Synthesis,Structural Control And Electrocatalytic Performance Of MOF Based Electrocatalysts

In recent years,increasingly serious environmental problems and the shortage of energy supply have triggered a great deal of attention for green and renewable hydrogen energy.The electrochemical splitting of water molecules to produce hydrogen is considered to be the most promising path due to its high efficiency,low energy consumption and environment friendly.It plays an indispensable role to use catalysts in improving the efficiency of water splitting.Among the hydrogen evolution reaction?HER?electrocatalysts,Pt and Pt-based electrocatalysts give the best performance,and the metal oxides IrO₂ and RuO₂ are considered as the best oxygen evolution reaction?OER?electrocatalysts,but their application has been limited by their low earth-abundance and high-cost,therefore,searching for cheap and efficient catalysts has become a research boom in recent years.Many researchers have started their subject on MOF-based non-precious metal catalysts.Our research is based on the MOF material which central ion is transition non-precious metal,then preparing them as a highly efficient and stable electrocatalysts for HER and OER.The following are our main research works:1.MOF199 and MOF199 precursors containing dimethylimidazole were synthesized by conventional hydrothermal method.Then they were annealed at high temperature under argon gas flow to obtain a low-cost Cu@C nanocomposite catalyst for HER,which was composed of porous carbon with copper-rich hollow spheres.It is beneficial to electron transfer and greatly improves the catalytic performance of HER.The overpotential at the current density of 10 mA·cm^-2is 390 mV,and the Tafel slope is only 121 mV·dec^-1.2.Mixed the NaBH₄ solution and the ZIF67 dispersion under hydrothermal conditions,and then calcined them at a high temperature in a tube furnace to obtain a Co/CoO/C@B three-phase composite material for OER.The rich phase interface exposed more active sites,which showed excellent OER catalytic performance.The three-phase CoO/Co/C@B catalyst material exhibits excellent OER catalytic performance with low onset potential of 1.444 V vs.RHE at 0.1 mA,a small overpotential?390 mV?to reach 10 mA·cm^-2,and better stability with9%of the initial polarization current density decline at the end of 10000s.The good catalytic stability is attributed to the Co/CoO/C@B structure with carbon layer containing a little B element.3.A kind of ultrathin NiFeZn-MOF nanosheets containing few metal oxides nano particles supported on nickel foam are successfully synthesized and used as catalyst for the oxygen evolution reaction?OER?and overall water splitting.The NiFeZn-MNS/NF behaves the most excellent electrocatalytic performance with the best overpotential of 350 mV at 50mA·cm^-2and has the best current density stability with the 5%drop of the initial polarization current density at the end of 120 h.The voltage of NiFeZn-MNS/NF as a bifunctional overall water-splitting catalyst is 1.52 V at the current density of 10 mA·cm^-2,which is superior to commercial noble metal electric catalyst combination RuO₂/NF?+?//Pt-C/NF?-??1.63V?.The structure and morphology of the nanosheets and the synergistic effect of nickel,iron and zinc ions enhanced the catalytic activity,while the addition of zinc ion promoted the rapid growth of nanosheets on nickel foams,which further improved the stability of nanosheets.