Engineering Tin Foam Electrodes for High‐Rate CO 2 Reduction: A Pathway to Sustainable Formic Acid Production

The electrochemical conversion of CO 2 into energy carriers or value‐added chemicals is of great significance for efficiently recycling CO 2 and mitigating its greenhouse effect. Formic acid is among the most attractive CO 2 electroreduction products. It can be obtained with high selectivity on catalysts based on non‐toxic and abundant metals, such as tin and bismuth. An important issue with these electrode materials is the low current density achieved on flat surfaces. In this study, we present an electrodeposition strategy for the preparation of Sn foam electrodes with dendritic architecture, high surface area, and enhanced activity for formic acid production. A design‐of‐experiments approach was used to define the optimal deposition conditions on Cu support. The optimized electrodes showed excellent performance in both potentiostatic and galvanostatic electrolyses, exhibiting high Faradaic efficiencies and productivities for formic acid. The best results were obtained at E app = −1.20 V versus RHE in potentiostatic conditions and J app = 35 mA cm −2 under galvanostatic control. Long‐term electrolysis tests showed good stability of the electrocatalyst, which maintained a stable high current density. Interestingly, these tests evidenced an unprecedented negative effect related to the accumulation of formic acid in the catholyte.