Ben Hsia

High-performance all solid-state micro-supercapacitor based on patterned photoresist-derived porous carbon electrodes and an ionogel electrolyte

We report on the fabrication of an all solid-state micro-supercapacitor using patterned photoresist-derived porous carbon electrodes and an ionogel electrolyte. The interdigitated finger electrodes are synthesized via pyrolysis of the SPR-220 photoresist, which results in high surface area porous carbon via a highly scalable technique. The ionogel electrolyte is formed using 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid hybridized with fumed silica nanopowder. The fabricated device has an excellent long-term cycling stability. The maximum energy density obtained is about 3 mW h cm−3, higher than that of commercial Li-ion thin film batteries, with the maximum achieved power density of 26 W cm−3. Our results indicate that the novel combination of the pyrolyzed photoresist with an ionogel electrolyte holds promise for applications in integrated energy storage for all solid-state microsystems technologies.

Templated 3D Ultrathin CVD Graphite Networks with Controllable Geometry: Synthesis and Application As Supercapacitor Electrodes

Three-dimensional ultrathin graphitic foams are grown via chemical vapor deposition on templated Ni scaffolds, which are electrodeposited on a close-packed array of polystyrene microspheres. After removal of the Ni, free-standing foams composed of conjoined hollow ultrathin graphite spheres are obtained. Control over the pore size and foam thickness is demonstrated. The graphitic foam is tested as a supercapacitor electrode, exhibiting electrochemical double-layer capacitance values that compare well to those obtained with the state-of-the-art 3D graphene materials.

High-Temperature All Solid-State Microsupercapacitors based on SiC Nanowire Electrode and YSZ Electrolyte

We demonstrate a symmetric supercapacitor by using yttria-stabilized zirconia (YSZ) as the electrolyte and silicon carbide nanowires (SiC NWs) as the electrode. The stacked symmetric SiC NWs/YSZ/SiC NWs supercapacitors exhibit excellent thermal stability and high areal capacitance at temperatures above 300 °C. The supercapacitor functions well at a record high temperature of 450 °C, yielding an areal capacitance of 92 μF cm(-2) at a voltage scan rate of 100 mV s(-1). At this temperature, it is also capable of withstanding current densities up to 50 μA cm(-2), yielding a maximum areal power density of 100 μW cm(-2). Good cycling stability is demonstrated with a capacitance retention of over 60% after 10,000 cycles at the operation temperature of 450 °C and a scan rate of 200 mV s(-1).

Cycling characteristics of high energy density, electrochemically activated porous-carbon supercapacitor electrodes in aqueous electrolytes

Carbon-based supercapacitors typically have low energy density but high cycle lifetime relative to batteries. Surface functionalization can significantly increase charge storage through reversible faradaic reactions at the electrode/electrolyte interface, a phenomenon known as pseudocapacitance. However, pseudocapacitive reactions, if not completely reversible, can contribute to reduced cycling performance. In this letter, we describe an electrochemical activation procedure on porous carbon synthesized via pyrolysis of photoresist which yields high specific capacitance and energy density of ∼250 F cm−3 and 35 mW h cm−3. We also demonstrate that the choice of aqueous electrolyte has a significant effect on both overall capacitance and cycle lifetime, through a comparison of KCl and H2SO4 electrolytes. Cycling in acid electrolyte yields excellent capacitance retention of 97% after 10 000 cycles.

Flexible micro-supercapacitors from photoresist-derived carbon electrodes on flexible substrates

This paper reports a simple and scalable technique for the fabrication of flexible micro-supercapacitors. The supercapacitor electrodes are synthesized via the pyrolysis of patterned photoresist on a SiO2/Si substrate. The electrodes can then be moved to flexible substrates through a simple transfer process. The fabricated devices show excellent energy density of 0.3 mJ/cm2, maximum power density of 5 mW/cm2, and good performance under electrochemical cycling. The electrochemical performance is maintained after 300 mechanical bending cycles.