Multimodal Analysis of Light-Driven Water Oxidation in Nanoporous Block Copolymer Membranes**

Heterogeneous light-driven catalysis is a cornerstone of sustainable energy conversion. Most catalytic studies focus on bulk analyses of the hydrogen and oxygen evolved, which impede the correlation of matrix heterogeneities, molecular features, and bulk reactivity. Here, we report studies of a heterogenized catalyst/photosensitizer system using a polyoxometalate water oxidation catalyst and a model, molecular photosensitizer that were co-immobilized within a nanoporous block copolymer membrane. Via operando scanning electrochemical microscopy (SECM), light-induced oxygen evolution was determined using sodium peroxodisulfate (Na₂S₂O₈) as sacrificial electron acceptor. Ex situ element analyses provided spatially resolved information on the local concentration and distribution of the molecular components. Infrared attenuated total reflection (IR-ATR) studies of the modified membranes showed no degradation of the water oxidation catalyst under the reported light-driven conditions.     

基于多金属氧酸盐催化剂的光驱动产氢研究进展

能源和环境问题是21世纪人类面临的两个巨大挑战.鉴于此,为了实现人类社会的可持续发展,寻求能够替代化石能源的安全无污染可再生能源已迫在眉睫.太阳光驱动水分解是实现太阳能转化生产清洁可再生氢能的理想方法,其分解产物氢气和氧气在燃烧释放能量的同时生成洁净无污染的可饮用水,实现了完美的可持续能量循环,对于解决当今全球面临的能源危机与环境污染问题具有巨大的应用价值.然而,长期以来光驱动水分解所面临的巨大难题是半反应动力学非常缓慢,通常需要克服较高的能量势垒,导致整体能量转化效率低.利用非贵金属制备高催化效能、低成本的水分解催化材料成为该领域的研究热点和难点.目前,已报道的光驱动产氢催化剂可以被归纳为两大类:均相催化剂和异相催化剂.均相催化剂通常具备高催化活性、高选择性以及易于进行机理研究等优点,而异相催化剂则具备廉价、易得和高稳定性等优点;然而它们也存在一些不容忽视的问题,如均相催化剂的低稳定性、易分解失活,异相催化剂表面易被毒化失活、低催化转化数及转化频率等.如何设计合成兼具二者优点的产氢催化剂吸引了领域内研究者的广泛关注.作为一类新兴的多电子转移催化剂,多金属氧酸盐因其丰富多样的合成策略以及高度可调的物理化学及光化学性质,已被广泛用于催化水分解制氢气研究.该类多金属氧酸盐催化剂具备了介于均相分子化合物和异相金属氧化物之间的结构,这种独特的结构赋予它们同时具备均相分子催化剂的高活性、高选择性、高可控性、易于进行机理性研究等优点,又具备异相金属氧化物催化剂的廉价易得及稳定性高等优势.随着研究的开展,基于多金属氧酸盐的光催化产氢体系已由当初的贵金属辅助逐渐转变为丰产元素参与,光源的选择方面也从与太阳光谱匹配度低的紫外光转变为可见光.本文对30多年来基于多金属氧酸盐催化剂的光驱动产氢成果进行了综述,主要包括有/无贵金属辅助的多金属氧酸盐,多酸@金属有机框架复合物,多酸-半导体复合材料在紫外光或可见光条件下的光催化产氢研究;同时讨论总结了不同类型催化体系的反应机理;并对该领域的未来发展趋势及研究方向进行了展望.     

Photosensitized hydrogen evolution from water using conjugated polymers wrapped in dendrimeric electrolytes

High-efficiency light-driven hydrogen evolution from water was demonstrated by using poly(phenyleneethynylene) bearing negatively charged, [G3] poly(benzyl ether) dendrimeric side groups 3(L4) as photosensitizer. Three-dimensional wrapping of the conjugated backbone suppressed self-quenching of the photoexcited state, while methyl viologen (MV(2+)), a positively charged electron acceptor, was trapped on its negatively charged surface, to form a spatially separated donor-acceptor supramolecular complex. Studies with time-resolved fluorescence spectroscopy showed that the quenching rate constant (k(q) = 1.2 x 10(15) M(-1) s(-1)) is much greater than diffusion control rate constants. Upon excitation of 3(L4) in the presence of a mixture of MV(2+), triethanolamine (TEOA; sacrificial electron donor), and a colloidal PVA-Pt, hydrogen evolution took place with an overall efficiency of 13%, 1 order of magnitude better than precedent examples. Comparative studies with several reference sensitizers showed that spatial isolation of the conjugated backbone and its long-range pi-electronic conjugation, along with electrostatic interactions on the exterior surface, play important roles in achieving the efficient photosensitized water reduction.     

