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Although great progress has been made in the field of electrochemical CO2 reduction reaction (eCO2RR), inducing product selectivity is still difficult. We herein report that a thiocyanate ion (SCN-) switched the product selectivity of copper catalysts for eCO2RR in an H-cell. A cuprous thiocyanate-derived Cu catalyst was found to exhibit excellent HCOOH selectivity (faradaic efficiency = 70-88%) over a wide potential range (-0.66 to -0.95 V vs RHE). Furthermore, it was revealed that the formation of CO and C2H4 over commercial copper electrodes could be dramatically suppressed with the presence of SCN-, switching to HCOOH. Density functional theory calculations disclosed that SCN- made the formation of HCOO* easier than COOH* on Cu (211), facilitating the HCOOH generation. Our results provide a new insight into eCO2RR and will be helpful in the development of cheap electrocatalysts for specific utilization.

Photoelectrochemical (PEC) fuel generation from water splitting and CO2 reduction (CO2R) utilizing solar energy holds immense potential to solve the current energy and environmental issues. In the past decades, numerous studies have been devoted to this fast-growing research field, and it is essential to develop efficient photoelectrodes with earth-abundant materials for the practical application of PEC systems. A thorough review of earth-abundant materials and associated devices for PEC fuel generation is beneficial to uncover the inherent obstacles and pave the way for future research. Herein, we summarize the recent progress of earth-abundant light-absorbers and cocatalysts in the PEC systems. The unbiased configurations and scaling-up strategies of PEC devices using earth-abundant materials are examined. A comparison between PEC water splitting and CO2R is carried out to promote better understanding of the design principles for practical materials and devices. Last, the prospects on advanced materials, underlying mechanisms, and reaction systems of PEC water splitting and CO2R are proposed.

Photoelectrochemical (PEC) water splitting is a very attractive approach to produce clean hydrogen using abundant natural resources such as solar energy and (sea)water. As its primary step, light absorption controls the available amount of photons for the subsequent processes. Light management in PEC water splitting is essential to obtain high performance and efficiency. Herein, light management strategies via selective material choices and device engineering are comprehensively reviewed from two aspects: (1) improving light trapping ability; and (2) extending light absorption range. From a material design standpoint, morphology control of the photoelectrode components and application of surface-plasmon resonance are priorities. Besides these design priorities, approaches and strategies such as doping, solid–solution formation, and photon up-conversion will be briefly discussed. From a device engineering standpoint, tandem PEC devices are proposed to extend light absorption. The concentration of light is involved as an effective route to regulate the photon flux. In addition to experimental work, simulations of light distribution and absorption in PEC water splitting are examined to provide new device-oriented recommendations. This work features realistic and practical light management approaches for efficient and stable PEC water splitting materials, systems and devices by considering the synergistic effects of light absorption, charge transfer, and surface reactivity.

Environmentally friendly and low-cost Cu2ZnSnS4 (CZTS) is a promising light absorber for photoelectrochemical (PEC) hydrogen production from water splitting due to the earth-abundant elements, high absorption coefficient, and narrow bandgap. Herein, the hierarchical CZTS film with porous nanostructures was successfully synthesized by a template method. The hierarchical CZTS film was composed of flower-like particles, which were assembled with thin CZTS nanosheets. Macropores were generated owing to the aggregation of flower-like spheres, and mesopores were formed from the stacking of CZTS nanosheets. Compared to the dense CZTS film, the porous hierarchical CZTS film showed a much higher PEC property for water splitting. The improved performance could be attributed to three merits of the porous hierarchical morphology: enhanced light absorption, improved charge separation and transfer, and enlarged electrochemically active surface area. This study provides a useful idea to design efficient semiconductor photoelectrodes for water splitting with delicately controlled morphology.

Herein, a cross-linked porous Ta3N5 film was prepared via a simple solution combustion route followed by a high-temperature nitridation process for photoelectrochemical (PEC) water oxidation. Meanwhile, the metal cations (Mg2+ and Zr4+) were incorporated into the porous Ta3N5 to enhance the PEC performance. The porous Mg/Zr co-doped Ta3N5 photoanode yielded a photocurrent density of 1.40 mA cm−2 at 1.23 V vs RHE, which is 5.6 times higher than that of the dense Ta3N5 photoanode. The enhanced performance should be ascribed to the synergistic effect of porous structure and cation doping, which can enlarge the electrochemical active surface area and accelerate the charge transfer by introducing ON substitution defects. Subsequently, Co(OH)2 cocatalyst was loaded on the Mg/Zr-Ta3N5 photoanode to negatively shift the onset potential to 0.45 V vs RHE and further improve the photocurrent density to 3.5 mA cm−2 at 1.23 V vs. RHE, with a maximum half-cell solar to hydrogen efficiency of 0.45%. The present study provides a new strategy to design efficient Ta3N5 photoelectrodes via the simultaneous control of the morphology and composition.

Semiconductor-catalyst heterostructures have shown promising performances for light-driven H2 generation, although further development of these materials is hindered by the lack of cost effective and efficient catalysts. In this paper, we adopt a colloidal method to prepare few-layer WSe2 nanosheets without exfoliation and apply them as catalysts for forming heterostructures with a wide range of semiconductor absorbers (CdS nanorods, CdSe/CdS dot-in-rods, TiO2 nanoparticles, g-C3N4 nanosheets). These WSe2-semiconductor heterostructures show enhanced solar-to-hydrogen conversion efficiencies compared with semiconductors without WSe2. The detailed mechanism of this enhancement has been investigated using WSe2 nanosheets decorated CdSe/CdS dot-in-rods as a model system, which display ~5.5-fold higher hydrogen generation apparent quantum efficiency compared with free CdSe/CdS dot-in-rods. Transient absorption spectroscopic studies reveal efficient charge separation in WSe2 decorated CdSe/CdS dot-in-rods, suggesting its key role in enhancing the H2 generation efficiency of WSe2-semiconductor heterostructures. This work demonstrates the great potentials of WSe2 nanosheets as catalysts for light-driven hydrogen production and demonstrate the important effect of forming WSe2-semiconductor heterostructures in facilitating charge separation and photocatalysis.

