Cation‐Engineered Iron Porphyrin Boosting Electrocatalytic Reduction of Nitrite to Ammonia

Abstract

Excessive discharge of nitrite (NO2−) into the natural environment disrupts the nitrogen cycle and poses significant health risks. Metalloporphyrins are recognized as ideal electrocatalysts owing to their well‐defined M─N4 coordination and tunable structural properties. In this study, iron 4,4′,4′′,4′″‐(porphyrin‐5,10,15,20‐tetrayl)tetrakis(N, N‐dimethylaniline) (FeDMA) and iron 4,4′,4′′,4′″‐(porphyrin‐5,10,15,20‐tetrayl)tetrakis(N, N, N‐trimethylbenzenaminium) (FeTMA) were synthesized from iron tetraphenylporphyrin (FeTPP) by introducing electron‐donating dimethylammonio and electron‐withdrawing trimethylammonio substituents. We systematically investigated the influence of substituent effects on the catalytic activity of iron porphyrins for the nitrite reduction reaction (NO2RR). FeTMA achieved exceptional performance, maintaining >90% Faradaic efficiency (FE) for NH3 over a broad potential range (−1.1 to −1.5 V versus Ag/AgCl) and a peak NH3 yield rate of 458 ± 4 µmol h−1 cm−2. The NH3 yield rate was 1.9 and 1.5 times that of FeDMA and FeTPP, respectively. Homogeneous electrochemical and spectroscopic analyses identified FeI as the active center for the NO2RR. Theoretical simulations and experimental results revealed that trimethylammonio cations enhance NO2− adsorption and facilitate NH4+ desorption through Coulombic interactions, ultimately enhancing the catalytic activity. This study demonstrates that cation‐engineered metalloporphyrins are a robust strategy for NO2RR, providing valuable guidance for ammonia synthesis.