Electrochemical Hydrogen Pump Research Articles

Purifying Hydrogen from Dilute Hydrogen–Natural Gas Mixtures Using HT-PEM Electrochemical Hydrogen Pumps

Purifying Hydrogen from Dilute Hydrogen–Natural Gas Mixtures Using HT-PEM Electrochemical Hydrogen Pumps

Multi-objective optimization of a hydrogen production process for polymer membrane coupled with electrochemical hydrogen pump from hydrogen-doped natural gas by NSGA-II

In this work, a novel process of polymer membrane coupled with electrochemical hydrogen pump (EHP) was proposed to achieve efficient hydrogen production from hydrogen-doped natural gas (HDNG), and was simulated by UniSim Design. A hydrogen separation unit of two-stage polymer membrane was used for achieving hydrogen enrichment from low H2 concentration HDNG. Due to the hydrogen upgrade, EHP was operated at a H2 concentration much higher than HDNG, resulting in low energy consumption. Benefiting from the synergy between hydrogen upgrade and purification, the coupling process brought substantial effect while improving the hydrogen purity and recovery rate and reducing the hydrogen separation cost. The real natural gas components were considered into HDNG to ensure the effectiveness of process simulation. An optimization strategy considering both product yield and production cost was proposed to achieve the trade-off between hydrogen recovery rate and separation cost. However, the impact of process parameters on the objectives is nonlinear and difficult to describe with mathematical expressions. Therefore, an agent model of the proposed process was established based on back propagation neural network (BPNN), and multi-objective optimization of H2 recovery rate and total annual cost (TAC) of hydrogen separation unit was achieved using non-dominated sorting genetic algorithm-II (NSGA-II). Investigations with HDNG under various operating conditions (feed pressure of 8–40 bar and feed H2 concentration of 5–25 mol%) were performed, which proved that 90 % overall H2 recovery rate and 99.99 mol% H2 purity of hydrogen product can be achieved at low cost, with the lowest hydrogen separation cost of 1.00 $/kg H2 achievable at 40 bar feed pressure and 25 mol% feed H2 concentration. In summary, this coupling process can provide engineering solutions for efficient hydrogen production from HDNG and promote the development of green hydrogen.

Electrochemical hydrogen pump based on proton exchange membrane for rapid separation of hydrogen and helium

The separation and purification of hydrogen play an essential role in the field of new energy. In addition, it has great significance and economic value in recovering hydrogen isotope gas from plasma ash discharge gas faced by nuclear fusion reactors. Here, we studied the rapid separation of hydrogen and helium by electrochemical hydrogen pump (EHP), a new hydrogen separation and purification method. In the experiment of the hydrogen-helium separation, the recovery rate of hydrogen can reach 97.4%, and the proportion of hydrogen can reach 99.99%. Furthermore, the effects of catalyst layer structure, membrane materials and working conditions for its performance were analyzed. This experiment found that proton conduction in the catalyst layer and proton exchange membrane became the speed-control step of the process. Moreover, efficient catalyst layer design and membrane materials with high proton conductivity are beneficial to improve EHP's performance further. This study could guide further enhancing the hydrogen-helium separation rate in EHP. It aims to promote the development of hydrogen separation and purification of EHP, making it an efficient method of hydrogen-helium separation instead of palladium membrane.

Failure mechanism of dielectric breakdown in electrochemical hydrogen pumps

Electrochemical hydrogen pump (EHP) cells, employing ultra-thin (This article refers specifically to films with a thickness of 12μm) proton exchange membranes (PEMs), are used in different fields such as hydrogen purification, hydrogen compression, and the rapid activation of hydrogen fuel cells. However, under certain extreme conditions, the voltage of an EHP cell with an ultra-thin proton exchange membrane can rise rapidly and trigger dielectric breakdown of the PEM, resulting in a PEM perforation and cell failure due to an internal short circuit. In order to investigate the failure mechanism, this paper comprehensively analyzes the electrochemical failure process leading to the breakdown of EHP cells. This investigation is accomplished by monitoring characteristic parameters such as voltage and resistance. The research outcomes indicate that the failure process in EHP cells can be divided into three stages: (I) Normal operation stage, (II) Carbon corrosion stage, and (III) Dielectric breakdown stage. In stage-I, the main process is the EHP reaction itself, the cell is undamaged and the cell voltage is about −0.22 V. In stage-II, the localized water shortage at the anode leads to a rapid increase in the anode ohmic overpotential, and the cell voltage is around −1.9 V, which reaches the carbon corrosion threshold. As a result, the anode catalyst layer undergoes a severe carbon corrosion reaction, generating CO and CO2 gases, and the cell performance decreases but the PEM is not seriously damaged. As substantial amount of anode water is consumed, the cell enters into stage-III. At this stage, the anode overpotential further increases, and the cell voltage reaches above −14 V, resulting in dielectric breakdown of the PEM, internal short circuit of the cell, and the cell cannot work normally. This study can enhance the understanding of the electrochemical failure process in EHP cells, thereby providing a basis for improving their durability and reliability.

