Open AccessArticle

Electrochemical Hydrogen Pump/Compressor in Single- and Double-Stage Regime

Galin Borisov

Nevelin Borisov

and

Evelina Slavcheva

Acad. Evgeni Budevski Institute of Electrochemistry and Energy Systems Bulgarian Academy of Sciences, Acad. G. Bonchev bl. 10, 1113 Sofia, Bulgaria

Author to whom correspondence should be addressed.

Hydrogen 2025, 6(1), 14; https://doi.org/10.3390/hydrogen6010014

Submission received: 3 February 2025 / Revised: 28 February 2025 / Accepted: 5 March 2025 / Published: 6 March 2025

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Figure 1
Operation principle of electrochemical hydrogen pump/compressor. "> Figure 2
Principal of operation of electrochemical hydrogen pump/compressor under stack operation (a) with serial electrical connection (bipolarity) and (b) with parallel electrical connection. "> Figure 3
XRD spectra of commercial GDEs applicable for HT-PEMFC with 40%wt. and catalytic loading of 0.38 mgpt·cm2 at the diffraction angle of 2θ in ranges of (a) 10° to 90° and (b) 40° to 90°. "> Figure 4
Voltampere characteristics U/j (a) and polarization curves E/j (b) of MEA with commercial gas diffusion electrode (0.38 mgPt·cm−2) recorded at room temperature (25 C) with a potential scan rate of 1 mV·s−1. "> Figure 5
U/j curves of membrane electrode assembly in EHP/C regime with 51.3 mL·min−1 hydrogen inflow at varying temperature; potential scan rate, 1 mV·s−1. "> Figure 6
Influence of differential pressure on the cell voltage at a constant current density of 0.6 A·cm−2, temperature of 60 °C, and hydrogen inflow rate of 51.3 mL·min−1. "> Figure 7
Influence of differential pressure (Pdiff) on hydrogen crossover (Jx-over,/mole cm−2·s−1) at different temperatures. "> Figure 8
Comparative data for MEAs with different working areas: (a) U/Pdiff curves recorded at a current density of 0.6 A·cm−2, temperature of 60 °C, and hydrogen inflow rate 51.3 mL·min; (b) calculated difference in the cell voltage measured at 1 and 10 bar differential pressure. "> Figure 9
U/Pdiff curve of the membrane electrode assembly in a double-stage compression regime with a current density of 0.6 A·cm−2, temperature of 60 °C, and a hydrogen inflow rate in the first single cell of 51.3 mL·min. ">

Versions Notes

Abstract

This study presents the integration and evaluation of commercially available gas diffusion electrodes (GDEs), specifically designed for high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) within membrane electrode assemblies (MEA) for electrochemical hydrogen pump/compressor applications (EHP/C). Using Nafion 117 as a solid polymer electrolyte, the MEAs were analyzed for cell efficiency, hydrogen evolution, and hydrogen oxidation reactions (HER and HOR) under differential pressure up to 16 bar and a temperature ranging from 20 °C to 60 °C. Key properties of the GDEs, such as electrode thickness and conductivity, were investigated. The catalytic layer was characterized via XRD and EDX analyses to assess its surface and bulk composition. Additionally, the effects of increasing MEA’s geometric size (from 1 cm² to 5 cm²) and hydrogen crossover phenomena on the efficiency were examined in a single-cell setup. Electrochemical performance tests conducted in a single electrochemical hydrogen pump/compressor cell under hydrogen flow rates from 36.6 Ml·min⁻¹·cm⁻² to 51.3 mL·min⁻¹ cm⁻² at atmospheric pressure provided insights into the optimal operational parameters. For a double-stage application, the MEAs demonstrated enhanced current densities, achieving up to 0.6 A·cm⁻² at room temperature with further increases to 1 A·cm⁻² at elevated temperatures. These results corroborated the single-cell data, highlighting potential improvements in system efficiency and a reduction in adverse effects. The work underscores the potential of HT-PEMFC-based GDEs for the integration of MEAs applicable to advanced hydrogen compression technologies.

