Solar-to-hydrogen efficiency of more than 9% in photocatalytic water splitting.

Production of hydrogen fuel from sunlight and water, two of the most abundant natural resources on Earth, offers one of the most promising pathways for carbon neutrality1-3. Some solar hydrogen production approaches, for example, photoelectrochemical water splitting, often require corrosive electrolyte, limiting their performance stability and environmental sustainability1,3. Alternatively, clean hydrogen can be produced directly from sunlight and water by photocatalytic water splitting2,4,5. The solar-to-hydrogen (STH) efficiency of photocatalytic water splitting, however, has remained very low. Here we have developed a strategy to achieve a high STH efficiency of 9.2 per cent using pure water, concentrated solar light and an indium gallium nitride photocatalyst. The success of this strategy originates from the synergistic effects of promoting forward hydrogen-oxygen evolution and inhibiting the reverse hydrogen-oxygen recombination by operating at an optimal reaction temperature (about 70 degrees Celsius), which can be directly achieved by harvesting the previously wasted infrared light in sunlight. Moreover, this temperature-dependent strategy also leads to an STH efficiency of about 7 per cent from widely available tap water and sea water and an STH efficiency of 6.2 per cent in a large-scale photocatalytic water-splitting system with a natural solar light capacity of 257 watts. Our study offers a practical approach to produce hydrogen fuel efficiently from natural solar light and water, overcoming the efficiency bottleneck of solar hydrogen production.

Controlled preparation of hollow Zn0.3Cd0.7S nanospheres modified by NiS1.97 nanosheets for superior photocatalytic hydrogen production.

Developing durable and efficient photocatalysts for H2 evolution is highly desirable to expedite current research on solar-chemical energy conversion. In this work, a novel photocatalytic H2 evolution system based on Zn0.3Cd0.7S/NiS1.97 nanocomposite was rationally designed for the first time. In this advanced composite structure, NiS1.97 nanosheets as a co-catalyst were intimately coupled to the inner surface of the hollow spherical Zn0.3Cd0.7S. The construction of the hollow spherical shell shortened the distance of charge migration to the surface site and increased the multiple absorption of incident light. The introduction of NiS1.97 nanosheets increased the light absorption capacity of the composite system and also greatly improved the separation and migration behavior of photo-generated carriers due to its narrower band gap and relatively low conduction band position, which had been confirmed by DRS, EIS and PL. As a result, the hollow Zn0.3Cd0.7S/NiS1.97 composite material exhibited excellent photocatalytic activity. At the loading amount of NiS1.97 up to 15 at.%, the hollow Zn0.3Cd0.7S/NiS1.97 composite exhibited the best photocatalytic activity with a corresponding H2 production rate of 22.637 mmol g-1h-1, which was 1.42 times and 1.85 times that of hollow Zn0.3Cd0.7S and solid Zn0.3Cd0.7S, respectively. Moreover, this novel catalyst also displayed a long-term stability without apparent debasement in H2 evolution activity. It is expected that this work could provide new inspiration to the design and development of other highly active photocatalytic systems for water splitting.

Interface engineering in CeO2 (111) facets decorated with CdSe quantum dots for photocatalytic hydrogen evolution.

The interfaces of heterostructures have been widely studied in the field of photocatalytic H2 evolution reaction (HER). In the present study, the CdSe QDs/CeO2(111) heterostructures were synthesized by wet chemistry method. The CdSe QDs/CeO2(111)-0.075 showed higher photocatalytic H2 evolution with 283.32 µmol g-1h-1, because of the enhanced light absorbance intensity and edge, lower recombination, higher separation and transfer, as well as longer lifetime of the photogenerated carrier. Density functional theory (DFT) calculations further confirmed that the enhanced HER activity of CdSe QDs/CeO2(111) heterostructures is resulted from a stronger water adsorption, a lower energy barrier of water dissociation and a more optimal free energy of hydrogen adsorption than CdSe and CeO2. The strategy of construction heterostructures provides a promising pathway for enhancing the performance of photocatalytic H2 evolution as well as other catalytic reactions.

Boosting charge transfer via molybdenum doping and electric-field effect in bismuth tungstate: Density function theory calculation and potential applications.

