Scalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1

Particulate photocatalyst sheets based on non-oxide semiconductor materials for water splitting under visible light irradiation

Photocatalyst sheets active in visible-light-driven water splitting, potentially under irradiation of up to 600 nm, are developed.

Imaging photogenerated charge carriers on surfaces and interfaces of photocatalysts with surface photovoltage microscopy

Recent advances in imaging and characterizing charge separation on surfaces and interfaces of photocatalysts by surface photovoltage spectroscopy were reviewed and highlighted.

Self-assembled inorganic clusters of semiconducting quantum dots for effective solar hydrogen evolution

The catalytic activity of CdSe QDs could be enhanced more than 150-fold by forming self-assembled clusters with ZnSe QDs madeex situ.

Expansion of the photoresponse window of a BiVO4 photocatalyst by doping with chromium(vi)

Photocatalytic O₂ evolution is induced by electrons/holes generated by excitation of a new absorption band formed by doping with Cr⁶⁺.

Facile synthesis of a red light-inducible overall water-splitting photocatalyst using gold as a solid-state electron mediator

We have prepared a solid-state heterojunction photocatalyst, which can split pure water in nearly the entire range of visible light with wavelengths of up to 740 nm.

Activation of Kagome lattice-structured Cu3V2O7(OH)2·2H2O volborthite via hydrothermal crystallization for boosting visible light-driven water oxidation

A facile hydrothermal crystallization procedure for activating the photocatalytic reactivities of volborthite mineral for water oxidation and high-concentration dye removal.

Efficient photocatalytic degradation of gaseous acetaldehyde over ground Rh–Sb co-doped SrTiO3 under visible light irradiation

A visible-light-responsive Rh–Sb co-doped SrTiO₃ photocatalyst (STO:Rh,Sb) via a solid-state reaction was successfully developed, following pulverization by using ball-milling. The prepared STO:Rh,Sb exhibited a large surface area and showed efficient photocatalytic degradation of acetaldehyde. The photocatalytic activity of STO:Rh,Sb ground for 60 min exceeded that of STO:Rh ground for 60 min (photocatalyst doped without antimony), indicating that doped antimony plays an important role in suppressing the Rh⁴⁺, which works as a recombination center, in STO:Rh,Sb. Furthermore, the photocatalytic performance of STO:Rh,Sb ground for 60 min was sustained over 3 cycles, confirming the chemical stability of the photocatalyst. Therefore, ground STO:Rh,Sb has the potential to be applied to environmental remediation under visible light irradiation.

A visible-light-responsive Rh–Sb co-doped SrTiO₃ photocatalyst (STO:Rh,Sb) via a solid-state reaction was successfully developed, following pulverization by using ball-milling.

Controllable synthesis of graphitic carbon nitride nanomaterials for solar energy conversion and environmental remediation: the road travelled and the way forward

This review discusses advances in the synthesis and design of g-C₃N₄-based nanomaterials and their various photocatalytic and photoredox applications.

Photocatalytic CO2 conversion by polymeric carbon nitrides

CO₂ is a vital compound for life, and its concentration significantly affects the living environment of the Earth. By mimicking nature photosynthesis, we herein discusses the uses of polymeric carbon nitrides to balance CO₂ concentration by artificial photocatalysis.

TiO2/TiN core/shell nanobelts for efficient solar hydrogen generation

TiO₂/TiN core/shell NBs are successfully synthesized, and used as highly efficient photocatalytic H₂ evolution catalysts (120 μmol h⁻¹ g⁻¹) from methanol solution.

Controllable synthesized heterostructure photocatalyst Mo2C@C/2D g-C3N4: enhanced catalytic performance for hydrogen production

Electrons can be trapped and exported to participate in HER reaction by Mo₂C@C co-catalyst effectively.

Artificial photosynthesis by light absorption, charge separation, and multielectron catalysis

We highlight recent novel approaches in the field of artificial photosynthesis. We emphasize the potential of a highly modular plug-and-play concept that we hope will persuade the community to explore a more inclusive variety of multielectron redox catalysis to complement the proton reduction and water oxidation half-reactions in traditional solar water splitting systems.

Unique physicochemical properties of two-dimensional light absorbers facilitating photocatalysis

The emergence of two-dimensional (2D) materials with a large lateral size and extremely small thickness has significantly changed the development of many research areas by producing a variety of unusual physicochemical properties.

