Brownmillerite‐Type Crystalline Ca 2 FeCoO 5 Ultrasmall Particles with Single‐Nanometer Dimensions as an Active Cocatalyst for Oxygen Photoevolution Reaction

• Published in: Particle & particle systems characterization Vol. 37; no. 5
• Main Authors: Tsuji, Etsushi, Nanbu, Ryosuke, Degami, Yoshiki, Hirao, Kei, Watanabe, Takeyuki, Matsumoto, Naoya, Suganuma, Satoshi, Katada, Naonobu
• Format: Journal Article
• Language: English
• Published: 01.05.2020
• ISSN: 0934-0866; 1521-4117
• DOI: 10.1002/ppsc.202000053

Abstract Brownmillerite‐type Ca 2 FeCoO 5 (CFCO) is one of the most effective catalysts for oxygen evolution reaction (OER), comparable with noble metal oxides. In this study, crystalline CFCO ultrasmall particles with nanometric dimension are synthesized by a reverse micelle method on TiO 2 nanoparticles. The particle size decreases with decreasing molar ratio of water to surfactant. The precursors of CFCO must be calcined after loading on TiO 2 nanoparticles to achieve CFCO ultrasmall particles with several nanometers in size. Interaction between the precursors and TiO 2 is speculated to suppress aggregation of the precursors during calcination. The photocatalytic activity of TiO 2 for OER is improved by loading of CFCO ultrasmall particles with 5 nm, whereas the activity decreases by loading of CFCO with more than 15 nm. Photocatalytic activity of the most active CFCO/TiO 2 is comparable to that of RuO 2 /TiO 2 . Both the lower edge of conduction band and higher edge of valence band of CFCO are lower and higher than those of TiO 2 , respectively, leading to transfer of excited holes and electrons transferred to CFCO and recombination. When the particle size of CFCO becomes several nanometric dimensions, the transferred holes rapidly reach the surface of CFCO and oxidize water molecules before recombination with electrons.