Disordered interfacial HO promotes electrochemical C-C coupling.

There is growing interest in the conversion of CO and CO into energy-dense multi-carbon products to help mitigate climate change, but guiding selectivity remains challenging due to competing pathways. Here we show that tuning the structure of interfacial water using highly concentrated NaClO electrolytes enhances CO electroreduction to CH. Increasing the NaClO concentration from 0.01 to 10 molal increased the CO reduction rate 18-fold, achieving a Faradaic efficiency of 91% for multi-carbon products at -1.43 V versus the normal hydrogen electrode. Temperature-dependent CO reduction, combined with surface-enhanced Raman spectroscopy, revealed that changes in the interfacial HO structure correspond to variations in the apparent activation enthalpy and entropy for the reduction of CO to CH. At higher ionic strength, increases in activation entropy were linked to disrupted hydrogen bonding and the emergence of non-hydrogen-bonded water modes, suggesting that disordered interfacial HO layers facilitate CO reduction to CH. These findings offer valuable insights into how manipulating the structure of interfacial water can enhance the reduction of CO to multi-carbon products.