High Photocatalytic Activity For Hydrogen Evolution Research Articles

Photochemical tuning of dynamic defects for high-performance atomically dispersed catalysts.

Developing active and stable atomically dispersed catalysts is challenging because of weak non-specific interactions between catalytically active metal atoms and supports. Here we demonstrate a general method for synthesizing atomically dispersed catalysts via photochemical defect tuning for controlling oxygen-vacancy dynamics, which can induce specific metal-support interactions. The developed synthesis method offers metal-dynamically stabilized atomic catalysts, and it can be applied to reducible metal oxides, including TiO2, ZnO and CeO2, containing various catalytically active transition metals, including Pt, Ir and Cu. The optimized Pt-DSA/TiO2 shows unprecedentedly high photocatalytic hydrogen evolution activity, producing 164 mmol g-1 h-1 with a turnover frequency of 1.27 s-1. Furthermore, it generates 42.2 mmol gsub-1 of hydrogen via a non-recyclable-plastic-photoreforming process, achieving a total conversion of 98%; this offers a promising solution for mitigating plastic waste and simultaneously producing valuable energy sources.

Aggregation of oligomeric Ir photosensitizers promotes efficient and long-lifetime photocatalytic hydrogen evolution

This work first reports the aggregation effect of Ir oligomeric photosensitizers, which provides extra intermolecular electron transfer path and leads to a high photocatalytic hydrogen evolution activity and a long lifetime of the photosensitizers.

Enhanced electron delocalization on pyrimidine doped graphitic carbon nitride for boosting photocatalytic hydrogen evolution

The photocatalytic activity of graphitic carbon nitride (g-C3N4) depends to a large extent on its morphology and electronic band structure. In order to design a photocatalyst with suitable structural property and high efficiency of photo-generated carrier separation, herein, the pyrimidine doped g-C3N4 is prepared by a conventional one-pot copolymerization of urea and 2,4,6-Triaminopyrimidine (TAP). Such TAP organic molecule can not only regulate the electronic structure of conjugated system and distort heptazine units, but also affect the polymerization of precursor urea. As expected, the optimized photocatalyst shows a high photocatalytic hydrogen evolution activity of 453 μmol·h−1 under visible light irradiation, which is 4.41 times over that of pure g-C3N4. Such enhanced photocatalytic performance is attributed to the introduction of pyrimidine ring which facilitates the electrons delocalization in the in-plane structure, enlarges the specific surface area, and broadens the visible light absorption range.

Design of ultrathin CoAl-LDHs/ZnIn2S4 with strong interfacial bonding and rich oxygen vacancies for highly efficient hydrogen evolution activity

Designing a semiconductor-based heterostructure photocatalyst is very important way to enhance the hydrogen production activity. Here, a novel 2D/2D CoAl-LDHs/ZnIn2S4 S-scheme heterostructure with an ultrathin structure was synthesized by electrostatic attraction between CoAl-LDHs and ZnIn2S4 nanosheets. The presence of oxygen vacancies in the monolayer CoAl-LDHs nanosheet promotes the formation of Co-SX bonds, which serve as charge transfer channels at the interface of the CoAl-LDHs/ZnIn2S4 heterostructure. The ultrathin CoAl-LDHs/ZnIn2S4 exhibits broadened light absorption in the near-infrared range due to the occurrence of Co-SX chemical bonds. The CoAl-LDHs/ZnIn2S4 with a mass ratio of 1:2 demonstrated the highest photocatalytic hydrogen evolution activity (1563.64 μmol g−1 h−1) under the simulated sunlight, which is 4.6 and 9.7 times than that of the ZnIn2S4 and CoAl-LDHs/ZnIn2S4(bulk), respectively. The enhanced photocatalytic activity of ultrathin 2D/2D CoAl-LDHs/ZnIn2S4 should attributed to the shorter carriers path that benefit from the ultrathin structure and the quicker photogenerated charge transfer and the S-scheme migration pathway accelerated by the charge channel of Co-SX bonds. These new ideas should be inspiring for the design and construction of heterostructures for higher photocatalytic hydrogen evolution activity.

