High H2 Production Activity Research Articles

Synergistic Effect of Rutile and Brookite TiO2 for Photocatalytic Formic Acid Dehydrogenation.

Solar energy is an ideal clean and inexhaustible energy source. Solar-driven formic acid (FA) dehydrogenation is one of the promising strategies to address safety and cost issues related to the storage, transport, and distribution of hydrogen energy. For FA dehydrogenation, the O-H and C-H cleavages are the key steps, and developing a photocatalyst with the ability to break these two bonds is critical. In this work, both density functional theory (DFT) calculation and experimental results confirmed the positive synergistic effect between brookite and rutile TiO2 for O-H and C-H cleavage in HCOOH. Further, brookite TiO2 is beneficial to the generation of the •OH radical and significantly promotes C-H cleavage in formate. Under optimized conditions, the H2 production efficiency of FA dehydrogenation can reach up to 30.4 μmol·mg-1·h-1, which is the highest value compared with similar reported TiO2-based systems and over 1.7 times the reported highest value of Au0.75Pd0.25/TiO2 photocatalysts. More importantly, after more than 42 days (>500 h) of irradiation, the system still demonstrated high H2 production activity, indicating the potential for practical application. This work provides a valuable strategy to improve both the efficiency and stability of photocatalytic FA dehydrogenation under mild conditions.

Electron-transfer dynamics and photocatalytic H2-production activity of PbS@Cu2S nanocomposites

BackgroundLead citrate is a precursor that can be prepared by recycling the spent lead paste of lead-acid batteries. Lead citrate is used to synthesize lead oxide, which can be repeatedly utilized for the lead-acid battery application. MethodsWe report a new application of lead citrate precursor to synthesize PbS@Cu2S nanomaterials for photocatalytic H2 production. PbS@Cu2S was prepared by microwave-assisted hydrothermal and ion-exchange processes. The electron-transfer dynamics and H2-production activity of PbS@Cu2S photocatalysts were studied. Significant findingsA S-scheme heterojunction is proposed based on the results of Tauc plots, ultraviolet photoelectron spectroscopy, the electron paramagnetic resonance scavenger test, and in situ near-edge X-ray absorption fine structure (NEXAFS) analysis. Results of in situ NEXAFS reveal the transfer of photoexcited electrons from PbS to Cu2S. By loading an optimized amount of Cu2S, the carrier separation and photocatalytic activity of PbS@Cu2S photocatalysts are improved. This technology can transform the lead citrate precursor to the PbS@Cu2S photocatalyst with excellent high H2 production activity (3824 μmol g−1 h−1).

Construction of multi-interfacial charge transfer paths in the NiS/CdS@CuS composite for efficient and broadband visible light photocatalytic H2 production

Broad-spectrum response and high charge separation are two important prerequisites and also challenges for a photocatalyst to achieve excellent activity. Herein, we developed a closely-contacted NiS/CdS@CuS hybrid photocatalyst to construct multi-interfacial charge transfer paths to address these two challenges. Different from previously reported, limited charge transfer for the CdS system, the synergy between photoinduced interfacial charge transfer (IFCT) at the intimate CdS/CuS interface and the superior H2 production cocatalyst (NiS) enables a multi-interfacial charge transfer, which greatly accelerates charge separation and achieves broadband H2 production. The optimal NiS/CdS@CuS composite exhibits the high H2 production activity of 25.02 mmol g−1 h−1 with an apparent quantum efficiency of 27.21% at 420 nm. This activity is even higher than that of the optimized Pt/CdS system. The creation of photoinduced IFCT allows the photocatalytic H2 production of CdS extended to 610 nm. Multiple comparison systems are constructed to understand the reaction mechanisms and highlight the importance of synergy between the three components. This work supplies a paradigm for fabricating efficient H2 production photocatalyst with both enhanced charge transfer dynamics and expanded light response range.

