Catalyst coating electrochemical deposition

The use of the catalyst coating of porous electrodes is one of the main features of fuel cells. Platinum exhibits the best catalytic reactivity. However, only economically reasonable methods for the Pt deposition are preferred because of platinum high cost. So, an electrochemical deposition that allows a selective coating of desired surfaces with precise control of Pt thickness and quality is seen to be one of the most efficient techniques for the fuel cell production. 

Several methods for the incorporation of catalysts into microreactors exist, which differ in the phase-contacting principle. The easiest way is to fill in the catalyst and create a packed-bed microreactor. If catalytic bed or catalytic wall microreactors are used, several techniques for catalyst deposition are possible. These techniques are divided into the following parts. For catalysts based on oxide supports, pretreatment of the substrate by anodic or thermal oxidation [93, 94] and chemical treatment is necessary. Subsequently, coating methods based on a Uquid phase such as a suspension, sol-gel [95], hybrid techniques between suspension and sol-gel [96], impregnation and electrochemical deposition methods can be used for catalyst deposition [97], in addition to chemical or physical vapor deposition [98] and flame spray deposition techniques [99]. A further method is the synthesis of zeoUtes on microstructures [100, 101]. Catalysts based on a carbon support can be deposited either on ceramic or on metallic surfaces, whereas carbon supports on metals have been little investigated so far [102]. 

Electrochemical-deposition Electrode. Vilambi-Reddy et al. [62] presented the early research on the electrochemical deposition electrode. They developed an electrochemical catalyzation (ECC) technique to deposit platinum catalyst particles selectively in the regions accessible to both ions and electrons. In the ECC technique, a hydrophobic porous carbon paper was first coated with dispersed carbon particles and PTFE to form a substrate. Then the Nafion ionomer was impregnated onto this carbon substrate. This substrate was then placed into a platinum acid-plating bath, along with a platinum counter electrode. One side of this substrate, without Nafion, was masked with a non-conducting film, which... 

The current density of a single-wall carbon nanotube sheet electrode, with infused platinum nanoparticles as the cathode in a microbial fuel cell, was approximately an order of magnitude higher than that with an e-beam-evapo-rated platinum cathode. The enhancement of catalytic activity can be associated with the increase of the catalyst surface area in the active cathode layer [61]. In another study, MFCs with carbon nanotube mat cathodes produced a maximum power density of 329 mW m , more than twice of that obtained with carbon cloth cathodes (151 mW m ) [62]. A similar twofold improvement was obtained by electrochemically depositing Pt nanoparticles on a CNT textile cathode for aqueous cathode MFCs, with only 19.3% Pt loading of a commercial Pt-coated carbon cloth cathode [63]. 

A GCE coated with a film of Prussian Blue (Fe4[Fe(CN)6]3) mimics HRP as catalyst for selective electrochemical reduction of H2O2 in the presence of O2. A careful deposition method has to be followed to prevent leakage of the oxidized form of the pigment from the coating into the solution. Amperometric determinations in phosphate buffer at pH 6.0, with an apphed potential of —50 mV vs. SCSE, shows Unearity in the 0.1 to 100 p,M range. ... 

The activities of CNTs have been evaluated by Girishkumar et al. [7] using ex situ EIS. Their study was conducted in a three-compartment electrochemical cell using a GDE electrode (a carbon fibre paper coated with SWCNTs and Pt black as an anode or cathode). Electrophoretic deposition was used to deposit both the commercially available carbon black (CB) for comparison and the SWCNT onto the carbon Toray paper. Commercially available Pt black from Johnson Matthey was used as the catalyst. In both cases, the loading of the electrocatalyst (Pt), the carbon support, and the geometric area of the electrode were kept the same. EIS was conducted in a potentiostatic mode at either an open circuit potential or controlled potentials. 

Very recently Chen and coworkers [56] demonstrated the use of ElS for label-free electrochemical detection of DNA sequences relevant to anthrax lethal factor on gallium nitride (GaN) nanowires. The GaN nanowires were grown on a silicon substrate coated with Au catalyst using Ga as the source material and NH3 as the reactant gas in a tubular furnace via air pressure chemical vapor deposition. ElS measurements of the "as grown" GaN nanowires, observed in the Nyquist plot in Fig. 14.12A, exhibited a semicircle and a straight vertical line, indicative of finite impedance at the GaN/electrol3Ae... 

Using underpotential deposition with the redox replacement technique a novel electrochemical approach for nanoparticle-based catalyst has been designed. Here, the as-prepared Pt-coated Au nanoparticle monolayer at atomic level on the electrode surface can reduce O2 predominately by 4e to H2O, which was confirmed by rotating ring disk electrode technique (Figure 8). 

Atanasoski RT, Atanasoska LL, Cullen DA, Haugen GM, More KL, Vemstrom GD (2012) Fuel cells catalyst for start-up and shutdown conditions electrochemical, XPS, and STEM evaluatitm of sputter-deposited Ru, Ir, and Ti on Pt-coated nanostmctured thin film supports. Electrocatalysis. Electrocatal 3 284—297... 

Liquid-phase deposition is a method for the non-electrochemical production of polycrystalline ceramic films at low temperatures, along with other aqueous solution methods [chemical bath deposition (CBD), successive ion layer adsorption and reaction (SILAR), and electroless deposition (ED) with catalyst] has been developed as a potential substitute for vapor-phase and chemical-precursor systems. The method involves immersion of a substrate in an aqueous solution containing a precursor species (commonly a fluoro-anion) which hydrolyzes slowly to produce a supersaturated solution of the desired oxide, which then precipitates preferentially on the substrate surface, producing a conformal coating... 

In 1959, William Grubbs used organic cation exchange polymers in fuel cells. As shown in Fig. 1.9, the cell consists of polymer electrolyte sandwiched between platinum impregnated porous electrodes. Teflon is coated on the electrodes to make them hydrophobic. The operation temperature of PEFMC can be within 80-200°C. The low operation temperature of PEMFC offers quick start-up but platinum catalysts are required to promote the electrochemical reaction. Platinum particles are deposited very finely onto carbon powders to attain the maximum surface area. The contact between gas, electrolyte and platinum catalyst should be good for the uninterrupted function of PEFMC. 

In this paper, while taking the conductivity of FeCrAlY supports into account, the electrochemical in situ synthesis/deposition of Ni- and noble-metal-containing HT compounds on a FeCrAlY foam was studied, with the aim of obtaining catalysts for H2 production processes - such as the endothermic steam methane reforming (SMR) [16,17] or the exothermic catalytic partial oxidation (CPO) of methane. The effect of the synthesis parameters on the properties of the film coating and catalytic activity were studied, while paying special attention to the influence of the composition of the HT precursor. 

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