Influence of active hydrogen on pathway selection in electrochemical nitrate reduction

Electrochemical nitrate reduction reaction in alkaline condition involves two reactants, the nitrate (${{\text{NO}}_3}^{-}$) and the water (H₂O). Although the significance of the active ∗H species produced from the dissociation of H₂O 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.