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Ion Transport Control in Alkaline Water Electrolyzers at Elevated Temperatures Revealed by Molecular Simulations and Multiphysics Modeling

Anusha Tripathi, Viraj Bhatt, Shaswat Srivastava, Sanjeev Kumar, and Ananth Govind Rajan*

  • *Contact author: ananthgr@iisc.ac.in
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PRX Energy 5, 033008 – Published 30 July, 2026

DOI: https://doi.org/10.1103/8zs3-7ynk

Abstract

Alkaline water electrolyzers (AWEs) offer a carbon dioxide-emission-free route to convert renewable electricity into hydrogen. Improving their efficiency requires a deep understanding of transport and kinetics within an electrolytic cell. By combining molecular simulations of ion diffusivities with detailed multiphysics simulations, we report here a surprising finding that neglecting the temperature dependence of ion transport in an AWE could lead to erroneous predictions of current density reducing with increasing temperature. This is because ion mobilities reduce with temperature, leading to severe transport limitations if diffusivities are considered to be independent of temperature. We model ion diffusion, migration, and convection via the Nernst-Planck formulation, fluid dynamics via the continuum Euler-Euler approach, along with electrode kinetics at the Butler-Volmer level of theory. We carry out molecular dynamics simulations to determine the temperature dependence of OH− and K+ diffusivities and show that considering temperature-dependent diffusivities leads to the current density increasing with temperature. We also demonstrate that gas bubble formation and OH− concentration gradients lead to reduced electrolyte conductivity near the electrodes. The higher levels of cathodic gas production, as compared to those at the anode, lead to asymmetries in the concentration profiles. We provide physical understanding regarding these observations, including that at high cell potentials, transport limitations play a crucial role in modulating AWE performance. Overall, our findings provide critical insights into the interplay between ion transport, temperature, and electrochemical performance, which are crucial for accurate multiscale simulations and modeling-based optimization of such devices.

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Alkaline water electrolyzers (AWEs) are a promising technology for producing clean hydrogen using renewable electricity. However, improving their efficiency requires a clear understanding of how ions move and react inside the device, especially at higher temperatures. In this work, the authors combine atomic-scale simulations with macroscale multiphysics modeling to uncover how temperature affects ion transport and overall performance in AWEs. They find that the typical assumption of constant ion transport properties across changing temperatures can lead to a misleading prediction that performance worsens at higher temperatures. In contrast, when the temperature dependence of ion diffusivity is properly taken into account, the current density increases as temperature rises. The authors’ simulations capture the coupled effects of ion diffusion, electrical migration, fluid flow, and electrode reactions. They also show that gas bubbles formed during operation impede ion transport by reducing ionic conductivity near the electrodes. Notably, differences in gas production rates between the cathode and anode lead to asymmetries in electrolyte behavior. Overall, this study highlights the critical role of temperature-dependent ion transport and coupled physical effects in determining electrolyzer performance, providing valuable insights for designing more efficient hydrogen production systems.

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PRX Energy 5, 033008– Published 30 July, 2026
  • Received 10 October 2025
  • Revised 29 May 2026
  • Accepted 18 June 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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