Miao Liu,Zhenghao Lu,Linghan Yang,Renmin Gao,Xinying Zhang,Yongjing Wang,Yonghao Wang
Electrocatalytic reduction of nitrate to ammonia is an effective method for the recycling of NO 3 - -N in the field of nitrate polluted water treatment . In this work, Co-N-C was prepared in this work by pyrolysis of Co-based metal organic framework at 700 °C and it can achieve 100 % selectivity to ammonia under the optimum experiment conditions. Impressively, no harmful nitrite generated in the reduction process because the reduction rate constant of Co-N-C for NO 2 - -N is higher than that of NO 3 - -N. Experiment results show that the chemical adsorption rather than electrostatic adsorption dominated among Co-N-C and free NO 3 - , which is significant for the subsequent electronic reduction process. Mechanism analysis indicated the active hydrogen (H*) reduction mechanism is predominate for Co-N-C but the direct electron mechanism is predominate for Co-C during the reduction from NO 3 - to NO 2 - . While for Co-N-C and Co-C, the subsequent reduction of NO 2 - to NH 4 + was conducted by the direct electron mechanism. The present work not only explores high performance for the selectively electrocatalytic reduction from nitrate to ammonia but also promote new inspiration for the preparation of other Co-based functional materials for reducing the production of nitrite.
Engineering anodic and cathodic half-reactions with more favorable thermodynamics and techno-economics in water-splitting cells for electrorefining offers a promising approach to producing green fuels and fine chemicals. Herein, we demonstrated a coelectrolysis system integrating nitrate reduction reaction (NO3RR) and biomass oxidation reaction (BOR), where a well-designed CuNi alloy acted as the catalyst at the cathode and anode. The CuNi delivered a yield rate of 2.87 mmol h–1 cm–2 (8.44 mmol h–1 mgcat–1) at 0 V vs RHE and a FE of 95.33% (a current density of −136 mA cm–2) at −0.2 V vs RHE for ammonia synthesis from nitrate reduction. Mechanistic studies revealed that Cu centers rapidly converted NO3– to NO2–, while Ni sites promoted water dissociation, generating *H species for intermediate deoxygenation and hydrogenation via stepwise proton transfer. At the anode, the CuNi efficiently catalyzed the oxidative upgradation of biomass derivatives, with a Faradaic efficiency of >90% and a long-term stability over 240 h for formate production. In situ experiments demonstrate that Cu substantially enhances the dynamic transformation efficiency of the NiIII–O active species on CuNi catalysts. The integrated NO3RR||BOR system demonstrated an efficient and stable electrosynthesis (>120 h) of ammonia (∼3.9 mmol h–1 cm–2 or 11.47 mmol h–1 mgcat–1) and formate (∼38.3 mmol h–1 cm–2 or 112.65 mmol h–1 mgcat–1). This study emphasizes the design of a hybrid system for electrocatalytic refining of waste feedstocks into commodity chemicals.
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