ELECTROCHEMICAL AND PHOTOELECTROCHEMICAL BEHAVIOR OF PASSIVATED NIOBIUM ELECTRODES DURING HYDROGEN EVOLUTION

The electrochemical and photoelectrochemical behavior of niobium electrodes passivated in 0.5 M H2SO4 and 1 M HNO3 has been investigated. High intensity pulse lasers were used as light sources. This technique allows photoelectrochemical measurements with light wavelengths smaller than the band gap of the semiconducting passive film. The donor concentration and the flat band potential of the passive films were calculated from capacity measurements. The effect of cathodic hydrogen evolution on the behaviour of the oxide film formed was found to depend on the time of the cathodic treatment of the electrode. The results showed that the behaviour of the passive film formed on niobium in nitric acid is different from that formed in sulphuric acid. The calculated donor concentrations and the extrapolated flat band potentials indicate that the nature of the passive film depends on the formation medium. The adsorption of hydrogen on the passivated Nb-electrode up to a time limit of 1 ms could be traced using photocharge measurements with excitation energies less than the band gap energy of the semiconducing oxide film. © 1990 Chapman and Hall Ltd.