Charge carriers in alkaline direct oxidation fuel cells

Abstract

Contrary to conventional wisdom, this study demonstrates that the main charge carrier of alkaline direct oxidation fuel cells (DOFCs) running on ethanol with a cation exchange membrane (typically Nafion) is OH À ions, rather than Na + ions.

Comparison of different types of membrane in alkaline direct ethanol fuel cells

“…It can be seen that the conductivities of the three membranes show an approximate Arrhenius-type temperature dependence, and the respective apparent activation energy is 13.30 kJ mol À1 for the AEM, 15.84 kJ mol À1 for the CEM and 16.97 kJ mol À1 for the APM. The apparent activation energy of the three membranes is comparable, implying that the three membranes have the similar ionic conduction mechanism [30], which is consistent with our recent work [22].…”

“…This finding is similar to that reported elsewhere [28]. The comparison in the peak ionic conductivity of the three membranes shows that the AEM has much higher conductivity (30.1 mS cm À1 ) than that of both the CEM and APM do (10.7 mS cm À1 and 17.2 mS cm À1 ), because both functional groups and alkali-doped free volumes can conduct anions [22]. Hence, in terms of the ionic conductivity, the AEM is the best membrane among the three membranes.…”

“…The reason why there exists the peak conductivity is explained as follows. Generally, ions through the membrane in the alkaline DEFC system are conducted by both functional groups and alkali-doped free volumes [22]. Once a membrane is soaked in an alkaline solution, the membrane state is changed: alkali-doped free volumes are formed, which can conduct ions under an electric field in a fashion similar to an aqueous solution [10].…”

Measurement of water uptake in thin-film Nafion and anion alkaline exchange membranes using the quartz crystal microbalance

“…Whilst the exact chemical composition of the Tokuyama membrane is not certain, it is known to be made up of a hydrocarbon backbone with terminated quaternary ammonium functional groups. Many experiments have been conducted to characterise AAEM performance, durability and electroosmotic drag [20][21][22] and it is proposed that as with Nafion, the ionomer hydrates and hydrophilic regions will swell, though little is understood about how AAEMs take up water or how swelling affects ion conductivity. It has been well documented that AAEMs have a significantly lower ionic conductivity than the PEM equivalent [13,14].…”

Three-dimensional nanoporous gold–cobalt oxide electrode for high-performance electroreduction of hydrogen peroxide in alkaline medium

“…Oxygen from ambient air is generally required as an oxidant in fuel cell devices [3], while an additional oxygen tank in the system is needed in oxygen-free environments such as underwater and outer space, which significantly decreases the energy density of fuel cells. In this context, there has been considerable interest in developing liquidbased fuel cells that use hydrogen peroxide as an alternative oxidant [4]. Examples of these types of fuel cells include metal/ hydrogen peroxide fuel cell [5], direct borohydride/hydrogen peroxide fuel cell [6] and hydrazine/hydrogen peroxide fuel cell [7].…”