NDLI: Different catalytic behavior of amorphous and crystalline cobalt tungstate for electrochemical water oxidation

Content Provider	Royal Society of Chemistry (RSC)
Author	Ling, Chen Zhou, Li Qin Sekito, Takeshi Markin, Zachary Jia, Hongfei Stark, Jason
Copyright Year	2012
Abstract	Amorphous and crystalline cobalt tungstate (CoWO4) particles, synthesized by solution co-precipitation and subsequent heat treatment, were examined on rotating disk electrodes as water oxidation catalysts. In close to neutral electrolyte (0.2 M Na2WO4, pH 8.0), amorphous CoWO4 exhibited much higher catalytic activity than its crystalline counterpart over an overpotential range of 0.25 to 0.45 V. Calculated Tafel slopes are ∼60 mV per decade for amorphous and ∼110 mV per decade for crystalline electrodes, while the exchange current density of crystalline catalysts is two orders of magnitude higher than that of amorphous. Elemental analysis did not identify substantial composition changes in either amorphous or crystalline films on indium tin oxide (ITO) electrodes, after being used for multiple cyclic voltammetry and bulk electrolysis tests. However, X-ray photoelectron spectroscopy (XPS) revealed that the oxidation state of the surface Co atoms on amorphous catalyst film changed from +2 to +3, although no difference was found in crystalline CoWO4 . The characteristics of the amorphous catalyst closely resemble the well known self-repairing cobalt phosphate catalytic film (Co–Pi), in which the cooperative interaction of adsorbants on neighboring Co sites plays an important role in its high activity. In the case of crystalline CoWO4, density functional theory (DFT) calculations showed that its most stable surface should be along the (010) plane, featuring Co atoms located at least 4.69 Å apart, which is significantly larger than the reported 2.82 Å in the cubane structure of Co–Pi. We believe this longer interatomic span hinders the adsorbant interaction and thus results in a different mechanism for oxygen evolution on the surface of crystalline CoWO4.
Starting Page	10874
Ending Page	10881
Page Count	8
File Format	HTM / HTML PDF
ISSN	20462069
Volume Number	2
Issue Number	29
Journal	RSC Advances
DOI	10.1039/c2ra21993j
Language	English
Publisher	Royal Society of Chemistry
Access Restriction	Open
Subject Keyword	Overpotential Photoemission spectroscopy Tafel Cobalt Tungstate Exchange current density Cyclic voltammetry Electrolyte Electrolysis Phosphate Elemental analysis Tin Oxygen evolution Density functional theory SoltyRei Cubane Coprecipitation X-ray photoelectron spectroscopy
Content Type	Text
Resource Type	Article
Subject	Chemistry Chemical Engineering

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