Nitrogen vacancies enriched Ce-doped Ni_(3)N hierarchical nanosheets triggering highly-efficient urea oxidation reaction in urea-assisted energy-saving electrolysis

Urea oxidation reaction (UOR),which has favorable thermodynamic energy barriers compared with oxygen evolution reaction (OER),can provide more cost-effective electrons for the renewable energy systems,but is trapped by its sluggish UOR kinetics and intricate reaction intermediates formation/desorption process.Herein,we report a novel and effective electrocatalyst consisting of carbon cloth supported nitrogen vacancies-enriched Ce-doped Ni_(3)N hierarchical nanosheets (Ce-Ni_(3)N @CC) to optimize the flat-footed UOR kinetics,especially the stiff rate-determine CO_(2)desorption step of UOR.Upon the introduction of valance state variable Ce,the resultant nitrogen vacancies enriched Ce-Ni_(3)N @CC exhibits an enhanced UOR performance where the operation voltage requires only 1.31 V to deliver the current density of 10 mA cm^(-2),which is superior to that of Ni_(3)N @CC catalyst (1.36 V) and other counterparts.Density functional theory (DFT) results demonstrate that the incorporation of Ce in Ni_(3)N lowers the formation energy of nitrogen vacancies,resulting in rich nitrogen vacancies in Ce-Ni_(3)N @CC.Moreover,the nitrogen vacancies together with Ce doping optimize the local charge distribution around Ni sites,and balance the adsorption energy of CO_(2)in the rate-determining step (RDS),as well as affect the initial adsorption structure of urea,leading to the superior UOR catalytic performance of Ce-Ni_(3)N @CC.When integrating the Ce-Ni_(3)N catalyst in UOR//HER and UOR//CO_(2)R flow electrolyzer,both of them perform well with low operation voltage and robust long-term stability,proofing that the thermodynamically favorable UOR can act as a suitable substitute anodic reaction compared with that of OER.Our findings here not only provide a novel UOR catalyst but also offer a promising design strategy for the future development of energy-related devices.