Nanopillar composite electrodes for solar-driven water splitting (original) (raw)
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Nature communications, 2016
Production of chemical fuels by direct solar energy conversion in a photoelectrochemical cell is of great practical interest for developing a sustainable energy system. Various nanoscale designs such as nanowires, nanotubes, heterostructures and nanocomposites have been explored to increase the energy conversion efficiency of photoelectrochemical water splitting. Here we demonstrate a self-organized nanocomposite material concept for enhancing the efficiency of photocarrier separation and electrochemical energy conversion. Mechanically robust photoelectrodes are formed by embedding self-assembled metal nanopillars in a semiconductor thin film, forming tubular Schottky junctions around each pillar. The photocarrier transport efficiency is strongly enhanced in the Schottky space charge regions while the pillars provide an efficient charge extraction path. Ir-doped SrTiO3 with embedded iridium metal nanopillars shows good operational stability in a water oxidation reaction and achieves...
APL Materials, 2014
Photoelectrochemical (PEC) water splitting to hydrogen is an attractive method for capturing and storing the solar energy in the form of chemical energy. Metal oxides are promising photoanode materials due to their low-cost synthetic routes and higher stability than other semiconductors. In this paper, we provide an overview of recent efforts to improve PEC efficiencies via applying a variety of fabrication strategies to metal oxide photoanodes including (i) size and morphology-control, (ii) metal oxide heterostructuring, (iii) dopant incorporation, (iv) attachments of quantum dots as sensitizer, (v) attachments of plasmonic metal nanoparticles, and (vi) co-catalyst coupling. Each strategy highlights the underlying principles and mechanisms for the performance enhancements.
Enhancing Solar‐Driven Water Splitting with Surface‐Engineered Nanostructures
Solar RRL, 2018
Functional nanoscale interfaces that promote the transport of photoexcited charge carriers are fundamental to efficient hydrogen production during photoelectrochemical (PEC) splitting of water. Here, the realization of a functional one-dimensional nanostructure achieved through surface engineering of hematite (α-Fe 2 O 3) nanorods with a TiO 2 overlayer is reported. The surface-engineered hematite nanostructure exhibits significantly improved PEC performance as compared to untreated α-Fe 2 O 3 , with an increase in the maximum incident photon-to-current efficiency (IPCE) of nearly 400% at 350 nm. While addition of the TiO 2 overlayer did not alter the lifetime of photoexcited charge carriers, as evidenced from transient absorption spectroscopy, it is found that the presence of TiO 2 could enhance oxygen electrocatalysis by interfacial electron enrichment, largely attributed to enhanced O(2p)ÀFe(3d) hybridization. Moreover, the interfacial electronic structure revealed from XANES measurements of the α-Fe 2 O 3 /TiO 2 nanorods suggests that photoexcited holes in α-Fe 2 O 3 may efficiently transfer through the TiO 2 overlayer to the electrolyte while electrons migrate to the external circuit along the one-dimensional nanorods, thereby promoting charge separation and enhancing PEC splitting of water.
Energies
Photocatalytic water splitting and organic reforming based on nano-sized composites are gaining increasing interest due to the possibility of generating hydrogen by employing solar energy with low environmental impact. Although great efforts in developing materials ensuring high specific photoactivity have been recently recorded in the literature survey, the solar-to-hydrogen energy conversion efficiencies are currently still far from meeting the minimum requirements for real solar applications. This review aims at reporting the most significant results recently collected in the field of hydrogen generation through photocatalytic water splitting and organic reforming, with specific focus on metal-based semiconductor nanomaterials (e.g., metal oxides, metal (oxy)nitrides and metal (oxy)sulfides) used as photocatalysts under UVA or visible light irradiation. Recent developments for improving the photoefficiency for hydrogen generation of most used metal-based composites are pointed out. The main synthesis and operating variables affecting photocatalytic water splitting and organic reforming over metal-based nanocomposites are critically evaluated.
