Electrodes For Micro-supercapacitors Research Articles

On-chip micro-supercapacitors for operation in a wide temperature range

Onion-like carbon (OLC) based micro-supercapacitor electrodes prepared by electrophoretic deposition (EPD) were combined with a eutectic mixture of ionic liquids (IL), producing a micro-supercapacitor which is able to function from −50°C to 80°C. This device was electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy at different scan rates and different temperatures. At 20°C, a capacitance of 1.1 mF.cm−2 per footprint area of device at 200mV.s−1 within 3.7V was measured, hence a specific energy of 15mJ.cm−2 and a specific power of 240mW.cm−2. At −50°C, 76% of the capacitance was maintained at 10mV.s−1 within 3.7V. By integrating with IL, this micro-supercapacitor can be potentially used in portable electronic devices that are required to work under temperature extremes.

Direct prototyping of patterned nanoporous carbon: a route from materials to on-chip devices.

Prototyping of nanoporous carbon membranes with three-dimensional microscale patterns is significant for integration of such multifunctional materials into various miniaturized systems. Incorporating nano material synthesis into microelectronics technology, we present a novel approach to direct prototyping of carbon membranes with highly nanoporous structures inside. Membranes with significant thicknesses (1 ~ 40 μm) are rapidly prototyped at wafer level by combining nano templating method with readily available microfabrication techniques, which include photolithography, high-temperature annealing and etching. In particular, the high-surface-area membranes are specified as three-dimensional electrodes for micro supercapacitors and show high performance compared to reported ones. Improvements in scalability, compatibility and cost make the general strategy promising for batch fabrication of operational on-chip devices or full integration of three-dimensional nanoporous membranes with existing micro systems.

Silicon carbide nanowires as highly robust electrodes for micro-supercapacitors

The effectiveness of silicon carbide (SiC) nanowires (NW) as electrode material for micro-supercapacitors has been investigated. SiC NWs are grown on a SiC thin film coated with a thin Ni catalyst layer via a chemical vapor deposition route at 950 °C. A specific capacitance in the range of ∼240 μF cm−2 is demonstrated, which is comparable to the values recently reported for planar micro-supercapacitor electrodes. Charge–discharge studies demonstrate the SiC nanowires exhibit exceptional stability, with 95% capacitance retention after 2 × 105 charge/discharge cycles in an environmentally benign, aqueous electrolyte.

Ultra high capacitance values of Pt@RuO2 core–shell nanotubular electrodes for microsupercapacitor applications

Arrays of Pt@RuO2 core–shell nanotubes were prepared by electrodeposition of RuO2 on Pt nanotubes and evaluated as electrochemical microsupercapacitor electrodes. Specific capacitance of ca. 1585 and 1280Fg−1RuO2 is obtained at sweep rates of 2 and 500 mV s−1, respectively, demonstrating high utilization factor of RuO2 due to facilitated transport of protons and electrons. The specific geometric capacitance for the Pt@RuO2 core shell nanotubes electrode is 320 mF cm−2 at 2 mV s−1 and 256 mF cm−2 at 500 mV s−1.

Silicon carbide coated silicon nanowires as robust electrode material for aqueous micro-supercapacitor

The development of passivated silicon nanowire (SiNW) based micro-supercapacitor electrodes for on-chip applications using an environmentally benign aqueous electrolyte is reported. The SiNWs, produced by low-temperature (50 °C) electrochemical etching, corrode during charge/discharge cycling in the aqueous environment, but upon coating with a silicon carbide passivation layer, the corrosion is mitigated. The as-formed materials are in electrical contact with the substrate, requiring no additional current collector. The passivated NWs achieve capacitance values up to ∼1.7 mF/cm2 projected area (comparable to state-of-the art carbon based micro-supercapacitor electrodes), exhibit robust cycling stability, and maintain capacitive behavior over a wide range of charge/discharge rates.

Preparation and Electrochemical Characteristics of Three-dimensional Manganese Oxide Micro-supercapacitor Electrode

In order to increase the electrode surface area and enhance the charge storage capacity, we study the micro electro mechanical system technology to fabricate three-dimensional high aspect ratio micro-electrode structure based on glass. The anodic constant potential method is employed to deposit manganese oxide as electroactive substances on the micro-electrode surface. Cyclic voltammetry and constant current charge-discharge method are both used to prepare electrode electrochemical performance testing, with a two-dimensional electrode without structure for comparison. Experimental results show that three-dimensional electrode structure can effectively enhance the charge storage capacity. At 1.0 mA/cm2 charge-discharge density, the three-dimensional electrode shows a capacitance of 17.88 mF/cm2, seven times higher than the two-dimensional electrode.

Nanoscale Surface Morphology and Monomer Concentration Dependence on Impedance of Electrocoated 2,2-Dimethyl-3,4-Propylene-dioxythiophene on Carbon Fiber Microelectrode

Poly(2,2-Dimethyl-3,4-propylenedioxythiophene) (PProDOT-Me2) thin films have been cyclovoltametrically coated onto carbon fiber microelectrode (CFME) as an active functionalized microelectrode. An electrochemical impedance spectroscopic study on the prepared electrodes is reported in this paper which electropolymerization performed under different initial monomer concentrations. The electrochemical impedance data fitted to equivalent circuit model, used to find out numerical values of the proposed components. Effect of the parameters on the capacitive behavior of the (PProDOT-Me2) coated carbon fiber microelectrode and morphology of films obtained by AFM and SEM was discussed. Highly porous coating was obtained at 100 mV/s scan rate and 10 cycles. EDX and ATR-FTIR results indicated the doping of anion of electrolyte due to formation of polaronic and bipolaronic sites. The presence of surface functional groups were determined by ATR-FTIR. Nanoscale conjugated polymer modified carbon fiber microelectrodes exhibited high capacitance of approximately 90 degrees phase angle, and vertical line in Nyquist plot. The capacitive behavior of CFME was increased by this very thin film coating of PProDOT-Me2. The electroactivity of Poly 2,2-Dimethyl-3,4-propylenedioxythiophene on the carbon fiber microelectrode open the possibility of using these coated electrodes for electrochemical microsupercapacitors and biosensor electrodes.

Correlation between the microstructures and the cycling performance of RuO2 electrodes for thin-film microsupercapacitors

We have fabricated all solid-state thin-film microsupercapacitors (TFSCs) using RuO2 electrodes and LiPON electrolytes. The RuO2 electrodes were grown at oxygen gas flow ratios [O2/(O2+Ar)] of 10% and 30%. Room-temperature charge–discharge measurements show that specific capacitance is dependent on the oxygen gas flow ratio. Glancing angle x-ray diffraction (GXRD) and transmission electron microscopy (TEM) results show that the RuO2 electrodes grown at 10% contain nanocrystallites (0.7–10 nm across) embedded in the amorphous matrix, while the electrodes grown at 30% are polycrystalline (with grains of 0.7–15 nm in diameter). Based on the GXRD, TEM, Auger electron spectroscopy depth profile, and scanning electron microscopy results, the oxygen flow ratio dependence of the cycling performance of the RuO2-based TFSCs are discussed in terms of the combined effects of the microstructures of the electrodes, interfacial products, and the surface morphology of the electrodes.