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Impact of Ionomer Containing Particles on the
Selective Mechanical Separation Processes of PEM Water
Electrolyzer Recycling for PGM Recovery
Sohyun Ahn, Martin Rudolph
Helmholtz Institute Freiberg for Resource Technology (HIF),
Helmholtz-Zentrum Dresden–Rossendorf e.V. (HZDR), Freiberg, Germany
ABSTRACT: As water electrolysis technology becomes more established, the development of the recycling
processes for critical raw materials is important. This study presents the investigation of mechanical recycling
processes of polymer electrolyte membrane (PEM) electrolyzers containing noble metals. According to a
previous study, the representative materials of the catalyst containing particles showed a clear difference in their
hydrophobicity and effective separation was achieved in binary particle systems. This study demonstrates the
impact of ionomer used in catalytic inks on separation process. The ionomer, which is a fluorinated polymer
with ionizable groups (in our case sulfonic acid for hydrogen ion transport) is not only used to separate two
electrodes in the form of a solid film but is also used in the process of manufacturing catalyst ink in the form of
Nafion resin acting as a binder influencing the wettability of the catalyst particles. The surface characterizations
of ionomer-containing particles and the selective separation process exploiting liquid-liquid extraction allow us
to estimate particle behaviors. The results showed that the presence of ionomer had a negligible effect on the
wettability of the cathode material, regardless of its content, but changed the wettability of the anode material
from hydrophilic to partially hydrophobic.
INTRODUCTION
Water electrolysis technology is considered one of the
promising technologies for green hydrogen production.
Hydrogen has a high energy density of about 140 MJ/kg,
which is three times higher than that of typical present fuels
such as gasoline (44 MJ/kg). For that reason, hydrogen is
accounted as an attractive energy source. In electrolysis sys-
tems, electricity generated from renewable energy sources
is supplied and water is electrochemically converted into
green hydrogen without carbon containing emissions.
Currently, researchers are actively working on improving
the performance of water electrolyzers, developing better
materials, designing processes for mass production, and
standardizing them. The most widely investigated elec-
trolyzers are alkaline electrolytic cells, polymer electrolytic
cells, and solid oxide electrolytic cells. Especially, polymer
electrolyte membrane water electrolysis (PEM-EL) shows
high efficiency compared to other electrolysis types at
ambient temperature conditions.
A PEM electrolyzer stack is structured as follows: sepa-
rating plates, current collectors, and catalyst coated mem-
branes (CCMs). The current separating plate is made of
titanium, graphite, or coated stainless steel to provide a
conductive path for the heat and electrons. The materials
for the current collector must be corrosion resistant due to
the overall reaction such as oxygen evolution reaction and
Impact of Ionomer Containing Particles on the
Selective Mechanical Separation Processes of PEM Water
Electrolyzer Recycling for PGM Recovery
Sohyun Ahn, Martin Rudolph
Helmholtz Institute Freiberg for Resource Technology (HIF),
Helmholtz-Zentrum Dresden–Rossendorf e.V. (HZDR), Freiberg, Germany
ABSTRACT: As water electrolysis technology becomes more established, the development of the recycling
processes for critical raw materials is important. This study presents the investigation of mechanical recycling
processes of polymer electrolyte membrane (PEM) electrolyzers containing noble metals. According to a
previous study, the representative materials of the catalyst containing particles showed a clear difference in their
hydrophobicity and effective separation was achieved in binary particle systems. This study demonstrates the
impact of ionomer used in catalytic inks on separation process. The ionomer, which is a fluorinated polymer
with ionizable groups (in our case sulfonic acid for hydrogen ion transport) is not only used to separate two
electrodes in the form of a solid film but is also used in the process of manufacturing catalyst ink in the form of
Nafion resin acting as a binder influencing the wettability of the catalyst particles. The surface characterizations
of ionomer-containing particles and the selective separation process exploiting liquid-liquid extraction allow us
to estimate particle behaviors. The results showed that the presence of ionomer had a negligible effect on the
wettability of the cathode material, regardless of its content, but changed the wettability of the anode material
from hydrophilic to partially hydrophobic.
INTRODUCTION
Water electrolysis technology is considered one of the
promising technologies for green hydrogen production.
Hydrogen has a high energy density of about 140 MJ/kg,
which is three times higher than that of typical present fuels
such as gasoline (44 MJ/kg). For that reason, hydrogen is
accounted as an attractive energy source. In electrolysis sys-
tems, electricity generated from renewable energy sources
is supplied and water is electrochemically converted into
green hydrogen without carbon containing emissions.
Currently, researchers are actively working on improving
the performance of water electrolyzers, developing better
materials, designing processes for mass production, and
standardizing them. The most widely investigated elec-
trolyzers are alkaline electrolytic cells, polymer electrolytic
cells, and solid oxide electrolytic cells. Especially, polymer
electrolyte membrane water electrolysis (PEM-EL) shows
high efficiency compared to other electrolysis types at
ambient temperature conditions.
A PEM electrolyzer stack is structured as follows: sepa-
rating plates, current collectors, and catalyst coated mem-
branes (CCMs). The current separating plate is made of
titanium, graphite, or coated stainless steel to provide a
conductive path for the heat and electrons. The materials
for the current collector must be corrosion resistant due to
the overall reaction such as oxygen evolution reaction and