Visible Light-driven Water Oxidation Research Articles

Post-modification engineering of cerium metal-organic frameworks for efficient visible light-driven water oxidation

Post-modification engineering of cerium metal-organic frameworks for efficient visible light-driven water oxidation

BiVO4/CuIn5S8 heterojunction with rich sulphur vacancies for boosting visible light-driven photocatalytic water oxidation

The efficient conversion of water into clean energy using solar energy presents a sustainable solution to environmental challenges, albeit constrained by the slow kinetics of the oxygen evolution reaction. This study introduces a series of novel BiVO4/CuIn5S8 heterojunctions, developed and employed as photocatalysts for water oxidation. The photocatalytic activity of these heterojunctions was systematically enhanced by optimizing the BiVO4/CuIn5S8 ratio and hydrothermal reaction temperature. Notably, the heterojunction comprising BiVO4 coupled with 5 % CuIn5S8, synthesized at 180 °C (BiVO4/CuIn5S8/180–5), exhibited superior photocatalytic performance compared to its individual components. This enhancement was further augmented by the introduction of sulfur vacancies (VS) in VS-BiVO4/CuIn5S8/180–5, achieving approximately 3 and 1.4 times the photocatalytic activity of BiVO4 and BiVO4/CuIn5S8/180–5, respectively. Our findings demonstrate that CuIn5S8 effectively grows on decahedral BiVO4, forming n-n heterojunctions that not only improve visible light absorption but also facilitate the separation of photogenerated carriers. The incorporation of VS significantly lowers the charge carrier recombination rate and promotes the formation of additional active sites for H2O adsorption, thereby further elevating the efficiency of photocatalytic water oxidation.

A Cobalt Complex from Terpyridine‐Based Peptoid as an Efficient Catalyst for Visible Light Driven Water Oxidation

AbstractWe report on the first peptoid‐based catalyst for visible light driven water oxidation, the complex TPT2Co. Peptoids are N‐substituted glycine oligomers, and TPT is a peptoid trimer incorporating terpyridine ligand, an ethanolic group as a proton acceptor and a non‐catalytic benzyl group. We explored the ability of TPT2Co to perform as a catalyst for water oxidation in phosphate buffer at pH 9.5, in the presence of the photosensitizer [Ru(bpy)3]2+ and the sacrificial electron acceptor Na2S2O8. We demonstrated that TPT2Co can catalyze water oxidation by a blue LED with an intensity of only 1.5 mW/cm2 towards oxygen production at pH 9.5 with a maximal TON of 28.1 in 45 min. The stability of TPT2Co during the light‐driven water oxidation as well as its ability to stabilize the photosensitizer were confirmed by a combination of UV‐Vis, IR and ESI‐MS analysis.

Self-assembled Ru(bda) Coordination Oligomers as Efficient Catalysts for Visible Light-Driven Water Oxidation in Pure Water.

Water-soluble multinuclear complexes based on ruthenium 2,2'-bipyridine-6,6'-dicarboxylate (bda) and ditopic bipyridine linker units are investigated in three-component visible light-driven water oxidation catalysis. Systematic studies revealed a strong enhancement of the catalytic efficiency in the absence of organic co-solvents and with increasing oligomer length. In-depth kinetic and morphological investigations suggest that the enhanced performance is induced by the self-assembly of linear Ru(bda) oligomers into aggregated superstructures. The obtained turnover frequencies (up to 14.9 s-1 ) and turnover numbers (more than 1000) per ruthenium center are the highest reported so far for Ru(bda)-based photocatalytic water oxidation systems.

