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Preparation of Polyoxometalate-based Photo-responsive Membranes for the Photo-activation of Manganese Oxide Catalysts
Published on: August 7, 2018
Electrosynthesis of Biomimetic Manganese-Calcium Oxides for Water Oxidation Catalysis--Atomic Structure and
Diego González-Flores1, Ivelina Zaharieva1, Jonathan Heidkamp1
1Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
Abstract:
Water-oxidizing calcium-manganese oxides, which mimic the inorganic core of the biological catalyst, were synthesized and structurally characterized by X-ray absorption spectroscopy at the manganese and calcium K edges. The amorphous, birnesite-type oxides are obtained through a simple protocol that involves electrodeposition followed by active-site creation through annealing at moderate temperatures. Calcium ions are inessential, but tune the electrocatalytic properties. For increasing calcium/manganese molar ratios, both Tafel slopes and exchange current densities decrease gradually, resulting in optimal catalytic performance at calcium/manganese molar ratios of close to 10 %. Tracking UV/Vis absorption changes during electrochemical operation suggests that inactive oxides reach their highest, all-Mn(IV) oxidation state at comparably low electrode potentials. The ability to undergo redox transitions and the presence of a minor fraction of Mn(III) ions at catalytic potentials is identified as a prerequisite for catalytic activity.
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