Efficient Photoelectrochemical Water Splitting with Ultrathin films of Hematite on Three-Dimensional Nanophotonic Structures

• Published in: Nano letters Vol. 14; no. 4; pp. 2123 - 2129
• Main Authors: Qiu, Yongcai, Leung, Siu-Fung, Zhang, Qianpeng, Hua, Bo, Lin, Qingfeng, Wei, Zhanhua, Tsui, Kwong-Hoi, Zhang, Yuegang, Yang, Shihe, Fan, Zhiyong
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 09.04.2014
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Devices; Electrodes; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic structure of nanoscale materials : clusters, nanoparticles, nanotubes, and nanocrystals; Exact sciences and technology; Fullerenes and related materials; Hematite; Light absorption; Nanostructure; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Physics; Surface area; Three dimensional; Visible and ultraviolet spectra; Water splitting; nanophotonics; nanospike; hematite; water splitting; Electrochemical; Ultrathin films; Band structure; High density; Chemical stability; Active layer; Theoretical study; Layer thickness; Scattering lengths; Nanophotonics; Electronic structure; Three dimensional structure; Modelling; Oxidation; Light absorption; Absorption spectra; Surface area; Current density; Active material; Optical absorption; Photoelectrode; Hydrogen production
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl500359e

Photoelectrochemical (PEC) solar water splitting represents a clean and sustainable approach for hydrogen (H2) production and substantial research are being performed to improve the conversion efficiency. Hematite (α-Fe2O3) is considered as a promising candidate for PEC water splitting due to its chemical stability, appropriate band structure, and abundance. However, PEC performance based on hematite is hindered by the short hole diffusion length that put a constraint on the active layer thickness and its light absorption capability. In this work, we have designed and fabricated novel PEC device structure with ultrathin hematite film deposited on three-dimensional nanophotonic structure. In this fashion, the nanophotonic structures can largely improve the light absorption in the ultrathin active materials. In addition, they also provide large surface area to accommodate the slow surface water oxidation process. As the result, high current density of 3.05 mA cm–2 at 1.23 V with respect to the reversible hydrogen electrode (RHE) has been achieved on such nanophotonic structure, which is about three times of that for a planar photoelectrode. More importantly, our systematic analysis with experiments and modeling revealed that the design of high performance PEC devices needs to consider not only total optical absorption, but also the absorption profile in the active material, in addition to electrode surface area and carrier collection.