Efficient ammonia synthesis from nitrate reduction over a conjugated nickel phthalocyanine polymer in a wide potential and nitrate concentration range

Abstract

The electrocatalytic nitrate reduction reaction (NO₃⁻RR) to ammonia is 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 in the 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, the NiPcP achieves a maximum faradaic efficiency of 99.7% and an NH₃ yield rate of 14.2 g h⁻¹ g_cat⁻¹, maintaining over 80% efficiency across a broad potential window (from −0.5 to −0.9 V vs. RHE) and a 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 a 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 for sustainable ammonia synthesis and nitrate pollution remediation.