Realigning the melon chains in carbon nitride by rubidium ions to promote photo-reductive activities for hydrogen evolution and environmental remediation

The photocatalytic efficiency of polymeric carbon nitride (PCN) suffers from unsatisfactory charge separation because of its amorphous structure. Herein, we report a simple bottom-up method to synthesize a novel structure of rubidium ion inserted PCN (Rb-PCN), which involves the regular alignment of melon chains to endow a crystalline feature in PCN. The insertion of Rb+ decreased not only the N p electrons in the heptazine ring but also the plane angle of the heptazine motifs in the melon chain, which promoted the long-range periodicity and crystallinity of carbon nitride. This structurally rearranged crystalline Rb-PCN demonstrated considerably enhanced separation of charge carriers, resulting in six-fold higher photocatalytic hydrogen evolution activity than its amorphous counterpart. Furthermore, the photoexcited electrons can be efficiently trapped by O2 to generate H2O2, which facilitates the production of reactive oxygen species to inactivate bacteria and degrade organic pollutants, showing great potential for use in both energy and environmental applications.

A novel Co1.29Ni1.71O4/glycerolate-derived oxygen-vacancies-containing TiO2 composite for highly efficient photocatalytic hydrogen evolution

Charge separation and migration is still a big challenge for photocatalysis. Constructing heterojunction interface structure is a useful way to improve charge separation efficiency. Here, a novel glycerolate-derived n-type TiO2 with oxygen vacancies was hybridized with Co1.29Ni1.71O4 by a facial ultrasonication method to achieve such a purpose. The optimized 2.5 % Co1.29Ni1.71O4/TiO2 hybrid showed a photocatalytic hydrogen evolution rate of 1685 μmol g−1 h−1 under 365 nm LED light irradiation, 26.7-fold higher than that of pure TiO2 (63 μmol g−1 h−1). Besides, the hydrogen production amount kept a linear increase with the increase of irradiation time for the 2.5%Co1.29Ni1.71O4/TiO2 catalyst during a 24 h-long continuous hydrogen release test, confirming the excellent catalytic stability. Detailed characterizations demonstrated that Co1.29Ni1.71O4 nanosheet was closely contacted with TiO2 nanoparticles, which increases specific surface area and widens the light absorption window of TiO2. Moreover, Co1.29Ni1.71O4 addition facilitated highly efficient separation of photogenerated carriers and prolongs lifetimes of the excited electrons. First principles calculations confirmed that there existed strong interaction between Co1.29Ni1.71O4 and TiO2 in the composite, and electrons were directly transferred from Co1.29Ni1.71O4 to TiO2 at the interface by the Ni-O and Co-O pathway. All of these leaded to a high photocatalytic hydrogen evolution activity for the Co1.29Ni1.71O4/TiO2 composite. This work revealed Co1.29Ni1.71O4 to be a promising heterojunction counterpart material and able to promote photocatalysis through unique cross-boundary charge transfer.

An Efficient Electron Donor for Conjugated Microporous Polymer Photocatalysts with High Photocatalytic Hydrogen Evolution Activity.

