MOF-Transformed In₂O_3-x@C Nanocorn Electrocatalyst for Efficient CO₂ Reduction to HCOOH

For electrochemical CO₂ reduction to HCOOH, an ongoing challenge is to design energy efficient electrocatalysts that can deliver a high HCOOH current density (J_HCOOH) at a low overpotential. Indium oxide is good HCOOH production catalyst but with low conductivity. In this work, we report a unique corn design of In₂O_3-x@C nanocatalyst, wherein In₂O_3-x nanocube as the fine grains dispersed uniformly on the carbon nanorod cob, resulting in the enhanced conductivity. Excellent performance is achieved with 84% Faradaic efficiency (FE) and 11 mA cm^-2 J_HCOOH at a low potential of - 0.4 V versus RHE. At the current density of 100 mA cm^-2, the applied potential remained stable for more than 120 h with the FE above 90%. Density functional theory calculations reveal that the abundant oxygen vacancy in In₂O_3-x has exposed more In³⁺ sites with activated electroactivity, which facilitates the formation of HCOO* intermediate. Operando X-ray absorption spectroscopy also confirms In³⁺ as the active site and the key intermediate of HCOO* during the process of CO₂ reduction to HCOOH.