Structure Determination of the Oxygen Evolution Catalyst Mössbauerite

Layered double hydroxides (LDHs) of various compositions have been shown to be potent photo- and electrocatalysts. Recently, mössbauerite, obtained by chemical oxidation of an all-iron, mixed-valence green rust (GR) LDH, was introduced as an efficient oxygen evolution reaction (OER) electrocatalyst. An accurate characterization of the structure of mössbauerite is necessary for a knowledge-based future optimization of OER performance. However, as is typical for layered materials, massive defects hamper the understanding of its true structure. In this work, we elucidate the structure of mössbauerite and gain insight into the structure–property relationships relevant to its potential as an OER catalyst. Density functional theory calculations show that upon oxidation of a GR precursor to mössbauerite, the direct grafting of interlayer anions to octahedral iron becomes energetically feasible. This indicates that the grafted and interlayer carbonate anions may coexist in a random interstratification. This prediction is supported by analysis of infrared spectroscopy and X-ray powder diffraction data, which show that an interstratified model with turbostratic planar disorder provides a good fit with the experiment.