Deconvolution of Charge-Transfer, Mass Transfer, and Ohmic Resistances of Phosphonic Acid-Sulfonic Acid Ionomer Binders in Electrochemical Hydrogen Pumps

Ion-pair high-temperature polymer electrolyte membranes (HT-PEMs) paired with phosphonic acid ionomer electrode binders have substantially improved the performance of HT-PEM electrochemical hydrogen pumps (EHPs)1, 2 and fuel cells3. Recently, blending poly(pentafluorstyrene-co-tetrafluorostyrene phosphonic acid) (PTFSPA) with NafionTM improved ionomer conductivity under anhydrous conditions in the temperature range of 100 °C to 250 °C. Using the said polymer blend as an electrode binder resulted in a 2 W.cm-2 peak power density of fuel cells4 at 240 °C (a HT-PEM fuel cell record). However, much is still unknown about how phosphonic acid ionomers blended with perfluorosulfonic acid (PFSA) materials affect electrode kinetics and gas transport in porous electrodes. In this work, we studied the ionic conductivity, electrode kinetics, and gas transport resistance of 3 types of phosphonic acid ionomers, poly(vinyl phosphonic acid), poly(vinyl benzyl phosphonic acid) by themselves and when blended with Aquivion®. These studies were performed in the context of an EHP platform – both membrane electrode assemblies (MEAs) and interdigitated electrode arrays (IDAs) decorated with nanoscale platinum electrocatalysts with thin film ionomer electrolytes. For all phosphoric acid ionomer types, the addition of Aquivion® promoted ionic conductivity, hydrogen oxidation/evolution reaction kinetics (HOR/HER), and hydrogen gas permeability. Solid-state 31P NMR revealed that the addition of Aquivion® significantly reduced phosphate ester formation in phosphoric acid ionomers and this played a vital role in enhancing ionomer blend conductivity. Using the best blend variant, PTFSPA-Aquivion®, a remarkable EHP performance of 5.1 A.cm-2 at 0.4 V at T = 200 °C was attained. Density functional theory (DFT) simulations identified that phosphonic acids with electron-withdrawing moieties reduced the propensity of the phosphonic acid to adsorb to platinum electrocatalyst surfaces. All phosphonic acid ionomers are anticipated to have a greater affinity for adsorption on platinum when compared to sulphonic acid ionomers (PFSAs). The relative adsorption affiliation of the various phosphoric acid ionomers from DFT is consistent with an explanation that stronger anion-specific adsorption has a detrimental impact and is commensurate with experimentally obtained MEA charge-transfer kinetics. A machine learning-aided compositional model5 revealed that the addition of Aquivion® reduced activation and concentration overpotentials in EHP MEAs and improved exchange current density and diffusivity in EHP IDAs. Future work involves employing the EHPs in a real-world application for separating and compressing hydrogen from the natural gas mixture.References Venugopalan, G.; Bhattacharya, D.; Andrews, E.; Briceno-Mena, L.; Romagnoli, J.; Flake, J.; Arges, C. G., Electrochemical Pumping for Challenging Hydrogen Separations. ACS Energy Letters 2022, 7 (4), 1322-1329.Venugopalan, G.; Bhattacharya, D.; Kole, S.; Ysidron, C.; Angelopoulou, P. P.; Sakellariou, G.; Arges, C. G., Correlating high temperature thin film ionomer electrode binder properties to hydrogen pump polarization. Materials Advances 2021, 2 (13), 4228-4234.Atanasov, V.; Lee, A. S.; Park, E. J.; Maurya, S.; Baca, E. D.; Fujimoto, C.; Hibbs, M.; Matanovic, I.; Kerres, J.; Kim, Y. S., Synergistically integrated phosphonated poly(pentafluorostyrene) for fuel cells. Nat Mater 2021, 20 (3), 370-377.Lim, K. H.; Lee, A. S.; Atanasov, V.; Kerres, J.; Park, E. J.; Adhikari, S.; Maurya, S.; Manriquez, L. D.; Jung, J.; Fujimoto, C.; Matanovic, I.; Jankovic, J.; Hu, Z.; Jia, H.; Kim, Y. S., Protonated phosphonic acid electrodes for high power heavy-duty vehicle fuel cells. Nature Energy 2022, 7 (3), 248-259.Briceno-Mena, L. A.; Venugopalan, G.; Romagnoli, J. A.; Arges, C. G., Machine learning for guiding high-temperature PEM fuel cells with greater power density. Patterns 2021, 2 (2), 100187. Figure 1

