Construction Of Nickel-Cobalt-Based Compound Self-Supporting Materals And Their Electrochemical Performance

At present,with the depletion of traditional fossil energy and the increasingly serious problem of environmental pollution,the development of renewable energy is an important topic for human society to achieve sustainable development.It has become a research hotspot that the electrochemical technologies including fuel cells,supercapacitors and electrochemical water splitting are used to store and convert energy to achieve the exchange of electrical energy and chemical energy.The supercapacitors,a high-efficient energy storage device,are equipped with high power density,high energy conversion efficiency and excellent cycling stability.The electrochemical water splitting is an important technology for hydrogen energy production,which has the advantages of simple process and pollution-free products.Electrode materials are the key factors for the performance of supercapacitors and electrochemical water splitting.Exploring self-supporting electrode materials that can be applied to supercapacitors and electrolytic water is an important research hotspot in the field of electrochemistry in recent years.In this work,the composition and micro morphology of nickel-cobalt based oxide/sulfide/phosphide composites are adjusted through hydrothermal method and in-situ phosphating/sulfuration process,resulting in the optimization of nickel-cobalt based composite nanoarrays.Therefore,the energy storage and electrocatalytic performances of electrode materials are improved.The main research and results are as followed:（1）Ni-Co oxide/Co-Mo phosphide self-supporting composite materials on nickel foam were synthesized through hydrothermal method and in-suit phosphorization.The second hydrothermal process has optimized the micromorphology of electrode materials by introducing Mo element.The introduction of metal-phosphide gives electrode materials with the fast reaction kinetics and more reaction active sites.As electrode materials of supercapacitors,the specific capacitance value for Ni Co Mo O-P was obtained to be 2878.6 F g^-1at a current density of 1 A g^-1(equivalent to 2.23 m A cm^-2).The hybrid supercapacitor device fabricated using Ni Co Mo O-P possesses a high specific energy density of 45.3 Wh kg^-1.As electrode materials of OER,Ni Co Mo O-P shows a low overpotential of 284 m V and a small Tafel slope of 92.5 m V dec^-1at a current density of 100 m A cm^-2.The results of electrochemical test indicate that the Ni-Co oxide/Co-Mo phosphide self-supporting composite materials have great potential in the fields of supercapacitors and electrochemical water splitting.（2）Ni-Co-Mo nanosheets self-supporting precursors on nickel foam were firstly prepared through hydrothermal method.Then the precursors were converted into Ni-Co oxide/Co-Mo sulfide after in-suit sulfurization.The micromorphology of electrode materials has been optimized by hydrothermal method.The introduction of metal-sulfides gives electrode materials with the fast reaction kinetics and more reaction active sites.In supercapacitor tests,the specific capacitance of Ni Co Mo O-S was up to 3061.9 F g^-1 at a current density of 1 A g^-1(equivalent to 2.82 m A cm^-2).Moreover,this electrode material exhibited good cycling stability.The hybrid supercapacitor device that was made of Ni Co Mo O-S can obtain high specific energy density of 17.3 Wh kg^-1.In OER tests,Ni Co Mo O-S only needs overpotential of 290 m V and Tafel slope of 87.2m V dec^-1 to achieve a current density of 100 m A cm^-2.Furthermore,the Ni Co Mo O-S catalyst maintains oxygen evolution for 60 h at different current densities,suggesting an excellent stability.The results of electrochemical test indicate that the Ni Co Mo O-S have bright application prospects in the fields of energy storage and conversion.（3）Nickel-cobalt oxide/phosphide/sulfide self-supporting composite matrials on Ni foam were synthesized through hydrothermal method and a simulataneous one-step in-suit phosphorization and sulfurization.The Ni Co O-2P/S have large accseeible surface,many holes in the internal structure of nanowires and good interface effects between Nickel-cobalt oxide/phosphide/sulfide,which is conductive to give full play to the potential of the performance of the supercapacitor and electrochemical water splitting.The maximum specific capacitance of Ni Co O-2P/S was up to 2915.6 F g^-1.Moreover,the Ni Co O-2P/S shows a great rate performance.The hybrid supercapacitor device fabricated using Ni Co O-2P/S possesses high specific energy density of26.7 Wh kg^-1.As electrode material of electrochemical water splitting,the Ni Co O-2P/S arrays show low overpotential of 143 m V at 10 m A cm^-2 for HER and 254 m V at 100 m A cm^-2 for OER.The small Tafel slopes of 82 m V dec^-1 for HER and 88 m V dec^-1 for OER indicate that the Ni Co O-2P/S catalyst has more favorable reaction kinetics for water splitting.The two-electrode electroyzer using the Ni Co O-2P/S as both the anode and the cathode can be driven at low cell voltage of 1.50 V to achieve a current density of 10 m A cm^-2.This work provides an alternative strategy for preparing cost-effective and high-performance self-supporting electrode materials for energy storage and conversion.