Preparation Of Nickel-iron Hydroxide Nano-film Doped With Mo(VI) And W(VI) And Electrocatalytic Oxygen Evolution Reaction

Hydrogen,as a clean and renewable energy resource,Electrochemical water splitting provides us a simple method for mass production of pure hydrogen,but sluggish kinetics of oxygen evolution reaction(OER)on the anode requires efficient water oxidation electrocatalysts to reduce the overpotential and improve the efficiency.Therefore,it is highly desirable to develop highly efficient,stable and cheap water oxidation catalysts.Ni-base has been used as a higher efficiency activity to make anode materials in alkaline water electrolysis,including oxides,hydroxides,chalcogenides,phosphides,nitrides.In addition,incorporation of Fe into the nickel hydroxide electrodes leads to significantly enhanced OER activity,and CoMoO4 catalysts with higher efficiency activity and prolonged stability water electrolysis.This paper is based on the nickel-iron hydroxide catalyst reported,the Mo-doped nickel iron hydroxide catalyst(NiFeMo/NF)electrode were electrodeposited on surface of nickel foam(NF)by cyclic voltammetry(CV)method in electrolyte solution,containing 3.0 mM NiCl2,3.0 mM FeCl3 and different contents of Na2MoO4.The electrodeposition was carried out at potential ranging from-1.2 to 0.2 V(vs.Ag/AgCl)at a scan rate of 5 mV s-1.The effects of catalysis of NiFeMo/NF electrode were investigated at different contents of Na2MoO4 and electrodeposition time for OER.The NiFeMo/NF electrode obtained the best performance,when the Na2MoO4 concentration is 0.6 mM and electrodeposits 8 cycles.Further,NiFeMo/NF electrodes were analysed,the SEM images further indicating that the NiFeMo is a meso-porous nanosheets with length about 100?200 nm which are assembled on the surface of NF,and the Ni,Fe,Mo,and O elements are uniformly distributed in the nanosheets by the EDX,respectively.The NiFeMo catalysts are composed of nanosheets and are amorphous in nature without detection of typical lattice fringes by the TEM and XRD.The XPS spectras of the NiFeMo catalyst indicate that OH-ions react with Ni(II)and Fe(III)to form NiFe hydroxide,and Mo(VI)mostlys is oxidation state in the NiFeMo catalyst.The electrochemical performance of NiFeMo/NF electrode was investigated in 1.0 M KOH solution for OER by linear sweep voltammetry(LSV).The NiFeMo/NF electrode shows a good catalytic activity requiring low overpotential(j20mA cm2= 230 mV).The overpotential of the NiFeMo/NF electrode was reduced 22 mV compared with NiFe/NF electrode for the OER.The resulting Tafel plot of NiFeMo/NF electrode is mere 41.8 mV dec-1,which is much smaller than that of NiFe/NF electrode(47.8 mV dec-1),demonstrating that Mo(VI)-doping can be beneficial to reduce an overpotential of NiFeMo/NF electrode catalyst for OER and expedite kinetics reaction rate of OER,the results that the catalytic activity of the electrode was improved.The NiFeMo/NF electrode has a fast electron transfer rate and fast mass transfer for OER by LSV and Multi-current test.In addition,the stability of NiFeMo/NF electrode was studied in KOH alkaline solution by chronoptentiometry,which is shows prolonged stability for OER.Furthermore,the reason of improving the catalytic activity of NiFeMo/NF electrode was studied by Electrochemical and other methods.The results show that the electrochemical active surface area of NiFeMo/NF electrode is enlarged,the charge transfer resistance is reduced and the hydrophilicity of the catalyst surface is enhanced compared with NiFe/NF electrode.The catalytic activity is improved for OER by increasing the active sites of OER and favoring OH" adsorption on the catalyst surface.Another content of this paper is prepared the nickel iron wolfram(NiFeW)catalyst by electrodeposition.The best condition of deposition was investigated by preliminary experiment results.W-doped nickel iron hydroxide catalyst(NiFeW/NF)electrodes were electrodeposited by cyclic voltammetry(CV)method in electrolyte solution,containing 10.0 mM NiCl2,10 mM FeCl3 and 0,6 mM Na2WO4 for 10 cycles.The NiFeW/NF electrode was analysed,the SEM images demonstrate that the NiFeW is a meso-porous nanosheet with length of 50?100 nm,and the Ni,Fe,W,and O elements are uniformly distributed in the nanosheets by the EDX,respectively.The NiFeW nanosheets are amorphous by the TEM and XRD.The XPS spectras of the NiFeW catalyst indicate that OH" ions react with Ni(II)and Fe(III)to form NiFe hydroxide,and W(VI)mostlys is oxidation state in the NiFeW catalyst.The electrochemical performance of NiFeW/NF electrode was investigated in 1.0 M KOH solution for OER by LSV.The NiFeW/NF electrode shows a good catalytic activity requiring a low overpotential(j10 mA cm-2 = 220 mV).The Tafel slope of NiFeW/NF is 44.3 mV dec-1.NiFeW/NF electrode has a fast electron transfer rate and fast mass transfer effect lead to quicken rate of kinetics for OER.The stability of NiFeW/NF electrode was studied for OER by chronopotentiometric,which is shows enduring stability.