Synthesis Of Nonprecious Metal Nanoparticles Supported On Three-dimensional Graphene For Efficient Electrocatalytic Water Splitting

In the past decades,the search for sustainable and sanitary energy carriers to displace fossil fuels has attracted extensive research attention,which is expected to solve the global energy crisis and environmental pollution.Due to its high mass energy density,cleanliness and abundance,hydrogen is considered as an ideal energy carrier to satisfy the growing energy consumption.Water electrolysis provides an environmentally friendly way to produce sustainable hydrogen.Due to the slow kinetics of hydrogen evolution from electrolyzed water(HER),effective electrocatalysts are needed to promote the reactions.At present,Pt based metals are the most effective electrocatalysts for HER,but their scarcity and high cost,which is difficult to commercialize,prevent their many potential applications.Therefore,it is urgent to explore and synthesize non-noble metal electrocatalysts with low input cost and high efficiency.Transition metal phosphides(TMPs)have been proved to be one of the high performance electrocatalysts for HER.In particularly,Ni2P has good electrochemical activity,favourable stability in broad field of pH,and high content of Ni and P elements.By designing three-dimensional nanostructures,the active sites on the catalyst surface can be exposed to a certain extent.Three-dimensional graphene has the characteristics of rich macroporosity and multi-dimensional electron transmission path,which can be used as catalyst carrier;In addition,the construction of heterogeneous structure interface can effectively increase the electroactive sites,and introduce a strong synergistic effect on the electrocatalyst,so as to improve the catalytic performance.Three dimensional nitrogen doped graphene supported Ni2P/Ni5P4 nanocomposites were successfully synthesized(Ni2P/Ni5P4@3DNG),Its electrocatalytic hydrogen evolution performance was also investigated.The primary contents are as follows:1)Graphene oxide(GO)was self-assembled into three-dimensional graphene(3DG)using a hydrothermal process.Then it was immersed in the precursor containing Ni2+ and H2PO2-,and then through phosphorization to prepare three-dimensional graphene loaded Ni2P particles(Ni2P@3DG).At the same time,the factors affecting the synthesis process were studied such as precursor concentration.2)Furthermore,by doping N on three-dimensional graphene,then Ni2P nanoparticles loaded on three-dimensional N-doped graphene were prepared(Ni2P@3DNG).The performance of the catalyst under acidic condition was studied.In the process of synthesis,the effect of P:Ni ratio of precursor on the preparation and catalytic performance of HER were studied.3)The three-dimensional nitrogen doped graphene supported Ni2P/Ni5P4 heterogeneous particles were synthesized(Ni2P/Ni5P4@3DN-G)by using a similar preparation process and adding N source to the graphene.And we studied the HER performance of Ni2P/Ni5P4@3DNG catalyst under acidic conditions.The results show that Ni2P/Ni5P4@3DNG has some advantages compared with other non noble metal catalysts.With a current density of-10 mA cm-2,the Ni2P/Ni5P4@3DNG catalyst only requires an overpotential of 139 mV in 0.5 M H2SO4 electrolyte,and the obtained Tafel slope of 59 mV dec-1.The excellent HER catalytic performance of Ni2P/Ni5P4@3DNG electrocatalysts can be attributed to(1)the high specific surface area of the cross-linked macroporous/mesoporous structure provides more HER catalytic active sites,(2)the three-dimensional network structure can promote the electron transfer and ion diffusion,thus increasing the conductivity of the catalyst and improving the HER reaction kinetics.(3)Synergistic effect between Ni2P/Ni5P4 particles and support.