Developing active photocatalysts using wide-spectrum light is crucial to promote the application of photocatalytic water splitting. Elemental red phosphorus (RP) has attracted much attention as a p...

Three-dimensional ZnO/CdS hierarchical films with uniform CdS deposition on the ZnO nanorods surface is prepared by a two-step hydrothermal method. The morphology of CdS nanostructure can be adjusted from particles to sheets and then blocks by changing amount of the surfactant in the precursor solution. The ZnO/CdS hierarchical film as photoelectrode with optimized morphology shows significant enhancement to the light harvesting and photoelectrochemical performance. Under light irradiation of 100 mW/cm2, the three-dimensional ZnO/CdS hierarchical film yields a photocurrent density of 4.5 mA/cm2, approximately two times higher than that of film without three-dimensional structure. The photoelectrochemical property improvement is attributed to the (1) enhanced light absorption due to the multi-scattering and multi-reflection of the unique three-dimensional hierarchical structure, (2) improved photogenerated carrier separation and transportation because of the hierarchical and heterojunction structure, and (3) facilitated hole transfer and reaction at the photoelectrode-electrolyte interface due to the large surface area.

Photoelectrochemical (PEC) water splitting represents a promising route to convert solar energy into clean hydrogen. Constructing tandem cells has emerged as a feasible approach and attracted treme...

Efficient Fe/N/C electrocatalysts for oxygen reduction reaction (ORR) have been prepared from a nonporous 8-fold interpenetrated metal–organic framework (Fe–Zn-TTPA) bearing dense Zn(II)–carboxylat...

To enhance the electrocatalytic performance of transition metal and nitrogen codoped carbon (M–N–C) for the CO2 electroreduction reaction, we present a Fe and N codoped porous carbon nanosphere (Fe...

Although numerous cocatalysts in photocatalytic water splitting have been studied, the fundamental understanding of factors affecting the function of cocatalysts is limited. This brief review summarizes the progress of cocatalysts in the last 3 years. The effects of intrinsic characters of cocatalysts including morphology, crystallization, and composition are first examined. The influence of interfacial coupling of cocatalysts with host photocatalysts, such as cocatalyst location, built-in electric field, and contact manner, is subsequently discussed. To confirm the active species of cocatalysts, some in situ/operando characterization techniques are finally introduced. It is expected that this brief review would provide useful information to design efficient cocatalysts for photocatalytic water splitting.

Solar-driven photocatalytic water splitting for hydrogen production has emerged as one of the foremost scientific issues. However, the efficient, low-cost, and large-scale operable system is still missing. Photocatalytic water splitting has multiple processes that involve light absorption, charge excitation and transfer, mass transfer, and chemical reaction, making it extremely complicated and challenging. Herein, we review the whole-process photocatalytic water splitting from two kinds of “flow”: energy flow and mass flow. The energy flow represents transmission and conversion of solar energy through the concentrator, reactor, reaction solution, and photocatalyst. The mass flow refers to transfer of reactants and products in the gas-liquid-solid multiphase environment. For the first time, we clearly describe the energy flow and mass flow in photocatalytic water splitting from multiple spatiotemporal scales, and point out that the low efficiencies of photocatalytic water splitting are attributed to obstacles in energy flow and mass flow, as well as non-coupling and mismatching of energy flow and mass flow. The mechanistic insights learned from this perspective indicate that, in addition to the material optimization, the scientific and engineered design of sunlight collection, interfacial reaction, and mass transfer is of great significance.

Developing efficient metal sulfides for pure water splitting is a challenging topic in the field of photocatalysis. Herein, inspired by natural photosynthesis, an all-solid-state Z-scheme photocatalyst was constructed with Cd0.9 Zn0.1 S (CZS) for water reduction, red phosphorus (RP) for water oxidation, and metallic CoP as the electron mediator. RP@CoP core-shell nanostructures were uniformly attached on the CZS nanorods, which gave rise to multiple monodispersed nanojunctions. The integrated Z-scheme nanosystem exhibited an apparent quantum efficiency of 6.4 % at 420 nm for pure water splitting. Theoretical analysis and femtosecond transient absorption results revealed that the impressive performance was mainly due to efficient hole transfer of CZS, resulting from the intimate atomic contacts between CoP mediator and photocatalysts, together with favorable band alignment. Meanwhile, the multiple monodispersed Z-scheme nanojunctions could provide abundant reaction sites, which was also important for the boosted activity.

The past decade has witnessed a growing interest in metal halide perovskite (MHP) materials, driven by their promising applications in photovoltaics and optoelectronics. The further pursuit of impr...

A series of self-doped Cu2ZnSnS4 (CZTS) nanocrystal films with Sn ions partially replaced by Zn ions were prepared from their colloidal solutions by electrophoretic deposition. The self-doped CZTS photocathodes yielded higher photocurrents than the pristine one, which was ascribed to the upper shift in the conduction band and the formation of a shallow defect level.

