An experimentally validated model of electrolyte effects in alkaline water electrolysis

Alkaline water electrolysis is a key technology for green hydrogen production, yet the performance of small-scale systems operating with low electrolyte concentrations remains underexplored. This study addresses this gap by developing and experimentally validating a numerical model for a laboratory-scale, bipolar alkaline electrolyser. An electrochemical model, accounting for reversible voltage, activation, and ohmic overpotentials, including the effects of gas bubble formation, was created to simulate the electrolyser's performance across potassium hydroxide concentrations ranging from 3 to 15% by mass. The model demonstrated good agreement with experimental polarisation curves, particularly at an operating voltage of 12 V, yielding mean relative errors between 1.4 and 10.5%. Results confirmed that higher potassium hydroxide concentrations significantly enhanced current density due to improved ionic conductivity. Voltage decomposition analysis identified activation overpotential as the dominant source of efficiency loss across all conditions. Furthermore, the model showed that gas bubble formation contributes progressively more to overpotentials at higher current densities, with its impact most significant in the electrolyte and at the cathode. This work presents a validated tool for predicting electrolyser performance and underscores the critical role of electrolyte composition in balancing ionic conductivity and electrochemical losses, offering valuable insights for optimising simpler and safer off-grid hydrogen systems.