Metal-organic frameworks (MOFs) have attracted a lot of attention due to their diverse structures, favorable porous properties, and tunable chemical compositions in the multiple fields. Notably, MOF-based materials (including pristine MOFs, MOF composites, and their derivatives) play the vital role in electrochemical energy storage and conversion systems, due to their ability for regulating chemical composition at the molecular level and their highly porous frameworks for facilitating the mass and charge transfer. Supercapacitors and fuel cells are used as one of energy storage and conversion systems respectively, and it is unstoppable to design and synthesize high-efficiency electrode materials for them. This review starts with the strategies for designing targeted MOF-based materials in electrochemical energy storage and conversion applications followed by the state-of-the-art MOF-based materials discussed as to their potential applications in supercapacitors and electrocatalytic oxygen reduction reaction (ORR). Finally, the challenges and perspectives of MOF-based materials applied for supercapacitors and electrocatalytic ORR are discussed.

Microcapsules have been widely used in drug carriers, nano/microreactors, artificial organelles for their empty space and functional shell. Microcapsules synthesized from spherical liquid-liquid interface show ultrathin shell and large cavities. However, spherical liquid-liquid interfaces generated by stirring or sonicating are difficult in controlling the droplet size and preventing their coalescence, which results in inhomogeneous capsules. Here, we demonstrate a microfluidic interfacial synthetic method to produce microcapsules using the hot covalent organic polymers (COPs) coupled with Schiff-base reaction. A very high throughput of uniform and individual microdroplets about ~1400 min⁻¹ was generated under high flow rate for COP capsules fabrication. Acidic catalyst promoted amine and aldehyde condensation that reacted less than 1 ​s assured the polymerization occurred at the liquid-liquid interface regardless of the diffusion intensification in microfluidic system. COP capsules with shell thickness around 50 ​nm were flexible enough to response to slight interior capillary force and exterior filtration force to form origami structure and sealed flat membrane, respectively. Each of the interfacial synthesized capsule expressed large capacity by encapsulating 1.41 ​× ​10⁻² ​μg SiO₂ nanoparticles as theoretically calculated. Thus, these properties make the COP capsules promising in, but not limited to, fast drug delivery and microreactors.