Effects of 3D structure on electrochemical oxygen reduction characteristics of Pt- nanoparticle-supported carbon nanowalls

For polymer electrolyte fuel cell applications, effects of Pt-nanoparticle-supported 3D carbon nanostructures, i.e. carbon nanowalls (Pt/CNWs), on electrochemical characteristics were determined by alternating current impedance analysis of resistive elements, which contribute to the oxygen reduction reaction. CNWs were fabricated by radical-injection plasma-enhanced chemical vapor deposition (RI-PECVD), and Pt catalysts were formed on the template of CNWs by supercritical fluid metalorganic chemical fluid deposition. CNWs of different wall densities were synthesized during RI-PECVD by varying the deposition pressure. The resistive elements can be consisted of three regions with different corresponding frequencies, and the resistive elements of mass diffusion, which showed up in the lowest frequency region of less than 100 Hz, increased as the wall density of CNWs increased. It was found that the wall density of CNWs was one of the essential parameters of Pt/CNWs for the electrochemical reaction involving the fluid flow and the mass transfer of active materials.