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Highly crystalline Ni-doped β-FeOOH(Cl) nanorod catalysts for efficient electrochemical water oxidation were successfully synthesized by a one-pot ambient temperature synthesis.

Crystallized mesoporous tantalum pentoxide spheres (CMTS) with particle diameters of ca. 100-500 nm and composed of Ta 2 O 5 nanocrystals were synthesized for the first time by a combination of the sol-gel process and heat-treatment with the aid of carbon reinforcement. The specific surface area of the CMTS was up to 105 m 2 g À1 and the pore diameter was controllable in the range of 5.6-17 nm by changing the crystallization temperature. Visible light-sensitive p-type N-doped Ta 2 O 5 (N-CMTS) containing 5 at% N was successfully obtained by treatment of CMTS with ammonia, while retaining the mesoporosity and morphology of CMTS. N-CMTS exhibited excellent photocatalytic activity for hydrogen evolution and CO 2 reduction (with ruthenium-complex) under visible light irradiation ($410 nm) due to their larger surface area and controlled morphology compared with previously reported Ndoped Ta 2 O 5 fine particles.

received her bachelor and master degrees from Nara Women's University. She joined Toyota CRDL in 1992 and received he Ph.D. Degree from Tokyo Institute of Technology in 2009. Currently, she is a senior researcher of the Morikawa Senior Fellow Laboratory in Toyota CRDL. She has been working on development of inorganic catalyst materials for artificial photosynthesis. Takeshi MorikawaTakeshi Morikawa received his bachelor and master degrees from Nagoya University. He joined Toyota CRDL in 1989 and received his Ph.D. Degree in 2005. He has been working on development of sensors for automotive controls, magnetic materials, semiconductor photocatalyst, and CO 2 recycling systems by artificial photosynthesis. He is currently a manager of the Morikawa Senior Fellow Laboratory in Toyota CRDL. AbstractA highly crystalline, 10 nm-sized red rust water oxidation catalyst composed of pure β-phase FeOOH(Cl) nanorods (ca. 3 © 13 nm) doped with Ni ions (β-FeOOH(Cl):Ni) and surfacemodified with amorphous Ni(OH) 2 (a-Ni(OH) 2 , at a Ni to Fe ratio of 22 at.%) was synthesized by a facile one-pot process at room temperature. The overpotential during the electrochemical oxygen evolution reaction (OER) over the β-FeOOH:Ni/ a-Ni(OH) 2 stacked nanorod anodes was 170 mV, and an OER current of 10 mA/cm 2 was obtained at an overpotential of 430 mV in a 0.1 M KOH solution. X-ray absorption fine structure analysis, Mössbauer spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, X-ray diffraction and impedance spectroscopy suggested that surface modification with the a-Ni(OH) 2 lowered the OER overpotential of β-FeOOH(Cl):Ni, resulting in the very high current density at low potential compared with Fe-rich oxide and oxyhydroxide electrodes reported previously. Mössbauer spectroscopy suggested interaction between Fe and Ni species, which may be crucial evidence for the enhanced activity in the Fe-rich OER system.