Alkaline URFCs

Support and catalyst materials suitable for use in oxygen electrodes operated with 30% KOH at 80 °C are investigated in terms of 

Current (Acm- ) Voltage Ely (V) Voltage FC (V) Efficiency Ely Efficiency FC Efficiency round trip 

The mechanisms of oxygen evolution and reduction on Teflon-bonded NiCo204 spinel in alkaline solutions were also examined. The influence on the electrode performance of KOH concentration from 0.1 to 1 M and electrolyte temperature from 25 to 75 °C was also studied [48]. A selection of values measured in real cell operation at an electrolyte temperature of80°Cand 30% KOH is given in Table 8.6. The column round-trip efficiency is the product of the efficiency in electrolyzer (Ely) and PC modes. 

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Patent concerning the alkaline URFC (Apollo program) [26]... 

From the mid-1970s to the end of the 1980s, the existing FC concepts were further improved. The development of electrodes and cells for alkaline URFCs started and powerful and durable electrodes were identified [15, 16]. Research was also focused on the development of SOE electrolyzers. In Europe, the USA, and Japan, different programs were implemented focusing on the improvement of this technology [17, pp. 227-242]. 

If an RFC system has a separate FC and electrolyzer, it is possible to choose different materials for the electrolyzer and for the FC electrodes. The materials can be adapted in terms of ideal performance and high durabihty. If a URFC system is considered, the electrodes have to be suitable for both hydrogen consumption and evolution or oxygen consumption and evolution. This bifunctional operation subjects the electrodes to considerable stress and can reduce their performance and durability. In addition to the type of operation (conventional or bifunctional), the composition of the electrodes is greatly dependent on the electrolytes used. In the following subsections, the different electrolytes (alkaline, PEM, SOE) are described and also suitable electrodes for each type of operation. 

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