Metal–organic framework coated titanium dioxide nanorod array p–n heterojunction photoanode for solar water-splitting

• Published in: Nano research 2019-03, Vol.12 (3), p.643-650
• Main Authors: Yang, Hui, Bright, Joeseph, Kasani, Sujan, Zheng, Peng, Musho, Terence, Chen, Banglin, Huang, Ling, Wu, Nianqiang
• Format: Article
• Language: English
• Subjects: Arrays; Atomic/Molecular Structure and Spectra; Biomedicine; Biotechnology; Charge efficiency; Charge injection; Chemistry and Materials Science; Coatings; Condensed Matter Physics; Current carriers; Electrolytes; Heterojunctions; Injection; Irradiation; Materials Science; Metal-organic frameworks; Nanorods; Nanotechnology; P-n junctions; Photoanodes; Photoelectric effect; Photoelectric emission; Photoelectrochemical devices; Porphyrins; Radiation; Research Article; Self-assembly; Splitting; Thin films; Titanium; Titanium dioxide; Water splitting
• ISSN: 1998-0124; 1998-0000
• DOI: 10.1007/s12274-019-2272-4

This paper presents a p–n heterojunction photoanode based on a p-type porphyrin metal–organic framework (MOF) thin film and an n-type rutile titanium dioxide nanorod array for photoelectrochemical water splitting. The TiO 2 @MOF core–shell nanorod array is formed by coating an 8 nm thick MOF layer on a vertically aligned TiO 2 nanorod array scaffold via a layer-by-layer self-assembly method. This vertically aligned core–shell nanorod array enables a long optical path length but a short path length for extraction of photogenerated minority charge carriers (holes) from TiO 2 to the electrolyte. A p–n junction is formed between TiO 2 and MOF, which improves the extraction of photogenerated electrons and holes out of the TiO 2 nanorods. In addition, the MOF coating significantly improves the efficiency of charge injection at the photoanode/electrolyte interface. Introduction of Co(III) into the MOF layer further enhances the charge extraction in the photoanode and improves the charge injection efficiency. As a result, the photoelectrochemical cell with the TiO 2 @Co-MOF nanorod array photoanode exhibits a photocurrent density of 2.93 mA/cm 2 at 1.23 V (vs. RHE), which is ~ 2.7 times the photocurrent achieved with bare TiO 2 nanorod array under irradiation of an unfiltered 300 W Xe lamp with an output power density of 100 mW/cm 2 .