In Situ Construction of Metal-Organic Frameworks as Smart Channels for the Effective Electrocatalytic Reduction of Nitrate at Ultralow Concentrations to Ammonia

Electrochemical conversion of nitrate, a widespread waterpollutant,into high-value-added ammonia is a renewable and delocalized routeto restore the globally perturbed nitrogen cycle. However, prematuredesorption of catalytic intermediates and the competitive reactionof hydrogen evolution make the current performance still far fromsuitable for practical applications. In this work, a Zr-based metal-organicframework (MOF) is in situ constructed at the reaction interface toserve as a smart channel for the highly selective electrocatalyticreduction of nitrate to ammonia. The secondary coordination interactionintroduced by the pendant Bronsted acidic groups of MOF not onlyeffectively stabilize the catalytic intermediates to facilitate theoverall reaction process but also certainly increase the proton activationbarrier to suppress the competing hydrogen evolution reaction. Whencoupled with a nanocluster active center, the proof-of-concept systemachieves simultaneous improvement in three critical parameters, witha nitrate conversion rate of 97.6%, an ammonia selectivity of 95.2%,and a Faradaic efficiency of 91.4% at -1.0 V (vs RHE) underultralow nitrate concentration conditions. This strategy providesan interesting route for the application of MOFs and paves the wayfor the removal of nitrate and its reduction to ammonia.