Lang Sandra M, Zimmermann Nina, Bernhardt Thorsten M, Barnett Robert N, Yoon Bokwon, Landman Uzi
Institute of Surface Chemistry and Catalysis, University of Ulm, 89069 Ulm, Germany.
School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, United States.
J Phys Chem Lett. 2021 Jun 10;12(22):5248-5255. doi: 10.1021/acs.jpclett.1c01299. Epub 2021 May 28.
Gas-phase ion-trap reactivity experiments and density functional simulations reveal that water oxidation to HO mediated by (calcium) manganese oxide clusters proceeds via formation of a terminal oxyl radical followed by oxyl/hydroxy O-O coupling. This mechanism is predicted to be energetically feasible for MnO ( = 2-4) and the binary CaMnO, in agreement with the experimental observations. In contrast, the reaction does not proceed for the tetramanganese oxides MnO ( = 4-6) under these experimental conditions. This is attributed to the high fluxionality of the tetramanganese clusters, resulting in the instability of the terminal oxyl radical as well as an energetically unfavorable change of the spin state required for HO formation. Ca doping, yielding a symmetry-broken lower-symmetry three-dimensional (3D) CaMnO cluster, results in structural stabilization of the oxyl radical configuration, accompanied by a favorable coupling between potential energy surfaces with different spin states, thus enabling the cluster-mediated water oxidation reaction and HO formation.
