Thin porous coating electrodes

Perez J, Gonzalez ER, Ticianelli EA (1998) Impedance studies of the oxygen reduction on thin porous coating rotating platinum electrodes. J Electrochem Soc 145 2307-13... 

Figure 3.70 Steady state ring-disk polarization in 0.1 M NaOH before (A) and after pyrolysis curves for O2 reduction on a thin porous coating 800 °C, 2 h in Ar (B). Electrode cross-sectional electrode containing 4.7% w/w CoTMPP XC-72 area, 0.196cm2, co = 2500rpm, room (solid triangles), 4.8% w/w (FeTMPP)20 XC-72 temperature, Au Ering = +0.1 V versus SCE, (solid circles), 4.4% w/w H2TMPP XC-72 (solid N = 0.38. squares) and Vulcan XC-72 carbon (open circles)...

Electrochemical studies of the electrocatalysts were carried out using the thin porous coating technique [12,13]. An amormt of 20 mg of the eletrocatalyst was added to a solution of 50 mL of water containing 3 drops of a 6% polytetrafluoroethylene (PTFE) suspension. The resulting mixture was treated in an ultrasound bath for 10 min, filtered and transferred to the cavity (0.30 mm deep and 0.36 cm area) of the working electrode. The quantity of electrocatalyst in the working electrode was determined with a precision of... 

Perez, J, E.R, Gonzalez, and E.A. Ticianelli, Oxygen electrocatalysis on thin porous coating rotating platinum electrodes. Electrochimica Acta, 1998, 44 pp. 1329-1339 Song, H,-K, H,-Y, Hwang, K.-H. Lee, and L.H, Dao, The effect of pore size distribution on the frequency dispersion of porous electrodes. Electrochimica Acta, 2000. 45 pp. 2241-2257 Srikumar, A, T.G. Stanford, and J.W, Weidner, Linear sweep voltammetry in flooded porous electrodes at low sweep rates. Journal of Electroanalytical Chemistry, 1998. 458 pp. 161-173... 

Lima FHB, Ticianelli EA (2004) Oxygen electrocatalysis on ultra-thin porous coating rotating ring/disk platinum and platinum-cobalt electrodes in alkaline media. Electrochim Acta 49 4091-4099... 

Lima, B. Ticianelli, A. (2004). Oxygen Electrocatalysis on Ultra-thin Porous Coating Rotating Ring/Disk Platinum and Platinum-Cobalt Electrodes in Alkaline Media. Electrochimica Acta, Vol.49, No.24, (September 2004), pp. 4091-4099, ISSN 00134686 Kotz, R Yeager, E. (1980). Raman Studies of the Silver/Silver Oxide Electrode. Journal of Electroanalytical Chemistry, Vol.lll, No.l, (July 1980), pp. 105-110, ISSN 00220728 Demarcormay, L., Coutanceau, C. Leger, M. (2004). Electroreduction of Dioxygen (ORR) in Alkaline Medium on Ag/C and Pt/C Nanostructured Catalysts - Effect of the Presence of Methanol. Electrochimica Acta, Vol.49, No.25, (October 2004), pp. 4513-4521, ISSN 00134686... 

The FPI principle can also be used to develop thin-film-coating-based chemical sensors. For example, a thin layer of zeolite film has been coated to a cleaved endface of a single-mode fiber to form a low-finesse FPI sensor for chemical detection. Zeolite presents a group of crystalline aluminosilicate materials with uniform subnanometer or nanometer scale pores. Traditionally, porous zeolite materials have been used as adsorbents, catalysts, and molecular sieves for molecular or ionic separation, electrode modification, and selectivity enhancement for chemical sensors. Recently, it has been revealed that zeolites possess a unique combination of chemical and optical properties. When properly integrated with a photonic device, these unique properties may be fully utilized to develop miniaturized optical chemical sensors with high sensitivity and potentially high selectivity for various in situ monitoring applications. 

Fig. 1 shows the cyclic voltammetry of an FePc/XC-72 dispersion, heated at 280°C in an inert atmosphere, in the form a thin porous Teflon bonded coating electrode in a 1 M NaOH solution. A description of the methodology involved in the preparation of this type of electrode may be found in Ref. 3. As can be clearly seen, the voltammetry of this specimen exhibits two sharply defined peaks separated by about 330 mV. The potentials associated with these features are essentially identical to those found by other workers for the reduction and oxidation of films of iron oxy-hydroxide formed on a number of host surfaces, including iron and carbon.(5)... 

