Study On Electrocatalytic Activity Of Molybdenum Disulfide Thin Films Prepared By Pulsed Electro-deposition

Molybdenum disulfide is a very promising layered structure and semiconductormaterial for various applications such as lubrication, catalysis, field effect transistorsand sensors. A reasonable method for preparing molybdenum disulfide is important.Firstly, we used mainly solutions of freshly-prepared dark red sodiumtetrathiomolybdate formed in a chemical reaction in a solution of sodium molybdatedehydrate and excess sodium sulphide. Red brown thin films were deposition onsubstrates including titanium, nickel, copper using constant current. Electrochemicalproperties were compared in0.5mol/L sulfuric acid electrolytes, and results showedthat Ti substrate was more appropriate. Energy dispersive spectrometer and X-rayphotoelectron spectroscopy results showed that the as-deposition molybdenum disulfidethin films were made of molybdenum and sulfur.Secondly, the difference of electrodeposition technology beween direct current andpulse were compared. Scanning electron microscope results showed that neither theelectro-deposition technique nor the solution concentration were impact on the surfacetopography of the thin films. The stability and aging time of molybdenum sulphide thinfilms prepared by direct current and pulse electro-deposition were compared in0.5mol/L sulfuric acid electrolytes, and molybdenum disulfide thin films prepared by pulseelectro-deposition had a smaller hydrogen evolution potential and long constant voltageplatform at constant current.The duty cycle, current, solution concentration, time, temperature duringprepareing molybdenum disulfide thin films were studied, molybdenum disulfide thinfilms had better electro-catalytic activity at jp=2mA/cm2, Ton=1s, Toff=1s, Q=0.8C.The onset potential was-0.405V (vs.SCE), tafel slope was51mV/dec. Electrochemicalimpedance spectroscopy showed that the semicircle at higher frequencies was dutycycle, current, solution concentration, time and temperature independent represented thecharge transfer process. But the charge transfer resistance was potential-dependent. Thesemicircle at higher frequencies was largely potential independent represented thecontact between the titanium electrode and the catalyst.Finaly, three possible reaction steps had been suggested for the hydrogen evolutionreaction in acidic media. In the present work, for a complete HER process,combinations of steps, i.e. Volmer-Heyrovsky or Volmer-Tafel mechanism, should be involed to produce molecular hydrogen.