Preparation Of Taixi Coal-based W-WC And Its Application In Photocatalytic H₂ Evolution

Photocatalytic hydrogen production is an ideal way to solve energy crisis and environmental problems.Co-catalyst is an important factor affecting photocatalytic hydrogen production.Therefore,it is of great significance to develop efficient and inexpensive co-catalysts.Taixi coal is the highest quality coal in the country.If Taixi coal is used as a carbon source to synthesize carbide co-catalysts,it will effectively reduce the cost of photocatalysis and increase the added value of Taixi coal.Based on the rich coal resources characteristics of Ningxia region,this paper designed a method of directly synthesizing W-WC composites by a one-step calcination method using coal-based coal as a carbon source.The W-WC composite was used as a co-catalyst in combination with CdS,which was applied in photocatalytic hydrogen production,and the mechanism of hydrogen production for W-WC/CdS composite photocatalyst was studied.Firstly,we used four different coal types as carbon sources to prepare W-WC composites from coal-based carbon sources.By comparing the ash content of carbon sources,the products synthesized under mass ratio of tungsten to carbons,calcination temperatures and the calcination time,the optimal carbon source was found as Taixi coal.The suitable mass ratio of tungsten to carbon is 0.725:1,and the W-WC composite is generated in a temperature range of 1000 ? to 1200 ?,and the minimum production time is 3 hours.It was found that the production process of tungsten carbon during high-temperature calcination as follows:WO3? WO2 ? W? W2C ? WC.Secondly,we used the co-precipitation method to combine the W-WC composite and CdS and studied the photocatalytic activity of hydrogen production of W-WC/CdS.It was found that W-WC is an effective photocatalytic hydrogen production non-noble metal co-catalyst.Its co-catalytic performance is not only higher than pure W and pure WC,and even higher than noble metal Pt.In W-WC/CdS photocatalyst,W-WC is synthesized at an optimum calcination temperature of 1000 ? and its optimal loading is 8%.The optimal photocatalytic hydrogen production activity of W-WC/CdS reaches 331.4 ?mol·h-1,which is 17.4 times higher than pure CdS and 2.6 times higher than Pt/CdS.Finally,the co-catalyst properties of W-WC and the photocatalytic hydrogen production mechanism of W-WC/CdS were studied by photoelectrochemical and electrochemical performance tests.The cyclic voltammetry,galvanostatic charge-discharge experiments show that WC has the largest specific capacitance(Cw = 9.13 F/g,CW-WC = 14.33 F/g,Cwc = 28.04 F/g),indicating that WC has the best electron storage ability.The linear voltammetry experiments show W-WC has the highest catalytic activity for hydrogen production,followed by W and WC(when the cathode current density is-30 mA/cm2,the active potentials of W-WC,W,and WC are-1.327 V,-1.366 V,and-1.375 V,respectively).Electrochemical impedance experiments revealed that the radii of W and W-WC were nearly equal,indicating that W-WC has the same small resistance as W,while the radius WC is the largest,indicating WC has the highest resistance(The W-WC,W,and WC curve inflection points are 14.16 ?/cm2,13.46 ?/cm2 and 18.92 ?/cm2,respectively).The photocurrent experiments revealed that W-WC has the largest photocurrent(W-WC current density is 15.87 ?A/cm2).HRTEM characterization revealed that W-WC formed a heterojunction.The highest photo co-catalytic H2 production of W-WC is attributed to not only high catalytic hydrogen production ability similar to that of W,but also relatively high electron storage capability similar to that of WC.Furthermore,W-WC has a smaller resistance benefiting the transmission of photo-generated electrons.The mechanism of photocatalytic hydrogen production of W-WC/CdS is proposed.The photogenerated electrons of CdS are transferred to W-WC under light irradiation,photocatalytic hydrogen production occurs on W-WC,and photocatalytic oxidation occurs on the surface of CdS.The different components of W-WC play different roles in photocatalytic hydrogen production.Photogenerated electrons in W can transfer to WC through the heterojunction formed in W-WC.WC mainly catalyzes the proton to product hydrogen with large storage electron ability(inhibit recombination of photoelectron in CdS),while W mainly plays a role of transmitting electrons.Finally,the ability of photocatalytic hydrogen production of W-WC/CdS has been greatly improved.