Ion-exchange membrane coated with porous catalyst metal (Solid Polymer Electrolyte, SPE) as well as GDE can provide gas phase electrolysis of CO2. The first attempt was published by Ito et al., communicating thin porous Au layer electrode coated on a cation exchange membrane. The SPE could not enhance the cathodic current of CO2 reduction.2" DeWulf et al. applied an SPE with Cu as the catalyst layer on a cation exchange membrane (CEM) Na-fion 115. The SPE reduced CO2 to CH4 and C2H4 for a while, but the current density for CO2 reduction dropped below 1 mA cm after 70 min electrolysis. " ... 

Platinised titanium anodes (titanium carrying a thin surface film of platinum, of the order of 0-0025 mm thick) have proved successful in cathodic-protection systems employing impressed-current techniques, as electrodes for electrodialysis of brackish water, and in many applications where established anode materials suffer significant corrosion. Platinum-coated titanium anodes can operate without breakdown at very high current densities, of the order of 5 0(X)A/m, in sea water, as although the very thin platinum coating may be porous the underlying titanium exposed at the pores will become anodically passivated... 

A variant of the enhanced reaction zone concept is to utilize as catalyst support various porous three-dimensional electrodes with thickness between 200 to 2,000 pm. Thus, the electric contact resistance between the individual layers is eliminated. The three-dimensional matrix (such as various graphite felts, reticulated vitreous carbon, metal mesh, felt, and foam) supporting uniformly dispersed electrocatalysts (nanoparticles or thin mesoporous coating) could assure an extended reaction zone for fuel (methanol, ethanol, and formie aeid) electrooxidation, providing an ionic conductor network is established to link the catalytically active sites and the proton exchange membrane. The patent by Wilkinson et al. also suggests such electrode configurations (e.g., carbon foam, expended metal and reticulated metal) but experimental results were not provided [303]. 

A PEMFC consists of two electrodes and a solid polymer membrane, which acts as an electrolyte. The proton exchange membrane is sandwiched between two layers of platinum porous electrodes that are coated with a thin layer of proton conductive material. This assembly is placed between two gas diffusion layers such as carbon cloth, carbon paper enabling transfer of electrical current and humidified gas. Some single cell assemblies can be mechanically compressed across electrically conductive separators to fabricate electrochemical stacks. 

Mesoporous or macroporous matrices often provide a suitable environment for immobilisation of proteins over electrodes. They are highly ordered porous thin films coated over the electrodes with pore sizes ranging from micrometres (macroporous) to few nanometres (mesoporous) where protein could either be adsorbed or cross-linked. Immobilisation of redox proteins into these pores provides them with much desired mechanical stability besides hindering their direct interaction with some of the physical denaturants such as gas bubbles, unsterile surfaces, etc. One of the important characteristics of porous materials is their high surface area/volume ratio that provides more loading space for proteins compared to flat electrode surfaces. Large surface area also favours the interaction with... 

FIGURE 9. Cyclic voltammetry of 7% w/w iron phthalocyanine dispersed on Vulcan XC-72 carbon, after a heat treatment at 300°C in a flowing inert atmosphere. The measurement was conducted with the material in the form of a thin porous Teflon-bonded coating electrode in 1 M NaOH at 25 C. Sweep rate 5 mV s" ... 

FIGURE 12, In situ Mossbauer spectra of a 50% w/w Fe-enriched hydrated ferric oxide precipitated on Shawinigan black high-area carbon in the form of a Teflon-bonded electrode in 4 M KOH at (a) -0.3 V and (b) -1.1 V versus Hg/HgO, OH". Inset Cyclic voltammogram of the same, although nonenriched, material as in (a) in the form of a thin porous Teflon-bonded coating electrode deposited on an ordinary pyrolytic graphite electrode, in 4 M KOH. Scan rate 10 mV s" ... 

A typical Ag/AgCl electrode is shown in figure 11.9 and consists of a silver wire, the end of which is coated with a thin film of AgCl. The wire is immersed in a solution that contains the desired concentration of KCl and that is saturated with AgCl. A porous plug serves as the salt bridge. The shorthand notation for the cell is... 

---