Network Size Control in Coordination Polymer Glasses and Its Impact on Viscosity and H⁺ Conductivity

Network structures of glasses are essential to understanding their bulk mechanical and functional properties. Despite growing interests in coordination polymer (CP) and metal–organic framework (MOF) glasses, the macromolecular tuning of the coordination networks (CN) of CP/MOF glasses remains unexplored. Here, we propose the use of the CN size of CP glasses to investigate their network-dependent viscoelastic properties and proton (H+) conductivities. Structural analysis of the CP glasses having different ratios of Zn/HnPO4 (1:3, 0.875:3, 0.75:3) exhibits ratio-dependent CN sizes. These diverse CN sizes resulted in a wide range of viscosity (η = 106–101 Pa·s). The CP glasses with a wide range of viscosity exhibit, counterintuitively, similar high H+ conductivities (σ > 10–2 S·cm–1 at 120 °C) with slight network-dependent behavior. This tunable viscosity with high H+ conductivity enables the comparative analysis of CP glasses as an electrolyte layer in H2/O2 fuel cells. Each CP glass showed a high open-circuit voltage (>0.95 V) in the fuel cell, and the maximum power densities (75–150 mW·cm–2) were dominated by its viscosity rather than H+ conductivities. The CN size control provides a new class of electrolytes that overcome the trade-off between mechanical properties and ion transport dynamics.

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