Regulating internal electronic structure of photocatalysts via elements doping holds huge potential in tuning efficient charge transfer and boosting high-performance. Herein, molybdenum embedded bismuth tungstate (Bi2WO6) is employed to explore the electronic structures and various performances via the assistance of experimental verification and density function theory (DFT) simulation. The band structures and Mo ions doping behaviors of Bi2MoxW1-xO6 are systematically measured. Doping can induce the distortion of intrinsic electric density and internal electric-field, resulted in efficient charge transfer of Bi2Mo0.4W0.6O6. It exhibits much efficient photocatalytic activities under visible-light irradiation, also manifests huge potential as an anode material in lithium-ion batteries (LIBs) which is rarely reported before. This work may provide insights in the development of bismuth-based semiconductors in energy related applications.

Boosted electrocatalytic activity of nitrogen-doped porous carbon triggered by oxygen functional groups.

The development of high-performance, low-price and durable doped carbon-based materials as multifunctional oxygen reduction reaction and oxygen evolution reaction catalysts is of great significance for the sustainable energy conversion devices. Adopting zinc zeolitic imidazolate framework and graphitic carbon nitride as nitrogen-sources and templates, we herein design a facile route to fabricate an oxygen (6.11%) functionalized and heavy nitrogen (23.54%) doped porous carbon (NOC-800) with high graphitization degree, high surface area and total pore volume. Electrochemical measurements indicate that as-obtained NOC-800 sample has satisfactory multifunctional oxygen-involving electrocatalytic properties in alkaline media, showing an onset and half-wave potential of -0.141 and -0.249 V vs. Ag/AgCl for oxygen reduction and an overpotential of 377 and 448 mV at 10 and 50 mA cm-2 for electrocatalytic oxygen evolution, respectively, even comparable to commercial RuO2 catalyst and majority of present mainstream metal-free catalysts. Moreover, the desirable stability of NOC-800 catalyst for both oxygen reduction and oxygen evolution reaction is also demonstrated. Combined with the analysis and discussion of the physicochemical characterization and electrochemical measurements, it is proposed and highlighted that oxygen functional groups introduced into nitrogen-doped carbon profitably contributes to high-efficiency overall oxygen-involving electrocatalytic activities.

One-pot nitridation route synthesis of SrTaO2N/Ta3N5 type II heterostructure with enhanced visible-light photocatalytic activity.

Rationally and skillfully constructing semiconductor heterostructured photocatalysts, benefited from the facilitated the carrier separation and transfer, have attracted intensive attention and been demonstrated as a manageable and effective strategy to develop high-performance photocatalysts. Herein, a novel SrTaO2N/Ta3N5 heterostructured photocatalyst were fabricated by one-pot nitridation of Sr2Ta2O7/Ta2O5 precursor under ammonia flow. The as-prepared SrTaO2N/Ta3N5 is a type-II heterostructure with an intimate interface contact, and the photocatalytic hydrogen production over the optimized heterostructure SrTaO2N(0.1)/Ta3N5 is about 14.1 times higher than that of individual SrTaO2N. The experimental results suggest that the formation of type-II heterostructure and intimate interface contact between Ta3N5 and SrTaO2N accelerates the separation and transfer of electrons and holes under visible light irradiation, consequently contribute to the improved hydrogen production rate. Moreover, we highlight that one-pot nitridation has the great potential to apply as an underlying general strategy of designing and fabricating other types of high-efficiency tantalum oxynitride-based heterostructured photocatalysts.

Sulphur and nitrogen dual-doped mesoporous carbon hybrid coupling with graphite coated cobalt and cobalt sulfide nanoparticles: Rational synthesis and advanced multifunctional electrochemical properties.

Doping-type carbon matrixes not only play a vital role on their electrochemical properties, but also are capable of suppressing the crush and aggregation phenomenon in the electrode reaction process for pristine metallic compound. Herein, graphite coated cobalt and cobalt sulfide nanoparticles decorating on sulphur and nitrogen dual-doped mesoporous carbon (Co@Co9S8/S-N-C) was fabricated by a combined hydrothermal reaction with pyrolysis method. Benefited from g-C3N4 template and original synthetic route, as-obtained Co@Co9S8/S-N-C possessed high specific surface area (751.7m2g-1), large pore volume (1.304cm3g-1), S and N dual-doped component and relative integrated graphite skeleton, as results it was developed as decent oxygen reduction electro-catalyst and ultra-long-life Li-ion battery anode. Surprisingly, compared with commercial Pt/C, it displayed a higher half-wave potential (0.015V positive) and lower Tafel slop (66mVs-1), indicating its superior ORR activities. Moreover, the ultra-long-life cyclic performances were revealed for lithium ion battery, exhibiting the retention capacities of 652.1mAhg-1 after 610 cycles at 0.2Ag-1, 432.1 and 405.7mAhg-1 at 5 and 10Ag-1 after 1000 cycles, respectively. We propose that the synergistic effect of structure and chemical component superiorities should be responsible for the remarkable electrochemical behaviors of the Co@Co9S8/S-N-C.