Keywords:

hydrogen; electrochemical hydrogen pump/compressor; membrane electrode assemblies; gas diffusion electrodes; double-stage compression mode

1. Introduction

The hydrogen economy holds significant promise in the global energy landscape, providing a stable, scalable, and highly efficient energy source with zero carbon emissions and an inexhaustible resource base [1,2,3]. These advantages position hydrogen as a pivotal component of a sustainable energy future. However, a primary obstacle to the widespread commercialization of green hydrogen is the still inefficient storage and transportation of the gas [4,5]. Currently, green hydrogen is typically stored in high-pressure cylinders or metal hydride compounds, both requiring a pressure exceeding 30 bar [6,7]. These high-pressure requirements introduce complexities, including the need for energy-intensive compression and storage systems, which ultimately reduce the overall efficiency of the green hydrogen cycle. Consequently, these challenges highlight the need for optimized hydrogen compression and storage solutions to enhance system efficiency and reliability, driving increased interest in innovative approaches. One promising solution for improving hydrogen storage and transportation efficiency is the use of electrochemical hydrogen pumps/compressors [8,9,10]. These devices present several key advantages over conventional piston-based systems, including significantly higher energy efficiency (exceeding 85%), extended service life, silence, and reliable operation during the compression process [11,12]. Electrochemical hydrogen pumps/compressors are a low-maintenance alternative that aligns with the demands of green hydrogen applications, reducing the mechanical complexity and energy losses associated with traditional methods. The core component of an EHP/C is the membrane electrode assembly, which comprises two gas diffusion electrodes, facilitating the hydrogen oxidation and evolution reactions (according to Equations (1)–(3)).

Anode: H₂ → 2H⁺ + 2e⁻

(1)

Cathode: 2H⁺ + 2e⁻ → H₂

(2)

Overall reaction: H₂ → H₂

(3)

The electrodes are separated by a polymer proton-conductive membrane that enables selective proton transfer while preventing gas leakage. The operating principle for a single-stage EHP/C providing an efficient and compact mechanism for hydrogen pumping is illustrated in Figure 1.

On the anode side of the cell, hydrogen gas dissociates into protons and free electrons (Equation (1)). The protons migrate through the polymer proton-conductive membrane to the cathode side, where they recombine with the electrons supplied by the external power source, reforming hydrogen atoms and, subsequently, hydrogen molecules (Equation (2)). The overall reaction is given with Equation (3). The pressure difference between the cathode (P_cathode) and anode (P_anode), known as the differential pressure (P_differential) marked in Equation (4), indicates the achieved compression. The hydrogen evolution rate depends on the applied current (according to Faraday’s law Equation (5)):

P_cathode − P_anode = P_differential

(4)

W/M = I t/z F

(5)

Like many emerging technologies, electrochemical hydrogen pumps/compressors face challenges, some of which are related to integrated gas diffusion electrodes and polymer proton-conductive membranes (PPMs) [13]. During operation, effects such as hydrogen crossover, back-diffusion pressure, and electroosmotic drag may deteriorate the efficiency of the pumping process [14,15,16]. The described negative effects are strongly connected with the water management in the polymer membrane and partly with the gas diffusion electrodes. Running the process with high current density increases the debit of the EHP/C, but it also increases the electroosmotic drag (from the anode to the cathode), which has a negative influence on the water distribution in the polymer membrane structure [17]. Aside from this, the high differential pressure misbalances the water amount in the PEM from opposite directions (from the cathode to the anode), an effect known as back-diffusion pressure. Hydrogen crossover (the permeation through the membrane) tends to increase as the differential pressure rises, impacting the cell efficiency [18,19]. This not only counts the lost hydrogen during the pumping process but also affects the back-diffusion pressure negatively [20].

Additionally, as the differential pressure increases (P_differential), the cell voltage also rises (U_EHP/C), as described by the Nernst equation (Equation (6)).

