Impregnation-reduction method

Lawrence, R. J., and Wood, L. D. Method of making solid polymer electrolyte catalytic electrodes and electrode made thereby. U.S. Patent 4,272,353,1981. Fedkiw, P. S., and Her, W. H. An impregnation-reduction method to prepare electrodes on Naifon SPE. Journal of the Electrochemical Society 1989 136 899-900. Aldebert, P, Novel-Cattin, R, Pineri, M., Millet, P, Doumain, G., and Durand, R. Preparation and characterization of SPE composites for electrolyzers and fuel cells. Solid State Ionics 1989 35 3-9. 

FIGURE 9.15 TEM photograph of a Pt/C catalyst prepared by the impregnation-reduction method of an anionic metal salt (30 wt% metal loading). 

A/cm, Kolbe current efficiencies of 10 to 90 % were reported. The best results were obtained using PEM s plantinized by a non-equilibrium impregnation-reduction method. The results obtained by these authors are encouraging for Kolbe electrolysis in a PEM cell. It would be interesting to see, whether similar results can be attained using a liquid-phase reactant. 

The impregnation-reduction method has been frequently used for the synthesis of PtSn supported on inorganic carriers such as SiOg, AlgOs, or SAPO, but this approach has rarely been employed for the synthesis of carbon supported electrocatalysts. ° In general, the metal content in those samples is ca. 1-2 wt%, well below the demands of a state of the art fuel-cell electrocatalyst. A number of routes have been explored for the synthesis of carbon supported bimetallic PtSn samples. In general, they lead to materials composed of a wide range of phases, such as metallic and/or oxide Pt, Sn oxides, or PtSn solid solutions of different stoichiometry. 

In a variety of preparation methods, impregnation-reduction method is one of the mostly used methods in preparing Pt-based catalysts without the help of protective reagents and thermal treatments. Compared to other methods, impregnation-reduction method is relatively simple and direct, easier to conduct as well. This method only includes two steps impregnation and reduction. The first step is that the support such as carbon or other inert material is dissolved in a solvent such as water, ethanol, isopropanol, or their mixture to form a support containing mixed solution. A mount of metal precursor are impregnated into this support solution, and then the pH of the... 

Evaporative deposition [115] Low Pt loadings CLs can be prepared by this method. The differenee with the impregnation reduction method is that after the Pt precursor is evaporatively deposited onto a membrane, the entire membrane is immersed in a reduetive solution rather than only one side contacting the solution. Catalyst loadings of < 0.1 mg Pt cm can be prepared. 

Fedkiw P, Her W. An impregnation reduction method to prepare electrodes on Nafion SPE. J Electrochem Soc 1989 136 899-900. 

Chemical-deposition Electrode. Chemical techniques can also be employed in the fabrication of catalyst layers by platinizing the surface of a Nafion membrane. One approach [65, 66] is to expose one side of the Nafion membrane to a reductant solution (e.g., hydrazine solution) and the other side to a platinic acid solution. The reductant diffuses across the membrane to react with platinic acid and form a Pt catalyst layer. In another impregnation-reduction method [3, 67, 68] a cationic salt, such as Pt(NH3)4Cl2, is first impregnated into the Nafion membrane, followed by exposing this membrane to a reductant, such as NaBUj. As shown in Figure 19.13, a dense and porous platinum film can be formed using this chemical deposition technique. 

Particle size, morphology, and structure have strong influence on the activities of catalysts, so it is important to develop a simple but effective method to be capable of controlling the particle size and even the microstructure of nanoparticles. Several preparation methods, including impregnation-reduction method (formaldehyde was used as the reducing agent) [38], hydroperoxide oxidation decomposition method [39-41], and the modified polyol method [42-44], were attempted in our laboratory. 

In order to clarify the relations between the microstructure of PtRu/C catalyst and the corresponding performance, HRTEM and HR-EDS experiments were carried out on particles employing the PtRu/C prepared by impregnation-reduction method (denoted as PtRu-IM) and modified polyol method (denoted... 

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