Anode catalysts electrochemical deposition

Recently, carbon nanotubes, an important class of one-dimensional nanostructures, have been fabricated within the pores of anodic alumina via CVD (Davydov et al, 1999 Li et al, 1999 Iwasaki et al., 1999 Suh et al, 1999). A small amount of metal (e.g., Co) is first electrochemically deposited on the bottom of the pores as a catalyst for the carbon nanotube growth, and the template is heated to 700 to 800°C in a flowing gas mixture of N2 and acetylene or ethylene. The hydrocarbon molecules are then pyrolyzed to... 

The research involves the development of techniques for deposition of porous catalyst layers by defining the conditions of pressure, sputter rates, and target configurations that will result in appropriate compositions and morphology for the catalyst layer. The effect of catalyst structure and composition on the activity of the catalyst layers will be characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), x-ray absorption spectroscopy (XAS), and electrochemical polarization studies in half cells and full cells. New base metal and noble metal alloys and oxides will also be studied with an aim to identify new compositions that will result in enhanced activity. The catalyst activity target is 2500 mW/mg of anode catalyst. 

Witham CK, Oran W, Valdez n, Narayanan SR (2000) Performance of direct methanol fuel cells with sputter-deposited anode catalyst layers. Electrochem Solid State Lett 3 497—500... 

For comparative purposes. Fig. 25 reports also the polarization and power density curves exhibited by a DEFC containing a Pd/C anode catalyst obtained by reduction with ethylene glycol of Vulcan XC-72-adsoibed PdCl2. " Although providing good results, there is little doubt that the Pd/C catalyst is much less efficient, especially in terms of potential output and electrochemical stabihty, than the Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C catalysts, obtained by the spontaneous deposition procedure. 

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]. 

Uhm S, Chung ST, Lee J (2007) Activity of Pt anode catalyst modified by underpotential deposited Pb in a direct formic acid fuel cell. Electrochem Commun 9 2027-2031... 

Wang JX, Brankovic SR, Zhu Y,Hans(utJC, Adzic RR (2003) Kinetic characterization of PtRu fuel cell anode catalysts made by spontaneous Pt deposition rat Ru nanoparticles. J Electrochem Soc 150 A1108-All 17... 

In the case of a direct formic acid fuel cell equipped with Ti mesh anode support, Chetty and Scott carried out a comprehensive comparative investigation of Pd and PtSn catalysts prepared by either thermal or electrochemical deposition [309]. Generally, PtSn/Ti mesh performed better than Pd/Ti mesh the maximum power output for each at 333 K using 1 M HCOOH was about 20 mW cm and 37 mW cm, respectively. It is noteworthy that according to this study the Ti mesh-supported PtSn gave about three times higher peak power density than the GDE with commercial carbon supported PtSn [309]. Furthermore, the performance of the three-dimensional anode improved with formic acid concentration up to 7 M, and excellent catalyst stability was observed during 72 h of continuous operation. 

Sivakumar P, Tricoli V. PtRulr nanoparticles prepared by vapor deposition as a very efficient anode catalyst for methanol fuel cells. Electrochem Solid-State Lett 2006 9 A167-70. 

The catalytic problems associated with the anodic oxidation of methanol are very similar to those associated with the anodic oxidation of CO-containing technical hydrogen. At present, the standard catalyst for both reactions is a mixed Pt-Ru catalyst (with about 50 at% of each metal) obtained by their joint chemical or electrochemical deposition from solutions of simple or complex compounds on carbon black. 

An electrochemical cell [93,94] was used to obtain an efficient anodic deposition of no carrier added F-fluoride solubilized in the target water. The radioisotope is electrochemically adsorbed on the anode (glassy carbon electrode) and can be easily dried. An opposite electrical field releases the radionuclide directly into a solution of a phase transfer catalyst in dipolar aprotic solvents. The nucleophilic fluorination can be performed simultaneously if the electrochemically and thermally induced desorption of radioactivity is done in the presence of the precursor. However, the yields remain poor (3 % in the electrochemical n.c.a [ F]fluorination of anisole). 

Several, different, electrochemical oxidations of 26 to 27 have been reported. Using a variety of electrodes (copper, Monel metal, nickel, or silver), 26 was oxidized in aqueous potassium hydroxide solution containing potassium chromate or potassium permanganate, to afford 27 in 70-85% yield.118,119 This electrochemical oxidation has been conducted in aqueous, alkaline solution in the presence of a surfactant, but with added metal catalyst, to give 27 in 85-95% yield.120 Alternatively, the oxidation has been performed by using an anode on which nickel oxide was deposited. This anode, in a solution of 26 at pH >9, with or without nickel salts, afforded 27 in >90% yield.121 A number of additional publications described122-140 other modifications of the... 

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. 

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