3252 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
hydrogen evolution reaction. Carbon materials cannot be
used as gas diffusion layers but sintered titanium particles
is sufficient for long term operation. A PEM is also called
proton exchange membrane and as the name implies, in the
center of the electrode assembly, the polyelectrolyte mem-
brane allows proton transport from the anode to the cath-
ode. The commercial polymer Nafion ®, which is a so-called
ionomer, is regarded as the most common membrane mate-
rial. The CCM is prepared with this thin membrane and
porous catalyst particles on both sides, acting as the elec-
trodes. During the manufacturing processes of the CCM,
different content of the ionomer is added in the catalysts
ink for better stability and better performances. However,
the state-of-the-art materials used as the electrodes have
high supply risk and economic value. For instance, Iridium
oxide or Ruthenium oxide are considered the most efficient
materials for the oxygen evolution reactions and platinum/
palladium (often coated nanoscopically on carbon black)
are used as catalyst for the hydrogen evolution reactions.
These platinum group metals (PGMs) are defined as critical
raw materials by the European Union, which are strategi-
cally to be recycled (European Commission, Smes, Grohol,
&Veeh, 2023). However, despite the importance of recy-
cling, there has been a lack of research on the mechanical
recycling of PEM electrolyzers so far.
Not only to avoid the waste of high value materials, but
also to consider the development of alternative materials
of PGMs, carbon black and TiO2 were taken into account
as representative materials in the previous study and are
applied in this study as well. In our previous work, an inves-
tigation of the wetting characteristics of representative cata-
lyst materials for mechanical separation processes and the
wettability of used catalyst materials in PEM-EL showed a
significant difference between the two electrode materials
(Ahn &Rudolph, 2024). Compared to the other chemical
recycling strategies, physical recycling processes consume
less energy and have shorter recovery routes (Zhou, Yang,
Du, Gong, &Luo, 2020). However, traditional mechanical
separation technologies such as froth flotation have a chal-
lenge with ultra-fine particles (well below 10 μm). Hence,
the development of novel mechanical selective separation
of fine catalyst particles shall offer an environmentally
friendly approach for the recycling. It was confirmed that
materials used on the anode side have rather hydrophilic
surface characteristics, while the cathode catalysts appear
hydrophobic. The particle mixture of representing catalyst
materials, TiO2 and Carbon black were selectively sepa-
rated with recovery rates of 97 %and 99 %.Investigating
the representative materials plays an important role for fur-
ther investigations because many studies have concentrated
on reducing and replacing PGMs on CCMs and TiO2 has
the potential to be considered as an alternative material.
However, the influence of ionomer in the catalyst ink
was not covered in the previous study. Since ionomer has
both hydrophobic tetrafluoroethylene (PTFE) backbone
and hydrophilic sulfonic acid group, distribution of iono-
mer will change surface properties of the particles, which
affects the separation processes based on particle wettabil-
ity difference. For instance, it is reported that the sulfonic
acid group attracts polar molecules and makes the catalyst
layer more hydrophilic (Carmo, Fritz, Mergel, &Stolten,
2013). On the contrary, it acts as a hydrophobic agent for
the catalyst layer (Vol’fkovich, Sosenkin, &Nikol’skaya,
2010). Therefore, wettability characterization of ionomer
containing particles is essential for the development of fur-
ther separation processes to improve catalyst recovery. As
an extension of the previous study, the corresponding com-
mercial materials including different ionomer content are
considered as the feed materials. The impact of the pres-
ence of different concentrations of the ionomer (Nafion ®)
is being investigated first with the application of different
characterization techniques. Consequently, particles are
separated by using a method based on liquid-liquid extrac-
tion but applied to particles.
EXPERIMENTAL
Materials and Sample Preparation
As described in the previous section, a commercial carbon
black (Vulcan XC 72, 99 %)offered from Cabot, USA is
used as cathode material and for the anode representing
material, Titanium (IV) oxide (637262, rutile, 99.5 %)is
purchased from Sigma Aldrich, Germany. As an ionomer,
the Nafion ™ Solution (NS-5, PFSA 5 wt. %)is purchased
from QuinTech, Germany.
Ionomer containing particles are prepared by follow-
ing the equation introduced in the paper from Scheepers
et al.(2018) The Nafion content (%)is defined as Nafion
weight (g) by the sum of dry catalysts weight (g) and Nafion
weight (g). Dispersions are prepared with 90 %by weight
of liquid medium consisting of isopropanol (AE73.1,
99.95%, Carl Roth, Germany) and DI water, 10 %by
weight of sum of catalysts particles and Nafion. The pre-
pared catalyst ink is dispersed using sonication, Bandelin
Sonoplus UW 2200, for homogenizing and dried under
atmospheric condition without artificial drying methods.
To date, a few studies focused on an optimal loading range
of ionomer which was reported in the range of 20 to 30 %.