Cadmium (II) Organo Tetrakis-[1,2]-Oxathiin (CdOTOT): A 3D sandwiched frameworks with efficient hydrogen production

For over a decade, the structure, reactivity, and mechanism of graphene based photocatalysts have been of great interest for hydrogen (H2) generation. Several studies have been done on the edge side groups (ESGs) of graphene oxide (GO), but the basal plane groups (BPGs)-epoxide and hydroxide have acquired far less attention. This is because the GO layers are strongly held with van der waals forces as well as H-bonding which prevents the foreign body from entering inside the layers. To overcome these problems, this study presents the successful synthesis and application of four coordinated sandwiched (FCS) Cadmium (II) Organo Tetrakis-[1,2]-Oxathiin (CdOTOT) in rGO-CdS composite (A 3D sandwiched framework). Additionally, experimental outcomes have been further supported using density functional theory (DFT), which suggest that CdOTOT is more stable than its precursors as well as thermodynamically favourable. The CdOTOT shows high H2 production activity ∼ 67.5 mmol/g or 13.5 mmol/g/h in presence of 1 % Pt cocatalyst and sacrificial reagents (Na2S/Na2SO3). It is around 33 times higher than pristine CdS, and stable up to around 15 hrs without adding any cocatalyst. This mesmerising outcome is over with reported various CdS-rGO based photocatalysts. The higher activity was further explained through the proposed mechanism and observed low electronic work function of CdOTOT. This innovative and extendable (with other metals) approach provides a revolutionary impact on numerous cutting-edge research applications like photocatalysis, water splitting, solar cell, etc.

Direct Z-scheme photochemical hybrid systems: Loading porphyrin-based metal-organic cages on graphitic-C3N4 to dramatically enhance photocatalytic hydrogen evolution

The rational design of photochemical molecular device (PMD) and its hybrid system has great potential in improving the activity of photocatalytic hydrogen production. A series of Pd6L3 type metal-organic cages, denoted as MOC-Py-M (M = H, Cu, and Zn), are designed for PMDs by combining metalloporphyrin-based ligands with catalytically active Pd2+ centers. These metal-organic cages (MOCs) are first successfully hybridized with graphitic carbon nitride (g-C3N4) to form direct Z-scheme heterogeneous MOC-Py-M/g-C3N4 (M = H, Cu, and Zn) photocatalysts via π–π interactions. Benefiting from its better light absorption ability, the MOC-Py-Zn/g-C3N4 catalyst exhibits high H2 production activity under visible light (10348 μmol g−1 h−1), far superior to MOC-Py-H/g-C3N4 and MOC-Py-Cu/g-C3N4. Moreover, the MOC-Py-Zn/g-C3N4 system obtains an enhanced turn over number (TON) value of 32616 within 100 h, outperforming the homogenous MOC-Py-Zn (TON of 507 within 100 h), which is one of the highest photochemical hybrid systems based on MOC for visible-light-driven hydrogen generation. This confirms the direct Z-scheme heterostructure can promote effective charge transfer, expand the visible light absorption region, and protect the cages from decomposition in MOC-Py-Zn/g-C3N4. This work presents a creative example that direct Z-scheme PMD-based systems for effective and persistent hydrogen generation from water under visible light are obtained by heterogenization approach using homogeneous porphyrin-based MOCs and g-C3N4 semiconductors.

Electron transfer dynamics and enhanced H2 production activity of hydrangea-like BiOBr/Bi2S3-based photocatalysts with Cu-complex as a redox mediator

A composite photocatalyst consisting of the BiOBr/Bi2S3 heterojunction and a Cu complex exhibited high H2 production activity through an efficient transport of charge by redox couple Cu(II)/Cu(I) of the complex. BiOBr was prepared by a microwave solvothermal method. Then, the BiOBr/Bi2S3 composite was prepared as a heterojunction photocatalyst by an ion-exchange process. The copper complex was then introduced as a co-catalyst or a redox mediator. The morphology, crystal properties, optical properties, surface chemistry, photocurrent response, and photocatalytic activity of these BiOBr/Bi2S3/copper complex composites were investigated. The formation of a BiOBr/Bi2S3 heterojunction and the introduction of Cu complex improved the performance of the photocatalysts. For the first time, operando X-ray absorption spectra were recorded in situ to unveil the local interaction at the reactant-photocatalyst interface toward the photocatalysis reaction of BiOBr/Bi2S3-Cu complex photocatalyst in the sacrificial agent solution (Na2S, Na2SO3).

A Robust Photocatalytic Hybrid Material Composed of Metal-Organic Cages and TiO2 for Efficient Visible-Light-Driven Hydrogen Evolution.

