Water Oxidation at Hematite Photoelectrodes with an Iridium-Based Catalyst

Badia-Bou, Laura; Mas‐Marzá, Elena; Rodenas, Pau; Barea, Eva M.; Fabregat‐Santiago, Francisco; Giménez, Sixto; Peris, Eduardo; Bisquert, Juan

doi:10.1021/jp311983n

Cited by 136 publications

(126 citation statements)

References 54 publications

(100 reference statements)

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“…12b(ii) that CoAc deposition does not the alter the flatband potential. A similar behavior was also observed upon deposition of the Ir 39 and Co 40 based co-catalysts on hematite photoanodes. These experiments clearly indicate that the improved photoresponse observed in the presence of CoAc deposit on ZnO is not due to any modification in the bandgap or band positions of the ZnO substrate.…”

Section: Effect Of Concentration Of Cosupporting

confidence: 74%

Photochemical Deposition of Co-Ac Catalyst on ZnO Nanorods for Solar Water Oxidation

Irshad

Munichandraiah

2015

J. Electrochem. Soc.

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The preparation of ZnO nanorod films decorated with cobalt-acetate (CoAc) electrocatalyst and its activity for photoelectrolysis of water have been demonstrated. The photochemically prepared CoAc catalyst is chemically and morphologically similar to the electrochemically prepared CoAc catalyst. The on-set potential of oxygen evolution reaction is lower on CoAc-ZnO photoanode in relation to bare ZnO photoanode. There is a three to four fold increase in photooxidation current of OER due to the presence of CoAc co-catalyst on ZnO. Thus, the photochemically prepared CoAc on ZnO is an alternative and efficient co-catalyst for photoelectrochemical oxygen evolution reaction. The enhancement in photocatalytic activity of ZnO by the CoAc catalyst photochemically deposited from acetate buffer solution is significantly greater than the cobalt-phosphate (CoPi) co-catalyst deposited from phosphate buffer solution. Hydrogen is a convenient fuel for the future owing to its high energy density and eco-friendliness.1,2 Currently, around 48 million metric tons of H 2 is produced globally each year mainly from natural gas by steam-methane reforming method. 3,4 As this process leads to the emission of a large amount of CO 2 (240 mega tons per year), it is challenging to develop alternate, clean methods to produce hydrogen. Generation of hydrogen gas from water requires energy of 273 kJ mol −1 . If this energy is available from a renewable energy source such as solar energy, hydrogen can be considered as an economical and green energy source, which is an alternative to fossil fuels.A simple approach is to use photovoltaic cells to power water electrolyzers. However, diurnal variation in the sunlight intensity, a high cost and a low conversion efficiency impede successful commercialization of the present photovoltaic cells. 5 Another approach is to store solar energy directly in the chemical bonds of small molecules, similar to the photosynthesis route adopted by vegetation. A typical example is the photodissociation of water to generate hydrogen fuel. 6 The first report on photodissociation of water into H 2 and O 2 using ntype TiO 2 photoanode and Pt black cathode was reported by Fujishima and Honda 7 in 1972. Following this report, numerous investigations have been reported for photocatalytic and photoelectrochemical water splitting.8 Most of the studies suffer from poor solar to hydrogen conversion efficiency due to fast recombination of photogenerated charge carriers and poor catalytic activity of semiconductor electrodes toward multi-electron oxygen evolution reaction (OER) at the photoanode. 8,9 Several metal oxides such as RuO 2 , 10,11 IrO 2 12,13 etc., are coupled with semiconductor anodes (TiO 2 , ZnO, etc.) as co-catalysts to enhance the sluggish kinetics of water oxidation. However, high cost of Ru and Ir limit their widespread application. Recently, a cobaltphosphate complex (CoPi) are no reports on the photochemical deposition of CoAc catalyst on a n-type semiconductor electrode and its utilization as a co-catalyst i...