An efficient and cost-effective tri-functional electrocatalyst based on cobalt ferrite embedded nitrogen doped carbon

The development of efficient, cost-effective and long-lived electro-catalyst is necessary for the realization of practically viable water-splitting systems. A trifunctional electrocatalyst for water splitting (hydrogen evolution, oxygen reduction and oxygen evolution reaction, HER/ORR/OER) was designed via eco-friendly and facial way. CoFe₂O₄ nanoparticles embedded in nitrogen doped mesoporous carbon were prepared using chicken egg white/albumin after pyrolysis at different temperatures, 700, 800, 900 and 1000 °C. The specific surface area, pore size and the interaction between CoFe₂O₄ nanoparticles and carbon matrix were tuned via pyrolysis temperature. The catalyst prepared at 900 °C, (N/CF-EC-900) exhibit superior catalytic activity as well as the superior stability than that other nanocomposites prepared and other commercial catalyst (Pt/C, RuO₂) for water splitting. Our findings emphasize the importance of CoFe₂O₄ nanoparticles embedded in the carbon and suggest the catalytic activities with low onset potential, high current densities, small Tafel slope in basic medium.

Photocatalytic Oxygen Evolution from Functional Triazine-Based Polymers with Tunable Band Structures

Conjugated polymers (CPs) are emerging and appealing light harvesters for photocatalytic water splitting owing to their adjustable band gap and facile processing. Herein, we report an advanced mild synthesis of three conjugated triazine-based polymers (CTPs) with different chain lengths by increasing the quantity of electron-donating benzyl units in the backbone. Varying the chain length of the CTPs modulates their electronic, optical, and redox properties, resulting in an enhanced performance for photocatalytic oxygen evolution, which is the more challenging half-reaction of water splitting owing to the sluggish reaction kinetics. Our results could stimulate interest in these functional polymers where a molecular engineering strategy enables the production of suitable semiconductor redox energetics for oxygenic photosynthesis.

Effect of Nitrogen Doping Level on the Performance of N-Doped Carbon Quantum Dot/TiO2 Composites for Photocatalytic Hydrogen Evolution

Carbon quantum dots (CQDs) have attracted widespread interest for photocatalytic applications, owing to their low cost and excellent electron donor/acceptor properties. However, their advancement as visible-light photosensitizers in CQDs/semiconductor nanocomposites is currently impaired by their poor quantum yields (QYs). Herein, we describe the successful fabrication of a series of nitrogen-doped CQDs (NCDs) with N/C atomic ratios ranging from 0.14-0.30. NCDs with the highest N-doping level afforded a remarkable external QY of 66.8 % at 360 nm, and outstanding electron transfer properties and photosensitization efficiencies when physically adsorbed on P25 TiO₂ . A NCDs/P25-TiO₂ hybrid demonstrated excellent performance for hydrogen evolution in aqueous methanol under both UV and visible-light illumination relative to pristine P25 TiO₂ . Controlled nitrogen doping of CQDs therefore represents a very effective strategy for optimizing the performance of CQDs/semiconductor hybrid photocatalysts.

Strategies for Efficient Charge Separation and Transfer in Artificial Photosynthesis of Solar Fuels

Converting sunlight to solar fuels by artificial photosynthesis is an innovative science and technology for renewable energy. Light harvesting, photogenerated charge separation and transfer (CST), and catalytic reactions are the three primary steps in the processes involved in the conversion of solar energy to chemical energy (SE-CE). Among the processes, CST is the key "energy pump and delivery" step in determining the overall solar-energy conversion efficiency. Efficient CST is always high priority in designing and assembling artificial photosynthesis systems for solar-fuel production. This Review not only introduces the fundamental strategies for CST but also the combinatory application of these strategies to five types of the most-investigated semiconductor-based artificial photosynthesis systems: particulate, Z-scheme, hybrid, photoelectrochemical, and photovoltaics-assisted systems. We show that artificial photosynthesis systems with high SE-CE efficiency can be rationally designed and constructed through combinatory application of these strategies, setting a promising blueprint for the future of solar fuels.

Metal Phosphides as Co-Catalysts for Photocatalytic and Photoelectrocatalytic Water Splitting

Solar-to-hydrogen conversion based on photocatalytic and photoelectrocatalytic water splitting is considered as a promising technology for sustainable hydrogen production. Developing earth-abundant H₂ -production materials with robust activity and stability has become the mainstream in this field. Due to the unique properties and characteristics, transition metal phosphides (TMPs) have been proven to be high performance co-catalysts to replace some of the classic precious metal materials in photocatalytic water splitting. In this Minireview, we summarize the recent significant progress of TMPs as cocatalysts for water splitting reaction with high activity and stability. Firstly, the characteristic of TMPs is briefly introduced. Then, we mainly discuss the recent research efforts toward their application as photocatalytic co-catalysts in photocatalytic H₂ -production, O₂ -evolution and photoelectrochemical water splitting. Finally, the catalytic mechanism, current existing challenges and future working directions for improving the performance of TMPs are proposed.

