Abstract
Producing pure, compressed hydrogen from gas mixtures is a crucial, but expensive, aspect of hydrogen distribution. Electrochemical hydrogen pumps offer a promising energy-efficient solution, but struggle with gas mixtures containing less than 20% hydrogen. Here we show that electrochemical hydrogen pumps equipped with phosphate-coordinated quaternary ammonium ion-pair polymer membranes can overcome this challenge. By using a protonated phosphonic acid ionomer and selective cathode humidification, mass transport of the device is enhanced, boosting hydrogen production from low-concentration hydrogen gas mixtures. A tandem ion-pair electrochemical hydrogen pump system achieves high-purity hydrogen (>99.999%) from a 10% hydrogen–methane mixture with nearly 100% faradaic efficiency and hydrogen recovery. A techno-economic analysis reveals that electrochemical hydrogen pumps can reduce hydrogen delivery costs by up to 95% and energy consumption by up to 65% by allowing the use of existing natural gas pipelines, compared to traditional pressure swing adsorption and mechanical compression techniques.
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Data availability
All relevant data of this study are available within the paper and Supplementary Information. Source data are provided with this paper.
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Acknowledgements
Dedicated to the late Shimshon Gottesfeld, who reviewed this paper. The research presented in this article was supported by the Laboratory Directed Research and Development (LDRD) programme of Los Alamos National Laboratory under project number 20230340ER. Los Alamos National Laboratory is operated by Triad National Security under US DOE contract number 89233218CNA000001. We thank E. de Castro at Advent Technologies for providing the quaternized membranes. We also thank V. Atanasov at the University of Stuttgart for providing the PWN ionomer. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the US DOE.
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Y.S.K. conceived the idea and supervised the project. M.C. and Y.S.K. designed the experiments. M.C., D.P.L. and Y.K. performed EHP experiments. A.K. and L.E. synthesized the MCAG catalyst. P.S. performed the energy efficiency calculations. N.G. and M.R. conducted the techno-economic and cost analysis. S.M., C.K. and Y.S.K. helped review experimental progress and directions. M.C., P.S., N.G. and Y.S.K. cowrote the paper. All authors discussed the results and contributed to the preparation of the paper.
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M.C., D.P.L., S.M. and Y.S.K. filed US patent applications (63/493,524, 31 March 2023; 18/623,958, 1 April 2024; 63/674,017, 22 July 2024), related to the ion-pair EHP described in this article. N.G. and M.R. are employed by Gemini Energy. The other authors declare no competing interests.
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Extended data
Extended Data Fig. 1 Effect of cathode humidification on the performance of the ion-pair EHP.
Complex plane plot of EIS data (Nyquist plot) of a P-PWN-bonded ion-pair MEA under the effect of different cathode water partial pressure (PH2O). Inset show the equivalent circuit used to fit the data and extract charge transport values. The table in the right panel summarize the high frequency resistance (HFR), charge transport resistance (Rct) and mass transport resistance (Rmt) for both anode and cathode in the EHP cell operated at different PH2O at cathode at cell temperature of 160 °C and pure H2 flow at 500 mL min−1 at anode feed.
Extended Data Fig. 2 Effect of humidification on the short-term stability of the ion-pair EHP.
Voltage required by EHP device using P-PWN-bonded ion-pair MEAs at different current densities with PH2O = 5.9 kPa at anode a and cathode b side respectively. The operation at 0.5 and 1 A cm−2 for cathode side humidification is stable at a low level of humidification. c and d show the stability trend of the EHP device using P-PWN-bonded ion-pair MEA at different current densities with PH2O = 47.3 kPa at anode or cathode side respectively. Note how the stability is improved even at higher current density (voltage vs. time) with selective humidification at cathode side as compared to anode side.
Extended Data Fig. 3 Recoverable EHP performance during start-stop cycling test.
Start-stop cycling test of an EHP device using P-PWN-bonded ion-pair MEA at a current density of 3 A/cm2. The EHP device was rested for 30 minutes after every 2 hours of operation before restarting the test. Minimum of 60 cycles is represented in the graph with a partial pressure of water at cathode side, PH2O = 47.3 kPa.
Extended Data Fig. 4 Energy Efficiency comparison between state-of-the-art EHPs reported in literature (Electrochemical and Electrothermal cells).
Net Energy consumption to operate EHP cells. The data for H2 production rate were collected from references indicated in figure. The operational temperature for each cell is indicated. Using the modeling procedure described in Methods Energy efficiency modelling, the net energy consumption was calculated from the data inputs using polarization curves reported in respective literature. The P-SOC in ref. 34 functioned as SMR and WGS at the anode as well. Therefore, the energy consumption for the device includes the reforming process.
