Influence of active hydrogen on pathway selection in electrochemical nitrate reduction

Electrochemical nitrate reduction reaction in alkaline condition involves two reactants, the nitrate ( NO 3 − ) and the water (H 2 O). Although the significance of the active ∗H species produced from the dissociation of H 2 O has been proved, the correlation between the reaction pathways and the ∗H species is often overlooked. Herein, Co(OH) 2 –CoP supported Ru nanoclusters is designed for electrocatalytic nitrate reduction and shows a record-high faradaic efficiency of 99.7% at an ultralow potential of 0.1 ​V versus reversible hydrogen electrode. Experiments and theoretical calculations reveal that in addition to the faster proton transfer kinetics, the reaction pathway is strongly correlated with ∗H supply with the aid of CoP, that is, the direct hydrogenation of ∗NOH instead of deprotonation over Ru sites with the lowest energy barrier is promoted with the moderate production of ∗H species. This work provides new insights into the impact of ∗H species on the thermodynamics and kinetics of electrocatalytic nitrate reduction. • Ru/Co(OH) 2 –CoP shows a faradaic efficiency of 99.7 ​% ​for NH 3 at 0.1 ​V vs. RHE in electrocatalytic nitrate reduction. • The nitrate reduction reaction pathway is strongly correlated with ∗H supply. • The direct hydrogenation of ∗NOH is promoted with the moderate production of ∗H species.