Conjugated microporous polymers (CMPs) with donor-acceptor (D-A) molecular structure show high photocatalytic activity for hydrogen evolution due to the efficient light-induced electron/hole separation, which is mostly determined by the nature of electron donor and acceptor units. Therefore, the selection of electron donor and acceptor holds the key point to construct high performance polymer photocatalysts. Herein, two dibenzo[b,d]thiophene-S,S-dioxide (BTDO) containing CMP photocatalysts using tetraphenylethylene (TPE) or dibenzo[g,p]chrysene (DBC) as the electron donor to investigate the influence of the geometry of electron donor on the photocatalytic activity are design and synthesized. Compared with the twisted TPE donor, DBC has a planar molecular structure with extended π-conjugation, which promotes the charges transmission and light-induced electron/hole separation. As a result, the polymer DBC-BTDO produced from DBC donor shows a remarkable photocatalytic hydrogen evolution rate (HER) of 104.86mmolh-1 g-1 under full arc light (λ>300nm), which is much higher than that of the polymer TPE-BTDO (1.80mmolh-1 g-1 ), demonstrating that DBC can be an efficient electron donor for constructing D-A polymer photocatalysts with high photocatalytic activity for hydrogen evolution.

Ti3C2 MXene coupled with CdS nanoflowers as 2D/3D heterostructures for enhanced photocatalytic hydrogen production activity

As a novel co-catalyst, Ti3C2 MXene has an excellent prospect in the field of photocatalysis. Herein, the 2D/3D Ti3C2 MXene@CdS nanoflower (Ti3C2@CdS) composite was successfully synthesized by a hydrothermal method. The combination of 2D Ti3C2 MXene and 3D CdS nanoflowers can promote carrier transfer and separation, which can improve the performance of CdS. Compared to pure CdS nanoflowers, Ti3C2@CdS composite presents lower photoluminescence intensity, longer fluorescence lifetime, higher photocurrent density and smaller electrochemical impedance. The Ti3C2@CdS composite with 15 wt% Ti3C2 adding amount presents high photocatalytic hydrogen evolution activity (88.162 μmol g−1 h−1), 91.57 times of pure CdS. The improved photocatalytic activity of Ti3C2@CdS composite is ascribed to the addition of lamellar Ti3C2 MXene, which improves the electrical conductivity of the photocatalytic system and effectively accelerates the excited electrons transfer from CdS to Ti3C2 MXene.

Insight into the Real Efficacy of Graphene for Enhancing Photocatalytic Efficiency: A Case Study on CVD Graphene-TiO2 Composites

Construction of graphene-based composites has been a popular theme in solar energy harvesting and conversion, yet the understanding of the real efficacy of graphene for enhancing photocatalytic efficiency is hampered by the gap of physicochemical properties between the defined graphene and the graphene used in research laboratories. Here, we purposely synthesize a high-quality chemical vapor deposition graphene (CVDG) as a model material to integrate with TiO2, which demonstrates that photocatalytic performance can be greatly improved by controlling the quality of graphene. Under the same reaction conditions, the as-prepared CVDG-TiO2 displays a 26.2-times and 10-times higher photocatalytic hydrogen evolution activity than bare TiO2 and its counterpart, reduced graphene oxide (RGO)-TiO2, respectively. Experimental characterization reveals that the few-layer CVDG with a low defect density is able to better unleash the excellent electrical conductivity potential of graphene, by which the separation and lifetime of photoexcited charge carriers of graphene-TiO2 could be improved more efficiently. The research highlights the significant effect of the quality of graphene for the construction of more efficient semiconductor-graphene composites, which is anticipated to inform ongoing efforts on exploiting high-quality graphene to advance solar energy harvesting and conversion.

Robust hollow tubular ZnIn2S4 modified with embedded metal-organic-framework-layers: Extraordinarily high photocatalytic hydrogen evolution activity under simulated and real sunlight irradiation

