Gold‐Stabilized Copper Enables Anodic Hydrogen Evolution for Ultralow‐Voltage CO‐to‐Ethylene Electrolysis

ABSTRACT Electrochemical upgrading from CO 2 and CO to ethylene has typically been coupled with the oxygen evolution reaction (OER), whose high standard reduction potential leads to full‐cell voltages above 2.2 V at 200 mA/cm 2 . Here we explored an alternative anodic reaction, where furfural is oxidized to furoic acid, a reaction having a low onset potential ( E 0 ≈ 0.05 V vs. RHE), and which reaction is accompanied by the evolution of H 2 : an anodic hydrogen evolution reaction (a‐HER). In early experiments, copper oxide as a‐HER catalyst exhibit limited stability (< 10 min) and activity (80 mA/cm 2 at 0.8 V cell ). We found, using operando spectroscopy, that hydroxide forms on the surface of copper and deactivates the desired a‐HER process. When we screened candidate metal dopants, we found the best to be Au, for it served to stabilize the Cu surface, enablinained a‐HER: 260 mA cm −2 at 0.8 V cell and stable operation for 16 h. Integrated into a paired CO‐to‐ethylene electrolyzer, this delivered 0.92 V fullcell at 400 mA cm −2 , required 40 GJ electricity per ton of ethylene, and co‐produced 460 kg H 2 per ton ethylene. To enable comparison with CO 2 ‐to‐ethylene reports, which require an additional CO 2 ‐to‐CO step, we estimate ∼ 69 GJ/tonC 2 H 4 .