(Invited) Ultrafast Solar Energy Conversion with Earth-Abundant Complexes

Transition-metal complexes are widely used as photosensitizers and photocatalysts, and in light-emitting devices.[1] We have studied ultrafast proceses in a variety of DSSC and photocatalytic aplications.[2,3] More recently we demonstrated the first iron complex [FeIII(btz)3]3+ exhibiting room temperature photoluminescence from a CT state and show that it has a 100 ps excited state CT lifetime which is unprecedented for any iron complex.[4] This was characterized as a rare low-spin FeIII d5 complex with emission from a long-lived doublet ligand-to-metal charge transfer (2LMCT) state. Absence of intersystem crossing (ISC) in this complex avoids significant excited state energy losses as encountered in the prevailing class of d6 TM complexes of e.g. FeII and RuII. Furthermore, we have also shown [FeII(btz)3]2+ low-spin complex [5], a FeII analogue to [FeIII(btz)3]3+. It exhibits strong metal-to-ligand charge transfer (MLCT) absorption bands throughout the visible spectrum, and excitation of these bands gives rise to a 3MLCT state with a 528 ps excited state lifetime in CH3CN solution that is more than one order of magnitude longer compared to the MLCT lifetime of any previously reported FeII complex. Together, these results show that the FeII and FeIII oxidation states of the same Fe(btz)3 complex feature long lived MLCT and LMCT states, respectively. This demonstrates the versatility of iron N-heterocyclic carbene complexes as promising light-harvesters for a broad range of photophysical and photochemical applications, and on-going efforts for further improvements of the excited state dynamics of such systems will be outlined, including the very latest development of an iron compound [Fe(phtmeimb)2]+ with an excited state stable enough to emit light for 2 ns and able to engage in bimolecular electron transfer [6].1 Ponseca, C. S., Jr.; Chabera, P.; Uhlig, J.; Persson, P.; Sundstrom, V. Ultrafast Electron Dynamics in Solar Energy Conversion. Chem Rev 2017, 117 (16), 10940.2 H. Imahori et al, Photoinduced Charge Carrier Dynamics of Zn−Porphyrin−TiO2 Electrodes: The Key Role of Charge Recombination for Solar Cell Performance, J. Phys. Chem. A 2011, 115, 16, 3679-36903 M. Yamamoto et al, Visible light-driven water oxidation with a subporphyrin sensitizer and a water oxidation catalyst, Chem. Commun. 2016,52, 13702-137054 Chabera, P. et al. A low-spin Fe(III) complex with 100-ps ligand-to-metal charge transfer photoluminescence. Nature 2017, 543 (7647), 695.5 Chabera, P. et al. Fe(II) Hexa N-Heterocyclic Carbene Complex with a 528 ps Metal-to-Ligand Charge-Transfer Excited-State Lifetime, J Phys Chem Lett 2018, 9, 459−463.6 Kjær, K. S. et al. Luminescence and reactivity of a charge-transfer excited iron complex with nanosecond lifetime. Science 2019, 363 (6424), 249-253. Figure 1

Resorcin[4]arene-based [Co12] supermolecule cage functionalized by bio-inspired [Co4O4] cubanes for visible light-driven water oxidation

The design and assembly of efficient water oxidation catalysts (WOCs) is quite desirable, but still remains a synthetic challenge. Herein, we researched remarkable calix[4]resorcinarene-based [Co12] coordination cages with bio-inspired [Co4O4] cubanes. Markedly, the coordination cage features efficient visible light-driven water oxidation activity, and represents a unique example of calix[4]resorcinarene-based [Co4O4] cubane WOC. It afforded an optimal turnover number (TON) of 119, corresponding to a quite high turnover frequency (TOF) of 793 h−1 and an oxygen yield of 17.0%. A possible mechanism for the water oxidation reaction was also proposed by means of density functional theory (DFT) calculations.

