Catalyst For Photocatalytic Water Oxidation Research Articles

Molecular confined synthesis of magnetic CoOx/Co/C hybrid catalyst for photocatalytic water oxidation and CO2 reduction

Photosynthesis [6CO2 + 12H2O → (CH2O)6 + 6O2 + 6H2O] in nature contains a light reaction process for oxygen evolution and a dark reaction process for carbon dioxide (CO2) reduction to carbohydrates, which is of great significance for the survival of living matter. Therefore, for simulating photosynthesis, it is desirable to design and fabricate a bifunctional catalyst for promoting photocatalytic water oxidation and CO2 reduction performances. Herein, a molecular confined synthesis strategy is reasonably proposed and applied, that is the bifunctional CoOx/Co/C-T (T = 700, 800 and 900 °C) photocatalysts prepared by the pyrolysis of molecular Co-EDTA under N2 and air atmosphere in turn. Among the prepared photocatalysts, the CoOx/Co/C-800 shows the best photocatalytic water oxidation activity with an oxygen yield of 51.2%. In addition, for CO2 reduction reaction, the CO evolution rate of 12.6 µmol/h and selectivity of 75% can be achieved over this catalyst. The improved photocatalytic activities are attributed to the rapid electron transfer between the photosensitizer and the catalyst, which is strongly supported by the current density-voltage (j-V), steady-state and time-resolved photoluminescence spectra (PL). Overall, this work provides a reference for the preparation and optimization of photocatalysts with the capacity for water oxidation and CO2 reduction reactions.

Two-phase solvothermal preparation of Co3O4/GO compound materials as catalysts for photocatalytic water oxidation

• (0D/2D) Co 3 O 4 /GO composites with good visible light response were successfully prepared by two-phase solvothermal method. • The photocatalytic water oxidation performance of the Co 3 O 4 /Go is higher than that of pure Co 3 O 4 . • The photocatalytic mechanism relies on the enhancement of effective electron transport. Zero-dimensional/two-dimensional (0D/2D) Co 3 O 4 /GO composites with good visible light response were successfully prepared by adding a certain amount of GO to the nano Co 3 O 4 synthesized by two-phase solvothermal method. The results show that the photocatalytic water oxidation performance of the synthesized Co 3 O 4 /Go is higher than that of pure Co 3 O 4 . The turnover frequency (TOF) of Co 3 O 4 /GO (15%) is 1.62 × 10 -2 s −1 per metal atom, and the initial quantum yield is 25.12%. The improvement of photocatalytic water oxidation activity and stability of Co 3 O 4 /Go were attributed to the enhancement of effective electron transport, which helps to reduce photoelectric recombination rate. The application of 0D/2D composites in the field of photocatalysis is expanded.

Ligand Controls the Activity of Light-Driven Water Oxidation Catalyzed by Nickel(II) Porphyrin Complexes in Neutral Homogeneous Aqueous Solutions.

Finding photostable, first‐row transition metal‐based molecular systems for photocatalytic water oxidation is a step towards sustainable solar fuel production. Herein, we discovered that nickel(II) hydrophilic porphyrins are molecular catalysts for photocatalytic water oxidation in neutral to acidic aqueous solutions using [Ru(bpy)3]2+ as photosensitizer and [S2O8]2− as sacrificial electron acceptor. Electron‐poorer Ni‐porphyrins bearing 8 fluorine or 4 methylpyridinium substituents as electron‐poorer porphyrins afforded 6‐fold higher turnover frequencies (TOFs; ca. 0.65 min−1) than electron‐richer analogues. However, the electron‐poorest Ni‐porphyrin bearing 16 fluorine substituents was photocatalytically inactive under such conditions, because the potential at which catalytic O2 evolution starts was too high (+1.23 V vs. NHE) to be driven by the photochemically generated [Ru(bpy)3]3+. Critically, these Ni‐porphyrin catalysts showed excellent stability in photocatalytic conditions, as a second photocatalytic run replenished with a new dose of photosensitizer, afforded only 1–3 % less O2 than during the first photocatalytic run.

