Highly Active and Selective Electrochemical CO2 Reduction to Formate Enabled By Structural Defects on Converted Bi2O3 Nanotubes

Abstract

Electrochemical CO2 reduction to fuels and commodity chemicals offers an attractive solution for energy and environmental sustainability. Formic acid (or formate) is suggested to be one of the most economically viable products. However, in order to realize its commercial viability, a drastic improvement of the electrocatalyst materials on both activity and selectivity is required. Here we report that structural defects have a profound positive impact on the electrocatalytic performance of Bi for selective CO2 reduction to formate. Bi2O3 double-walled nanotubes with fragmented outer surface are prepared as the template. They are cathodically converted to highly defective Bi nanotubes as evidenced by operando X-ray absorption spectroscopy measurements. This converted electrocatalyst enables CO2 reduction to formate with excellent activity, selectivity and stability. Importantly, its current density reaches ~288 mA cm-2 at -0.61 V versus reversible hydrogen electrode within a flow cell reactor under ambient conditions, which substantially exceeds the commercialization requirement. Using density functional theory calculations, the excellent activity and selectivity are rationalized as the outcome of abundant defective Bi sites that stabilize the *OCHO intermediate. Furthermore, this electrocatalyst is coupled with Si photocathodes and achieves high-performance photoelectrochemical CO2 reduction.