High performance nanoporous carbon microsupercapacitors generated by a solvent-free MOF-CVD method

Abstract

Micro power sources that support higher power capabilities, specific energies, and ultra-long cycling lifetimes are required for next generation microelectro-mechanical systems (MEMS) and miniaturized portable microdevices. We demonstrated a simple, solvent-free method to coat interdigitated gold electrodes with a conformal layer of nanoporous carbon. Initially the electrodes were coated with a film of ZnO via electrodeposition to serve as the zinc source. These films were exposed to 2-methylimidazole vapor to transform the ZnO into a metal organic framework (MOF) called ZIF-8. The thickness of the ZnO film and the duration of the MOF conversion process created ZIF-8 films with different morphologies, cross-sections and elemental compositions. The ZIF-8 films were then carbonized at 800 °C under a flowing environment of N2 gas to generate nanoporous carbon film electrodes for supercapacitors. The devices have superior capacitance retention, in addition to high power and energy densities. Our 16-electrode microsupercapacitor had a stack power of 232.8 W⋅cm−3, which could be attained even at a scan rate of 1000 V ⋅s−1, without rapid stack energy attenuation. The process of combining an inexpensive ZnO electrodeposition method with solvent-free MOF deposition and subsequent carbonization generates high surface area carbon electrodes with good electrochemical performance.