Ligand Controls the Activity of Light‐Driven Water Oxidation Catalyzed by Nickel(II) Porphyrin Complexes in Neutral Homogeneous Aqueous Solutions

AbstractFinding photostable, first‐row transition metal‐based molecular systems for photocatalytic water oxidation is a step towards sustainable solar fuel production. Herein, we discovered that nickel(II) hydrophilic porphyrins are molecular catalysts for photocatalytic water oxidation in neutral to acidic aqueous solutions using [Ru(bpy)3]2+ as photosensitizer and [S2O8]2− as sacrificial electron acceptor. Electron‐poorer Ni‐porphyrins bearing 8 fluorine or 4 methylpyridinium substituents as electron‐poorer porphyrins afforded 6‐fold higher turnover frequencies (TOFs; ca. 0.65 min−1) than electron‐richer analogues. However, the electron‐poorest Ni‐porphyrin bearing 16 fluorine substituents was photocatalytically inactive under such conditions, because the potential at which catalytic O2 evolution starts was too high (+1.23 V vs. NHE) to be driven by the photochemically generated [Ru(bpy)3]3+. Critically, these Ni‐porphyrin catalysts showed excellent stability in photocatalytic conditions, as a second photocatalytic run replenished with a new dose of photosensitizer, afforded only 1–3 % less O2 than during the first photocatalytic run.

High-valence-state nickel-iron phosphonates with urchin-like hierarchical architecture for highly efficient oxygen evolution reaction

The exploitation of highly efficient, low-cost, and durable catalysts for photocatalytic water oxidation is highly desirable in the field of sustainable energy conversion and storage. Here, we demonstrate the preparation of urchin-like 3D nickel-iron phenyl phosphonates (NiFeP) hierarchical architecture fabricated by ultrathin nanosheets for photocatalytic water oxidation with high efficiency. The urchin-like NiFeP hierarchical architecture is prepared by a facile solvothermal synthesis without any organic additives. The urchin-like 3D hierarchical architecture exhibits a large specific surface area and abundant mesopores distribution, which affording more active catalytic sites and multi-electron transport channel. In the presence of high-valence Ni3+ sites could act as the main redox site to decrease the overpotential of water oxidation reaction. In consequence, using [Ru(bpy)3]Cl2 photosensitizer under visible light irradiation, the urchin-like NiFeP photocatalyst demonstrates a high oxygen evolution activity, giving a superior O2 yield of 76% and O2 production rate of 23.66 umol s−1 g−1. Moreover, the urchin-like NiFeP photocatalyst is highly stable for reuse. This work extends the development of transition metal phosphonates and provides a platform for designing high performance, economic and stable catalysts.

Efficient Co@Co3O4 core-shell catalysts for photocatalytic water oxidation and its behaviors in two different photocatalytic systems

Co@Co 3 O 4 photocatalyst was prepared in situ to investigate its water splitting performance and mechanism in two photocatalytic systems. • Photocatalytic activity of catalyst 1 in two systems were compared for the first time. • Catalyst 1 exhibited excellent photocatalytic performances. • Core-shell structure of Catalyst 1 can promote light capture and electron transmission. The photocatalytic performances of water oxidation were usually carried out in two different systems, photosensitizer and non-photosensitizer systems. There is few report about the same catalyst used in two systems and therefore it is of great significant to compare its role of the same catalyst in two systems and explore its different reaction mechanisms. In this work, first 4 kinds of metallic Co microparticles were obtained by different reduction methods through hydrothermal processes, and Co@Co 3 O 4 core-shell microparticles (1–4) were obtained from these metallic Co microparticles oxidized in air or in the reacting solution in situ. The core-shell structure of 1 was characterized by a series of analytical techniques. 1–4 exhibited excellent activities and stabilities in the [Ru(bpy) 3 ] 2+ /S 2 O 8 2− /light system when they were used as catalysts for the photocatalytic water oxidation. The maximum O 2 evolution of 1 after 20 min’s illumination was 98.2 μmol, the O 2 yield was 65.5%, the initial turnover frequency was 6.6 × 10 −3 , the initial quantum efficiency ( Φ QY initial ) was 15.0% higher than Co (8.3%), CoO (11.7%), Co 2 O 3 (1.2%), Co 3 O 4 (2.8%) and 5 (2.2%). Even after the sixth run, the catalytic activity of recovered 1 still remained 85.1% of initial activity. In addition, the photocatalytic performances of 1 in the [Ru(bpy) 3 ] 2+ /S 2 O 8 2− /light system and S 2 O 8 2− /light system were compared for the first time. In the non-photosensitizer system, 1 shows bifunctional roles and acts as optical absorption center and active catalytic site, and oxygen evolution rate is lower and it takes longer time. In the photosensitizer system, 1 only acts as a catalyst, the photosensitizer enhances the light absorption and promotes water oxidation reaction with higher O 2 yield and QE, meanwhile the photosensitizer brings the defect of high cost and instability into the system. Based on the results the two different reaction mechanisms were deeply discussed.

