Water Cleavage Research Articles

Boosting electrocatalytic hydrogen generation from water splitting with heterostructured MoS2/NiFe2O4 composite in alkaline media

Design and synthesis of earth-abundant and robust bifunctional electrocatalysts have been greatly sought for commercialization of the technology for clean and renewable energy and replacement of the energy equipment based on fossil fuels. In this work, a facile hydrothermal approach is used to synthesize MoS2/NiFe2O4-based nanocomposite as a novel electrocatalyst for alkaline water splitting. Surface analysis was conducted using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Benefiting from the synergy of lamellar MoS2 and crystalline NiFe2O4, the obtained MoS2/NiFe2O4 composite shows excellent hydrogen evolution reaction (η10 = 190 mV, η50 = 279 mV) and oxygen evolution reaction (OER) (η50 = 350 mV, η100 = 360 mV) activity with high TOF (0.01 s−1@190 mV for HER and 0.24 s−1 @360 mV for OER) and displays good electrochemical stability. Explicitly, the electrocatalyst requires a cell voltage of 1.69 V to drive overall water splitting at a current density of 10 mA cm−2. Density functional theory (DFT) results demonstrated that the MoS2/NiFe2O4 composite electrocatalyst has smaller hydrogen adsorption free energy (|ΔGH*|) than pristine MoS2 and NiFe2O4, which demonstrates the effective adsorption and cleavage of water on the catalyst surface. This work thus presents an approach for the synthesis and rational design of metal oxide/metal sulfide hybrids as an electrocatalyst with high performance for overall water splitting.

Oxygen vacancies prompt the formation of hydrated hydroxyzinc in Zn-based catalysts to enhance acetylene hydration

Herein, the Zn-based catalysts with oxygen vacancies were obtained via the simple and effective method, and the oxygen-vacancy (Ov)-rich anatase TiO2 was as carrier, which was introduced oxygen-vacancy through heat treatment. The catalysts performance test results showed that the Zn/TiO2-300-10 with oxygen-vacancy (Ov)-rich exhibited excellent catalytic performance (acetylene conversion >89 % for 30 h) at the reaction temperature of 260 °C. Electron paramagnetic resonance spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy revealed the formation of oxygen-vacancy in treated TiO2 carriers. Subsequently, all the Zn-based catalysts were characterized by a series of characterization techniques. The results showed that the Zn/TiO2-300-10 catalyst with Ov-rich could produce more hydroxyl‑containing Zn species and improve Zn dispersion than that of the untreated Zn/c-TiO2 catalysts. Meanwhile, the DFT calculation results showed that, for the oxygen-vacancy-rich Zn-based catalysts, the OH− species from (ZnOH)+ species participated in acetylene hydration, thereby reducing the activation energy of acetylene hydration, and allowing the regeneration of (ZnOH)+ species via water cleavage. While, the reactant C2H2 was directly reacted with water dissociation with higher activation energy for the Zn/TiO2 catalyst without oxygen-vacancy. This study lays the foundation for further developing other Ov-rich carriers more suitable for Zn loading.

Engineered interface of three-dimensional coralliform NiS/FeS2 heterostructures for robust electrocatalytic water cleavage

Engineered interface of three-dimensional coralliform NiS/FeS2 heterostructures for robust electrocatalytic water cleavage

Synthesis of the 3,3'-(Ethane-1,2-diylidene)bis(indolin-2-one) Unit Promoted by Thermally-activated Electron Transfer andPhotoreduction of CO2 to CH4and CO.