Enhanced methanol reforming gas fuel cell system with electrochemical hydrogen pump: Conceptual design, system analysis, and multi-objective optimization

In this work, two methanol-reforming gas fuel cell systems coupled with an electrochemical hydrogen pump (EHP), namely, EHP pre-coupling and post-coupling fuel cell systems were proposed to achieve performance enhancement. A back propagation neural network surrogate model was established for the two systems to accurately describe system behavior, and a second-generation multi-objective non-dominated genetic algorithm was utilized for addressing the multi-objective optimization problem encompassing net output power, carbon mass-specific emission and the levelized cost of electricity. The linear non-weighted multi-attribute preference and technique for order preference by similarity to ideal solution multi-attribute decision-making methods were employed to select the optimal solutions. The optimized EHP pre-coupling fuel cell system exhibited lower carbon emissions (0.69 kgCO2/(kW·h)) and higher net output power (126.02 kW) compared to previous studies. While the EHP post-coupling system achieves a lower levelized cost of electricity (0.36 USD/(kW·h)), and stronger system stability (total efficiency reduction less 1 %). Both EHP-coupling systems offer viable process enhancements for fuel cell systems.

Features of Electrochemical Hydrogen Pump Based on Irradiated Proton Exchange Membrane.

An electrochemical hydrogen pump (EHP) with a proton exchange membrane (PEM) used as part of fusion cycle systems successfully combines the processes of hydrogen extraction, purification and compression in a single device. This work comprises a novel study of the effect of ionizing radiation on the properties of the PEM as part of the EHP. Radiation exposure leads to nonspecific degradation of membranes, changes in their structure, and destruction of side and matrix chains. The findings from this work reveal that the replacement of sulfate groups in the membrane structure with carboxyl and hydrophilic groups leads to a decrease in conductivity from 0.115 to 0.103 S cm-1, which is reflected in halving the device performance at a temperature of 30 °C. The shift of the ionomer peak of small-angle X-ray scattering curves from 3.1 to 4.4 nm and the absence of changes in the water uptake suggested structural changes in the PEM after the irradiation. Increasing the EHP operating temperature minimized the effect of membrane irradiation on the pump performance, but enhanced membrane drying at low pressure and 50 °C, which caused a current density drop from 0.52 to 0.32 A·cm-2 at 0.5 V.

The effect of concentration polarization and chemical interactions on electrochemical hydrogen pump

Electrochemical hydrogen pump is expected to play an important role in, e.g., H2 extraction from natural gas pipelines, by-product hydrogen purification. The influence of typical concomitant CH4 and CO2 on electrochemical hydrogen pump is systematically investigated in this study over a wide range of gas content (CH4 or CO2: 10-80 %) and temperature (26-60 °C), with the focus on two main inhibition effects, i.e., concentration polarization and chemical interaction. An Faradaic efficiency of 86–96 %, i.e., below 100 %, is obtained as to the H2/CH4 mixture separation due to concentration polarization effect, which is even lower in case of H2/CO2, due to additional chemical interactions between CO2 and Pt anode catalysts. The inhibition of concentration polarization is more significant than that of chemical interactions, and the former can be suppressed by increasing the operating temperature and pressure due to enhance catalytic activity and proton conductivity. As to these two gas mixtures, the energy consumption ranged from 0.2 to 2.0 kWh/m3 with the increase of applied current from 125 to 1250 mA. The electrochemical pump exhibits limited H2 purity of 98.6 %–99.7 % due to the existence of nafion membrane defects, which requires to be further improved.

