A Bioinspired Iron-Centered Electrocatalyst for Selective Catalytic Reduction of Nitrate to Ammonia

Nitrate has been commonly used in fertilizers, synthetic materials, and explosives; however, its irregular release leads to extensive contaminants in many sources of drinking water because of its high solubility and mobility. Unfortunately, efficient nitrate removal at low concentrations has been challenging for a long time. Inspired by nitrate reductase with iron as the active center in plants, we constructed a novel nanozyme catalyst, FeNPs@MXene, and proved that the confinement effect of Cl size facilitates the formation of FeOOH nanoshuttles. The FeNPs@MXene electrocatalyst can achieve selective catalytic reduction of nitrate to ammonia, including up to 97.8% conversion of nitrate and high selectivity toward ammonia (76.8%). By precisely analyzing in situ electrochemical online differential electrochemical mass spectrometry (DEMS) and 15N isotope labeling experiments, the electroreduction of nitrate to ammonia was clearly proven. Using density functional theory (DFT) calculations and conductive atomic force microscopy (C-AFM), the built-in electric field formed between FeOOH and MXene is proven to be beneficial to nitrate adsorption and can lower the reaction barrier of key intermediates. This design of iron-based nanozymes offers new illuminating insight into the NO3RR.