Study On Electrocatalytic Performance Of Porous Silicon Electrode And Its Application

In recent years, with the rapid development of portable electronic products such as mobile telephone, personal digital assistant and portable computer, the MH-Ni and lithium ion battery have couldn't meet their requirement for high energy, so the development of new energy sources have been regarded highly. With virtues of environment friendly, high energy conversion efficiency and theoretical specific energy density, the micro proton exchange membrane fuel cells (PEMFC) attract a world of interest. Especially micro PEMFC based on silicon are studied widely.To improve the efficiency of catalyst and minish the diffusion path and transmission resistance, the porous silicon was used as the diffusion layer in micro PEMFCs. Electrodeposition of Pt nanoparticles by cyclic voltammetry on the porous silicon electrodes (Pt/Si) could be used as catalytic electrodes in micro PEMFCs. Their catalytic performance was evaluated by the hydrogen adsorption/desorption and methanol oxidation. The performance of H₂/air self-breathing micro PEMFC was tested.The porous silicon for micro PEMFCs with pore diameter of ca. 350nm, 500nm and 750nm, porosity of ca. 40%, depth of ca. 50⁶0μm was prepared. As-deposited Pt nanoparticles with a mean diameter of ca. 7nm are highly dispersed on the surface of porous silicon. As compared to the electrode prepared by brushing nanosized Pt/C catalyst on the surface of porous silicon (Pt-C/Si), the Pt /Si modified electrodes exhibited high Pt utilization and enhanced catalytic performances for the hydrogen adsorption/desorption and for methanol oxidation. The maximum electrochemical specific area of ca. 148 cm²Â·mg^-1 was obtained with an electrodeposited Pt loading of ca. 0.38 mg cm^-2, which is ca. 2 times higher than that of the Pt-C/Si electrode with similar Pt loading of ca. 0.40 mg·cm^-2. Such a Pt/Si electrode shows an enhanced catalytic activity for methanol oxidation. After polarization at 0.5V/(vs SCE) for one hour in 0.5mol·L^-1 CH₃OH + 0.5mol·L(-1) H)2SO)4, the obtained current density on this electrode is 4.52mA·cm^-2, which is much higher than that on Pt-C/Si electrode with a current density of 0.36mA·cm^-2, again assessing high catalytic activity and good stability of electrodeposited Pt modified electrodes.When porous silicon electrodes modified with Pt nanoparticles were used as cathodes, the micro PEMFCs with pore diameter of 5μm and 350nm have the peak power density of 5.8mW·cm^-2and 7.5mW·cm^-2 respectively. These results are better than that reported.