Transition-Metal Sulphides Composite:Preparation And Their Application For Photocatalytic/Electrocatalytic Water Splitting

Photoelectrocatalytic decomposition of water technology is a promising technology,it can convert solar and electrical energy into hydrogen energy and alleviate the energy crisis caused by fossil fuel shortages.However,Photoelectrocatalytic decomposition of water has the disadvantages of complex kinetic processes and large overpotentials,which limits its application in industry.Usually,precious metal catalysts such as iridium oxide(IrO2)and ruthenium oxide(RuO2)can reduce the overpotential of photoelectrocatalytic reactions and accelerate the efficiency of photoelectrocatalytic decomposition of water.However,they are scarce reserves,high cost and poor stability characteristics,these characteristics seriously hinder the large-scale use of precious metal catalysts.In view of this problem,this paper uses the transition metal widely existing in nature as a raw material to attempt to construct a transition metal sulphide composite material to replace the precious metal photoelectrocatalyst,and the specific work is as follows:(1)In this paper,a simple method was used to synthesize MoS2/TiO2 water splitting electrocatalyst.SEM,XRD and other characterizations showed that the nanoflower-like MoS2 was successfully grown on porous TiO2 to prepare the stable MoS2/TiO2 heterostructure.This special structure increases the surface areas of the electrocatalyst,which can provide abundant channels for charge transfer,thus enabling TiO2 to have high catalytic performance.The electrochemical measurements results showed that the 12%MoS2/TiO2 composites have the best HER performance,in acidic electrolyte(a potential of～108 mV at 10 mA/cm2 and a Tafel slope of 55 mV/dec)and alkaline electrolyte(a potential of～127 mV at 10 mA/cm2 and a Tafel slope of 59 mV/dec),respectively.The above excellent HER activity is derived from the improvement of the separation and migration capacity of the charge carrier in the HER process by the MoS2/TiO2 composites.(2)In this paper,cactus-shaped CdS-Cu9S5 composites were syntheszied on copper foam.The as-prepared CdS-Cu9S5-CF showed a highly efficient catalyst for photoelectrochemical(PEC)water splitting,and its high performance was contributed to its unique cactus-shaped structure,which provided abundant surface catalytic active sites,and numerous charge transfer channels,thereby enhanced the transport and separation of CdS-Cu9S5-CF photo-induced charge carriers during the PEC process.In addition,because the synergistic effect between Cu9S5 and CdS can significantly inhibit the recombination of photo-induced carriers in the PEC process,the optimized 3%CdS-Cu9S5-CF(the molar ratio of CdS to Cu9S5 is 3:100)and pure Cu9S5 and other CdS-Cu9S5-CF,exhibited higher photocurrent density.(3)Metal sulfides are considered as excellent catalysts for oxygen evolution reaction(OER)because of their excellent electrical conductivity and high electrocatalytic activity.In this article,NiS-Cu2S composites were prepared on copper foam(NiS-Cu2S-CF)using a simple synthesis strategy.Cold field scanning electron microscopy(SEM)results showed that NiS nano-needles were successfully loaded on Cu2S nanosheets,which can significantly increase the active sites on the surface of the nanosheets during the OER process.15%NiS-Cu2S-CF composite has an overpotential of 308 mV at a current density of 20 mA/cm2,which is much smaller than that of precious metal-based electrocatalysts and other NiS-Cu2S-CF composites,the above enhanced OER activity is attributed to its unique morphology and synergistic effect between NiS and Cu2S.