Ag-modified ZnO nanorods and its dual application in visible light-driven photoelectrochemical water oxidation and photocatalytic dye degradation: A correlation between optical and electrochemical properties

In this work, Ag-ZnO composite was prepared at different weight percentages using a modified hydrothermal method for application to the photoelectrochemical (PEC) water oxidation and photocatalytic dye degradation. The resulting samples were studied using structural, surface, optical and photoelectrochemical (PEC) characterization methods. The surface plasmon resonance (SPR) of the optimal catalyst played an essential role in the synergistic improvement of the optical response and the photoinduced charge carrier separation process. The optimal Ag modified ZnO (3 wt% of Ag) showed superior photocatalytic and water oxidation performance. The inclusion of Ag has also played a vital role in the defect concentration and the Schottky junction at the metal–metal oxide interface. As a result, the PEC behavior of the optimal samples showed drastic improvements in terms of water oxidation current response under visible light illumination. Consequently, the photocatalytic performance of the samples also exhibits a linear relationship with the PEC water oxidation performance. The PEC and photocatalytic performance of the optimal sample showed almost five and seven times superior performance than the pristine ZnO in terms of photocurrent value and rate constant value, respectively. This can be attributed to the existence of the Schottky junction leading to the minimum charge transfer resistance and better charge transport across the interface. The superiority of the optimal sample is explained in terms of the physicochemical properties and electrochemistry of the material. To the best of the authors’ knowledge, this is the first report on the role of optimal Ag content in ZnO for its dual application. The combined study offering complete information, the work provides guidelines for noble metal-modified catalyst research moving forward.

Visible-light driven water oxidation and oxygen production at soft interfaces.

The visible light driven water oxidation reaction (WOR) by the organic electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (TCNQF4) was studied at the water|butyronitrile interface. The WOR was performed at neutral pH, and without any metal or organometallic catalysts. The oxygen generated was measured by GC-MS and cyclic voltammetry, and the protons produced were monitored by measuring the aqueous pH. This work opens novel perspectives for water photo-oxidation in liquids and artificial photosynthesis.

Covalent triazine-based frameworks with cobalt-loading for visible light-driven photocatalytic water oxidation

Incorporating Co through the bipyridine coordination sites within CTF results in rapid charge-separation, thus improving the photocatalytic water oxidation performance.

Multimodal analysis of visible light-driven water oxidation catalysis in nanoporous block copolymer membranes

Multimodal analysis of visible light-driven water oxidation catalysis in nanoporous block copolymer membranes

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.

Observation of a potential-dependent switch of water-oxidation mechanism on Co-oxide-based catalysts

Summary O–O bond formation is a key elementary step of the water-oxidation reaction. However, it is still unclear how the mechanism of O–O coupling depends on the applied electrode potential. Herein, using water-in-salt electrolytes, we systematically altered the water activity, which enabled us to probe the O–O bond-forming mechanism on heterogeneous Co-based catalysts as a function of applied potential. We discovered that the water-oxidation mechanism is sensitive to the applied potential: At relatively low driving force, the reaction proceeds through an intramolecular oxygen coupling mechanism, whereas the water nucleophilic attack mechanism prevails at high driving force. The observed mechanistic switch has major implications for the understanding and control of the water-oxidation reaction on heterogeneous catalysts.

Au decorated BiVO4 inverse opal for efficient visible light driven water oxidation.

Photocatalytic water splitting provides an effective way to prepare hydrogen and oxygen. However, the weak light utilization and sluggish kinetics in the oxygen evolution reaction (OER) process substantially retard the photocatalytic efficiency. In this context, modification of the semiconductors to overcome these limits has been the effective strategy for obtaining highly-efficient photocatalytic water oxidation. Here, plasmonic Au has been loaded onto BiVO4 inverse opal (IO) for photocatalytic water oxidation. It is discovered that the IO structure provides higher specific surface area and favors light absorption on BiVO4. In the meantime, the plasmonic Au can simultaneously enhance the light-utilization capability and photogenerated charge carrier utilization ability of the BiVO4 IO. As a result, a high photocurrent density and long photogenerated charge carrier lifetime can be achieved on the optimized Au–BiVO4 IO, thereby obtaining a superior photocatalytic activity with an oxygen production rate of 9.56 μmol g−1 h−1.

Precious Metal-Free Photocatalytic Water Oxidation by a Layered Double Hydroxide-Prussian Blue Analogue Hybrid Assembly.

