Light-driven Hydrogen Evolution Research Articles

Vanadium tetrasulfide as an earth-abundant and noble-metal-free cocatalyst for a solar-to-hydrogen conversion reaction

Oxygen doped vanadium tetrasulfide (VS4) nanoparticles as an excellent cocatalyst was developed to facilitate efficient charge separation for visible light-driven hydrogen evolution reaction.

Selective adsorption of cysteamine molecules on Au/TiO2 boosts visible light-driven photocatalytic hydrogen evolution

Photocatalytic evolution of hydrogen is becoming a research hotspot because it can help to produce clean energy and reduce environmental pollution. Titanium dioxide (TiO2) and its composites are photocatalysts that are widely used in hydrogen evolution because of their high abundance in nature, low price, and high photo/chemical stability. However, their catalytic performances still need to be further improved, particularly in the visible light spectrum. Herein, visible light-driven photocatalytic evolution of hydrogen on Au/TiO2 nanocomposite is enhanced ∼ 10 folds by selectively functionalizing the nanocomposite with cysteamine molecules. It is revealed that the amine group (–NH2) in cysteamine favors the transfer and separation of photo-generated hot carriers. The rate of hydrogen produced can be further tuned by varying the ionization of the functionalized molecules at different pH values. This work provides a simple, convenient, and effective method that can be used to improve the photocatalytic evolution of hydrogen. This method can also be used for many other nanocatalysts (e.g., Au-MoS2, Au-BiVO4) and catalytic reactions (e.g., carbon dioxide reduction, nitrogen reduction).

Electron Coupling between the Linear-Conjugated Polymer Nanocluster and TiO2 Nanoparticle Enables a Quantum Leap for Visible Light-Driven Hydrogen Evolution

Considering the futuristic importance of hydrogen for the production of sustainable fuels; in this study, we developed an organic–inorganic hybrid semiconductor material comprising a heterogeneous interface between linear-conjugated polymers (PF3T) and titanium dioxide (TiO2) nanoparticles (denoted as PF3T@TiO2) for visible light-driven hydrogen production via water splitting. The as-developed PF3T@TiO2 composite exhibits a strong electron coupling between the terthiophene groups of PF3T and the oxygen atoms at the heterogeneous interface. Such a phenomenon induces an electron injection to TiO2 and effectively extends the lifetime of the photogenerated carriers of PF3T by several orders. Consequently, as compared to PF3T, the H2 production yield of PF3T@TiO2 is improved by 36-fold (11,783 μmol g–1 h–1), which outperforms all the existing hybrid materials in similar configurations. We envision current findings to be a strong foundation for further exploration of noble-metal free materials for photocatalytic hydrogen production.

Cover Feature: Ligand Substituent Effects on Light‐Driven Hydrogen Evolution by Cobalt(II) Tripodal Iminopyridine Catalysts under Precious‐Metal‐Free Conditions (Eur. J. Inorg. Chem. 31/2022)

The Cover Feature shows light-driven hydrogen evolution mediated by cobalt(II) tripodal iminopyridine complexes, using tri(n-butyl)triazatriagulenium (TATA+) as the organic sensitizer and triethylamine (TEA) as the sacrificial donor in aqueous acetonitrile. The activity of the complexes depends highly on the electronic properties of the substituents on the pyridine moieties. Under acidified conditions, the activity for H2 production was enhanced for the substituted catalysts. The 5-Cl derivative showed higher activity and lower catalytic potential (Ecat), which can be attributed to the stabilized CoI, favorable for the formation of CoIII(H). The improved H2 productivity and lower Ecat of the 5-CH3O, 6-CH3O, and 5-CH3 derivatives are suggested to be associated with the increased electron density on the CoIII(H) intermediate, which is more susceptible to protonation. More information can be found in the Research Article by J. Xiang, C.-F. Leung, C.-C. Ko and co-workers.

