Electrochemical Property Of Mesoporous Tungsten Carbide Nanosheets Supported Platinum

Tungsten carbide is regarded as a potential catalyst which can substitute for noble metals such as platinum,due to its platinum-like catalytic properties and resistance to CO poisoning.How to improve its catalytic activity has become a hot research.In this work,the structural characteristics,preparation methods and application fields of tungsten carbide have first been comprehensively reviewed.Then mesoporous tungsten carbide nanosheets were prepared by a hydrothermal method followed by an in-situ reduction and carbonization approach,to whose surface Pt nanoparticles were finally loaded.The crystal phase,morphology,microstructure and composition elements of the samples were characterized by XRD,SEM,TG-DTG,TEM,HRTEM and EDX.The electrocatalytic properties of the samples for methanol and p-nitrophenol were also investigated.The main results of above mentioned research works are as follows:（1）Tungstic acid（H₂WO₄）nanosheest were synthesized by hydrothermal method.The effects of additives,adding dosage,reaction time and temperature and sol concentration on sizes and morphologies of tungstic acid nanosheets were investigated,showing that sol concentration played the most important role.In addition,a formation mechanism of tungstic acid nanosheets with different sizes was proposed based on some relevant literatures.（2）Mesoporous tungsten carbide nanosheets were prepared by temperature programmed reduction using tungstic acid nanosheets as precursor under CH₄/H₂atmosphere,showing that the phase transformation were as follows:WO₃·H₂O→WO₃→WO₂→W→W₂C→WC.The effects of carbonization temperature,carbonization time and gas flow ratio on the morphology,phase and microstructure of the product were investigated.The crystal phase of mesoporous tungsten carbide nanosheets,with a size distribution at about 10 nm,were mainly composed of W₂C when the carbonaization temperature was 550℃,CH₄/H₂ was 1/2 and carbonaization time was 11 h.The formation mechanism of mesoporous tungsten carbide nanosheets was proposed.（3）Pt nanoparticles were modified onto the surface of mesoporous tungsten carbide nanosheets by impregnation liquid phase reduction method and impregnation vapor phase reduction method.It was shown that sodium metaborate had a better reduction ability than that of formaldehyde,while the Pt nanoparticles prepared by using HCHO as reductant were well dispersed with an average diameter of 3 nm.Pt nanoparticles with different supports had different growth places and crystal orientations.（4）The electrochemical catalytic property for methanol oxidation of the samples was investigated by a cyclic voltammetry technique.Contrast tests by using commercial platinum carbon catalyst were also performed.The results showed that the catalytic properties of the tungsten carbide nanosheets could be effectively improved by reasonably adjusting their morphologies and Pt-loading amounts.In addition,electrochemical reduction of p-nitrophenol（PNP）by using tungsten carbide nanosheets as catalysts was also primarily explored.