Water Oxidation Catalysts Research Articles

Kinetic Pathway Control in the Synthesis of Well‐Defined Ruthenium Coordination Oligomers

Ruthenium complexes with 2,2′‐bipyridine‐6,6′‐dicarboxylate (bda) ligands have emerged as highly potent catalysts for water oxidation. In this context, the accumulation of active Ru centers in macrocyclic arrays or coordination oligomers and polymers has proven to be very beneficial for an enhanced stability under operating conditions and to facilitate surface adhesion in heterogeneous systems. For a better insight into structure–activity relationships though, well–defined systems with a precise control over stoichiometry and constitution are highly desired. Herein, the synthesis and characterization of a series of structurally precise and monodisperse linear coordination oligomers [(Ru(bda))nLn−1pic2] (n = 4 or 5, L = 4,4′‐bipyridine or 1,4‐bis‐(pyridine‐4‐yl)benzene derivatives, pic = 4‐picoline), in excellent purity and yields are reported. Based on detailed mechanistic investigations, a complex network of interconnected and competing reactions is proposed that fully explains both the high overall turnover and the kinetic pathway selection between alternative endcapping and dissociation–elongation sequences.

Breaking linear scaling relationships in oxygen evolution via dynamic structural regulation of active sites

The universal linear scaling relationships between the adsorption energies of reactive intermediates limit the performance of catalysts in multi-step catalytic reactions. Here, we show how these scaling relationships can be circumvented in electrochemical oxygen evolution reaction by dynamic structural regulation of active sites. We construct a model Ni-Fe2 molecular catalyst via in situ electrochemical activation, which is able to deliver a notable intrinsic oxygen evolution reaction activity. Theoretical calculations and electrokinetic studies reveal that the dynamic evolution of Ni-adsorbate coordination driven by intramolecular proton transfer can effectively alter the electronic structure of the adjacent Fe active centre during the catalytic cycle. This dynamic dual-site cooperation simultaneously lowers the free energy change associated with O–H bond cleavage and O–O bond formation, thereby disrupting the inherent scaling relationship in oxygen evolution reaction. The present study not only advances the development of molecular water oxidation catalysts, but also provides an unconventional paradigm for breaking the linear scaling relationships in multi-intermediates involved catalysis.

O2 evolution reaction by tri barium-coordinated polyoxometalate as a potential water oxidation catalyst

Recently, earth-abundant compounds can be coordinated to the vacant site(s) of lacunary polyoxometalates as water oxidation catalysts (WOCs). Herein, a new catalyst was synthesized based on potassium salt of tri barium-coordinated polyoxometalate (K9[PW9Ba3O34] (denoted as Ba-POM) by reaction of [PW12O40]3- and BaCl2 at pH = 7.5. The prepared PW9Ba3O37 indicated excellent chemical water oxidation activity in the presence of ceric (IV) ammonium nitrate (CAN) as a sacrificial electron acceptor. The synthesized catalyst was characterized by Ultraviolet-visible spectroscopy (UV-vis), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) techniques. In following, the effect of Ba substitution in the structure of POM unit, the role of oxidation activity in water splitting, and also the effect of temperature and acid conditions were discussed.

Nearly Barrierless Four-Hole Water Oxidation Catalysis on Semiconductor Photoanodes with High Density of Accumulated Surface Holes.

The sluggish water oxidation reaction (WOR) is considered the kinetic bottleneck of artificial photosynthesis due to the complicated four-electron and four-proton transfer process. Herein, we find that the WOR can be kinetically nearly barrierless on four representative photoanodes (i.e., α-Fe2O3, TiO2, WO3, and BiVO4) under concentrated light irradiation, wherein the rate-limiting O-O bond formation step is driven by accumulated surface photogenerated holes that exhibit a superior fourth-order kinetics. The activation energy is about 0.03 eV for the fourth-order kinetic pathway, which is quantitatively estimated by combining the Population model and Butler-Volmer model with the Eyring-like equation and is further confirmed by density functional theory calculations. The WOR rate under this condition shows more than 1 order of magnitude enhancement compared with that of first-, second-, or third-order kinetics. Focusing on α-Fe2O3, the accumulated high-density surface holes form adjacent FeV═O intermediates that effectively activate surface-adsorbed H2O molecules via the hydrogen-bonding effect, as revealed by operando Raman measurements and ab initio molecular dynamics simulations. This work discloses a systematic understanding of the internal relations between activation energy and reaction orders of surface holes for future WOR study.

