Hierarchically Porous Co-Doped Molybdenum Nickel Nitride Nanowires For Photoassisted Electrocatalytic Hydrogen Evolution

Large-scale utilization of renewable and clean energy is a highly efficient approach to solve increasing energy crisis problem.Most renewable and clean energy sources such as solar and wind energies are intermittently supplied.Thus,high-efficiency energy storage is highly required for the usage of the renewable and clean energy sources.Electrochemical water splitting can converse and storage the renewable and clean energy sources.Electrochemical water splitting involves hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.To achieve high conversion efficiency of electrochemical water splitting,electrocatalysts are highly needed for catalyzing HER and OER.To date,precious metals such as Pt are the best electrocatalysts for HER,while RuO₂ and IrO₂ exhibit high activities for OER.However,the scarcity and high cost limit their large-scale applications in electrochemical water splitting.Over the last few decades,non-precious transition-metal compounds have been widely exploited to replace the precious electrocatlysts for electrochemical water splitting.For example,transition-metal sulfides or selenides,phosphides and carbides for HER,and transition-metal oxides and hydroxides/?oxy?oxides for OER,respectively.Although some electrocatalysts that can catalyze HER or OER,have fabricated so far,bifunctional electrocatalysts that can catalyze HER and OER simultaneously in the same electrolyte have been reported rarely.Therefore,the development of high-performance Bifunctional electrocatalysts for overall water splitting is still challenging.To date,several strategies have been developed to improve the activities of electrocatalysts.Reducing the size and designation of porous or hollow the electrocatalysts to make more exposed active sites are usually adopted for the enhancement of the activity.Besides,improving the conductivities of the electrocatalysts can significantly enhance the kinetics characteristics,and thereby increase the electrochemical performance.For example,the activities of electrocatalysts after coupling with various carbonaceous scaffolds were remarkably improved compared to the bare electrocatalysts.Furthermore,introducing heteroatom into the electrocatalysts can tune the electronic structure and thus affect the catalytic activity.Typically,Ni-Fe films showed 2-3 orders of magnitude higher OER activities than that of Ni and Fe parent film.In addition,establishing the defects in the electrocatalysts is an efficient approach for improving the catalytic performance.For example,more defects existed in the MoS2 nanosheets,more active edge sites were exposed to the electrolyte.Based on the reports above,considering the strategies mentioned above for reasonable design of bifunctional electrocatalysts for overall water splitting.Herein,we develop a facile method to fabricated hierarchical trimetal?Ni,Co,Mo?nitride nanowires with open ends through the Co incorporation and subsequent thermal treatment under NH3 atmosphere.After the Co incorporation,the active surface area is enhanced,while and the charge-transfer and mass-transfer resistances are reduced significantly.As bifunctional electrocatalysts for overall water splitting,due to the dual modulation in the electric conductivity and active surface area induced by the Co doping,the hierarchically porous nanowires containing defects have porous feature and high conductivity,exhibiting excellent HER and OER activities.The two-electrode alkaline electrolyzer assembled by the hierarchically porous nanowires can drive a current density of 10 mA cm^–2at a low voltage of 1.57 V,superior to the counterpart without Co doping and the most reported HER/OER electrocatalysts.Our study in the present work offers opportunities to the rational designation of multi-metal based bifunctional electrocatalyst for full water splitting.On this basis,the photocatalytic electrocatalytic performance test of the synthesized catalyst was carried out.The experiment proves that the catalyst has a good response to sunlight.The irradiation of sunlight can significantly improve the HER and OER activities of the nanowire,and has a good improvement on the stability of Co-NiMoN-400 NWs.