New high-performance bulky N-heterocyclic group functionalized poly(terphenyl piperidinium) membranes for HT-PEMFC applications

Highly proton-conductive and low swelling polymeric membranes achieved by hydrophilic covalent cross-linking

Proton exchange membranes (PEMs) applied in fuel cell technology suffer from the trade-off between fast proton conduction and durable operation involving dimensional stability, mechanical strength, and oxidative resistance. To address this issue, a novel branched polybenzimidazole (brPBI) was synthesized, covalently cross-linked with (3-chloropropyl)triethoxysilane (CTS), and doped with a novel proton conductor FeATMP to prepare brPBI-CTS/FeATMP membranes. The branching degree of brPBI was optimized to achieve high molecular weight while the branching structure offered high free volume, abundant end-groups, and self-cross-linking moiety that enhanced proton conduction and dimensional/mechanical/oxidative stability. Covalent cross-linking with CTS enhanced the dimensional, mechanical, and oxidative stability while improving the water-assisted proton conduction owing to the hydrophilic nature of siloxane structure formed. At 180 ℃, the proton conductivity of the brPBI3-CTS/FeATMP composite membrane reached 0.136, 0.073, and 0.041 S cm-1 at 100 % RH, 50 % RH, and 0 % RH, respectively, while its swelling ratio after immersion in water at 90 ℃ for 24 h was 4.69 %. The performance of the membranes demonstrated that construction of hydrophilic structure by covalent cross-linking was a successful strategy to break the trade-off effect for PEMs.

Preparation of novel membranes with multiple hydrogen bonding sites and π-conjugated structure for high temperature proton exchange membrane fuel cells

A novel poly(dibenzofuran isatin) (PBFI) with π conjugated structure was synthesized. Through the facile ring-opening reaction, flexible and hydrophilic side chains with hydroxyl and quaternary ammounium groups were grafted into PBFI. Obtained PBFI-x%GTA membranes with twisted polymer structure and multiple hydrogen bonding sites displayed high HT-PEMFC performance.

Rational Materials and Structure Design for Improving the Performance and Durability of High Temperature Proton Exchange Membranes (HT-PEMs)

Hydrogen energy as the next-generation clean energy carrier has attracted the attention of both academic and industrial fields. A key limit in the current stage is the operation temperature of hydrogen fuel cells, which lies in the slow development of high-temperature and high-efficiency proton exchange membranes. Currently, much research effort has been devoted to this field, and very innovative material systems have been developed. The authors think it is the right time to make a short summary of the high-temperature proton exchange membranes (HT-PEMs), the fundamentals, and developments, which can help the researchers to clearly and efficiently gain the key information. In this paper, the development of key materials and optimization strategies, the degradation mechanism and possible solutions, and the most common morphology characterization techniques as well as correlations between morphology and overall properties have been systematically summarized.

Impact of Separator Thickness on Temperature Distribution in Single Cell of Polymer Electrolyte Fuel Cell Operated at Higher Temperature of 90 °C and 100 °C

The New Energy and Industry Technology Development Organization (NEDO) road map (Japan, 2017) has proposed that a polymer electrolyte fuel cell (PEFC) system, which operates at a temperature of 90 °C and 100 °C, be applied for stationary and mobility usage, respectively. This study suggests using a thin polymer electrolyte membrane (PEM) and a thin gas diffusion layer (GDL), at the same time, to achieve better power-generation performance, at a higher temperature than usual. The focus of this paper is to clarify the effect of separator thickness on the distribution of temperature at the reaction surface (Treact), with the relative humidity (RH) of the supply gasses and initial operation temperature (Tini), quantitatively. In this study, separator thickness is investigated in a system using a thin PEM and a thin GDL. Moreover, this study investigates the difference between the maximum temperature and the minimum temperature obtained from the distribution of Treact as well as the relation between the standard deviation of Treact − Tini and total voltage, to clarify the effect of separator thickness. The impact of the flow rates of the supply gases on the distribution of Treact is not large, among the investigated conditions. It is noticed that the temperature distribution is wider when a separator thickness of 2.0 mm is selected. On the other hand, it is observed that the temperature increases along with the gas flow through the gas channel, by approximately 2 °C, when using a separator thickness between 1.5 mm and 1.0 mm. The impact of the RH on the distributions of Treact − Tini is larger at Tini = 100 °C, when a separator thickness of 1.0 mm is selected. It is revealed that the wider temperature distribution provides a reduction in power-generation performance. This study proposes that the thin separators, i.e., with a thickness of 1.5 mm and 1.0 mm, are not suitable for higher temperature operation than usual.

Numerical Simulation on Impacts of Thickness of Nafion Series Membranes and Relative Humidity on PEMFC Operated at 363 K and 373 K

The purpose of this study is to understand the impact of the thickness of Nafion membrane, which is a typical polymer electrolyte membrane (PEM) in Polymer Electrolyte Membrane Fuel Cells (PEMFCs), and relative humidity of supply gas on the distributions of H2, O2, H2O concentration and current density on the interface between a Nafion membrane and anode catalyst layer or the interface between a Nafion membrane and cathode catalyst layer. The effect of the initial temperature of the cell (Tini) is also investigated by the numerical simulation using the 3D model by COMSOL Multiphysics. As a result, the current density decreases along with the gas flow through the gas channel irrespective of the Nafion membrane thickness and Tini, which can be explained by the concentration distribution of H2 and O2 consumed by electrochemical reaction. The molar concentration of H2O decreases when the thickness of Nafion membrane increases, irrespective of Tini and the relative humidity of the supply gas. The current density increases with the increase in relative humidity of the supply gas, irrespective of the Nafion membrane thickness and Tini. This study recommends that a thinner Nafion membrane with well-humidified supply gas would promote high power generation at the target temperature of 363 K and 373 K.