In Situ Construction of Ta:Fe<sub>2</sub>O<sub>3</sub>@CaFe<sub>2</sub>O<sub>4</sub> Core–Shell Nanorod p–t–n Heterojunction Photoanodes for Efficient and Robust Solar Water Oxidation
Kyoungwoong Kang, Chenke Tang, Jeong Hun Kim, Woo Jin Byun, Jin Ho Lee, Jin Ho Lee, Min Hee Lee, Hemin Zhang, Jae Sung Lee, Jae Sung Lee
Abstract
In order to ameliorate the poor charge transfer characteristics of hematite (α-Fe 2 O 3 ) photoanodes for photoelectrochemical (PEC) water splitting, heterojunction formation with p-CaFe 2 O 4 is attempted. Here, we report the in situ construction of a highly crystalline p-CaFe 2 O 4 shell on the surface of n-Ta:Fe 2 O 3 nanorods to form Ta:Fe 2 O 3 @CaFe 2 O 4 core–shell nanorod p–t–n heterojunction photoanodes with a transition layer (t) between them by a combined strategy of hybrid microwave annealing (HMA) and in situ Ta doping. The successful fabrication of the elaborate heterostructure is due to effective crystallization of p-CaFe 2 O 4 by HMA and prevention of Ca diffusion by already doped Ta atoms in hematite. The optimized Ta:Fe 2 O 3 @CaFe 2 O 4 photoanode loaded with the FeNiO x cocatalyst achieves a photocurrent density of 2.70 mA cm –2, a low onset potential of 0.63 V RHE, and long-time stability in PEC water oxidation at 1.23 V RHE under 100 mW cm –2 solar irradiation, which represent marked improvements over bare hematite photoanodes and already reported hematite-based heterojunction photoanodes.