Chemical Engineering September 2020 - 29

Evonik; Source: Maximilian Nertinger
The reaction in the electrode
The electrode layer also consists of an ionconducting
polymer within which metallic
catayst particles are suspended
Ion-conducting membrane
The heart of the electrolyzer
is the membrane, which is
made from a polymer that is
permeable to hydroxide ions
but not to the hydrogen that
arises
Bipolar plate
This surrounds the
membrane-electrode unit and
is equipped with channels for
the water and gas transport
Gas diffusion layer
The gases that arise at the
electrodes are led off via a
layer of porous material
Carbon
fibers
H2O
Seal
This ensures that gas and water only enter
and leave the cell via the desired routes
FIGURE 4. AEM electrolyzers are poised to combine the benefits of alkaline and PEM electrolyzers, which
are currently the dominant technologies on the market
area components to find defects that
could impact durability. " Some of the
other major areas of development include:
membrane-coating techniques
and simplifying membrane fabrication;
optimizing the porous transport layer;
and reducing precious-metals content.
In addition, H2@Scale is working on
two first-of-their-kind nuclear-to-H2
projects in the U.S.
H2@Scale is focusing on multiple
hydrogen production, storage, distribution
and utilization needs, including
PEM electrolyzers, which are gaining
traction in the market, but still have
potential for major cost reductions.
Feedwater quality is another emerging
area of research for the project, says
Satyapal. " We have a few early-stage
projects investigating the ability to use
dirty water or salt water, as opposed
to requiring high-purity water for electrolysis, "
she adds. " We also have
a first-of-its-kind project in the U.S.
where we are producing H2 with an
electrolyzer and using a biological system
to make renewable methane with
H2 and CO2, " says Satyapal.
Synergy with natural gas is another
area with significant interest, specifically
in blending H2 and natural gas,
with the potential to inject hydrogen
into natural-gas pipelines. However,
with H2 blending, materials compatibility
can be a major concern depending
on materials used, and much research
activity involves the effects of hydrogen
on embrittlement and its impact
on both metals and polymers, as addressed
by DOE's H-Mat consortium.
A significant milestone in H2 blending
took place in July, when Baker Hughes
(Houston; www.bakerhughes.com)
and Snam (San Donato Milanese, Italy;
www.snam.it) completed testing of the
world's first " hybrid " hydrogen turbine
designed for a gas network, with the
ultimate goal of injecting H2 blended
with natural gas into Snam's current
transmission infrastructure.
Advancing PEM electrolysis
Hoeller Electrolyzer GmbH (Wismar,
Germany; www.hoeller-electrolyzer.
com) has developed an optimized
cell-surface technology for compact
PEM electrolyzers (Figure 3) that reduces
the amount of precious metals
required and increases operating
pressure. Hoeller is designing its PEM
cell stacks with demanding installations
in mind, such as integrating the
stack directly into the head of a wind
turbine. " The key advantage of PEM
electrolysis is that the H2 production
almost instantaneously changes with
the energy provided, so processes
with a changing need for H2 are an
ideal match, " says Matthias Kramer,
chief financial officer at Hoeller. According
to Hoeller, its stacks can handle
load changes from 0 to 100% of nominal
load within seconds. While PEM is
versatile in the face of shifting demand,
Kramer also emphasizes its ability to
operate continuously. Furthermore,
the stack is capable of pressurization
to 50 bars or higher, making direct
ChemiCal engineering www.Chemengonline.Com September 2020
Catalyst
particles
H2O
O2
Anode
H2O
O2
Cathode
OH-
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e-
OH-
H+
H+
H2O
H2
H2O
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29
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Chemical Engineering September 2020

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