Experimental study of the electrochemical hydrogen pump based on proton exchange membrane for the application in fusion fuel cycle

An electrochemical hydrogen pump (EHP) can be used in the fuel cycle of fusion devices for purifying (separating) and compressing fuel (a mixture of hydrogen isotopes). One of the distinguishing features of the fuel cycle of fusion devices is a relatively narrow range of operating pressures of the fuel mixture from high vacuum (∼1–10 Pa) to several atmospheres (2–3·105 Pa), and in most of the fuel cycle systems, especially in transmission systems (like gas lines), the pressure shall not exceed atmospheric. In this study, the possibility of using EHP with a proton exchange membrane (PEM) in the fuel cycle of fusion devices in the pressure range of 0.01 – 0.30 MPa and temperatures of 20 – 70 °C was considered, and i-V curves were obtained. A regression analysis of the i-V curves was carried out. The temperature dependence of limiting current and resistance of EHP cell was obtained as follows: lnilim=−1140±1001T+(3.0±0.3) and lnρ=1780±2801T+(6.5±1.1). It is shown that there is no dependence of these parameters on pressure. The EHP cell productive capacity was determined in the studied ranges of pressure and temperature as follows: lni2F=−0.0119×T−4.2×Ecell0.05+Ecell+20.4. The results obtained allow one to predict the performance of the EHP device under conditions of subatmospheric hydrogen pressure at the anode and to select the most effective operating parameters of the EHP.

High Purity Hydrogen and Carbon Dioxide Separation with Electrochemical Pump Operation of HT-PBI Fuel Cell at 120°C

A commercially available, polybenzimidazole (PBI) membrane based electrochemical hydrogen pump (EHP) platform was thoroughly evaluated to generate a benchmark set of performance. A primary gas mixture of CO2 and H2 with a ratio of 4:1 was selected to demonstrate the performance of EHPs while addressing concerns of CO2 poisoning effect. There is no indication of significant CO poisoning as a result of reverse water gas shift reaction (RWGS), and nearly Faradaic current efficiencies were successfully achieved. It was found that humidification of the feed gas at room temperature improved polarization performance while also improving energy efficiency, thus reducing the need for tightly controlled relative humidity of feed gas. A new perspective on EHP energy efficiency calculation methodology is also provided by inclusion of the cell heating requirement into the calculation. In this manner, an overall improvement to energy efficiency nearing 20% was realized by dropping the cell temperature to 120°C while paying no significant penalty to electrochemical performance. Nearly 99.99% pure H2 and 99.93% pure CO2 were produced with a hydrogen yield of 99.34%.

Design and Optimization of a Novel Hybrid Membrane-Electrochemical Hydrogen Pump Process for Recovering Helium from NRU off Gas.

Due to the low boiling point of helium, the nitrogen-rich off gas of the nitrogen rejection unit (NRU) in the liquefied natural gas (LNG) plant usually contains a small amount of CH4, approximately 1-4% He, and associated gases, such as H2. However, it is difficult to separate hydrogen and helium. Here, we propose two different integrated processes coupled with membrane separation, pressure swing adsorption (PSA), and the electrochemical hydrogen pump (EHP) based on different sequences of hydrogen gas removal. Both processes use membrane separation and PSA in order to recover and purify helium, and the EHP is used to remove hydrogen. The processes were strictly simulated using UniSim Design, and an economic assessment was conducted. The results of the economic assessment show that flowsheet #2 was more cost-effective due to the significant reduction in the capacity of the compressor and PSA because of the pre-removal of hydrogen. Additionally, using the response surface methodology (RSM), a Box-Behnken design experiment was conducted, and an accurate and reliable quadratic response surface regression model was fitted through variance analysis. The optimized operating parameters for the integrated process were determined as follows: the membrane area of M101 was 966.6 m2, the permeate pressure of M101 was 100 kPa, and the membrane area of M102 was 41.2 m2. The maximum recovery fraction was 90.66%, and the minimum cost of helium production was 2.21 $/kg. Thus, proposed flowsheet #2 has prospects and value for industrial application.