U_EHP/C = E⁰ + (RT/nF) * ln (P_cathode/P_anode)

(6)

The electrochemical hydrogen pumps/compressors typically consist of single cells connected electrically in series in a stack configuration (bipolar configuration). The inflow of hydrogen is supplied in parallel to each cell through internal channels with low hydraulic resistance [21,22]. This configuration is schematically represented in Figure 2.

Series-connected membrane electrode assemblies increase the operating voltage, following Equation (7a), while the current through a single MEA remains constant with minor variations mainly due to deviations in the cells’ ohmic resistance, as described in Equation (7b).

U_(cell-1) + U_(cell-2) = U_stack

(7a)

I_(cell-1) = I_(cell-2) = I_stack

(7b)

In this electrical configuration, the final compression of the stack strictly depends on the number of cells, while the differential pressure of each single cell is determined by its individual efficiency [23].

If the single cells are connected in parallel (Figure 2b), then U_stack and I_stack are described with Equation (8a) and Equation (8b), respectively.

U_(cell-1) = U_(cell-2) = U_stack

(8a)

I_(cell-1) + I_(cell-2) = I_stack

(8b)

In this case, the stack voltage is equal to the single-cell voltage, while the current doubles, meaning the system’s power is also doubled [24].

Despite the type of electrical connection, the power of the hydrogen electrochemical compressor in a multistage regime follows Equation (9).

P_stack = I_stack * U_stack

(9)

At the same time, the differential pressure of the individual cells and, as a result, the final pressure of the compressed hydrogen gas depend on the efficiency of each cell, resp., of the efficiency of the polymer proton-conductive membrane, which is a key factor for the functionality of the EHC/P stack.

To address some of the described challenges, we developed electrochemical hydrogen pumps/compressors using commercially available GDEs and MEAs with the Nafion 117 polymer electrolyte membrane and tested their performance in both single-cell and short-stack double-stage compression regimes. These configurations were systematically investigated to evaluate and optimize the efficiency of the hydrogen pumping process, with a focus on mitigating the issues related to hydrogen crossover, differential pressure, and flow rate limitations.

2. Materials and Methods

The experimental work comprises four main steps: (1) the preparation of the gas diffusion electrodes, (2) the physical characterization of the samples, (3) the preparation of the membrane electrode assemblies, and (4) the electrochemical characterization of the MEAs’ performance in a single-cell and stack compression mode. Additionally, artificial intelligent tools were used for text correction and translation of this article.

2.1. Preparation of the Gas Diffusion Electrodes

The used gas diffusion electrodes (both anode and cathode) are commercially available products by BASF, designed and developed for the high-temperature (140–160 °C) polymer electrolyte membrane fuel cell with a multilayer structure and a PBI-based membrane soaked with phosphoric acid. The catalyst was a 40% wt. Pt dispersed over a carbon-based catalytic carrier, and the catalyst loading was 0.38 mg_Pt·cm⁻². The thickness of the electrode was measured by the micrometer with a resolution of 1 µm in each cm². The electrode geometric sizes were 1 cm², 2 cm², and 5 cm²). The electrodes were treated with deionized water for 1 h and later dried at room temperature for 24 h.

2.2. Physical Characterization of the Samples

The structural and phase composition of the as-delivered GDLs were examined by X-ray diffraction (XRD) using the model Malvern PANalytical B.V. in compact size. The diffraction data were collected using an X-ray diffractometer Philips ADP15 with Cu-Kɑ radiation (1.54178 Å) at a constant rate of 0.02 s⁻¹ over an angle range of 2 Ɵ = 4° ÷ 80°. The metal content in the catalyst layer was determined using energy-dispersing X-ray analysis, while the element analysis was carried out by EDX technics using Oxford Ultim Max 40 (Oxford Instruments, Abingdon, UK). The methodology is described in detail in [25].