ZnO microrod arrays films with the surface modification by two steps ion-exchange approach have been investigated as photoanodes in photoelectrochemical (PEC) cells. X-ray diffraction, Raman, scanning electron microscope, energy dispersive X-ray detector, UV–vis techniques and PEC measurement have been used in the pristine and surface modified ZnO microrod films. The results show that ZnS and CdS layer can be deposited on ZnO microrod surface through a two steps ion-exchange procedure. What's more, it is found that ion-exchange method is a simple approach to adjust CdS content on the samples surface via changing experimental temperature. Consequently, the PEC property of films can be improved through optimizing CdS content on the ZnO microrods surface. In this experiment, it is found that the optimized condition for preparing film is 70 °C (first step) and 100 °C (second step). These results suggest that surface tuning via ion-exchange method should represent a viable strategy to further improve the efficiency of ZnO microrods photoanodes.

Colloidal nanocrystals (NCs) have emerged as a new kind of photocatalysts for solar hydrogen production due to the tunable optical and photoelectrical properties. Herein, size- and composition-tunable alloyed Cd1-xZnxSe NCs were successfully prepared via a one-step hot injection method for photocatalytic hydrogen production under visible light irradiation. By prolonging the reaction time, CdSe NCs with the varied particle sizes were firstly fabricated. It is found that the driving force derived from the difference between conduction band position of CdSe NCs and water reduction potential played a key role in determining the photocatalytic performance. The larger driving force from smaller particle size would give rise to a faster electron transfer and better photocatalytic activity. Furthermore, a series of alloyed Cd1-xZnxSe NCs with different compositions were prepared. With the increased zinc amount, the photocatalytic activity of Cd1-xZnxSe NCs was initially increased and then decreased. Cd1-xZnxSe with the moderate Zn content exhibited the best photocatalytic hydrogen production. It is inferred that the photocatalytic performance of Cd1-xZnxSe NCs has a close relationship with the driving force and crystal structure. The present study can provide a guidance to develop efficient nanocrystal photocatalysts by simply controlling the particle size and composition.

A yolk–shell structured Co-C/Void/Co9S8 ternary composite composed of a Co nanoparticle-embedded porous carbon core and Co9S8 shell was synthesized by the sulfidation of a Co-based zeolitic imidazolate framework and subsequent pyrolysis. The composition and interior cavity of the Co-C/Void/Co9S8 composite could be precisely modulated by controlling the sulfidation reaction. Due to the abundant heterointerfaces, well-controlled cavity, and magnetic–dielectric synergistic effects, the Co-C/Void/Co9S8 exhibited excellent and tunable microwave-absorbing properties. The optimized Co-C/Void/Co9S8, having a loading of 25 wt.% and thickness only 2.2 mm, displayed an ultrabroad absorption bandwidth of 8.2 GHz at high frequencies. Moreover, the composite could achieve an extremely high reflection loss of–54.02 dB at low frequencies by adjusting its loading to 30 wt.%. This study provides a new insight into promising lightweight microwave-absorbing materials with ultrabroad absorption bandwidths and strong low-frequency absorption.

Developing efficient heterostructured photocatalysts to accelerate charge separation and transfer is crucial to improving photocatalytic hydrogen generation using solar energy. Herein, we report for the first time that p-type copper phosphide (Cu 3 P) coupled with n-type graphitic carbon nitride (g-C 3 N 4 ) forms a p-n junction to accelerate charge separation and transfer for enhanced photocatalytic activity. The optimized Cu 3 P/g-C 3 N 4 p-n heterojunction photocatalyst exhibits 95 times higher activity than bare g-C 3 N 4 , with an apparent quantum efficiency of 2.6% at 420 nm. A detail analysis of the reaction mechanism by photoluminescence, surface photovoltaics and electrochemical measurements revealed that the improved photocatalytic activity can be ascribed to efficient separation of photo-induced charge carriers. This work demonstrates that p-n junction structure is a useful strategy for developing efficient heterostructured photocatalysts.

Herein, p- and n-type switchable Cu–In–S microcrystals with a grooved pyramid-like morphology are facilely synthesized by transforming binary In2S3. A cation exchange and in situ growth mechanism is proposed to illustrate the generation of grooved pyramid-like Cu–In–S samples. It is demonstrated that the structure, composition, and semiconducting properties of Cu–In–S films could be controlled by maneuvering the rate of cation exchange, which can be simply adjusted by varying the amount of the sulfur precursor. With an increased amount of added thiourea, p-type CuInS2 and n-type CuIn5S8 as well as a mixture of CuInS2 and CuIn5S8 are prepared. The p-type CuInS2 and n-type CuIn5S8 photoelectrodes respectively exhibit a cathodic photocurrent of −0.18 mA cm−2 at −0.4 V vs. RHE and an anodic photocurrent of 0.61 mA cm−2 at 0.7 V vs. RHE in 0.1 M Na2SO4 solution (pH = 3) under AM 1.5G illumination. More importantly, an unassisted water splitting system in parallel mode composed of a CoOx/CuIn5S8 photoanode and a Pt/CuInS2 photocathode is constructed, which shows a photocurrent density of 0.015 mA cm−2. The present work could provide a new idea for constructing efficient unassisted photoelectrochemical water splitting devices using copper-based chalcogenides. Meanwhile, the capability to switch p–n semiconducting properties provides a great inspiration to enable the development of novel semiconductor materials for photoelectric applications.