Bioinspired Artificial Photosynthetic Systems

Mimicking photosynthesis using artificial systems, as a means for solar energy conversion and green fuel generation, is one of the holy grails of modern science. This perspective presents recent advances towards developing artificial photosynthetic systems. In one approach, native photosystems are interfaced with electrodes to yield photobioelectrochemical cells that transform light energy into electrical power. This is exemplified by interfacing photosystem I (PSI) and photosystem II (PSII) as an electrically contacted assembly mimicking the native Z-scheme, and by the assembly of an electrically wired PSI/glucose oxidase biocatalytic conjugate on an electrode support. Illumination of the functionalized electrodes led to light-induced generation of electrical power, or to the generation of photocurrents using glucose as the fuel. The second approach introduces supramolecular photosensitizer nucleic acid/electron acceptor complexes as functional modules for effective photoinduced electron transfer stimulating the subsequent biocatalyzed generation of NADPH or the Pt-nanoparticle-catalyzed evolution of molecular hydrogen. Application of the DNA machineries for scaling-up the photosystems is demonstrated. A third approach presents the integration of artificial photosynthetic modules into dynamic nucleic acid networks undergoing reversible reconfiguration or dissipative transient operation in the presence of auxiliary triggers. Control over photoinduced electron transfer reactions and photosynthetic transformations by means of the dynamic networks is demonstrated.     

Consecutive Charging of a Perylene Bisimide Dye by Multistep Low-Energy Solar-Light-Induced Electron Transfer Towards H2 Evolution

A photocatalytic system containing a perylene bisimide (PBI) dye as a photosensitizer anchored to titanium dioxide (TiO₂) nanoparticles through carboxyl groups was constructed. Under solar-light irradiation in the presence of sacrificial triethanolamine (TEOA) in neutral and basic conditions (pH 8.5), a reaction cascade is initiated in which the PBI molecule first absorbs green light, giving the formation of a stable radical anion (PBI^.−), which in a second step absorbs near-infrared light, forming a stable PBI dianion (PBI²⁻). Finally, the dianion absorbs red light and injects an electron into the TiO₂ nanoparticle that is coated with platinum co-catalyst for hydrogen evolution. The hydrogen evolution rates (HERs) are as high as 1216 and 1022 μmol h⁻¹ g⁻¹ with simulated sunlight irradiation in neutral and basic conditions, respectively.     

Consecutive Charging of a Perylene Bisimide Dye by Multistep Low‐Energy Solar‐Light‐Induced Electron Transfer Towards H2 Evolution

A photocatalytic system containing a perylene bisimide (PBI) dye as a photosensitizer anchored to titanium dioxide (TiO₂) nanoparticles through carboxyl groups was constructed. Under solar‐light irradiation in the presence of sacrificial triethanolamine (TEOA) in neutral and basic conditions (pH 8.5), a reaction cascade is initiated in which the PBI molecule first absorbs green light, giving the formation of a stable radical anion (PBI^.?), which in a second step absorbs near‐infrared light, forming a stable PBI dianion (PBI^2?). Finally, the dianion absorbs red light and injects an electron into the TiO₂ nanoparticle that is coated with platinum co‐catalyst for hydrogen evolution. The hydrogen evolution rates (HERs) are as high as 1216 and 1022 μmol h^?1 g^?1 with simulated sunlight irradiation in neutral and basic conditions, respectively.     

Energy Transfer in a Hybrid IrIII Carbene–PtII Acetylide Assembly for Efficient Hydrogen Production

A new heterometallic supramolecular complex, consisting of an iridium carbene‐based unit appended to a platinum terpyridine acetylide unit, representing a new Ir^III–Pt^II structural motif, was designed and developed to act as an active species for photocatalytic hydrogen production. The results also suggested that a light‐harvesting process is essential to realize the solar‐to‐fuel conversion in an artificial system as illustrated in the natural photosynthetic system.     