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Section: Effect Of Concentration Of Cosupporting

confidence: 74%

Photochemical Deposition of Co-Ac Catalyst on ZnO Nanorods for Solar Water Oxidation

Irshad

Munichandraiah

2015

J. Electrochem. Soc.

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“…68 For instance, the origin of unrevealed water oxidation mechanism at Fe 2 O 3 was recently explored by photoholes accumulation at surface states through EIS results. 69,70 Analogous EIS experiments were demonstrated on photoelectron trapping at surface states by many researchers. 71,72 In the present work, EIS spectra of both pristine and Gd 3+ doped TiO 2 electrodes were recorded for low and high light intensities at different applied potential (−0.8 to 0.8 V vs RHE).…”

Section: (Degrees)mentioning

confidence: 98%

Enhanced Photoelectrocatalytic Water Splitting at Hierarchical Gd³⁺:TiO₂Nanostructures through Amplifying Light Reception and Surface States Passivation

Sudhagar

Devadoss

Nakata

et al. 2014

J. Electrochem. Soc.

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The influence of rare earth gadolinium (Gd 3+ ) ion doping on optical and photoelectrochemical properties of TiO 2 is studied. The hierarchical clump-type TiO 2 nanostructure was fabricated using poly-vinyl acetate as soft-template. The optical absorbance quantity of TiO 2 was strikingly promoted at bandgap energy region (380 nm) by Gd 3+ doping, as well as it extend a wide absorbance in visible wavelength region (400 -800 nm) elucidating the sub-bandgap formation. As a result, Gd 3+ :TiO 2 exhibits high photocurrent density than undoped TiO 2 in photoelectrocatalytic experiments. Another plausible reason for enhancing the photocurrent density at Gd 3+ :TiO 2 was analyzed through electrochemical impedance spectroscopy. The underlying mechanism of surface states controlled charge transfer at TiO 2 /electrolyte interfaces affected the photoelectrocatalytic hydrogen fuel generation, and compete with Gd 3+ ion doping through bottlenecking of photoelectrons trapping at surface states. The improved charge separation (e − /h + ) at Gd 3+ :TiO 2 result effective photoelectron collection and thus yield 180 % higher hydrogen gas (∼ 2.34 mL.h −1 .cm −2 ) generation compare to pristine TiO 2 (1.28 mL.h −1 .cm −2 ) under UV light irradiation. The improved optical and charge transfer characteristics of hierarchical TiO 2 by Gd 3+ ions can be implemented to wide range of other metal oxide based photocatalytic fuel generation. The photoelectrocatalytic (PEC) water oxidation phenomenon configured with light and semiconductor opens new pathways in cost-effective fuel generation (hydrogen and oxygen) using water as feed stock.1 Merits counting the zero-emission of harmful CO 2 into environment, 2 possibility of beneficial simultaneous process of pollutant treatment, 3,4 and/or biomass reformation toward hydrogen fuel generation foster PEC water oxidation as an emerging technology in green energy fuels. Nanostructured titanium dioxide (TiO 2 ) is one of the most studied candidates in PEC applications including fuel generation, 5-7 organic pollutant degradation, 8,9 photoelectrochemical biosensors, 10,11 photocatalytic self-cleaning coatings 12,13 and antimicrobial coatings.14 The clean fuel generation from photoelectrolysis of water using TiO 2 mesoporous electrodes received much attention, despite its bandgap (3.2 eV) lies in UV region, due to the appreciable chemical stability and environmentally begin nature. One of the approaches to promote PEC performance of TiO 2 in solar to fuel generation is extending the visible light activity of TiO 2 by bandgap modification through doping with metal ions (Fe,15 21 or inducing defects in crystallite lattice. 22,23 However the doping material perhaps shift the TiO 2 valence band more negative than the water oxidation potential 1.2 V vs RHE, which in turn might affect the PEC water oxidation rates. 24The lanthanide (Ln) rare earth ion (RE) doping at TiO 2 matrix is an alternative approach to enhance the light reception at TiO 2 . Furthermore, RE ions doping can alter the bandgap structure o...