Developing well-designed architectures plays an important role in accelerating the charge transfer between different components in the hybrid photocatalysts. Herein, we report a simple one-step hydrothermal method to achieve CdS/ZnO heterostructure with a novel spatial arrangement. It was revealed that CdS nanorods were attached on the surface of ZnO microrods with an intimate face-to-face contact, and the heterointerfaces corresponded to {100} facets of CdS and {100} facets of ZnO. It was discovered that Zn(OH)2 intermediates were formed at first and then grew to hexagonal ZnO microrods via a solid-solid phase transformation. Simultaneously, CdS nuclei grew to nanorods on the {100} facets of ZnO by the oriented attachment during the one-step hydrothermal process. Under visible-light irradiation, the obtained CdS/ZnO exhibited enhanced photocatalytic hydrogen generation due to improved charge separation from the two-phase intergrowth effect. This work provides a facile hydrothermal route to construct intergrown heterostructures with desired spatial arrangements for improved photocatalytic properties.

Constructing heterostructured photocatalysts to facilitate spatial charge separation is deemed to be central to improving photocatalytic hydrogen production. Herein, we reported the synthesis of Ni2P-Cd0.9Zn0.1S/graphitic carbon nitride (g-C3N4) heterostructure for photocatalytic hydrogen production under visible-light irradiation. It was revealed that the ternary photocatalysts exhibited a one-dimensional morphology. Ni2P nanoparticles and a layer of g-C3N4 were tightly deposited on the surface of Cd0.9Zn0.1S nanorods. The optimal hydrogen evolution rate over Ni2P-Cd0.9Zn0.1S/g-C3N4 was ∼2100 μmol h−1 mg−1, corresponding to an apparent quantum yield as high as 73.2% at 420 nm. Meanwhile, the g-C3N4 layer could effectively collect the photo-induced holes from Cd0.9Zn0.1S, which substantially alleviated the photocorrosion of metal sulfide and led to an excellent stability for 90 h. A detail analysis of the action mechanism by photoluminescence, surface photovoltage, and electrochemical measurements revealed that the dramatically improved photocatalytic activity should be ascribed to highly efficient spatial separation of photo-induced charge carriers, as well as accelerated surface reaction by Ni2P cocatalysts. It is believed that the present work supplies an effective way to obtain non-precious heterostructured photocatalytic system for high-quantum-yield and stable hydrogen production.

One-dimensional CdS nanorods film and conifer like CdS planar film electrode were prepared using hydrothermal method and ultrasonic spray pyrolysis method. The SEM image and fluorescence spectrum revealed that different carrier transportation dynamics of two samples, which explained why CdS nanorods film showed better photoelectrochemical (PEC) property and hydrogen production activity. Compare the H2 evolution results and PEC results of films, the linear relation of H2 gas volume practically measured and computed referring to photocurrent value was discussed and confirmed. However, CdS nanorods film experienced severe photocorrosion compare with CdS planar film, because photogenerated holes were not consumed by electrolyte efficiently. The stability of samples can be improved by adding sodium sulfite in the electrolyte.

Herein, the pyramid-like In2S3 film was synthesized for photoelectrochemical (PEC) hydrogen generation using a facile hydrothermal route for the first time. The hydrothermal time was crucial to determine the morphology and composition of the as-prepared films. When the hydrothermal time lasted for 24 h, the pyramid-like In2S3 film could be achieved. With the increased hydrothermal time, the photocurrent first increased and then decreased, and the pyramid-like In2S3 film prepared for 24 h showed the highest photocurrent. After an annealing treatment, the photocurrent could be improved to 2.7 mA cm−2 at 0.78 V vs. RHE, and a substantial hydrogen generation was observed. Compared to previously reported In2S3 films with different morphologies, the pyramid-like In2S3 film exhibited better PEC property. It was revealed that the remaining In2O3 after the synthesis of In2S3 had a great influence on the PEC performance. The pyramid-like In2S3 film with a moderate amount of In2O3 induced an efficient charge separation and transfer, as well as good light-absorption ability, which led to the superior PEC performance. This work has demonstrated great potentials of the pyramid-like In2S3 film for PEC hydrogen generation and opened a promising avenue towards the design and fabrication of novel pyramid-like nanostructures.

Hematite (α-Fe2O3) is a promising photoanode material for photoelectrochemical (PEC) water splitting due to its appropriate bandgap, good stability, and earth-abundance. However, the poor charge transfer property and sluggish kinetics of water oxidation limit the PEC performance of α-Fe2O3 photoanodes. Herein, a thin NiOx buffer layer was introduced between the Ti doped α-Fe2O3 (Fe2O3-Ti) layer and the fluorine-doped tin oxide (FTO) substrate without affecting the nanowire morphology and light absorption property of Fe2O3-Ti. This buffer layer can apparently suppress the charge recombination by mitigating the lattice mismatching between the Fe2O3-Ti film and the FTO substrate. In addition, the good conductivity of the NiOx film from the non-stoichiometric composition is also beneficial to the charge transfer. As a consequence, the photocurrent density was greatly improved by adding the NiOx layer in the Fe2O3-Ti photoanode, reaching 1.32 mA·cm−2 at 1.23 VRHE without any co-catalyst and sacrificial agent. This work gives a detailed analysis of the back contact in the hematite-based photoanode and provides an effective strategy for underlayer interface optimization.

