Research Progress in the Development of High-Temperature Proton Exchange Membranes Based on Phosphonic Acid Group

Increasing the operating temperature of proton exchange membrane fuel cells (PEMFCs) can not only increase their electrocatalytic activities and their tolerance to impurities, such as CO, in feed gas, and decrease the precious metal loading on the electrocatalysts, but also simplify the hydrothermal management system and increase the overall energy conversion efficiency. The core obstacle to realize high-temperature PEMFCs is the development of high-temperature proton exchange membranes (HT-PEMs), so this has attracted much research interest. Among the many types of HT-PEMs, HT-PEMs based on polymeric phosphonic acid are one of the best candidates, and thus is an essential research field. In this article, we review recent research progress in HT-PEMs based on polymeric phosphonic acid, discuss the proton transport mechanism, and compare the proton conductivities, physical and chemical stabilities, and mechanical properties of pristine polymeric phosphonic acid, polymers grafted with phosphonic acid, copolymers consisting of phosphonic acid and heterocyclic bases, and composite membranes based on phosphonic acid and other materials. We finally summarize and give an overview of some of the development trends in HT-PEMs based on polymeric phosphonic acid.