Mechanism Of Water Oxidation Research Articles

The influence of the pH on the reaction mechanism of water oxidation by a Ru(bda) catalyst

Recent results of Concepcion’s group (Chem. Com51 (2015) 4105) on water oxidation catalysis (WOC) by a ruthenium complex suggest that, at pH = 8, O2 release takes place after formation of a rhomboid bis(μ-oxo)-RuV2 species and not after generation of the typical μ-η1:η1-peroxo-RuIV2 intermediate, coming from the coupling of two RuV=O moieties (I2M mechanism), which is widely accepted to be formed at pH = 1. To analyze the differences between the reaction mechanisms of this WOC at different pHs, we performed DFT calculations of the full mechanism at pH = 1 and 8 of the WOC process catalyzed by the 2,2′-bipyridine-6,6′-dicarboxylate Ru complex. At pH = 8, we found that barriers leading to the hypothetic formation of rhombic RuV2O2 species are higher than those involved in the canonical I2M mechanism. The rate determining step at the latter pH is found to be the dimer formation while the bond cleavage for the O2 liberation process is barrierless. The computational results confirm that the most common I2M mechanism is preferred at both pHs, as the new proposal comprising formation of bis(μ-oxo)-RuV2 species involves higher energy barriers.

Calcium Valence-to-Core X-ray Emission Spectroscopy: A Sensitive Probe of Oxo Protonation in Structural Models of the Oxygen-Evolving Complex.

Calcium is an abundant, nontoxic metal that finds many roles in synthetic and biological systems including the oxygen-evolving complex (OEC) of photosystem II. Characterization methods for calcium centers, however, are underdeveloped compared to those available for transition metals. Valence-to-core X-ray emission spectroscopy (VtC XES) selectively probes the electronic structure of an element’s chemical environment, providing insight that complements the geometric information available from other techniques. Here, the utility of calcium VtC XES is established using an in-house dispersive spectrometer in combination with density functional theory. Spectral trends are rationalized within a molecular orbital framework, and Kβ2,5 transitions, derived from molecular orbitals with primarily ligand p character, are found to be a promising probe of the calcium coordination environment. In particular, it is shown that calcium VtC XES is sensitive to the electronic structure changes that accompany oxo protonation in Mn3CaO4-based molecular mimics of the OEC. Through correlation to calculations, the potential of calcium VtC XES to address unresolved questions regarding the mechanism of biological water oxidation is highlighted.

Fourier transform infrared and mass spectrometry analyses of a site-directed mutant of D1-Asp170 as a ligand to the water-oxidizing Mn4CaO5 cluster in photosystem II

The Mn4CaO5 cluster, the catalytic center of water oxidation in photosystem II (PSII), is coordinated by six carboxylate and one imidazole ligands. The roles of these ligands in the water oxidation mechanism remain largely unknown. In this study, we constructed a D1-D170H mutant, in which the Asp ligand bridging Mn and Ca ions was replaced with His, in the cyanobacterium Synechocystis sp. PCC 6803, and analyzed isolated PSII core complexes using Fourier transform infrared (FTIR) difference spectroscopy and mass spectrometry (MS). The S2-minus-S1 FTIR difference spectrum of the PSII complexes of the D1-D170H mutant showed features virtually identical to those of the wild-type PSII. MS analysis further showed that ~70% of D1 proteins from the PSII complexes of D1-D170H possessed the wild-type amino acid sequence, although only the mutated sequence was detected in genomic DNA in the same batch of cells for PSII preparations. In contrast, a D1-S169A mutant as a control showed a modified FTIR spectrum and only a mutated D1 protein. It is thus concluded that the FTIR spectrum of the D1-D170H mutant actually reflects that of wild-type PSII, whereas the Mn4CaO5 cluster is not formed in PSII with D1-D170H mutation. Although the mechanism of production of the wild-type D1 protein in the D1-D170H mutant is unknown at present, a caution is necessary in the analysis of site-directed mutants of crucial residues in the D1 protein, and mutation has to be confirmed not only at the DNA level but also at the amino acid level.