CdS/ZnS core-shell microparticles were prepared by a simple two-step method combining ultrasonic spray pyrolysis and chemical bath deposition. The core-shell structures showed enhanced photocatalytic properties compared with those of CdS or ZnS spherical particles. CdS/ZnS photocatalysts with different amount of ZnS loaded as shells were prepared by adjusting the concentrations of Zn and S precursors during synthesis. The optical properties and photocatalytic activity for hydrogen production were investigated and the amount of ZnS loaded as shell was optimized. Thermal annealing and hydrothermal sulfurization treatments were applied to the core-shell structure and both treatments enhanced the material's photocatalytic activity and stability by eliminating crystalline defects and surface states. The result showed that thermal annealing treatment improved the bulk crystallinity and hydrothermal sulfurization improved the surface properties. The sample subjected to both treatments showed the highest photocatalytic activity. These results indicate that CdS/ZnS core-shell microspheres are a simple structure that can be used as efficient photocatalysts. The hydrothermal sulfurization treatment may also be a useful surface treatment for metal sulfide photocatalysts. The simple two-step method provides a promising approach to the large-scale synthesis of core-shell microsphere catalysts.

Developing suitable cocatalysts is crucial to promoting photocatalytic hydrogen and oxygen generation using solar energy. Herein, non-precious NiCoP-based cocatalysts were synthesized by a facile solid-state phosphorization reaction, and coupled with metal-free graphitic carbon nitride (g-C3N4) for photocatalytic reactions. It was revealed that NiCoP-based nanoparticles exhibited a core/shell structure, where the NiCoP core was surrounded by amorphous-like nickel cobalt phosphate (NiCo–Pi) shell. The detailed spectroscopic and electrochemical studies demonstrated that NiCoP cores behaved as the active sites for the photocatalytic reductive half-reaction, and NiCo–Pi shells could serve as the active sites for the photocatalytic oxidative half-reaction. As a consequence, the improved surface reaction rate through the bifunctional NiCoP-based cocatalyst, as well as the enhanced charge separation efficiency, cooperatively boosted the separate photocatalytic hydrogen and oxygen generation in the presence of appropriate sacrificial reagents. The apparent quantum efficiency for hydrogen generation over the NiCoP@NiCo–Pi/g-C3N4 photocatalyst can reach 9.4% at 420 nm, which is one of the best values for noble-metal-free g-C3N4-based photocatalysts. To our knowledge, this is the first demonstration of the NiCoP-based cocatalyst to promote both photocatalytic hydrogen and oxygen generation, which is expected to pave a new way to exploit efficient bifunctional cocatalysts for overall water splitting.

Recently, direct chemical vapor deposition (CVD) growth of graphene on various types of glasses has emerged as a promising route to produce graphene glass, with advantages such as tunable quality, excellent film uniformity and potential scalability. Crucial to the performance of this graphene-coated glass is that the outstanding properties of graphene are fully retained for endowing glass with new surface characteristics, making direct-CVD-derived graphene glass versatile enough for developing various applications for daily life. Herein, recent advances in the synthesis of graphene glass, particularly via direct CVD approaches, are presented. Key applications of such graphene materials in transparent conductors, smart windows, simple heating devices, solar-cell electrodes, cell culture medium, and water harvesters are also highlighted.

Photocatalytic hydrogen generation from water is an appealing strategy for solar energy conversion, and fabricating heterostructured photocatalysts is demonstrated to be an effective way to improve the photocatalytic performance. Herein, we applied a facile one-step hydrothermal method to construct Zn x Cd 1− x S/ZnO heterostructures for photocatalytic hydrogen production. By varying the initial S 2− /Cd 2+ molar ratio, the composition, structure, and morphology of Zn x Cd 1− x S/ZnO heterostructures could be gradually tuned. It was demonstrated that the photocatalytic activity of Zn x Cd 1− x S/ZnO first increased and then underwent a decrease with the increased S 2− /Cd 2+ molar ratio. Zn x Cd 1− x S/ZnO sample showed a highest photocatalytic hydrogen production rate of 1.89 mmol/h with an apparent quantum yield of 26.0% at 420 nm. To our knowledge, this value was the highest for the reported Zn x Cd 1− x S/ZnO composite photocatalysts. The excellent performance could be attributed to the balance of the light absorption and conduction band offset of Zn x Cd 1− x S/ZnO heterostructures, as well as the intimate contact of two components at the interface. This work not only provided a facile one-step route to fabricate efficient composite photocatalysts, but also demonstrated the importance of balancing the band-gap and band offset of heterostructured photocatalysts for the improved hydrogen production.

Photoelectrochemical (PEC) water splitting for hydrogen generation has been considered as a promising route to convert and store solar energy into chemical fuels. In terms of its large-scale application, seeking semiconductor photoelectrodes with high efficiency and good stability should be essential. Although an enormous number of materials have been explored for solar water splitting in the last several decades, challenges still remain for the practical application. P-type copper-based chalcogenides, such as Cu(In, Ga)Se2 and Cu2ZnSnS4, have shown impressive performance in photovoltaics due to narrow bandgaps, high absorption coefficients, and good carrier transport properties. The obtained high efficiencies in photovoltaics have promoted the utilization of these materials into the field of PEC water splitting. A comprehensive review on copper-based chalcogenides for solar-to-hydrogen conversion would help advance the research in this expanding area. This review will cover the physicochemical properties of copper-based chalco-genides, developments of various photocathodes, strategies to enhance the PEC activity and stability, introductions of tandem PEC cells, and finally, prospects on their potential for the practical solar-to-hydrogen conversion. We believe this review article can provide some insights of fundamentals and applications of copper-based chalco-genide thin films for PEC water splitting.

