Nanonet-Based Hematite Heteronanostructures for Efficient Solar Water Splitting

Abstract

We report the highest external quantum efficiency measured on hematite (α-Fe(2)O(3)) without intentional doping in a water-splitting environment: 46% at λ = 400 nm. This result was enabled by the introduction of TiSi(2) nanonets, which are highly conductive and have suitably high surface areas. The nanonets serve a dual role as a structural support and an efficient charge collector, allowing for maximum photon-to-charge conversion. Without the addition of any oxygen-evolving catalysts, we obtained photocurrents of 1.6 and 2.7 mA/cm(2) at 1.23 and 1.53 V vs RHE, respectively. These results highlight the importance of charge transport in semiconductor-based water splitting, particularly for materials whose performance is limited by poor charge diffusion. Our design introduces material components to provide a dedicated charge-transport pathway, alleviating the reliance on the materials' intrinsic properties, and therefore has the potential to greatly broaden where and how various existing materials can be used in energy-related applications.

Dynamics of photogenerated holes in surface modified α-Fe 2 O 3 photoanodes for solar water splitting

“…As such, these results emphasize that one materials design strategy to enhance performance of water oxidation photoanodes, particularly those whose efficiency is limited by electron-hole recombination losses, is to target specifically the enhancement of electron depletion within the photoelectrode while still ensuring sufficient conductivity through the film to allow electron extraction without large ohmic losses. Such strategies could include not only surface modification but also new architectures to enable efficient electron conduction without the requirement for chemical doping, such as core/shell and related approaches (13,14).…”

“…This limitation is particularly severe for materials with lower optical bandgap, such as Fe 2 O 3 and BiVO 4 (10,12), which on the other hand are of interest due to their enhanced absorption in the visible part of the of the solar irradiation spectrum. The development of strategies to reduce or remove this electrical bias requirement is therefore a key target of ongoing research (14,15).…”

Water Oxidation at Hematite Photoelectrodes: The Role of Surface States

“…[13][14][15] Importantly, the self-limiting gas phase mechanism of ALD is an ideal technique for depositing thin films on high aspect ratio scaffolds which are deposited identically to the thin films used herein. 16 Thus, the lessons learned on the model thin films can be directly applied to nanostructured electrodes prepared by ALD. The thin, planar films used herein provide an ideal electrode for fundamental studies as they avoid the complexity and irregularities of most nanostructured surfaces.…”

Electrochemical and photoelectrochemical investigation of water oxidation with hematite electrodes

“…[33][34][35] Also, because ALD is not a line-of-sight technique, it can be used to make nanostructured 'thin films' which are prepared in an identical fashion to the model thin films, but have increased light absorption. [36][37][38] Thus lessons learned with our thin film model system can be directly applied to nanostructured architectures with precisely controlled dimensions fabricated via ALD. 39 We compare the PEC behavior of hematite with ideallybehaving hole collector, [Fe(CN) 6 ] 3-/4-, with the behavior under water oxidation conditions.…”