A Sonogashira coupling reaction leads to the formation of a serendipitous product C with the 3,3'-(ethane-1,2-diylidene)bis(indolin-2-one) unit. To our knowledge, our study provides the first example demonstrating that electron transfer between isoindigo and triethylamine can be thermally activated and be employed in synthesis. The physical properties of C suggest that C possesses decent photo-induced electron-transfer capabilities. Under the illumination of 136 mW cm-2 intensity, C furnishes ~2.4 mmol gcat-1 (per gram of catalyst) of CH4 and ~0.5 mmol gcat-1 of CO in 20 hours in the absence of additional metal, co-catalyst, and amine sacrificial agent. The primary kinetic isotope effect suggests that the bond cleavage of water is a rate-determining step in the reduction. Moreover, the CH4 and CO production can be boosted as the illuminance increases. This study demonstrates that organic donor-acceptor conjugated molecules are potential photocatalysts for CO2 reduction.

RuS2@CN-x with exposed (200) facet as a high-performance photocatalyst for selective C–C bond cleavage of biomass coupling with H–O bond cleavage of water to co-produce chemicals and H2

RuS2@CN-x with exposed (200) facet as a high-performance photocatalyst for selective C–C bond cleavage of biomass coupling with H–O bond cleavage of water to co-produce chemicals and H2.

Hydrolytic dehydrogenation of NH3BH3 over Cu/CoOx(OH)y nanocomposite for H2 evolution

Although a variety of noble-metal-based nanocatalysts, such as Pd, Pt, Au, Rh, and Ru, have been developed for the efficient H2 evolution from hydrolytic dehydrogenation of NH3BH3, it is extremely desirable to design and develop noble-metal-free nanomaterials as the high-efficiency nanocatalysts for H2 generation from hydrolytic dehydrogenation of NH3BH3. Herein, we first designed and synthesized a string of CoOx(OH)y colloid-stabilized Cu, Ni, Co and Fe nanoparticles (Cu/CoOx(OH)y, Ni/CoOx(OH)y, Co/CoOx(OH)y and Fe/CoOx(OH)y), by immobilization of Cu, Ni, Co or Fe nanoparticles at the surface of CoOx(OH)y colloid, for the efficient H2 evolution from hydrolytic dehydrogenation of NH3BH3 at 30 °C. The optional Cu/CoOx(OH)y nanohybrid exhibits the super-high catalytic property, with the highest TOF of 67.5 mol(H2)·molCu-1·min−1, in the H2 evolution from hydrolytic dehydrogenation of NH3BH3 at 30 °C. More Interestingly, the TOF of Cu/CoOx(OH)y nanohybrid catalyzed hydrolytic dehydrogenation of NH3BH3 reaches to 630.58 mol(H2)·molCu-1·min−1 (2789 mL(H2)·gcat-1·min−1) under 0.3 mol/L NaOH, which exceeds all or almost all non-noble metal nanocatalysts, even some noble metal nanocatalysts. The comparison of other common supports, including Fe(OH)3, Ni(OH)2 and Cu(OH)2, has highlighted the vital role of CoOx(OH)y in NH3BH3 hydrolytic dehydrogenation. A large KIE of 2.7 with D2O has illustrated that the oxygen-hydrogen bond cleavage of water was the rate-determining step in the hydrolytic dehydrogenation of NH3BH3. This work not only provides a new explication for the cost-effective design and synthesis of magnetic nanomaterials, but also offers a high-efficiency noble-metal-free nanocatalyst for H2 evolution from hydrolytic dehydrogenation of NH3BH3.

NiFeOxHy/Ni3Fe interface design via electropassivation for superior catalysis of HER

