Preparation of Catalyst Ink

This chapter focuses on the preparation of catalyst inks, catalyst layers, and MEAs. 

Hviii tmliobit- ink Hvdiooliilic ink colloid ink Catalvsl ion iuliitioii itik Pi foil 

Hydrcijliobic electro da HydropliUic electrode Deposition electrode 

Hydrophobic ink, containing a catalyst and a hydrophobic agent (such as Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF)), is used to prepare a hydrophobic type of catalyst layer. The typical process for the preparation can be summarized as follows  

Stir a mixture of Pt/C catalyst and solvent (e.g., ethanol) highly and disperse it in an ultrasonic machine  

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In Abaoud et al. s work [18], the details of using polyethylene oxide (PEO) as a suspension agent in the preparation of catalyst ink for PEMFC electrodes were... 

To overcome these disadvantages, a thin-film CL technique was invented, which remains the most commonly used method in PEM fuel cells. Thin-film catalyst layers were initially used in the early 1990s by Los Alamos National Laboratory [6], Ballard, and Johnson-Matthey [7,8]. A thin-film catalyst layer is prepared from catalyst ink, consisting of uniformly distributed ionomer and catalyst. In these thin-film catalyst layers, the binding material is not PTFE but rather hydrophilic Nafion ionomer, which also provides proton conductive paths for the electrochemical reactions. It has been found that the presence of hydrophobic PTFE in thin catalyst layers was not beneficial to fuel cell performance [9]. 

Cobaltous acetate. CAS 71-48-7], Co(CHiCO )>. is obtained as a pink salt by the dehydration of the tetrahydrate which is prepared by dissolving the hydroxide or carbonate in acetic acid. The tetrahydrate. which is the commercial form, is widely used in the preparation of catalysts, c.g.. OXO synthesis, and dryers for inks and vamlshes. 

Figure 24 shows a cross section of a Nafion membrane catalyzed by direct application of catalyst inks to its two major surfaces, as observed by SEM [52], The thin slice of MEA required for SEM imaging was generated by microtome from the MEA encapsulated in epoxy. This figure actually describes an MEA prepared for a DMFC, with PtRu black and Pt black catalyst layers of relatively high loading, resulting in catalyst layers 10 and 14 pm thick (Fig. 24). The SEM image well depicts two generic characteristics of CCMs prepared by direct, ink-based application of the catalysts to the ionomeric membrane the interface between the catalyst layer and the membrane is sharp on the SEM scale and the thickness of the catalyst layer measured from the...

Regarding the solvent used to prepare the catalyst ink, its properties in catalyst ink should be mentioned as it also plays an important role in determining the microstructure and cataljAic activity of the CL. When ionomer such as Nafion solution is mixed with solvent, the mixture may become a solution, a colloid, or a precipitate due to the different dielectric constants of the solvent. When the dielectric constant is more than 10, a solution is formed between three and 10, a colloidal solution is formed and less than 3, precipitation occurs.If the mixture is a solution (i.e., the solution method ), excessive ionomer may cover the carbon surface, resulting in decreased Pt utilization. However, when the mixture is a colloid (the colloidal method ), ionomer colloids adsorb on the catalyst powder and the size of the catalyst powder agglomerates increases, leading to an increased porosity of the CL. In this case, the mass transfer resistance could be diminished because of the continuous network of ionomers throughout the CL, which then improves the proton transport from the catalyst to the membrane. ... 

Spray the as-prepared composite catalyst ink directly on one side of the membrane to form a catalyst layer. 

A necessary step in conducting these measurements is preparation of the WE. A well-developed procedure for electrode preparation is described by Mayrhofer et al. [3]. A small amount of catalyst power (Pt- or Pt alloy-based catalyst) is first mixed ultrasonically with deionized water, followed by the addition of alcohol or isopropanol ( 1.0 ml alcohol to 5 mg catalyst) and 5 wt.% Nation ionomer solution (-1/40 volume ratio with the alcohol) to form a well-mixed catalyst ink. Then a small amount of catalyst ink is pipetted and coated onto a disk electrode surface such as GC or gold electrode, with a geometric area of 0.2-0.5 cm. The coated electrode is then left to air dry. The total catalyst loading on a GC electrode can be adjusted to 0.02-0.2 mg cm . ... 