The design of photochemical molecular devices (PMDs) for photocatalytic H2 production from water is a meaningful but challenging subject currently. Herein, a Pd2 L4 type metal-organic cage (denoted as MOC-Q2) is designed as a PMD, which consists of two catalytic centers (Pd2+ ) and four photosensitive ligands (L-2) with four pyridine anchoring groups. Subsequently, the MOC-Q2 is combined with TiO2 to form TiO2 -MOC-Q2 hybrid materials with different MOC-Q2 contents by a facile sol-gel method, which have micro/mesoporous structures and large surface areas. The optimized TiO2 -MOC-Q2 (6.5 wt%) exhibits high H2 production activity (7.9 mmol g-1 h-1 within 5 h) and excellent durability, giving a TON value of 23477 or 11739 (based on MOC-Q2 or Pd moles) after recycling for 7 rounds. By contrast, the pure MOC-Q2 only shows an ordinary photocatalytic H2 production rate (0.84 mmol g-1 h-1 within 5 h) in the homogeneous system. It can be deduced that TiO2 drives the photocatalysis and simultaneously acts as the structure promoter. This study presents a meaningful and distinctive attempt of a new approach for the design and development of MOC-based heterogeneous photocatalysts.

Simultaneous realization of direct photodeposition and high H2-production activity of amorphous cobalt sulfide nanodot-modified rGO/TiO2 photocatalyst

Simultaneous realization of direct photodeposition and high H2-production activity of amorphous cobalt sulfide nanodot-modified rGO/TiO2 photocatalyst

Graphitic C2N3: An Allotrope of g-C3N4 Containing Active Azide Pentagons as Metal-Free Photocatalyst for Abundant H2 Bubble Evolution

A g-C3N4 allotrope, a curved leaf-like graphitic C2N3 (g-C2N3) with an intrinsic spontaneous polarization electric field (ISPEF), has been constructed for efficient solar energy conversion into H2 energy via photocatalytic H2O splitting. The curved leaf-like π-delocalization g-C2N3 was composed of aromatic azide pentagons and normal triazine hexagons obtained by cycloaddition between -C≡N groups from dicyandiamide polymerization and azide from the heat-treated polypyrrole fibers. Under light irradiation (λ > 420 nm), photo-generated charges are driven to separate efficiently and transfer from bulk to active sites of the surface under ISPEF that is opposite to the Coulomb field. Consequently, without any cocatalyst, g-C3N4 allotrope demonstrates a very high H2-production activity of 14.9 mmol g-1 h-1 accompanied by a lot of H2 bubbles, which is 2.6 times of g-C3N4 loading with Pt. In comparison with the reported metal-free photocatalysts or those supported with noble metals, g-C3N4 allotrope (i.e., leaf-like g-C2N3) is confirmed to be the best metal-free photocatalyst for H2O splitting into H2 fuel so far. The contructed leaf-like g-C2N3 with SPEF supplies a suitable platform for solar energy conversion into H2 fuel, which actively contributes to clean energy production.

Long-term Operation of Continuous Culture of the Hyperthermophilic archaeon, Thermococcus onnurineus for Carbon Monoxide-dependent Hydrogen Production

In this study, we performed a kinetic analysis of CO-dependent H2 production by metabolically engineered Thermococcus onnurineus NA1, MC01 in terms of the cell activity as well as mass transfer rate. We conducted continuous cultures with varying dilution rate, CO flow rate, or agitation speed. Despite oscillations in cell density, the cultures reached steady states at all operating conditions. As the dilution rate increased from 0.1 to 0.3 h−1, specific activity of H2 production (SAHP) and volumetric cell production rate were linearly increased. Also, the SAHP remained almost constant at the fixed dilution rate of 0.3 h−1 even though the CO transfer rate was changed by adjusting the CO flow rate or the agitation speed. This relationship could be expressed as a typical Luedeking-Piret model, implying that high cell density culture with a sufficient growth rate is essential to obtain higher H2 productivity. On the other hand, more elevated CO transfer at the same dilution rate improved H2 production rate (HPR) by the increase of the cell density, not in the rise of SAHP. Through the continuous culture, 108 mmol/g-cell/h and 121 mmol/L/h of SAHP and HPR, respectively, could be achieved at a dilution rate of 0.3 h−1 with CO supply rate of 0.07 vvm and agitation speed of 700 rpm. Considering high H2 production activity and long-term stability of the strain over 1,000 h, MC01 is confirmed to have an outstanding potential for CO-dependent H2 production.

