Photoelectrochemical study of lanthanide zirconium oxides, Ln2Zr2O7 (Ln = La, Ce, Nd and Sm)

Photocatalytic activities for hydrogen evolution of lanthanide zirconium oxides, Ln2Zr2O7 (Ln = La, Ce, Nd and Sm) prepared by a solution reaction method were investigated. Under the illumination of 500 W Xenon lamps, hydrogen gas was clearly evolved in a distilled water suspension of La2Zr2O7, Sm2Zr2O7 and Nd2Zr2O7. Under the visible-light illumination, hydrogen gas was evolved in a distilled water suspension of Nd2Zr2O7 and Sm2Zr2O7. From the photoelectrochemical measurements, the values of the flat band potential were estimated to be −0.64, −0.52, −0.31 and +0.04 eV for La2Zr2O7, Sm2Zr2O7, Nd2Zr2O7 and Ce2Zr2O7, respectively, versus the normal hydrogen electrode (NHE). The values of the band gap energy were calculated to be about 3.52, 2.86, 2.67 and 2.53 eV for La2Zr2O7, Sm2Zr2O7, Nd2Zr2O7 and Ce2Zr2O7, respectively. Due to the effect of 4f orbital electrons, the band gap energy of these compounds becomes narrower than in ZrO2 and as a consequence, Sm2Zr2O7 and Nd2Zr2O7 show the photocatalytic activity under the visible-light.