Controlled Synthesis Of Metal Organophosphonates On Nickel Foam And Their Oxygen Evolution Properties

In order to solve the problem of serious environmental pollution,it is urgent to develop some renewable clean energy to replace fossil fuels.Water splitting technology has received widespread attention since it can produce sustainable clean hydrogen energy with high calorific value.However,the oxygen evolution reaction(OER)during electrochemical water splitting is slow and complex in kinetics.Therefore,it is very urgent to develop highly efficient,stable and inexpensive OER electrocatalyst.Transition metal phosphates have gained a lot of attractions due to their high activities and good kinetic characteristics.Different organic phosphonate ligands can be used to optimize their properties by switching the different organic phosphonate ligands.Besides,metal organic phosphonates also possess the advantages of larger specific surface area,adjustable pore size,chemical stability etc.,which make them exhibit excellent performance in the water splitting.However,metal phosphates have poor conductivity and tendency to congregate.Loading it on the substrate can effectively solve this problem.Based on the above purposes,a series of precursors and corresponding derivatives were prepared by directly growing metal organic phosphonate on foamed nickel.The morphology,structure,composition and OER properties of the derivatives were studied by means of related tests,and the corresponding influencing factors were further analyzed.The details are as follows:(1)The samples were prepared by a simple one-step solvothermal method.By using different solvents,the metal organic phosphonate precursors with different morphologies were grown in situ on the surface of nickel foam,and then the precursors were converted to carbon and nitrogen doped cobalt phosphate by calcining at H2(10%)/Ar atmosphere at different temperatures.The results show that the morphology of the samples obtained by reaction with different solvents is very different.The morphology of nanowire array is obtained in pure water solvent,while the nanosheet array is obtained in mixed solvent of water and ethanol.Among them,the CoPiNF-800 samples synthesized in pure water showed the best electrochemical performance.They exhibit extraordinary catalytic activity with very low overpotential of 222 mV at 100 mA·cm2,the corresponding Tafel slope is 62 mV·dec-1.In addition,they have the smallest impedance and excellent electrochemical stability.(2)Based on the experiments in the previous chapter,the effects of different Co Fe feed ratio on the morphology,structure and electrochemical performance of the products were investigated.A series of cobalt iron bimetallic organic phosphonate(CoFePMP)nanowire arrays loaded on foam nickel were prepared by controlling the ratio of cobalt and iron sources.Cobalt iron bimetallic phosphates(CoFePiNF-600)were further synthesized by calcination in H2(10%)/Ar atmosphere.Electrochemical test results show that bimetallic phosphate has better catalytic activity than single metal due to the synergistic effect of cobalt and iron.When the ratio of cobalt and iron is 6:4,the products CoFePiNF(6:4)-600 have good OER catalytic performance.Only 334 mV overpotential to achieve 100 mA·cm-2 current density,and the corresponding Taffel slope is the smallest(122 mV·dec-1).It also has the smallest charge transfer impedance and larger electrochemical active surface area.