Study On Electrocatcalytic Performances Of Cu-MOF And It's Dereratives

As a critical carrier of energy,hydrogen plays an important role on electrolysis of water and fuel cell.On the one hand,hydrogen evolution reaction?HER?is the cathodic reaction of electrolysis of water.On the other hand,Hydrogen oxidation reaction?HOR?as its inverse reaction is the anode reaction in fuel cells.However,producing hydrogen by electrolysis of water still limited by high consumption.There is still an urgent need to explore less expensive,earth-abunbant substitutes for HER.Due to the intriguing porous of nets structure and various active centers,metal-organic frameworks?MOFs?opens a new approach to obtain catalyst for HER.In this paper,the mixed-ligand strategy is used to construct a stable metal active center.Transition metal organic framework was synthesized with 3,5-pyrazole dicarboxylic acid and the 1,10-phenanthroline as organicligands and copper as metal node.Next is to investigative the electrocatalytic performance and mechanism of primaeval Cu-MOF and it's derivatives for HER in acidic medium.Firstly,copper-based organic framework?Cu-MOF?was obtain by hydrothermal method with 3,5-pyrazole dicarboxylic acid and the 1,10-phenanthroline as organic ligands and copper sulphate as metal source.In order to study the mechanism of Cu-MOF,mix the Cu-MOF with graphite to prepare a solid carbon paste electrode?Cu-MOF/sCPE?.The cathodic polarization curve,Tafel slope,cyclic voltammetry scanning and electrochemical impedance spectroscopywere used to evaluate the performanceof Cu-MOF/sCPE for hydrogen evolution reaction in acidic medium.Meanwhile,the purity,morphology and chemical environment of Cu-MOF were analysised clearly by a series of characterization techniques like FTIR,XRD,XPS,FESEM,FETEM.It proved that the slight doping of the Cu-MOF in the carbon pastecould significantly enhance the electrocatalytic activity for HER,comparing with the sCPE.The overpotentialof Cu-MOF/sCPE were positively shifted by 440 mV at the current density of 10 mA cm^-2.In view ofthe datas of cyclic voltammetry scanningat different rate and research ofsurface state,we proposed the catalyticmechanism of Cu-MOF for HER.The first step occurs only at the start of HER and transforms all the surface Cu^II ions into Cu^I.Then one-electron transfer step produces the highly active Cu⁰ centers,which chemically reduces H⁺ions to yield adsorbed H atoms.And XPS and FTIR-ATR of Cu-MOF after electrochemical reduction provided further evidence that Cu-MOF has a significant effect on the first electron transfer during the hydrogen evolution process for giving a positive onset potential of about 100 mV vs.RHE.In addition,extensive efforts were to explore the formation and overflow of adsorbed hydrogen in MOF.It is proved that the existence of the intermediate product?adsorbed hydrogen atom?.All the work provide a new insights into the mechanism of catalytic activity of Cu in MOF.Based on previous work,we proposed the idea of designing and synthesizing specific synergistic catalysts which can synergize with Cu-MOF to catalyze the second electron transfer step to improve the overall performance of electrocatalytic hydrogen evolution.Derivatives of Mo,Pd and Pt doping the Cu-MOF:Mo/Cu-MOF,Pd/Cu-MOF and Pt/CuNC were obtained by immerging and carbonization.Similarly,the catalytic performances for HER in acid medium were tested.The catalytic mechanism on the electrode surface were investigated by electrochemical impedance spectroscopy of Mo/Cu-MOF/sCPE,Pd/Cu-MOF@sCPE and Pt/CuNC@sCE.Assistant with XRD,XPS,FETEM and FESEM technologies,the morphology and chemical environment of derivatives were characterized.Results shows that,the over potential of the Mo/Cu-MOF/sCPE,Pd/Cu-MOF@sCPE and the Pt/CuNC@sCE were positively shifted by234,,398 mV and 522 mV(the current density was 10 mA cm^-2),respectively.The exchange current density of Mo/Cu-MOF/sCPE,Pd/Cu-MOF@sCPE and the Pt/CuNC@sCE were found to be 10^5.5,10^7.5,10^8.2 times higher than that of the Cu-MOF/sCPE,respectively.It can be concluded from the EIS study that the introduction of the metal Mo can significantly reduce the surface electron transfer impedance during hydrogen evolution and achieve the purpose of improving catalytic hydrogen evolution activity.The derivative doped with the noble metal Pd can increase the specific surface area of the catalysts and the active sites of the catalysts,thus improving their catalytic hydrogen evolution performance.The catalytic activity of derivatives doped noble metal Pt is similar to that of commercial PtC,but the amount of Pt is much less.