Impregnation reduction

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. 

Despite the convenience of handling and separation in heterogeneous catalysis, many other parameters have a strong influence on the stereochemical outcome pressure temperature modifier purity of substrates high substrate specificity catalyst preparation, which includes type, texture, and porosity of the support dispersion impregnation reduction and pretreatment of the metal.22 Reproducibility of catalyst activities and enantioselectivities can often be a problem attributed to variations in catalyst preparations and purity of the substrate.5-22... 

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. 

Figure 10.13 MIL-101-supported palladium nanoparticles made by impregnation/reduction.

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... 

Impregnation reduction [115] The membrane is pre-exchanged to the Na form. One side of the membrane is faced to an aqueous Pt salt-containing solution for impregnation and the other side of the membrane is in contact with aqueous NaBIL reduetant. The Pt precursor on the other side is reduced to metal Pt by diffusing the reduetant through the membrane. Pt loadings in the order of mg Pt cm can be deposited. 

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. 

Figure 19.13. SEM top view and TEM side view of a nan-equilibrium impregnation-reduction electrode. Deposition conditions 0.6 mM Pt(NH3)4Cl2,1 mM NaBHi, 40 minutes impregnation time, 2 hours reduction time, 50 C [3]. (Reprinted by permission of ECS— The Electrochemical Society, from Liu R, Her W-H, Fedkiw PS. In situ electrode formation on a Nafion membrane by chemical platinization.)...

Two different methods, known as reductant permeation (RP) and impregnation reduction (IR), have been successfully developed for plating the electrodes for the ion exchange... 

The described impregnation-reduction steps are typically repeated 1-3 times in order to increase the thickness and electric conductivity of the electrodes. The third step is the secondary plating (or surface electroding) process to deposit additional Pt at the outer surface of the electrode to further increase the electrode surface conductivity. The composite is immersed in the Pt complex solution, and by using reducing agents such as hydroxylamine hydrochloride and hydrazine monohydrate, the platinum is deposited on the top of the initial Pt electrode layer. A detailed description of the fabrication process can be found in (Kim and Shahinpoor 2003). 

Many types of bimetallic catalysts have been used to investigate electrocatalytic performance, including single-crystal surfaces [6], sputtered particles [5,7], carbon-supported catalysts fabricated by impregnation reduction, and colloidal nanocrystals (NCs). Bimetallic single crystals are indispensable when investigating facet-specific electrocatalytic properties sputtered bimetallic particles can be used as model catalysts with a clean surface to study the effect of composition on... 

In the development of fuel ceU catalysts, catalyst synthesis plays a critical role in improving catalyst activity and stability. Over the last several decades, many syntheses methods have been developed, including the impregnation-reduction, colloid, sol-gel, and microwave-assisted methods. Experimental results showed all these methods to be effective in synthesizing catalysts for PEM fuel cells. The most important progress in recent years has been in the synthesis of nanostructured catalysts for fuel cell applications [52]. Nanostractured Pt-based catalysts are claimed to be much more active than the commercially available Pt/C catalysts. 

S. Garcia-Rodriguez, M.A. Pena, J.L.G. Fierro, S. Rojas, Controlled synthesis of carbon-supported Pt3Sn by impregnation-reduction and performance on the electrooxidation of CO and ethanol, J. Power Sources 195... 

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