A Reviewof the Evolving Landscape of Sn-Based Electrocatalystsfor CO2 Electroreduction to Formate

Abstract The electrochemical reduction of carbon dioxide (CO2RR) to formic acid/formate has emerged as a promising strategy for simultaneously addressing carbon mitigation, renewable energy storage, and sustainable chemical production. Among the various catalysts studied, tin (Sn)-based materials have established themselves as benchmark systems due to their inherent ability to selectively stabilize the *OCHO intermediate while suppressing competing hydrogen evolution reaction (HER) and C–C coupling pathways. In recent years, design strategies spanning nanostructuring, heteroatom doping, alloying, and single-atom engineering have improved performance, while operando spectroscopy and theoretical modeling have established the central role of mixed-valence Sn/SnOx surfaces in stabilizing the *OCHO intermediate. A key emerging conclusion is that formate selectivity is now routinely high across catalyst families; therefore, the decisive challenges have shifted to partial current density, operational stability, and carbon efficiency under flow conditions. This Review provides an overview of advances in Sn-based electrocatalysts reported from 2020 to the present (2026). We systematically discuss recent developments in metallic Sn, oxide-derived Sn, doped alloys, and single-atom catalysts, highlighting structure–activity relationships. Emphasis is placed on the mechanistic insights into the *OCHO pathway, proton-coupled electron-transfer processes, and the dynamic evolution of catalyst surfaces under operating conditions. Furthermore, we examine progress in reactor engineering, including gas-diffusion electrodes, flow electrolyzers, and emerging reactor configurations designed to improve the formate concentration and support scale-up toward practical implementation. Finally, key challenges and future research directions are outlined to guide the rational design of next-generation Sn-based catalysts and accelerate the practical deployment of CO2-to-formate electrochemical technologies.