Synthesis And Electrocatalytic Properies Of Transition Metalbased Composite Nanomaterials

The choke point still facing hydrogen production from electrolytic water lies in the development of catalysts.Although a lot of effort and progress has been made by research developers in this area.However,current catalyst materials are still not available on a large scale for real-life applications.The design of catalysts for electrolytic water can be considered in two ways:the first increases the number of effective active sites in the catalyst,the second increases the intrinsic activity of the nanomaterial catalyst.In this paper,transition metal-based composite nanomaterials were synthesised for the electrolytic water reaction using a one-step chloride ion etching method,a mechanochemical synthesis method and a microwave pyrolysis method,respectively.The main research work done is as follows:(1)In situ synthesis of Pt clusters anchored in amorphous nickel-molybdenum hydroxide/nickel foam(Pt-NiMo-OH/NF)nanosheets by a one-step chloride etching method at room temperature.Pt-NiMo-OH/NF exhibits outstanding catalytic activity and superior stability for hydrogen precipitation reactions(HER)and oxygen precipitation reactions(OER)compared to Pt/C/NF and Ru O₂/NF in 1.0 M KOH solutions.At the same time,the all-water decomposition requires only 1.83 V to reach1000 m A cm^-2 and shows good stability and catalytic activity in 160 hours.The excellent catalytic activity and stability of Pt-Mi Mo-OH/NF nanosheets may be due to synergistic electron transfer effects between Pt and amorphous NiMo hydroxides.The first leads to an increase in the electron cloud density of the Pt cluster,optimising the binding energy of Pt and H.Secondly it also leads to the formation of high-valent Niand Mo to promote the conversion of OER active species.The nanosheet structure also provides more catalytic active sites for catalytic reactions.(2)High-entropy phosphate/carbon(HEPi/C)hybrid nanosheets were successfully prepared by a two-step method.First,high-entropy metal-organic framework(HE-MOF)nanosheets were synthesized by an entropy-driven mechanochemical approach at room temperature,followed by high-temperature phosphating.The overpotential of HEPi/C hybrid nanosheets at 10 m A cm^-2 in 0.5 M H₂SO₄ solution is only 40 m V,which is comparable to that of commercial Pt/C(?₁₀=48 m V).More importantly,when the overpotential is 50 m V,the mass active current density of HEPi/C hybrid nanosheets can be as high as 1.6 A mg^-1 _{noble metal}.The excellent HER properties of the HEPi/C hybrid nanosheets are attributed to the high entropic effect that enhances their intrinsic activity.(3)NiFe-Fe₃C@CNT nanoparticles were successfully prepared by a scalable microwave pyrolysis method.NiFe-Fe₃C@CNT exhibits outstanding OER performance in 1.0 M KOH solution with an overpotential of only 274 m V at 10 m A cm^-2.Interestingly,NiFe-Fe₃C@CNT nanoparticles maintains good activity and stability at high current densities of 500 m A cm^-2(?₅₀₀=420 m V)for up to 100 hours.The excellent OER performance and stability of NiFe-Fe₃C@CNT nanoparticles can be attributed to the doping of Nileading to a local redistribution of electron cloud density and a strong metal-coupled electronic synergy between the catalyst and the carrier carbon nanotubes,which in turn increases the intrinsic activity and the number of active sites of the NiFe-Fe₃C@CNT catalyst.