Herein, a novel tailor-tuned NiFeOxHy/Ni3Fe catalyst is introduced for use as an efficient cathode for the hydrogen evolution reaction (HER). It shows a marked electrocatalytic activity among several NiFe-based catalysts approaching those of noble-metal-based catalysts. That is, low overpotentials of −70 mV and −196 mV are enough to drive 10 mA cm–2 and 100 mA cm–2, respectively, of hydrogen generation in 1.0 M KOH. A foam-like film of Ni3Fe alloy is electrodeposited using the dynamic hydrogen bubble template (DHBT) method and shows a reasonable HER activity by delivering 10 mA cm–2 at −190 mV. Ni3Fe alloy is subsequently electropassivated by controlled repetitive cycling of potential in 1.0 M KOH solution to create NiFeOxHy/Ni3Fe interfaces, so a fast water cleavage occurs during HER boosting the overall rate. The electropassivation treatment is proven a successful technique to develop such metal/oxygenated metal junctions for improved HER kinetics in alkaline media. Various physicochemical analysis techniques such as XRD, SEM, EDS-mapping, ICP-OES, and XPS are employed to characterize the designed catalysts. The proposed NiFeOxHy/Ni3Fe catalyst layer is among the promising earth-abundant catalytic materials used for the electrolytic production of hydrogen in alkaline media.

Solar-driven Photocatalyzed Hydrogen Production from Water cleavage: Evaluation and Process Life Cycle Assessment

Hydrogen is proper chemical storage for solar energy and is considered a green and non-pollution energy. The feasibility of solar-driven hydrogen generation from water cleavage is investigated using commercial TiO2 nanoparticles, and the process of life cycle assessment (LCA) is estimated. TiO2 is fully characterized. The results confirm the efficacy of TiO2 for solar-driven photocatalytic water splitting with the same production rate of H2. The maximum calculated photocatalytic rate of hydrogen over PC was 4.76 µmole/h under sunlight. As well the rate of produced H2 is dependent PC dose. There is a signification corelation between Kapp with PC dose with r2 of 0.96. Reaction rate constant for hydrogen production is significantly dependent concentration of TiO2. The outcome emphasized the practical application of solar-driven, cost-effective technology for production renewable energy. Also, LCA study of solar-driven H2 production is showed that higher carbon dioxide and as well as global warming potential with lower climatic change impact originated from operation of system.

Impact of Pd:Pt ratio of Pd/Pt bimetallic catalyst on CH4 oxidation

Bimetallic Pd/Pt catalysts have recently attracted considerable attention in controlling emission control of methane. Here, we show the impact of Pd/Pt ratio (1:0, 9:1, 3:1, 1:1, 1:3, 1:9, 0:1) on the catalytic methane oxidation under simulated exhaust environments from the CH4-rich to -lean feed. Under dry feed conditions, the CH4 oxidation activity was linear to the Pd:Pt ratio, where the Pd-only (1:0) exhibited the best performance. However, under wet feed conditions containing 5% of water vapor, bimetallic Pd/Pt catalysts having a small fraction of Pt showed superior overall activities in a wide range of reaction environments. The interaction of Pd-Pt, forming active PdO-Pt pair sites, was confirmed by a series of analysis such as STEM-EDS, XPS and H2-TPR. The evidence by DFT calculations relates the distinct properties of bimetallic Pd/Pt sites to (i) stable CH4 adsorption, (ii) facile C–H bond cleavage and (iii) weaker adsorption of water on Pt site.

Sharp Volcano-Type Synergy and Visible Light Acceleration in H2 Release upon B2(OH)4 Hydrolysis Catalyzed by Au-Rh@Click-Dendrimer Nanozymes

Hydrogen (H2) formation from hydrogen-rich precursors is a hot topic, whereby carbon-free energy perspectives, mechanistic features, and synthetic applications are actively searched. Here, we report oxygen atom uptake from water under ambient conditions, producing H2 in the presence of alloyed Au-Rh nanoparticle catalysts encapsulated in a “click”-dendrimer. These systems are named nanozymes (NZs) because their function and mechanism resemble those of hydrogenase enzymes. The Au-Rh NZs with variable proportions of Au and Rh exhibit positive sharp volcano-type synergy and visible light-induced acceleration. The best synergy in the dark is disclosed in Au4Rh1, achieving a turnover frequency (TOFs) of 5100 molH2 molcata–1 min–1 in dark, 3.4 times higher than the related Au NZ and 8.9 times higher than the related Rh NZ at 25 ± 1 °C. The catalytic activity of Au-Rh for H2 evolution is enhanced by visible light irradiation due to the Au plasmon, so that the synergistic effect in the dark and the visible light-induced rate enhancement cumulate for Au4Rh1, allowing for complete B2(OH)4 hydrolysis in 39 s at 25 ± 1 °C (TOFs = 6000 molH2 molcata–1 min–1). Upon increasing the Rh content, Au-Rh provides less synergy in the dark, whereas the light enhancement of the reaction rate increases, reaching a maximum for Au1Rh2. Experiments using D2O, including kinetic isotope effect determination, suggest that the rate-determining step of the reaction involves concerted O–H bond cleavage of water and support the proposed catalytic reaction mechanism.