On the Mechanism of Light-Driven O2 Evolution by the Mn(III) Complex [Mn(salpd)(OH2)]+ and Quinone.

In this study, we apply TD-DFT and DFT calculations to explore the mechanistic details of O2 evolution in an artificial system that closely resembles Photosystem II (PSII). The reaction involves mononuclear Mn(III) complex [Mn(salpd)(OH2)]+ and p-benzoquinone under light-driven conditions. Our calculations reveal that the Schiff-base ligand salpd plays a crucial role in several key steps of the reaction, including the light-mediated oxidation of [Mn(salpd)(OH2)]+ to [Mn(salpd)(OH)]+ by p-benzoquinone, the subsequent oxidation of [Mn(salpd)(OH)]+ to the key Mn(V) intermediate [Mn(salpd)(O)]+, and the critical O-O bond formation step. This role is primarily due to the high propensity of the salpd ligand to undergo oxidation by one unit. This characteristic allows the salpd ligand to reduce Mn(IV) in the intermediate [Mn(salpd)(OH)]+ to Mn(III), triggering a Jahn-Teller effect that increases the ionic character of the hydroxide ligand. This transformation makes the resulting complex a strong nucleophile, facilitating O-O bond formation through a reaction between [Mn(salpd)(OH)]+ and [Mn(salpd)(O)]+ with a moderate overall activation free energy of 18.6 kcal/mol. The mechanistic insights presented in this study may provide a useful foundation for developing novel systems that catalyze water oxidation under light-driven conditions, mimicking Photosystem II, and could potentially contribute to advancements in sustainable energy generation.

Chemical design of metal complexes for electrochemical water oxidation under acidic conditions.

The development of viable, stable, and highly efficient molecular water oxidation catalysts under acidic aqueous conditions (pH < 7) is challenging with Earth-abundant metals in the field of renewable energy due to their low stability and catalytic activity. The utilization of these catalysts is generally considered more cost-effective and sustainable relative to conventional catalysts relying on precious metals such as ruthenium and iridium, which exhibit outstanding activities. Herein, we discussed the effectiveness of transition metal complexes for electrocatalytic water oxidation under acidic conditions. We focus on important aspects of 3d first-row metal complexes as they relate to the design of water oxidation systems and emphasize the importance of the fundamental coordination chemistry perspective in this field, which can be applied to the understanding of catalytic activity and fundamental structure-function relationships. Finally, we identified the scientific challenges that should be overcome for the future development and application of water oxidation electrochemical catalysts.

Alkaline modified bismuth vanadate coupled with reduced graphene oxide as efficient photoelectrochemical catalysts for water oxidation

Alkaline modified bismuth vanadate coupled with reduced graphene oxide as efficient photoelectrochemical catalysts for water oxidation

Reconstructed Hydroxyl Coordination Field Enhances Mass Transfer for Efficient Electrocatalytic Water Oxidation

AbstractMass transfer factor plays an indispensable role in high current density to accelerate the oxygen evolution reaction (OER) process, yet research on modulating reactant mass transport remains limited. Herein, by leveraging the dual acid‐base properties of aluminum sites, both the activation of the electronic activity of the layer for layered double hydroxides (LDH) and construction of the interlayer hydroxide coordination field (IHCF) have been achieved through in situ electrochemical reconstruction. It not only facilitates charge transfer and the surface catalytic transformation of reaction intermediates but, most notably, the presence of the IHCF significantly enhances the mass transport of reactants. As a result, the overpotential of LDHs with IHCF is only 164 mV, significantly better than the reported Ni‐based catalysts. Deuterium kinetic isotope effect experiments and pH‐dependence measurements demonstrate that the IHCF effectively enhances substrate mass transport capability and structural stability, thereby accelerating the proton‐coupled electron transfer process. To further validate the high mass transport characteristics, stability tests of the alkaline flow electrolyzer show that catalysts maintain over 1000 h of stability at a high current density. This work suggests that the IHCF effect can be utilized for further design and synthesis of efficient water oxidation catalysts for practical application.

