Steering CO ₂ Electroreduction to Methane and Deuterated Methane via Hydrogen‐Bond Engineering on Copper–Phenolic Networks

Electrochemical CO 2 reduction (eCO 2 R) powered by renewable electricity offers a sustainable route for carbon cycling and value‐added chemical synthesis. Among possible products, methane (CH 4 ) is particularly attractive due to its high energy density and direct compatibility with existing natural gas infrastructure. However, it remains challenging to selectively produce CH 4 with conventional copper catalysts. Herein, we developed a copper–phenolic network catalyst featuring atomically dispersed Cu─O 4 sites, where adjacent uncoordinated hydroxyl groups from tannic acid (TA) act as intrinsic hydrogen‐bond donors to stabilize the oxygen‐bound formate intermediate (*OCHO). This hydrogen‐bond‐enabled microenvironment redirects eCO 2 R from the conventional *CO‐mediated pathway toward a formate‐derived route, while simultaneously suppressing the competing hydrogen evolution reaction. As a result, the optimized Cu‐PTA catalyst delivers a high CH 4 Faradaic efficiency of 75.5% with a partial current density of 302.0 mA cm −2 in aqueous electrolyte. Notably, this pathway‐steering strategy is readily applicable to deuterated electrolytes, enabling efficient production of deuterated methane (CD 4 ) with a record‐high Faradaic efficiency of 83.1% and a partial current density of 415.6 mA cm −2 . This work establishes hydrogen‐bond engineering as a general approach for manipulating reaction pathways through local stabilization of oxygen‐bound intermediates toward sustainable synthesis of high‐value chemicals.