Electrochemical Stabilities

The redox flow battery (RFB) has been the subject of state-of-the-art research by several groups around the world. Most work commonly involves the application of various low-cost carbon-polymer composites, carbon felts, cloth, paper and their different variations for the electrode materials of the RFB. Usually, the carbon-polymer composite electrode has relatively high bulk resistivity and can be easily corroded when the polarised potential on the anode is more positive than that of oxygen evolution and this kind of heterogeneous corrosion may lead to battery failure due to electrolyte leakage. Therefore, carbon electrodes with high electrical conductivity, acid-resistance and electrochemical stability are highly desirable. This review discusses such issues in depth and presents an overview on future research directions that may help commercialise RFB technology. A comprehensive discussion is provided on the advances made using nanotechnology and it is envisaged that if this is combined with ionic liquid technology, major advantages could be realised. In addition the identification of RFB failure mechanisms by means of X-ray computed nano tomography is expected to bring added benefits to the technology. © 2013 Elsevier B.V. All rights reserved.

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Tantalum has been cited to have many biomaterial applications, exhibiting biocompatibility and
outstanding corrosion resistance. Tantalum may be covered with tantalum oxide using the electrochemical
process of anodic oxidation. The oxide surface is known to be bioactive and more corrosion resistant.
In this research, compact tantalum oxide films were obtained by potentiostatic and potentiodynamic
methods in H2SO4 and H3PO4 (1 mol.L-1) electrolytes. By XPS analysis the stoichiometry Ta2O5 was
detected. The thermodynamic stability of those oxides was compared and the results indicated that Ta2O5
obtained in H2SO4 has higher thermodynamic stability than Ta2O5 obtained in H3PO4. The incorporation
of (PO4)3- ions and the formation of a bilayer oxide are responsible for the reduced stability. Also,
the better control of chemical kinetic of oxide formation allows potentiodynamic oxides to be more
stable. Ta2O5 shows spontaneous dissolution in artificial blood, nevertheless, it remains stable even
after 60 days of immersion. By scratching tests was possible to notice that Ta2O5 is highly adherent to
the tantalum metallic substrate and by mechanical indentation was possible to measure a lower elastic
modulus for the Ta2O5 than the metallic