2.3. MEA Preparation and Electrochemical Characterization

The MEAs were prepared directly into the cell, as described previously in [26]. The assembling cell procedure includes the preparation of the water management tampon (glass fiber net) soaked with deionized water (approximately 2 mL of water) for each department in the cell. The placing of gaskets with a thinness of 220–250 µm (Teflon-based materials) smeared with high-density lubricant was conducted in order to prevent hydrogen leakage. The MEA assembling was performed under the strength of 24 Nm for each scroll in the cell body. The reference electrodes consisting of commercial gas diffusion electrodes ETEK (40% wt. Pt supported on XC72 with a catalytic loading of 1 mg cm⁻² and geometric size of 0.5 cm²) were attached directly to the MEAs. The differential pressure under the pumping regime was measured by an analog flow controller GESA in the range of 0 to 16 bars (for the single-cell and stack modes) with a resolution of 0.5 bar before pumping for test leakage and, afterward, under the compression mode. All measurements were performed in a self-designed EHP/C single cell and EHP/C short stack for double-stage compression registered in the Bulgarian Patent Office (patent number 67663 B1 and utility model 4293 U1).

2.4. Electrochemical Characterization

The measurements were carried out using Gamry Reference 3000 and Gamry 1010E Potentiostat/Galvanostat. The electrochemical activity and cell performance of the developed MEAs were characterized by U/j and steady-state polarization curves under a scan rate of 1 mV·s⁻¹. In order to receive multi-point measurements concerning the double-stage compression DAQ recorder 6008, National instruments were used in combination with Signal Express 2015 software for control and diagnostic purposes.

2.4.1. Hydrogen Source

The hydrogen used for the electrochemical characterization and conceptualization proof of the developed EHC/P was produced by PEM water electrolyzer H₂Planet (model: 3.3 L·min⁻¹) with a hydrogen output pressure of up to 16 bar and a flow rate of up to 4.2 L per minute. The hydrogen used for the reference electrode was delivered by a custom-made Zero-gap electrolyzer registered as utility model 4552 U1 in the Bulgarian Patent Office.

2.4.2. Hydrogen Crossover Measurements

Hydrogen crossover was measured using a Gamry 1010E potentiostat/galvanostat (maximum current flow: 1A) to ensure precise control and high current resolution. The measurements were conducted directly in the cell under controlled conditions. The anode chamber was filled with inert argon gas, while the cathode chamber was supplied with hydrogen generated by a PEM electrolyzer at pressures of up to 16 bar. The electrochemical measurements were performed incrementally at every 1 bar of differential pressure over a temperature range of 20 °C to 60 °C. The procedure involved setting the differential pressure and cell temperature, allowing the cell to reach its open circuit potential (OCP), and then recording the cell voltampere U/j curve at a scan rate of 1 mV s⁻¹ within a potential window from the OCP (approximately 100 mV) to 0.4 V. The current recorded within this potential range correlates directly with the amount of hydrogen permeating from the cathode to the anode, providing quantitative insights into the hydrogen crossover under varying operating conditions. The procedure is described in detail in [27].

2.5. Artificial Intelligent Tools (AI Model)

This work is part of Nevelin Rusev Borisov’s PhD thesis. Artificial intelligence tools, such as ChatGPT 3.5 and Gemini, were used solely for language refinement without making significant changes to the original content. The authors take full responsibility for the final version of the article.

3. Results and Discussion

XRD measurements were conducted to characterize the catalytic material within the gas diffusion electrodes and to assess their crystallographic state. The obtained data are presented in Figure 3a,b, where the diffraction angle (2θ) ranges from 10° to 90° and from 40° to 90°, respectively.

In Figure 3a, the XRD spectra reveal several prominent peaks corresponding to various components present in the gas diffusion electrodes. These include Pt in a crystalline form, carbon from the catalytic carrier and diffusion layer, hydrophobic agents such as polytetrafluoroethylene, PTFE (commonly employed as a binder between the diffusion layer and the microporous layer), and high-density polyethylene. Figure 3b offers a more detailed view of the catalyst dispersed over the carbon catalytic carrier. The XRD spectra exhibit a well-defined crystalline peak associated with the Pt, highlighting its uniform distribution across the carbon carrier. The presence of these peaks confirms the complex and heterogeneous composition of the gas diffusion electrodes (3-layer structure), with each material contributing to the overall functionality and structural stability of the electrode.

