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Heterogeneous Water Oxidation: Surface Activity versus Amorphization Activation in Cobalt Phosphate Catalysts
Author(s) -
GonzálezFlores Diego,
Sánchez Irene,
Zaharieva Ivelina,
Klingan Katharina,
Heidkamp Jonathan,
Chernev Petko,
Menezes Prashanth W.,
Driess Matthias,
Dau Holger,
Montero Mavis L.
Publication year - 2015
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201409333
Subject(s) - catalysis , cobalt , amorphous solid , oxidizing agent , cobalt oxide , oxide , crystallite , chemical engineering , chemistry , inorganic chemistry , electrolyte , electrochemistry , materials science , heterogeneous catalysis , crystallography , electrode , organic chemistry , engineering
Is water oxidation catalyzed at the surface or within the bulk volume of solid oxide materials? This question is addressed for cobalt phosphate catalysts deposited on inert electrodes, namely crystallites of pakhomovskyite (Co 3 (PO 4 ) 2 ⋅8 H 2 O, Pak) and phosphate‐containing Co oxide (CoCat). X‐ray spectroscopy reveals that oxidizing potentials transform the crystalline Pak slowly (5–8 h) but completely into the amorphous CoCat. Electrochemical analysis supports high‐TOF surface activity in Pak, whereas its amorphization results in dominating volume activity of the thereby formed CoCat material. In the directly electrodeposited CoCat, volume catalysis prevails, but not at very low levels of the amorphous material, implying high‐TOF catalysis at surface sites. A complete picture of heterogeneous water oxidation requires insight in catalysis at the electrolyte‐exposed “outer surface”, within a hydrated, amorphous volume phase, and modes and kinetics of restructuring upon operation.