Interfacial MoO₂ nanograins assembled over graphitic carbon nanofibers boosting efficient electrocatalytic reduction of nitrate to ammonia

Electrocatalytic nitrate reduction reaction (NO3-RR) for sustainable carbon-free hydrogen carrier (NH3) production from polluted NO3- sources of industrial wastewater is very promising. Mo-based catalysts are defined as popular electrocatalytic materials, but the rational performance achievement of Mo-based catalysts in the NO3-RR remains limited. In this study, to overcome the NO3-RR activity limitation, the interfacial MoO2 nanograins assembled on the N-functional carbon nanofibers (defined as MoO2/C) were constructed by electrospun and controlled graphitizing process. The comparative catalysts dominated by molybdenum oxides namely MoO2/ MoO3 were synthesized by controlled calcination in air atmosphere. The MoO2 nanograins anchored in situ on carbon nanofibres could afford more interfacial active regions and accelerate the electron transfer efficiency of the electrocatalytic process by graphitic carbon fiber network. More importantly, MoO2/C was endowed with more oxygen vacancy sites which can trap the free NO3- ions over the reactive sites to enhance the surface interaction of NO3- with catalytic sites during the reaction process. The experimental results showed that the electrocatalytic nitrate reduction performance of the catalyst MoO2/C obviously outperformed that of MoO2/ MoO3 in the light of the atomic activity efficiency with a near 7.5 folds enhancement. The MoO2/C affords the highest NH3 yield of 4838.5 mu g h-1 mgcat- 1 and Faraday efficiency of 30 % at -0.9 V vs.RHE and was endowed with 50 h of continuous reaction stability, proving the potential in practical electrochemical water treatment involving nitrate contamination.