The development of earth-abundant photocatalytic assemblies has been one of the bottlenecks for the advancement of scalable water splitting cells. In this study, a ZnCr layered double hydroxide and a CoFe Prussian blue analogue are combined to afford an earth-abundant photocatalytic assembly involving a visible light-absorbing semiconductor (SC) and a water oxidation catalyst (WOC). Compared to bare ZnCr-LDH, the SC-WOC hybrid assembly exhibits a threefold enhancement in photocatalytic activity, which is maintained for 6 h under photocatalytic conditions at pH 7. The band energy diagram was extracted from optical and electrochemical studies to elucidate the origin of the enhanced photocatalytic performance. This study marks a straightforward pathway to develop low-cost and precious metal-free assemblies for visible light-driven water oxidation.

Encapsulating band gap engineered CoSnO3 mixed metal oxide nanocomposite in rGO matrix: A novel catalyst towards LED light induced photoelectrocatalytic water oxidation at neutral pH

Abstract Most of the semiconductor nanocatalysts, for visible light driven water oxidation, exhibit low electrochemical performance either due to wide band structures or rapid recombination of photogenerated excitons. Considering the synergistic effect of band gap engineered mixed metal oxide CoSnO3 and good conductivity of reduced graphene oxide (rGO), we report a novel integrated CoSnO3-rGO nanocomposite towards light emitting diode (LED) induced photoelectrocatalytic water splitting. The surface decorated quantum sized CoSnO3-rGO nanoheterojunction has been synthesized using simple hydrothermal technique and characterized using sophisticated analytical instruments. The photoelectrocatalytic activity was evaluated with linear sweep voltammetry and Controlled potential electrolysis. The CoSnO3-rGO nanocomposite catalyst showed excellent photoelectrocatalytic activity towards water oxidation under neutral condition with a low overpotential of ~340 mV at 1.0 mAcm−2 with Tafel slope of 68 mV per decade. The catalyst exhibited good oxygen evolution with Faradic efficiency (86%), good structural stability and reproducible response over six days of operation with two days interval. The band gap engineered mixed metal oxide nanocomposite have been found to harvest the white LED light effectively and hybridization with electron acceptor rGO further increased the lifetime of charge carriers thereby increasing the photoelectrocatalytic performance.

Study two kind different catalytic behaviors for K4H1.2[Co0.6(H2O)0.6SiW11.4O39.4]-cocatalyzed visible light driven water oxidation in pH 1–7 media

Efficient water oxidation remains a particular challenge in water splitting that calls for developing robust and economic water oxidation catalysts (WOCs), preferably based on earth-abundant transition metals. Herein, we report a robust and noble metal-free catalytical system using BiVO4 as an effective light-harvesting material, a cobalt-containing polyoxometalate K4H1.2[Co0.6(H2O)0.6SiW11.4O39.4] (1) as molecular cocatalyst, and NaIO3 as a sacrificial electron acceptor for visible-light-driven water oxidation in a wide pH range 1–7. The combination of 1 + BiVO4 samples gives better oxygen evolution activities than that of pristine BiVO4. A turnover number (TON) of 326.3, apparent quantum efficiency (AQE) of 10.0%, and an O2 yield of 21.8% are obtained under pH 4. This work investigates two kind different catalytic behaviors for 1-cocatalyzed visible light driven water oxidation at pH 1–7 media, which exhibits a pH-induced dynamic change on the catalytic active species. Catalytic behavior, XPS, SEM and TEM collectively testify that 1 remains intact during photocatalytic water oxidation under pH 4–5. Conversely, under pH 1–3 and 6–7, the heterogeneous CoOx originated from 1 is formed on the BiVO4 surface, which is responsible for the enhancement of BiVO4 photocatalytic activity. Our work uncovers the borderline between homogeneous and heterogeneous WOCs using a cobalt-based polyoxometalate at different pH media, which helps to the study of stability for polyoxometalates when semiconducting material is used as the light-harvesting material.