This work reported a facile one-step method for constructing hollow tubular ZnIn2S4 modified by metal-organic-framework-layers (MOFL) with In-MOF as precursor to be efficient photocatalysts (ZnIn2S4-MOFL) for robust photocatalytic hydrogen evolution (PHE). The dominant catalyst of ZnIn2S4 and cocatalytic role of MOFL synergistically promoted the separation of electron and hole pairs due to the direct Z-scheme photocatalytic system, leading to an extraordinarily high PHE activity. The density functional theory (DFT) results revealed the remarkably decreased density of states (DOS) of ZnIn2S4 after coupling with the organic ligands of MOFL, indeed proving an effectively suppressed recombination of charge carriers and benefited the performance of photocatalytic reactions. Experimental PHE results showed that a large number of hydrogen bubbles were visible to naked eyes and the optimal hydrogen evolution reached 28.2 mmol/g/h, the highest value reported so far among ZnIn2S4-based photocatalysts, and almost 14.8 times higher than that of pristine ZnIn2S4. More importantly, the superior apparent quantum efficiencies (AQEs) of 22.67 % at monochromatic light (350 nm) and the stable hydrogen generation capability (5.7 mmol/g/h) under real sunlight irradiation all confirmed a promising catalyst of ZnIn2S4-MOFL for hydrogen evolution applications.

Interfacial modification and band modulation for dramatically boosted photocatalytic hydrogen evolution

Interfacial modification and band modulation to narrow the band gap and improve light-harvesting ability of TiO2 are promising strategies to dramatically promote photocatalytic activity. Herein, efficient Co(OH)2-TiO2 nanocomposites were reasonably designed and constructed by a facile room temperature solid-state synthetic strategy for interfacial modification and matched band gap to achieve the conversion of solar energy to hydrogen. Modifying transition metal hydroxide Co(OH)2 on commercial TiO2 can effectively narrow the band gap and accelerate the separation and migration of photo-induced carriers, which will extend light absorption range and facilitate more electrons transferring to the surface of photocatalyst, therefore the reducibility of photocatalysts is enhanced. The modified photocatalyst exhibits high photocatalytic hydrogen evolution activity and stability. Specifically, the obtained TCO-0.6 shows excellent photocatalytic hydrogen evolution rate of 21343.01 μmol g−1 and is 23 times superior to commercial TiO2. This work not only emphasizes a facile strategy for interfacial modification and band modulation under mild condition, but also provides a novel avenue for improving the performance of photocatalytic hydrogen evolution.

Enhancement of photocatalytic hydrogen evolution from dye–sensitized amide–functionalized carbon nanospheres by superior adsorption performance

Due to the high–efficiency and stable solar–to–hydrogen conversion efficiency, dye–sensitized photocatalytic hydrogen evolution is considered to be one of the ideal ways to solve today's energy and environmental problems. The coupling interaction between sensitization matrix and light–absorbing dye play an important role for the activity of the dye–sensitized photocatalytic hydrogen evolution. In this work, amide–functionalized carbon nanospheres as a new–style sensitization matrix is prepared by a low–cost and uncomplicated two–step liquid phase reactions. Because amide groups on the surface of carbon nanospheres add additional adsorption sites by introducing H–bonding and enhancing coupling interaction between the sensitization matrix and dye molecules, the adsorption capacity of amide–functionalized carbon nanospheres increase 6.7 times compared with bare carbon nanospheres. Based on the material excellent adsorption performance, the Eosin Y dye–sensitized amide–functionalized carbon nanospheres with Pt co–catalyst exhibits high–efficiency activity for H2 generation (607.4 μmol for testing 2 h), which is 14.3 and 6.4 times higher photocatalytic hydrogen evolution activity than Pt and carbon nanospheres with Pt assist. Moreover, the highest apparent quantum efficiency of photocatalyst can reach to 32.9% at 430 nm. The significantly improved photocatalytic hydrogen evolution performance of catalyst could be mainly ascribed to enhance amino groups adsorption active sites, which can fix the light–absorbing dyes on the surface of sensitization matrix and shorten the transmission distance of photogenerated charges.