Capturing the Role of Phosphate in the Ni‐PY5 Catalyzed Water Oxidation

AbstractThe mononuclear Nickel complex Ni‐PY5 [PY5=2, 6‐bis(1,1‐bis(2‐pyridyl)ethyl)pyridine] has been disclosed to catalyze water oxidation electrochemically with an applied potential of 1.5 V at pH 10.8 in aqueous phosphate buffer solution. Density functional calculations were used to elucidate the reaction mechanism of water oxidation catalyzed by this nickel complex and to capture the role of the phosphate. The calculations demonstrated that the oxidations of the starting [OH2−NiII‐PY5]2+ complex by two sequential proton‐coupled electron‐transfer processes lead to the formation of a key intermediate [O=NiIV‐PY5]2+. O−O bond formation then takes place through a water nucleophilic attack on the high‐valent NiIV=O moiety of the catalyst, facilitated by a hydrogen phosphate anion, with a total barrier of 11.5 kcal mol−1. The calculated barrier agrees very well with the experimental turnover frequency of about 2000 s−1, which corresponds to a barrier of 12.9 kcal mol−1. The calculated deuterium kinetic isotope effect of 1.99 is also in excellent agreement with the experimental value of 2.06. Finally, we also predicted the catalytic activity of other PY5‐based first‐row transition metal complexes, namely, involving Mn, Fe, Co and Cu. The calculations showed that the Mn, Fe, Co complexes have higher barrier for water oxidation, while the Cu complex has lower barrier and higher water oxidation activity compared with the Ni complex.

Multihole water oxidation catalysis on haematite photoanodes revealed by operando spectroelectrochemistry and DFT.

Water oxidation is the key kinetic bottleneck of photoelectrochemical devices for fuel synthesis. Despite advances in the identification of intermediates, elucidating the catalytic mechanism of this multi-redox reaction on metal-oxide photoanodes remains a significant experimental and theoretical challenge. Here, we report an experimental analysis of water oxidation kinetics on four widely studied metal oxides, focusing particularly on haematite. We observe that haematite is able to access a reaction mechanism that is third order in surface-hole density, which is assigned to equilibration between three surface holes and M(OH)-O-M(OH) sites. This reaction exhibits low activation energy (Ea ≈ 60 meV). Density functional theory is used to determine the energetics of charge accumulation and O-O bond formation on a model haematite (110) surface. The proposed mechanism shows parallels with the function of the oxygen evolving complex of photosystem II, and provides new insights into the mechanism of heterogeneous water oxidation on a metal oxide surface.

Proton Release Process during the S2-to-S3 Transition of Photosynthetic Water Oxidation As Revealed by the pH Dependence of Kinetics Monitored by Time-Resolved Infrared Spectroscopy.

Photosynthetic water oxidation takes place at the Mn4CaO5 cluster in photosystem II via a light-driven cycle of intermediates called S states (S0-S4). Clarifying how electron and proton transfer reactions are coupled with each other in the S2 → S3 transition, which occurs just before O-O bond formation, is crucial for understanding the water oxidation mechanism. Here, we investigated the pH dependence of the kinetics of the S2 → S3 transition using time-resolved infrared (TRIR) spectroscopy to identify the proton release phase in this transition. TRIR measurements of YD-less PSII core complexes from the D2-Y160F mutant of Thermosynechococcus elongatus showed that the last phase in this transition (τ ∼ 350 μs at pH 6) was strongly dependent on pH, and its time constant at pH 5 was larger than that at pH 8 by a factor of >3. In contrast, the earlier phase with a time constant of ∼100 μs was virtually independent of pH. These results strongly support the view that proton release is a rate-limiting step of the proton-coupled electron transfer in the last phase of the S2 → S3 transition. This proton release enables electron transfer by removing an excessive positive charge from the catalytic center and hence decreasing its redox potential.

Insights into Proton-Transfer Pathways during Water Oxidation in Photosystem II.