Bimetallic Cooperativity of a Ferrocene-Based Iridium NHC Complex in Water Oxidation Catalysis: A New Frontier for Efficient Oxygen Evolution.

Bimetallic catalysts have gained attention as promising contenders, owing to the synergistic interaction between two distinct metal centers. In this study, we present two N-heterocyclic carbene iridium(III) pentamethylcyclopentadienyl complexes [Cp*Ir(fcpyNHC)Cl]PF6 (1) and [Cp*Ir(pyNHC)Cl]PF6 (2) where 1 includes a ferrocene moiety making it a bimetallic complex. Using ceric ammonium nitrate as a sacrificial oxidant, both complexes were tested for water oxidation. Complex 2 achieved a maximum turnover number (TONmax) of 3240 and a turnover frequency (TOFmax) of 231 min-1. In comparison, complex 1 demonstrated nearly double the activity with a TONmax of 6047 and TOFmax of 431 min-1 compared to 2, which was attributed to the cooperative effect of the catalyst in water oxidation reaction. This bimetallic Fe Ir catalyst (1) exhibited outstanding catalytic efficiency for oxygen evolution from water at ambient conditions. We identified a proposed FeIII IrIV intermediate experimentally via UV-Vis spectroscopy and XPS study. Theoretically, this intermediate was more stable by 7.84 kcal/mol than the traditional FeII IrV electromer intermediate. This delineates the pronounced bimetallic cooperative participation of both Fe and Ir metal centres for better activity.

Formation and Reactivity of a MnIV(O)(μ-O)CeIV Species: A Closest Mimic of Photosystem II.

Understanding the basic structure of the oxygen-evolving complex (OEC) in photosystem II (PS-II) and the water oxidation mechanism can aid in the discovery of more efficient and sustainable catalysts for water oxidation. In this context, we present evidence of the formation of a [(TPA)MnIV(O)(μ-O)CeIV(NO3)3]+ (2) complex (TPA = tris(pyridyl-2-methyl)amine) by adding aqueous ceric ammonium nitrate to an acetonitrile solution of the [(TPA)MnII]2+ (1) complex. This unique intermediate (2) was analyzed by using various spectroscopic techniques and electrospray ionization mass spectrometry. Remarkably, 2 closely mimics the structure of MnV(O)(μ-O)CaII(OH2) proposed in the OEC of PS-II. Notably, 2 reacts effectively with ferrocene derivatives, indicating that redox-active CeIV binding enhances the electron transfer efficiency. Additionally, 2 demonstrated the ability to perform oxygen atom transfer and hydrogen atom abstraction reactions. The discovery of this reactive [(TPA)MnIV(O)(μ-O)CeIV(NO3)3]+ species provides exciting opportunities for investigating the structure of the MnV(O)(μ-O)CaII(OH2) unit in the OEC.

Synergistic Integration of a Ru(bda)‐Based Catalyst in a Covalent Organic Framework for Enhanced Photocatalytic Water Oxidation

AbstractTo address the urgent need for sustainable energy processes, there is a growing demand for multifunctional materials that mimic natural photosynthetic enzyme functions, specifically light‐harvesting, efficient photoinduced charge separation, and integration of molecularly defined catalysts, synergistically interacting within these structures. Herein, the successful synthesis of an innovative Covalent Organic Framework (COF‐TFPT‐IsoQ) constructed from optically active triazine (TFPT) and isoquinoline units (IsoQ) as building blocks is reported. Post‐synthetic incorporation of a Ru(bda)‐based water oxidation catalyst (WOC) is achieved through the IsoQ moieties acting as coordinating sites. Leveraging the synthetic flexibility of the designed COF architecture featuring binding sites on its pore walls, various Ru@COF‐TFPT‐IsoQ systems at different Ru:COF ratios are synthesized and tested in the photoinduced (λ &gt; 400 nm) oxygen evolution reaction (OER) under sacrificial conditions. All synthesized Ru@COF‐TFPT‐IsoQ systems demonstrate efficiency in the photocatalytic OER, with the highest turnover number (TON) of 9.1 observed for the system where the Ru‐based WOC is incorporated every fourth COF‐TFPT‐IsoQ unit cell. This work provides valuable insights into the structural integration and catalytic behavior of Ru‐based complexes within COF architectures, highlighting the potential of Ru@COF‐TFPT‐IsoQ as a robust, efficient, and synthetically flexible multifunctional material for light‐induced water oxidation catalysis.