An artificial [FeFe]-hydrogenase mimic with organic chromophore-linked thiolate bridges for the photochemical production of hydrogen

An artificial [FeFe]-hydrogenase ([FeFe]-H₂ase) mimic 3II, consisting of dual organic chromophores covalently assembled to the [Fe₂S₂] active site, was constructed for light-driven hydrogen evolution. The structural conformation of synthetic photocatalyst was characterized crystallographically and spectroscopically. The photo-induced intramolecular electron transfer was evidently demonstrated by the combination of electrochemical, steady-state, and transient absorption spectroscopic studies. Finally, a remarkable activity was obtained in the present photocatalytic system, indicating the covalent incorporation of photosensitizer and catalytic center as a promising strategy to construct inexpensive, easily accessible [FeFe]-H₂ase model photocatalysts.     

Solar Fuels: Visible‐Light‐Driven Generation of Dihydrogen at p‐Type Silicon Electrocatalysed by Molybdenum Hydrides

We show that a robust molybdenum hydride system can sustain photoelectrocatalysis of a hydrogen evolution reaction at boron‐doped, hydrogen‐terminated, p‐type silicon. The photovoltage for the system is about 600–650 mV and the current densities, which can be sustained at the photocathode in non‐catalytic and catalytic regimes, are similar to those at a photoinert vitreous carbon electrode. The kinetics of electrocatalysed hydrogen evolution at the photocathode are also very similar to those measured at vitreous carbon—evidently visible light does not significantly perturb the catalytic mechanism. Importantly, we show that the doped (1–10 Ω cm) p‐type Si can function perfectly well in the dark as an ohmic conductor and this has allowed direct comparison of the cyclic voltammetric behaviour of the response of the system under dark and illuminated conditions at the same electrode. The p‐type Si we have employed optimally harvests light energy in the 600–700 nm region and with 37 mW cm^?2 illumination in this range; the light to electrochemical energy conversion is estimated to be 2.8 %. The current yield of hydrogen under broad tungsten halide lamp illumination at 90 mW cm^?2 is (91±5) % with a corresponding chemical yield of (98±5) %.     

Supramolecular Control of Singlet Oxygen Generation

Singlet oxygen (¹O₂) is the excited state electronic isomer and a reactive form of molecular oxygen, which is most efficiently produced through the photosensitized excitation of ambient triplet oxygen. Photochemical singlet oxygen generation (SOG) has received tremendous attention historically, both for its practical application as well as for the fundamental aspects of its reactivity. Applications of singlet oxygen in medicine, wastewater treatment, microbial disinfection, and synthetic chemistry are the direct results of active past research into this reaction. Such advancements were achieved through design factors focused predominantly on the photosensitizer (PS), whose photoactivity is relegated to self-regulated structure and energetics in ground and excited states. However, the relatively new supramolecular approach of dictating molecular structure through non-bonding interactions has allowed photochemists to render otherwise inactive or less effective PSs as efficient ¹O₂ generators. This concise and first of its kind review aims to compile progress in SOG research achieved through supramolecular photochemistry in an effort to serve as a reference for future research in this direction. The aim of this review is to highlight the value in the supramolecular photochemistry approach to tapping the unexploited technological potential within this historic reaction.     

Development of Strong Visible-Light-Absorbing Cyclometalated Iridium(III) Complexes for Robust and Efficient Light-Driven Hydrogen Production

Weak light absorption of common Ir(III) complexes (e. g., using phenylpyridine as the ligand) has hindered their applications in photocatalytic hydrogen generation from water as an efficient photosensitizer. To address this issue, a series of cyclometalated Ir(III) complexes (Ir1–Ir5), featuring different electron-donating substituents to enhance the absorptivity, have been synthesized and studied as photosensitizers (PSs) for light-driven hydrogen production from water. Ir6–Ir7 were prepared as fundamental systems for comparisons. Electron donors, including 9-phenylcarbazole, triphenylamine, 4,4′-dimethoxytriphenylamine, 4,4′-di(N-hexylcarbazole)triphenylamine moieties were introduced on 6-(thiophen-2-yl)phenanthridine-based cyclometalating (C^N) ligands to explore the donor effect on the hydrogen evolution performance of these cationic Ir(III) complexes. Remarkably, Ir4 with 4,4′-dimethoxytriphenylamine achieved the highest turn-over number (TON) of 12 300 and initial turnover frequency (TOF_i) of 394 h⁻¹, with initial activity (activity_i) of 547 000 μmol g⁻¹ h⁻¹ and initial apparent quantum yield (AQY_i) of 9.59 %, under the illumination of blue light-emitting diodes (LEDs) for 105 hours, which demonstrated a stable three-component photocatalytic system with high efficiency. The TON (based on n(H₂)/n(PSr)) in this study is the highest value reported to date among the similar photocatalytic systems using Ir(III) complexes with Pt nanoparticles as catalyst. The great potential of using triphenylamine-based Ir(III) PSs in boosting photocatalytic performance has also been shown.     