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“…22,23 Figure 1a shows the effect of a pretreatment in dark conditions at different anodic potentials V 0 during 60 s. The voltammetry plots were recorded at a fixed scan rate (500 mV/s). This figure displays a clear cathodic capacitive peak whose height increases as the pretreatment anodic potential increases.…”

Section: Irect Transformation Of Solar Energy Into Chemical Energymentioning

confidence: 99%

“…35 It has also been shown by IS that IrO x enhances charge transfer. 23 Additionally, it should be remarked that a second cathodic peak appears under illumination. We believe that this peak corresponds to the surface states created by oxidation of the hematite surface, as already observed for bare hematite.…”

Section: Irect Transformation Of Solar Energy Into Chemical Energymentioning

confidence: 99%

Interpretation of Cyclic Voltammetry Measurements of Thin Semiconductor Films for Solar Fuel Applications

Bertoluzzi

Badia-Bou

Fabregat‐Santiago

et al. 2013

J. Phys. Chem. Lett.

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A simple model is proposed that allows interpretation of the cyclic voltammetry diagrams obtained experimentally for photoactive semiconductors with surface states or catalysts used for fuel production from sunlight. When the system is limited by charge transfer from the traps/catalyst layer and by detrapping, it is shown that only one capacitive peak is observable and is not recoverable in the return voltage scan. If the system is limited only by charge transfer and not by detrapping, two symmetric capacitive peaks can be observed in the cathodic and anodic directions. The model appears as a useful tool for the swift analysis of the electronic processes that limit fuel production. SECTION:Energy Conversion and Storage; Energy and Charge Transport D irect transformation of solar energy into chemical energy by hydrogen production through water splitting with semiconductor materials in a photoelectrochemical cell constitutes an attractive solution to our energy needs. However, despite the intense efforts carried out in the last decades, no single material has been identified satisfying all of the efficiency, stability, and cost conditions needed for industrial deployment of this technology. 1−4 Hematite (α-Fe 2 O 3 ) has emerged as a promising candidate 5−9 due to its abundance in the earth crust, visible light absorption, and good stability in the harsh environmental conditions needed for operation, although the obtained solarto-fuel efficiencies still remain low for commercial exploitation. One of the main causes of the low performance of hematite is related to the large overpotentials required for water oxidation (around 500 mV), and surface treatments have proven to enhance notably water splitting performances. 10−12 It has been suggested that the reasons for these large overpotentials are related to sluggish hole transfer to the electrolyte 13,14 and to the existence of traps in the bulk and at the semiconductor/ electrolyte interface, 15−17 leading to high recombination. 18,19 Clearly, the separation of the different processes that constitute the oxidative current and the identification of the main kinetic bottlenecks are complex tasks. Therefore, the accurate interpretation of the results provided by characterization techniques constitutes a key tool to rationalize materials development and device optimization. Recently, we have proposed a simple physical model that allows the interpretation of impedance spectroscopy (IS) spectra for water splitting applications. 20 In this model, we have considered a monoenergetic level of surface states where both electron and holes can recombine or transfer from/to the solution.In the present study, we propose a complementary simple model to predict the curves obtained by cyclic voltammetry (CV). This characterization technique allows a quick test of the faradic behavior associated with charge transfer and the capacitive behavior associated with the separated modes of carrier storage, which depend on the thermodynamics and kinetics of the system at stake. 21 ...

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Water Oxidation at Hematite Photoelectrodes with an Iridium-Based Catalyst

Cited by 136 publications

References 54 publications

Photochemical Deposition of Co-Ac Catalyst on ZnO Nanorods for Solar Water Oxidation

Photochemical Deposition of Co-Ac Catalyst on ZnO Nanorods for Solar Water Oxidation

Enhanced Photoelectrocatalytic Water Splitting at Hierarchical Gd³⁺:TiO₂Nanostructures through Amplifying Light Reception and Surface States Passivation

Interpretation of Cyclic Voltammetry Measurements of Thin Semiconductor Films for Solar Fuel Applications

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Water Oxidation at Hematite Photoelectrodes with an Iridium-Based Catalyst

Cited by 136 publications

References 54 publications

Photochemical Deposition of Co-Ac Catalyst on ZnO Nanorods for Solar Water Oxidation

Photochemical Deposition of Co-Ac Catalyst on ZnO Nanorods for Solar Water Oxidation

Enhanced Photoelectrocatalytic Water Splitting at Hierarchical Gd3+:TiO2Nanostructures through Amplifying Light Reception and Surface States Passivation

Interpretation of Cyclic Voltammetry Measurements of Thin Semiconductor Films for Solar Fuel Applications

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Enhanced Photoelectrocatalytic Water Splitting at Hierarchical Gd³⁺:TiO₂Nanostructures through Amplifying Light Reception and Surface States Passivation