Preparation And Properties Of Transition Metal Hydroxyphosphite And Selenide Electrode Materials For Supercapacitor

With the rapid development of economy,the problems of rapid energy consumption and environmental pollution are becoming more and more serious,so it is urgent to find new energy storage devices.In recent years,supercapacitors have been widely concerned because of their long cycle life,fast charge and discharge rate and high power density.However,the low energy density restricts the development of supercapacitors.In order to expand the research and application of supercapacitors,researchers strive to improve the specific capacitance and energy density by designing and synthesizing new nano/micro electrode materials.In this paper,a series of Nidoped Co₁₁^?(HPO₃)₈(OH)₆/NF nanomaterials and metal doped NiSe₂-dien/NF(dien=diethylenetriamine)nanomaterials were prepared by using a simple water(solvent)thermal method based on porous nickel foam(NF),and their applications in the field of supercapacitor electrode materials were tested.The specific research contents are as follows:(1)Ni-doped Co₁₁(HPO₃)₈(OH)₆with different morphologies were directly grown on Nifoam hydro(solvo)thermally under different synthetic conditions.The optimum condition is solvothermally reaction for 6 h in an ethanol/water solution(5 mL/5 mL)with a 0.5:0.1 of NaH₂PO₂/Co(NO₃)₂ molar ratio,and the obtained S0.5-6h-EW shows three-dimensioanal(3D)porous nanowire bundles.Whereas in the water-only solution,microrods are obtained,suggesting the nanowires in bundles are aggregated together via the lateral(400)direction.Long reaction time and low molar ratio of reactants all are beneficial for the lateral growth of the nanowires,and the possible formation mechanism is proposed.All the obtained Ni-doped Co₁₁(HPO₃)₈(OH)₆/Nifoam samples are directly used as supercapacitor electrode,and S0.5-6h-EW shows the best electrochemical performance with a specific capacity of 159 mAh g^-1 at 0.5 A g^-1,which is close to the theoretical value of 212 mAh g^-1 for Co₁₁(HPO₃)₈(OH)₆,and it is the largest reported value so far.The excellent capacitive behavior of S0.5-6h-EW is ascribed to the 3D porous nanowire bundles directly grown on Nifoam collector without additive and binder,as well as the doping of Niinto the cobalt phosphite.The S0.5-6h-EW//activated carbon asymmetrical supercapacitor(ASC)shows a maximum energy density of 58.7 Wh kg^-1at power density of 532 W kg^-1 and good cycling stability with capacity retention of 90.5%after 10000 charging-discharging cycles at5.5 A g^-1.(2)A series of MSe₂-dien(M=metal(?)ion,dien=diethylenetriamine)were grown on Nifoam(NF)based on Co(?)/Mn(?)salts with different molar ratios.It was found the free-Co sample exhibits hollow tubes built by numerous interconnected nanowires,whereas nanosheets were observed in other Co-involved samples.The formation of nanosheets is associated with Co(?),which is due to the fact that Co(?)would promote the metal selenide nanosheets to grow along its(01?)facet(thickness direction).It was investigated the formation and compositional/morphological evolutions of the samples.Among them,(Co,Mn)-NiSe₂-dien/NF(2:1-Co/Mn sample)shows the largest specific capacity of 288.6 mAh g^-1 at 1 A g^-1 with a retention of 69%at 10 A g^-1(198.6 mAh g^-1),which is associated with its ultrathin nanosheet arrays and the co-doping of(Co,Mn)into NiSe₂-dien,leading to the redistribution of electron densities around Niand Se centers.XPS and density functional theory(DFT)calculations prove the electron transfer from NiSe₂-dien to the adsorbed OH^-ions from electrolyte solution,which can facilitate the redox reaction between active sites and electrolyte ions to enhance the electrochemical performance.The hybrid supercapacitor,(Co,Mn)-NiSe₂-dien/NF//activated carbon,displays energy density of 50.9 Wh kg^-1at power density of 447.3 W kg^-1 and good cycling stability with 84%of capacity retention after 10000 charge-discharge cycles.(Co,Mn)-doped NiSe₂-dien nanosheets can be transformed into(Co,Mn,Sn)-doped NiSe₂ nanowire arrays after immersion in Sn Cl₂alcoholic solution due to the cation exchange and kirkendall effect,and the obtained sample exhibits a decent areal capacity of 0.267 mAh cm^-2 at 5 mA cm^-2.