Tuning the electrochemical and catalytic ORR performance of C60 by its encapsulation in ZIF-8: a solid-state analogue of dilute fullerene solution

Abstract

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.