Microscopic insight into phase separation of poly (arylene piperidine)s-based high-temperature proton exchange membrane: A molecular simulation study

The formation of micro-phase separation is an effective solution to improve the mechanical property of phosphoric acids (PA) doped high temperature proton exchange membranes (HT-PEMs) while keeping the proton conductivity. However, it's still a challenge to understand the regulation of PA distribution during phase-separation formation at microscopic level. In this work, we investigated the influence of polymer structures on PA distribution in poly (arylene piperidine)s (PAPs)-based membranes using molecular simulation methods. The study reveals the electron localization and density of acidophilic groups in polymers play crucial roles for the PA distribution during phase-separation formation. Stronger electron localization of acidophilic groups contribute to the phase separation, resulting in PA aggregation around acidophilic groups and benefiting the hydrogen bonds network continuity, which could improve proton conductivity of membrane. The hydrogen bond formed around polymers is proportional to acidophilic groups density, while tensile strength is inversely proportional to the density. As a result, the piperidine with terphenyl exhibits a rational polymer structure for PAPs-based HT-PEM to keep high proton conductivity and mechanical property. This work provides a microscopic insight to understand the phase separation for the design of HT-PEMs.