Tailoring manganese oxide with atomic precision to increase surface site availability for oxygen reduction catalysis

Abstract

Controlling the structure of catalysts at the atomic level provides an opportunity to establish detailed understanding of the catalytic form-to-function and realize new, non-equilibrium catalytic structures. Here, advanced thin-film deposition is used to control the atomic structure of La2/3Sr1/3MnO3, a well-known catalyst for the oxygen reduction reaction. The surface and sub-surface is customized, whereas the overall composition and d-electron configuration of the oxide is kept constant. Although the addition of SrMnO3 benefits the oxygen reduction reaction via electronic structure and conductivity improvements, SrMnO3 can react with ambient air to reduce the surface site availability. Placing SrMnO3 in the sub-surface underneath a LaMnO3 overlayer allows the catalyst to maintain the surface site availability while benefiting from improved electronic effects. The results show the promise of advanced thin-film deposition for realizing atomically precise catalysts, in which the surface and sub-surface structure and stoichiometry are tailored for functionality, over controlling only bulk compositions.

Correlating Surface Crystal Orientation and Gas Kinetics in Perovskite Oxide Electrodes

“…It is interesting to note that, despite similar surface terminations among the three surfaces, a high degree of near‐surface or subsurface B ‐site cations still enhances the catalytic reactivity. [ 14,15 ] Ultimately, these differences in surface chemistry explain the lack of mechanistic differences among the three surfaces. With a charge‐transfer‐limited reaction, surface vacancies and near‐surface B ‐site cations are needed for the formation of and subsequent reduction.…”

“…[7][8][9][10][11] Other studies have focused on the relative importance of both surface-termination and sub-surface chemistry of (001)-oriented perovskite surfaces in dictating electrochemical reaction rates. [12][13][14][15] Perovskite electrodes with different exposed crystallographic orientations have also been reported to have different electrochemical reaction rates. [16][17][18] Attempts to study surfaceorientation effects on the gas-exchange kinetics of perovskite electrodes have been accomplished by growing single-layer-perovskite electrodes on perovskite substrates, typically employing techniques such as isotope-tracer diffusion, electrical-conductivity relaxation, and solution-based electrochemical cells.…”

Trends of epitaxial perovskite oxide films catalyzing the oxygen evolution reaction in alkaline media

“…The need to align energy levels does not necessarily impact catalysis negatively. Eom et al [114] and Akbashev et al [99] used atomically controlled multi layers to optimize adsorption properties, stability and the alignment for optimal charge transfer. The prospects of these efforts have also been highlighted by Weber and Gunkel in this Special Issue [150].…”

Carbonate formation lowers the electrocatalytic activity of perovskite oxides for water electrolysis

“…[8][9][10] Epitaxial thin lms allow investigation of oxide catalysts fabricated with unit-cell precision. 11 Recently, we used epitaxial LaNiO 3 layers to demonstrate the important role of the surface terminating layer composition, 12 an activity descriptor that is difficult to recognize in catalysts fabricated using traditional routes. 13,14 Beyond the intrinsic oxide surface composition, surface contaminants may alter the catalyst surface composition and electronic properties, as has been demonstrated extensively at solid/gas interfaces, where trace amounts of CO, CO 2 , and H 2 S are "poisonous" for fuel cell operation.…”