Transition-Metal-Free, Pure p-Block Alloy Electrocatalysts for the Highly Efficient Nitrate Reduction to Ammonia
Hanqing Yin, Xin Mao, Stuart Bell, Dmitri Golberg, Aijun Du
Abstract
Nitrate reduction to ammonia (NRA) is a promising technology, as it can remove polluting nitrate from sewage and transform it into value-added chemical products. Electrocatalysis has become a popular topic in recent years and has been naturally applied to electrochemical NRA. Currently, those reported metal electrocatalysts for NRA are predominantly based on transition metal (TM) elements and the reaction mechanisms on these catalysts were not well understood. Herein, using density functional theory (DFT) calculations, we propose unparalleled TM-free alloy catalysts, which are indium-based and constituted by only p-block elements, for the electroreduction of nitrate to ammonia. Especially on the In 3 Sn(100) surface, we identified a novel reaction pathway along which the free energy evolution goes completely downhill, indicating an extraordinary performance in NRA. Additionally, proton adsorption was found to be extremely weak on the In 3 Sn(100) surface, resulting in substantial suppression of the parasitic hydrogen evolution reaction (HER). The intrinsically high activity and inhibition of the competing reaction on these p-block metal-based catalysts jointly contribute to their excellent performance in NRA.