Optimally Selecting Photo- and Electrocatalysis to Facilitate CH4 Activation on TiO2(110) Surface: Localized Photoexcitation versus Global Electric-Field Polarization.

Photo- and electrocatalytic technologies hold great promise for activating inert chemical bonds under mild conditions, but rationally selecting a more suitable method in between to maximize the performance remains an open issue, which requires a fundamental understanding of their different catalytic mechanisms. Herein, by first-principles calculations, we systematically compare the activation mechanisms for the C–H bond of the CH4 molecule on TiO2(110) under the photo- and electrocatalytic modes without or with water involved. It quantitatively reveals that the activation barrier of the C–H bond decreases dramatically with a surprising 74% scale by photoexcitation relative to that in thermocatalysis (1.12 eV), while the barrier varies with a maximum promotion of only 5% even under −1 V/Å external electric field (EEF). By detailed geometric/electronic analysis, the superior photocatalytic activity is traced to the highly oxidative lattice Obr•– radical excited by a photohole (h+), which motivates the homolytic C–H bond scission. However, under EEF from −1 V/Å to 1 V/Å, it gives a relatively mild charge polarization on the TiO2(110) surface region and thus a limited promotion for breaking the weakly polar C–H bond. By contrast, in the presence of water, we find that EEF can facilitate CH4 activation indirectly assisted by the surface radical-like OH* species from the oxidative water cleavage at high oxidative potential (>1.85 V vs SHE), which explains the high energy cost to drive electrocatalytic CH4 conversion in experiment. Alternatively, we demonstrate that more efficient CH4 activation could be also achieved at much lower oxidative potential when integrating the light irradiation. In such a circumstance, EEF can not only promote the h+ accumulation at the catalyst surface but also help H2O deprotonation to form hydroxide, which can serve as an efficient hole-trapper to generate OH• radical (OH– + h+ → OH•), unveiling an interesting synergistic photoelectrocatalytic effect. This work could provide a fundamental insight into the different characteristics of photo- and electrocatalysis in modulating chemical bond cleavage.

Hierarchical FeO(OH)-CoCeV (Oxy)hydroxide as a Water Cleavage Promoter.

The search for a bifunctional electrocatalyst having water cleavage promoting ability along with the operational stability to efficiently generate oxygen and hydrogen could lead to robust systems for applications. These fundamental ideas can be achieved by designing the morphology, tuning the electronic structure, and using dopants in their higher oxidation states. Herein, we have fabricated a binder-free FeO(OH)-CoCeV-layered triple hydroxide (LTH) bifunctional catalyst by a two-step hydrothermal method, in which the nanograin-shaped FeO(OH) coupled with CoCeV-LTH nanoflakes provides more electrocatalytically active sites and enhances the charge-transfer kinetics for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The composition-optimized electrocatalyst (FeO(OH)-Co0.5Ce0.05V0.15-LTH) acts as an efficient water cleavage composite by virtue of its favorable oxidation states leading to cyclic redox couples, which yields an overpotential of 53 mV for HER and 227 mV for OER to drive 10 mA/cm2 current density in 1 M KOH with a corresponding Tafel slope of 70 mV/dec for HER and 52 mV/dec for OER. Furthermore, for the overall water splitting reaction, the heterostructure FeO(OH)-Co0.5Ce0.05V0.15-LTH acts as a dual-functional electrocatalyst, which requires a cell voltage of 1.52 V versus RHE to drive 10 mA/cm2 current density.

