hydrogen production from water using solar cells powered nafion ...

another optimization should be done between the electricity price, purchased membrane
cost and the produced hydrogen price to find the ideal temperature for a PEM electrolyzer.
There are several theoretical models to explain the current voltage and temperature
characteristics of PEM electrolyzers. Choi and coworkers model assumes that the efficiency
of a single or a stack of electrolyzer cells could be affected by either component(s) or
operating parameter(s) of the electrolyzer (Choi et al. 2004). In fact their model separates
the components of electrolyzer and reveals its electric circuit equivalent. The model
provides a fairly good relation between the voltage and the current in Nernst potential
through the exchange current densities of anode and cathode electrodes according to Butler-
Volmer kinetics.
2.2.1.2. Proton Exchange Membrane of an Electrolyzer Cell
Proton exchange membrane (PEM) is a proton conducting polymeric membrane
which acts as an electrolyte for both the fuel cell and the electrolysis applications. The first
PEM used in a fuel cell is developed by General Electric in early sixties for use in a space
mission for NASA. This premature copolymer showed insufficient oxidative stability under
its operating conditions and it could work properly for only 500h during the mission. A
major breakthrough in PEM technology came up with the announcement of
perfluorosulfonic acid membranes called Nafion ® by DuPont in 1967. (Larminie and Dicks
2003).
Typically perfluorosulfonic acid membranes are poor proton conductors unless
water is present in the medium. Therefore the hydration of PEM is very important with
respect to the performance of the cell. Although this is important for fuel cells, it is usually
not the case for the electrolysis applications since the one side of the membrane is always
introduced with water as a reactant.
Einsla 2005 reported that a typical proton exchange membrane had to match the
following requirements in order to be able to be used in fuel cells and electrolyzers;
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