The Preparation Of Mo-based Carbides And Their Application In Electrocatalytic Water Splitting

Hydrogen energy is considered a renewable energy source with promising application.Electrocatalytic water splitting is an important route to produce hydrogen.Mo-based carbides,particularly Mo₂C,exhibits excellent catalytic hydrogen evolution reaction?HER?performance,due to its similar electronic structure with platinum group metals.The precurors are synthesized by vacuum rotary evaporation method and hydrothermal method,and a series of Mo-based carbides are synthesized by high temperature calcination in this paper.The structure of the catalysts is characterized by XRD,XPS and TEM.The properties of electrocatalytic water splitting are studied by means of the cyclic voltammentry and chronopotentiometry.The dicyandiamide and phosphomolybdic acid are mixed to be the raw materials for DCD-PMA series catalysts,which are synthesized by ratary evaporating under vacuum condition and high-temperature calcinating.The prepared catalysts have good Mo₂C crystal structure.These catalysts also exhibit well HER activity.Among these catalysts,5DCD-PMA-700 has the best HER activity in 0.5 M H₂SO₄,and its overvoltage at 10 mA cm^-2 is 181 mV,and the Tafel slope is 65.3 mV dec^-1;At 10 mA cm^-2,the HER overvoltage of 5DCD-PMA-800 in 0.1 M KOH is 244 mV,and he Tafel slope is 99.1 mV dec^-1.5DCD-PMA/Ni series catalysts are prepeared by doping Ni on the catalyst of the above-described optimization?dicyandiamide and phosphomolybdic acid at a mass ratio of 5:1?.The crystal structure of the prepared catalyst is Mo₂C and metallic Ni.These catalysts also exhibit better HER/OER activity in 0.5 M H₂SO₄ and 0.1 M KOH.Among these catalysts,the HER overvoltage of 5DCD-PMA/0.25Ni-800 at 10 mA cm^-2 are 206 mV and 239 mV,and the Tafel slopes are 66.9 mV dec^-1 and 107.5 mV dec^-1.The OER overvoltage at 10 mA cm^-2 in 0.1 M KOH is 391 mV and the Tafel slope is 68.3 mV dec^-1.The stability test during 8 h shows that the catalyst has great HER/OER stability,which is better than that of 20 wt%Pt/C and Ir02 under same condition.5DCD-PMA/0.25Ni-800 shows that the HER/OER activity has been significantly improved compared with non-doped Ni?5DCD-PMA-800?.The?lmi-HMT?-PMA-Ni series catalysts are prepared by hydrothermal method and high-temperature calcination.In 0.1 M KOH solution,the HER overvoltage of?lmi-HMT?-PMA-Ni-2-600 at 10 mA cm^-2 is 201 mV,the Tafel slope is 143.9 mV dec^-1,and double layer capacitance is 9.96 mF.?lmi-HMT?-PMA-Ni-2-600 is supirior than DCD-PMA,5DCD-PMA/Ni series catalysts.And the OER overvoltage of?lmi-HMT?-PMA-Ni-2-800 is 419 mV closing to IrO₂.