Electrocatalysis electrolyte concentration

Phosphoric-acid fuel cell (PAFC) — In PAFCs the -> electrolyte consists of concentrated phosphoric acid (85-100%) retained in a silicon carbide matrix while the -> porous electrodes contain a mixture of Pt electrocatalyst (or its alloys) (-> electrocatalysis) supported on -> carbon black and a polymeric binder forming an integral structure. A porous carbon paper substrate serves as a structural support for the electrocatalyst layer and as the current collector. The operating temperature is maintained between 150 to 220 °C. At lower temperatures, phosphoric acid tends to be a poor ionic conductor and poisoning of the electrocatalyst at the anode by CO becomes severe. 

Theory. Since electrocatalysis is one of the major uses for modified electrodes, theoretical work has centered around optimization of electrocatalytic processes. When electron transfer between catalyst and substrate is slow, it is useful to increase the concentration of catalytic sites at the surface of the electrode. When this is done via adsorption of a catalyst-containing polymer, the thickness and permeability toward substrate and electrolyte of the polymeric film will help determine the efficiency of electrocatalysis (51,52). 

The further development in the field of electrochemical power sources will be considerably influenced by the interaction of fundamental research (e.g. on electrocatalysis, solid state structure, transport phenomena, electrochemical kinetics and technology) and applied research, where progress will depend decisively on a successful cooperation in science between electrochemists, physicists, experts in materials, engineering, chemical engineering, electrical engineers a.o. Research work will probably concentrate on special power sources which are advantageously applied only in certain fields, as illustrated by the lithium solid electrolyte cell for pacemakers. 

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