Water oxidation by photosystem II (PSII) involves the release of O2, electrons, and protons at the oxygen-evolving complex (OEC). These processes are facilitated by a hydrogen-bonded network of amino acid residues and waters surrounding the OEC. It is crucial to probe the proton-transfer pathways from the OEC as proton release helps to maintain the charge balance required for efficient water oxidation. In this study, we generate point mutations in the cyanobacterium Synechocystis sp. PCC 6803 at secondary-shell amino acid residues surrounding the OEC: D2-K317, D1-S169, CP43-R357, D1-D61, and D1-N181. We employ direct experimental methods to study the O2 evolution rate under varying pH ranging from 3-8. The pH dependence follows a bell-shaped curve in both wild-type and mutated PSII from which we can derive the effective acidic pKa. The effective acidic pKa provides insights into the protonation states of the amino acid residues participating in the proton-transfer process during the rate-determining step of water oxidation. The presence of an additional effective pKa in D1-S169A PSII and D2-K317A PSII indicates the possibility of multiple proton-transfer pathways during the rate-determining step of water oxidation. We also studied the O2 evolution rate in H2O and D2O with varying pL (L = H or D) to identify the amino acid residues participating in the proton-transfer process. We find that replacing the positively charged lysine with a neutral alanine in D2-K317A PSII and aspartate with alanine in D1-D61A PSII significantly enhances the kinetic solvent isotope effect (KSIE), indicating that proton transfer becomes rate-limiting at the optimal pH in these mutated PSII. However, the KSIE remains unchanged for D1-N181A, D1-S169A, and CP43-R357K PSII. Thus, perturbing the channel defined by the D1-D61 and D2-K317 residues strongly hampers the proton-transfer mechanism, and in turn, the water oxidation reaction of PSII. Hence, our study provides a direct experimental probe to identify that the D1-D61 and D2-K317 residues participate in the proton-transfer process. These results, thereby, provide us a deeper understanding of the proton-transfer processes in the water oxidation mechanism.

Understanding the Active Sites and Reaction Mechanism for Water Oxidation on Ruthenium Dioxide

Rutile Ruthenium Dioxide (RuO2) is a gold standard catalyst for water splitting in acidic solutions1-3. It can also undergo fast surface redox reactions in the electrochemically stable potential window of water, making it an ideal material for electrochemical capacitors that can charge and discharge in a much shorter time scale than batteries. However, there is a lack of fundamental understanding of the active sites and atomic scale processes occurring at the oxide-electrolyte interface upon interaction with water as previous work has been confined to the ultra high vacuum environment, and to the thermodynamically stable (110) surface4. In this work, we use three different facets of RuO2, (110), (100) and (101) to demonstrate how changing the local environment of surface Ru and O atoms can enable tuning the electronic structure of the active site and alter its intrinsic oxygen evolution reaction (OER) activity. Using synchrotron based ambient pressure X-ray photoelectron spectroscopy and in situ surface diffraction on single crystal surfaces coupled with density functional theory calculations, we show that at 1.0 VRHE, water adsorbs molecularly or dissociatively on the coordinatively unsaturated site (CUS), depending on the surface orientation. This is followed by successive deprotonation occuring at potentials greater than 1.0 VRHE . At oxygen evolution potentials (1.5 VRHE), surface diffraction measurements reveal the presence of an –OO species on the CUS site for the (110) and (100) surface. Computation results show that this –OO group is stabilized by a neighboring –OH group suggesting that the final deprotonation step is rate-limiting. On the other hand, for the (101) surface that binds oxygen more weakly, a completely oxidized surface has been detected, implying a change in the rate-limiting step to the dissociation and deprotonation of the second water molecule on the oxidized surface. The mechanistic insight gained from in situ methods will be used to discuss the difference in OER activity and Tafel slope observed on the different RuO2 facets. Finally, the results obtained using single crystals will be extended to understanding the distinct redox peaks of RuO2 nanoparticles in the electrochemically stable potential window of water as well as the nature of intermediates prior to the evolution of oxygen. Thus, by using different experimental and theoretical techniques on model surfaces, this study identifies the active sites for oxygen electrocatalysis and demonstrates how catalyst surface structure can be altered to improve OER kinetics.

Photocatalytic Water Splitting Cycle in a Dye-Catalyst Supramolecular Complex: Ab Initio Molecular Dynamics Simulations

A dye-sensitized photoelectrochemical cell (DS-PEC) is a promising device for direct conversion of solar energy into fuel. The basic idea, inspired by natural photosynthesis, is to couple the photoinduced charge separation process to catalytic water splitting. The photo-oxidized dye coupled to a water oxidation catalyst (WOC) should exert a thermodynamic driving force for the catalytic cycle, while water provides the electrons for regenerating the oxidized dye. These conditions impose specific energetic constraints on the molecular components of the photoanode in the DS-PEC. Here, we consider a supramolecular complex integrating a mononuclear Ru-based WOC with a fully organic naphthalene-diimide (NDI) dye that is able to perform fast photoinduced electron injection into the conduction band of the titanium-dioxide semiconductor anode. By means of constrained ab initio molecular dynamics simulations in explicit water solvent, it is shown that the oxidized NDI provides enough driving force for the whole photocatalytic water splitting cycle. The results provide strong evidence for the significant role of spin alignment and solvent rearrangement in facilitating the proton-coupled electron transfer processes. The predicted activation free energy barriers confirm that the O–O bond formation is the rate-limiting step. Our results expand the current understanding of the photocatalytic water oxidation mechanism and provide guidelines for the optimization of high-performance DS-PEC devices.

