Iron and nickel based alloy nanoparticles anchored on phosphorus-modified carbon-nitrogen plane enhances electrochemical nitrate reduction to ammonia

Abstract

The catalysts of iron and nickel nanoparticles anchored on carbon–nitrogen plane (FeNi-CN) are considered as the potential candidates for promising electrochemical nitrate reduction to ammonia (ENO₃RR). However, the high d-orbital energy levels of iron and nickel sites coordinated with nitrogen atoms often lead to overly strong adsorption of reaction intermediates on active sites, severely limiting the improvement of catalytic performance. Herein, a catalyst FeNi₃@P-NC consisting FeNi₃ alloy nanoparticles confined in phosphorus (P)-modified carbon–nitrogen plane is successfully fabricated, where the electron withdrawal effect induced by P on the carbon–nitrogen plane decreases the d-orbital energy, and optimizes the d-band center of FeNi alloy, thus weakening the overly strong adsorption of intermediates at the metal-N sites and thereby improving NO₃RR activity. The prepared FeNi₃@P-NC catalyst exhibits exceptional NO₃RR performance with a 93 ± 4.5 % Faradaic efficiency of NH₃ production (FE_NH3) and a high NH₃ yield rate (Y_NH3) of 9633 ± 227.3 μg h⁻¹ cm⁻² at −0.7  V versus Reversible Hydrogen Electrode (vs. RHE) under alkaline medium. Importantly, FeNi₃@P-NC also demonstrates superior catalytic stability and durability, which maintains stability over twenty-five successive electrochemical cycles and for 50 h of continuous electrolysis at 100 mA cm⁻².