Hydrothermal-carbonization To Prepare A Highly Active Tungsten Carbide-based Electrocatalyst

In recent years,the low-temperature fuel cell as a kind of new energy is catching the attentions of countries in the condition of serious environmental pollution and energy shortage nowadays on account of its advantages that is environment friendly,rich,renewable,etc.However,the fuel cell catalyst platinum(Pt)is expensive and is easy to be poised by CO that absorbs Pt on the surface in the process of reaction,which limits the development of fuel cells.The tungsten carbide(WC)is prospected to replace Pt or partly replace Pt to become fuel cell catalysts due to its similar surface electronic properties with platinum,certain electro-catalytic property,better toxic resistance,stability,and low price.But the catalytic activity of WC is far from enough as a catalyst alone,though it has certain catalytic activity.To reduce the dosage of Pt,in this paper,the WC-based catalyst with a small amount of Pt was fabricated,which has high specific area,high stability,high toxic resistance and high activity.This paper firstly fabricated WC samples with uniform morphology,high dispersion,and high specific area mainly by hydro-thermal synthesis of special WC precursor.Then a small amount of Pt was loaded on WC samples.Finally the preparation of highly active WC-based catalyst was achieved.This paper’s researches were mainly carried out from the following several aspects:(1)Samples which were obtained by adding organic solvent and CNTs or not in the process of precursors’ preparation were researched by phase analysis and morphology structure comparison.Results indicate that precursors with bar structures of small particles and uniform morphology can be synthesized effectively by adding organic solvent.The precursor’s length is 50 to 150 nm and diameter is 10 to 20 nm.CNTs’ adding can effective improve the agglomeration of nanoparticles and make samples’ sizes distribute evenly.All these provide a good base for WC’s preparation.(2)The highly dispersed WC and CNTs/WC samples with nanoscales were prepared by dehydrating precursor powder separately in air and nitrogen atmosphere at 600℃ and carbonizing it rapidly by the liquid carbon source.The samples have bar structures as same as precursors and their particle sizes don’t change much.The prepared WC and CNTs/WC have a relatively high specific surface area which is 15.6m2/g and 32.2 m2/g,respectively.The analysis of the pore size distribution of mesoporous structure indicates that the samples have a large number of mesoporous structure and the distribution range is wide,which show that they have potential for electro-catalytic application.(3)WC-based catalysts which were loaded by Pt(Pt/WC、highly dispersed Pt/WC and Pt/CNTs/WC)were prepared by the microwave-assisted ethylene glycol reduction method.It was founded that the Pt particles are small with the size ranging from 5 to 15 nm.They are distributed uniformly on the surface of WC-based carrier and have a good crystalline structure.(4)The prepared WC-based catalyst electrode was tested in the sulfuric acid electrolyte.Results show that the highly dispersed Pt/WC and Pt/CNTs/WC catalyst exhibit excellent electro-catalytic activity which is attributed to the small size and high dispersion of WC-based carriers and the CNT’s excellent conductivity.The dehydrogenation efficiency of Pt is greatly improved and the specific surface area of the high dispersed Pt/WC and Pt/CNTs/WC catalyst electrode reaches 404m2/g and 458 m2/g,respectively.It is indicated that the two kinds of catalysts can be applied to the electro-catalysis field.(5)The excellent methanol oxidation performance of the highly dispersed Pt/WC and Pt/CNTs/WC catalyst was indicated by the test in the mixed electrolyte of sulfuric acid and methanol as the methanol fuel cells.The current density of the methanol oxidation peak reaches 0.20A/cm 2 and 0.16 A/cm2,respectively.The toxic resistance value reaches 1.45 and 1.11,respectively.The excellent methanol oxidation and toxic resistance performance of the WC-based catalyst show that it can coordinate with Pt well.All these reveal that the WC-based catalyst has a good prospect for the application in methanol fuel cells.(6)The oxygen reduction mechanism of three kinds of WC-based catalysts was discussed by the linear sweeping method using rotating disk test.It was founded that the half wave potential of the highly dispersed Pt/WC catalyst is 0.58V(vs.NHE),which has excellent oxygen reduction activity.The oxygen reduction process of the highly dispersed Pt/WC and Pt/WC/CNTs catalyst is the four electronic process.This paper’s work is beneficial to improve the performance of the catalyst,so as to realize the improvement of the performance of fuel cells,which will speed up the promotion and application of fuel cells.