Nickel fluoride is used in marking ink compositions (see Inks), for fluorescent lamps (4) as a catalyst in transhalogenation of fluoroolefins (5), in the manufacture of varistors (6), as a catalyst for hydrofluorination (7), in the synthesis of XeF (8), and in the preparation of high purity elemental fluorine for research (9) and for chemical lasers (qv) (10). 

Acetates. Anhydrous iron(II) acetate [3094-87-9J, Ee(C2H202)2, can be prepared by dissolving iron scraps or turnings in anhydrous acetic acid ( 2% acetic anhydride) under an inert atmosphere. It is a colorless compound that can be recrystaUized from water to afford hydrated species. Iron(II) acetate is used in the preparation of dark shades of inks (qv) and dyes and is used as a mordant in dyeing (see Dyes and dye intermediates). An iron acetate salt [2140-52-5] that is a mixture of indefinite proportions of iron(II) and iron(III) can be obtained by concentration of the black Hquors obtained by dissolution of scrap iron in acetic acid. It is used as a catalyst of acetylation and carbonylation reactions. 

Cobalt(II) hydroxide [1307-86-4], Co(OH)2, is a pink, rhombic crystalline material containing about 61% cobalt. It is insoluble in water, but dissolves in acids and ammonium salt solutions. The material is prepared by mixing a cobalt salt solution and a sodium hydroxide solution. Because of the tendency of the cobalt(II) to oxidize, antioxidants (qv) are generally added. Dehydration occurs above 150°C. The hydroxide is a common starting material for the preparation of cobalt compounds. It is also used in paints and Hthographic printing inks and as a catalyst (see Paint). 

The catalyst inks were prepared by dispersing the catalyst nanoparticles into an appropriate amoimt of Millipore water and 5wt% Nafion solution. Then, both the anode and cathode catalyst inks were directly painted using a direct painting technique onto either side of a Nafion 117 membrane. A carbon cloth diffusion layer was placed on to top of both the anode and cathode catalyst layers [3-5]. The active cell area was 2.25cm. ... 

In practice, the catal5Tic layers are prepared by brushing or spraying catalyst ink (a suspension of the catalyst particles in water and/or an organic solvent with addition of ionomer) either onto diffusion media (carbon paper or carbon cloth, also referred to as substrates), resulting in so-called catalyst-coated substrates (CCS), or directly onto... 

Saha et al. [109] have proposed an improved ion deposition methodology based on a dual ion-beam assisted deposition (dual IBAD) method. Dual IBAD combines physical vapor deposition (PVD) with ion-beam bombardment. The unique feature of dual IBAD is that the ion bombardment can impart substantial energy to the coating and coating/substrate interface, which could be employed to control film properties such as uniformity, density, and morphology. Using the dual lABD method, an ultralow, pure Ft-based catalyst layer (0.04-0.12 mg Ft/cm ) can be prepared on the surface of a GDL substrate, with film thicknesses in the range of 250-750 A. The main drawback is that the fuel cell performance of such a CL is much lower than that of conventional ink-based catalyst layers. Further improvement... 

Cobalt(II) hydroxide is used as a drier for paints and varnishes and is added to hthographic printing inks to enhance their drying properties. Other applications are in the preparation of cobalt salts as a catalyst and in storage battery electrodes. 

Cobalt nitrate is used in the decoration of porcelain and stones in the manufacture of invisible inks and cobalt pigments in hair dyes in animal feeds as an additive to sods in catalysts preparation and in vitamin supplements. 

Other applications. Phenylmercuric acetate has been used in aqueous preparations such as inks, adhesives, and caulking compounds, as a catalyst for the manufacture of certain polyurethanes, and as a fungicide in seed dressings and interior and exterior paints (IARC 1993 Reese 1990). Dimethylmercury is used to prepare mercury nuclear magnetic resonance standards (Blayney et al. 1997) and mass spectrometer mercury calibration standards (Toribara et al. 1997). 

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