Monolithic Nanoporous In-Sn Alloy for Electrochemical Reduction of Carbon Dioxide

Nanostructured metal catalysts to convert CO₂ to formate, which have been extensively studied over decades, have many problems such as durability, lifetime, high process temperature, and difficulty in controlling the morphology of nanostructures. Here, we report a facile method to fabricate monolithic nanoporous In-Sn alloy, a network of nanopores, induced by electroreduction of indium tin oxide nanobranches (ITO BRs). The electroreduction process concentrated a local electric field at the tip of the nanostructure, leading to current-assisted joule-heating to form a nanoporous In-Sn alloy. Scanning electron microscopy images showed that the nanopore size of In-Sn alloy could be controlled from 1176 to 65 nm by tuning the electroreduction condition: the applied potential and the time. As a result, formate Faradaic efficiency could be improved from 42.4% to 78.6%. Also, current density was increased from -6.6 to -9.6 mA/cm² at -1.2 V_RHE, thereby resulting in the highest HCOO^- production rate of 75.9 μmol/(h cm²). Detachment of catalysts from the substrate was not observed even after a long-term (12 h) electrochemical measurement at high potential (-1.2 V_RHE). This work provides a design rule to fabricate highly efficient and stable oxide-derived electrocatalysts.