(16a) Quantifying and Mitigating Mass Transfer Losses in Zero-Gap Proton Exchange Membrane Electrochemical H2 Pumps.

Proton exchange membrane (PEM) electrochemical H₂ pumps (EHPs) are an emerging technology for on demand H₂ purification. PEM EHPs have received significant contemporary interest since they enable H₂ to be cheaply transported over long distances using existing natural gas pipelines. EHPs operate by selectively oxidizing H₂ to H⁺ over the anode, transporting the H⁺ through the PEM, and reducing the H⁺ back into pure H₂ over the cathode.¹ The large majority of research efforts aimed at advancing PEM EHP technologies is currently focused on the development of superior PEMs, since ohmic drop is presumed to be the primary mode of voltage losses in these systems. In the present study, we incorporate a reference electrode (RE) into a PEM EHP for the first time in order to assess the validity of this assumption. We demonstrate a rigorous and comprehensive method for designing, calibrating, and validating 3 electrode measurements in zero-gap electrochemical devices. RE calibration is quickly and accurately performed using the anode as an internal reversible H₂ electrode.² Validation is accomplished by demonstrating that 2 and 3 electrode measurements produce identical iR-corrected polarization curves. Our measurements reveal that ohmic drop is the dominant mode of voltage loss at low currents. However, our measurements reveal that polarization losses due to mass transfer at the anode are the dominant mode of voltage loss at high currents. We then develop porous anode electrocatalyst coatings using electrospinning to reduce these polarization losses.³ We demonstrate that these electrospun coatings outperform conventional coatings of identical platinum (Pt) mass loading. As a result, electrospinning reduces mass transfer losses and device cost by improving Pt utilization. The systematic method we have developed for validating 3 electrode measurements in zero-gap electrochemical devices will be of broad interest to the electrocatalysis community.

References

(1)Arunagiri, K.; Wong, A. J.-W.; Briceno-Mena, L.; Elsayed, H. M. G. H.; Romagnoli, J. A.; Janik, M. J.; Arges, C. G. Deconvoluting Charge-Transfer, Mass Transfer, and Ohmic Resistances in Phosphonic Acid–Sulfonic Acid Ionomer Binders Used in Electrochemical Hydrogen Pumps. Energy Environ. Sci.2023, 16 (12), 5916–5932. https://doi.org/10.1039/d3ee01776a.

(2)He, W.; Van Nguyen, T. Edge Effects on Reference Electrode Measurements in PEM Fuel Cells. Electrochem. Soc.2004, 151 (2), A185. https://doi.org/10.1149/1.1634272.

(3)Waldrop, K.; Wycisk, R.; Pintauro, P. N. Application of Electrospinning for the Fabrication of Proton-Exchange Membrane Fuel Cell Electrodes. Opin. Electrochem.2020, 21, 257–264. https://doi.org/10.1016/j.coelec.2020.03.007