Short-Side-Chain Membranes with Stabilized Superacid on Graphitic Carbon Nitride for Polymer Electrolyte Fuel Cells under Low-Humidity Conditions

The integration of superacid-like heteropolyacids offers a promising route to develop highly proton-conducting membranes for energy storage and conversion. However, the inherent hydrophilicity of these acids can cause leaching, which undermines the fuel cell performance. In our research, we engineered a proton-conductive membrane with a facile hydrothermal synthesis approach to form stabilized hybrid superacids, namely, phosphotungstic acid (PTA), with graphitic carbon nitride (PCN) and its incorporation in a short-side-chain ionomer, namely, Aquivion. This unique approach via PCN nanohybrids enhances the proton transport within the membrane. These nanohybrids effectively combined the strong acidity of PTA with continuous 2D proton-transport pathways via a short side chain, resulting in a notable proton conductivity of 0.228 S cm^–1 at 80 °C under 95% relative humidity. The real impact was evident in the performance of fuel cells using the Aquivion/PCN nanocomposite membrane, which demonstrated a significant improvement of 34% in the peak power density (1.0 W cm^–2), and 44% cell performance (0.98 A cm^–2) was retained for the nanocomposite membrane at a low relatively humidity (30% RH) at 0.6 V. This advancement represents a major leap in energy conversion and storage technologies at low-humidity conditions.