Nanomaterials for photoelectrochemical water splitting – review
International Journal of Hydrogen Energy, 2018
Photoelectrochemical (PEC) water splitting using nanomaterials is one of the promising techniques to generate hydrogen in an easier, cheaper and sustainable way. By modifying a photocatalyst with a suitable band width material can improve the overall solar-tohydrogen (STH) energy conversion efficiency. Nanomaterials can tune their band width by controlling its size and morphology. In many studies, the importance of nanostructured materials, their morphological and crystalline effects in water splitting is highlighted. Charge separation and transportation is the major concern in PEC water splitting. Nanomaterials are having high surface to volume ratio which facilitates charge separation and suppress electron-hole pair recombination. This review focuses on the recent developments in water splitting techniques using PEC based nanomaterials as well as different strategies to improve hydrogen evolution.
Strategies for Semiconductor/Electrocatalyst Coupling toward Solar‐Driven Water Splitting
Advanced Science
with the consumption of fossil fuels. [1,2] Hydrogen (H 2) and fuel cell technologies have shown significant potential to empower this transition, able to substantially reduce carbon dioxide (CO 2) emissions and create a huge new market, as predicted recently by the Hydrogen Council. [3] Although H 2 is a clean energy carrier and shows flexibility of linking different energy sectors and energy transmission and distribution networks, the production of H 2 is currently not that "clean"-nearly 96% of global H 2 production is from thermochemical processes, [4] which not only deplete fossil fuels but also emit a large amount of CO 2. To decarbonize H 2 production, fossil-free processes such as electrochemical water splitting using "green" electricity or direct photoelectrochemical (PEC) water splitting must be widely deployed. PEC water splitting takes advantage of semiconductors as both the light absorber and energy converter, to store solar energy in the form of H 2 fuel. To make full use of the photogenerated electron-hole pairs, effective separation of electrons from holes and rapid charge transfer from the space charge region to the semiconductor/liquid junction that enables the chemical reaction are very important. For most semiconductors, even if their conduction/valence band edge is properly positioned with respect to the proton reduction potential or the water oxidation potential, the hydrogen evolution reaction (HER) or the oxygen evolution reaction (OER) kinetics on the bare semiconductor surfaces is usually so sluggish that Hydrogen (H 2) has a significant potential to enable the global energy transition from the current fossil-dominant system to a clean, sustainable, and low-carbon energy system. While presently global H 2 production is predominated by fossil-fuel feedstocks, for future widespread utilization it is of paramount importance to produce H 2 in a decarbonized manner. To this end, photoelectrochemical (PEC) water splitting has been proposed to be a highly desirable approach with minimal negative impact on the environment. Both semiconductor light-absorbers and hydrogen/oxygen evolution reaction (HER/OER) catalysts are essential components of an efficient PEC cell. It is well documented that loading electrocatalysts on semiconductor photoelectrodes plays significant roles in accelerating the HER/OER kinetics, suppressing surface recombination, reducing overpotentials needed to accomplish HER/OER, and extending the operational lifetime of semiconductors. Herein, how electrocatalyst coupling influences the PEC performance of semiconductor photoelectrodes is outlined. The focus is then placed on the major strategies developed so far for semiconductor/ electrocatalyst coupling, including a variety of dry processes and wet chemical approaches. This Review provides a comprehensive account of advanced methodologies adopted for semiconductor/electrocatalyst coupling and can serve as a guideline for the design of efficient and stable semiconductor photoelectrodes for use in water splitting.
Monolithic Solar Water-Splitting Systems: Towards a Sustainable Hydrogen-Energy Future
Proceedings of 1st International e-Conference on Energies, 2014
On of challenging routes to convert solar energy in storable fuels is the lightinduced water-splitting on integrated tandem-systems based on the assembly of stable and efficient semiconducting photoelectrodes. In an inorganic approach, efficient photoelectrodes are pursued by embedding electro-catalytic centers in a passivated semiconductor substrate having an extremely low concentration of surface reaction sites. Condition (i) requires high absorptivity of the semiconducting material, whereas condition (ii) requires control of the electronic properties of the various interfaces and (iii) implies a better understanding and steering of the electro-catalytic process occurring at the surface of reactive centers that convert sunlight directly to fuels. The future implementation of surface modified materials into tandem structures is discussed and future directions concerning the exploitation of photonic effects at metal arrangements of plasmonic materials and the implementation of bio-electrocatalysts in advanced devices is outlined.