Cubic Co-Co prussian blue MOF-based transition metal phosphide as an efficient catalyst for visible light-driven water oxidation

Designing and developing an efficient, economic and stable catalyst for photocatalytic water oxidation is a forefront topic of sustainable energy research. Herein, we rationally designed a CoP/NC (CoP nanoparticles embedded in nitrogen and carbon matrices) nanocube catalysts via a pyrolysis phosphidation strategy derived from Co-Co/PB (Co-Co prussian blue) MOF-based precursor, which was employed as a robust heterogeneous catalyst for photocatalytic water oxidation for the first time. The TEM and SEM tests exhibit that Co-Co/PB contributes to well-defined nanocube architecture features after phosphidation. Furthermore, the photocatalytic performance of CoP/NC nanocube catalyst was examined in photocatalytic water oxidation system using [Ru(bpy)3]2+ as photosensitizer and S2O82− as sacrificial electron acceptor. The result shows CoP/NC has a modest high O2 evolution rate of 901.5 mmol h−1 g−1, O2 yield of 36.1%, TOF of 34.5 × 10−3 molO2 molmetal−1 s−1, and quantum yield of 61.5%. Noteworthily, an amorphous CoOx layer on CoP/NC surface was observed by HRTEM test after light reaction. The amorphous CoOx layer and CoP form a core-shell structure (CoP@CoOx), which facilitates the electron transport effectively. Additionally, the CoP/NC nanocube catalyst shows good electrocatalytic oxygen evolution performance, which has a higher current density and smaller Tafel slope than CoS2/NC and Co3O4/NC derived from the same precursor of Co-Co/PB with CoP/NC. This strategy of using prussian blue analogue as template to create metal phosphide will provide a platform for exploring highly efficient and stable catalysts for energy conversion reactions.

One-step solvothermal synthesis of Co3O4/Co(OH)2 hybrids as a catalyst for visible-light-driven water oxidation

Co3O4/Co(OH)2 hybrid material was synthesized by a facile solvothermal method and applied as a catalyst for photocatalytic water oxidation. The results show the as-synthesized product is a hybrid structure of nano-cubic Co3O4 and hexagonal lamellar Co(OH)2. Such unique nanostructure has been shown to be superior to the single component of Co3O4 and Co(OH)2 in photocatalytic applications. A high turnover frequency (TOF) of 1.85 × 10−2 s−1 per metal atom was obtained over Co3O4/Co(OH)2 catalyst, which also shows an initial quantum yield of 29.42%. This unique Co3O4/Co(OH)2 catalyst has good photocatalytic activity and is expected to be an efficient and cheap photocatalyst for water oxidation.