Implications of structural heterogeneity for the electronic structure of the final oxygen-evolving intermediate in photosystem II

Heterogeneity in intermediate catalytic states of the oxygen-evolving complex (OEC) of Photosystem II is known from a wide range of experimental and theoretical data, but its potential implications for the mechanism of water oxidation remain unexplored. We delineate the consequences of structural heterogeneity for the final step of the catalytic cycle by tracing the evolution of three spectroscopically relevant and structurally distinct components of the last metastable S3 state to the transient O2-evolving S4 state of the OEC. Using quantum chemical calculations, we show that each S3 isomer leads to a different electronic structure formulation for the active S4 state. Crucially, in addition to previously hypothesized Mn(IV)-oxyl species, we establish for the first time, how a genuine Mn(V)-oxo can be obtained in the catalytically active S4 state: this takes the form of a five-coordinate and locally high-spin (SMn = 1) Mn(V) site. This formulation for the S4 state evolves naturally from a preceding S3-state structural intermediate that contains a quasi-trigonal-bipyramidal Mn(IV) ion. The results strongly suggest that water binding in the S3 state is not prerequisite for reaching the oxygen-evolving S4 state of the complex, supporting the notion that both substrates are preloaded at the beginning of the catalytic cycle. This scenario allows true four-electron metal-centered hole accumulation to precede OO bond formation and hence the latter can proceed via a genuine even-electron mechanism. This can occur as intramolecular nucleophilic coupling of two oxo units synchronously with the binding of a water substrate for the next catalytic cycle.

Mechanistic Investigations of Photoelectrochemical Water and Methanol Oxidation on Well-Defined TiO2 Anatase (101) and Rutile (110) Surfaces

The mechanisms of photoelectrochemical water and methanol oxidation on TiO2 anatase (101) and rutile (110) surfaces have been studied using the intensity modulated photocurrent spectroscopy (IMPS) technique. The phenomenological rate constants for the photogenerated charge carriers transfer and recombination have been determined at different band bending values in the presence and absence of methanol as well as at different methanol concentrations. The obtained results have been analyzed based on the IMPS theory for a bulk semiconductor surface together with a model to define the nature of the surface-bound intermediates. The results of the analysis indicated that (i) water oxidation proceeds via coupling of two >OH•br radicals on both surfaces and the coupling of >OH•br radicals is about 1 order of magnitude faster on the anatase (101) surface than that on the rutile (110) surface; (ii) the rate constant of surface recombination at the flatband potential on anatase (101) surface is much lower than that o...

Half‐sandwich Ir (III) and Rh (III) complexes as catalysts for water oxidation with double‐site

A series of neutral binuclear iridium and rhodium complexes were synthesized based on bis‐imine ligands under mild conditions. These half‐sandwich late transition metal complexes were isolated in good yields and characterized by elemental analysis, 1H NMR, 13C NMR, HR‐MS, and FT‐IR spectroscopies, and the solid state structure of complexes 1 and 2 were further confirmed by single‐crystal X‐ray diffraction. Cyclic voltammetry (CV) characterization indicated that the complex 1 has the best catalyst for water oxidation process with TOF of 0.8 s−1 at low overpotential of 0.325 V in methanol‐phosphate buffer. The proposed double‐site water oxidation mechanism had been also speculated.

Theoretical Investigation of Water Oxidation Mechanism on Pure Manganese and Ca-Doped Bimetal Oxide Complexes

Understanding the role of Ca2+ ion in the oxygen-evolving complex of photosystem II is essential to design commercially viable and efficient water oxidation catalysts. To this end, small pure manganese oxide and calcium-doped manganese oxide model complexes saturated with water-derived ligands are investigated in this work. Density functional theory calculations are performed to investigate the water oxidation process on Mn2(μ-OH)(μ-O)(H2O)3(OH)5 (Mn2O4·6H2O) and CaMnO(μ-OH)2(H2O)5(OH)2 (CaMnO3·7H2O) complexes. Many reaction pathways are considered, and the three lowest energy water oxidation mechanisms on CaMnO3·7H2O have highest reaction energy steps of 1.37, 1.67, and 1.81 eV compared to the highest reaction energy step of 2.25 eV for the lowest energy mechanism of the pure Mn2O4·6H2O complex. Doping of the manganese dimer complex with calcium decreases the highest reaction energy of the water oxidation process. Consequently, the inclusion of calcium appears to improve the catalyst's efficiency for water splitting.

