Facet-oriented Cu2O and oxygen vacancies synergistically promoting CO2 electroreduction to formate on Cu-based hollow fiber

Electrochemical reduction of carbon dioxide (CO2) to value-added chemicals is an attractive route to utilize CO2 as resources and contribute carbon neutrality. As one of common products from CO2 electroreduction, formate is an economically viable liquid fuel under current techno-economic conditions. However, the current densities of CO2 electroreduction remain insufficient yet challenging due to the limited CO2 solubility and the unclear mechanisms on electrocatalyst surface. Herein, an exquisite Cu2O surface on copper-based hollow fiber (HF) was developed as a gas penetration electrode for CO2 electroreduction that can enhance mass transfer and boost three-phase interface reactions. Moreover, the (111)-oriented Cu2O and abundant oxygen vacancies synergistically promoted CO2 electrochemical reduction to formate, resulting in a high formate Faradaic efficiency of 92.3% with a partial current density of 84.4 mA·cm−2 at a potential of − 1.18 V vs. RHE. Operando Raman spectra suggested that carboxylate anion *CO2- was the key intermediate of CO2 reduction to formate, which was further reduced to formate via the subsequent proton-electron transfer.