Table 1 provides the elemental composition of the gas diffusion electrode, as determined by the EDX characterization technique. The weight percentages of the elements—carbon (C), fluorine (F), and platinum (Pt)—correlate directly with the materials identified in the XRD analysis, further validating the structural and functional components of the electrodes.

The fluorine (F) detected in the catalyst layer originates from the binder material, which is proton-conductive and ensures proton conductivity within the deeper regions of the catalytic layer. The presence of fluorine is a result of the liquid Nafion, commonly used as a proton conductor in catalytic layers for hydrogen energy-converting devices [28,29].

According to the technical specifications, the thickness of the as-purchased gas diffusion electrodes is 250 µm. The results from the performed controlling measurements at five random points on the electrode surface are presented in Table 2.

The obtained values range from 252 µm to 256 µm, with minimal variations proofing the electrode uniformity.

The gas diffusion electrodes were integrated into MEA using a proton-conductive Nafion^® 117 membrane. Figure 4 presents the electrochemical performance of the thus-prepared MEA operating in the hydrogen compression mode.

The U/j curves (Figure 4a) were obtained at varying hydrogen inflow rates. They exhibit a stable operation profile of the MEA within a potential window from 0 to 0.8 V. The electrochemical behavior of the cell remains unaffected by the variations in the input hydrogen flow rate (from 51.3 mL·min⁻¹ to 36.5 mL·min⁻¹) delivered from alkaline water electrolyze under atmospheric pressure. For all three values of the hydrogen delivered in the anode department of the cell, the application of an external potential deviating the system from equilibrium leads to an immediate evolution of hydrogen at the cathode. The resulting U/j curve is linear up to 0.20–0.25 V, indicating that the process is under charge transfer control. At higher cell voltages (U > 0.3 V), diffusion limitations become evident, suggesting an insufficient hydrogen inflow.

To verify the origin of these limitations, cathodic and anodic partial reactions were studied under quasi-steady-state conditions. The obtained polarization curves are shown in Figure 4b. It is seen that in the potential range up to 0.05 V, the hydrogen oxidation reaction (HOR) proceeds under charge transfer control, reaching a limiting current density of 0.6 A·cm⁻², beyond which the diffusion constraints dominate the process. In similarity to HOR, the rate of hydrogen evolution increases linearly with a potential up to −0.05 V; however, the achieved limiting current density is much higher, around 1 A·cm⁻².

The HER strongly depends on the efficiency of the HOR in delivering the reactant protons as well as on the ohmic resistance (resp., on the proton conductivity of the membrane). In order to increase the proton conductivity, the operating temperature was increased stepwise up to 60 °C. The resultant U/j curves are presented in Figure 5.

Figure 5 demonstrates that increasing the temperature reduces the ohmic resistance of the MEA, which, according to Equation (5), leads to an increase in the current density while maintaining a constant cell voltage. For instance, raising the temperature by 20 °C results in an approximate increase in the current density of 0.4 A·cm⁻². At 60 °C, the current density reaches approximately 1.2 A·cm⁻² and the diffusion limitations are shifted to higher cell voltage.

The slope and shape of the U/j curves remain consistent despite the changes in temperature, reflecting the dominant effect of the reduced ohmic resistance on overall MEA performance. These results complement the observations in Figure 4, emphasizing the critical role of the operating temperature in optimizing the electrochemical response of the cell.

To further investigate the behavior of the cell under an elevated temperature and differential pressure, an experimental setup was designed with a closed cathode chamber. The differential pressure was controlled and maintained up to 16 bar in order to evaluate its effect on cell performance, while the operating temperature was set at 60 °C. The results of these tests are presented in Figure 6. They provide valuable insights into the impact of differential pressure on the electrochemical behavior of the cell, complementing the findings related to the temperature and flow rate from Figs. 4 and 5. The combination of elevated temperature and controlled pressure reveals the critical parameters for optimizing performance and stability under varying operating conditions.

