Efficient Photoelectrochemical Water Splitting with Ultra-thin film of Hematite on Three-dimensional Nanophotonic Structures.

Nano letters

PubMedID: 24601797

Qiu Y, Leung SF, Zhang Q, Hua B, Lin Q, Wei Z, Tsui KH, Zhang Y, Yang S, Fan Z. Efficient Photoelectrochemical Water Splitting with Ultra-thin film of Hematite on Three-dimensional Nanophotonic Structures. Nano Lett. 2014;.
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 (a-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 which 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 ultra-thin hematite film deposited on three-dimensional nanophotonic structure. In this fashion, the nanophotonic structures can largely improve the light absorption in the ultra-thin 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 vs 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.