Molybdenum-based Bimetallic Nitrogen (carbon) Compounds Derived From Metal-organic Complexes Are Used To Electrolyze Water

The depletion of the unsustainable fossil fuels drives the exploration of renewable and clean energy.Hydrogen is considered as the primary choice for the future energy supply.Electrocatalytic overall water splitting is an important method for preparing high-purity,high-yield hydrogen,and has been thought as a clean and environmentally friendly route.The process requires a high overpotential,so an efficient electrocatalyst needs to be prepared to speed up the reaction kinetics,reduce the barrier,and thus reduce the overpotential.As well know,the precious metal Pt is the best catalyst for hydrogen production,but its high price and scarce resource are limited application.The molybdenum（Mo）is cheap and has a variety of valence states（+6,+4,+3,+2）.Molybdenum plays an important role in the field of electrocatalysis,especially combination with the post-transition metals（Fe,Co,Ni） could improve the electrocatalytic performance.We are based on the advantages of metal organic compounds,such as:tunable components,and multiple metals could be bound through of ligands.In particular,metal-organic framworks（MOFs） are chatacteristics of porosity and regular morphology,and metals could be introduced of MOFs to obtain catalysts with special morphology.Mo-based nitrogen（carbon） compounds were important class of electrocatalytic materials.Hydrogen is easily absorbed on the surface of the nitride,thereby promoting the improvement of performance.But Mo-based single metals exhibit slower electrochemical performance,we are synthesize bimetal nitrogen（carbon） compounds to optimize the electrocatalytic performance,which has the advantages of easy diffusion and electron transfer.Based on the advantages of MOFs,we introduced Mo to synthesize bimetal catalysts containing Mo compounds.In this paper,Mo-based bimetallic nitrogen（carbon） compounds are used as electrocatalysts for the electrocatalytic overall water splitting.The research content is as follows:1.β-cyclodextrin（β-CD） has a hydrophobic inner cavity.As a host,it can envelop an appropriate guest.The matching effect of host and guest forms an assembly system with many organic and inorganic molecues.In this part of the work,β-CD was used as a“bridge”to connect nickel and molybdenum.The three were nickel nitrate（Ni（NO₃）₂·6H₂O）,β-CD and phosphomolybdic acid hydrate(PMo₁₂) directly assembled at room temperature to obtain a complex.The complex is by pyrolysis to obtain the corresponding bimetallic catalyst.Especially under the additional carbon source（dicyanodiamine）,the performance is best when the pyrolysis temperature is 700℃,and HER has a current density of 10 mA cm^-2,the overvoltage is 108 mV.2.Powder catalysts are prone to particle agglomeration though high temperature treatment.The synthesis of self-supporting catalysts can solve this problem.Our work used a method of in situ release of metallic Ni from foamed nickel（NF）.Phosphomolybdic acid was used a etching agent,and a ligand was added to obtain a self-supporting molybdenum-nickel complex.After the controllable treatment,the corresponding bimetal catalyst was obtained,which performance is better than the single metal catalysts.The HER performance is 34 mV at a current density of 10 mA cm^-2 and OER performance is at 100 mA cm^-2 the overvoltage is 1.61 V.3.The above research content is a one-step assembly method,which is relatively simple,but the morphology of the catalyst is not easy to control.Therefore,in this part of the work,we obtained the hollow structure catalysts based on a step-by-step assembly method.Firstly,synthesized Co-based MOF,secondly etched through Na₂MoO₄ to obtained the corresponding bimetallic catalysts.The HER performance is 65 mV when the current density is 10 mA cm^-2 and it is fully hydrolyzed solar cells.The driving voltage is 1.57 V.