Thiocyanate “Passivation” Unlocks Highly Selective and Efficient Acidic CO 2 Electroreduction to CH 4 on Cu-Based Catalysts

Electrocatalytic reduction of CO 2 to CH 4 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 CO 2 -to-CH 4 systems exhibit low carbon utilization due to the loss of CO 2 into (bi)carbonate. Conducting CO 2 electroreduction in acid can alleviate carbonation issues but suffers from moderate CH 4 selectivity owing to competing hydrogen evolution. Herein, we report that thiocyanate (SCN – ), a well-known poison in electrocatalysis, can remarkably enhance acidic electrocatalytic CO 2 -to-CH 4 performance, specifically resulting in a record-high CH 4 Faradaic efficiency of 81.8% (accompanied by a CH 4 partial current density of 213.3 mA cm –2 ) and a single-pass carbon efficiency of 65.2% when using a CeO 2 -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 CH 4 production. This work highlights the unique role of thiocyanate in promoting the selective reduction of CO 2 to CH 4 and offers insights into the design of surface chemistry for precise regulation of catalytic processes to achieve targeted product production.