Catalytic Activity For Water Oxidation Research Articles

Bioinspired octanuclear copper cubane complex as an efficient molecular electrocatalyst for water oxidation

Water oxidation catalysts (WOCs) with excellent activity and stability are highly desired. Numerous efforts have been dedicated to develop WOCs mimicking the cubic structure and activity of Mn4CaO5 cluster in oxygen-evolving center (OEC) of photosynthesis system II (PSII). Herein, a octanuclear Cu cluster [Cu8(dpy{OH}O)8(OAc)4]4+ (1, dpy{OH}O− = the monoanion of the hydrated, gem-diol form of di-2-pyridyl ketone) that contains two Cu4O4 cubic fragments with bioinspired structure mimicking the Mn4CaO5 cluster of OEC of natural PSII is developed as efficient homogeneous catalyst for electrochemical water oxidation under near neutral condition for the first time. It exhibits outstanding water oxidation catalytic activity via accelerating oxygen evolution with onset overpotential of 730 mV and appreciable turnover frequency of 20.1 s−1. Collective experiments together confirmed the homogeneity and stability of cluster 1 under long-term water oxidation catalytic cycle. Kinetic study reveals the water nucleophilic attack (WNA) catalytic mechanism occurs on the coordination unsaturated Cu center of the cluster. This work provides the inspiration of the development of robust bioinspired catalyst for electrochemical water oxidation.

Improvements in Long-Term Durability of CO2 Electrolyzer Producing Formate Designed for Integration with Solar Cells for Artificial Photosynthesis

Artificial photosynthetic cells have been extensively studied for carbon neutrality, yet in lab-scale. We have previously constructed practically large-sized cells consisting of CO2 electrolyzers and crystalline silicon solar cells.1,2 Our CO2 electrolyzers adopt a facing cathode-anode configuration, using a Ru complex polymer (RuCP) catalyst realizing a low overpotential for CO2 reduction and an IrO x -based catalyst with a high catalytic activity for water oxidation.3 1000 cm2-sized cells achieved a solar-to-chemical energy-conversion efficiency (η STC) of 7.2%,1 and a further scaled-up 1 m2-cell demonstrated a higher η STC of 10.5%, yielding a large formate production rate of 1.2 mol/h.2 In the present study, we improved the long-term durability of the CO2 electrolyzer. We prepared the 75 cm2-sized CO2 electrolyzer using the improved cathode and the anode, and achieved high formate Faradaic efficiencies (FE) exceeding 80% and electricity-to-chemical energy-conversion efficiencies (η ETC) of around 60% even after 3000 h operation under practical conditions, as shown in Fig. 1.In the previous large-sized cells, the operating current gradually decreased during continuous operation within dozen of hours. We investigated the causes of the degradation and identified three key factors. Two of these factors were associated with the cathode electrodes: detachment of the RuCP catalyst from the carbon supports and peeling off of the carbon supports from the conducting Ti substrates. An introduction of a pyrrole derivative containing amino group in the RuCP, coupled with an application of a UV-ozone treatment to create carboxyl groups on the carbon supports, effectively reduced the detachment of the RuCP catalyst by forming strong chemical bonds. A newly-developed chemically-resistant graphite adhesive composed of graphite particles and a polyvinylidene fluoride (PVDF) binder prevented the carbon supports from peeling off from the Ti-plates. The post-loading process of the RuCP, i.e., RuCP-loading on the carbon supports already-bonded on the Ti-plates using the new adhesive eliminated the detrimental impact of the heat treatment for curing the adhesive. The third factor involved detachment of the anode catalyst of IrO x particles from the Ti-plates.4 Therefore, we replaced the IrO x anodes with highly durable counterparts comprising IrO x -TaO x /Pt-Metal oxide/Ti-plates.Another critical issue we addressed was the validity of laboratory-based evaluations for reflecting outdoor operations. In our previous study, we vertically installed the integrated CO2 electrolyzers and solar cells on the ground and evaluated their performance under continuous simulated sunlight (ca. 1 sun).2,3 This vertical setup was chosen to prevent a decrease in η STC caused by crossover reactions that would occur when the electrolyzers are inclined. Indeed, it has been reported that oxygen reduction reaction (ORR) of the O2 bubbles generated at the anode and transferred to the cathode can be substantial in a single-chamber water-splitting reactor.5 By contrast, although the present CO2 electrolyzer was installed at an inclined angle of 30 °, which is approximately the optimal value for receiving more solar energy, the crossover reactions were well-suppressed because the porous separator film inserted between the facing cathode and anode impeded the transfer of O2 bubbles from the anode to the cathode. However, the use of a separator film raised another issue: the O2 bubbles trapped on the film narrowed the effective film area. Intermittent operation corresponding to changes in solar energy during the day mitigates the detrimental impact of the second issue.Thus, we established the groundwork for the widespread use of integrated CO2 electrolyzers and solar cells for artificial photosynthesis, demonstrating high durability, exceptional FE, and η ETC.References N. Kato, et al., A large-Sized Cell for Solar-Driven CO2 Conversion with a Solar-to-Formate Conversion Efficiency of 7.2%, Joule, (2021) 5, 687.N. Kato, et al., Solar Fuel Production from CO2 using 1 m-square-sized Reactor with a Solar-to-Formate Conversion Efficiency of 10.5%, ACS Sustain. Chem. Eng.,(2021) 9, 16031.T. Arai, S. Sato, T. Morikawa, A Monolithic Device for CO2 Photoreduction to Generate Liquid Organic Substances in a Single-Compartment Reactor, Energy Environ. Sci., (2015) 8, 1998.M. Shiozawa, et al., Improved Durability of Highly Active IrO x Electrodes for Electrocatalytic Oxygen Evolution Reaction, Electrocatalysis, (2022) 13, 830.K. Obata, et al., Multiphase Fluid Dynamics Simulations of Product Crossover in Solar-driven, Membrane-less Water Splitting, Cell Rep. Phys. Sci, (2021) 2, 100358. Figure 1

