Nanoscale Copper–Tin Dioxide Interfaces for Efficient CO2 Electroreduction to Formic Acid and Formate at High Rates

This study reports highly selective and stable electrocatalysts consisting of Cu and Sn for efficient reduction of CO2 to formate (HCOO−) and formic acid (HCOOH). The copper–tin dioxide catalyst (CuSn) is prepared through a one-pot microwave-assisted solvothermal method. Different samples are obtained by varying Cu-to-Sn atomic ratios from 4 to 1. When Sn content is low, the CuSn sample shows a main crystalline phase of cuprous oxide (Cu2O), with low amounts of surface CuO and SnO2 species. An increase in Sn percentage leads to the appearance of the crystalline phase of metallic Cu and SnO2, which becomes dominant for the sample with the highest Sn content. During CO2 electrolysis, the optimal CuSn material shows a faradaic efficiency (FE) for HCOO− greater than 90% at −200 mA cm−2 in a flow cell with alkaline electrolyte. It also performs well under acidic condition (pH 3) to produce HCOOH with an FE of 70% at the same current density. A long-term test is carried out in 1 M KOH at −100 mA cm−2 for over 20 h, showing good retention in FEHCOO−. This study highlights the potential of implementing low-cost catalysts for CO2 conversion at an industrial scale.