(Invited) Isotropic Hydrogen Evolution Reactions Induced By Plasmon Excitation

The efficient visible light energy conversion to the electrochemical reaction system is an important challenge in the field of photoelectrochemistry. The visible light driven hydrogen evolution reaction can be recognized as one of the important targets. Recently, the introduction of the plasmonic metal nanostructures into the semiconductor electrodes has been received much attention because the system which is recognized as the plasmonic photoconversion electrode realizes the visible light response characters. Although various systems have been achieved both the cathodic and anodic reactions through the selection of the materials, the molecular process or charge transfer process have not been fully understood yet. In this study, we have proposed the plasmonic cathode system by combining the p-type semiconductor electrode with the plasmonic nanostructures and examined the both the electron transfer process.We have confirmed the unique isotope effects which cannot be observed the conventional cathode system, reflecting novel characteristics of molecular process at the plasmonic cathodes.

Scanning Electrochemical Cell Microscopy: A Tool for Nanoscopic Deposition of Light-Driven Photocatalysts

Single and multi-barrel nanopipettes and nanopipette-based scanning electrochemical probe microscopy techniques like scanning electrochemical cell microscopy (SECCM) have gained significant attention as tools for localized, maskless, three-dimensional surface modifications [1,2]. The nanometer-sized orifices of nanopipettes allow delivering molecules to solution inducing concentration-confined electrodepositions. Also, electroless nanoscale depositions like the fountain pen technique [3] can be achieved by this technique.In this study, we present the deposition of various cobaloxime-based earth-abundant Co catalysts for light-driven hydrogen evolution reaction (HER) [4]. Arrays of different cobalt(III) complexes were deposited via SECCM and investigated in respect with their HER activity using scanning electrochemical microscopy (SECM) in combination of Pd-microsensors [5] for in situ hydrogen (H2) measurements under illumination. In addition, AFM studies revealed possible degradation of the commercially available neutral benchmark complex [Co(dmgH)2(py)Cl] in these studies. First results will also be presented in respect with the deposition of nanowires via co-deposition of HER catalyst and Ruthenium photosensitizer. First spatially resolved photocatalytic studies at such nanowires, which are characterized by high surface area, will be presented. Also, the influence of the substrate will also be discussed.

Efficient Access of Phenyl-Spaced 5,5′-Bridged Dinuclear Ruthenium Metal Complexes and the Effect of Dynamic Ligand Exchange on Catalysis

Herein, we present the synthesis, characterization, and light-driven hydrogen evolution activity of two dinuclear Ru-Pt complexes, Rup(ph)pPtX2 (X = Cl, I), comprising a new phenyl-spaced 5,5′-bis-phenanthroline p(ph)p bridging ligand. The two complexes only differ in the nature of the halide ligand at the catalytic center. Structural, photophysical, electrochemical, as well as photochemical characterization techniques revealed that the variations of single components of the intramolecular system provide a strong influence on the stability even in non-catalytic conditions. Interestingly, varying electron density at the catalytic center, mainly influenced by the coordinating halide at the catalytic center, as shown by 195Pt NMR spectroscopy, strongly influences the photocatalytic efficiency. Furthermore, intensive investigations on the potential catalytic mechanism showed that small structural variations (e.g., halide exchange) not only affect catalytic activity but can also switch the main catalytic mechanism from an initially molecular one to a fully heterogeneous, colloid-driven hydrogen evolution.

Electrochemical Properties of a Rhodium(III) Mono-Terpyridyl Complex and Use as a Catalyst for Light-Driven Hydrogen Evolution in Water.