At the imposed current density of 0.6 A·cm⁻², the cell voltage immediately reaches 0.28–0.29 V and then increases with the rising differential pressure. The slope of the voltage–pressure curve demonstrates a linear trend up to the maximum differential pressure of 16 bar at which the test was terminated, indicating a predictable and consistent response under these operating conditions.

To evaluate the hydrogen crossover through the Nafion membrane, the test procedure described in the experimental section of this publication was implemented. The results of these experiments are summarized in Figure 7.

For all three test temperatures, increasing the differential pressure enhances the hydrogen crossover between the gas diffusion electrodes (Figure 7). Moreover, the rise in the operating temperature further increases the hydrogen permeability of the membrane. However, even at a high temperature of 60 °C and differential pressure (up to 16 bar), the hydrogen crossover remains below 0.01% from the compressed gas. However, in all measurements, the hydrogen losses are below 0.01%. The next stage in the research was to scale up the system dimensions and check the reproducibility of the established performance; MEAs with larger working areas (2 cm² and 5 cm²) were assembled. The results obtained are presented in Figure 8.

Increasing the electrode surface does not affect the differential pressure of the EHP/C, but it does influence the system’s efficiency. As shown in Figure 8a,b, enlarging the electrode surface from 1 cm² to 5 cm² results in an increase in cell voltage of 4.5–5 mV per cm². However, a closer examination of Figure 8a reveals that the curve shape at 5 cm² demonstrates a slight slope during the pumping process, which shows better stability.

To maintain the stability and efficiency of the pumping process, MEAs with an active surface area of 5 cm² were integrated into a short-stack electrochemical hydrogen compressor consisting of two identical single cells designed and developed at IEES-BAS. The electrical connections of this prototype and the flow field zone were configured so that the performance of each single cell could be evaluated separately. In this setup, the first single cell operates at 8 bars, while the pressure in the cathode department of the second one increases to 16 bars. The system was operated in the galvanostatic mode, imposing a constant current through both MEAs during pumping. The obtained results are presented in Figure 9.

The hydrogen gas enters the first single cell of the short stack with an inflow rate of 51.3 mL·min at atmospheric pressure. The cathode department is hermetically closed, and the hydrogen pressure there gradually increases. The compressed gas is stored in the buffer zone (the area between both MEAs) with an approximate volume of 50 mL. This zone is equipped with input and output fittings for technical manipulations, as well as a manometer for pressure measurements, and is hermetically sealed. Once the hydrogen gas fills the buffer zone between both cells and the pressure reaches 8 bar, the second cell is set in operation. The initial hydrogen pressure in its anode department is 8 bar. The test is terminated when the pressure at the cathode increases to 16 bar. In other words, the stack configuration enables equal differential pressure in each cell (8 bar) while the output pressure of the stack is doubled. (16 bar). The slope and shape of the U/P_diff curves in Figure 9 are in full accordance with the expected operation of the developed hydrogen compression system.

4. Conclusions

An electrochemical hydrogen pump/compressor was designed and assembled in both single-cell and double-stage compression modes, with the capability of achieving pumping pressures of up to 16 bars. Commercial gas diffusion electrodes (Pt-based), originally designed and developed for HT-PEMFC applications, were used in the setup. The electrochemical conversion demonstrated a high current density of 1.2 A·cm⁻². During the pumping operation, the compression reached a value of approximately 16 bars. Hydrogen crossover was measured, indicating a low percentage of hydrogen losses compared to the amount being pumped. The influence of the gas diffusion electrode surface area increased from 1 cm² to 5 cm² and was also investigated, revealing an increase of approximately 4–5 mV in cell voltage per 1 cm² increase in the surface area. Finally, the performance of a double-stage compression short stack was demonstrated, which proved the system’s capability to achieve a hydrogen compression of 16 bars with each MEA operating under a differential pressure of 8 bars. The process can be reliably maintained by keeping the current flow identical across all MEAs in the system.