Herein, sandwich structured tungsten trioxide (WO3) nanoplate arrays were first synthesized for photoelectrochemical (PEC) water splitting via a facile hydrothermal method followed by an annealing treatment. It was demonstrated that the annealing temperature played an important role in determining the morphology and crystal phase of the WO3 film. Only when the hydrothermally prepared precursor was annealed at 500 °C could the sandwich structured WO3 nanoplates be achieved, probably due to the crystalline phase transition and increased thermal stress during the annealing process. The sandwich structured WO3 photoanode exhibited a photocurrent density of 1.88 mA cm(-2) and an incident photon-to-current conversion efficiency (IPCE) as high as 65% at 400 nm in neutral Na2SO4 solution under AM 1.5G illumination. To our knowledge, this value is one of the best PEC performances for WO3 photoanodes. Meanwhile, simultaneous hydrogen and oxygen evolution was demonstrated for the PEC water splitting. It was concluded that the high PEC performance should be attributed to the large electrochemically active surface area and active monoclinic phase. The present study can provide guidance to develop highly efficient nanostructured photoelectrodes with the favorable morphology.

MOF-5 is an excellent self-sacrificed template with fascinating advantages (e.g. thermal robustness, ultrahigh surface area) to prepare highly porous carbon materials for diverse applications but Fe-N-C catalysts derived from MOF-5 seem yet unexplored. Through a dual strategy of cation-exchange and guest-encapsulation, an excellent MOF-5-derived Fe-N-C electrocatalyst toward oxygen reduction reaction was accomplished involving three steps. First, bimetallic Fe/Zn-MOF-5 was obtained by solid-liquid cation exchange between MOF-5 and Fe(BF4)2 solution. Second, infiltration of imidazole molecules into the channels of MOF-5 was achieved via a wet impregnation method, giving the precursor of imidazole@Fe/Zn-MOF-5. Finally, pyrolysis of imidazole@Fe/Zn-MOF-5 under the optimal conditions produced a porous Fe-N-C carbon catalyst decorated by iron carbide (Fe3C) nanoparticles, which exhibits a better ORR catalytic performance (E1/2 = 0.86 V vs. RHE) and higher stability than the benchmark Pt/C in the alkaline electrolyte. Application in the homemade primary Zn-air battery as the cathode catalyst also achieves a maximum-power density of 85 mW cm−2, and a satisfactory durability (slight decay by 8.4% in voltage @ 5 mA cm−2 for 70 h). The current work provides a facile and general method to convert MOF-5 into efficient Fe-N-C catalysts with the tunable ORR performance, which may offer more insights into designing highly efficient MOF-derived Fe-N-C electrocatalysts toward ORR.

Superhydrophobic sponge as potential absorbing material for oil/water separation is attracting great attention recently. However, there are still some challenges to feasibly fabricate superhydrophobic sponge with large scale and low cost. Herein, a novel photochromic superhydrophobic melamine sponge (PDMS-SP sponge) is fabricated by facilely dip-coating and thermocuring of hydroxyl-terminated polydimethylsiloxanes mixed with photochromic spiropyran. FT-IR, EDS, and XPS results confirm the successful coating of PDMS-SP upon melamine sponge. The resultant sponge not only possesses excellent water repellency with a contact angle of 154.5° and oil-water separation efficiency with an oil absorption capacity of 48–116 folds of itself weight, but also shows photochromic phenomenon between colorless and purple when it is successively exposed to UV irradiation and visible light.

In the field of photocatalytic hydrogen generation, cocatalysts play a vital role in enhanced properties. Delicate control of the physicochemical properties of cocatalysts and systematic optimization of the coupling between cocatalysts and host photocatalysts are essential. Herein, a simple one-step hydrothermal method was proposed to synthesize noble-metal-free NiSx/CdS photocatalysts for the first time. Time-dependent growth studies revealed that NiSx cocatalysts and CdS host photocatalysts were intergrown with each other in the one-step hydrothermal process. Compared with NiSx@CdS photocatalysts prepared by the common two-step method, the intergrowth effect induced close contact between NiSx and CdS, as well as smaller size and better dispersity of NiSx nanoparticles. These specific characters of NiSx/CdS finally resulted in efficient charge separation and rapid surface reaction, giving rise to significantly improved photocatalytic activity with the apparent quantum efficiency at 420 nm as high as 60.4%. To our knowledge, this value is the highest efficiency for NiSx modified CdS photocatalysts and is among the best efficiencies for visible-light-driven photocatalysts. It is believed that the present work can provide a general guidance to develop an efficient heterostructured cocatalyst/photocatalyst system for hydrogen generation.

We report the facile one-pot synthesis of a unique cadmium sulfide (CdS) intergrowth structure in the form of zincblende nanoparticle-decorated wurtzite microrods. The success of this preparation relies on a process involving both dissolution and regrowth. The growth of CdS crystals started from rapid generation of small zincblende nanoparticles, followed by dissolution of some nascent nanoparticles due to the strong alkalinity and relatively high reaction temperature. The resultant CdS monomers, capped by ethanediamine, nucleated again and went through further one-dimensional regrowth, leading to the formation of wurtzite microrods. This transformation gives rise to the generation of a novel intergrowth homojunction that consists of zincblende nanoparticle-decorated wurtzite microrods. Such a close contacted homojunction, having a type-II band alignment, shows an enhanced photocatalytic activity without loading any co-catalyst for solar hydrogen production in comparison to the use of either nanoparticles or microrods alone. This work not only enriches our knowledge on the fundamentals of homojunction formation, but also reveals an important fact that the intergrowth of a rationally designed junction structure shall bring about enhanced photocatalytic activity and thus deserves attention.

