Abstract
Solar water splitting is a promising method for producing renewable fuels. Thermodynamically, the overall water splitting reaction is an uphill reaction involving a multiple electron transfer process. The oxygen evolution reaction (OER) has been identified as the bottleneck process. Hematite (α-Fe2O3) is one of the best photoanode material candidates due to its band gap properties and stability in aqueous solution. However, the reported efficiencies of hematite are notoriously lower than the theoretically predicted value mainly due to poor charge transfer and separation ability, short hole diffusion length as well as slow water oxidation kinetics. In this Review Article, several emerging surface modification strategies to reduce the oxygen evolution overpotential and thus to enhance the water oxidation reaction kinetics will be presented. These strategies include co-catalysts loading, photoabsorption enhancing (surface plasmonic metal and rare earth metal decoration), surface passivation layer deposition, surface chemical etching and surface doping. These methods are found to reduce charge recombination happening at surface trapping states, promote charge separation and diffusion, and accelerate water oxidation kinetics. The detailed surface modification methods, surface layer materials, the photoelectrochemical (PEC) performances including photocurrent and onset potential shift as well as the related proposed mechanisms will be reviewed.
Highlights
Solar water splitting is a technology that can potentially produce a clean, environmentally friendly and cheap hydrogen fuel by using renewable energy sources
In order to enhance the water oxidation kinetics and reduce the applied potential, various surface modification strategies have been developed for hematite photoanodes
Fluorine doped tin oxide scanning (SEM)image imageofof fluorine doped tin oxide (FTO)/hematite and (b) curves for bare hematite and after electrodeposition of of (FTO)/hematite and (b) steady-state I-V curves for bare hematite and after electrodeposition pentamethylcyclopentadienyl (Cp*) iridium(III) [Cp*Ir(III)] from differently concentrated solutions pentamethylcyclopentadienyl (Cp*) iridium(III) [Cp*Ir(III)] from differently concentrated solutions (5 (5 μM, 10 μM, 1 mM and 5 mM)
Summary
Solar water splitting is a technology that can potentially produce a clean, environmentally friendly and cheap hydrogen fuel by using renewable energy sources. The nanostructured morphology strategy cannot speed up the slow water oxidation process, which limits the solar to fuel energy conversion efficiency. Surface modification of the photoanode with a co-catalyst, loading a surface passivation layer, or doing surface chemical corrosion were found to improve the overall system efficiency [14]. These methods may reduce charge recombination occurring at surface trapping states, promote separation and diffusion of carrier species and accelerate water oxidation kinetics [15]. Forming heterojunctions at the nanoscale by coupling hematite to a second semiconductor has been evidenced as an effective way to engineer the band structure for enhanced optical absorption and promoting charge separation [15]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
