Bipolar membranes with optimized interfacial catalyst loading and 3-D interface design facilitating performance in self-humidifying hydrogen fuel cell

Abstract

Bipolar membranes (BPMs) are emerging as potential polymer electrolyte material for energy conversion technologies like fuel cells, redox-flow batteries, and CO₂ electrolyzers. Water formation at the interface of forward bias BPM facilitates self-humidification in fuel cell and presence of different pH conditions (acidic-anode and alkaline-cathode) in this assembly promotes faster electrode half reactions. Amount of interface catalyst and design of interface in BPM play crucial role in kinetics of water formation. TiO₂ nanoparticles (interface catalyst) of varying loading 0, 1, 2, 3, and 4 mg cm⁻² were used to fabricate BPMs, and their electrochemical performance under forward bias were compared with that of commercial FBM fumasep® membrane. The BPM with 3 mg cm⁻² (BPM-3) of TiO₂ loading showed lowest potential drop, 0.20 V at applied current density of 50 mA cm⁻² compared to BPM-0 (0.375 V) and FBM (0.24 V). The smooth interface of BPM was subsequently modified introducing square and cylindrical shape (3D corrugations over anion exchange layer), which was coated with 3 mg cm⁻² (optimized) catalyst to obtain BPMs with modified interface geometry. BPMs with square corrugation (BPM-3-S) showed potential drop of 0.17 V at 50 mA cm⁻² followed by BPM with cylindrical shape (BPM-3-C), 0.195 V under identical conditions. Finally, fuel cell performance test (without external humidification) was conducted with BPM-3-S, BPM-3, and BPM-0 based membrane electrode assemblies. The peak power densities noted were 578.1 mW cm⁻² (BPM-3-S), 489.6 mW cm⁻² (BPM-3), and 247.5 mW cm⁻² (BPM-0). These findings elucidate catalyst loading and interface geometry strongly influence the performance of BPM under forward bias conditions.