Promoted hydrogen and acetaldehyde production from alcohol dehydrogenation enabled by electrochemical hydrogen pumps

The dehydrogenation reaction of bioderived ethanol is of particular interest for the synthesis of fuels and value-added chemicals. However, this reaction historically suffered from high energy consumption (>260 °C or >0.8 V) and low efficiency. Herein, the efficient conversion of alcohol to hydrogen and aldehyde is achieved by integrating the thermal dehydrogenation reaction with electrochemical hydrogen transfer at low temperature (120 °C) and low voltage (0.06 V), utilizing a bifunctional catalyst (Ru/C) with both thermal-catalytic and electrocatalytic activities. Specifically, the coupled electrochemical hydrogen separation procedure can serve as electrochemical hydrogen pumps, which effectively promote the equilibrium of ethanol dehydrogenation toward hydrogen and acetaldehyde production and simultaneously purifies hydrogen at the cathode. By utilizing this strategy, we achieved boosted hydrogen and acetaldehyde yields of 1,020 mmol g-1 h-1 and 1,185 mmol g-1 h-1, respectively, which are threefold higher than the exclusive ethanol thermal dehydrogenation. This work opens up a prospective route for the high-efficiency production of hydrogen and acetaldehyde via coupled thermal-electrocatalysis.

A Pseudo-2D Model of the Reaction: Competitive Adsorption Kinetics for High-Temperature Electrochemical Hydrogen-Pump-Based Membrane Technology

In this work, a pseudo-2D model including electrode reaction and membrane separation of the high-temperature electrochemical hydrogen pump (HT-EHP) was proposed to separate a CO-containing hydrogen mixture. Rigorous kinetics of electrochemical reaction and competitive adsorption was introduced to reach accurate performance prediction. The simulated polarization curves of three different feed gases, namely, no-CO and narrow and wide CO content ranges, at different temperatures were consistent with the experimental data (R2 ≥ 0.90). Compared to previous work, the accuracy of the developed pseudo-2D model has been improved by 78.8% and 62.2%, respectively, under two feedstock conditions. Quantitative analysis of current density and catalyst coverage was achieved under various process conditions, demonstrating the applicability of HT-EHP pseudo-2D model. Feasible suggestions for the optimization design of HT-EHP were provided by analyzing the relationship between equipment scale, feed flow rate, current density and hydrogen recovery rate. Thus, the developed pseudo-2D model can be beneficial in the design and optimization of the HT-EHP system, and HT-EHP as an efficient membrane based technology is promising for the separation of CO-containing hydrogen mixtures in the future.

PEM Electrochemical Hydrogen Compression with Sputtered Pt Catalysts.

This work presents research on thin magnetron-sputtered platinum (Pt) films deposited over commercial gas diffusion electrodes and applied to convert and pressurize hydrogen in an electrochemical hydrogen pump. The electrodes were integrated into a membrane electrode assembly with a proton conductive membrane. Their electrocatalytic efficiency toward hydrogen oxidation and hydrogen evolution reactions was studied in a self-made laboratory test cell by means of steady-state polarization curves and cell voltage measurements (U/j and U/pdiff characteristics). The achieved current density at a cell voltage of 0.5 V, the atmospheric pressure of the input hydrogen, and a temperature of 60 °C was more than 1.3 A cm-2. The registered increase in the cell voltage with the increasing pressure was only 0.05 mV bar-1. Comparative data with commercial E-TEK electrodes reveal the superior catalyst performance and essential cost reduction of the electrochemical hydrogen conversion on the sputtered Pt films.