Utilization of core-shell nanoparticles to evaluate subsurface contribution to water oxidation catalysis of [CoII(H2O)2]1.5[CoIII(CN)6] nanoparticles

Nanoparticles of a cyano-bridged polynuclear metal complex, [CoII(H2O)2]1.5[CoIII(CN)6], have been reported as highly efficient heterogeneous catalysts for photocatalytic water oxidation, however, reasons for the high catalytic activity have yet to be clarified. Herein, the water oxidation catalysis was investigated for a series of core-shell nanoparticles composed of cyano-bridged polynuclear metal complexes employing [CoII(H2O)2]1.5[CoIII(CN)6] as the shell to assess subsurface contribution. The catalytic activity of the core-shell nanoparticles closely related to that of the core parts suggests that the subsurface contributes to the nanoparticle catalysis. Then, catalysis of the core-shell nanoparticles employing [CuII(H2O)2]1.5[FeIII(CN)6] as the catalytically inactive core but isostructural to [CoII(H2O)2]1.5[CoIII(CN)6] was examined to determine the thickness directly involved in the catalytic reaction. The catalytic activity depending on the thickness of the [CoII(H2O)2]1.5[CoIII(CN)6] shell suggests the involvement of CoII ions at the subsurface up to 7 nm. These results suggest that the microporous structure of [CoII(H2O)2]1.5[CoIII(CN)6] enlarged by intrinsic defects is a reason for the high catalytic activity, where the photosensitizer and water molecules utilize the subsurface CoII ions as active sites.

Enhanced photocatalytic oxygen evolution activity by formation of Ir@IrOx(OH)y core–shell heterostructure

Developing efficient catalysts to accelerate the rate of oxygen evolution reaction (OER) is critical for photocatalytic water-splitting. In this work, metallic Ir, IrOx(OH)y, and core–shell Ir@IrOx(OH)y were synthesized and employed as OER catalysts for photocatalytic water oxidation. It was found that the Ir@IrOx(OH)y core–shell heterostructure catalyst showed the best photocatalytic performance among these three catalysts, with the oxygen evolution rate as high as 59.63 mmol g−1 h−1. Detailed investigations revealed that the excellent photocatalytic activity of Ir@IrOx(OH)y could be attributed to both the outstanding intrinsic activity of IrOx(OH)y shell and the efficient electron transfer between the photosensitizer and catalyst.

Co@Co3O4 Prepared in Situ from Metallic Co as an Efficient Semiconductor Catalyst for Photocatalytic Water Oxidation

This paper reported the first attempt of using Co@Co3O4 core–shell nanoparticles obtained in situ from a metallic Co precursor as a highly active and stable catalyst for the photocatalytic water oxidation. Co nanoparticle precursor was prepared through a hydrothermal process. The components of precursor and catalyst were confirmed by multiple measurements (X-ray diffraction, field emission scanning electron microscopy, scanning transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, line scanning analysis, UV–vis diffuse reflectance spectroscopy, Mott–Schottky curve). The Co@Co3O4 semiconductor catalyst exhibited excellent activity for the photocatalytic water oxidation without any addition of photosensitizer or cocatalyst, with an average O2 evolution rate of 2778 μmol h–1 g–1, and the Co@Co3O4 maintained 90% of the initial activity even after the sixth run; its oxygen evolution reaction performance under λ = 600 and 765 nm still remained 16% ...

An octanuclear Cu(ii) cluster with a bio-inspired Cu4O4 cubic fragment for efficient photocatalytic water oxidation.

An octanuclear Cu(ii) cluster [Cu8(dpk·OH)8(OAc)4](ClO4)4 (dpk·OH = the monoanion of the hydrated, gem-diol form of di-2-pyridyl ketone) that contains two Cu4O4 cubic fragments similar to the Mn4CaO5 cluster in photosystem II (PSII) was found to be an efficient catalyst for photocatalytic water oxidation. In the [Ru(bpy)3]2+/Na2S2O8 system, it afforded an optimal oxygen yield, turnover number (TON) and turnover frequency (TOF) of 35.6%, 178 and 3.6 s-1, respectively, which are the highest values amongst all of the Cu-based photocatalytic water oxidation catalysts (WOCs).

