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 VRHE, 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 VRHE). This work provides a design rule to fabricate highly efficient and stable oxide-derived electrocatalysts.