Solid-State\nHydroxide Ion Conductivity in Silver(I)\nOxide, Ag<sub>2</sub>O

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