Exploring the Water Oxidation Catalytic Activity of a Mn-Based Magnetic Metal-Organic Framework: The Role of Proton Conductivity and Oxygen Evolution Reaction Overpotential.

The present work evaluates the water oxidation catalytic activity of a Mn-based metal-organic framework (MOF), which we envisioned to reduce the oxygen evolution reaction (OER) overpotential because of its high electrical conductivity, facilitated by solvent-encapsulated structural features. The presence of Mn centers induces interesting magnetic features in the MOF, which exhibits impressive cryogenic magnetic refrigeration with a ΔSM value of 29.94 J kg-1 K-1 for a field change of ΔH = 5T at 2.3 K. To the best of our knowledge, the ΔSM value of the current system ranked the highest position among the published examples. The crystal structure aligns perfectly with the thematic expectations and features as many as ten metal-coordinated water molecules, forming an extensive web of a hydrogen-bonded network while facing toward the porous channel filled with another set of much-anticipated entrapped lattice water molecules. Such structural features are expected to manifest high proton conductivity, and detailed investigation indeed yields the best value for the system at 1.57 × 10-4 S/cm at 95% humidity and 85 °C. In order to evaluate the thematic notion of a one-to-one relationship between OER and improved electrical conductivity, extensive electrocatalytic water splitting (WS) investigations were carried out. The final results show highly encouraging WS ability of the Mn-MOF, showing the electrocatalytic surface area value of the active species as 0.0686 F/g with a turnover frequency value of 0.043 [(mol. O2) (mol. Mn-MOF)-1 s-1]. Another fascinating aspect of the current communication is the excellent synergy observed between the experimental WS outcomes and the corresponding theoretical data calculated using density functional theory (DFT). Consequently, a plausible mechanism of the overall OER and the role of the Mn-MOF as a water oxidation catalyst, along with the importance of water molecules, have also been derived from the theoretical calculations using DFT.

Mott–Schottky Barrier Enabling High‐Performance Hydrazine‐Assisted Hydrogen Generation at Ampere‐Level Current Densities

