Light‐Induced Dynamic Activation of Copper/Silicon Interface for Highly Selective Carbon Dioxide Reduction

Abstract

Numerous studies have shown a fact that phase transformation and/or reconstruction are likely to occur and play crucial roles in electrochemical scenarios. Nevertheless, a decisive factor (such as facet, phase etc.) behind the diverse photoelectrochemical activity and selectivity of various copper/silicon photoelectrodes is still largely debated and missing in the community, especially for possibly dynamic behaviors of metal catalyst/semiconductor interface. Herein, through in situ X‐ray absorption spectroscopy and transmission electron microscope, a model system of Cu nanocrystals with well‐defined facets on black p‐type silicon (BSi) is demonstrated to unprecedentedly reveal the dynamic phase transformation of forming irreversible silicide at Cu nanocrystal‐BSi interface, which is validated to originate from the atomic interdiffusion between Cu and Si driven by light‐induced dynamic activation process. The presence of in situ formed silicide can significantly enhance photovoltage and deliver a record‐high onset potential above ‐0.4 V versus reversible reference electrode (RHE) for photoelectrochemical CH4 production. Significantly, the adaptive junction at Cu/Si interface is activated by an expansion of interatomic Cu‐Cu distance, which efficiently restricts the C‐C coupling pathway but strengthens the bonding with key intermediate of *CHO for CH4 yield, resulting in a remarkable 16‐fold improvement in the product ratio of CH4/C2 products.