WS₂ Thin Films Prepared By Magnetron Sputtering And Their Electrocatalytic Hydrogen Evolution Properties

Noble metal Pt is a commonly used catalyst for hydrogen evolution in water electrolysis,but its content in the crust is low and its price is high.The development of new low-cost hydrogen evolution catalysts to replace Pt is a research hotspot at present.The edge of WS₂ with layered structure has active sites for hydrogen evolution,and it is a potential catalyst for electrocatalytic hydrogen evolution reaction.WS₂ thin films were prepared by radio frequency magnetron sputtering.The effects of different process parameters?power of radio frequency power supply,working pressure,deposition time,negative bias of substrate?on the phase structure,composition and surface morphology of WS₂ were systematically studied.The electrocatalytic hydrogen evolution performance of WS₂ prepared under different conditions was tested by electrochemical method.Furthermore,for the films with the best catalytic performance,surface modification was carried out by RF counter-sputtering and Ar plasma etching.The effects of power supply,sputtering time,screen voltage and modification time on the morphology and catalytic hydrogen evolution performance of the films were studied.The effects of RF magnetron sputtering parameters on the phase structure,composition and surface morphology of WS₂ thin films were obtained.With the increase of power of RF power supply,the crystallinity of WS₂ in?101?direction increases,and the loss of S atom occurs in the film composition.The sulfur-tungsten ratio of WS₂ is less than stoichiometric ratio,i.e.S:W<2.The surface structure is uniform and fine worm-like at 200W.With the increase of working pressure,the crystallinity of WS₂ in?101?direction decreases,the value of S:W increases,and the surface structure becomes uniform and fine at 1.0Pa.With the increase of deposition time,the crystallinity of WS₂ in?101?direction increases,the value of S:W does not change significantly,and the surface structure is uniform and fine worm-like structure in90 minutes.After applying negative bias,the crystallinity of WS₂ in?101?direction increases,the value of S:W decreases,and the surface structure becomes uniform and fine worm-like structure without negative bias.The electrocatalytic hydrogen evolution properties of WS₂ thin films prepared under different conditions were obtained.It was found that the composition of the film,i.e.S:W value and surface morphology,had a great influence on its electrocatalytic hydrogen evolution performance.The more the S:W deviates from the stoichiometric ratio,the smaller the S:W value,the more the S atom loss on the film surface,the more S-vacancies are generated,the more W-edges are exposed and the catalytic activity is enhanced.The more uniform and fine the surface structure is,the more active sites are exposed and the catalytic activity is enhanced.When the power of RF power supply is200 W,the working pressure is 1.0 Pa,the deposition time is 90 minutes,and the negative bias voltage is not applied,the S:W ratio of the film is 1.87,there are a certain number of S vacancies,the surface structure is fine,the electrocatalytic hydrogen evolution performance of WS₂ film is the best,the overpotential corresponding to the current density of 10 mA/cm² is the smallest,and the Tafel slope is the smallest.The effects of RF backsputtering and ion beam etching on the catalytic properties of WS₂ films prepared by surface modification were obtained.For RF anti-sputtering method,the larger the power of RF power supply,the longer the sputtering time,the bigger the surface structure and the smaller the value of S:W.When the power is 150 W and the sputtering time is 2 min,the balance between them is achieved.The surface structure is finer,the value of S:W is also reduced to a certain extent compared with the unmodified film,resulting in more S-vacancies,and its electrocatalytic hydrogen evolution performance is the best.For ion beam etching,the larger the screen voltage,the longer the etching time,the thicker the surface structure and the smaller the S:W value.When the screen voltage is 900V and the etching time is 30s,the balance between them is achieved.The surface structure is finer.The S:W value is also reduced to a certain extent compared with the unmodified film,resulting in more S-vacancies,and its electrocatalytic hydrogen evolution performance is the best.Compared with ion beam etching,RF backsputtering can improve the electrocatalytic hydrogen evolution performance of WS₂ thin films more obviously.Through the above research,the optimum technological conditions for preparing WS₂ thin films were obtained:the power of RF power supply was 200 W,the working pressure was 1.0 Pa,the deposition time was 90 minutes,the negative bias voltage of substrate was 0 V,the backsplash power of prepared thin films was 150 W,and the backsplash time was 2 minutes.The optimum electrocatalytic hydrogen evolution performance corresponds to this:when the current density is 10 mA/cm²,the overpotential is 170 mV,the Tafel slope is 59 mV/dec,the charge transfer resistance Rct is 20.4?;and the hydrogen evolution performance of WS₂/rGO nanosheets after annealing is better than that of MoS₂ films which belong to the same transition metal sulfide.