Predicting and extending the bubble-free operating limit of capillary-fed water electrolysis

Abstract

Gas bubbles impose large penalties in water electrolysis at industrially relevant rates. Capillary-fed electrolyzers greatly mitigate them by wicking electrolyte to electrodes and venting gas from the backside, but only below a threshold current density. We show that the separator pore size sets this threshold through two opposing effects: smaller pores raise the supersaturation required for nucleation but reduce the permeability for electrolyte replenishment. A coupled electrochemical-transport model, anchored to a single measured onset, quantifies both mechanisms across 0.1-8 μm pores. Experimentally, reducing pore size from 8 to 1.2 μm raises the bubble onset limit from 0.18 to 1.73 A cm⁻² and lowers cell voltage by 0.11 V at 1 A cm⁻², primarily by suppressing bubble-induced overpotential. At 0.45 μm and below, the replenishment limit takes over and the cells dry out before bubbles form. Our findings establish the bubble-free operation limit as designable rather than purely empirical.

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BibTeX RIS

BibTeX

@misc{khodabandeh2026predicting,
  title = {{Predicting and extending the bubble-free operating limit of capillary-fed water electrolysis}},
  author = {Farkhondeh Khodabandeh and Zhengmao Lu},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.03782},
  eprint = {2610.03782},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.03782},
}

RIS

TY  - UNPB
TI  - Predicting and extending the bubble-free operating limit of capillary-fed water electrolysis
AU  - Farkhondeh Khodabandeh
AU  - Zhengmao Lu
PY  - 2026
DA  - 2026/10/01
PB  - arXiv
DO  - 10.48550/arxiv.2610.03782
UR  - https://arxiv.org/abs/2610.03782
AB  - Gas bubbles impose large penalties in water electrolysis at industrially relevant rates. Capillary-fed electrolyzers greatly mitigate them by wicking electrolyte to electrodes and venting gas from the backside, but only below a threshold current density. We show that the separator pore size sets this threshold through two opposing effects: smaller pores raise the supersaturation required for nucleation but reduce the permeability for electrolyte replenishment. A coupled electrochemical-transport model, anchored to a single measured onset, quantifies both mechanisms across 0.1-8 μm pores. Experimentally, reducing pore size from 8 to 1.2 μm raises the bubble onset limit from 0.18 to 1.73 A cm^−2 and lowers cell voltage by 0.11 V at 1 A cm^−2, primarily by suppressing bubble-induced overpotential. At 0.45 μm and below, the replenishment limit takes over and the cells dry out before bubbles form. Our findings establish the bubble-free operation limit as designable rather than purely empirical.
ER  -

Abstract

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