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.