Kinetic origin of the sub-Nernstian cell voltage response in pressurised PEM water electrolysis

Authored by

Katende Jonathan Kabamba, Tobias Binninger, Boris Bensmann, Rhiyaad Mohamed

Abstract

Proton-exchange-membrane water electrolysers (PEMWEs) can directly produce pressurised hydrogen, thereby reducing the need for downstream compression. Experimental studies have consistently reported a sub-Nernstian increase in PEMWE operating voltage under elevated pressure; however, existing modelling approaches have struggled to provide a satisfactory explanation for this behaviour. Here, a combined theoretical–experimental study is presented to elucidate the kinetic origin of pressure effects in PEMWE operation. Experiments conducted under differential and balanced pressurisation demonstrate a sub-Nernstian response of the PEMWE polarisation curve governed by cathode pressure, while anode pressurisation shows no kinetic effect. This behaviour is explained using a novel kinetic modelling framework that explicitly accounts for the distinct contributions of the oxygen evolution (OER), hydrogen evolution (HER), and hydrogen oxidation (HOR) reactions to the activation losses, formulated on a fixed reference potential scale. The model accurately reproduces the experimentally observed sub-Nernstian voltage response through simultaneous fitting of the polarisation data acquired at multiple operating pressures. In addition, the model provides a kinetic explanation for the deviations from linear Tafel behaviour observed at intermediate current densities.

Details

Organisation(s): Section Electrical Energy Storage Systems
External Organisation(s): University of Cape Town (UCT)
Forschungszentrum Jülich
Type: Article
Journal: International Journal of Hydrogen Energy
Volume: 226
ISSN: 0360-3199
Publication date: 16.04.2026
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Renewable Energy, Sustainability and the Environment, Fuel Technology, Condensed Matter Physics, Energy Engineering and Power Technology
Sustainable Development Goals: SDG 7 - Affordable and Clean Energy
Electronic version(s): https://doi.org/10.1016/j.ijhydene.2026.154454 (Access: Open )