Author Contributions

Conceptualization, N.B. and G.B.; methodology, G.B.; software, N.B.; validation, G.B. and E.S.; formal analysis, N.B.; investigation, N.B.; resources, E.S.; data curation, G.B.; writing—original draft preparation, G.B., N.B. and E.S.; writing—review and editing, G.B.; visualization, N.B.; supervision, E.S.; project administration, E.S.; funding acquisition, E.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

The authors kindly acknowledge the financial support of project № BG05M2OP001-1.002-0014, Center of Competence HITMOBIL—Technologies and systems for generation, storage and consumption of clean energy, funded by the Operational Program “Science and Education for Smart Growth” 2014–2020, co-funded by the EU from European Regional Development Fund, as well as the artificial intelligent tools Chat GPT 3.5 and Gemini for language checking and proofing.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Operation principle of electrochemical hydrogen pump/compressor.

Figure 2. Principal of operation of electrochemical hydrogen pump/compressor under stack operation (a) with serial electrical connection (bipolarity) and (b) with parallel electrical connection.

Figure 3. XRD spectra of commercial GDEs applicable for HT-PEMFC with 40%wt. and catalytic loading of 0.38 mg_pt·cm² at the diffraction angle of 2θ in ranges of (a) 10° to 90° and (b) 40° to 90°.

Figure 4. Voltampere characteristics U/j (a) and polarization curves E/j (b) of MEA with commercial gas diffusion electrode (0.38 mg_Pt·cm⁻²) recorded at room temperature (25 C) with a potential scan rate of 1 mV·s⁻¹.

Figure 5. U/j curves of membrane electrode assembly in EHP/C regime with 51.3 mL·min⁻¹ hydrogen inflow at varying temperature; potential scan rate, 1 mV·s⁻¹.

Figure 6. Influence of differential pressure on the cell voltage at a constant current density of 0.6 A·cm⁻², temperature of 60 °C, and hydrogen inflow rate of 51.3 mL·min⁻¹.

Figure 7. Influence of differential pressure (P_diff) on hydrogen crossover (Jx-over,/mole cm⁻²·s⁻¹) at different temperatures.

Figure 8. Comparative data for MEAs with different working areas: (a) U/Pdiff curves recorded at a current density of 0.6 A·cm⁻², temperature of 60 °C, and hydrogen inflow rate 51.3 mL·min; (b) calculated difference in the cell voltage measured at 1 and 10 bar differential pressure.

Figure 9. U/P_diff curve of the membrane electrode assembly in a double-stage compression regime with a current density of 0.6 A·cm⁻², temperature of 60 °C, and a hydrogen inflow rate in the first single cell of 51.3 mL·min.

Table 1. EDX analysis of the prepared gas diffusion electrodes.

Element	Weight, %
Carbon (C)	34.20
Fluorine (F)	29.76
Platinum (Pt)	29.04

Table 2. Thickness measurements of the gas diffusion electrodes.

Number of Points	Measured Thickness, µm	Deviation, µm
Point 1	254 µm	4 µm
Point 2	256 µm	6 µm
Point 3	253 µm	3 µm
Point 4	252 µm	2 µm
Point 5	256 µm	6 µm

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Borisov, G.; Borisov, N.; Slavcheva, E. Electrochemical Hydrogen Pump/Compressor in Single- and Double-Stage Regime. Hydrogen 2025, 6, 14. https://doi.org/10.3390/hydrogen6010014

AMA Style

Borisov G, Borisov N, Slavcheva E. Electrochemical Hydrogen Pump/Compressor in Single- and Double-Stage Regime. Hydrogen. 2025; 6(1):14. https://doi.org/10.3390/hydrogen6010014

Chicago/Turabian Style

Borisov, Galin, Nevelin Borisov, and Evelina Slavcheva. 2025. "Electrochemical Hydrogen Pump/Compressor in Single- and Double-Stage Regime" Hydrogen 6, no. 1: 14. https://doi.org/10.3390/hydrogen6010014

APA Style

Borisov, G., Borisov, N., & Slavcheva, E. (2025). Electrochemical Hydrogen Pump/Compressor in Single- and Double-Stage Regime. Hydrogen, 6(1), 14. https://doi.org/10.3390/hydrogen6010014

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