Three-Dimensional Porous Indium Single-Atom Catalysts with Improved Accessibility for CO 2 Reduction to Formate.

Single-atom catalysts (SACs) present substantial potential in electrocatalytic CO 2 reduction reactions; however, inferior accessibility of single-atom sites to CO 2 limits the overall CO 2 RR performances. Herein, we propose to improve the accessibility between In sites and CO 2 through the construction of a three-dimensional (3D) porous indium single-atom catalyst (In 1 /NC-3D). The NaCl template-mediated synthesis strategy generates the unique 3D porous nanostructure of In 1 /NC-3D. Multiple characterizations validate that In 1 /NC-3D exhibits increased exposure of active sites and enhanced CO 2 transport/adsorption capacity compared to the bulk In 1 /NC, thus improving accessibility of active sites to CO 2 . As a result, the In 1 /NC-3D presents superior CO 2 RR performance to the bulk In 1 /NC, with a partial current density of formate of 67.24 mA cm -2 at -1.41 V, relative to a reversible hydrogen electrode (vs RHE). The CO 2 RR performances with high formate selectivity at a large current density also outperform most reported In-based SACs. Importantly, the In 1 /NC-3D is demonstrated to maintain an FE formate of >82% at -66.83 mA·cm -2 over 21 h. This work highlights the design of a 3D porous single-atom catalyst for efficient CO 2 RR, promoting the development of advanced catalysts toward advanced energy conversion.