Molecular Nature of Structured Water in the Light-Induced Interfacial Capacitance Changes at the Bioelectric Interface.

Uncovering the function of structured water in the interfacial capacitance at the molecular level is the basis for the development of the concept and model of the electric double layer; however, the limitation of the available technology makes this task difficult. Herein, using surface-enhanced infrared absorption spectroscopy combined with electrochemistry, we revealed the contribution of the cleavage of loosely bonded tetrahedral water to the enhancement of model membrane capacitance. Upon further combination with ionic perturbation, we found that the interface hydrogen bonding environment in the stern layer was greatly significant for the light-induced cleavage of tetrahedral water and thus the conversion of optical signals into electrical signals. Our work has taken an important step toward gaining experimental insight into the relationship between water structure and capacitance at the bioelectric interface.

Versatile Fabrication of Binary Composite SnO2-Mn2O3 Thin Films by AACVD for Synergistic Photocatalytic Effect

In the present study, we prepared a SnO2-Mn2O3 binary composite thin-film electrode by a single-step solution-based aerosol assisted chemical vapor deposition (AACVD) technique for photovoltaic applications. The grown composite thin films were characterized to determine their properties, such as structure, composition, morphology and band gap by field emission scanning electron microscopy (FESEM), x-ray diffractometry (XRD), Raman scattering, energy-dispersive x-ray spectrometry (EDX), x-ray photoelectron spectroscopy (XPS) and UV-Vis absorption spectrophotometry. The evaluation of photoelectrochemical (PEC) response of as-synthesized SnO2-Mn2O3 composite photoelectrode, in comparison to the individual thin films of pristine SnO2 and Mn2O3 prepared from their respective precursors under the same conditions, engendered a promising improvement in photocurrent density. The synergistic effect between SnO2 and Mn2O3, the relevance of ball-like morphology, suitable and tunable energy band gap, and better absorbance under the visible range of light resulted in improved photocurrent of ~6.6 mA cm-2 at +0.7 V versus Ag/AgCl electrode of the binary composite, which was 16.5- and 3.4-fold higher than that of the pure SnO2 and Mn2O3, respectively. No apparent photocurrent decrease was observed during prolonged stability measurements for 300 s under one-sun illumination of 100 mW cm-2. The results confirmed the enhancement in PEC activity due to reduced recombination rate of photoinduced electron-hole pairs and improved interfacial charge transfer between electrode/electrolyte interface, which boost the PEC performance of SnO2-Mn2O3 binary composite thin film electrode towards water cleavage.

Air-engaged fabrication of nitrogen-doped carbon skeleton as an excellent platform for ultrafine well-dispersed RuNi alloy nanoparticles toward efficient hydrolysis of ammonia borane

Functional carbons that can provide abundant anchoring sites for metal nanoparticles (NPs) have shown great promise in boosting the catalytic activity for hydrolysis of ammonia borane (AB), while the synthetic recipes for some of them are complicated, time-consuming and hazardous together with a low yield. Herein, we develop a facile and easily scalable one-pot synthetic strategy to nitrogen-doped carbon skeleton (NCS) via direct pyrolysis of ethylenediamine tetra-acetic acid tetra-sodium salt in air. Attributing to the anchoring sites from abundant nitrogen-dopant and nanoporous structure of NCS, ultrasmall RuNi alloy NPs are highly distributed on NCS. The as-prepared RuNi/NCS can be used as a highly active catalyst for hydrogen production from AB hydrolysis at room temperature. Specifically, the optimal Ru1Ni1.90/NCS delivers an excellent catalytic activity with a very high turnover frequency of 1017 min−1 in basic solution, superior to many previous results. The kinetic studies indicate that AB hydrolysis catalyzed by Ru1Ni1.90/NCS is first-order and zero-order in terms of Ru and AB concentrations, respectively. Additionally, the isotopic analysis reveals that the O–H bond cleavage of water is the rate-determining step. The high catalytic activity of Ru1Ni1.90/NCS can be assigned to the ultrasmall RuNi nanostructure, highly nanoporous carbon matrix, and abundant N-dopant and the synergistic catalysis between the two metals. This study offers a simple synthetic protocol for construction of metal-carbon hybrid toward hydrogen generation from the hydrolysis of chemical storage materials.