Deblending and purification of hydrogen from natural gas mixtures using the electrochemical hydrogen pump

This work evaluates the use of Electrochemical Hydrogen Pumps (EHPs) for H2 deblending from natural gas (NG) grids for use in H2 refuelling stations which need to meet the high ISO 14687-2019-D purity standards. Concentrations of 20, 50 and 80% H2 in either CH4 or NG were tested at current densities of 0.2 and 0.3 A cm−2. Moreover, the impact of adding O2 and O2/O3 bleeds to the inlet EHP feeds were investigated for their effectiveness in mitigating poisoning of the EHP catalysts. The CH4 concentration requirement of <100 μmol mol−1 was met using NG at 0.3 A cm−2 (20–80% H2) or with 80% H2 at 0.2 A cm−2; however, the CO2 limit of <2 μmol mol−1 could not be met, due to the high permeability of CO2 in Nafion®. Moreover, the other hydrocarbon concentrations limit of <2 μmol mol−1 could be met when operating with 80% H2 in NG at 0.3 A cm−2. Additionally, the EHP demonstrated low energy consumption, particularly at 0.2 A cm−2 ranging from 3.5 to 12.5 kWh kgH2−1.

Distribution of relaxation times analysis of electrochemical hydrogen pump impedance spectra

Polybenzimidazole-based electrochemical hydrogen pumps (EHPs) allow hydrogen separation from gas mixtures at low cell overpotential. An operating temperature of up to 180 °C provides robustness towards catalyst poisoning by common impurities in steam reformate, like CO or sulfur compounds. Electrochemical impedance spectroscopy (EIS) coupled with the distribution of relaxation times (DRT) analysis is performed on single-cell EHPs supplied by H2 contaminated with N2, CO2, and CO to investigate and quantify the underlying physicochemical processes. By systematically varying the operating parameters, five different processes were identified in the DRT spectrum: the proton transport in the electrode, the hydrogen evolution reaction (HER), the hydrogen oxidation reaction (HOR), the mass transport (MT) in the anode gas diffusion electrode, and the movement of phosphoric acid anions from the cathode to the anode at high current densities. At high contaminant concentrations, the HOR and the MT resistances increase. The HOR inhibition is dominant for CO, while for N2 and CO2, the MT resistance increase is more pronounced. At 180 °C cell temperature, the performance with 50% CO2 in the gas feed was worse than with 1% CO, highlighting the possibility of operating an EHP with a CO-contaminated gas feed at elevated operating temperature.

High Purity Hydrogen Separation with HT-PBI Based Electrochemical Pump Operation at 120 °C

Electrochemical Hydrogen Pumps (EHP) provide a unique highly efficient means of separating and compressing hydrogen with continuous steady-state operation. In this paper, we demonstrate the performance of a commercially available, polybenzimidazole (PBI) membrane based platform as a benchmark for ultra-high efficiency performance. A primary gas mixture of CO2 and H2 with a ratio of 4:1 respectively was selected to demonstrate the performance of EHPs with near theoretical Faradaic efficiency with negligible CO poisoning due to reverse water gas shift reaction (RWGS). It was found that humidification of the feed gas at room temperature improved polarization performance while also improving energy efficiency, thus reducing the need for a tightly controlled relative humidity of feed gas. A new perspective on EHP energy efficiency calculation methodology is also provided by including the cell heating requirement in the calculation. In this manner, an overall improvement to the energy efficiency of nearly 20% was realized by dropping the cell temperature to 120 °C while paying no significant penalty to electrochemical performance. Nearly 99.99% pure H2 and 99.93% pure CO2 were produced with a hydrogen yield of 99.34%.

Deconvoluting charge-transfer, mass transfer, and ohmic resistances in phosphonic acid–sulfonic acid ionomer binders used in electrochemical hydrogen pumps

This work reveals how electrode binders affect reaction kinetics, ionic conductivity, and gas transport in electrochemical hydrogen pumps (EHPs). Using a blend of phosphonic acid and perfluorosulfonic acid ionomers as the electrode binder, an EHP was operated at 5 A cm−2.

