Solid-State Hydroxide Ion Conductivity in Silver(I) Oxide, Ag₂O

Silver(I) oxide, Ag₂O, precipitated as microcrystals by combining aqueous silver(I) nitrate and KOH solutions, was found to be a solid-state hydroxide ion conductor with ionic conductivity on the order of 10^-3 S/cm. The proton chemical shifts at 4.87 and −7.35 ppm measured by solid-state ¹H NMR experiments are attributed to water molecules and in-lattice OH^- coordinated to silver, respectively. The lack of spinning sidebands around the 4.87 ppm peak indicates rapid reorientation on the NMR time scale, suggesting that the water molecules are adsorbed to the surface of the Ag₂O crystals. Pulsed field gradient measurements gave similar diffusion coefficients (2 × 10^-7 cm²/s at 298 K) for all three proton environments, indicating chemical exchange between sites on the millisecond time scale. The activation energy for OH^- diffusion measured by NMR (0.18 eV) was comparable to that obtained by conductivity measurements and density functional theory (DFT) electronic structure calculations. The calculated Pourbaix diagram of Ag₂O is consistent with the slightly lower sample density observed in He pycnometry and thermogravimetric measurements.