Efficient Ammonia Synthesis from Nitrate Reduction over Conjugated Nickel Phthalocyanine Polymer under Wide Potential and Nitrate Concentration Range

Abstract

Electrocatalytic nitrate reduction to ammonia (NO3⁻RR) provides a promising approach for converting nitrate pollutants to ammonia under mild conditions. Metal phthalocyanine-based conjugated polymers, with their well-defined structures and tunable functionality, are emerging as efficient two-dimensional (2D) catalysts for this reaction. Herein, we report a 2D-conjugated nickel phthalocyanine polymer (NiPcP) that demonstrates high efficiency and selectivity towards NO3⁻RR. The material features high-density, well-defined Ni–N4 sites and the nitrogen-bridged tetra-isoindole structures create a hydrophobic microenvironment and electron-rich Ni centers, which facilitate nitrate adsorption and electron transfer, and suppress the hydrogen evolution reaction (HER). As a result, NiPcP achieves a maximum Faradaic efficiency of 99.7% and an NH3 yield rate of 14.2 g h⁻1 gcat⁻1, maintaining over 80% efficiency across a broad potential window (from −0.5 to −0.9 V vs. RHE) and wide nitrate concentration range (from 10.0 mmol L⁻1 to 2.0 mol L⁻1). It is the first noble metal-free Ni-based catalyst that exhibits such high FE in such a broad potential window and wide nitrate concentration range simultaneously. This work offers an effective molecular design strategy for developing metal–organic electrocatalysts toward sustainable ammonia synthesis and nitrate pollution remediation.