CoAl LDH@Ni-MOF-74 S-Scheme Heterojunction for Efficient Hydrogen Evolution

Metal–organic frameworks (MOFs) and layered double hydroxides (LDHs) have been considered to be one of the most promising and worthy hot spot materials to develop advanced catalysts for efficient hydrogen evolution due to their prominent characteristics, including unique structures, environmentally friendly nature, high redox activities, and homogeneously effective utilization of transition metal atoms. In this work, the delicate S-scheme heterojunction photocatalyst, CoAl LDH@Ni-MOF-74, was rationally designed and successfully constructed by coupling Ni-MOF-74 with CoAl LDH based on their peculiar structure, excellent electronic properties, and opposite surface potential for enhancing hydrogen generation activity under visible light irradiation. The CoAl LDH nanolayers evenly and dispersedly load on the surface of Ni-MOF-74. The CoAl LDH@Ni-MOF-74 exhibited higher photocatalytic hydrogen evolution activity compared with Ni-MOF-74 and CoAl LDH alone, mainly because the formation of the CoAl LDH@Ni-MOF-74 S-scheme heterojunction accelerated the recombination of several electrons (from conduction band (CB) of Ni-MOF-74) and holes (from valence band (VB) of CoAl LDH) and prevented the recombination of other electrons (from CB of CoAl LDH) and holes (from VB of Ni-MOF-74).

A Z-scheme BiVO4/CdS hollow sphere with a high photocatalytic hydrogen evolution activity

A Z-scheme BiVO4/CdS hollow sphere was prepared by a simple yet effective design. According to the morphology of the composite, the photo-generated carriers were spatially separated due to the well-designed structure and bandgap alignment. The highest HER activity reached 4.2 mmol·g−1·h−1 which is 105 and 1.75 folds of CdS nanoparticles and CdS/Pt nnanoparticles, respectively. The samples were investigated by TEM, XRD, XPS, UV–vis spectrum and BET. The band structure of BiVO4/CdS heterojunction was discussed.

Bmmim]6[In10Se16Cl4]·(MIm)2: an organic-ligand free discrete T3 cluster for efficient hydrogen evolution under visible light irradiation.

An indium selenide [Bmmim]6[In10Se16Cl4]·(MIm)2 (Bmmim = 1-butyl-2,3-dimethylimidazolium, MIm = 1-methylimidazole) cluster has been synthesized and characterized. The discrete T3 cluster could be stably dispersed in dimethyl sulfoxide, exhibiting photocatalytic hydrogen evolution activity at least six times that of the pristine in the solid state due to the exposure of more active sites.

Unraveling the Interfacial Charge Migration Pathway at the Atomic Level in a Highly Efficient Z-Scheme Photocatalyst.

A highly efficient Z-scheme photocatalytic system constructed with 1D CdS and 2D CoS2 exhibited high photocatalytic hydrogen-evolution activity of 5.54 mmol h-1 g-1 with an apparent quantum efficiency of 10.2 % at 420 nm. More importantly, its interfacial charge migration pathway was unraveled: The electrons are efficiently transferred from CdS to CoS2 through a transition atomic layer connected by Co-S5.8 coordination, thus resulting in more photogenerated carriers participating in surface reactions. Furthermore, the charge-trapping and charge-transfer processes were investigated by transient absorption spectroscopy, which gave an estimated charge-separation yield of approximately 91.5 % and a charge-separated-state lifetime of approximately (5.2±0.5) ns in CdS/CoS2 . This study elucidates the key role of interfacial atomic layers in heterojunctions and will facilitate the development of more efficient Z-scheme photocatalytic systems.

Further activation of g-C3N4 with less N-H defects for enhancing photocatalytic hydrogen evolution

g-C3N4 was further treated with N2-assisted pyrolysis, during which some gaseous derivatives were released from the surface of g-C3N4 at 550 °C, producing novel carbon nitride (CNH) with the high surface area and less N-H defects. As a result, CNH shows 14 times higher photocatalytic hydrogen evolution activity than the pristine g-C3N4. To some extent, this work provides deep understanding for the activation or reactivation of g-C3N4 in the catalysis.

