Anodic deposition of a robust iridium-based water-oxidation catalyst from organometallic precursors

Blakemore, James D.; Schley, Nathan D.; Olack, Gerard; Incarvito, Christopher D.; Brudvig, Gary W.; Crabtree, Robert H.

doi:10.1039/c0sc00418a

Cited by 221 publications

(244 citation statements)

References 32 publications

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Section: Methodssupporting

confidence: 54%

“…As observed previously with related Ir(Cp*) complexes, 67 addition of CAN induced a color change of the initial yellow solution to blue within seconds. While the formation of a blue mixture or a blue layer 67 has periodically been attributed to IrO x formation due to the oxide's general tendency to absorb broadly around 580 nm 30,33 similar color changes have previously been noted in high-valent iridium aquo complexes. 68 To further investigate this issue with complex 4a, an experiment was performed using the previously described digital pressure transducers to manometrically follow the evolution of oxygen from several equal additions of oxidant with concurrent UV/Vis measurements When a single addition of 20 equivalents of CAN was added to a 0.5 mM solution of 4a no measurable oxygen production was observed ( Figure 6) though there is a rapid color change from yellow to blue and back over the course of 15 minutes (Figure 7, Top).…”

Section: Methodssupporting

confidence: 54%

See 1 more Smart Citation

Carbene iridium complexes for efficient water oxidation: scope and mechanistic insights

Woods

Lalrempuia

Petronilho

et al. 2014

Energy Environ. Sci.

105

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Iridium complexes of Cp* and mesoionic carbene ligands were synthesized and evaluated as potential water oxidation catalysts using cerium ammonium nitrate as a chemical oxidant. Performance was evaluated by turnover frequency at 50% conversion and by absolute turnover number, and the most promising precatalysts were subjected to further study. Molecular turnover frequencies varied from 190 to 451 per hour with a maximum turnover number of 38,000. While the rate of oxygen evolution depends linearly on iridium concentration, 10 concurrent spectroscopic and manometric monitoring of stoichiometric additions of oxidant suggests oxygen evolution occurs as two sequential first order reactions. Under the conditions herein, the oxygen evolving species appears to be well defined and molecular based on the kinetic effects of careful ligand design, reproducibility, and the absence of persistent dynamic light scattering signals. Outside of these conditions, the complex mechanism is highly dependent on reaction conditions. While confident characterization of the catalytically active species is difficult, especially under high-turnover conditions, this work indicates IrOx is not essential for the 15 formation of catalytically active water oxidation species.

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Section: Methodssupporting

confidence: 54%

Section: Methodssupporting

confidence: 54%

Carbene iridium complexes for efficient water oxidation: scope and mechanistic insights

Woods

Lalrempuia

Petronilho

et al. 2014

Energy Environ. Sci.

105

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“…More specifically, it has been ascribed to an Ir(III)/Ir(IV) redox process, which involves a two-electron, three-proton process. 27,28 However, it is interesting to discuss how the redox catalyst is electronically coupled to the semiconductor film. Similar observations have been reported with cobalt−phosphate (Co−Pi) catalyst layers covering hematite electrodes.…”

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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“…For example, for an electrodeposited Ir-based amorphous electrocatalyst recently an overpotential of only 200 mV (at 0.5 mA cm À2 ) was reported. 48 For technological use, improvement of the MnCat to reduce the overpotential will be of high importance.…”

Section: Functional Characterizationmentioning

confidence: 99%

Electrosynthesis, functional, and structural characterization of a water-oxidizing manganese oxide

Zaharieva

Chernev

Risch

et al. 2012

Energy Environ. Sci.

410

583

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In the sustainable production of non-fossil fuels, water oxidation is pivotal. Development of efficient catalysts based on manganese is desirable because this element is earth-abundant, inexpensive, and largely non-toxic. We report an electrodeposited Mn oxide (MnCat) that catalyzes electrochemical water oxidation at neutral pH at rates that approach the level needed for direct coupling to photoactive materials. By choice of the voltage protocol we could switch between electrodeposition of inactive Mn oxides (deposition at constant anodic potentials) and synthesis of the active MnCat (deposition by voltage-cycling protocols). Electron microscopy reveals that the MnCat consists of nanoparticles (100 nm) with complex fine-structure. X-ray spectroscopy reveals that the amorphous MnCat resembles the biological paragon, the water-splitting Mn 4 Ca complex of photosynthesis, with respect to mean Mn oxidation state (ca. +3.8 in the MnCat) and central structural motifs. Yet the MnCat functions without calcium or other bivalent ions. Comparing the MnCat with electrodeposited Mn oxides inactive in water oxidation, we identify characteristics that likely are crucial for catalytic activity. In both inactive Mn oxides and active ones (MnCat), extensive di-m-oxo bridging between Mn ions is observed. However in the MnCat, the voltage-cycling protocol resulted in formation of Mn III sites and prevented formation of well-ordered and unreactive Mn IV O 2 . Structure-function relations in Mn-based wateroxidation catalysts and strategies to design catalytically active Mn-based materials are discussed. Knowledge-guided performance optimization of the MnCat could pave the road for its technological use. Broader contextThreatening global climate changes and unsecured supply of fossil fuels call for a global transition toward sustainable energyconversion systems. The storage of wind or solar energy by formation of energy-rich fuel molecules could play a central role in both transient storage of the intermittently provided energy and replacement of fossil fuels in the transportation sector. Whether hydrogen or a carbon-based fuel is the target, in any event the extraction of reducing equivalents and protons from water (that is, water oxidation) is pivotal. In search of water-oxidation catalysts that ultimately could play a role at a global scale, we and others are aiming at development of simple routes towards formation of Mn-based catalysts. Manganese excels by high availability and low toxicity; and in oxygenic photosynthesis, nature has demonstrated that a Mn-based catalyst can oxidize water efficiently. When aiming at an 'artificial leaf' with a Mn-based catalyst directly coupled to a solar-energy-converting material, the activity of the catalyst (per area) needs to cope with the incoming photon flux. Moreover the device design typically requires the use of benign synthesis and operation conditions, that is, temperatures close to room temperature and pH close to neutral. As an important first step, we report a simple protocol for e...

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Anodic deposition of a robust iridium-based water-oxidation catalyst from organometallic precursors

Cited by 221 publications

References 32 publications

Carbene iridium complexes for efficient water oxidation: scope and mechanistic insights

Carbene iridium complexes for efficient water oxidation: scope and mechanistic insights

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

Electrosynthesis, functional, and structural characterization of a water-oxidizing manganese oxide

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