In this study, 0, 20, 40 %of Nafion content for each elec-
trode material is prepared. After the complete evaporation
of solvent, the dried samples are ground by mortar and
hydrogen evolution reaction. Carbon materials cannot be
used as gas diffusion layers but sintered titanium particles
is sufficient for long term operation. A PEM is also called
proton exchange membrane and as the name implies, in the
center of the electrode assembly, the polyelectrolyte mem-
brane allows proton transport from the anode to the cath-
ode. The commercial polymer Nafion ®, which is a so-called
ionomer, is regarded as the most common membrane mate-
rial. The CCM is prepared with this thin membrane and
porous catalyst particles on both sides, acting as the elec-
trodes. During the manufacturing processes of the CCM,
different content of the ionomer is added in the catalysts
ink for better stability and better performances. However,
the state-of-the-art materials used as the electrodes have
high supply risk and economic value. For instance, Iridium
oxide or Ruthenium oxide are considered the most efficient
materials for the oxygen evolution reactions and platinum/
palladium (often coated nanoscopically on carbon black)
are used as catalyst for the hydrogen evolution reactions.
These platinum group metals (PGMs) are defined as critical
raw materials by the European Union, which are strategi-
cally to be recycled (European Commission, Smes, Grohol,
&Veeh, 2023). However, despite the importance of recy-
cling, there has been a lack of research on the mechanical
recycling of PEM electrolyzers so far.
Not only to avoid the waste of high value materials, but
also to consider the development of alternative materials
of PGMs, carbon black and TiO2 were taken into account
as representative materials in the previous study and are
applied in this study as well. In our previous work, an inves-
tigation of the wetting characteristics of representative cata-
lyst materials for mechanical separation processes and the
wettability of used catalyst materials in PEM-EL showed a
significant difference between the two electrode materials
(Ahn &Rudolph, 2024). Compared to the other chemical
recycling strategies, physical recycling processes consume
less energy and have shorter recovery routes (Zhou, Yang,
Du, Gong, &Luo, 2020). However, traditional mechanical
separation technologies such as froth flotation have a chal-
lenge with ultra-fine particles (well below 10 μm). Hence,
the development of novel mechanical selective separation
of fine catalyst particles shall offer an environmentally
friendly approach for the recycling. It was confirmed that
materials used on the anode side have rather hydrophilic
surface characteristics, while the cathode catalysts appear
hydrophobic. The particle mixture of representing catalyst
materials, TiO2 and Carbon black were selectively sepa-
rated with recovery rates of 97 %and 99 %.Investigating
the representative materials plays an important role for fur-
ther investigations because many studies have concentrated
on reducing and replacing PGMs on CCMs and TiO2 has
the potential to be considered as an alternative material.
However, the influence of ionomer in the catalyst ink
was not covered in the previous study. Since ionomer has
both hydrophobic tetrafluoroethylene (PTFE) backbone
and hydrophilic sulfonic acid group, distribution of iono-
mer will change surface properties of the particles, which
affects the separation processes based on particle wettabil-
ity difference. For instance, it is reported that the sulfonic
acid group attracts polar molecules and makes the catalyst
layer more hydrophilic (Carmo, Fritz, Mergel, &Stolten,
2013). On the contrary, it acts as a hydrophobic agent for
the catalyst layer (Vol’fkovich, Sosenkin, &Nikol’skaya,
2010). Therefore, wettability characterization of ionomer
containing particles is essential for the development of fur-
ther separation processes to improve catalyst recovery. As
an extension of the previous study, the corresponding com-
mercial materials including different ionomer content are
considered as the feed materials. The impact of the pres-
ence of different concentrations of the ionomer (Nafion ®)
is being investigated first with the application of different
characterization techniques. Consequently, particles are
separated by using a method based on liquid-liquid extrac-
tion but applied to particles.
EXPERIMENTAL
Materials and Sample Preparation
As described in the previous section, a commercial carbon
black (Vulcan XC 72, 99 %)offered from Cabot, USA is
used as cathode material and for the anode representing
material, Titanium (IV) oxide (637262, rutile, 99.5 %)is
purchased from Sigma Aldrich, Germany. As an ionomer,
the Nafion ™ Solution (NS-5, PFSA 5 wt. %)is purchased
from QuinTech, Germany.
Ionomer containing particles are prepared by follow-
ing the equation introduced in the paper from Scheepers
et al.(2018) The Nafion content (%)is defined as Nafion
weight (g) by the sum of dry catalysts weight (g) and Nafion
weight (g). Dispersions are prepared with 90 %by weight
of liquid medium consisting of isopropanol (AE73.1,
99.95%, Carl Roth, Germany) and DI water, 10 %by
weight of sum of catalysts particles and Nafion. The pre-
pared catalyst ink is dispersed using sonication, Bandelin
Sonoplus UW 2200, for homogenizing and dried under
atmospheric condition without artificial drying methods.
To date, a few studies focused on an optimal loading range
of ionomer which was reported in the range of 20 to 30 %.
In this study, 0, 20, 40 %of Nafion content for each elec-
trode material is prepared. After the complete evaporation
of solvent, the dried samples are ground by mortar and