COORDINATION COMPOUNDS OF COPPER, COBALT AND NICKEL FORMATES WITH FORMAMIDE AND CARBAMIDE

The synthesis of mixed ligand coordination compounds of copper, cobalt and nickel formates with formamide and urea in an aqueous solution was carried out. The metal content in the complexes was determined by complexometric titration. Using IR spectroscopy, it was proved that the coordination of formamide and urea with the complexing atom is carried out through the oxygen atom of the carbonyl group. The absorption spectrum of coordinated water is also present in the IR spectrum. The nature of the change in the frequency of stretching vibrations of the –OH group in the composition of water indicates its location in the nearest coordination sphere of the central atom. Derivatographic analysis investigated the thermal behavior of the obtained compounds. Based on the nature of the heating curves, sequential cleavage of water and ligands is shown and a molecular formula for synthesized compounds is proposed. The equation of the synthesis reaction of these coordination compounds is also given.

Well-connection of micro-platinum and cobalt oxide flower array with optimized water dissociation and hydrogen recombination for efficient overall water splitting

Integrating the merits of various catalytic materials into one novel hybrid is significant yet challenging in developing multifunctional electrode for overall water splitting. In this work, micro-platinum modification strategy is developed to construct the bifunctional Pt@Co3O4/Ni foam (NF) hybrid electrode for overall water splitting. The resultant Pt@Co3O4/NF electrode exhibits low overpotentials and favorable kinetics for both hydrogen (30 mV@10 mA cm−2, 31 mV dec−1) and oxygen evolution (263 mV@10 mA cm−2, 69 mV dec−1). Moreover, a voltage of ~ 1.53 V can drive a current density of 10 mA cm−2 for the two-electrode electrolyzer. The enhanced performance of Pt@Co3O4/NF hybrid could be attributed to the synergistic effect of micro-Pt modified Co3O4 nanorod array with the optimized water cleavage and hydrogen recombination. This work not only reports an efficient hybrid electrode for overall water splitting but also offers valuable insights in designing multifunctional electrocatalysts for energy conversion technologies.

Redirecting photosynthetic electron flux in the cyanobacterium Synechocystis sp. PCC 6803 by the deletion of flavodiiron protein Flv3

BackgroundOxygen-evolving photoautotrophic organisms, like cyanobacteria, protect their photosynthetic machinery by a number of regulatory mechanisms, including alternative electron transfer pathways. Despite the importance in modulating the electron flux distribution between the photosystems, alternative electron transfer routes may compete with the solar-driven production of CO2-derived target chemicals in biotechnological systems under development. This work focused on engineered cyanobacterial Synechocystis sp. PCC 6803 strains, to explore possibilities to rescue excited electrons that would normally be lost to molecular oxygen by an alternative acceptor flavodiiron protein Flv1/3—an enzyme that is natively associated with transfer of electrons from PSI to O2, as part of an acclimation strategy towards varying environmental conditions.ResultsThe effects of Flv1/3 inactivation by flv3 deletion were studied in respect to three alternative end-products, sucrose, polyhydroxybutyrate and glycogen, while the photosynthetic gas fluxes were monitored by Membrane Inlet Mass Spectrometry (MIMS) to acquire information on cellular carbon uptake, and the production and consumption of O2. The results demonstrated that a significant proportion of the excited electrons derived from photosynthetic water cleavage was lost to molecular oxygen via Flv1/3 in cells grown under high CO2, especially under high light intensities. In flv3 deletion strains these electrons could be re-routed to increase the relative metabolic flux towards the monitored target products, but the carbon distribution and the overall efficiency were determined by the light conditions and the genetic composition of the respective pathways. At the same time, the total photosynthetic capacity of the Δflv3 strains was systematically reduced, and accompanied by upregulation of oxidative glycolytic metabolism in respect to controls with the native Flv1/3 background.ConclusionsThe observed metabolic changes and respective production profiles were proposedly linked with the lack of Flv1/3-mediated electron transfer, and the associated decrease in the intracellular ATP/NADPH ratio, which is bound to affect the metabolic carbon partitioning in the flv3-deficient cells. While the deletion of flv3 could offer a strategy for enhancing the photosynthetic production of desired chemicals in cyanobacteria under specified conditions, the engineered target pathways have to be carefully selected to align with the intracellular redox balance of the cells.