Exploring Mechanistic Details and Catalyst Resilience in Electrocatalytic Water Oxidation With a Cu(II) Complex Bearing a Redox‐Active Ligand

AbstractHerein, we report that a copper complex [Cu(dpaq)](ClO4) (1) (H‐dpaq = 2‐[bis(pyridin‐2‐ylmethyl)]amino‐N‐quinolin‐8‐yl‐acetamide) acts as a molecular water oxidation catalyst (WOC) under strong basic condition. Complex 1 oxidizes water to dioxygen in 0.1 M phosphate buffer solution at pH 12.0, exhibiting a turnover frequency of 3.1 × 102 s−1 at a low overpotential (η) of ∼550 mV versus NHE at 1 mA cm−2. A turnover number of 4.0 can be obtained during controlled potential electrolysis (CPE) using 0.25 mM complex 1 at a potential of 1.5 V at pH 12.0 for 3 h. Postelectrolysis analysis, rinse tests, and chelating assays collectively support the homogeneous nature of the electrocatalyst. Mechanistic investigations and quantum chemical calculations reveal a pathway wherein two successive ligand‐centered oxidations transform the catalyst into a Cu(II)(dpaq•)O•. intermediate. Absence of any metal centered oxidation renders the oxidized intermediate less electrophilic, resulting in the survival of the methylene groups present on the ligand backbone against oxidation. The formation of the O─O bond is proposed to proceed via two consecutive single electron transfers (SET) from incoming hydroxide ions to the formal CuIV–oxo species.

Lattice modulation strategy toward efficient and durable RuO2‐based catalysts for acidic water oxidation

AbstractRutile RuO2 is recognized for its outstanding acidic oxygen evolution reaction (OER) activity and notable cost advantage compared to iridium oxide for proton exchange membrane water electrolyzers (PEMWEs). However, the unsatisfactory stability of RuO2 hinders its practical application. Here, we report a lattice modulation strategy to enhance both the OER activity and stability of RuO2. Interestingly, the newly synthesized Mo0.15Nb0.05‐RuO2, with Mo doped first and then Nb, presents the greatest lattice spacing and possesses an overpotential of merely 205 mV at 10 mA cm−2, which significantly outperforms Nb0.05Mo0.15‐RuO2 (239 mV), where Nb was doped first followed by Mo, as well as the initial RuO2 (323 mV). Remarkably, Mo0.15Nb0.05‐RuO2 requires only 1.76 V to achieve 1 A cm−2 and exhibits exceptional stability in PEMWE testing, with a voltage rise of only 58 mV at 200 mA cm−2 for more than 80 h.

The Catalytic Mechanism of a Highly Active Cobalt Chlorin Complex for Photocatalytic Water Oxidation.

Highly active catalysts for electrocatalytic and photocatalytic water oxidation are strongly demanded to realize artificial photosynthesis. A cobalt complex with a chlorin derivative ligand (CoII(Ch)) exhibited high activity for electrocatalytic water oxidation with an overpotential of 0.45 V at pH 9.0. Spectroelectrochemistry (UV-vis) unveiled the formation of two intermediates by successive one-electron oxidations. Also, the Pourbaix diagram depicted by the pH dependence of redox potentials indicated that the water oxidation proceeded after the oxidation of both the central cobalt ion and chlorin ligand with proton-coupled electron transfer (PCET). Then, the photocatalytic activity of CoII(Ch) was examined for water oxidation using [RuII(bpy)3]2+ (bpy: 2,2'-bipyridine) and S2O82- as a photosensitizer and a sacrificial electron acceptor, respectively. The turnover number, turnover frequency, and oxygen yield reached as high as 980, 5.2 s-1, and 98%, respectively, under optimized conditions. The O2-evolution rates increased in proportion to the square of the catalyst concentration in the reaction solution, suggesting that the formation of the O-O bond regarded as the rate-determining step of water oxidation proceeded by the interaction of two metal centers (I2M) mechanism in which two molecules of high-valent metal oxo or oxyl radical species react with each other.

