The_Catalyst_Review_October_2023 - 9

SPECIAL FEATURE
PEM and SOEC are achieving exceptional improvements
driven by advances in efficiency, capital cost reduction
and use of sustainable electrical power. In the following
paragraphs, we will describe the key nature of these
three electrolysis technologies in more detail.
2.1. Alkaline Electrolysis Technology
Alkaline water electrolysis (AEL) is a mature and safe
technology that has been used in many industrial
applications. Figure 3 is a block diagram of an AEL
system to produce hydrogen (and oxygen as by-product),
while Figure 4 is a picture of the Fukushima AEL plant in
Japan. Several megawatt industrial electrolysis plants are
running for the large-scale production of hydrogen. From
an economic viewpoint, the lifetime of these systems
(several tens of thousands of hours of operation) can be
considered as satisfactory for continuous operation, and
which has been proven to be profitable. However, the
process requires significant operation and maintenance
costs and investment capital, which are not as large as
for PEM or SOEC technology [O. Schmidt et al, 2017]. In
addition, current alkaline electrolysis cells can hardly run
at low current density, which is a limitation in view of the
emerging hydrogen markets of transportation requiring
to work with renewable energy sources. In the past, the
electric efficiency was about 60%, but modern plants can
achieve 75%.
2.2. PEM Electrolysis Technology
PEM water electrolysis is a relativity new development.
A diagram of the PEM technology is shown in Figure
5. In this electrolysis system, water is electrochemically
dissociated into H2
at the cathode and oxygen at the
anode, using a solid proton-conducting membrane
to separate the electrodes. The supplied power helps
the flow of electrons while the H2
ions move to the
cathode through the semipermeable proton exchange
membrane. At the cathode, these electrons recombine
with the two protons to give one molecule of H2
. The H2
gas generated has a remarkably high purity of 99.99%.
Platinum group metals are used for electrodes. At this
moment, the electric power efficiency is estimated to
be 65%, working at around 100 °C and at less than
two hundred bars. Economic information obtained
from " Giner elx " in 2018, showed that for generating
hydrogen at 740 Ton/year, one needed a hydrogen sales
price of $5293/Ton. Electricity was used at a price of
$0.0625/kWh. By 2050, the company targets to produce
hydrogen in units of 10.000 Ton/year, at an efficiency
of 82% and a lower electricity cost of $0.03/kWh. The
calculated required hydrogen sales price will drop, which
will be achieved with a lower investment cost.
Figure 4. Fukushima AEL Hydrogen plant
Modified diagram based on Matzen et al, (2015)
Figure 3. Block diagram of hydrogen production by AEL electrolysis
Modified diagram based on Matzen et al, (2015)
Figure 5. Diagram of Polymer Electrolyte Membrane (PEM) technology
Based on information from www.siemens-energy.com
The Catalyst Review
October 2023
9
http://www.siemens-energy.com
The_Catalyst_Review_October_2023

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