MOF-Transformed In2O3-x@C Nanocorn Electrocatalyst for Efficient CO2 Reduction to HCOOH

Highlights The nanocorn design enables In 2 O 3- x @C a high Faradaic efficiency of 98% and a high formate current density of 320 mA cm −2 at a low potential of -1.2 V versus hydrogen electrode without iR correction. The rich O vacancy activates In 3+ sites on the nanocube shell of In 2 O 3- x @C and the carbon cob enhances conductivity. Operando X-ray absorption spectroscopy unveils the active site of In 3+ for formate production although reduction of In 3+ to In is conceivable at the applied negative potentials during CO 2 reduction reaction. For electrochemical CO 2 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 In 2 O 3- x @C nanocatalyst, wherein In 2 O 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 In 2 O 3- x has exposed more In 3+ sites with activated electroactivity, which facilitates the formation of HCOO* intermediate. Operando X-ray absorption spectroscopy also confirms In 3+ as the active site and the key intermediate of HCOO* during the process of CO 2 reduction to HCOOH.