Bicarbonate rescues damaged proton-transfer pathway in photosystem II

The membrane-protein complex photosystem II (PSII) catalyzes photosynthetic water oxidation. Proton transfer plays an integral role in the catalytic cycle of water oxidation by maintaining charge balance to regulate and ensure the efficiency of the process. The hydrogen-bonded amino-acid residues that surround the oxygen-evolving complex (OEC) provide an efficient pathway for proton removal. Hence, it is crucial to identify these pathways to provide deeper insights into the proton-transfer mechanisms. In this study, we have used bicarbonate as a mobile exogenous proton-transfer reagent to recover the activity lost by site-directed mutations in order to identify amino-acid residues participating in the proton-transfer pathway. We find that bicarbonate restores efficient S-state cycling in D2-K317A PSII core complexes, but not in D1-D61A and CP43-R357K PSII core complexes, indicating that bicarbonate chemical rescue can be used to differentiate single-point mutations affecting the pathways of proton transfer from mutations that affect other aspects of the water-oxidation mechanism.

Mono-/Multinuclear Water Oxidation Catalysts.

Water splitting, in which water molecules can be transformed into hydrogen and oxygen, is an appealing energy conversion and transformation strategy to address the environmental and energy crisis. The oxygen evolution reaction (OER) is dynamically slow, which limits energy conversion efficiency during the water-splitting process and requires high-efficiency water oxidation catalysts (WOCs) to overcome the OER energy barrier. It is generally accepted that multinuclear WOCs possess superior OER performances, as demonstrated by the CaMn4 O5 cluster in photosystem II (PSII), which can catalyze the OER efficiently with a very low overpotential. Inspired by the CaMn4 O5 cluster in PSII, some multinuclear WOCs were synthesized that could catalyze water oxidation. In addition, some mononuclear molecular WOCs also show high water oxidation activity. However, it cannot be excluded that the high activity arises from the formation of dimeric species. Recently, some mononuclear heterogeneous WOCs showed a high water oxidation activity, which testified that mononuclear active sites with suitable coordination surroundings could also catalyze water oxidation efficiently. This Review focuses on recent progress in the development of mono-/multinuclear homo- and heterogeneous catalysts for water oxidation. The active sites and possible catalytic mechanisms for water oxidation on the mono-/multinuclear WOCs are provided.

Applications of Advanced Oxidation Technologies for Sludge Treatment

Treatment of sludge is an important issue in water treatment. At present, the traditional sludge treatment process still faces problems such as high sludge production and low solid content, and it is impossible to achieve environmental and economic benefits. Advanced oxidation technology can not only reduce sludge dry base production, but also improve sludge dewatering performance, which has attracted much attention in the field of sludge treatment. On the basis of a brief description of Fenton reagent oxidation, ozone oxidation, wet air oxidation and supercritical water oxidation mechanism, the effects of several advanced oxidation techniques on sludge dry yield and dewatering performance are discussed, and various oxidation methods are introduced. Finally, the advantages and disadvantages of various advanced oxidation technologies are discussed, and the main research directions of advanced sludge oxidation are pointed out.

Bi2WO6 and FeWO4 Nanocatalysts for the Electrochemical Water Oxidation Process

Polyvinylpyrrolidone (PVP)-assisted nanocatalyst preparation was succeeded by employing a controlled solvothermal route to produce efficient electrodes for electrochemical water-splitting applications. Bi2WO6 and FeWO4 nanocatalysts have been confirmed through the strong signature of (113) and (111) crystal planes, respectively. The binding natures of Bi–W–O and Fe–W–O have been thoroughly discussed by employing X-ray photoelectron spectroscopy which confirmed the formation of Bi2WO6 and FeWO4. The freestanding nanoplate array morphology of Bi2WO6 and the fine nanosphere particle morphology of FeWO4 nanocatalysts were revealed by scanning electron microscopy images. With these confirmations, the fabrication of durable, long-term electrodes for electrochemical water splitting has been subjected to efficient oxidation of water, confirmed by obtaining 2.79 and 1.96 mA/g for 0.5 g PVP-assisted Bi2WO6 and FeWO4 nanocatalysts, respectively. The water oxidation mechanism of both nanocatalysts has been revealed with the support of 24 h stability test over continuous water oxidation and faster charge transfer achieved by the smaller Tafel slope values of 75 and 78 mV/dec, respectively. Generally, these nanocatalysts are utilized for photocatalytic applications. The present study revealed the PVP-assisted synthesis to produce electrocatalytically active nanocatalysts and their electrochemical water-splitting mechanism which will offer a pathway for research interests with regard to the production of multifunctional nanocatalysts for both electro- and photocatalytic applications in the near future.

