Promoting electrochemical conversion of CO2 to formate with rich oxygen vacancies in nanoporous tin oxides

Defect engineering, especially oxygen vacancies (O-vacancies) introduction into metal oxide materials has been proved to be an effective strategy to manipulate their surface electron exchange processes. However, quantitative investigation of O-vacancies on CO2 electroreduction still remains rather ambiguous. Herein, a series of nanoporous tin oxide (SnOx) materials have been prepared by thermal treatment at various temperatures and reaction conditions. The annealing temperature dependent O-vacancies property of the SnOx was revealed and attributed to the balance tunning of the desorption of oxygen species and the continous oxidation of SnOx. The as-prepared nanoporous SnOx with 300 °C treatment was found to be highest O-vacant material and showed an impressive CO2RR activity and selectivity towards the conversion of CO2 into formic acid (up to 88.6%), and superior HCOOH incomplete current density to other samples. The ideal performance of the O-vacancies rich SnOx-300 material can be ascribed to the high delocalized electron density inducing much enhanced adsorption of CO2 with O binding and benefiting the subsequent reduction with high selectively forming of formic acid.