Undervoltage Alkaline Water Electrolysis to Optimize Electrolyzer Efficiency for Sustainable Generation of Hydrogen

Abstract

This thesis investigates undervoltage electrolysis in alkaline water electrolyzers to enhance hydrogen production efficiency at voltages below the thermoneutral threshold (1.48V). Through theoretical modeling and experiments, key techniques for detecting evolved hydrogen under these conditions are explored. A thermodynamic and quantum tunneling model explains electrolysis behavior at sub-threshold voltages, supported by experimental data showing current onset below 1.23V. Elevated temperatures improve efficiency by lowering the thermodynamic threshold, while quantum tunneling reduces activation overpotential losses, enabling hydrogen production at lower voltages. Challenges in hydrogen detection under undervoltage conditions are examined using a metal oxide (MOx) H2 sensor and a residual gas analyzer (RGA). Nickel foam electrodes and modified electrolysis setups enhance current with increased anode size. The MOx sensor effectively tracks hydrogen evolution at 1.2V, whereas the RGA detects trace hydrogen only at 2V due to interference from high leak rates. A novel cyclic voltammetry-based dissolved hydrogen detection method is introduced by integrating the electrolyzer with a reference electrode. Results reveal hydrogen evolution occurs primarily in dissolved form at undervoltage levels, highlighting the role of thermal energy in sustaining undervoltage hydrogen production. These findings provide a foundation for leveraging waste thermal energy to minimize electrical input in sustainable hydrogen generation.