Structural Effects in Polyoxometalate-Based Supramolecular Assemblies for Enhanced Proton Conduction

Proton conductors with engineered charge-assisted hydrogen-bonding networks are pivotal for advancing proton exchange membrane fuel cells (PEMFCs). Herein, a novel proton-conducting supramolecular clusters, ([Bi₆O₅ (OH)₃]_2.24[PW₁₂O₄₀]₁[NO₃]_2.4[H₃O]_5.8, BPN) has been synthesized and characterized. Molecular dynamics (MD) simulations reveal that charge-assisted dynamic O─H⋯O hydrogen bonds mediate the supramolecular assembly, while water molecules facilitate proton transport pathways. The material exhibits a maximum proton conductivity of 0.12 S cm^-1 at 90 °C and 97% (RH) relative humidity, which is comparable to that of Nafion. The spin-lattice relaxation time (T₁) of the Bi-O adsorbed protons is significantly shorter than that of the W-O adsorbed protons, indicating that the protons at the Bi-O sites have a higher migration rate. ¹H magic-angle spinning NMR (¹H MAS NMR) and density functional theory (DFT) calculations reveal [Bi₆O₈] enhances proton mobility, while [PW₁₂O₄₀] stabilizes transition states, lowering the activation barrier to 0.14 eV. The BPN-Nafion hybrid membrane enhances direct methanol fuel cell performance with an open-circuit voltage of 0.82 V and power density of 86 mW cm^-2. This integrative design strategy-synergizing inorganic cluster units with dynamic hydrogen-bonding networks-establishes a scalable platform for developing PEMFC materials with programmable proton transport pathways and improved operational stability.