Morphology-Controlled Synthesis Of Carbon-Based Tungsten Dioxide And Carbide Composites For Hydrogen Evolution Reaction

Electrolysis of water is one of important routes of energy conversion and storage.In particular,the cathodic reaction,i.e.hydrogen evolution reaction(HER)is one of key technique for hydrogen production.The development of efficient and inexpensive HER catalysts is critical to the future sustainable energy system.As a substitute of Pt catalyst,tungsten carbide exhibits efficient electrocatalytic properties,and has many advantages in electrochemical activity,selectivity and resistance to carbon monoxide toxicity.Tungsten dioxide,as a transition metal oxide,has potential application in electrocatalytic hydrogen evolution.Carbon nanomaterials have high specific surface area and stability.Based on the above metioned,transition metal oxides/carbides are dispersed on the surface of carbon nanomaterials is an effective way to reduce cost,improve catalytic activity and stability.(1)At room temperature,by changing the proportion of carbon and tungsten raw materials and the calcination temperature,the hollow hemisphere porous carbon carrying tungsten dioxide complex with a diameter of 300 nm was obtained.The effects of different conditions on the properties of electrolysis water and hydrogen were investigated.When the molar ratio of phloroglucin to ammonium metatungstate is 1:1 and the treatment temperature is 900℃,the hydrogen evolution performance is best.When the current density is 10 mA/cm~2,the corresponding overpotential value is 444 mV,and the Tafel slope is 95.2mV/dec,between 40-116 mV/dec,conforms to the Volmer-Heyrovsky mechanism.In addition,a stability test was performed to show that the sample had good electrocatalytic stability.(2)Changing the amount of carbon source by hydrothermal method,the spherical carbon-carrying tungsten dioxide complex with diameter of 2.5μm-5μm was obtained.The change of carbon content has a certain effect on the property of hydrogen evolution by electrolysis.When the amount of ammonium metatungstate was 1 g and the amount ofβ-cyclodextrin was 0.5 g,the hydrogen evolution performance was the best.When the current density was 10 mA/cm~2,the overpotential value corresponding to the sample was 441 mV,and the Tafel slope was 163 mV/dec.In addition,a stability test was performed to show that the sample had good electrocatalytic stability.(3)Changing the hydrothermal reaction temperature and the tungsten source by hydrothermal method can adjust to obtain a spherical carbon-supported tungsten carbide composite having a diameter of 3-5μm.Both the change of the tungsten source and the hydrothermal reaction temperature of the precursor have a certain influence on the hydrogen evolution performance of the electrolyzed water.When ammonium metatungstate is used as the tungsten source and the hydrothermal temperature is 170℃,the hydrogen evolution performance is the best.when the current density is 10mA/cm~2,the sample has an overpotential value of 247 mV and a Tafel slope of84.8 mV/dec.In addition,a stability test was performed to show that the sample had good electrocatalytic stability.At the same time,the effects of hydrogen evolution performance of different Pt loadings were investigated.It was found that the hydrogen evolution performance increased with the increase of Pt loading.When the loading was1.5wt.%,the hydrogen evolution performance was the best.When the current density is 10 mA/cm~2,the corresponding overpotential value of the sample is27.4 mV,the Tafel slope is 32 mV/dec,and its performance is better than that of the activated carbon with 1.5wt.%Pt.In addition,a stability test was performed to show that the sample had good electrocatalytic stability.