Abstract
The electrochemical behaviour of hafnium was investigated in acid (pH = 0), neutral (pH = 7.2), and alkaline (pH = 13.8) solutions. At potentials exceeding the equilibrium potential of the oxide electrode, ε0 = -16.9 V -0.059 V pH, the oxide grows irreversibly by 2 nm/V. The influence of the pH is explained by the reaction H2O ⇌ O2- (ox) + 2H+. aq, which determines the potential drop ΔøH at the oxide-electrolyte interface. Anodic breakdown is observed in acid solutions. Critical potentials decrease from nitrate to perchlorate and chloride solutions. Electronic properties of the film were investigated by measurements of capactiy, electron transfer, and photocurrent. Capacity measurements show the insulating character of the HfO2-film (D = 13.8). A space charge could not be detected, and the carrier concentration must be less than 1018 cm-3. All anodic electron transfer reactions are blocked, but cathodic hydrogen evolution and Cu-deposition take place with current densities up to 10mA/cm2. Flaws and fissures play an important role for these reactions. Photoelectrochemical measurements indicate a band gap energy of 5.1 eV and flatband potential near 0V.
Original language | English |
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Pages (from-to) | 129-140 |
Number of pages | 12 |
Journal | Electrochimica Acta |
Volume | 27 |
Issue number | 1 |
DOIs | |
State | Published - Jan 1982 |
Externally published | Yes |