Visible-Light Augmented Lithium Storage Capacity in a Ruthenium(II) Photosensitizer Conjugated with a Dione-Catechol Redox Couple

Controlling redox activity of judiciously appended redox units on a photo-sensitive molecular core is an effective strategy for visible light energy harvesting and storage. The first example of a photosensitizer - electron donor coordination compound in which the photoinduced electron transfer step is used for light to electrical energy conversion and storage is reported. A photo-responsive Ru-diimine module conjugated with redox-active catechol groups in [Ru(II)(phenanthroline-5,6-diolate)₃]⁴⁻ photosensitizer can mediate photoinduced catechol to dione oxidation in the presence of a sacrificial electron acceptor or at the surface of an electrode. Under potentiostatic condition, visible light triggered current density enhancement confirmed the light harvesting ability of this photosensitizer. Upon implementation in galvanostatic charge-discharge of a Li battery configuration, the storage capacity was found to be increased by 100 %, under 470 nm illumination with output power of 4.0 mW/cm⁻². This proof-of-concept molecular system marks an important milestone towards a new generation of molecular photo-rechargeable materials.     

Strong,Self-Healable,and Recyclable Visible-Light-Responsive Hydrogel Actuators

The most pressing challenges for light-driven hydrogel actuators include reliance on UV light, slow response, poor mechanical properties, and limited functionalities. Now, a supramolecular design strategy is used to address these issues. Key is the use of a benzylimine-functionalized anthracene group, which red-shifts the absorption into the visible region and also stabilizes the supramolecular network through π–π interactions. Acid–ether hydrogen bonds are incorporated for energy dissipation under mechanical deformation and maintaining hydrophilicity of the network. This double-crosslinked supramolecular hydrogel developed via a simple synthesis exhibits a unique combination of high strength, rapid self-healing, and fast visible-light-driven shape morphing both in the wet and dry state. As all of the interactions are dynamic, the design enables the structures to be recycled and reprogrammed into different 3D objects.     

Light-driven hydrogen production by a hybrid complex of a [NiFe]-hydrogenase and the cyanobacterial photosystem I

In order to generate renewable and clean fuels, increasing efforts are focused on the exploitation of photosynthetic microorganisms for the production of molecular hydrogen from water and light. In this study we engineered a 'hard-wired' protein complex consisting of a hydrogenase and photosystem I (hydrogenase-PSI complex) as a direct light-to-hydrogen conversion system. The key component was an artificial fusion protein composed of the membrane-bound [NiFe] hydrogenase from the beta-proteobacterium Ralstonia eutropha H16 and the peripheral PSI subunit PsaE of the cyanobacterium Thermosynechococcus elongatus. The resulting hydrogenase-PsaE fusion protein associated with PsaE-free PSI spontaneously, thereby forming a hydrogenase-PSI complex as confirmed by sucrose-gradient ultracentrifuge and immunoblot analysis. The hydrogenase-PSI complex displayed light-driven hydrogen production at a rate of 0.58 mumol H(2).mg chlorophyll(-1).h(-1). The complex maintained its accessibility to the native electron acceptor ferredoxin. This study provides the first example of a light-driven enzymatic reaction by an artificial complex between a redox enzyme and photosystem I and represents an important step on the way to design a photosynthetic organism that efficiently converts solar energy and water into hydrogen.     