Extended Data Fig. 5 Energy efficiency calculations over range of current density.
The net energy consumption of different EHP devices reported in literature. The data for the best performing cell was collected for each reference under their respective operating conditions.
Extended Data Fig. 6 Loss of activity due to H2 transport limitation using carbon cloth based GDL.
Polarization curves of P-PWN based ion-pair MEA EHP using carbon cloth (CT Carbon cloth with MPL W1S1011 from Fuel Cell Store) with different H2 feed concentrations. The total flow of the anode was kept at 500 ml min-1. For gas blend, H2 and N2 were mixed in different proportions.
Extended Data Fig. 7 Improved effect of more hydrophobic GDL in reducing anode mass transport limitations in ion-pair MEA.
a, Nyquist plot of P-PWN ion-pair MEA at mixed activation and diffusion region under cathode water partial pressure PH2O = 47.3 kPa with different H2 molar concentration at anode inlet. Hydrogen inlet was diluted with CO2 and N2 gas. The numbers in the legend represent H2-N2-CO2 flow rates (in mL min-1). The gas diffusion layer used in the MEA was carbon cloth with MPL (CeTech, W1S1011 from Fuel Cell Store). b, Nyquist plot of P-PWN-bonded MEA at mixed activation and diffusion region under cathode water partial pressure PH2O = 47.3 kPa with different H2 molar concentration at anode inlet. The gas diffusion layer used in the MEA was carbon paper (Sigracet 39BB, SGL carbon from Fuel Cell Store). The data were collected under potentiostatic mode at 0.1 V (corresponding to the current density of 2–3 A cm−2).
Extended Data Fig. 8 HPF of tandem EHP process and Faraday’s law.
The hydrogen permeation flux (HPF) a, low differential pressure, LDP-EHP. b, high differential pressure HDP-EHP devices operating at 10% H2 and 90% H2 volume percent of anode feed respectively. The balance gas was CO2. The total flow rate at anode feed was maintained at 1000 mL min-1. The dotted lined represent the theoretically predicted flow rates based on Faraday’s law (assuming 100% Faradaic efficiency).
Extended Data Fig. 9 Effect of total flow rate on the limiting current density for diluted H2 anode feed.
Polarization curve for same vol% of H2 in the anode feed (10 vol%) but with different total flow rates. For the total flow rate of 1000 mL min−1, the H2 contribution is 100 mL min−1 and for 2300 mL/min the H2 contribution is 230 mL min−1. Tus the hydrogen availability is higher in the latter case.
Extended Data Fig. 10 Tandem EHP cell performance and energy calculation for deblending H2 from H2-CH4 mixture.
a, The polarization curve of LDP-EHP cell with H2 concentration (in CH4) from 10–100%. The cell was operated at 160 °C and 47.3 kPa H2O partial pressure at cathode side, while for 100% pure H2 was operated with 23.5 kPa H2O partial pressure. b, The net feed flow and the amount of water required to humidify the cathode side for unit hydrogen production. c, Energy bifurcation for different deblending 100% H2. The electrical energy is calculated using equation 9, equivalent electrical energy for gas heating is calculated using equation 12 and the equivalent electrical energy for water heating is the calculated using equation 14. Lower feed flow rate and water required reduces the net energy required for H2 deblending. d, Energy bifurcation for different deblending 10% H2. Higher feed flow rate (73 times compared to 100% H2) and high water (17 times compared to 100% H2) significantly increase the energy required for H2 deblending. e, The energy comparison for deblending of H2 as a function of different H2 feed concentration. The energy required here is equivalent electrical energy required (equation 15), which accounts for heating of feed mixture to 160 °C and heating the water to 60 °C and then to water vapor at 160 °C. f, The energy comparison for deblending of H2 as a function of different H2 feed concentration with heat integration. The pure H2, retentate gas and water vapor leaving the EHP is still at high temperature. Its energy can be recovered via feed pre-heating thereby resulting in 33% reduction in net energy required. The energy required here is equivalent electrical energy required (equation 16) accounting for energy recovery.
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Chhetri, M., Leonard, D.P., Maurya, S. et al. Electrochemical pumps based on ion-pair membranes for separation of hydrogen from low-concentration mixtures. Nat Energy 9, 1517–1528 (2024). https://doi.org/10.1038/s41560-024-01669-6
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DOI: https://doi.org/10.1038/s41560-024-01669-6