|dc.description.abstract||The use of potassium carbonate-bicarbonate buffers as an
alternative to strong acids as CO2 rejecting electrolytes for low
temperature fuel cells has been investigated.
The physical properties which determine the suitability
of buffer electrolytes for fuel cells, conductivity and pu, have
been measured for solutions of K2C03 (a) under N2 and (b) under
CO2 at 1 atmosphere pressure; and the behaviour of fuel cell
electrodes in these electrolytes has also been studied. These
conditions were chosen to represent the best and worst situations
likely to occur with potassium carbonate-bicarbonate electrolytes
in fuel cells.
Conductance measurements have been carried out at 25°C, 40°C,
60°C and 75°C, measurements at low concentrations were carried
out with a conventional conductance cell, those at high concentrations
were carried out with an 'electrodeless' conductance cell.
Concentrations up to saturation have been studied. These experiments
represent the first complete study of such solutions over the full
concentration range and at temperatures other than 25°C.
pH measurements on these solutions were made by use of a
novel method in which e.m.f values of cells containing hydrogen
ion responsive glass electrodes and potassium ion responsive glass
electrodes were determined. These measurements covered the full
concentration range at 25°C, 45°C and 65°C. (Attempts to obtain
reproducible results at 85°C failed.)
Density measurements were made, primarily to interpret
trio conductivity results, by a pyknometric technique over the full
range of concentration at 25°C, 40°C, 60°C and 75°C. The results
obtained for the K2CO3 solutions under N2 are compared and
contrasted with the only available data and the values reported in
this work are shown to be preferable. The results obtained for
solutions under CO2 are not available elsewhere.
The behaviour of fuel cell electrodes showed that
limiting current densities with hydrogen electrodes can be
increased by the use of thinner electrode substrates (a
quantitative analysis of these results is given).
'ohmic free' polarisation is reduced with oxygen electrodes as
the ph of the buffer electrolyte is increased and a quantitative description of the variation at two current densities is given.
1mpirical expressions are given for the variaions of
conductivity and density with concentration. i method of
calculation of the ph values of the solutions under various
conditions of temperature and partial pressure of CO2 is reported
and is shown to agree well with the experimental results. The
sum of this information provides the means to estimate the optimum
conditions for the use of the potassium carbonate—bicarbonate electrolyte in fuel cells.
New values of limiting conductivity and apparent molal volume have been obtained for the species K2CO3, KHCO3 and CO2
(for C02 limiting apparent molal volume only) in aqueous solution from the analysis of the results at low concentrations.||en