2013
For the last few decades plasmonic noble metal nanoparticles (NPs) have been used in the semiconductor-based phocatalytic water splitting processes as effi ciency boosters. In most of these works it is claimed that the effi ciency enhancement is due to the charge transfer from the semiconductor to the metal. However it is only recently that more focus is being put on developing an understanding of the precise nature of the contribution(s) of such metal NPs in the observed enhancements of photocatalytic or photoelectrochemical (PEC) performance of different materials. [ 3 , 4 ] Thus far most of the work regarding plasmonic enhancement of PEC water splitting has been reported on TiO 2 -Au systems and in most such cases Au nanoparticles have been deposited on the surface of TiO 2 fi lm or TiO 2 nanoparticles. It has been shown that for particle size less than 50 nm (above this the scattering effect is predominant), gold can act as a sensitizer to TiO 2 by absorbing in the visible region of solar spectrum due to localized surface plasmons (LSP) and transferring hot electrons to the conduction band of TiO 2 . This is mainly possible because of the tendency of the gold nanoparticles to undergo charging and causing negative shift of the Fermi level of TiO 2 to achieve Fermi level equilibration. However, it has also been noticed that although there is plasmonic enhancement in the visible region in the TiO 2 -Au photoelectrode, the performance in the near-UV region gets deteriorated. This is due to the lower photon fl ux reaching to TiO 2 and less area of TiO 2 exposed to the electrolyte. Therefore, the overall enhancement for the entire solar spectrum is compromised. In line with this, most of the other semiconductor photocatalysts such as Fe 2 O 3,
Nanostructured bilayered thin films in photoelectrochemical water splitting – A review
International Journal of Hydrogen Energy, 2012
In the quest for achieving the desired efficiency, balanced economics and prolonged durability of the photoelectrochemical (PEC) system for hydrogen generation, heterostructures consisting of two or more semiconductors are being looked upon as favourite material alternatives. This communication describes the basic principles involved and summarizes most of the work done in this domain. Band gap, electronic band edge alignment of the materials with each other and with the redox potential of water, lattice mismatch of the materials and optimization of thickness of each layer at the junction in the PEC devices appear to be crucial for attaining enhanced photoresponse and efficiency. Based on the studies reported in the literature and from our own studies, heterojunction systems are considered as effective tool towards extending the spectrum to the visible range and for effective separation of charge carriers leading to development of efficient solar hydrogen production system.
Bifunctional doping effect on the TiO2 nanowires for photoelectrochemical water splitting
Electrochimica Acta, 2013
Rutile TiO 2 nanorods (TONRs) with a length of 3.7 m were synthesized using a simple hydrothermal method. In order to control the morphology of the film and doping effect, Si was then added to the reaction solution. Si-doped TONRs (Si-TONRs) film shows distinct morphological properties such as thinner diameter, shorter length, and large surface area coverage of nanorods (NRs) compared to those of the pristine TONRs film. Furthermore, a Mott-Schottky analysis confirmed that a small amount of increased carrier concentration was induced by the Si doping while the flat-band potential (E FB) is maintained as constant. The linear sweep voltammograms displayed an outstanding photocurrent density of Si-TONR film with 2.75 mA/cm 2 at 0 V vs. Ag/AgCl, compared with 0.88 mA/cm 2 of the TONR film. Also, Si-TONR film revealed a solar-to-hydrogen (STH) conversion efficiency exceeding 2%, which is a 3-fold increased efficiency compared to that of TONR film and is ascribed to the favorable charge transportation through the novel nanoarchitecture which minimizes the charge recombination due to the increased electron concentration.