Polymer Networks Assembled by Ruthenium Catalysts for Enhanced Water Splitting Performance in Calixarene Dye-Sensitized Photoelectrochemical Cells.

Metal-free photosensitizers for the construction of low-cost and eco-friendly dye-sensitized photoelectrochemical cells (DSPECs) have recently been greatly improved, but the optimization of water oxidation catalysts (WOCs) used in DSPECs based on metal-free dyes has received little attention. Herein, a series of polymer networks (RuTPA, RuCz, RuPr and RuTz) assembled by ruthenium WOCs (RuCHO) with various organic donors are constructed and combined with calixarene dyes to prepare DSPEC devices. The FTO|TiO2|C4BTP+RuTPA photoanode shows the best performance with 85 % Faraday efficiency for oxygen production and 477 μA cm-2 photocurrent density after 200 s chopping irradiation at 0 V vs. Ag/AgCl, one of the highest records among other reported dye-sensitized photoanodes. Compared to monomeric RuCHO, Ru-based polymers with lower Ru content have higher activity and stability due to their rapid electron transfer and anti-aggregation ability. Meanwhile, RuTPA loaded electrodes show better performance due to the lower overpotential of the water oxidation reaction caused by the higher electron donating ability of its donor. This pioneering work incorporates Ru polymer networks as WOCs into the calixarene-sensitized DSPEC system, which has significant potential as a highly efficient and stable photoelectrochemical water splitting device.

Efficient electrochemical water oxidation catalyzed by a novel nickel complex: Critical effect of the flexibility of pyridine-amine based pentadentate ligand on catalytic property

Efficient electrochemical water oxidation can be realized by reasonable modulation of the ligand structure of metal complex-based molecular water oxidation catalysts (WOCs). Herein, the synthesis and prowess in electrocatalytic water oxidation of a mononuclear water-soluble nickel complex, [Ni(tmbptu)(OH2)](ClO4)2 (1, tmbptu = 2,6,10-trimethyl-1,11-bis(2-pyridyl)-2,6,10-triazaundecanone), is reported for the first time. Complex 1 is found to be an efficient homogeneous WOCs under near neutral condition with long-term catalytic stability by a series of characterizations, including dynamic light scattering (DLS) measurement, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) analysis, chelation experiment, and Fe3+ test. Electrochemical tests reveal that water oxidation is accomplished via the generation of NiIV species generated by two successive e−/H+ proton coupled electron transfer (PCET) processes. Astonishingly, compared to the homologous complex [Ni(tmbptn)(OH2)](ClO4)2 (2, tmbptn = 2,5,8-trimethyl-1,9-bis(2-pyridyl)-2,5,8-triazanonane), which is a well-defined molecular WOC with high catalytic onset overpotential, 1 displays lower onset overpotential and much higher catalytic activity. This work suggesting that though the tertiary amine coordination environment have gain effect on the redox potential of metal center due to its poor sigma-donor effect, resulting in high onset overpotential of metal complex for water oxidation, this negative impact of the pyridine-amine ligand on the catalytic properties of complex can be weaken by adjusting the flexibility of backbone of those ligands.

Deciphering Water Oxidation Catalysts: The Dominant Role of Surface Chemistry over Reconstruction Degree in Activity Promotion

HighlightsDemonstrate that the key factor to determine the activity of reconstructed surfaces is the surface chemistry, instead of reconstruction degree using the popular perovskite LaNi1-xFexO3 oxides as model materials.Fe content can influence both the surface reconstruction degree, the activation degree, and the activity of reconstructed surfaces.The oxygen evolution reaction activity of reconstructed catalysts is primarily governed by the chemistry of the reconstructed surface species.

