Stabilizing indium sulfide for CO₂ electroreduction to formate at high rate by zinc incorporation

Recently developed solid-state catalysts can mediate carbon dioxide (CO₂) electroreduction to valuable products at high rates and selectivities. However, under commercially relevant current densities of > 200 milliamperes per square centimeter (mA cm^-2), catalysts often undergo particle agglomeration, active-phase change, and/or element dissolution, making the long-term operational stability a considerable challenge. Here we report an indium sulfide catalyst that is stabilized by adding zinc in the structure and shows dramatically improved stability. The obtained ZnIn₂S₄ catalyst can reduce CO₂ to formate with 99.3% Faradaic efficiency at 300 mA cm^-2 over 60 h of continuous operation without decay. By contrast, similarly synthesized indium sulfide without zinc participation deteriorates quickly under the same conditions. Combining experimental and theoretical studies, we unveil that the introduction of zinc largely enhances the covalency of In-S bonds, which "locks" sulfur-a catalytic site that can activate H₂O to react with CO₂, yielding HCOO* intermediates-from being dissolved during high-rate electrolysis.