Oxygen-vacancy-rich nickel hydroxide nanosheet: a multifunctional layer between Ir and Si toward enhanced solar hydrogen production in alkaline media

The combination of noble metal catalysts and semiconductors presents a typical avenue for boosting photoelectrochemical (PEC) hydrogen production. However, noble metal catalysts directly deposited on Si can easily aggregate into large clusters and tend to peel off from the Si surface, thereby limiting the effective use of noble metal and PEC performance of the Si photocathode. Here, we report that oxygen-vacancy-rich Ni(OH)(2) nanosheets are developed as an ideal multifunctional layer between an Ir catalyst and Ni protected Si photocathode, which could not only effectively capture and stabilize atomic Ir via the newly formed O-Ir-O bonds, but also significantly enhance the reaction kinetics by accelerating charge and mass transport and reducing the energy barriers of both the Volmer and Tafel steps. A benchmarking applied bias photon-to-current efficiency (ABPE) of 12.4% and a sustainable stability of more than 300 h are achieved under AM1.5G one sun illumination, outperforming all the previously reported Si photocathodes in alkaline media. Our findings emphasize the importance of the interlayer for the Si photocathode and offer the avenue to achieve highly efficient and durable PEC devices.