Tuning the electrochemical and catalytic ORR performance of C₆₀by its encapsulation in ZIF-8: A solid-state analogue of dilute fullerene solution

Metal-organic frameworks (MOFs) with intrinsic electrochemical activity have received significant attention in the last two decades, mainly because of the high density of physically separated active sites. Yet, the potential of chemical tunability, spatial confinement and scope of heterogenization in the electrochemically inactive MOFs have been less explored. Here, we have shown that fullerene C60, well-known for its rich reductive electrochemistry, when encapsulated inside zeolitic imidazolate framework-8 (ZIF-8) to prepare a heterogeneous composite (C60Z), can act as a catalyst for the oxygen reduction reaction (ORR) at a lower overpotential with better selectivity than bare C60per se. Spectroscopic and electrochemical characterization methods prove significant interactions between the ZIF-8 host and the C60 guest, which results in the modification of the electrochemical behavior of C60 inside ZIF-8 and thereby causes an enhanced electrochemical ORR performance of the guest. The mono-confinement of C60 inside ZIF-8 also results in spatial separation of C60 molecules, which is highly effective for preserving its dilute solution-like behavior in solid-state inside the framework matrix. Furthermore, we have explored the scope of device processability of this solid-state analogue of dilute C60 solution i.e., C60Z, by its fabrication into a polymer membrane (C60Z-PVA thin film) which could retain the physical properties of the C60Z.