Enhanced Photoelectrochemical and Photocatalytic Properties of CdS Nanowires Decorated with Ni3S2 Nanoparticles under Visible Light Irradiation

Ni3S2/CdS nanocomposites based on zero-dimensional Ni3S2 nanoparticles (NPs) and one-dimensional CdS nanowires (NWs) were synthesized via a two-step solvothermal approach. These nanocomposites were characterized using a combination of experimental techniques, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectroscopy, and photoelectrochemistry method. The Ni3S2/CdS nanocomposites exhibit much higher photocatalytic hydrogen evolution activity than individual CdS NWs or Ni3S2 NPs under visible light irradiation (λ ≥ 400 nm) from water. Photoelectrochemical (PEC) and photocatalytic properties of the Ni3S2/CdS nanocomposites were investigated as a function of the molar ratio between Ni3S2 and CdS. In addition, ultrafast transient absorption (TA) spectroscopy was employed to probe the charge carrier dynamics, which is about four times shorter in 10%-Ni3S2/CdS than pure CdS NWs. These results suggest efficient charge transfer between CdS and Ni3S2 at the interface, which is desired for PEC and photocatalytic applications.

Noble-metal-free Ni3N/g-C3N4 photocatalysts with enhanced hydrogen production under visible light irradiation.

The majority of visible-light photocatalysts show very low hydrogen evolution activity in the absence of noble metal co-catalysts due to their fast carrier recombination rate. Metallic interstitial nitrides have been recognized as excellent hydrogen evolution electrocatalysts and therefore are promising alternative co-catalysts for photocatalytic hydrogen production. Herein we report a low-cost, efficient, noble-metal-free visible-light-driven hydrogen evolution photocatalyst composed of Ni3N/g-C3N4 heterostructures. The as-prepared photocatalyst with a Ni3N loading content of 3 wt% shows a high hydrogen evolution rate of 169 μmol g-1 h-1, which is slightly higher than that of 3 wt% Pt modified g-C3N4 (152.0 μmol g-1 h-1). The Ni3N/g-C3N4 photocatalysts also exhibit remarkable photostability for four consecutive cycles of photocatalytic activity tests with a total reaction time of 12 hours. The excellent performance of the Ni3N/g-C3N4 photocatalyst is ascribed to the formation of an optimal number of Ni3N/g-C3N4 heterojunctions that improve photogenerated carrier separation and offer abundant photocatalytically active sites for surface reactions.

Understanding the charge separation and transfer in mesoporous carbonate-doped phase-junction TiO2 nanotubes for photocatalytic hydrogen production

Novel mesoporous carbonate-doped phase-junction TiO2 nanotubes were fabricated for the first time by a general simple and cost-effective strategy, namely, olive oil-assisted electrospinning. The as-prepared mesoporous carbonate-doped phase-junction TiO2 nanotubes show a high photocatalytic hydrogen evolution activity of 6108 μmol h−1 g−1, which is nearly six times higher than that of the commercially available P25. This outstanding photocatalytic performance originates from the morphology, electronic, crystal and textural structures of the photocatalysts. The refined porous structure can increase the optical path by multiple reflection effect, thus enhancing light harvesting. Particularly, first-principles calculations suggest that doping TiO2 with carbonate can effectively reduce the bandgap of TiO2, thus the absorbance of TiO2 in visible light region can be highly enhanced. Moreover, anatase-rutile phase junctions were elaborately introduced into TiO2 nanotubes by changing the anneal temperature and the roles of phase junctions are studied by photoelectrochemical measurements, which reveal that appropriate phase junction interface can significantly enhance the charge separation and transfer, hence achieving about 2 and 18 times photocurrent density enhancement compared to pristine anatase and rutile phase samples, respectively. Our study not only demonstrates a facile and eco-friendly strategy to synthesize highly efficient porous TiO2-based nanotubes photocatalysts, but also provides a new strategy for rational design and synthesis of advanced photocatalysts by combining the strong synergistic effects of the morphology, electronic, crystal and textural structures.