A rapid preparation of PPECu and plasmonic Ag/PPECu nanocomposites with high performance for photocatalytic hydrogen production

A new and rapid synthetic method toward polymer phenylethnylcopper (PPECu) nanowires is developed. PPECu nanowires have been firstly fabricated through using ascorbic acid instead of methanol as reducing agent. The preparation time of PPECu can be decreased from 48 to 2 h, even at a lower temperature. Ag/PPECu nanocomposites were prepared by the in situ reaction of PPECu and Ag (NH3)2+ ions with different concentrations. Ag/PPECu photocatalysts showed high visible-light H2 production activity, which originated from the combined action of electrons transfer, sacrificing reagent and SPR effect of Ag nanoparticles.

Bimetallic Manganese Cobalt Phosphide Nanodots–Modified Graphitic Carbon Nitride for High‐Performance Hydrogen Production

It is a huge challenge for exploiting new photocatalysts with low‐cost cocatalysts in place of precious metals to realize high‐efficiency H2 production from water. Herein, a new photocatalyst with a high H2 production activity is prepared via modification of bimetallic manganese cobalt phosphide (Mn0.67Co1.33P) nanodots on graphitic carbon nitride (g‐C3N4). Moreover, the largest H2 production rate of 113.1 μmol h−1 is obtained over the Mn0.67Co1.33P/g‐C3N4‐5 sample, which is about 2.75 times than that of Pt/g‐C3N4‐5 (41.2 μmol h−1). The high‐performance H2 production suggests page a page down that the modification effect of Mn0.67Co1.33P nanodots improves the visible harvest ability and separation efficiency of charge carriers. A typical example to improve the photocatalytic H2 production performance by fabricating heterostructures using bimetallic phosphide to modify graphitic carbon nitride is provided.

Unveiling Charge-Separation Dynamics in CdS/Metal–Organic Framework Composites for Enhanced Photocatalysis

Photocatalytic water splitting for H2 production becomes one of the most favorable pathways for solar energy utilization, while the charge-separation dynamics in composite photocatalysts is largely elusive. In the present work, CdS-decorated metal–organic framework (MOF) composites, namely, CdS/UiO-66, have been synthesized and exhibit high H2 production activity from photocatalytic water splitting, far surpassing the MOF and CdS counterparts, under visible light irradiation. Transient absorption (TA) spectroscopy has been adopted in this report to unveil the charge-separation dynamics in CdS/UiO-66 composites, a key process that dictates their function in photocatalysis. We show that, in addition to the preferable formation of fine CdS particles assisted by the MOF, effective electron transfer, which occurs from excited CdS to UiO-66, significantly inhibits the recombination of photogenerated charge carriers, ultimately boosting the photocatalytic activity for H2 generation. This report on charge-separat...

Amorphous FeCoPOx nanowires coupled to g-C3N4 nanosheets with enhanced interfacial electronic transfer for boosting photocatalytic hydrogen production

The building of an optimized interface between the cocatalyst and the photoactive materials is significant for understanding the charge transfer mechanism and designing high-performance catalysts at atomic level, however, still a great challenge. Herein, we develop a new method to synthesize a class of hybrid photocatalyst by coupling amorphous FeCoPOxnanowires (FeCoPOx(NWs)) tog-C3N4 photocataysts (denote as FeCoPOx(NWs)-C3N4) for greatly boosting the photocatalytic activity, which shows 3.5-fold higher H2-production activity than the state-of-art crystalline FeCoPOy nanoparticles/g-C3N4 hybrid photocataysts (denote as FeCoPOy(NPs)-C3N4). The structure analysis by X-ray absorption fine structure (XAFS) reveals that the Fe species in FeCoPOx(NWs)-C3N4 owns a lower coordination number than that in FeCoPOy(NPs)-C3N4, which can contribute to the formation of strong interface between FeCoPOx(NWs) and g-C3N4. The first-principles simulation confirms that the amorphous FeCoPOx(NWs) not only can build a stable interface with g-C3N4 by forming more Fe-N bonds, but also own an optimized electronic properties for enhancing electron transfer from g-C3N4 to FeCoPOx(NWs). The strong interfacial electronic effect of FeCoPOx(NWs)-C3N4 contributes to its high H2-production activity.This work not only develops a new method to prepare the high-performance low-cost cocatalyst as Pt alternative for H2 production, but also provide a new insight into optimizing the interface between cocatalyst and photocatalyst for photocatalytic reaction.