An AIE singlet oxygen generation system based on supramolecular strategy

The design of supramolecular system s with efficient singlet oxygen generation has attracted considerable interests.Herein,an AIE-based singlet oxygen generation system with chemiluminescence properties is reported in aqueous media based on supramolecular host-guest assembly between a water-soluble pillar[5]arene(WP5) and an AIE photosensitizer(TPEDM).The formed supramolecular nanoparticles exhibit significant singlet oxygen generation ability as well as enhanced fluorescence.In addition,by introducing catalase,this H_2 O_2-responsive supramolecular system shows increased ~1 O_2 generation efficiency compared with the blank nanoparticles.An efficient chemiluminescence system can also be achieved by entrapping an energy donor adamantane derivative(AMPPD).Moreover,the present system can function as nanoreactors to perform the photooxidation of dopamine to form polydopamine with visible light irradiation.This wo rk provides a new strategy for the construction of ~1 O_2 generation system based on supramolecular nanomaterials,which has potential applications in the fields such as chemiluminescence imaging and controlled photocatalysis.     

Highly Efficient Supramolecular Catalysis by Endowing the Reaction Intermediate with Adaptive Reactivity

A new strategy of highly efficient supramolecular catalysis is developed by endowing the reaction intermediate with adaptive reactivity. The supramolecular catalyst, prepared by host–guest complexation between 2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPO) and cucurbit[7]uril (CB[7]), was used for biphasic oxidation of alcohols. Cationic TEMPO⁺, the key intermediate, was stabilized by the electrostatic effect of CB[7] in aqueous phase, thus promoting the formation of TEMPO⁺ and inhibiting side reactions. Moreover, through the migration into the organic phase, TEMPO⁺ was separated from CB[7] and recovered the high reactivity to drive a fast oxidation of substrates. The adaptive reactivity of TEMPO⁺ induced an integral optimization of the catalytic cycle and greatly improved the conversion of the reaction. This work highlights the unique advantages of dynamic noncovalent interactions on modulating the activity of reaction intermediates, which may open new horizons for supramolecular catalysis.     

Hydrogen Production on a Hybrid Photocatalytic System Composed of Ultrathin CdS Nanosheets and a Molecular Nickel Complex

The production of clean and renewable hydrogen through water splitting by using solar energy has received much attention due to the increasing global energy demand. We report an economic and artificial photosynthetic system free of noble metals, consisting of ultrathin CdS nanosheets as a photosensitizer and nickel‐based complex as a molecular catalyst. Emission quenching and flash photolysis studies reveal that this hybrid system allows for effective electron transfer from the excited CdS nanosheets to the nickel‐based complex to generate reduced intermediate species for efficient hydrogen evolution. Notably, the unique morphological and structural features of the ultrathin CdS nanosheets contribute to the highly efficient photocatalytic performance. As a consequence, the resulting system shows exceptional activity and stability for photocatalytic hydrogen evolution in aqueous solution with a turnover number (TON) of about 28 000 versus catalyst and a lifetime of over 90 h under visible light irradiation.     

The Dual Role of Benzophenone in Visible‐Light/Nickel Photoredox‐Catalyzed C−H Arylations: Hydrogen‐Atom Transfer and Energy Transfer

A dual catalytic protocol for the direct arylation of non‐activated C(sp³)?H bonds has been developed. Upon photochemical excitation, the excited triplet state of a diaryl ketone photosensitizer abstracts a hydrogen atom from an aliphatic C?H bond. This inherent reactivity was exploited for the generation of benzylic radicals which subsequently enter a nickel catalytic cycle, accomplishing the benzylic arylation.     

Intermolecular electron transfer from photogenerated Ru(bpy)3+ to [2Fe2S] model complexes of the iron-only hydrogenase active site

Visible light-driven intermolecular electron transfer was observed from a reduced species Ru(bpy)3+, photogenerated via a reductive quenching of the ruthenium photosensitizer by a diethyldithiocarbamate anion, to bioinspired [2Fe2S] model complexes of the iron-only hydrogenase active site. The results indicate that Ru(bpy)32+ can act as a photoactive functional model of the [4Fe4S] cluster, playing the role of an electron-transfer relay. The photogenerated FeIFe0 species, which is proposed to be a crucial intermediate for proton reduction catalyzed electrochemically by the [2Fe2S] complexes, gives promise in the light-driven dihydrogen evolution using diiron complexes as surrogates of noble platinum catalysts.