AbstractLocal electron density manipulation can optimize the adsorption and desorption nature of catalysts leading to enhanced catalytic activity for water oxidation. Construction a Mott–Schottky barrier allows the electron transition in catalysts because of their different Fermi levels. Herein, a Pt@NiFc‐MOF Mott–Schottky heterojunction is constructed, in which electrons are transferred from NiFc‐MOF to Pt as triggered by the formed built‐in electric field at the interface. The as‐prepared Pt@NiFc‐MOF reveals exceptional performance toward the hydrazine oxidation reaction (HzOR), hydrogen evolution reaction (HER), and overall hydrazine splitting (OHzS) at ampere‐level current densities. The advanced nature of the configured Mott–Schottky heterojunction can also be further evidenced from a concept direct liquid N2H4/H2O2 fuel cell (Pt@NiFc‐MOF//Pt Net), yielding a maximum power density of 415.2 mW cm‒2 at 80°C and can work stably for 190 h at 500 mA cm‒2 (at 25°C). One more function of Pt@NiFc‐MOF is clarified as well, that is it can purify hydrazine‐rich wastewater from 718 to 6 ppb (less than the U.S. Environmental Protection Agency of 10 ppb) in 120 min at 500 mA cm‒2. This work represents a breakthrough in interface engineering of metal–organic frameworks (MOFs) toward industry‐level hydrogen generation and its beyond.

One-Step Synthesis of Ultrathin High-Entropy Layered Double Hydroxides for Ampere-Level Water Oxidation

The development of high-entropy anodes, known for their excellent catalytic activity for water oxidation, can depress the energy consumption of hydrogen production by water electrolysis. However, the complex preparation methods and poor stability hindered their practical application. In this work, a one-step co-precipitation method has been modified to rapidly synthesize ultrathin high-entropy layered double hydroxide containing Ni, Co, Fe, Cr, Zn. Through the rational selection of metal elements, the stability of the optimized anode under Ampere-level current density has been significantly improved. Compared to NiFe-LDH, the active site leaching of high-entropy LDH is reduced by 42.7%, and as a result, it achieves a performance decay that is approximately eight times lower than that of NiFe-LDH. Experiment results show that the active sites in the high-entropy LDH can maintain a relatively low oxidation state both before and after activation, thus preventing material deactivation caused by excessive oxidation.

Electronic Structure Variations of Cu‐Based Water Oxidation Catalysts Bearing Redox‐Active Ligands

AbstractThe physical and electrochemical properties of a series of Cu complexes bearing redox‐active ligands were investigated. The effect of the geometry and electronic structure on the redox potentials of the CuI/II and ligand‐based oxidation was investigated, in both MeCN and aqueous solutions. Here we found that the formation of a delocalized ligand radical is essential to obtain catalytic activity for water oxidation. Furthermore, we found that ligand‐based oxidation can be controlled by electronic effects of substituent methoxy groups on various positions on the ligand. This allows us to propose design principles for ligands employed in water oxidation catalysts that operate via a SET‐HA mechanism: 1) The redox‐active ligand should contain a negative charge of at least −1 or have the ability to oxidize the ligand via PCET whereby a proton is removed from the ligand. 2) The oxidation potential of the redox‐active ligands can be controlled by introduction of substituents. To decrease this potential, the electron density should be directed at the position of the ligand where oxidation occurs. 3) Stabilization of the oxidized ligand by electronic or delocalization effects decreases the oxidation potential.

Construction of p-n heterostructured BiOI/TiO2 nanosheets arrays for improved photoelectrochemical water splitting performance

The construction of p-n heterojunction is one of the effective strategies to improve the spatial charge separation due to built-in electric field. In this study, the p-type BiOI ultrathin 2D nanoplates decorated n-type TiO2 nanosheets arrays (TNS) heterojunction photoanode was successfully fabricated through hydrothermal methods. The photocurrent density achieved for optimized BiOI/TNS photoanode was 0.54 mA cm−2 at 1.23 V vs. RHE, which is 15 times higher than that of unmodified TNS photoelectrode (0.036 mA cm−2) under simulated sunlight irradiation without any cocatalyst. In addition, the onset potential of BiOI/TNS photoanodes has a certain negative shift from 0.5 to 0.3 V, which can demonstrate BiOI/TNS photoanodes possesses better catalytic activity and kinetics for water oxidation. The excellent photoelectrochemical activity of BiOI/TNS could be attributed to the type-II energy structure of BiOI/TiO2 photoanode, the built-in electric field of p-n heterojunction, and TiO2 nanosheets arrays with high exposed {0 0 1} facets.

