Composite electrode fabrication

Titanium/chromium oxide (Ti/Cr203 + Ti02) composite electrodes, fabricated by a ceramic method [168], may be used for oxidation of organic compounds. The chromium is oxidized to Cr03, which chemically oxidizes the substrate. The hfetime of the electrode may be improved by doping with Sb203. 

Hashmi and Upadhyaya compared the electrochemical properties of the electrochemically synthesized MnO /PPy composite electrodes, fabricated with different electrolytes, namely polymer electrolyte film (polyvinyl alcohol [PVA]-HjPO aqueous blend), aprotic liquid electrolyte (LiClO -propylene carbonate [PC]), and polymeric gel electrolyte (poly methyl methacrylate [PMMA]-ethylene carbonate [EC]-PC-NaClO ) [60]. The cell with aqueous PVA-H PO showed non-capacitive behavior owing to some reversible chemical reaction of MnO with water, while the MnO / PPy composite was found to be a suitable electrode material for redox supercapacitors with aprotic (non-aqueous) electrolytes. The solid-state supercapacitor based on the MnO /PPy composite electrodes with gel... 

PPy/graphite composite electrodes fabricated chemically by using sequential dipping methods, can be advantageous compared to the electrochemical composite method. ... 

A quite different approach was introduced in the early 1980s [44-46], in which a dense solid electrode is fabricated which has a composite microstructure in which particles of the reactant phase are finely dispersed within a solid, electronically conducting matrix in which the electroactive species is also mobile. There is thus a large internal reactant/mixed-conductor matrix interfacial area. The electroactive species is transported through the solid matrix to this interfacial region, where it undergoes the chemical part of the electrode reaction. Since the matrix material is also an electronic conductor, it can also act as the electrode s current collector. The electrochemical part of the reaction takes place on the outer surface of the composite electrode. 

The first CNT-modified electrode was reported by Britto et al. in 1996 to study the oxidation of dopamine [16]. The CNT-composite electrode was constructed with bro-moform as the binder. The cyclic voltammetry showed a high degree of reversibility in the redox reaction of dopamine (see Fig. 15.3). Valentini and Rubianes have reported another type of CNT paste electrode by mixing CNTs with mineral oil. This kind of electrode shows excellent electrocatalytic activity toward many materials such as dopamine, ascorbic acid, uric acid, 3,4-dihydroxyphenylacetic acid [39], hydrogen peroxide, and NADH [7], Wang and Musameh have fabricated the CNT/Teflon composite electrodes with attractive electrochemical performance, based on the dispersion of CNTs within a Teflon binder. It has been demonstrated that the electrocatalytic properties of CNTs are not impaired by their association with the Teflon binder [15]. 

While high temperatures do not severely limit fabrication of Ni—YSZ cermets, they can impact the way in which other composite electrodes are made. This is well-known for cathodes, where the most commonly used material is a composite of YSZ and Sr-doped LaMnOs (LSM). The primary reason for using LSM, rather than materials such as Sr-doped LaFeOs (LSF) or LaCoOs (LSC) that exhibit a better performance, is that LSM—YSZ mixtures can be... 

As COR and OER occur simultaneously in the cathode, their kinetics are particularly important in evaluating carbon-support corrosion. The kinetics of OER is material-specific, dependent on catalyst composition and electrode fabrication.35,37 -39 A number of OER kinetics studies were done on Pt metal electrodes.37-39 However, there is a lack of OER kinetics data on electrodes made of Pt nano-particles dispersed on carbon supports. Figure 2 shows the measured OER current density with respect to the overpotential defined by Eq. (6).35 The 02 concentration was measured at the exit of a 50-cm2 cell using a gas chromatograph (GC). The 02 evolution rate (= 02 concentration x cathode flow rate) was then converted to the OER current density, assuming 4e /02 molecule. Diluted H2 (10%) and a thicker membrane (50 p,m) were used in the measurement to minimize H2 crossover from anode to cathode, because H2 would react with 02 evolved at the cathode and incur inaccuracy in the measured OER current density. Figure 2 indicates that the OER... 

The lift-off process is usually employed to fabricate metal electrodes. This method, as opposed to the wet-etch process, allows the dual-composition electrode to be patterned in a single step [747]. In order to achieve well-defined metal electrodes in a channel recess using the lift-off technique, the metal (Pt/Ta) will not be deposited onto the sidewalls of the photoresist structure (see Figure 2.32). This discontinuity of the deposited metal layer around the sidewalls allows metal on the resist to be removed cleanly from the surface without tearing away from the metal on the surface. Thus negative resists were used because they can be easily processed to produce negatively inclined sidewalls. To achieve this, the photoresist is subjected to underexposure, followed by overdevelopment [141]. 

The changes of initial electrode capacity as a function of grinding time are presented in Fig. 4. It clearly shows that the specific capacity markedly increased with increasing grinding time up to 72 h and then dropped to nearly nil with 240 h of milling. In particular, the discharge capacity for the electrode fabricated from the composite ground for 72 h was ca 378 mAh/g at the first cycle. Flowever, the electrode capacity of the material milled for... 

Special studies with ring-disk electrodes showed that only metals with relatively positive deposition potentials silver and mercury [53, 494] and also probably copper can be cathodically deposited on HTSC substrates without partial reduction of the oxide surface. HTSC-silver composites are fabricated by multistage techniques that include an electrodeposition stage [498, 499]. It has been noted during deposition of silver and copper that their incorporation into the BSCCO lattice is possible (0.01 and 0.4 atom per molecule, respectively) with the formation of substituted phases [495]. 

Ti02 nanotubes composite electrode has been constructed for effective immobilization of cytochrome c and successful realization of its direct electrochemistry and electrocatalysis. The immobilized Cyt c/Ti02 bioactive electrode exhibits favorable electrocatalytic activity toward the reduction of H202 with good stability and sensitivity. The linear range was obtained is 2 x 10"6 to 3.49 x 10 mol /L"1 with detection limit of 1.21 x 10 6 mol/L"1. The fabricated biosensor retains 98.7% of the initial response after 30 days [27],... 

Electrodeposition is a unique, versatile technique for fabrication of metal oxide, polymer, and composite electrodes for electrochemical supercapacitors. Composition, crystal structure, and morphology of the deposits can be easily manipulated by adjusting the electrodeposition parameters to achieve improved capacitive behavior. Current progress, however, is far from the commercial expectations for electrochemical supercapacitors. 

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