Molecular hydrogen (H2) is considered one of the most promising fuels to decarbonize the industrial and transportation sectors, and its photocatalytic production from molecular catalysts is a research field that is still abounding. The search for new molecular catalysts for H2 production with simple and easily synthesized ligands is still ongoing, and the terpyridine ligand with its particular electronic and coordination properties, is a good candidate to design new catalysts meeting these requirements. Herein, we have isolated the new mono-terpyridyl rhodium complex, [RhIII(tpy)(CH3CN)Cl2](CF3SO3) (Rh-tpy), and shown that it can act as a catalyst for the light-induced proton reduction into H2 in water in the presence of the [Ru(bpy)3]Cl2 (Ru) photosensitizer and ascorbate as sacrificial electron donor. Under photocatalytic conditions, in acetate buffer at pH 4.5 with 0.1 M of ascorbate and 530 μM of Ru, the Rh-tpy catalyst produces H2 with turnover number versus catalyst (TONCat*) of 300 at a Rh concentration of 10 μM, and up to 1000 at a concentration of 1 μM. The photocatalytic performance of Ru/Rh-tpy/HA–/H2A has been also compared with that obtained with the bis-dimethyl-bipyridyl complex [RhIII(dmbpy)2Cl2]+ (Rh2) as a catalyst in the same experimental conditions. The investigation of the electrochemical properties of Rh-tpy in DMF solvent reveals that the two-electrons reduced state of the complex, the square-planar [RhI(tpy)Cl] (RhI-tpy), is quantitatively electrogenerated by bulk electrolysis. This complex is stable for hours under an inert atmosphere owing to the π-acceptor property of the terpyridine ligand that stabilizes the low oxidation states of the rhodium, making this catalyst less prone to degrade during photocatalysis. The π-acceptor property of terpyridine also confers to the Rh-tpy catalyst a moderately negative reduction potential (Epc(RhIII/RhI) = −0.83 V vs. SCE in DMF), making possible its reduction by the reduced state of Ru, [RuII(bpy)(bpy•−)]+ (Ru−) (E1/2(RuII/Ru−) = −1.50 V vs. SCE) generated by a reductive quenching of the Ru excited state (*Ru) by ascorbate during photocatalysis. A Stern–Volmer plot and transient absorption spectroscopy confirmed that the first step of the photocatalytic process is the reductive quenching of *Ru by ascorbate. The resulting reduced Ru species (Ru−) were then able to activate the RhIII-tpy H2-evolving catalyst by reduction generating RhI-tpy, which can react with a proton on a sub-nanosecond time scale to form a RhIII(H)-tpy hydride, the key intermediate for H2 evolution.

Incorporating NiCoP Cocatalyst into Hollow Rings of ZnCo-Metal–Organic Frameworks to Deliver Pt Cocatalyst like Visible Light Driven Hydrogen Evolution Activity

Incorporating NiCoP Cocatalyst into Hollow Rings of ZnCo-Metal–Organic Frameworks to Deliver Pt Cocatalyst like Visible Light Driven Hydrogen Evolution Activity

Insight into the Light-Driven Hydrogen Production over Pure and Rh-Doped Rutile in the Presence of Ascorbic Acid: Impact of Interfacial Chemistry on Photocatalysts.

The surface states of a semiconductor photocatalyst are essential for interfacial charge transfer in heterogeneous photocatalytic reactions. Here, we report that the light-driven hydrogen evolution reaction (HER) activity of 0.5 mol % Rh-doped rutile increases by more than 30 times compared with that of rutile when ascorbic acid is used as a sacrificial agent. Intensity-modulated photocurrent spectroscopy and surface photovoltage spectroscopy are employed to reveal the impact of surface states on the photo-oxidation reactions. It is found that the adsorption of ascorbic acid molecules dramatically reduces the activity of rutile due to coverage of the HER-active Ti sites. Nevertheless, for Rh-doped rutile, ascorbic acid neutralizes the Rh(IV) sites that would otherwise cause severe recombination of electron-hole pairs and resurrects its photocatalytic performance. This work demonstrates the key role of interfacial chemistry in photocatalytic reactions and provides a strategy for excavating the potential of various photocatalysts.