Effect of surface-deposited Ti3C2Tx MXene on the photoelectrochemical water-oxidation performance of iron-doped titania nanorod array

As a promising photoanode material, TiO2 confronts two challenges, weak visible light absorption and low catalytic activity for water oxidation, which limit its photoelectrochemical performance toward water oxidation. Doping and co-catalyst deposition provide effective ways to extending the light-absorption spectral range and accelerating the water-oxidation kinetics, respectively. Herein, an efficient TiO2-based photoelectrode for water oxidation is prepared by Fe doping and electrophoretic Ti3C2Tx deposition. The Fe doping effectively extends the light absorption of TiO2 toward visible region. Owing to the excellent water oxidation activity of Ti3C2Tx, its deposition greatly accelerates the water-oxidation kinetics, which in turn enhances the photocarrier separation and injection efficiencies. The well-designed Fe-TiO2/Ti3C2Tx exhibits a photoelectrochemical current density of 1.23 mA cm−2 at 1.23 V vs. RHE, which is much higher than those of Fe-TiO2. The maximum IPCE value is enhanced from 64.7% of Fe-TiO2 to 92.8% of Fe-TiO2/Ti3C2Tx at 380 nm. Our findings provide an effective way to fabricate efficient photoanode for water oxidation and are helpful to understanding the photoelectrochemical performance of hybrid nanostructures.

Autologous Mn oxides as electrocatalysts to identify the origin of the water oxidation activity

Different manganese oxides have been widely reported as catalysts for water oxidation. However, the best structure of Mn oxides for electrocatalytic water oxidation is still under debate. The convergence of different physical properties in those Mn oxides makes the assignment of the origin of the activity becoming confused. To eliminate the diverse influence factors among the Mn oxides for water oxidation, three sister Mn oxides (Mn2O3, Mn3O4, and MnO) are synthesized from the same parent precursor. The autologous Mn oxides have similarities in general physical properties, and the difference in phase structure becomes the only significant factor of their diversity. Through electrochemical analysis, Mn2O3 has the best catalytic performance among the Mn oxides. Based on this ideal platform, it is straightforwardly observed that the easy generation of MnIII in Mn2O3 is the origin of the higher catalytic activity for water oxidation.

Ce-induced regulation of electron density enhanced the catalytic activity of Co-Mn oxides for water oxidation.

The incorporation of Ce into Co-Mn oxides induced the charge redistribution of Co and Mn via electronic coupling, which facilitated the Co3+/Co4+ transition. Thus, the overpotential at 10 mA cm-2 was reduced significantly by 73 mV for the oxygen evolution reaction after Ce doping.

Multifunctional approach to improve water oxidation performance with MOF-based photoelectrodes

Metal-Organic Frameworks (MOFs) are a group of compounds with high porosity and diverse capabilities in photoelectrochemistry. The use of these compounds as photocatalysts and photoelectrodes is still a strong challenge due to bulk and surface recombination issues. To solve this problem, we applied a dual strategy to simultaneously enhance charge separation and catalytic activity in MIL-125-NH2 and UIO-66-NH2 MOF photocatalysts. Mesoporous TiO2 was used as electron-selective contact on the MOF surface (MOF/TiO2) to minimize bulk recombination. On the other hand, to increase the MOF catalytic activity for water oxidation, a well-matched Co3(PO4)2 (CoPi) co-catalyst (CoPi/MOF/TiO2) was used. The obtained results showed that CoPi and TiO2 were introduced in the MOF structure. The (CoPi/MOF/TiO2) photoelectrodes showed a photocurrent density 26 times higher compared to the reference MOF at 1.23 V vs. RHE for PEC water oxidation of artificial seawater, validating the developed strategy for further photocatalytic and photoelectrochemical applications.

Tuning the Catalytic Water Oxidation Activity through Structural Modifications of High-Nuclearity Mn-oxo Clusters [Mn18M] (M = Sr2+, Mn2+)

