Enhancement of ammonia synthesis via electrocatalytic reduction of low-concentration nitrate using co-doped MIL-101(Fe) nanostructured catalysts.

In the domain of electrocatalytic NO reduction (NORR) for the treatment of low-concentration nitrate-containing domestic or industrial wastewater, the conversion of NO into NH holds significant promise for resource recovery. Nevertheless, the central challenge in this field revolves around the development of catalysts exhibiting both high catalytic activity and selectivity. To tackle this challenge, we design a two-step hydrothermal combine with carbonization process to fabricate a cobalt-doped Fe-based MOF (MIL-101) catalyst at 800 °C temperatures. The aim was to fully leverage cobalt's demonstrated high selectivity in NO electroreduction and enhance activity by promoting electron transfer through the d-band of Fe. The results indicate that the synthesized catalyst inherits multiple active sites from its precursor, with the co-doping process optimized through the topological properties of the MOF. Elemental analysis and oxidation state testing were employed to scrutinize the fundamental characteristics of this catalyst type and comprehend how these features may influence its efficiency. Electrochemical analysis revealed that, even under conditions of low NO concentration, the Co@MIL-Fe catalyst achieved an impressive nitrate conversion rate of 98 % at -0.9 V vs. RHE. NH selectivity was notably high at 87 %, and the by-product NO levels remained at a minimal threshold. The Faradaic efficiency for NH reached 74 %, with ammonia yield approaching 0.08 mmol h cm. This study furnishes indispensable research data for the design of Fe-based electrocatalysts for nitrate reduction, offering profound insights into the modulation of catalysts to play a pivotal role in the electroreduction of nitrate ions.