Novel composite Zr/PBI-O-PhT membranes for HT-PEFC applications

Mikhail S Kondratenko,Marat O Gallyamov,Alexei R Khokhlov,Elena P Kharitonova,Yulia A Volkova,Dmitry Yu Razorenov,Igor I Ponomarev

doi:10.3762/bjnano.4.57

Abstract

Novel composite membranes for high temperature polymer-electrolyte fuel cells (HT-PEFC) based on a poly[oxy-3,3-bis(4′-benzimidazol-2″-ylphenyl)phtalide-5″(6″)-diyl] (PBI-O-PhT) polymer with small amounts of added Zr were prepared. It was shown in a model reaction between zirconium acetylacetonate (Zr(acac)4) and benzimidazole (BI) that Zr-atoms are capable to form chemical bonds with BI. Thus, Zr may be used as a crosslinking agent for PBI membranes. The obtained Zr/PBI-O-PhT composite membranes were examined by means of SAXS, thermomechanical analysis (TMA), and were tested in operating fuel cells by means of stationary voltammetry and impedance spectroscopy. The new membranes showed excellent stability in a 2000-hour fuel cell (FC) durability test. The modification of the PBI-O-PhT films with Zr facilitated an increase of the phosphoric acid (PA) uptake by the membranes, which resulted in an up to 2.5 times increased proton conductivity. The existence of an optimal amount of Zr content in the modified PBI-O-PhT film was shown. Larger amounts of Zr lead to a lower PA doping level and a reduced conductivity due to an excessively high degree of crosslinking.

Highlights

Polymer-electrolyte fuel cells (PEFC) based on polybenzimidazole (PBI) membranes doped with phosphoric acid (PA) as an electrolyte can be operated without any humidification of reactant gases at an elevated temperature range, in which the CO tolerance of the Pt catalyst becomes higher
For the present paper we examined the properties of composite membranes based on poly[oxy-3,3bis(4′-benzimidazol-2′′-ylphenyl)phtalide-5′′(6′′)-diyl] (PBI-OPhT, chemical structure is shown in Figure 1 ) [18,19] with the addition of small amounts of zirconium
According to the obtained data, Zr-based crystallites are not formed, so that Zr atoms should be uniformly distributed inside the PBI-O-PhT films

Summary

Introduction

Polymer-electrolyte fuel cells (PEFC) based on polybenzimidazole (PBI) membranes doped with phosphoric acid (PA) as an electrolyte can be operated without any humidification of reactant gases at an elevated temperature range, in which the CO tolerance of the Pt catalyst becomes higher. In order to confirm the active role of zirconium in the PBI-O-PhT crosslinking process we studied a model reaction of benzimidazole (BI) with Zr(acac)4 in a melt in the temperature range of 320–350 °C, which was applied for heating the films. 2000 hour durability test PBI-O-PhT modified by adding 0.75 wt % Zr(acac)4 and a nonmodified PBI-O-PhT reference membrane were tested in fuel cells operating at 160 °C at a constant current density of 0.4 A·cm−2 for 2000 h.

Results

Conclusion