The water oxidation half-reaction is considered the bottleneck in the development of technological advances to replace fossil fuels with sustainable and economically affordable energy sources. In natural photosynthesis, water oxidation occurs in the oxygen evolving complex (OEC), a manganese-oxo cluster {Mn4CaO5} with a cubane-like topology that is embedded within a redox-active protein environment located in photosystem II (PS II). Therefore, the preparation of biomimetic manganese-based compounds is appealing for the development of efficient and inexpensive water oxidation catalysts. Here, we present the water oxidation catalytic activity of a high-nuclearity mixed-metal manganese-strontium cluster, [MnIII12MnII6Sr(μ4-O8)(μ3-Cl)8(HLMe)12(MeCN)6]Cl2∙15MeOH (Mn18Sr) (HLMe = 2,6-bis(hydroxymethyl)-p-cresol), in neutral media. This biomimetic mixed-valence cluster features different cubane-like motifs and it is stabilized by redox-active, quinone-like organic ligands. The complex displays a low onset overpotential of 192 mV and overpotentials of 284 and 550 mV at current densities of 1 mA cm−2 and 10 mA cm−2, respectively. Direct O2 evolution measurements under visible light-driven water oxidation conditions demonstrate the catalytic capabilities of this cluster, which exhibits a turnover frequency of 0.48 s−1 and a turnover number of 21.6. This result allows for a direct comparison to be made with the structurally analogous Mn-oxo cluster [MnIII12MnII7(µ4-O)8(µ3-OCH3)2(µ3-Br)6(HLMe)12(MeOH)5(MeCN)]Br2·9MeCN·MeOH (Mn19), the water oxidation catalytic activity of which was recently reported by us. This work highlights the potential of this series of compounds towards the water oxidation reaction and their amenability to induce structural changes that modify their reactivity.

Hydrophobic Interactions of Ru-bda-Type Catalysts for Promoting Water Oxidation Activity

The catalytic activity of the bimolecular reaction was affected by many parameters. Although many efforts have been dedicated to investigate the influence of secondary interactions in pre-organizing catalysts, the hydrophobic effect on Ru-bda-type water oxidation catalysts remains unclear as a result of the lack of an ideal catalytic model. In this work, four catalysts 1–4 with variable hydrophobicity have been synthesized, and cerium(IV)-driven water oxidation results showed that the hydrophobic complexes 3 and 4 outperformed the hydrophilic complex 2. Steric mapping, nuclear magnetic resonance, and differential pulse voltammogram studies indicated that the increase in activity has no correlation with electronic and steric effects but has correlation with hydrophobicity. Molecular dynamics have shown that the modifications of the hydrophobicity on the axial pyridine ligands of the Ru-bda type of catalysts can improve the water oxidation catalytic activity by stabilizing the pre-reactive catalyst dimer.

Complex Impedance Analysis on Charge Accumulation Step of Mn3O4 Nanoparticles during Water Oxidation.

The development of efficient water-oxidizing electrocatalysts is a key issue for achieving high performance in the overall water electrolysis technique. However, the complexity of multiple electron transfer processes and large activation energies have been regarded as major bottlenecks for efficient water electrolysis. Thus, complete electrochemical processes, including electron transport, charge accumulation, and chemical bond formation/dissociation, need to be analyzed for establishing a design rule for film-type electrocatalysts. In light of this, complex capacitance analysis is an effective tool for investigating the charge accumulation and dissipation processes of film-type electrocatalysts. Here, we conduct complex capacitance analysis for the Mn3O4 nanocatalyst, which exhibits superb catalytic activity for water oxidation under neutral conditions. Charge was accumulated on the catalyst surface by the change in Mn valence between Mn(II) and Mn(IV) prior to the rate-determining O–O bond forming step. Furthermore, we newly propose the dissipation ratio (D) for understanding the energy balance between charge accumulation and charge consumption for chemical O–O bond formation. From this analysis, we reveal the potential- and thickness-dependent contribution of the charge accumulation process on the overall catalytic efficiency. We think that an understanding of complex capacitance analysis could be an effective methodology for investigating the charge accumulation process on the surface of general film-type electrocatalysts.

Interfacing or Doping? Role of Ce in Highly Promoted Water Oxidation of NiFe‐Layered Double Hydroxide

AbstractSurface engineering of transition metal layered double hydroxides (LDHs) provides an efficient way of enhancing their catalytic activity toward the oxygen evolution reaction (OER). However, the underlying mechanism of atomistic doping or heterogeneous interface with foreign atom is still ambiguous. Herein, a case study of NiFe‐LDHs that are homogeneously doped with Ce (CeNiFe‐LDH) and interfaced with Ce(OH)3 (Ce@NiFe‐LDH), which elucidates their electronic modulation, in situ evolution of active site, and catalytic reaction mechanisms by using X‐ray photoelectronic spectroscopy, operando electrochemical Raman spectroscopy, and first‐principles density functional theory (DFT) calculations, is reported. The results indicate that Ce and Fe atoms serve as the electron acceptors and facilitate the coupled oxidation of Ni3+/4+ in NiFe‐LDH, and the activated oxyhydroxide phase of the catalysts exhibits superior catalytic activity for water oxidation. Especially, Ce@NiFe‐LDH shows a stronger electron transfer between the loaded Ce(OH)3 and the matrix, which leads to a better catalytic activity than CeNiFe‐LDH. DFT calculations provide a clear picture with atomistic resolution for charge redistribution in the NiFe‐LDH surface induced by Ce, which eventually leads to the optimal free energy landscape for the enhanced OER catalytic activity.

