Thiocyanate "Passivation" Unlocks Highly Selective and Efficient Acidic CO₂ Electroreduction to CH₄ on Cu-Based...

Electrocatalytic reduction of CO₂ to CH₄ is a promising strategy for converting renewable energy into a desirable high-energy-density fuel with significant compatibility with the existing natural gas infrastructure. However, conventional alkaline and neutral CO₂-to-CH₄ systems exhibit low carbon utilization due to the loss of CO₂ into (bi)carbonate. Conducting CO₂ electroreduction in acid can alleviate carbonation issues but suffers from moderate CH₄ selectivity owing to competing hydrogen evolution. Herein, we report that thiocyanate (SCN^-), a well-known poison in electrocatalysis, can remarkably enhance acidic electrocatalytic CO₂-to-CH₄ performance, specifically resulting in a record-high CH₄ Faradaic efficiency of 81.8% (accompanied by a CH₄ partial current density of 213.3 mA cm^-2) and a single-pass carbon efficiency of 65.2% when using a CeO₂-supported Cu single-atom material as the model catalyst. We demonstrate that SCN^- enables the coordination with Cu single sites, forming the SCN^--stabilized Cu^(I) species, which effectively suppresses the competing hydrogen evolution reaction and, more importantly, manipulates the binding of *CHO to promote its protonation to *CHOH, thereby leading to selective and efficient CH₄ production. This work highlights the unique role of thiocyanate in promoting the selective reduction of CO₂ to CH₄ and offers insights into the design of surface chemistry for precise regulation of catalytic processes to achieve targeted product production.