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

Abstract

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.

Progress and Design Concerns of Nanostructured Solar Energy Harvesting Devices

“…[ 16,43 ] In addition to the above mentioned points, photo-carrier distribution is another factor to be considered when designing nanostructured solar energy harvesting devices, especially for PEC solar water splitting devices. [44][45][46] In this review, we will fi rstly summarize the progress of nanostructured solar energy harvesting devices with emphasis on introducing various nanotexturization strategies. Thereafter, we will discuss the key aspects when designing highly effi cient nanostructured solar energy harvesting devices, including PV thin fi lms nonuniformity on nanostructures, surface recombination, parasitic absorption and the importance of uniform distribution of photo-generated carriers.…”

Atomic Layer Deposition of Bismuth Vanadates for Solar Energy Materials

“…Typically, two reactants are used to deposit binary compounds such as M x O y where, for example, [M-O] cycles of metal and oxidant pulses are repeated to deposit conformal nanoscale layers. These capabilities have enabled significant progress for Fe 2 O 3 , [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Cu 2 O, [27][28][29][30] and other photoelectrodes. [6,31,32] There is a significant design advantage to using composite host-guest nanostructures for light-harvesting materials with low carrier mobilities.…”

Linking morphology and multi-physical transport in structured photoelectrodes

“…Therefore, nano and micro structuring of materials has been pursued in order to circumvent some of the critical limitations of bulk material properties. The decoupling of light absorption and charge transport can be achieved in well-controlled multi-step processes which create structured multi-dimensional arrays like 1D nanotubes [2], nanowires [3], or 3D structures like micron pillars [4]. It has been demonstrated in these morphologies that enhanced light absorption along the vertical axis can be achieved, while orthogonally, minority charge carriers then have a relatively short path to the semiconductor-electrolyte interface.…”