Hybrid photoanodes for visible light-driven water oxidation: the beneficial and detrimental effects of nickel oxide cocatalyst

Hybrid photoanodes comprising polymer-based light absorbers coupled to oxygen-evolving cocatalysts represent a promising, yes still underdeveloped, approach to photoelectrochemical splitting of water into hydrogen and oxygen. In this study, we investigate nickel oxide (NiOx) nanoparticles as a water oxidation catalyst in hybrid photoanodes based on polymeric carbon nitride (CNx) supported on electron-collecting mesoporous TiO2 support. The performance of the resulting TiO2–CNx/NiOx photoanodes is evaluated with respect to our previous results on hybrid TiO2–CNx photoanodes modified with IrOx and CoO(OH)x cocatalysts. The deposition of NiOx into TiO2–CNx photoanodes enhances significantly the photocurrent (from <8 μA to >250 μA cm–2 at 1.23 V vs. RHE) under visible light irradiation (λ > 420 nm, ∼200 mW cm−2) and triggers the photoelectrocatalytic oxygen evolution. No oxygen evolution was observed without a cocatalyst. As compared to photoanodes modified with IrOx or CoO(OH)x, the TiO2–CNx/NiOx photoanodes excel by the very negative photocurrent onset potential (0 V vs. RHE), which we ascribe to good hole-extracting properties of NiOx. However, the comparatively low Faradaic efficiencies for oxygen evolution (∼18%) and dramatically decreased operational stability of the photoanodes indicate that the extracted holes do not efficiently oxidize water to dioxygen, but instead accumulate in the NiOx particles and increase thus the oxidative photodegradation of the photoanodes. Our study highlights the fact that employing outstanding electrocatalysts like NiOx in photoelectrochemical water-splitting systems does not necessarily lead to satisfactory results, especially when the photoelectrode cannot be operated at optimal pH due to light absorber stability issues.

Strategies to improve the photoelectrochemical performance of hematite nanorod-based photoanodes

An overview on the recent progress in experimental strategies used to improve the photoelectrochemical response of hematite nanorod-based photoanodes for solar water splitting is provided. Emerging areas are identified that will require attention as the search continues for stable and efficient visible-light driven water oxidation systems that exploit the rational construction of different interface junctions. Increasing efforts have been focused on enhancing the performance of hematite-based photoanodes via morphology control, element doping, co-catalysts, surface modification, heterojunction construction, and via a combination between them. Particular attention has been given to heterojunctions, as these structures are more likely to utilize the benefits provided by combining elements with distinct properties, exhibiting functional behavior at the interfacial region, and increasing solar energy conversion by synergistic effects.

Visible light-driven simultaneous water oxidation and quinone reduction by a nano-structured conjugated polymer without co-catalysts.

In artificial photosynthesis, chemists are aiming to borrow principles from natural photosynthesis to develop photoelectrochemical cells (PEC) for water splitting. The water plastoquinone photo-oxidoreductase enzyme, also known as photosystem II, uses light to perform the four-electron, four-proton oxidation of water to dioxygen and stores reducing equivalents in reduced forms of quinones which are ultimately used in dark reactions for the synthesis of energy-rich molecules. We report a nano-structured semiconducting conjugated polymer based on poly(diphenylbutadiyne) (nano-PDPB) and its photocatalytic activities towards the water oxidation reaction under visible light irradiation when dispersed in water in the absence of any sacrificial agents or co-catalysts. Charge recovery at the nano-PDPB directly or delayed in time was exemplified by the reduction of quinone acting as a hydrogen reservoir. In the absence of quinones as electron acceptors H2O2 formation was detected, stemming from the partial reduction of O2.

Recent Advances in Catalysts Based on Molecular Cubanes for Visible Light-Driven Water Oxidation

Recent Advances in Catalysts Based on Molecular Cubanes for Visible Light-Driven Water Oxidation