Study On The Electrochemical Properties Of Nanodiamond-based Carrier Supported PtRu Catalyst

Nanodiamond （ND） powder is a novel carbon material. They not only have theproperties of diamond, for example extraordinary chemical stability, high thermalconductivity, the outstanding hardness and antiwear, etc., but also possess the features ofa nanoscale material, such as an ultrafine particle size and a giant specific surface area aswell as large numbers of surface defects. And their excellent electrochemistry propertiessuch as a wide potential window and a low background current in aqueous ornon-aqueous electrolytes have attracted the researchers’ attention. Due to a series ofproperties, such as ultrafine particle size, giant specific surface area and excellentelectrochemical properties, ND powders would be good supports and possess greatpotential in the field of electroanalysis, electrocatalysis, photoelectrochemistry andbiological electrochemistry.In this paper, the PtRu/ND was prepared by a microwave heating method in carrier ofND. The structures, morphology and composition of the catalysts were characterized byRaman spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy,field emission-scanning electron microscopy and energy-dispersive spectroscopy. Theelectrocatalytic activities of the catalysts for methanol oxidation were investigated bycyclic voltammetry, linear sweep voltammetry and chronoamperometry. In order toimprove the performance of original ND, the graphitized-nanodiamond（GND）and TiO₂coated nanodiamond（TiO₂/ND）were obtained by the surface graphitization and nano TiO₂modification process of pure ND. Then the PtRu/GND, Pt/TiO₂/ND and PtRu/TiO₂/NDcatalysts were also prepared by a microwave heating method in carriers of GND andTiO₂/ND, respectively, and then their electrocatalytic activities were investigated asbefore.The results suggested that the metal nanoparticles prepared by microwave heatinghave homogeneous shape and highly dispersed on the surfaces of supports, the alloyedPtRu nanoparticles were small and uniform with the size of 2⁵ nm. The electrochemicalmeasurements demonstrated that PtRu/ND catalyst exhibited higher activity and stability for methanol electrooxidation reaction than Pt/ND catalyst. Increased the PtRu loading ofthe catalyst, the methanol electrocatalytic activity would be improved, and the PtRu/NDcatalyst exhibited better tolerance of CO poisoning when only increased the loading massof Ru. Compared with the electrocatalytic activity of different size of ND suppored PtRunanoparticles, the specific surface area and the catalytic activity for methanolelectrooxidation increased as the particle size of ND decreased, in which the PtRu/ND5had the highest electrocatalytic activity. When the loading mass of PtRu was low, the twopeaks of methanol oxidation were not obvious, but the activity of the electrode could besignificantly improved with the addition of conductive agent into catalyst, such asacetylene black and CNTs, and the CNTs has the best effect. Surface graphitizationprocess was carried out by heat treatment at the temperature of 1200°C in vacuum for 3h,and then the GND which had a diamond core covered with 4-5 layers of graphene shellwas obtained. The GND exhibited good electrical conductivity and electrochemicalactivity, so compared with PtRu/ND catalyst, the PtRu/GND catalyst exhibited betterelectrocatalytic activity and stability. In addition, it was succeed to coat TiO₂（4 nm） onnanodiamond by microwave heating method, and the anatase TiO₂coating was obtainedon the surface of nanodiamond particles after 450°C treatment in the air. The methanoloxidation performances of the Pt/ND and PtRu/ND including TiO₂were significantlyimproved, compared to that of Pt or PtRu alone, and the catalytic activity would be betterthan before after the 450°C treatment of TiO₂.