In/ZnO@C hollow nanocubes for efficient electrochemical reduction of CO2 to formate and rechargeable Zn–CO2 batteries

Abstract

Indium (In)-based materials are considered promising electrocatalysts for CO₂ reduction to formic acid, but their performance is usually limited by low current density and poor stability. Here, we describe In/ZnO@C hollow nanocubes (NCs), derived from In(OH)₃-doped Zn-MOF (i.e. ZIF-8) solid nanocubes, as high-performance CO₂-reduction electrocatalysts. The unique nanocube morphology of Zn-MOF makes it an ideal matrix for dispersing In(OH)₃ which can avoid aggregation. The formation of a hollow structure is associated with metallic In formation and CO₂/CO gas release, resulting from the carbothermal reduction reaction between In(OH)₃ and the carbon matrix. In/ZnO@C NCs exhibit excellent catalytic activity and selectivity for formate production, reaching a partial current density of 23.5 mA cm⁻² with a Faradaic efficiency of 90% at −1.2 V vs. RHE in 0.5 M aqueous KHCO₃ solutions, which is greatly superior to In-free ZnO@C NCs and simple In nanoparticles. Solar-driven electrochemical CO₂/H₂O splitting can be realized by coupling the In/ZnO@C cathode with a RuO₂ anode, offering a promising route to the storage of renewable energy. As a promising technique for CO₂ fixation/utilization and energy conversion/storage, an aqueous rechargeable Zn–CO₂ battery with In/ZnO@C as the cathode is also constructed. It can output electrical energy with an open-circuit voltage of 1.35 V and a peak power density of 1.32 mW cm⁻² while simultaneously realizing CO₂ conversion to formate. The Zn–CO₂ battery with In/ZnO@C inspires the development of green energy conversion and storage systems combining eco-efficient CO₂ utilization.