Aqueous electrolyte-based fuel cells

Aqueous, alkaline fuel cells, as used by NASA for supplemental power in spacecraft, are intolerant to C02 in the oxidant. The strongly alkaline electrolyte acts as an efficient scrubber for any C02, even down to the ppm level, but the resultant carbonate alters the performance unacceptably. This behavior was recognized as early as the mid 1960 s as a way to control space cabin C02 levels and recover and recycle the chemically bound oxygen. While these devices had been built and operated at bench scale before 1970, the first comprehensive analysis of their electrochemistry was put forth in a series of papers in 1974 [27]. The system comprises a bipolar array of fuel cells through whose cathode chamber COz-containing air is passed. The electrolyte, aqueous Cs2C03, is immobilized in a thin (0.25 0.75 mm) membrane. The electrodes are nickel-based fuel cell electrodes, designed to be hydrophobic with PTFE. 

A second class [ 16] is one that may enjoy increased interest in the future because of the presence of one of its members in the first industrial IL process [lb], and also because of the new finding that its members can have aqueous solution-like conductivities [17] and can serve as novel electrolytes for fuel cells [18]. This class is closely related to the first but differs in that the cation has been formed by transfer of a proton from a Br0nsted acid to a Br0nsted base. The process is reversible, depending on how large the free energy of proton transfer is. When the gap across which... 

Recently, rhodium and ruthenium-based carbon-supported sulfide electrocatalysts were synthesized by different established methods and evaluated as ODP cathodic catalysts in a chlorine-saturated hydrochloric acid environment with respect to both economic and industrial considerations [46]. In particular, patented E-TEK methods as well as a non-aqueous method were used to produce binary RhjcSy and Ru Sy in addition, some of the more popular Mo, Co, Rh, and Redoped RuxSy catalysts for acid electrolyte fuel cell ORR applications were also prepared. The roles of both crystallinity and morphology of the electrocatalysts were investigated. Their activity for ORR was compared to state-of-the-art Pt/C and Rh/C systems. The Rh Sy/C, CojcRuyS /C, and Ru Sy/C materials synthesized by the E-TEK methods exhibited appreciable stability and activity for ORR under these conditions. The Ru-based materials showed good depolarizing behavior. Considering that ruthenium is about seven times less expensive than rhodium, these Ru-based electrocatalysts may prove to be a viable low-cost alternative to Rh Sy systems for the ODC HCl electrolysis industry. 

Direct methanol fuel cell (DMFC) was developed in 1950s-1960s, based on the liquid alkaline or aqueous acid solution as the electrolyte. It converts the methanol directly into electricity, instead of using indirectly produced hydrogen from methanol through the reforming process. Today, DMFC commonly refers to as the one that employs PEM as the electrolyte. Fuel for DMFC is a dilute solution of methanol, usually 3-5 wt% in water. The size of DMFC can be considerably smaller than PEMFC because of the elimination of fuel processor, and complex humidification and heat management systems. The performance of DMFC is relatively low compared to that of PEMFC. 

In a recent patent application, Angell et al. described a series of alkylammonimn PILs, which are potentially useful as nonaqueous electrolytes in high-temperature polymer membrane fuel cells. The PILs investigated were stable to temperatures between 200 and 250 C, had conductivities comparable to aqueous solutions, and could be enhanced through the addition of a base with a pA a value intermediate between that of the acid and the base. ... 

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