The potential of novel carbon nanocages as a carbon support for an enhanced methanolelectro-oxidationreaction in a direct methanol fuel cell

In this study, we introduce the potential for a new catalyst support, namely, carbon nanocages (CNCs) for anodic direct methanol fuel cell (DMFC). The synthesis, characterization and catalytic activities of four electrocatalysts, PtRu/CNC, PtNi/CNC, PtFe/CNC and PtCo/CNC, have been investigated. These electrocatalysts are synthesized using pyrolysis, followed by a microwave-assisted ethylene glycol reduction method. From X-ray diffraction analysis, PtNi/CNC and PtRu/CNC showed the smallest crystallite particle size of Pt-alloy, which corresponded to the (111) plane. The Raman spectra confirmed the presence of the carbon support material in all prepared electrocatalysts. The ratio value of the D band and G band (I-D/I-G) of all prepared samples was not much different within the electrocatalyst and CNC. TheI(D)/I(G)values calculated for the CNC, PtNi/CNC, PtRu/CNC, PtCo/CNC and PtFe/CNC electrocatalysts were 0.90, 0.89, 0.83, 0.78 and 0.77, respectively. Therefore, the number of defects of graphitization in increasing order (I-D/I-G) was PtFe/CNC < PtCo/CNC < PtRu/CNC < PtNi/CNC < CNC. Brunauer-Emmett-Teller analysis revealed that the CNC support has a mesoporous-type structure with a high surface area of 416 m(2)g(-1), which indicates that this support has a high potential to act as an excellent catalyst support. From the cyclic voltammetry curve, PtRu/CNC showed the highest catalytic activity in methanol electro-oxidation and reached a value of 427 mA mg(-1), followed by PtNi/CNC (384.11 mA mg(-1)), PtCo/CNC (150.53 mA mg(-1)) and PtFe/CNC (144.11 mA mg(-1)). PtFe/CNC exhibited a higher ratio value ofI(f)/I-b(3.24) compared with PtRu/CNC (2.34), PtNi/CNC (1.43) and PtCo/CNC (1.62). These values show that the combination of Pt and Fe catalysts in PtFe/CNC had better CO tolerance than PtRu/CNC, PtNi/CNC and PtCo/CNC electrocatalysts. The higher performance of PtRu/CNC was attributed to the fact that it had the smallest bimetallic-Pt crystallite; there was a smooth distribution of bimetallic-Pt on its CNC support, as shown by field emission scanning electron microscopy; it had the highest electrochemical surface area value (16.23 m(2)g(-1)); and it had an overall catalytic performance enhanced by the advantages of the unique and large surface area from the CNC as support material. In passive DMFC mode, PtRu/CNC showed a maximum power density of 3.35 mW cm(-2), which is 1.72 times higher than that of the PtRu/C commercial electrocatalyst.