Enhancing NO reduction to ammonia via porous aromatic frameworks: Co-modified PAF-TPP for efficient mass transfer and electrocatalytic performance

The electrocatalytic reduction of nitric oxide (NO) to ammonia (NH₃) (NORR) provides a sustainable solution for pollutant remediation and value-added chemical synthesis. In this study, we introduce porous aromatic frameworks (PAFs) into the NORR system for the first time, exploiting their unique channel structures to enhance gas adsorption and mass transport. By incorporating Co²⁺ ions into the PAF-TPP material, constructed from tetraphenylporphyrin (TPP), we created the PAF-TPP-Co catalyst, which offers active coordination sites. The PAF structure effectively regulates the interfacial enrichment of NO molecules and promotes mass transport, while the synergistic effect between the Co-N₄ active sites and the PAF framework optimizes both electronic structure and material transport. Through the combined action of microporous structure and active sites, PAF-TPP-Co significantly improves NO adsorption and transport efficiency, facilitating the multi-electron conversion of NO to NH₃. At a potential of −0.6 V vs. RHE, this catalyst achieves an ammonia production rate of 914.2 μg·h⁻¹·mg_cat⁻¹ and a Faradaic efficiency of 71.3%. Moreover, we propose a “adsorption-transport-catalysis” synergistic mechanism that not only enhances NO activation but also suppresses the competitive hydrogen evolution reaction. In situ infrared spectroscopy, Raman spectroscopy, and density functional theory (DFT) calculations were employed to further elucidate the catalytic mechanism. This study offers a new mechanistic perspective on NO electrocatalytic reduction based on PAF materials and provides an effective solution for the “waste-to-resource” conversion of industrial NO emissions.