Nanoscale Copper–Tin Dioxide Interfaces for Efficient CO 2 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 CO 2 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 (Cu 2 O), with low amounts of surface CuO and SnO 2 species. An increase in Sn percentage leads to the appearance of the crystalline phase of metallic Cu and SnO 2 , which becomes dominant for the sample with the highest Sn content. During CO 2 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 FE HCOO− . This study highlights the potential of implementing low‐cost catalysts for CO 2 conversion at an industrial scale.