Enhanced solar light-driven hydrogen evolution of activated carbon sphere supported TiO2 hybrid nanocomposites

Solar-driven photocatalytic water splitting has a great promising impact and versatile green approach to producing hydrogen gas from solar energy for future energy storage devices. Furthermore, noble metal free catalysts have significant benefits in photon induced charge carrier transfer and faradic reaction for photocatalytic water splitting. Herein, we successfully synthesized the garlic peel-derived activated carbon sphere (ACS) and nanocomposite with TiO2 nanoparticles (NPs) using a facile hydrothermal technique for photocatalytic water splitting. The surface morphology, optical property and photocatalytic water splitting activity of prepared hybrid nanocomposite are thoroughly investigated with respect to the different ratios of ACS. In photocatalyst water splitting analysis, the optimal hybrid catalyst of ACS (6 % wt) with TiO2 NPs shows enhanced photocatalytic performance with the hydrogen production rate of 203 μmol g−1 h−1 under solar irradiation. The excellent solar driven water splitting performance of optimal hybrid catalyst has been owing to the enhanced photon harvesting ability and formation of the favorable pathway to effective charge separation and migration on TiO2/ACS surface. Thus, the proposed biomass supported nanocomposite scheme as a hybrid photocatalyst represents to develop the effective bio-mass assisted photocatalyst for solar water splitting process.

Novel NiCo2Se4/Mn0.5Cd0.5S photocatalyst for visible light-driven hydrogen evolution

Novel NiCo2Se4/Mn0.5Cd0.5S photocatalyst for visible light-driven hydrogen evolution

Surface Anchoring and Active Sites of [Mo3S13]2- Clusters as Co-Catalysts for Photocatalytic Hydrogen Evolution.

Achieving light-driven splitting of water with high efficiency remains a challenging task on the way to solar fuel exploration. In this work, to combine the advantages of heterogeneous and homogeneous photosystems, we covalently anchor noble-metal- and carbon-free thiomolybdate [Mo3S13]2– clusters onto photoactive metal oxide supports to act as molecular co-catalysts for photocatalytic water splitting. We demonstrate that strong and surface-limited binding of the [Mo3S13]2– to the oxide surfaces takes place. The attachment involves the loss of the majority of the terminal S22– groups, upon which Mo–O–Ti bonds with the hydroxylated TiO2 surface are established. The heterogenized [Mo3S13]2– clusters are active and stable co-catalysts for the light-driven hydrogen evolution reaction (HER) with performance close to the level of the benchmark Pt. Optimal HER rates are achieved for 2 wt % cluster loadings, which we relate to the accessibility of the TiO2 surface required for efficient hole scavenging. We further elucidate the active HER sites by applying thermal post-treatments in air and N2. Our data demonstrate the importance of the trinuclear core of the [Mo3S13]2– cluster and suggest bridging S22– and vacant coordination sites at the Mo centers as likely HER active sites. This work provides a prime example for the successful heterogenization of an inorganic molecular cluster as a co-catalyst for light-driven HER and gives the incentive to explore other thio(oxo)metalates.

A novel Z-scheme NH2-MIL-125(Ti)/Ti3C2 QDs/ZnIn2S4 photocatalyst with fast interfacial electron transfer properties for visible light-driven antibiotic degradation and hydrogen evolution

Herein, a novel all-solid-state Z-scheme NH2-MIL-125(Ti)/Ti3C2 MXene quantum dots/ZnIn2S4 (Ti-MOF/QDs/ZIS) photocatalyst was prepared, then applied for photocatalytic antibiotic (tetracycline and sulfamethazine) degradation and hydrogen evolution under visible light. The Z-scheme Ti-MOF/QDs/ZIS photocatalyst afforded very efficient degradation of tetracycline (TC, 96% in 50 min) and sulfamethazine (SMZ, 98% in 40 min), as well as a high rate of hydrogen generation (2931.9 μmol g-1 h−1) under visible light irradiation. Trapping studies showed superoxide radicals (•O2−) to be the main active species for antibiotic degradation, with the intermediates formed during antibiotic photo-oxidation identified by liquid chromatography-mass spectrometry. Photocatalyst recycling studies showed the Z-scheme composite photocatalyst to be stable during both antibiotic photodegradation and hydrogen generation experiments. The Ti3C2 MXene quantum dots facilitated electron transfer between the semiconducting components of Z-scheme composite photocatalyst. This work identifies a promising new Z-scheme photocatalyst system for water purification and solar hydrogen production.

