Organic-inorganic composite membranes have been attracting attention for decades to improve the performance of membranes in many applications due to the various properties of inorganics. Their applications include membranes used to remove impurities from wastewater - , membrane reactors - , and separators for batteries such as lithium-ion batteries and redox-flow batteries . Among the several applications, the electrolyte membranes in polymer electrolyte membrane fuel cells (PEMFCs) have attracted significant attention. It is because PEMFCs are promising power generation devices with high energy efficiency and less environmental damage, and are expected to replace internal combustion engines in the future.