Catalytic Multilayers for Efficient Solar Water Oxidation through Catalyst Loading and Surface-State Passivation of BiVO4 Photoanodes.

We studied the kinetics of photoelectrochemical (PEC) water oxidation using a model photoanode BiVO4 modified with various water oxidation catalysts (WOCs) by electrochemical impedance spectroscopy. In particular, we prepared BiVO4 photoanodes with catalytic multilayers (CMs), where cationic polyelectrolytes and anionic polyoxometalate (POM) WOCs were assembled in a desired amount at a nanoscale precision, and compared their performance with those with well-known WOCs such as cobalt phosphate (CoPi) and NiOOH. Our comparative kinetics analysis suggested that the deposition of the CMs improved the kinetics of both the photogenerated charge carrier separation/transport in bulk BiVO4 due to passivation of surface recombination centers and water oxidation at the electrode/electrolyte interface due to deposition of efficient molecular WOCs. On the contrary, the conventional WOCs were mostly effective in the former and less effective in the latter, which is consistent with previous reports. These findings explain why the CMs exhibit an outstanding performance. We also found that separated charge carriers can be efficiently transported to POM WOCs via a hopping mechanism due to the delicate architecture of the CMs, which is reminiscent of natural photosynthetic systems. We believe that this study can not only broaden our understanding on the underlying mechanism of PEC water oxidation but also provide insights for the design and fabrication of novel electrochemical and PEC devices, including efficient water oxidation photoanodes.

Quantum Chemical Study of the Mechanism of Water Oxidation Catalyzed by a Heterotrinuclear Ru2 Mn Complex.

The heterotrinuclear complex A {[RuII (H2 O)(tpy)]2 (μ-[MnII (H2 O)2 (bpp)2 ])}4+ [tpy=2,2':6',2''-terpyridine, bpp=3,5-bis(2-pyridyl)pyrazolate] was found to catalyze water oxidation both electrochemically and photochemically with [Ru(bpy)3 ]3+ (bpy=2,2'-bipyridine) as the photosensitizer and Na2 S2 O8 as the electron acceptor in neutral phosphate buffer. The mechanism of water oxidation catalyzed by this unprecedented trinuclear complex was studied by density functional calculations. The calculations showed that a series of oxidation and deprotonation events take place from A, leading to the formation of complex 1 (formal oxidation state of Ru1IV MnIII Ru2III ), which is the starting species for the catalytic cycle. Three sequential oxidations of 1 result in the generation of the catalytically competing species 4 (formal oxidation state of Ru1IV MnV Ru2IV ), which triggers the O-O bond formation. The direct coupling of two adjacent oxo ligands bound to Ru and Mn leads to the production of a superoxide intermediate Int1. This step was calculated to have a barrier of 7.2 kcal mol-1 at the B3LYP*-D3 level. Subsequent O2 release from Int1 turns out to be quite facile. Other possible pathways were found to be much less favorable, including water nucleophilic attack, the coupling of an oxo and a hydroxide, and the direct coupling pathway at a lower oxidation state (RuIV MnIV RuIV ).

Recent progress in computational exploration and design of functional materials

In this review, we summarize our work for the computational study and design of functional materials. Emphasis is laid on computational spectroscopy in the condensed phase as well as exploration of solar light-driven water splitting. In particular, dynamic ab initio methods have been in the focus of recent developments. This has enabled computationally efficient access to spectroscopic signatures, local properties, and innovative analysis of complex systems. Examples involve periodic subsystem density functional theory and density functional perturbation theory as well as (vibrational) spectroscopy such as Raman (optical activity) spectroscopy or sum frequency generation for in-depth study of interfaces. In addition, sophisticated approaches for exploration of water splitting processes are outlined, especially for water oxidation as one of the limiting factors for efficient water splitting devices. In-depth study of water oxidation mechanisms and related reaction networks in combination with (dynamic) consideration of environmental effects has allowed unprecedented new insight and discovery of essential factors influencing water oxidation behaviour, thus paving the way for novel design approaches for more efficient catalysts.