Synergistic tailoring of band structure and charge carrier extraction in “green” core/shell quantum dots for highly efficient solar energy conversion

Environment-friendly colloidal core/shell quantum dots (QDs) with controllable optoelectronic characteristics are promising building blocks for future commercial solar technologies. Herein, we synergistically tailor the electronic band structure and charge carrier extraction of eco-friendly AgInS2 (AIS)/ZnS core/shell QDs via Mn-alloying and Cu-doping in the core and shell, respectively. It is demonstrated that the Mn-alloying in AIS core can broaden the band gap to facilitate delocalization of photogenerated electrons into the shell and further incorporation of Cu in the ZnS shell enables the creation of Cu-related states that capture the photogenerated holes from core, thus leading to charge carrier recombination and accelerated transfer of photogenerated electrons in the core/shell QDs. As-prepared Mn-AIS/ZnS@Cu QDs were assembled as light harvesters in a photoelectrochemical (PEC) device for light-driven hydrogen evolution, delivering a maximum photocurrent density of ∼ 6.4 mA cm−2 with superior device stability under standard one sun irradiation (AM 1.5G, 100 mW cm−2). Our findings highlight that simultaneously engineering the band alignment and charge carrier dynamics of “green” core/shell QDs endow the feasibility to design future high-efficiency and durable solar hydrogen production systems.

Defect-Mediated Electron Transfer in Pt-CuInS2/CdS Heterostructured Nanocrystals for Enhanced Photocatalytic H2 Evolution

The effective separation of photogenerated electrons and holes is the key to improve photocatalytic activity in hydrogen evolution reaction (HER). However, the mechanism of photoinduced charge transfer between the cocatalyst and the semiconducting heterojunction in a single nanocrystal is vague at present. Herein, the relationships between the crafted cocatalyst and the constructed semiconducting heterojunction in a single nanocrystal were verified. Manipulating these relationships will improve the performance of visible light-driven hydrogen evolution. As a model, we used CuInS2 (CIS) nanocrystals (NCs) modified by the cocatalyst platinum (Pt) NCs and the semiconductor cadmium sulfide (CdS), forming the ternary heterostructured NCs (HNCs). Under visible light irradiation, the photocatalytic activity in hydrogen evolution of Pt-CIS/CdS HNCs is 6.38 and 1.76 times higher than those of pristine CIS NCs and CIS/CdS HNCs, respectively. Transient absorption measurements certified that the high photocatalytic activity in the HER was attributed to the photoinduced electron transfer from the defect-mediated trap state in CIS to the cocatalyst Pt, which was superior to the direct Z-scheme heterojunction between CIS and CdS. This research paves a route for the design of a suitable cocatalyst and the formation of heterostructured semiconducting NCs for boosting the photocatalytic activity in solar energy conversion.

Triazine-Based Conjugated Microporous Polymers With Different Linkage Units for Visible Light-Driven Hydrogen Evolution.

Conjugated microporous polymers (CMPs), as a kind of two-dimensional material, have attracted extensive attention due to their advantages in visible light–driven photocatalytic splitting of water for hydrogen evolution. However, improving the microstructure and electronic structure of the material to enhance their photocatalytic performance for hydrogen evolution remains a challenge. We designed and reported two analogous CMPs including CMP-1 and CMP-2 that contain triazine and dibenzothiophene-S,S-dioxide units, which were prepared by Pd-catalyzed Suzuki-Miyaura coupling reaction. The main difference of two CMPs is that the triazine units are connected to benzene unit (CMP-1) or thiophene unit (CMP-2). Both of the CMPs exhibit excellent light capture capability, and compared with CMP-2, CMP-1 has faster separation rates and lower recombination rates for the charge carriers (electron/hole), and then, a higher hydrogen evolution rate was obtained from water decomposition reaction. We find the H2 production rate of CMP-1 can be up to 9,698.53 μmol g−1h −1, which is about twice of that of CMP-2. This work suggests that molecular design is a potent method to optimize the photocatalytic performance toward hydrogen evolution of the CMPs.