A partial element stage cut electrochemical hydrogen pump model for hydrogen separation and compression

In this work, a partial element stage cut electrochemical hydrogen pump (EHP) model for the separation of multiple H2-contaning gases and hydrogen compression was proposed to realize fast prediction of the EHP’s performance (nearly 10 s for one IEHP–E point). Three real factors, namely, anode impurity diffusion, hydrogen back-diffusion and anode catalyst deactivation, were embedded into the model. The model accuracy was verified for four aspects (current density distribution, polarization curve, hydrogen recovery and purity) under four feedstock systems (H2/N2, H2/CH4, H2/He and H2/CO2) and a wide cathode pressure range of 0.1–1.0 MPa. The model had good accuracy (R2≥0.90). Benefiting from the embedding of the real factor of the hydrogen back-diffusion, hydrogen back-diffusion ratio was simulated accurately under a wide cathode pressure range of 0.13–20 MPa. By considering the dual- effect on current density caused by PEM proton conduction and GDL mass transformation resistance, optimal region of hydrogen recovery rate, energy efficiency and hydrogen purity can be simulated. About 64 % and 53 % for hydrogen recovery rate and energy efficiency can be achieved under low hydrogen feedstock of 20 mol%. In summary, it is promising to realize the “hydrogen economy” in the future under the utilization of EHP.

Two-Dimensional Model of a High-Temperature Proton Exchange Membrane Hydrogen Pump for Efficient, Single-Stage Separation of Fuel Cell Quality Hydrogen Gas from Hydrogen-Enriched Natural Gas

A key component of the emerging hydrogen energy economy is the distribution system which facilitates the movement of hydrogen energy between production and end-use. There is interest in valorization of existing gas systems, which today are dedicated to natural gas movement, to facilitate the co-transportation of hydrogen via blending of hydrogen gas into these gas systems at concentrations up to 20% H2 by volume [1]. Fuel cell quality hydrogen, at a purity of 99.97%> H2, is required for the most valuable energy end-uses of hydrogen gas and thus the ability to efficiently extract H2 gas at such high purity is critical to the adoption of natural gas infrastructure as a means of co-transportation and distribution.Electrochemical hydrogen pump (EHP) utilizes a proton conducting membrane to separate hydrogen from mixtures by driving the electrochemical process of oxidation of hydrogen at an anode and subsequent evolution of hydrogen gas at a cathode, while other gaseous impurities are ideally unable to permeate through the membrane. HT-PEM EHP based on polybenzimidazole (PBI) membranes doped with phosphoric acid exhibit high proton conductivities at temperatures in the range of 160C Celsius while also exhibiting characteristics that are complimentary to their application in gas separation processes. These characteristics include a limited tolerance to common sources of platinum catalyst inhibition such as CO [1] and the presence of an aqueous phosphoric acid phase inhibits gas cross-over, providing better product purity although at the cost of performance in the form of catalyst inhibition.A two-dimensional model based on an HT-PEM system employing a phosphoric acid doped PBI membrane and free phosphoric acid as the proton conducting phase of the catalyst layer is developed to better understand the underlying processes governing the performance of the EHP. The model is validated with experimental measurements with mixtures as low as 2% H2 by volume in methane. In-operando micro-CT imaging of an HT-PEM EHP cell taken at the LBNL Advanced Light Source (ALS) is used to further validate physical parameters and assumptions of the model.The influence of differential pressure, relative humidity of the feed, and concentration of feed gases on separation performance are investigated. Losses due to back-permeation of hydrogen under pressure are accounted for. Power-loss voltage breakdown analysis indicates appreciable losses due to proton transport in the relatively thick catalyst layer, and the dependence of these losses on the volume fraction of acid present (Figure 1). The influence of CO2 as a catalyst inhibiting contaminant as was previously observed in low temperature EHP [3] is examined. The model and experiments show that a specific energy of separation of 5.1 kWh/kg H2 at a hydrogen recovery factor (HRF) of 50% can be achieved in a single stage with the EHP, producing 99.995% > H2 from a 2% H2 in CH4 blend, while pressurizing the product H2 at a product pressure ratio of 1.3 relative to feed pressure. Bibliography [1] C. J. Quarton and S. Samsatli, "Power-to-gas for injection into the gas grid: What can we learn from real-life projects, economic assessments and systems modelling?," Renewable and Sustainable Energy Reviews, vol. 98, pp. 302-316, 2018. [2] K. Perry and B. B. Eisman G.A., "Electrochemical hydrogen pumping using a high-temperature polybenzimidazole (PBI) membrane," Journal of Power Sources, pp. 478-484, 2008. [3] N. e. al., "Effect of CO2 on the performance of an electrochemical hydrogen compressor," Chemical Engineering Journal, vol. 329, 2020. Figure 1