The electrochemical reduction of carbon dioxide (CO2) into long-chain hydrocarbons (HCs), using protons from water and renewable electricity, is a potential pathway to synthesizing carbon-neutral liquid fuels. Recent studies have shown that nickel-based catalysts can drive this transformation; however, their ability to selectively generate hydrocarbons is often limited by the competing water reduction to hydrogen gas (H2). In this work, proton activity in an aprotic dimethyl sulfoxide (DMSO) electrolyte is systematically tuned by introducing a series of alcohol proton donors. Across this donor series, the selectivity of HCs exhibits a volcano-shaped dependence on the acidity of the proton donors. The Faradaic efficiency of C1-C6 HCs increases from 4.0% in aqueous 0.1 M KHCO3 electrolyte to 22.1% in DMSO electrolyte spiked with 0.2 M ethylene glycol (EG). Nuclear magnetic resonance (NMR) spectroscopy shows that at 0.2 M, EG preferentially forms DMSO-EG hydrogen bonds that inhibit EG-EG clustering, thereby maintaining a well-dispersed proton donor environment. This solvation structure establishes a moderate proton-activity regime that facilitates CO- hydrogen bonds that inhibit EG-EG clustering, thereby maintaining a well-dispersed proton donor environment. This solvation structure establishes a moderate proton-activity regime that facilitates CO2 activation and C-C chain growth, while suppressing H2 formation. Collectively, our results reveal that tuning both the molecular structure of the proton donor and its concentration-dependent solvation behavior in DMSO provides a strategy to delineate and access the proton-activity window that maximizes the CO2-to-HC conversion.
Ma et al. (2026) studied this question.