Bonded electrodes

Pocket and tubular electrodes have been described in detail by Falk and Salkind [1]. McBreen has reviewed work on both sintered plate and plastic-bonded electrode technology [9], More recent work is on the use of nickel foams and nickel mats. 

Abraham et al. were the first ones to propose saturating commercially available microporous polyolefin separators (e.g., Celgard) with a solution of lithium salt in a photopolymerizable monomer and a nonvolatile electrolyte solvent. The resulting batteries exhibited a low discharge rate capability due to the significant occlusion of the pores with the polymer binder and the low ionic conductivity of this plasticized electrolyte system. Dasgupta and Ja-cobs patented several variants of the process for the fabrication of bonded-electrode lithium-ion batteries, in which a microporous separator and electrode were coated with a liquid electrolyte solution, such as ethylene—propylenediene (EPDM) copolymer, and then bonded under elevated temperature and pressure conditions. This method required that the whole cell assembling process be carried out under scrupulously anhydrous conditions, which made it very difficult and expensive. 

Figure 3.79 Fe K-edge XANES of FeTMPPCl BP pyrolyzed at 800°C in powder form (solid line) and following incorporation into a Teflon-bonded electrode immersed in 0.1 M H3PO4 at open circuit (about 0.6 V versus DHE, in situ, dotted line). Also shown in this figure is the ex situ XANES of an Fe foil for comparison (dashed line).

Figure 3.6. Cyclic voltammograms of Teflon-bonded electrodes (2 mg active material, 0.15 cm projected area) containing intact (panel A) and heat treated ClFeTMPP/BP (panel B) in 1 M H3PO4 (according to Figure 1 in ref. [45] reproduced with permission of the American Chemical Society).

Another application is in ferroelectric devices used to bond electrode terminals to the crystals in stacks. These adhesives replace solders and welds where crystals tend to be deposited by soldering and welding temperatures. Bonding of battery terminals is another application when soldering... 

The PTFE-bonded electrode was introduced by Neidrach and Alford [11]. It consists of metal blacks or carbon supported metal catalysts that are hydrophilic, blended with fine particles of hydrophobic PTFE, that flow and bind the structure as a result of heat treatment during fabrication. Thanks to its physical properties, PTFE flows and penetrates the pores, thus allowing a good interfacial contact between catalyst and carbon and providing hydrophobic gas pores for reactants. 

Nowadays, the main type of H2 electrodes used in AFCs is a PTFE-bonded electrode with a Pt load of about 0.3 mg cm [12-14]. PAFCs employ H2-difiusion PTFE-bonded electrodes with Pt supported on carbon as catalyst for low loadings of O.l-l.O mg cm [15]. In contrast, PEFCs utilize H2 electrodes in which the catalyst (Pt/C) and the ionomer (Nafion ) are... 

Currently used electrodes are flexible, and the most commonly used electrodes are therefore PTFE-bonded electrodes. The degradation of PTFE-bonded electrodes is described below for different types of nickel anodes and one silver cathode. 

The evolution of cell components from 1965 to the present day for PAFCs is summarized in Table 5-1. In the mid-1960s, the conventional porous electrodes were polytetrafluoroethylene (PTFE) - bonded Pt black, and the loadings were about 9 mg Pt/cm. During the past two decades, Pt supported on carbon black has replaced Pt black in porous PTFE-bonded electrode structures as the electro-catalyst. A dramatic reduction in Pt loading has also occurred the loadings are currently about 0.10 mg Pt/cm in the anode and about 0.50 mg Pt/cm in the cathode. 

Utilization. Compared to a PTFE-bonded electrode, much better fuel cell performance can be aehieved with an ionomer-pyrolyzed electrode, as shown in Figure 19.8. 

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