摘要
Fe-species distribution plays an important role in electrochemical nitrate reduction, yet its influence on the competing hydrogen evolution reaction (HER) remains insufficiently understood. Herein, carbon-supported Fe catalysts with distinct Fe-species distributions were prepared by controlling the Fe precursor concentration. FeAC consists of highly dispersed atomic-scale Fe species and FeO x nanoclusters, whereas Fe 2 O 3 /FeAC additionally contains crystalline alpha-Fe2O3 nanoparticles. X-ray absorption spectroscopy, X-ray diffraction, and electron microscopy confirm the distinct Fe dispersion states in the two catalysts. Electrochemical measurements reveal that FeAC achieves significantly higher NH3 Faradaic efficiency (79.6 +/- 2.2%) than Fe 2 O 3 /FeAC (37.8 +/- 3.1%) at -0.8 V versus RHE, whereas Fe 2 O 3 /FeAC exhibits a higher NH3 production rate accompanied by enhanced HER. Comparable electrochemically accessible surface areas and interfacial charge-transfer characteristics indicate that the observed catalytic differences are not primarily governed by electrochemical surface area or charge-transfer properties. Operando Raman spectroscopy reveals distinct surface reaction environments, while operando ATR-SEIRAS together with EPR measurements indicates enhanced formation of hydrogen-related Fe-H intermediates and hydrogen radicals on Fe 2 O 3 /FeAC, consistent with its stronger HER activity. In contrast, the absence of detectable Fe-H species on FeAC is associated with suppressed hydrogen adsorption and improved nitrate reduction selectivity. These results demonstrate that controlling Fe-species distribution provides an effective strategy for balancing activity and selectivity in carbon-supported Fe electrocatalysts for electrochemical nitrate reduction.