3276
Recycling of Raw Materials in Solid Oxide Cells: Ultrasonic
Decoating for Mechanical Liberation and Separation of
Perovskite Materials
Carlo Kaiser, Urs A. Peuker
Institute of Mechanical Process Engineering and Mineral Processing,
Technische Universität Bergakademie Freiberg, Germany
ABSTRACT: Solid oxide cells (SOC) are becoming increasingly important as hydrogen production capacity
increases. The layered cells contain high concentrations of critical raw materials, including nickel and rare
earths. However, there are currently no recycling processes available. Initial approaches published mostly depend
on manual labor or hydrometallurgical approaches that generate environmentally hazardous residues. A first
suitable recycling approach that avoids both of these problems is ultrasonic decoating. Ultrasonic decoating has
proven to selectively remove the perovskite layers from SOC. Although ultrasonic decoating is easy to apply in
theory, it can be challenging in a real recycling process due to the orientation dependency of the cells during
stressing combined with an easily broken cell. The aim of this study is therefore to adapt ultrasonic decoating to
comminuted SOC. To do this, a cell was comminuted and subsequently sieved. The coarse cell particle fractions
were then exposed to ultrasound. The particle size distribution and composition were employed to assess the
decoating and the selectivity of the comminution. It has been shown that perovskite materials accumulate in
the fine fractions as a result of comminution. Furthermore, perovskite materials can be selectively liberated and
separated from cell particles by ultrasound.
INTRODUCTION
Hydrogen plays a key role as an energy carrier in the current
energy transition (Capurso et al. 2022, Staffell et al. 2019).
Global hydrogen production capacity, water electrolyzers
in particular, is therefore being greatly expanded. Based
on announced projects, electrolyzer capacity is expected to
increase from 700 MW at the end of 2022 to 175–420 GW
in 2030 (IEA 2023).
Among conventional electrolyzers, solid oxide electro-
lyzers (SOEL) are characterized by particularly high electri-
cal efficiency and feasible reversible operation as fuel cells
(Capurso et al. 2022, Ji and Wang 2021, Sebbahi et al.
2022). Another advantage is that SOEL are not limited to
hydrogen, but are also suitable for the production of syn-
gas (Cinti et al. 2016, Wang et al. 2019). However, the high
operating temperature leads to a high wear of the materi-
als. This results in a short lifetime of 2–3 years (Nechache
and Hody 2021, Sun et al. 2015), which prevents SOEL
from achieving a market breakthrough (Ozturk and Dincer
2021, Pandiyan et al. 2019). This is further aggravated by
the lack of efficient, cost-effective and scalable end-of-life
strategies, which are essential in view of the raw materials
used (Kiemel et al. 2021, Valente et al. 2019).
SOELs generally consist of repeating, layered compo-
nents, with the core component being the solid oxide cell
Recycling of Raw Materials in Solid Oxide Cells: Ultrasonic
Decoating for Mechanical Liberation and Separation of
Perovskite Materials
Carlo Kaiser, Urs A. Peuker
Institute of Mechanical Process Engineering and Mineral Processing,
Technische Universität Bergakademie Freiberg, Germany
ABSTRACT: Solid oxide cells (SOC) are becoming increasingly important as hydrogen production capacity
increases. The layered cells contain high concentrations of critical raw materials, including nickel and rare
earths. However, there are currently no recycling processes available. Initial approaches published mostly depend
on manual labor or hydrometallurgical approaches that generate environmentally hazardous residues. A first
suitable recycling approach that avoids both of these problems is ultrasonic decoating. Ultrasonic decoating has
proven to selectively remove the perovskite layers from SOC. Although ultrasonic decoating is easy to apply in
theory, it can be challenging in a real recycling process due to the orientation dependency of the cells during
stressing combined with an easily broken cell. The aim of this study is therefore to adapt ultrasonic decoating to
comminuted SOC. To do this, a cell was comminuted and subsequently sieved. The coarse cell particle fractions
were then exposed to ultrasound. The particle size distribution and composition were employed to assess the
decoating and the selectivity of the comminution. It has been shown that perovskite materials accumulate in
the fine fractions as a result of comminution. Furthermore, perovskite materials can be selectively liberated and
separated from cell particles by ultrasound.
INTRODUCTION
Hydrogen plays a key role as an energy carrier in the current
energy transition (Capurso et al. 2022, Staffell et al. 2019).
Global hydrogen production capacity, water electrolyzers
in particular, is therefore being greatly expanded. Based
on announced projects, electrolyzer capacity is expected to
increase from 700 MW at the end of 2022 to 175–420 GW
in 2030 (IEA 2023).
Among conventional electrolyzers, solid oxide electro-
lyzers (SOEL) are characterized by particularly high electri-
cal efficiency and feasible reversible operation as fuel cells
(Capurso et al. 2022, Ji and Wang 2021, Sebbahi et al.
2022). Another advantage is that SOEL are not limited to
hydrogen, but are also suitable for the production of syn-
gas (Cinti et al. 2016, Wang et al. 2019). However, the high
operating temperature leads to a high wear of the materi-
als. This results in a short lifetime of 2–3 years (Nechache
and Hody 2021, Sun et al. 2015), which prevents SOEL
from achieving a market breakthrough (Ozturk and Dincer
2021, Pandiyan et al. 2019). This is further aggravated by
the lack of efficient, cost-effective and scalable end-of-life
strategies, which are essential in view of the raw materials
used (Kiemel et al. 2021, Valente et al. 2019).
SOELs generally consist of repeating, layered compo-
nents, with the core component being the solid oxide cell