In situ photodeposition of platinum clusters on a covalent organic framework for photocatalytic hydrogen production

Photocatalytic hydrogen production has been considered a promising approach to obtain green hydrogen energy. Crystalline porous materials have arisen as key photocatalysts for efficient hydrogen production. Here, we report a strategy to in situ photodeposit platinum clusters as cocatalyst on a covalent organic framework, which makes it an efficient photocatalyst for light-driven hydrogen evolution. Periodically dispersed adsorption sites of platinum species are constructed by introducing adjacent hydroxyl group and imine-N in the region of the covalent organic framework structural unit where photogenerated electrons converge, leading to the in situ reduction of the adsorbed platinum species into metal clusters by photogenerated electrons. The widespread platinum clusters on the covalent organic framework expose large active surface and greatly facilitate the electron transfer, finally contributing to a high photocatalytic hydrogen evolution rate of 42432 μmol g−1 h−1 at 1 wt% platinum loading. This work provides a direction for structural design on covalent organic frameworks to precisely manipulate cocatalyst morphologies and positions at the atomic level for developing efficient photocatalysts.

Enhanced visible Light-Driven photocatalytic hydrogen evolution and stability for noble Metal-Free MoS2/Zn0.5Cd0.5S heterostructures with W/Z phase junctions

A series of composite heterojunction-MoS2/Zn0.5Cd0.5S photocatalysts free of noble metal ions was prepared using a simple hydrothermal method. The X-ray diffraction spectra of the MoS2/Zn0.5Cd0.5S composites exhibit three strong intensive peaks, thereby explaining the existence of wurtzite (CdS) and zinc blende (ZnS) in the form of the wurtzite/zinc-blende phase junctions. Microstructural studies indicate that the sample displays a typical cubic crystal structure and that the MoS2 with flower-like structure uniformly wraps the granular Zn0.5Cd0.5S. X-ray photoelectron, Fourier transform infrared, and UV–Vis diffuse reflectance spectroscopic methods confirm that the heterojunction, which possesses outstanding photoresponse ability, is constructed between Zn0.5Cd0.5S nanoparticles and MoS2 nanoflowers. The fluorescence spectroscopy, surface photocurrent spectroscopy, and electrochemical studies indicate that Zn0.5Cd0.5S nanoparticles with specific amount of MoS2 nanoflowers can effectively suppress the recombination of photoinduced charge carriers of the composites. Therefore, pristine Zn0.5Cd0.5S nanoparticles loaded with 3%MoS2 exhibit optimum performance of hydrogen production (388.2 μmol/h), which is 1.3 times that of pristine Zn0.5Cd0.5S nanoparticles. A plausible mechanism for enhanced photocatalysis is provided in terms of the heterojunction assisted effective separation of charge carriers that are generated by irradiation.

Insights into the different mechanistic stages of light-induced hydrogen evolution of a 5,5'-bisphenanthroline linked RuPt complex.

Herein, the synthesis in conjunction with the structural, electrochemical, and photophysical characterization of a 5,5'-bisphenanthroline (phenphen) linked heterodinuclear RuPt complex (Ru(phenphen)Pt) and its light-driven hydrogen formation activity are reported. A single crystal X-ray diffraction (SC-XRD) analysis identified a perpendicular orientation of the two directly linked 1,10-phenanthroline moieties. The disruption of π-conjugation blocks intramolecular electron transfer as evidenced by a comparative time-resolved optical spectroscopy study of Ru(phenphen)Pt and the reference complexes Ru(phenphen) and Ru(phenphen)Ru. However, reductive quenching is observed in the presence of an external electron donor such as triethylamine. Irradiating Ru(phenphen)Pt with visible light (470 nm) leads to H2 formation. We discuss a potential mechanism that mainly proceeds via Pt colloids and provide indications that initial hydrogen generation may also proceed via a molecular pathway. As previous reports on related heterodinuclear RuPt-based photocatalysts revealed purely molecular hydrogen evolution, the present work thus highlights the role of the bridging ligand in stabilizing the catalytic center and consequently determining the mechanism of light-induced hydrogen evolution in these systems.