Explosive mixture formation in PEM electrolyzers: A safety review using fault tree analysis

Water electrolysis, particularly using polymer electrolyte membrane (PEM) technology, stands out for producing high-purity hydrogen efficiently. However, several safety and operational challenges that must be addressed before large-scale commercialization, includes design considerations, operating conditions, and membrane durability. This review explores potential pathways resulting in cross-permeation and membrane degradation in PEM electrolyzers, potentially forming an H2/O2 explosive mixture. A fault tree analysis approach is implemented, identifying the formation of an H2/O2 explosive mixture as the top event. The fault tree analysis highlights the main challenges associated with the design and setup of the membrane, as well as the conditions affecting the membrane electrode assembly. Additionally, a minimum cut set analysis is performed to simplify the fault tree analysis by identifying the smallest combinations of events that could result in the formation of H2/O2 explosive mixture. The fault tree analysis concludes that the formation of the explosive mixture is largely driven by significant hydrogen permeation, which is influenced by high cathode pressure, mass transfer limitations, and membrane damage caused by mechanical, chemical, and thermal factors. Thirteen basic events were categorized into human error, cell integrity, equipment integrity, and external factors. The analysis resulted in first-order cut sets, meaning any single failure could trigger the top event. Chemical poisoning also emerged as a persistent contributor affecting most failure pathways. This analysis lays the groundwork for future research to improve the reliability and safety of PEM electrolyzers.