The electrochemical reduction of nitrate to ammonia (ENRA) provides an efficient approach to remove nitrate pollution and achieve ammonia production simultaneously. Herein, inspired by bio-enzyme in denitrifying bacteria, a carbon-coated nickel phosphide (NiPC) nanosheet derived from metal-organic frameworks (MOFs) is proposed as an efficient catalyst for ENRA. Through electron engineering, controllable Ni^δ+ in nickel phosphide is achieved by regulating the degree of phosphating, which enhances its activity for the hydrogenation of nitrate. As the result, Ni^δ+ becomes one of dominating factors determining the efficiency of the ENRA reaction in nickel phosphide. The optimal NiPC catalyst exhibits impressive property toward ENRA: NH₄⁺ Faraday efficiency of 96.68%, NH₄⁺ selectivity of 99.04%, and nitrate conversion rate of 90.43% under low nitrate concentration (200 mg·L⁻¹). This work opens a new avenue for the design of next-generation catalysts through electron engineering for ENRA.

Transition metals are a kind of promising catalysts to apply into electrocatalytic synthesis ammonia by virtue of abundant reserves and low cost. However, many widely used transition metal catalysts usually face the challenge to realize satisfactory catalytic results mainly resulting from the match between catalytic active site and support. Here, a new-type ZnS/NC-X electrocatalyst was reported by in-situ sulfidation of zeolitic imidazolate framework-8 (ZIF-8), where the metal nodes of ZIF-8 reacted with dibenzyl disulfide (BDS) to obtain ZnS nanoparticles and the framework of ZIF-8 was carbonized to form the support. Especially, catalytic active sites (ZnS nanoparticles) and support (NC-X) were adjusted in detailed by changing the ratio of ZIF-8 and BDS. As a result, when the mass ratio of ZIF-8 and BDS was 1:1, the resulted ZnS/NC-2 catalyst achieved a remarkable NH₃ yield of 65.60 μg·h⁻¹·mg⁻¹_cat., Faradaic efficiency (FE) of 18.52% at −0.4 V vs reversible hydrogen electrode (RHE) in 0.05 M H₂SO₄ and catalytic stability, which outperformed most reported transition metal sulfides. The matching catalytic active site and support make our strategy promising for wide catalytic applications.

Heteroatom-doped porous carbon has attracted many researchers’ interests owing to their hierarchical porous and more active sites for nitrogen reduction reaction (NRR). However, the development of simple synthesis strategies to fabricate efficient catalyst is still remaining a challenge. In this work, a series of N, P co-doped porous carbon were prepared by one-step pyrolysis of zeolitic imidazolate framework (ZIF-8) and triphenylphosphine (TPP) under nitrogen atmosphere. The obtained catalyst by calcinating ZIF-8 and TPP with the mass ratio of 1: 5 for three hours was named as PN-C-ZIF-8, which exhibited a high yield rate of ammonia (43.39 μg·h^–1·mg^–1_cat.) and Faraday efficiency (16.67%) in 0.05 M H₂SO₄ at –0.3 V. More importantly, the PN-C-ZIF-8 catalyst had superior selectivity that no hydrazine by-products were detected and long-term durability for 72 h. This study provides an idea for the convenient design and preparation of heteroatom doped carbon materials.