Construction of Warped Graphitic Layers from Fullerene Soot and Study of Their Catalytic Oxygen Reduction Activity

Platinum is widely used in cathode catalysts for fuel cells; however, it is expensive, with limited reserves. Hence, the development of non-Pt catalysts has been extensively studied. Carbon alloy catalysts are considered the most potent alternatives to Pt-based catalysts. However, the catalytic activity of carbon, which is the primary constituent of carbon alloy catalysts, in oxygen reduction reactions (ORRs) has been insufficiently investigated. In this context, we demonstrate that warped graphitic layers (WGLs) are ORR active sites by investigating the factors that contribute to the ORR activity of WGL, a metal- and heteroatom-free carbon material. WGLs are prepared from fullerene extraction residues, and after heat treatment at 1250 °C, they exhibit a maximum ORR activity of 0.79 V and number of electrons involved in the reaction (n) of 3.7. The ORR activity of WGL-HTs is determined by the curvature radius of WGLs and its continuity. The curvature radius affects the adsorption state of oxygen, as revealed by the equilibrium constant obtained from oxygen adsorption measurements. The continuity of the graphitic layers also facilitates transport of electrons to the adsorbed oxygen, as determined by work function measurements. The ORR active sites of WGL-HTs act as oxygen adsorption sites, and the π-electron systems transfer electrons to the adsorbed oxygen. This study highlights the potential of carbon materials with continuous WGLs as carbon-based cathode catalysts for the development of efficient and cost-effective polymer electrolyte fuel cell systems.