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

electrolyzers, the high cost of membrane, electrocatalyst (doped with noble metal, such as
Pt, Ir, Ru), the requirement of highly “clean” water and a high cost of constructional
materials limit the wide usage of this type electrolyzer. In spite of their high costs, there are
several advantages of using PEM electrolyzers. They produce high purity (99.999%)
hydrogen and oxygen (Grigoriev et al. 2006) which are very important for some
applications, such as submarines and space shuttles. In addition, high purity hydrogen could
be used in PEM fuel cells without requiring after-purification step unlike the alkaline
electrolysis method. PEM electrolyzers could also work at high pressures up to 300 bar;
thus reducing the compressor cost. Up until now, the most efficient electrolysis using PEM
electrolyzers have been reported to operate at 1.556 cell voltage and 1Amp/cm 2 at 80 o C
(Yamaguchi et al. 2000), hence achieving 95.1% efficiency (based on high heating value of
hydrogen). Moreover, PEM electrolyzer can operate over a wide range of temperature,
pressure and current density as compared to alkaline-type water electrolyzer (Tsutomu and
Sakaki 2003). This unique feature makes PEM electrolyzers suitable for integrating with
renewable energy sources which usually have variable electricity output due to their
uncontrolled primary energy inputs. For example, the photovoltaic panels produce power
proportional to solar intensity, which looks like a bell shape curve during the day or wind
turbines produce power with the cubic function of the wind speed. Thus, hydrogen
production based on PEM technology is a promising option for many renewable sources as
it stores the uncontrolled production of electricity.
There are some difficulties with PEM electrolysis that need to be addressed before
being a viable choice of power generation for future “hydrogen economy”. The most
obvious and commonly known obstacle is cheap electricity supply for electrolysis reaction.
Theoretical electricity equivalent of 1kg hydrogen is about 40kWh, which is the main
hydrogen production cost. In order to reduce the electricity cost of the electrolysis
operation, researchers all over the world are trying to combine electrolyzers and renewable
electricity generators with more efficient coupling methods (Bilgen 2000, Ahmad et al.
2006). Also electrolyzers are being interconnected to currently available grid system during
the off-peak period to increase the load factor of the electric grid and use less expensive
electricity (Oi and Sakaki 2003). Another way of reducing the electricity usage is to
increase the efficiency of electrolyzers. Improvement of the membrane material and the
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