Graphitized Nanodiamond Supported Transition Metal And Alloy Electrocatalyst

Nanodiamond (ND) has properties of both diamond and nanomaterials. It hasoutstanding thermal stability and oxidation resistance. These properties make it haspotential to be a kind of electrode material. However, low conductivity and weak bindingwith Pt nanoparticle limit its application of ND in electrocatalyst support. In this paper,surface graphitized nanodiamond (GND) with a core-shell structure was produced by avacuum annealing process. Through this process a graphitized surface which improved itselectrical conductivity and a remained diamond core was synthesized. GND was used asthe support material in the preparation of PtNi/GND alloy electrocatalyst and Ni/GND andNi/MoC_x/GND non-Pt electrocatalyst by a microwave heating ethylene glycol method.Pt-Ni/MoC_x/GND composite electrocatalysts with a low loading of Pt (10wt%) were alsoprepared using Ni/MoC_x/GND as supports. The composition and morphology of theseelectrocatalysts were characterized by X-ray diffraction, transmission electron microscopyand energy dispersion spectra. The electrochemical stability of the GND supports wasstudied. The electrocatalytic activities of these electrocatalysts for methanol oxidationreaction (MOR) and oxygen reduction reaction (ORR) in the alkaline solution and acidicsolution were studied.The results showed that graphitic carbon layers with an average thickness of2nmformed on the surface of ND after vacuum annealing at1300, and the diamond structurewas remained in the core. In comparison with traditional carbon support Vulcan XC-72,GND showed higher oxidation-resistance during the continuous potential cycling.Nano-scaled PtNi alloy particles with an atomic ratio of approximately1:1were uniformlydeposited on the GND through co-reduction process. Compared with pure Ptelectrocatalysts, PtNi/GND exhibited better electrocatalytic activities both for MOR andORR, and better stability. The non-Pt electrocatalysts Ni/GND and Ni/MoC_x/GND werealso prepared by a microwave heating ethylene glycol method followed by a vacuumannealing. All the nanoparticles were fully deposited on the supports. Both Ni/GND andNi/MoC_x/GND exhibited electrocatalytic activities for MOR in the alkaline solution.Ni/MoC_x/GND exhibited better electrocatalytic activities and better stability. Pt-Ni/MoC_x/GND composite electrocatalysts with a low loading of Pt (10wt%) wereprepared using Ni/MoC_x/GND as supports by a microwave heating ethylene glycolmethod. Pt-Ni/MoC_x/GND composite electrocatalysts exhibited better stability than purePt electrocatalysts in the alkaline solution. The Pt-Ni/MoC_x/GND compositeelectrocatalysts (the loading of Pt was10wt%) showed slightly lower electrocatalyticactivities for ORR than Pt/GND catalyst (the loading of Pt was20wt%). HoweverPt-Ni/MoC_x/GND exhibited better electrocatalytic activities for ORR than Pt/GND afterADT. In the acidic solution, compared with Pt/GND electrocatalysts with high loading ofPt (20wt%), Pt-Ni/MoC_x/GND composite electrocatalysts with a low loading of Pt (10wt%) showed the similar electrocatalytic activities for ORR and better stability.