Active Performance And Stability Research Of Water Splitting For Prepared Electrocatalysts Anode Consist Of Common Transition Metal And Corresponding Sulfide Compounds

As the main reason for the greenhouse effect,carbon dioxide is a serious threat to the earth’s environment and biological survival.The development of new energy is imperative,among which hydrogen energy is the greenest and environmentally friendly choice at this stage.Moreover,hydrogen production by electrolysis of water is one of the best development directions among the many hydrogen production methods.The hydrogen production efficiency can range from 70% to 100% depending on different electrolyzers.The combustion heat of hydrogen is three times more than that of petroleum,making it an ideal energy carrier.Hydrogen production by electrolysis of water can greatly increase hydrogen production while greatly reducing pollution.Electrolysis water includes two half-reactions:HER and OER.Among them,the OER reaction of the anode has slow kinetics due to its multi-electron reaction process,which leads to more power consumption.In order to reduce the power consumption,many researchers have devoted themselves to the performance research of the anode catalysts for electrolysis of water.Many catalysts with excellent oxygen evolution activity have been studied recently,but the stability of them need to be proved.In this paper,the stability tests were carried out with high-purity transition metals,such as Fe,Ni,Co and Mn.Simultaneously,the dissolution rates of the four transition metals were obtained by ICP-MS.The dissolution rate of Fe and Mn is much higher than that of Ni and Co,which is nearly a hundred times of them.Meanwhile,this part provides support and ideas for the design and preparation of stable oxygen evolution materials through the study of dissolution rate and dissolution mechanism.Using carbon cloth as a carrier,a relatively stable nickel-based material was introduced into MoS₂ nanosheet,which effectively improves the intrinsic catalytic activity of MoS₂.Benefit from the in-situ growth of the catalyst on the carbon cloth,the substrate and the catalyst are combined closely,which further increases the stability performance of the catalyst.In addition,since Mo accounts for a larger proportion,the catalytic electrode NiS₂/MoS₂-CC can achieve both OER and HER.After the stability test,the electrode has good HER and OER stable activity at low current density.However,there was a large amount of Mo ions dissolved during the OER process,which leads to poor stability.The OER catalyst MoS₂@NiS₂ was prepared by the electrostatic adsorption method.Using NiS₂ as the main substrate and Mo as the doping element to prepare MoS₂@NiS₂ samples to improve stability of electrocatalyst.Its special morphology and structure were conducive to exposing more active sites and increasing the contact area with the electrolyte.The electrocatalyst has excellent OER activity trough the electrochemical testing.In addition,after the catalyst was subjected to a 24 h stability test at a current density of 20 m A cm^–2,the results showed that its performance did not degrade at all and still maintained excellent stability.The electrode was subjected to a chronoamperometry stability test at 1.51 and 1.81 V vs.RHE,and finally proved that the electrode exhibits excellent stability under low voltage,but there was drop in performance at high voltage.According to the ICP test,the Mo ions began to show a certain increase during the stability test.As the test time increased,the content of Mo ion remained almost constant.Therefore,the hypothesis that the OER active site of this catalyst is Ni-based compounds.Maintaining the structure of the nickel-based catalyst unchanged,a catalyst Fe S_x@NiS₂was synthesized,and the adsorption energy of Ni was improved by the doping Fe instead of Mo.According to the electrochemical performance test,the excellent OER catalytic activity was obtained,in which the Tafel slope was reduced to 52.3 m V dec^–1,and the kinetic rate of the OER catalytic process was accelerated.After 24 hours stability test at a current density of20 m A cm^–2,the electrolyte was detected by ICP-MS and found that Fe increased with time and did not increase after a certain period of time.Moreover,the OER catalytic performance of the catalyst remains stable,which means that the main active center of the catalyst is the Ni-based compound.Finally,we proposed a structure material with conductor-control layer-active layer.The Mn Co@Ni S-NF electrode was synthesized by a step-by-step electrodeposition method,and the bimetal in the middle layer is introduced into the outer layer of Ni.The based active site adsorption can play a regulatory role and achieve better kinetic performance and stability than Fe Ni compounds.The outer electroplated nickel-based coating can prevent the regulation layer from dissolving,maintain the overall structure of the catalytic electrode stable,and increase the stability of the catalyst under higher current density and voltage.According to the co-doping modification of Mn and Co of the control layer,the electron concentration distribution of the catalyst can be effectively controlled,and adsorption energy of the oxygen-containing substance of the reaction intermediate and the electrode catalyst can be optimized.The results showed that the OER activity and kinetics of the electrode have been improved.Meanwhile,the electrode has no changing under the 50 m A cm^–2 current density stability test for about 20h.The ICP results for anode dissolution also proved the structural stability of the catalytic electrode.this research provides important ideas for the commercial preparation of electrolyzed water catalysts.