An artificial photosynthetic system containing an inorganic semiconductor and a molecular catalyst for photocatalytic water oxidation

Water oxidation has long been considered to be the bottleneck of the water splitting reaction. Most semiconductor-based photocatalysts show low oxidation activity, mainly because of poor charge separation and transfer. Here, we construct an artificial photosynthetic system for photocatalytic water oxidation using BiVO4 as a photosensitizer and cubic Co complex as the oxygen-evolving catalyst. This system exhibits a high turnover frequency (TOF=2.0s−1) for O2 evolution in the presence of NaIO3 as an electron acceptor, with an apparent quantum efficiency (AQE) yield of 4.5% at 420nm, which is ninefold that of bare BiVO4 (0.5%), but the decomposition of the Co complex leads to decreased photocatalytic activity as time goes on. Spectroscopic studies confirmed an efficient interfacial hole transfer process from the semiconductor to the molecular catalyst. These results may shed light on designing artificial photocatalysts with highly efficient molecular catalysts and suitable semiconductor materials for water oxidation.

Cobalt salophen functionalized SBA-15 as an active catalyst for photocatalytic water oxidation

A new cobalt salophen functionalized SBA-15 is the cost-effective photocatalyst for water oxidation under mild conditions.

ChemInform Abstract: Catalysis of Nickel Ferrite for Photocatalytic Water Oxidation Using [Ru(bpy)3]2+ and S2O82‐.

AbstractNiFe2O4 is an excellent catalyst for photocatalytic water oxidation with Na2S2O8 as a sacrificial oxidant and [Ru(bpy)3]2+ as a photosensitizer.

LaCoO3 acting as an efficient and robust catalyst for photocatalytic water oxidation with persulfate

Cobalt-containing metal oxides [perovskites (LaCoO(3), NdCoO(3), YCoO(3), La(0.7)Sr(0.3)CoO(3)), spinel (Co(3)O(4)) and wolframite (CoWO(4))] have been examined as catalysts for photocatalytic water oxidation with Na(2)S(2)O(8) and [Ru(bpy)(3)](2+) as an electron acceptor and a photosensitizer, respectively. Catalysts with the perovskite structure exhibited higher catalytic activity as compared with the catalysts with the spinel and wolframite structures. LaCoO(3), which stabilizes Co(III) species in the perovskite structure, exhibited the highest catalytic activity in the photocatalytic water oxidation compared with CoWO(4), Co(3)O(4) and La(0.7)Sr(0.3)CoO(3) which contain Co(II) or Co(IV) species in the matrices. The high catalytic reactivity of LaCoO(3) possessing perovskite structure was maintained in NdCoO(3) and YCoO(3) which exclusively contain Co(III) species. Thus, the catalytic activity of Co ions can be controlled by the additional metal ions, which leads to development of highly reactive and robust catalysts for the photocatalytic water oxidation.

Catalytic activity of metal-based nanoparticles for photocatalytic water oxidation and reduction

Precious-metal catalysts, predominantly platinum (Pt), have been used to minimize the overpotentials for both the oxidation and reduction of water. This article focuses on the catalytic activity of non-Pt metal nanoparticles for the photocatalytic oxidation and reduction of water. Efficient photocatalytic hydrogen evolution was made possible by using ruthenium nanoparticles (RuNPs) instead of platinum nanoparticles (PtNPs) under basic conditions (pH 10) with 2-phenyl-4-(1-naphthyl)quinolinium ion (QuPh+–NA) as an organic photocatalyst and dihydronicotinamide adenine dinucleotide (NADH) as an electron source. Nickel nanoparticles (NiNPs) can also be used as a non-precious metal catalyst in the photocatalytic hydrogen evolution with QuPh+–NA and NADH maintaining 40% of the catalytic activity of PtNPs. On the other hand, some metal-based nanoparticles can also act as catalysts for photocatalytic water oxidation. Iridium hydroxide nanoparticles (Ir(OH)xNPs) formed during the thermal oxidation of water by (NH4)2[CeIV(NO3)6] as an oxidant and cobalt hydroxide nanoparticles (Co(OH)xNPs) were produced during the photocatalytic oxidation of water with Ru(bpy)32+ as a photocatalyst and persulphate as a sacrificial oxidant using Ir and Co complexes with organic ligands as precatalysts. The catalytic activity and stability of Ir(OH)xNPs and Co(OH)xNPs were improved significantly as compared with Ir and Co precatalysts.