Tuning long-chain hydrocarbon formation in CO electroreduction by modulating pH and alkali metal cations over a cobalt-based catalyst

The electrochemical CO 2 and CO reduction reactions on nickel and cobalt-based catalysts has attracted increasing attention, as these have been shown to exhibit a Fischer–Tropsch (FT)-like mechanism to yield long-chain hydrocarbons. Here we investigate the effect of pH and the alkali metal cations on hydrocarbon formation using Co(OH) 2 -derived catalysts during CO reduction. Across all tested pH conditions, the optimal potential for hydrocarbon production, as indicated by the highest Faradaic efficiency and current density for hydrocarbons, is identified just before water reduction becomes dominant. *CO–*CH x coupling is the rate-determining step (RDS) when H 3 O⁺ is the primary proton donor, while *CO hydrogenation is the RDS when H 2 O is the primary proton donor. The identity of the proton donor also affects *CH x coverage and the chain growth probability (α), which together, affects the formation of CH 4 and C 2+ hydrocarbons. Interestingly, unlike on copper-based catalysts, the different alkali metal cations (Li + , Na + , and K⁺) have limited influence on C–C coupling on Co-based catalysts. We attribute this to the stronger CO binding on Co sites which makes the effect of alkali metal cations in stabilizing *CO intermediates less pronounced . • The effect of pH and alkali metal cations on CO 2 electroreduction to long-chain hydrocarbon products using Co(OH) 2 -derived catalysts was studied. • *CO–*CH x coupling is the rate-determining step (RDS) when H 3 O⁺ is the primary proton donor, while *CO hydrogenation is the RDS when H 2 O is the primary proton donor. • Alkali metal cations (Li + , Na + , and K⁺) have limited influence on C–C coupling on cobalt-based catalysts.