatalysts onto Si Microwires Array for Photoelectrochemical Water Oxidation

High‐aspect‐ratio silicon microwire (Si MW) arrays are expected to act as potential absorbers for solar energy conversion due to their excellent optically absorption capability and shorter diffusion length for collecting charge carriers. To date, most of the studies on structured Si microwire arrays devices are focusing on photocathode for the photoelectrochemical hydrogen production, only a handful of reports attempt to use photoanode based on Si microwire arrays for water oxidation. Herein, a tunable electrodeposition technique for decorating isolated Ni nanoparticles as a both protecting and oxygen evolution electrocatalyst onto the n‐type Si MW is demonstrated. The Si microwire array photoanodes with optimized surface decoration show a stable photocurrent density of 10 mA cm −2 in 1 m KOH electrolyte for several hours without additional protecting layer in addition to Ni nanoparticles, in which the optimized photoanode is able to produce a maximum photocurrent density of 35.5 mA cm −2 .