Interfacial hydrogen bonding-involved electrocatalytic ammonia synthesis on OH-terminated MXene

MXene basal planes are generally considered catalytically inert, due to the passivation by inactive surface groups. However, theoretical calculation predicates that MXene basal planes can become active by tuning its terminal groups. The above understandings are ambiguous on whether the MXene basal planes are indeed electrocatalytically active, and in turn what are the true active sites on MXene. Herein, we functionalized Ti₃C₂ MXene by introducing terminal oxygen groups to reveal the active sites and probe the reaction mechanism for electrocatalytic nitrate reduction reaction (eNO₃^-RR). On the basis of the data presented, the in situ transformed surface hydroxyl groups were identified as a new active site for nitrate reduction. A novel reaction mechanism involving hydrogen-bonding (H-bonding) between nitrate and the -OH groups on the Ti₃C₂ MXene basal plane was proposed, which adequately explained the high applied potentials and low selectivity for HER on the OH-terminated Ti₃C₂ MXene during eNO₃^-RR. This hydrogen-bonding-mediated process is likely applicable to a wide range of other materials and reactions.