Electrochemical Characterization of Novel Polyantimonic-Acid-Based Proton Conductors for Low- and Intermediate-Temperature Fuel Cells

Olga Yu Kurapova,Artem A Glukharev,Vasily V Pazheltsev,Artem A Zaripov,Vladimir G Konakov,Pedro M Faia

doi:10.3390/app112411877

Abstract

The development of novel proton-conducting membrane materials for electrochemical power units, i.e., low temperature fuel cells (FCs), efficiently working up to 300 °C, is a critical problem related to the rapid shift to hydrogen energy. Polyantimonic acid (PAA) is characterized by high conductivity, sufficient thermal stability and can be regarded as a prospective proton-conducting material. However, the fabrication of bulk PAA-based membranes with high proton conductivity remains a challenging task. In the present work, for the first time, the authors report the investigation on proton conductivity of bulk PAA-based membranes in the temperature range 25–250 °C, both in dry air and in moisturized air. Using PAA powder and fluoroplastic as a binder, fully dense cylindrical membranes were formed by cold uniaxial pressing. The structures of the PAA-based membranes were investigated by SEM, EDX, XRD and Raman techniques. STA coupled with in situ thermo-XRD analysis revealed that the obtained membranes corresponded with Sb2O5·3H2O with pyrochlore structure, and that no phase transitions took place up to 330 °C. PAA-based membranes possess a high-grain component of conductivity, 5 × 10−2 S/cm. Grain boundary conductivities of 90PAA and 80PAA membranes increase with relative humidity content and their values change non-linearly in the range 25–250 °C.

Highlights

The increasing need in clean energy resources is promoting research in the field of proton-conducting materials for low- and intermediate-temperature fuel cells (FCs) [1,2,3].Membrane electrode assemblies (MEAs) play a key role in the overall fuel cell performance, because electrochemical reactions occur [4]
According to the STA results, a 10 wt.% binder addition caused a shift in the maximum of the first endothermic effect from 57.1 to 100.5 ◦ C, indicating the retention of 0.1 mol of non-specific adsorbed water in the Polyantimonic acid (PAA) after synthesis, in agreement with the schematic reactions presented in Equations (4) and (5)
Via STA and XRD data, it was shown that PAA after synthesis exhibits a pyrochlore structure corresponding with Sb2 O5 ·3H2 O

Summary

Introduction

Membrane electrode assemblies (MEAs) play a key role in the overall fuel cell performance, because electrochemical reactions occur [4]. These consist of dense membranes (electrolytes) placed between porous electrodes. The general requirements for electrolyte use as a membrane in electrochemical cells (such as fuel cells), electrochemical reactors and sensors are [9]: high conductivity in the required temperature range; fast proton transport; temperature and phase (structural) stability; absence of side reactions with anode and interconnect materials, i.e., chemical inertness; and high density of the membrane, making it impenetrable for the other components of a gas or fuel mixture

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