Graphene/Si Heterojunction Platform with a Multifunctional Atomic Bridging Layer for Photoelectrochemical CO2 Reduction

The facile integration and stability of Si-based photoelectrode architectures are the remaining challenges in the photoelectrochemical (PEC) conversion of CO2 to fuels. In this work, the single-atomic-layer graphene is used as a functional bridging layer to integrate both Si photocathodes and photoanodes, which enable the direct electrodeposition of metal-based electrocatalysts (Cu, Ag, and In–Sn alloys) and a semiconductor-based catalyst Ni–Fe layered double hydroxide (Ni–Fe LDH) on graphene/Si heterojunction electrodes for PEC CO2 reduction and O2 evolution reactions, respectively. We demonstrate a PEC device with a full-cell configuration consisting of an In–Sn/graphene/Si heterojunction photocathode and a Ni–Fe LDH/graphene/Si heterojunction photoanode, exhibiting a reduced photovoltage of ∼1080 mV compared to the electrochemical counterparts. A self-powered PEC CO2 reduction with a solar-to-fuel conversion efficiency of 3.2% can be obtained by integrating the graphene/Si heterojunction photocathode and photoanode with a Si photovoltaic. In addition, in situ PEC X-ray absorption spectroscopy analyses show that the electrodeposited catalysts on the graphene layer lead to the transport of photogenerated electrons and preserve durability throughout the reaction. Utilizing graphene as a chemically inert atomic bridging layer enables the seamless integration of Si photoelectrodes with various catalysts, providing a platform for the PEC CO2 reduction reaction.