The dynamic energetic response of a zero-gap PEM electrolyzer: tracking thermal losses and energy conversion efficiency

Efficient small-scale hydrogen production via proton exchange membrane (PEM) electrolysis is increasingly recognized as a key pathway for producing green hydrogen and supporting the transition toward low-carbon energy systems. Achieving this goal requires a detailed understanding of the coupled electrochemical, thermal, and energetic phenomena governing stack performance under dynamic operating conditions. This study experimentally investigates a five-cell zero-gap PEM electrolyzer stack equipped with Nafion™ 117 membranes, titanium mesh electrodes, and stainless steel bipolar plates. The system is designed for laboratory-scale hydrogen production and evaluated under controlled operating conditions to quantify energy losses, thermal behavior, and hydrogen generation efficiency.

The experimental protocol includes membrane hydration, stack thermal stabilization, low-current electrochemical conditioning, and systematic polarization testing over an applied current density up to 0.3 A/cm². Stack temperatures during operation range from approximately 312.1 at to 322.8 K, for water circulating at 55±3 °C at 200 mL/min. Hydrogen production is experimentally measured using a calibrated collection bag and compared against theoretical hydrogen generation calculated using Faraday’s law. The resulting Faradaic efficiency increased at relatively moderate current densities, indicating improved electrochemical utilization, to reach 98.03%.

Infrared (IR) thermography reveals non-uniform temperature distributions across the electrolyzer stack, with inter-cell and in-plane temperature gradients exceeding 9 °C, even under relatively low-current operation. As current density increases, localized hotspots become more pronounced, highlighting the role of ohmic heating and uneven current distribution.

Energy efficiency, calculated by combining electrical input power with measured hydrogen production rates, remains above 50% at relatively moderate current densities. However, efficiency declines significantly at higher currents due to the combined effects of increased ohmic losses, charge transfer limitations, and thermal non-uniformities. The results demonstrate a clear coupling between electrochemical resistance growth, thermal gradients, and reduced hydrogen production efficiency.

Overall, this work provides a comprehensive characterization of the dynamic energetic response of a small-scale zero-gap PEM electrolyzer. By directly linking experimental hydrogen production and spatially resolved thermal behavior, the study offers valuable insights into loss mechanisms that limit efficiency and operational stability. These findings underscore the importance of optimized thermal management, material selection, and operating strategies for improving the performance and durability of small-scale PEM electrolyzers in green hydrogen applications. These findings are particularly relevant for improving the energy efficiency and durability of PEM electrolyzers used in renewable-energy-driven hydrogen production, thereby contributing to the development of more environmentally sustainable hydrogen technologies.