Metalloid Te‐Doped Fe‐Based Catalysts Applied for Electrochemical Water Oxidation

AbstractMetal telluride nanocatalysts have been widely used in the catalytic reactions. However, there are few examples of electrocatalytic water oxidation with metal telluride as catalysts, especially Fe‐based telluride, to the best of our knowledge, has not yet been reported. In this work, the Te‐doped Fe‐based catalysts (FeTex) with crystalline and amorphous nanosheet structures have been successfully synthesized by chemical vapor deposition (CVD) as well as electrodeposition (ED) on the iron foam (IF), where the latter exhibited more remarkable electrocatalytic performance towards the oxygen evolution reaction (OER) in the alkaline electrolyte, requiring the overpotential (η) of only 264.4 mV to reach a current density of 10 mA cm−2 with a Tafel slope of 54.2 mV dec−1. The electrochemical study confirmed that the residual Te in ED‐FeTex does play a role in promoting the catalytic activity for the electrocatalytic water oxidation.

Chiral CuO@Ni with continuous macroporous framework and its high catalytic activity for electrochemical water oxidation

Electrochemical water splitting is considered as a promising approach to storing renewable electricity in the form of hydrogen fuel. In this work, we report the design and electrocatalytic properties of chiral CuO@Ni with three dimensional (3D) continuous macroporous framework. With the chiral CuO@Ni as anode, the OER overpotential required to achieve the current density of 10 mA/cm2 was as low as 110 mV in 0.1 M KOH electrolyte, and the hydrogen production rate of water splitting reaction could reach 1070 nL/s. Moreover, the OER overpotential could be regulated easily by controlling the deposition time of chiral CuO layer on Ni. The high catalytic activity of chiral CuO@Ni for water splitting is closely associated with the Chiral-induced spin selectivity (CISS) effect, the large reactive area provided by its 3D macroporous structure, and the effective cooperation between chiral CuO and Ni foam that facilitated the transportation of spin aligned electrons from chiral CuO layer to Ni. The results shown in this work indicate a simple and promising strategy to improve the electrocatalytic activity of other chiral earth-abundant catalysts for water splitting.

Interstitial polydopamine layer stabilizing catalysts/electrode interface for sustainable water oxidation

Cobalt-based oxygen-evolving catalyst (Co-OEC) exhibits high catalytic activity for water oxidation in the neutral pH regime. However, as the externally applied potential toward oxidation is lowered, the catalyst is slowly dissolved and eventually decomposed from the electrode because of their poor interfacial compatibility. Here, we introduce an interstitial polydopamine (PDA) layer to strengthen the Co-OEC/electrode interface for sustainable catalytic activity. The PDA layer efficiently stabilizes the catalyst/electrode interface as a redox-active adhesive interlayer. Under high applied potential conditions, the oxygen evolving catalytic activity is reduced by 95 % in the absence of the PDA layer. On the other hand, the Co-OEC/PDA/ITO electrode keeps the catalytic activity above 70 % under the same condition because the redox mediation of PDA suppresses the dissolution of Co2+ ions. The PDA layer also promotes water oxidation catalysis presumably through proton-coupled electron transfer. It is expected that the redox-active PDA can be applied to various catalysts as a means to improve their microenvironments for enhanced catalytic activity and sustainability.

NaBH4-reduction induced tunable oxygen vacancies in LaNiO2.7 to enhance the oxygen evolution reaction.

Tunable oxygen vacancies of LaNiO3 (LNO-Vo) are realized by theoretical prediction and the NaBH4-reduction approach. The LNO2.7 catalyst exhibits superior catalytic activity and long-term stability for water oxidation. Direct evidence of the active site center and the intermediates is observed from in situ Raman spectra and DFT calculations.

Modulating the water oxidation catalytic activity of iridium complexes by functionalizing the Cp*-ancillary ligand: hints on the nature of the active species

A comparative study on the behavior of a series of iridium dimeric WOCs with modified Cp* ligands reveals the key role played by the variable substituent.