Characterization of the [NiFeSe] hydrogenase from Desulfovibrio vulgaris Hildenborough.

The [NiFeSe] hydrogenases are a subgroup of the well-characterized family of [NiFe] hydrogenases, in which a selenocysteine is a ligand to the nickel atom in the binuclear NiFe active site instead of cysteine. These enzymes display very interesting catalytic properties for biological hydrogen production and bioelectrochemical applications: high H2 production activity, bias for H2 evolution, low H2 inhibition, and some degree of O2 tolerance. Here we describe the methodologies employed to study the [NiFeSe] hydrogenase isolated from the sulfate-reducing bacteria D. vulgaris Hildenborough and the creation of a homologous expression system for production of variant forms of the enzyme.

One-step facile synthesis and high H2-evolution activity of suspensible CdxZn1-xS nanocrystal photocatalysts in a S2-/SO32- system.

For a CdS-based photocatalyst, both the photocorrosion resistance and the rapid H2-production reaction are highly required for improving its photocatalytic H2-production performance. In this study, a facile strategy was reported to simultaneously realize an improved photocorrosion resistance and rapid interfacial H2-evolution reaction of CdxZn1-xS solid-solution photocatalysts in a sulfur-rich S2-/SO32- solution. Here, the suspensible CdxZn1-xS nanocrystal photocatalysts are prepared by a one-step co-precipitation route through the direct introduction of Zn2+/Cd2+ mixing ions in a sulfur-rich Na2S-Na2SO3 solution, and the resultant CdxZn1-xS nanocrystals (ca. 5 nm) display a suspensible structure owing to the numerous and selective adsorption of S2-/SO32- on the surface of these CdxZn1-xS nanocrystals. It is found that the bandgap structure of CdxZn1-xS (from 2.25 to 3.52 eV) nanocrystals can be easily controlled by adjusting the Cd2+/Zn2+ molar ratio. The photocatalytic experimental results suggested that the suspensible CdxZn1-xS nanocrystal photocatalysts clearly displayed an excellent photocatalytic H2-production performance, and the suspensible Cd0.6Zn0.4S nanocrystals exhibit the highest photocatalytic H2-generation performance of 717.19 μmol h-1, a value higher than that of the sole CdS (320.99 μmol h-1) and ZnS (5.89 μmol h-1) by a factor of 2.2 and 121.8 times, respectively. Based on the experimental results, a possible S2- active site-mediated mechanism accounted for the high H2-production activity of the suspensible CdxZn1-xS nanocrystals, namely the numerous adsorbed S2- ions not only function as efficient hole scavengers to rapidly consume the photogenerated holes, resulting in an improved photocorrosion resistance of suspensible CdxZn1-xS nanocrystals, but also serve as effective H+-capturing active sites to accelerate the interfacial H2-production reaction. Meanwhile, an optimum bandgap structure of suspensible CdxZn1-xS nanocrystals is also extremely required for promoting the photocatalytic H2-production activity. This research may provide advanced insights for developing stable and high-activity photocatalytic materials.

Precisely locate Pd-Polypyrrole on TiO2 for enhanced hydrogen production

Noble metal (Pd) and conducting polymer (PPy) are considered as two promising candidates to modify photocatalyst. In this work, TiO2-Pd-PPy was prepared via one-step simultaneous photoreduction of palladium chloride and photooxidation of pyrrole monomers on TiO2 (P25). The TiO2-0.5Pd-0.6PPy exhibits higher H2 production rate of 601 μmol h−1 under UV–visible light irradiation, which is about 3.1 and 11.7 times than that of TiO2-0.5Pd and TiO2, respectively. One-step simultaneous photo-deposited method allows for precisely locating Pd and PPy on TiO2, in other words, the places where Pd and PPy nanoparticles deposited are just the active sites that the photo-induced electrons and holes participate in the photocatalytic reaction, which is beneficial for separation of photo-induced carriers. As a result, TiO2-0.5Pd-0.6PPy synthesized by one-step simultaneous photo-deposited method displays much higher H2 production activity than TiO2-0.5Pd-0.6PPy synthesized by other methods.