Surface modification of p-type Cu2ZnSnS4 films with n-type semiconductors is an efficient way to enhance the properties for photoelectrochemical water reduction. However, the detailed optimization of the pn junction photoelectrodes and examination of the underlying mechanism are seldom reported. Herein, Cu2ZnSnS4-derived (Cu2Sn)0.45Zn1.65S3 (CTZS) nanocrystal films were first fabricated, and subsequently coated with n-type CdS layers to form CTZS/CdS photoelectrodes. To obtain an insight into the pn junction, we have examined the depletion region widths that extended into both CTZS and CdS layers. It was revealed that the CdS layer was fully depleted and the CTZS layer was partially depleted in CTZS/CdS photoelectrodes. Consequently, increased CTZS thickness led to the decreased charge separation, and increased CdS thickness resulted in the improved charge separation. Owing to the balance of light absorption and charge separation, CTZS/CdS films with moderate thicknesses of CTZS and CdS layers showed the highest photocurrent. Meanwhile, the annealing treatment for CTZS/CdS film was indispensable for the improved property. After Pt modification, the incident photon to current conversion efficiency could reach 24.7% at 450 nm, which was among the best values for Cu2ZnSnS4-based photocathodes. This work is expected to provide general guidance for exploring efficient photoelectrodes with pn junction structure.

Doping with metals is an effective strategy to improve the charge transport and photoelectrochemical (PEC) properties of hematite photoelectrode. Herein, we report a comparison study of various metal atoms doped hematites to look into the effect of metal doping on the physical and chemical properties as well as the PEC performance of planar hematite thin film under the same synthetic and measurement condition. The efficient dopants, Ti, Cr, W, Pb, Sn, Zr and Si were selected and further investigated for their morphological and electronic properties. Nanorod arrays shaped hematite electrodes were also used to investigate the doping effect for the selected typical dopant elements. It was found that Ti, Zr, and Sn doping could greatly improve the photocurrent response, and Ce and Pb doping mildly increased the photocurrent. In contrast, Mo doping had a negative effect on the PEC property of hematite photoelectrodes. Based on the results of Mott–Schottky plots, valence band XPS spectra, electrochemical impedance spectroscopy and photocurrent, it can be found that the improvement of PEC performance of doped hematite is largely due to positively shifted flat band potential, which significantly influence the surface states and interface charge transport property. While for most dopants, the charge carrier densities were not changed and show less influence on the overall performance.

(CuIn)0.2Zn1.6S2 (CIZS) hollow sub-microspheres were prepared by a simple one-step hydrothermal method using thioacetamide (TAA) as a sulfur source. It was demonstrated that the amount of TAA played a key role on the morphology of CIZS samples. Low amount of TAA led to the formation of solid sub-microspheres. Nevertheless, high amount of TAA gave rise to the growth of hollow sub-microspheres, which could be elucidated by a bubble template mechanism. The morphology transition, as well as the reduced crystallite size, led to the increased specific surface area with the increased amount of TAA. Meanwhile, the defect states in CIZS samples were gradually decreased, when the amount of TAA was increased. The improved specific surface area and decreased defects of CIZS products contributed to higher efficiencies of charge separation and surface chemical reaction. The photocatalytic performance of CIZS photocatalysts was closely influenced by the amount of TAA. CIZS samples prepared with 5 g of TAA showed the highest hydrogen production rate, with the apparent quantum yield of 11.5% at 420 nm. It was summarized that the superior photocatalytic activity should be attributed to the larger specific surface area, decreased defects and relatively clean surface. This work not only provided a simple route to prepare hollow-structured photocatalysts, but also demonstrated the importance of sulfur source on photocatalytic properties of metal sulfide photocatalysts.

The synthesis of semiconductor nanocrystals is usually limited to high-level symmetry, as constrained by the inherent, for example, face-centered cubic or hexagonal close-packed lattices of the crystals. Herein, we report a robust approach for breaking the symmetry of the CdS lattice and obtaining high-quality CdS ultrathin monopods, bipods, tripods, and tetrapods. The success relies on manipulating reaction kinetics by dropwise addition of a precursor solution, which permits deterministic control over the number of CdS monomers in the reaction solution. With rapid monomer supply by fast precursor injection, growth was restricted to only one {111} facet of the nascent CdS tetrahedron to produce an asymmetric ultrathin monopod (a zinc-blende tip with a wurtzite arm). Otherwise, growth monomers could access adjacent {111} facets through surface diffusion and thus lead to the switch of the growth pattern from asymmetric to symmetric to generate an ultrathin multipod (a zinc-blende tip/core with multi-wurtzite arms). These symmetry-controlled photocatalysts were characterized by a fine-tuned zinc blende-wurtzite intergrowth type-II homojunction. After evaluating their structure-dependent solar-hydrogen-production properties, the CdS ultrathin monopod with an appropriate length for controllable charge transportation showed the highest photocatalytic activity.

To replace the role of noble-metal cocatalysts (e.g. Pt) in photocatalytic hydrogen generation, low-cost alternatives with earth-abundant elements should not only possess high catalytic activities, but also have general applicability. Herein, nanocrystalline Ni2P cocatalysts are used to modify CdS, TiO2, and C3N4 host photocatalysts. It is observed that the Ni2P cocatalyst boosts hydrogen generation over all the host photocatalysts, which demonstrates its good catalytic property and general applicability. To investigate its action mechanism, nanocrystalline Ni2P was successfully integrated with TiO2 nanorods (TiNR) for the first time. The optimized Ni2P/TiNR sample exhibits an 85 times higher activity compared to single TiNR, and its apparent quantum efficiency was calculated to be 11.6% at 360 nm. Among the varied nickel-based semiconductor cocatalysts, Ni2P is also proven to be the best cocatalyst. Photoluminescence and electrochemical results reveal that the Ni2P cocatalyst promotes the charge transfer both in the photocatalyst and at the photocatalyst/solution interface, as well as accelerates the surface reaction. The enhanced charge transfer efficiency and improved surface reaction rate finally result in a dramatically improved performance. It is believed that the present work can provide basic principles for the development of noble-metal-free cocatalysts with high catalytic activity and general applicability.

