Wide Range pH-Tolerable Silicon@Pyrite Cobalt Dichalcogenide Microwire Array Photoelectrodes for Solar Hydrogen Evolution

Abstract

This study employed silicon@cobalt dichalcogenide microwires (MWs) as wide range pH-tolerable photocathode material for solar water splitting. Silicon microwire arrays were fabricated through lithography and dry etching technologies. Si@Co(OH)2 MWs were utilized as precursors to synthesize Si@CoX2 (X = S or Se) photocathodes. Si@CoS2 and Si@CoSe2 MWs were subsequently prepared by thermal sulfidation and hydrothermal selenization reaction of Si@Co(OH)2, respectively. The CoX2 outer shell served as cocatalyst to accelerate the kinetics of photogenerated electrons from the underlying Si MWs and reduce the recombination. Moreover, the CoX2 layer completely deposited on the Si surface functioned as a passivation layer by decreasing the oxide formation on Si MWs during solar hydrogen evolution. Si@CoS2 photocathode showed a photocurrent density of −3.22 mA cm–2 at 0 V (vs RHE) in 0.5 M sulfuric acid electrolyte, and Si@CoSe2 MWs revealed moderate photocurrent density of −2.55 mA cm–2. However, Si@CoSe2 presented high charge transfer efficiency in neutral and alkaline electrolytes. Continuous chronoamperometry in acid, neutral, and alkaline solutions was conducted at 0 V (vs RHE) to evaluate the photoelectrochemical durability of Si@CoX2 MWs. Si@CoS2 electrode showed no photoresponse after the chronoamperometry test because it was etched through the electrolyte. By contrast, the photocurrent density of Si@CoSe2 MWs gradually increased to −5 mA cm–2 after chronoamperometry characterization owing to the amorphous structure generation.