Membrane distillation for producing ultra-pure water for PEM electrolysis

The growing focus on water electrolysis in recent years suggests a significant future demand for ultra-pure water resources. At present, ultra-pure water, typically sourced from municipal drinking supplies, is utilized by proton exchange membrane (PEM) electrolysis. However, to satisfy the increasing hydrogen demand, exploring alternative water sources is imperative. This study assessed the feasibility of direct contact membrane distillation (DCMD) for purifying various water sources, including synthetic river, lake, groundwater, seawater, as well as real tap water and other natural water bodies for use in PEM electrolyzers. To evaluate the suitability of DCMD for PEM electrolysis, the assessment was conducted from three perspectives: (1) the purity of the permeate from DCMD, including conductivity, pH, total organic carbon, and ionic concentration; (2) the average flux of the output permeate; and (3) the effective utilization of waste heat from the PEM electrolyzer within the DCMD-PEM integrated system designed in this study. The results revealed that the conductivity of the permeate from synthetic water samples was as low as 1.34 μS/cm, while that from real water samples varied between 0.98 and 3.19 μS/cm. Additionally, the modeling of utilization of waste heat from PEM electrolyzer showed the optimal working conditions for the integrated system. This study provides new insights on integrated DCMD-PEM electrolysis system capable of extracting ultra-pure water from a wide range of water sources, thereby alleviating the potential strain on local freshwater resources caused by the adoption of electrolyzers. Furthermore, the system enables the effective utilization of waste heat, contributing to improved energy efficiency.