Controlling shape anisotropy of hexagonal CdS for highly stable and efficient photocatalytic H2 evolution and photoelectrochemical water splitting.

Photocorrosion and low solar conversion efficiency hindered widely applications of CdS in photocatalytic (PC) H2 evolution and photoelectrochemical (PEC) water splitting. Hence, this work reports the shape anisotropy of hexagonal CdS possesses highly stable and efficient PC H2 evolution and PEC water splitting by simply mixed diethylenetriamine (DETA) and deionized water (DIW) solvothermal. Here we demonstrate that the shape of hexagonal CdS plays an important role in their PC activity. The CdS-Nanorod yields optimal 5.4 mmol/g/h PC H2 production and photocurrent density 2.63 mA/cm2 at open circuit potential (OCP). The enhanced performance is attributed to the effective separation and transport of the photogenerated electron-hole pairs, which were verified by PL and transisent absorbance. Moreover, hexagonal CdS-Nanorod shows long-term PC H2 production and highly stable photocurrent density. As compared with CdS-Nanosphere, the hexagonal CdS-Nanorod exhibits 27 times and 19.2 times in H2 production and photocurrent density, respectively. What's more, STH efficiency of hexagonal CdS-Nanorod is 3.23% and an impressive applied bias photon-to-current efficiency (ABPE) is 2.63% at 0.134 V (vs. RHE). Temperature is also explored and reported. The possible mechanism of PC H2 evolution and PEC water spiltting are proposed for CdS-Nanorod. This work may provide a promising strategy to fabricate efficient PC and PEC systems for solar-to-fuel energy conversion.

Facet and morphology dependent photocatalytic hydrogen evolution with CdS nanoflowers using a novel mixed solvothermal strategy.

As the highest energy facet of wurtzite CdS, (0 0 2) facet is well worth investigating toward the contribution in photocatalytic hydrogen (H2) evolution. In this study, flower-like CdS with highly preferred (0 0 2) facet was fabricated through a low temperature mixed-solvothermal strategy. The mixted-solvent of diethylenetriamine (DETA) and ethyl alcohol (EtOH) was used to inhibit the growth of (1 0 0) and (1 0 1) facets. For comparison, porous flower-like, belt-like and net-like CdS samples with different preferred degrees of (0 0 2) facet were controllably synthesized by the addition of H2O in different proportions. The preferred orientation degrees of (0 0 2) facet were qualitative proved by the mathematical fitting of XRD patterns. As expected, the flower-like CdS exhibited the highest photocatalytic activity on H2 evolution under visible light without any co-catalyst. Meanwhile, the photocatalytic H2 production increased with the increasement of exposed (0 0 2) facet, which suggested that (0 0 2) facet of CdS played a critical role in improving the photocatalytic activity. Moreover, the growth mechanisms of CdS with various morphologies were investigated and proposed in detail.

Phase Transformation Synthesis of Strontium Tantalum Oxynitride-Based Heterojunction for Improved Visible Light-Driven Hydrogen Evolution.

Tantalum oxynitride-based materials, which possess narrow band gaps and sufficient band energy potentials, have been of immense interest for water splitting. However, the efficiency of photocatalytic reactions is still low because of the fast electron-hole recombination. Here, a Sr2Ta2O7- xN x/SrTaO2N heterostructured photocatalyst with a well-matched band structure was in situ constructed by the nitridation of hydrothermal-prepared Sr2Ta2O7 nanosheets. Compared to Sr2Ta2O7- xN x and pure SrTaO2N, the Sr2Ta2O7- xN x/SrTaO2N heterostructured photocatalyst exhibited the highest rate of hydrogen evolution, which is ca. 2.0 and 76.4 times of Sr2Ta2O7- xN x and pure SrTaO2N, respectively, under the similar reaction condition. The enhanced performance arises from the formation of suitable band-matched heterojunction-accelerated charge separation. This work provides a promising strategy for the construction of tantalum oxynitride-based heterojunction photocatalysts.