O-O Bond Formation and Liberation of Dioxygen Mediated by N5 -Coordinate Non-Heme Iron(IV) Complexes.

Formation of the O−O bond is considered the critical step in oxidative water cleavage to produce dioxygen. High‐valent metal complexes with terminal oxo (oxido) ligands are commonly regarded as instrumental for oxygen evolution, but direct experimental evidence is lacking. Herein, we describe the formation of the O−O bond in solution, from non‐heme, N5‐coordinate oxoiron(IV) species. Oxygen evolution from oxoiron(IV) is instantaneous once meta‐chloroperbenzoic acid is administered in excess. Oxygen‐isotope labeling reveals two sources of dioxygen, pointing to mechanistic branching between HAT (hydrogen atom transfer)‐initiated free‐radical pathways of the peroxides, which are typical of catalase‐like reactivity, and iron‐borne O−O coupling, which is unprecedented for non‐heme/peroxide systems. Interpretation in terms of [FeIV(O)] and [FeV(O)] being the resting and active principles of the O−O coupling, respectively, concurs with fundamental mechanistic ideas of (electro‐) chemical O−O coupling in water oxidation catalysis (WOC), indicating that central mechanistic motifs of WOC can be mimicked in a catalase/peroxidase setting.

Homolytic cleavage of water on magnesia film promoted by interfacial oxide−metal nanocomposite

The atomic−scale insights into the interaction of water with oxide surface are essential for elucidating the mechanism of physiochemical processes in various scientific and practical fields, since the water is ubiquitous and coats multifarious material surface under ambient conditions. By utilizing van der Waals density functional calculations, herein we report for the first time the energetically and dynamically favorable homolytic dissociative adsorption behavior of water over MgO(001) films deposited on metal substrate. The water adsorption on pristine MgO(001) is quite weak and the heterolytic dissociation is the only fragmentation pathway, which is highly endothermic with large activation barrier of 1.167 eV. The binding strengths for the molecular and dissociative adsorption configurations of water on MgO/Mo(001) are significantly larger than corresponding configurations on bare MgO(001). The homolytic dissociative adsorption energy of water on monolayer oxide is calculated to be −1.231 eV, which is even larger than all the heterolytic dissociative adsorption states. The homolytic dissociative adsorption structure could be obtained by transformation reaction from heterolytic dissociative adsorption structure, presenting activation barriers 0.733, 1.103, 1.306, 1.571, and 1.849 eV for reactions on 1–5 ML films. With the increase of the oxide thickness, the homolytic dissociative adsorption energy decreases promptly, indicating the nanoscale of oxide film play a crucial role during water splitting. Ab initio molecular dynamics (AIMD) simulations were performed to confirm the stability of the ultrathin oxide films and the homolytic fragmentation configuration of water on the hybrid surface. Electronic properties are characterized to interpret the enhancement of chemical reactivity and properties of insulating oxide toward homolytic fragmentation of water.