Parametric study on the performance of electrochemical hydrogen compressors
Introduction
In the past few years, the world's unrestrained use of fossil energy has yielded energy shortage and thus significant changes need to be made in energy production, distribution, storage, and usage [1,2]. Simultaneously, the climate crisis is adding pressure on the use of renewable energy sources [3,4]. Hydrogen energy has the potential to be an ideal solution for these changes because it can be produced and utilized everywhere on Earth based on environmentally friendly methods such as water electrolysis [5,6]. Once produced, hydrogen is typically stored as a highly pressurized gas and distributed to hydrogen refueling stations or other consumers [7]. Therefore, hydrogen compression technology plays an important role in the realization of a hydrogen-based society [8].
Currently, mechanical hydrogen compressors are generally used in the industry [9]. Typical mechanical hydrogen compressors involve reciprocating pistons, diaphragms, and linear compressors. Their operation characteristics and applications are listed in Table 1. Oil-free reciprocating piston compressors are commonly used in hydrogen applications as they prevent contamination with the lubricant [10,11]. However, the life expectancy of reciprocating piston compressors is relatively low because of the numerous moving parts and hydrogen embrittlement phenomena experienced by the cylinder material [[12], [13], [14]]. Diaphragm compressors are also highly effective devices for hydrogen applications. As direct contact between the gas and piston is prevented in diaphragm compressors, they are suitable for compressing chemically sensitive materials such as hydrogen [[15], [16], [17]]. However, the drawbacks of diaphragm compressors include the relatively low efficiency (up to 65%) and difficult maintenance owing to the complex diaphragm design [18,19]. Linear compressors are also promising for the compression of hydrogen gas because of their simple structure. In this design, the piston is directly connected to a linear motor coupled to a resonating spring system, which reduces the number of moving units because of the absence of a rod–crank assembly [20,21]. However, linear compressors must be operated under resonant conditions because the magnetic motors are designed to work at the mechanical resonance frequency [22]. Furthermore, liquid piston compressors [23] and ionic liquid compressors [24] were developed to increase compression efficiency when hydrogen is used. Such mechanical compressors have been widely used in hydrogen applications and are continuously being developed to improve their performance [25]. However, because of the low efficiency of mechanical compressors and poor lifespan caused by hydrogen embrittlement [26], other alternatives are needed for the hydrogen field.
Electrochemical hydrogen compressors are a good alternative to mechanical compressors [27,29] because they have a high compression efficiency, long lifetime, and are noise-free [30,31]. To determine the advantages of electrochemical compressors, numerical studies have been conducted. Dale et al. [32] developed an electrochemical model for an electrochemical hydrogen compressor to identify the energy requirements and efficiency of the system at different output pressures. The results showed that energy savings of up to 5 kWh kg−1 (23%) were possible when electrochemical hydrogen compressors were used in combination with mechanical compressors. Bampaou et al. [33] developed a zero-dimensional, steady-state electrochemical hydrogen compressor model for process design. They reported that hydrogen back diffusion caused substantial efficiency loss, especially at low current densities (<0.1 A cm−2) and increased cathode pressure, whereas this phenomenon subsided at higher current densities.
In addition, experimental studies have been conducted to investigate the performance of electrochemical compressors. Grigoriev et al. [34] experimentally studied the performance of an electrochemical hydrogen compressor. They achieved structural reinforcement using porous titanium as a cathode gas diffusion layer (GDL) and evaluated the main operation characteristics of the cell compressor at a high pressure. They conducted experiments at pressures up to 13 MPa and proposed the use of a multi-stack electrochemical hydrogen compressor system at pressures above 5 MPa. Graphene can also be an alternative for the structural reinforcement of electrochemical hydrogen compressors [35,36]. Rohland et al. [26] suggested the use of a special flexible graphite sheet and metal felt for the construction of the cathode and anode flow fields, respectively, to avoid the deformation of the membrane electrode assembly (MEA) caused by the high pressure. They realized electrochemical hydrogen compression from 0.1 to 4.3 MPa and yielded flow rates ranging from 0.04 to 5.7 Nm3 h−1. Ströbel et al. [37] discovered that the back diffusion of hydrogen mainly limits the output pressure of an electrochemical hydrogen compressor. They conducted experiments using a triple cell electrochemical hydrogen compressor and achieved an outlet pressure of 5.4 MPa at an inlet pressure of 0.1 MPa. Zou et al. [38] attempted to improve the performance of the electrochemical hydrogen compressor by controlling various operating parameters. They achieved compression ratio of up to 22 at an inlet pressure of 30 kPa. Previous experimental studies of electrochemical hydrogen compressors are summarized in Table 2. Although research on electrochemical hydrogen compressors has been extensively conducted, there is a lack of studies on internal phenomena. Therefore, it is necessary to investigate the mass transport inside electrochemical compressors in more detail.
In this study, the internal phenomenon was identified through the developed model. In addition, the performance of the electrochemical hydrogen compressor was evaluated through an experiment, and the parameters of the electrochemical compressor were investigated to understand the operating characteristics. The internal phenomena of the electrochemical compressor by considering electrochemical reactions affected by mass transport is also analyzed. First, an electrochemical hydrogen compressor model is developed and validated it with experimental results. Second, parametric study is conducted to determine the electrochemical characteristics under various current densities, operating temperatures, and inlet pressures. Finally, the power required for the high-efficiency operation of the compressor is identified. The findings of this study provide important insights into electrochemical hydrogen compressors and have practical significance for developing infrastructure aimed at the realization of a hydrogen-based society.
Section snippets
Methodology
A schematic of the operating principle of the electrochemical hydrogen compressor model is shown in Fig. 1. Hydrogen and water steam flow were calculated based on the relative humidity to compose an anode inlet. When electric power is supplied to the cell, hydrogen transfers from the anodic compartment to the cathodic compartment. In this model, the electrochemical reaction consists of the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) [34]:
Results and discussion
The developed model was validated by comparing it with experimental data, as shown in Fig. 4. In this study, the authors determined the cell's pressure ratio–voltage curve. The model predicted the voltage with high accuracy, with an average relative error of 5.37%. Despite an error because of hydrogen leakage, the model data and experimental results were in good agreement. Therefore, the developed model can be used to investigate the operating characteristics of electrochemical hydrogen
Conclusion
The authors conducted a parametric study on an electrochemical compressor to understand the operating characteristics. The authors not only evaluated the performance of the electrochemical hydrogen compressor through experiments but also analyzed internal phenomena through the developed model. The authors' analysis is focused on internal phenomena in the compressor during the interaction between electrochemical reactions and mass transport.
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A higher current density leads to a higher voltage at
CRediT authorship contribution statement
Min Soo Kim: Methodology, Software, Validation, Writing – original draft. Jungchul Kim: Visualization. So Yeon Kim: Investigation. Chan Ho Chu: Data curation. Kyu Heon Rho: Formal analysis. Minsung Kim: Funding acquisition. Dong Kyu Kim: Supervision, Writing – review & editing, Project administration.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by a Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean government [MOTIE; grant number 20212050100010]. This work was supported by the National Fir Agency and the Korea Institute of Energy Technology Evaluation and Planning(KETEP) (No. 20008021).
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These authors contributed equally to this work.