A flexible bio-inspired H2-production photocatalyst

Photocatalytic hydrogen generation from water splitting offers a viable potential solution for utilizing solar energy. Here we report a feasible synthesis of flexible bio-inspired Zn0.5Cd0.5S@PAN (polyacrylonitrile) mat-shaped photocatalyst with leaf-like structure, which shows high photocatalytic H2-production activity with a rate of 475μmolh−1 per 50mg of the photocatalyst and an apparent quantum efficiency of 27.4% at 420nm. The hierarchically porous structure of the mat-shaped Zn0.5Cd0.5S@PAN greatly enhances the molecular diffusion/transfer kinetics, and enlarges the utilization efficiency of light through the multiple reflections and scattering effect. Moreover, a good dispersion of Zn0.5Cd0.5S nanoparticles (NPs) on the surface of PAN nanofibers prevents their aggregation. These features account for high H2-production activity of Zn0.5Cd0.5S@PAN. Remarkably, the integrity and flexibility of Zn0.5Cd0.5S@PAN mat-shaped photocatalyst facilitate their separation and re-use after photocatalytic reaction. Hierarchically porous leaf-like mat-shaped photocatalysts with high photocatalytic activity and stability should also find potential applications in solar cells, catalysis, separation and purification processes.

Biomolecule-assisted hydrothermal synthesis of ZnxCd1−xS nanocrystals and their outstanding photocatalytic performance for hydrogen production

To achieve scalable applications in solar hydrogen production, it is necessary to develop visible-light-responsive photocatalysts that are highly efficient, cost-effective, stable and environmentally-benign. Here narrow bandgap Zn–Cd–S solid solution photocatalysts (Eg = 2.11–2.53 eV) were prepared via a facile and green hydrothermal strategy under mild conditions. Amazingly, over the naked Zn0.5Cd0.5S photocatalyst, an extraordinarily high H2 production activity in Na2S–Na2SO3 aqueous solution is achieved up to 18.3 mmol h−1 g−1 with an apparent quantum efficiency of 73.8% per 50 mg under 420 nm light irradiation, which, to our knowledge, outperforms cocatalyst-free metal sulfide photocatalysts previously reported to date. Such super high performance arises from the enhanced visible-light-absorption capacity, suitable conduction and valence band potential together with the facilitated charge transport in Zn–Cd–S solid solutions. This work may open an avenue for the green preparation of inexpensive photocatalysts for solar H2 production.

Citrobacter amalonaticus Y19 for constitutive expression of carbon monoxide-dependent hydrogen-production machinery

BackgroundCitrobacter amalonaticus Y19 is a good biocatalyst for production of hydrogen (H2) from oxidation of carbon monoxide (CO) via the so-called water–gas-shift reaction (WGSR). It has a high H2-production activity (23.83 mmol H2 g−1 cell h−1) from CO, and can grow well to a high density on various sugars. However, its H2-production activity is expressed only when CO is present as an inducer and in the absence of glucose.ResultsIn order to avoid dependency on CO and glucose, in the present study, the native CO-inducible promoters of WGSR operons (CO dehydrogenase, CODH, and CODH-dependent hydrogenase, CO-hyd) in Y19 were carefully analyzed and replaced with strong and constitutive promoters screened from Y19. One engineered strain (Y19-PR1), selected from three positive ones after screening ~10,000 colonies, showed a similar CO-dependent H2-production activity to that of wild-type Y19, without being affected by glucose and/or CO. Compared with wild-type Y19, transcription of the CODH operon in Y19-PR1 increased 1.5-fold, although that of the CO-hyd operon remained at a similar level. To enhance the activity of CO-Hyd in Y19-PR1, further modifications, including an increase in gene copy number and engineering of the 5′ untranslated region, were attempted, but without success.ConclusionsConvenient recombinant Y19-PR1 that expresses CO-dependent H2-production activity without being limited by CO and glucose was obtained.