Well-organized migration of electrons for enhanced hydrogen evolution: Integration of 2D MoS2 nanosheets with plasmonic photocatalyst by a facile ultrasonic chemical method.

The construction of a plasmonic photocatalyst is an efficient way to suppress detrimental electrons-holes recombination and extend the spectral range of light absorption in semiconductors. However, the facilitation effect in the aspect of electrons-holes separation is great limited as the lack of a driving force compelled the electrons or holes migration to surface catalytic sites makes them flow randomly in semiconductors. In this work, we confirm that the integration of MoS2 nanosheets formed two dimensional (2D) layered heterojunction with C3N4 with Au-C3N4 plasmonic photocatalyst can further enhance electrons-holes separation through the formation of Au-C3N4-MoS2 nanostructure by a facile ultrasonic chemical method. The integrated MoS2 nanosheets extract the electrons not only from C3N4 due to a building up of 2D layered heterojunction but also from plasmonic Au via a "pipe" played by C3N4. The electrons "pump" role of the 2D MoS2 nanosheets makes electrons flow randomly turn into the well-organized migration direction, promoting the electrons-holes more efficient separation and lifetime prolongation. Meanwhile, MoS2 nanosheets also increase the light absorption of the photocatalyst owing to its inherent strength of the narrower band gap. Enabled by integration of 2D MoS2 nanosheets, the hydrogen production rate is 2.08 times higher than that of its counterpart Au-C3N4. This work highlights a new window to employ 2D layered heterojunction for enhanced photocatalytic hydrogen evolution performance.

C-S bond induced ultrafine SnS2 dot/porous g-C3N4 sheet 0D/2D heterojunction: synthesis and photocatalytic mechanism investigation.

The construction of novel heterojunctions is precisely deemed to be an effective strategy to facilitate photo-generated carrier separation and boost charge utilization efficiency, leading to much enhanced photocatalytic activities. Herein, in situ of growing ultrafine SnS2 nanoparticles on a porous g-C3N4 sheet (SnS2/g-C3N4) 0D/2D heterojunction was achieved via a low-temperature solvothermal process. Combined with various characterization techniques, it is revealed that SnS2 dots with a diameter of 3 nm distribute evenly on the surface of the g-C3N4 substrate with strong C-S bonds. The photocatalytic activities are evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation, showing a much enhanced photodegradation efficiency of 96.8% over 105 min irradiation and an enhanced reaction rate constant (k = 3.3% min-1, 8.25 and 8.05 times that of pure g-C3N4 and SnS2). The improved photocatalytic activities could be ascribed to the efficient electron-hole separation of porous g-C3N4, which is caused by the ultrafine SnS2 dots linked with the g-C3N4 substrate through C-S bonds. Therefore, the recombination efficiency is decreased. In addition, reactive active species trapping experiments prove that the superoxide radical (˙O2-) and holes (h+) are the main active species in this photocatalytic system. The photodegradation mechanism of the SnS2/g-C3N4 heterojunction is analyzed and demonstrated in detail.

Simple and facile ultrasound-assisted fabrication of Bi(2)O2CO(3)/g-C(3)N(4) composites with excellent photoactivity.

Bi2O2CO3/g-C3N4 (BOC/CN) composites photocatalyst was fabricated via a facile ultrasonic-assisted method. The crystal structure, morphology, optical and photocatalytic properties of the as-prepared samples were characterized by various analytical techniques. The results indicated that the Bi2O2CO3 nanoflakes grew on the surface of the g-C3N4 nanosheets, forming closely contacted interfaces between the Bi2O2CO3 and the g-C3N4 component. BOC/CN composites with 50wt% of g-C3N4 showed the optimal photoactivity for the degradation of RhB under visible light, which was approximately 2.2 times higher than that of pure g-C3N4 and 7 times of pure Bi2O2CO3, respectively. The enhanced performance of the BOC/CN composites was mainly attributed to a synergistic effect including the accelerated separation and migration of photogenerated charge carriers, demonstrated by Photoluminescence (PL), electrochemical impedance spectra (EIS) and photocurrent density. Finally, a possible photocatalytic mechanism was proposed based on the experimental results. It is expected that such a facile route method could provide new insights into fabricating other g-C3N4-based composite photocatalysts for environmental remediation.