Electrocatalytic Nitrate Reduction to Ammonia on Conductive Metal-Organic Frameworks with Varied Metal Centers

Nitrate pollution in groundwater poses severe threats to ecosystems and human health, making the electrochemical nitrate reduction reaction (NO3RR) a promising remediation technology. Conductive metal–organic frameworks (cMOFs) with π-d conjugation, dispersed active sites, and tunable structures are ideal candidates for electrocatalysis. Herein, we synthesized a series of cMOFs (M3(HHTP)2, M = Fe, Zn, Cu, Co, Ni) via conjugated coordination between hexahydroxytriphenylene (HHTP) ligands and metal ions and systematically investigated their NO3RR performance. Electrochemical tests revealed that Fe3(HHTP)2 exhibits superior catalytic performance for nitrate reduction, achieving a high NH3 selectivity of 99.5% and a yield rate of 676.4 mg·gcat−1·h−1 at −1.0 V vs. RHE (reversible hydrogen electrode), along with excellent cyclic and structural stability. In situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy identified key intermediates (*NO2, *NH2OH) and proposed the reaction pathway: NO3− → *NO3 → *NO2 → *NO → *NOH → *NH2OH → *NH2 → *NH3. DFT calculations revealed that Fe center exhibited a lower energy barrier for NO3RR compared to other metal ions (Zn, Cu, Co, Ni). This study demonstrates the significant potential of Fe3(HHTP)2 for efficient NO3RR and provides new insights into the structure-function relationship of cMOF-based electrocatalysts.