Study of the Mechanism and Charge-Transfer Processes in Water Oxidation Catalysis by Nickel Hydroxide and Silk Fibroin: A Spectroelectrochemical Approach

Water electrolysis has emerged as a crucial electrochemical reaction on the generation of sustainable fuels, due to the ongoing climate crisis. To divert from expensive catalysts based on rare noble metals such as Ir and Ru, transition metal oxides seem to be promising candidates and several recent studies have deepened the investigation on the nickel oxide/hydroxide for water oxidation catalysis. It has been proposed that in the presence of elements such as iron and gold, a partial charge-transfer occurs between the nickel and the metal, facilitating the formation of superoxide species and nickel in higher oxidation states that enhance the oxygen evolution reaction (OER). 1–4 Rao et al (2022)5 developed a methodology combining UV-Vis spectroscopy and voltametric techniques to determine the number of these nickel species in higher oxidation levels during the OER for nickel oxides dopped with Zn, Fe, Co and Mn. From their results, they proposed a mechanism for the OER that involves two steps: 1) initial oxidation from NiII to NiIII and superoxide formation, which is limited by the potential and 2) coupling and desorption of the superoxide species, which is limited by rate. Next, they demonstrated that the different dopants modulated the bond strength between the nickel and the oxygen: too weak-bonding limited the ability to oxidize nickel and too strong-bonding limited the combination and desorption of the oxygen.In this work, monolayers of nickel hydroxide were electrodeposited, in the presence and the absence of silk fibroin (SF), on top of electrodes containing gold nanoparticles and used surface-enhanced Raman scattering (SERS)and UV-Vis spectroeletrochemical techniques to study the influence of the gold and SF on the catalytic performance of nickel hydroxide. Our previous results6 showed that the silk protein was able to stabilize the α-Ni(OH)2 nanoparticles and improved its electrochemical activity. Here, we followed the Rao et al’s methodology and found analogous results for the mechanisms of water oxidation. Figure 1A and B shows the number oxidized species and the calculated turnover frequency (TOF) as function of the potential for the samples with 1, 3, 6 and 9 monolayers, containing or not SF. While the number of oxidized species remains comparable across samples with the same number of monolayers, those containing fibroin generally exhibit higher TOFs. A volcano-like graph (Figure 1C) was obtained when the TOFs at an overpotential of 0.3 V is plotted against the NiII-NiIII redox potential, indicating a transition from potential-limited to rate-limited regions as monolayer thickness increases. We propose that this behavior is caused by the charge-transfer effect between nickel and gold, which is strongest for one monolayer and decreases as the number of nickel sites on the bulk moves away the gold surface. Notably, as monolayer thickness increases, samples containing SF show less susceptibility to decrease in TOFs, implying an additional charge-transfer effect between the protein and nickel, which contributes for the balance of the nickel bond strength with oxygen and facilitates its coupling and desorption.In summary, our study advances understanding of OER mechanisms and charge-transfer processes involving nickel hydroxide electrocatalysis, suggesting that proteins like SF can actively contribute to catalytic processes. However, further investigations are needed in order to elucidate the precise role of the protein and how to use them to optimize catalytic performance. REFERENCES 1. Diaz-Morales, O., Ferrus-Suspedra, D. & M. Koper, M. T. Chem. Sci. 7, 2639–2645 (2016).2. Yeo, B. S. & Bell, A. T. J. Phys. Chem. C 116, 8394–8400 (2012).3. Li, C.-F. et al. Angew. Chem. Int. Ed. 61, e202116934 (2022).4. Trotochaud, L., Young, S. L., Ranney, J. K. & Boettcher, S. W. J. Am. Chem. Soc. 136, 6744–6753 (2014).5. Rao, R. R. et al. J. Am. Chem. Soc. 144, 7622–7633 (2022). 6. do Nascimento, E. R. et al. ACS Appl. Electron. Mater. 4, 1214–1224 (2022). Figure 1

Deposition and Characterization of Photocatalytically Active Nanowires Viascanning Electrochemical Probe Microscopy

