Metal–Organic Framework Supercapacitors: Challenges and Opportunities

Supercapacitors offer superior energy storage capabilities than traditional capacitors, making them useful for applications such as electric vehicles and rapid large‐scale energy storage. The energy storage performance of these devices relies on electrical double‐layer capacitance and/or pseudocapacitance from rapid reversible redox reactions. Metal–organic frameworks (MOFs) have recently emerged as a new class of electrode materials with promising supercapacitor performances and capacitances that exceed those of traditional materials. However, the comparison of the supercapacitor performance of a porous carbon and a state‐of‐the‐art MOF highlights a number of challenges for MOF supercapacitors, including low potential windows, limited cycle lifetimes, and poor rate performances. It is proposed that the well‐defined and tuneable chemical structures of MOFs present a number of avenues for improving supercapacitor performance. Recent experimental and theoretical work on charging mechanisms in MOF‐based supercapacitors is also discussed, and it is found that there is a need for more studies that elucidate the charge storage and degradation mechanisms. Ultimately, a deeper understanding will lead to design principles for realizing improved supercapacitor energy storage devices. Metal–organic frameworks (MOFs) are promising electrode materials for supercapacitor energy storage devices. They have shown high capacitances, but have some disadvantages compared to traditional carbon electrodes. Here, strategies are discussed for tuning MOF structures to improve their energy storage performance, as well as approaches to better understand the underlying mechanisms of energy storage and degradation.