Cylindrical C₉₆ Fullertubes: A Highly Active Metal-Free O₂ -Reduction Electrocatalyst

A new isolation protocol was recently reported for highly purified metallic Fullertubes D_5h -C₉₀ , D_3d -C₉₆ , and D_5d -C_100, which exhibit unique electronic features. Here, we report the oxygen reduction electrocatalytic behavior of C₆₀ , C₇₀ (spheroidal fullerenes), and C₉₀ , C₉₆ , and C₁₀₀ (tubular fullerenes) using a combination of experimental and theoretical approaches. C₉₆ (a metal-free catalyst) displayed remarkable oxygen reduction reaction (ORR) activity, with an onset potential of 0.85 V and a halfway potential of 0.75 V, which are close to the state-of-the-art Pt/C benchmark catalyst values. We achieved an excellent power density of 0.75 W cm^-2 using C₉₆ as a modified cathode in a proton-exchange membrane fuel cell, comparable to other recently reported efficient metal-free catalysts. Combined band structure (experimentally calculated) and free-energy (DFT) investigations show that both favorable energy-level alignment active catalytic sites on the carbon cage are responsible for the superior activity of C₉₆ .