A Review of Fabrication Technologies for Carbon Electrode-Based Micro-Supercapacitors

The very fast evolution in wearable electronics drives the need for energy storage micro-devices, which have to be flexible. Micro-supercapacitors are of high interest because of their high power density, long cycle lifetime and fast charge and discharge. Recent developments on micro-supercapacitors focus on improving the energy density, overall electrochemical performance, and mechanical properties. In this review, the different types of micro-supercapacitors and configurations are briefly introduced. Then, the advances in carbon electrode materials are presented, including activated carbon, carbon nanotubes, graphene, onion-like carbon, and carbide-derived carbon. The different types of electrolytes used in studies on micro-supercapacitors are also treated, including aqueous, organic, ionic liquid, solid-state, and quasi-solid-state electrolytes. Furthermore, the latest developments in fabrication techniques for micro-supercapacitors, such as different deposition, coating, etching, and printing technologies, are discussed in this review on carbon electrode-based micro-supercapacitors.

Polypyrrole with Phosphor Tungsten Acid and Carbide-Derived Carbon: Change of Solvent in Electropolymerization and Linear Actuation

Linear actuators based on polypyrrole (PPy) are envisaged to have only one ion that triggers the actuation direction, either at oxidation (anion-driven) or at reduction (cation-driven). PPy doped with dodecylbenzenesulfonate (PPy/DBS) is the most common applied conducting polymer having cation-driven actuation in aqueous solvent and mainly anion-driven actuation in an organic electrolyte. It is somehow desired to have an actuator that is independent of the applied solvent in the same actuation direction. In this research we made PPy/DBS with the addition of phosphorus tungsten acid, forming PPyPT films, as well with included carbide derived carbon (CDC) resulting in PPyCDC films. The solvent in electropolymerization was changed from an aqueous ethylene glycol mixture to pure EG forming PPyPT-EG and PPyCDC-EG composites. Our goal in this study was to investigate the linear actuation properties of PPy composites applying sodium perchlorate in aqueous (NaClO4-aq) and propylene carbonate (NaClO4-PC) electrolytes. Cyclic voltammetry and square potential steps in combination with electro-chemo-mechanical-deformation (ECMD) measurements of PPy composite films were performed. The PPyPT and PPyCDC had mixed ion-actuation in NaClO4-PC while in NaClO4-aq expansion at reduction (cation-driven) was observed. Those novel PPy composites electropolymerized in EG solvent showed independently which solvent applied mainly expansion at reduction (cation-driven actuator). Chronopotentiometric measurements were performed on all composites, revealing excellent specific capacitance up to 190 F g−1 for PPyCDC-EG (best capacitance retention of 90% after 1000 cycles) and 130 F g−1 for PPyPT-EG in aqueous electrolyte. The films were characterized by scanning electron microscopy (SEM), Raman, Fourier-transform infrared (FTIR) and energy dispersive X-ray spectroscopy (EDX).