Producing clean energy is one of the world's greatest challenges today. The use of solar energy to split water into hydrogen and oxygen is therefore of great interest. In addition to semiconductor materials, heterogenized molecular catalysts for the hydrogen evolution reaction (HER) and water oxidation catalysts (WOC) have attracted considerable interest. The development and design of artificial molecular devices (i.e. artificial photosynthesis systems) using visible light requires the heterogenization of catalysts (CAT) and photosensitizers (PS). However, the correlation of structural heterogeneity, leaching of active components and degradation processes during illumination, as well as the continuous monitoring of reactivity have not been fully addressed.1,2 Scanning electrochemical probe microscopy such as atomic force microscopy (AFM), scanning electrochemical microscopy (SECM), scanning electrochemical cell microscopy (SECCM), and scanning photoelectrochemical microscopy (SPEM), have been used to map light-driven water splitting and local electron transfer kinetics under in situ and operando conditions.3-5 In this contribution, we present the deposition of mixed CAT/PS nanowires using earth-abundant BPh2-bridged, organometallic cobaloxime CATs and Ru-based ([Ru(tbbpy)2(mmip)]Cl3) PS on various substrates using SECCM. Based on different studies an cabolime microarrays6, the nanowires are characterized with respect to their stabilty, elemental composition as well as their light-driven H2 evolution activity. The H2 evolution of nanowire arrays is imaged via SECM using Pd- and Pt-Black modified microelectrodes. In addition, submicron-sized electrocatalytically active cantilever-based probes, recently developed by our group, are used for improved lateral resolution. These probes can be used for colloidal force spectroscopy7,8 providing nanomechanical properties of the studied materials. A thorough characterisation of the cantilever-based sensors will be presented together with nanomechanical and activity mapping of nanowires with different CAT/PS ratios.

(Invited) Extending the Success of Halide Perovskites to Photoelectrochemical and Photocatalytic Solar Fuel Production

To address the pressing global energy demands with clean and sustainable methods, solar-powered photoelectrochemical and photocatalytic transformations of water and carbon dioxide present viable solutions. Achieving this requires the development of cost-effective photoelectrodes and photocatalysts capable of efficiently harnessing solar light and promoting charge transfer to drive water and carbon dioxide reactions. In this presentation, I will outline the advances my team has made in the field, focusing on novel halide perovskites like CsPbBr3, Cs2AgBiBr3, and Cs3Bi2Br9 and bulk heterojunctions of organic semiconductors. These materials exhibit high solar light absorption and outstanding optoelectronic properties, making them excellent candidates for photoelectrochemical and photocatalytic uses. We have developed innovative approaches to enhance their stability in aqueous environments, such as encapsulating halide perovskites and organic bulk heterojunctions within carbon layers modified with Ni nanopyramids and NiFeOOH, a water-oxidation catalyst. This approach exploits different carbon allotropes, from mesoporous carbon to graphite, glassy carbon and boron-doped diamond, in order of chemical and mechanical stability. The use of layers and sheets of these carbon allotropes has led to the creation of photoanodes with low onset potentials and high photocurrents, efficiently translating excellent photocurrents and photovoltages from solar cells to photoelectrodes. For example, organic bulk heterojunction devices result in 25 mA/cm2 photocurrents in three-electrode systems and unassisted 5% solar to hydrogen in two-electrode systems Our approaches significantly extend the lifespan of photoanodes, maintaining for example a projected operation of months with CsPbBr3. In the field of photocatalysts, we have employed mechanochemical synthesis and antisolvent crystallization to create innovative composites like CsPbBr3/Cu-RGO, Cs2AgBiBr3/Cu-RGO, Cs2AgBiBr3/bismuthene, and Cs3Bi2Br9/RGO/g-C3N4, demonstrating efficient activity in converting CO2 into CO and CH4. Through thorough material characterization, we have shed light on their structural and charge-transfer properties, laying a solid foundation for their ongoing development and practical application.Daboczi, M.; Eisner, F.; Luke, J.; Yuan, S.W.; Al Lawati, N.; Müller, J.S.; Kim, J.S. Nelson, J.; Eslava, S. under reviewZhu, Daboczi, Chen, Xuan, Liu and Eslava, Nat. Commun. 2024, 2791.Daboczi, M.; Cui, J.; Temerov, F.; Eslava, S. Adv. Mater. 2023, 2304350Baghdadi, Y.; Temerov, F.; Cui, J. Daboczi, M.; Rattner, E.; Sena, M.S.; Eslava, S. Chem. Mater. 2023, 35, 20, 8607Sena, M.S.; Cui, J.; Baghdadi, Y.; Rattner, E.; Daboczi, M.; Lopes-Moriyama, A.L.; dos Santos, A.G.; Eslava, S. ACS Appl. Energy Mater. 2023, 6, 10193.Kumar, S.; Hassan, I.; Regue, M.; Gonzalez-Carrero, S.; Rattner, E.; Isaacs, M.A.; Eslava, S. J. Mater. Chem. A 2021, 9, 12179