Catalyst-free and scalable synthesis of graphene on various glass substrates at low temperatures is of paramount significance to numerous applications such as low-cost transparent electronics and state-of-the-art displays. However, systematic study within this promising research field has remained scarce thus far. Herein, we report the direct growth of graphene on various glasses using a low-temperature plasma-enhanced chemical vapor deposition method. Such a facile and scalable approach guarantees the growth of uniform, transfer-free graphene films on various glass substrates at a growth temperature range of 400–600 °C. The morphological, surface wetting, optical, and electrical properties of the obtained graphene can be tailored by controlling the growth parameters. Our uniform and high-quality graphene films directly integrated with low-cost, commonly used glasses show great potential in the fabrication of multi-functional electrodes for versatile applications in solar cells, transparent electronics, and smart windows.

Direct growth of graphene on traditional glasses is of great importance for various daily life applications. We report herein the catalyst-free atmospheric-pressure chemical vapor deposition approach to directly synthesizing large-area, uniform graphene films on solid glasses. The optical transparency and sheet resistance of such kinds of graphene glasses can be readily adjusted together with the experimentally tunable layer thickness of graphene. More significantly, these graphene glasses find a broad range of real applications by enabling the low-cost construction of heating devices, transparent electrodes, photocatalytic plates, and smart windows. With a practical scalability, the present work will stimulate various applications of transparent, electrically and thermally conductive graphene glasses in real-life scenarios.

Chemical vapor deposition (CVD) synthesis of large-domain hexagonal boron nitride (h-BN) with a uniform thickness is very challenging, mainly due to the extremely high nucleation density of this material. Herein, we report the successful growth of wafer-scale, high-quality h-BN monolayer films that have large single-crystalline domain sizes, up to ~72 µm in edge length, prepared using a folded Cu-foil enclosure. The highly confined growth space and the smooth Cu surface inside the enclosure effectively reduced the precursor feeding rate together and induced a drastic decrease in the nucleation density. The orientation of the as-grown h-BN monolayer was found to be strongly correlated to the crystallographic orientation of the Cu substrate: the Cu (111) face being the best substrate for growing aligned h-BN domains and even single-crystalline monolayers. This is consistent with our density functional theory calculations. The present study offers a practical pathway for growing high-quality h-BN films by deepening our fundamental understanding of the process of their growth by CVD.

To establish a finite element (FE) model of the pig head for simulating firearm wounds. An experimental study was carried out by measuring impact load parameters from 17 fresh pig heads that were shot at the right part of cranium by a standard 7.62 mm M43 bullet. FE analysis was executed through the LS-DYNA code under impact loads similar to those obtained from the experimental study. The residual velocity, the transferred energy from the bullet to the cranium, and the surface area of the entrance showed no statistical differences between the FE simulation and the experimental study. However, the mean surface area of the exit wounds was significantly larger than that of the entrance wounds in the experimental and FE study. Although the results of FE analysis corresponded with the experiment study, FE analysis further revealed that the stress zones were mainly located at the impact region of the cranium, mainly located in occipital lobe, frontal lobe and skull base of brain, with a lower speed of stress distribution. The FE model was appropriate and conformed to the basic principles of wound ballistics.

In this work, V ions were doped into ZnO nanorod arrays via an advanced ion implantation method for photoelectrochemical water splitting under visible light. It was indicated that the V dopants were incorporated into ZnO lattice as V 4+ and V 5+ ions. V ion doping expanded the optical absorption of ZnO nanorod arrays into visible light region and led to considerable photoelectrochemical performance under visible light illumination ( λ > 420 nm). The photocurrent density of V ions doped ZnO nanorod arrays could achieve 10.5 μA/cm 2 at 0.8 V (vs. Ag/AgCl), which was about 4 times higher than that of the pure ZnO nanorod arrays. The enhancement in photoelectrochemical performances for V ions doped ZnO nanorod arrays should be attributed to the improved visible light absorption ability and the increased charge carrier density induced by V ion doping.

Developing efficient noble-metal-free photocatalysts is of great importance for the large-scale application of photocatalytic hydrogen production. Herein, low-cost and environment-friendly p-type Cu2S was successfully loaded on n-type CdS photocatalyst by an in situ method to achieve efficient Cu2S/CdS hybrid photocatalysts. Cu2S nanoparticles of ca. 50 nm were intimately assembled on the surface of polyhedral CdS nanocrystals, giving rise to the formation of numerous nanoscale p–n junctions between p-type Cu2S and n-type CdS. Compared to single CdS, Cu2S/CdS exhibited increased photocatalytic hydrogen production under visible light irradiation. The generated nanoscale p–n junctions in Cu2S/CdS, leading to the enhanced charge separation efficiency and better utilization of visible light, were crucial to the improved photocatalytic activity. During the photocatalytic reaction, Cu2S nanoparticles captured the photogenerated holes in CdS and served as the active sites for the surface oxidation reaction. The photocatalytic property of Cu2S/CdS photocatalysts was influenced by the Cu/Cd molar ratio, with the optimal one of 0.05. P-type Cu2S could also be utilized for improving the photocatalytic activities of n-type ZnIn2S4 and n-type TiO2 by forming efficient p–n junctions, indicating the general applicability of p-type Cu2S. This work demonstrates that forming p–n junction structure was a useful strategy for developing efficient noble-metal-free hybrid photocatalysts.