Electrolyte Engineering towards Efficient Water Splitting at Mild pH

The development of processes for the conversion of H₂ O and CO₂ driven by electricity generated by renewable means is essential to achieving sustainable energy and chemical cycles, in which the electrocatalytic oxygen evolution reaction (OER) is one of the bottlenecks. In this study, the influences of the electrolyte molarity and identity on the OER at alkaline to neutral pH were investigated at an appreciable current density of around 10 mA cm^-2 , revealing both the clear boundary of reactant switching between H₂ O/OH^- , owing to the diffusion limitation of OH^- , and the substantial contribution of the mass transport of the buffered species in buffered mild-pH conditions. These findings suggest a strategy of electrolyte engineering: tuning the electrolyte properties to maximize the mass-transport flux. The concept is successfully demonstrated for the OER, as well as overall water electrolysis in buffered mild-pH conditions, shedding light on the development of practical solar fuel production systems.

Visualizing the Nano Cocatalyst Aligned Electric Fields on Single Photocatalyst Particles

The cocatalysts or dual cocatalysts of photocatalysts are indispensable for high efficiency in artificial photosynthesis for solar fuel production. However, the reaction activity increased by cocatalysts cannot be directly ascribed to the accelerated catalytic kinetics, since photogenerated charges are involved in the elementary steps of photocatalytic reactions. To date, diverging views about cocatalysts show that their exact role for photocatalysis is not well understood yet. Herein, we image directly the local separation of photogenerated charge carriers across single crystals of the BiVO₄ photocatalyst which loaded locally with nanoparticles of a MnO_x single cocatalyst or with nanoparticles of a spatially separated MnO_x and Pt dual cocatalyst. The deposition of the single cocatalyst resulted not only in a strong increase of the interfacial charge transfer but also, surprisingly, in a change of the direction of built-in electric fields beneath the uncovered surface of the photocatalyst. The additive electric fields caused a strong increase of local surface photovoltage signals (up to 80 times) and correlated with the increase of the photocatalytic performance. The local electric fields were further increased (up to 2.5 kV·cm^-1) by a synergetic effect of the spatially separated dual cocatalysts. The results reveal that cocatalyst has a conclusive effect on charge separation in photocatalyst particle by aligning the vectors of built-in electric fields in the photocatalyst particle. This effect is beyond its catalytic function in thermal catalysis.

Colloidal zinc oxide-copper(I) oxide nanocatalysts for selective aqueous photocatalytic carbon dioxide conversion into methane

Developing catalytic systems with high efficiency and selectivity is a fundamental issue for photochemical carbon dioxide conversion. In particular, rigorous control of the structure and morphology of photocatalysts is decisive for catalytic performance. Here, we report the synthesis of zinc oxide-copper(I) oxide hybrid nanoparticles as colloidal forms bearing copper(I) oxide nanocubes bound to zinc oxide spherical cores. The zinc oxide-copper(I) oxide nanoparticles behave as photocatalysts for the direct conversion of carbon dioxide to methane in an aqueous medium, under ambient pressure and temperature. The catalysts produce methane with an activity of 1080 μmol g_cat⁻¹ h⁻¹, a quantum yield of 1.5% and a selectivity for methane of >99%. The catalytic ability of the zinc oxide-copper(I) oxide hybrid catalyst is attributed to excellent band alignment of the zinc-oxide and copper(I) oxide domains, few surface defects which reduce defect-induced charge recombination and enhance electron transfer to the reagents, and a high-surface area colloidal morphology.

Photocatalytic reduction and oxidation reactions, involving multiple electrons and operating in tandem, are extremely challenging to achieve. Here, with a hybrid structure of ZnO and Cu₂O, the authors report photocatalytic carbon dioxide reduction to methane with >99% selectivity using electrons from water.

Efficient Photocatalytic Hydrogen Evolution via Band Alignment Tailoring: Controllable Transition from Type-I to Type-II

Considering the sizable band gap and wide spectrum response of tin disulfide (SnS₂ ), ultrathin SnS₂ nanosheets are utilized as solar-driven photocatalyst for water splitting. Designing a heterostructure based on SnS₂ is believed to boost their catalytic performance. Unfortunately, it has been quite challenging to explore a material with suitable band alignment using SnS₂ nanomaterials for photocatalytic hydrogen generation. Herein, a new strategy is used to systematically tailor the band alignment in SnS₂ based heterostructure to realize efficient H₂ production under sunlight. A Type-I to Type-II band alignment transition is demonstrated via introducing an interlayer of Ce₂ S₃ , a potential photocatalyst for H₂ evolution, between SnS₂ and CeO₂ . Subsequently, this heterostructure demonstrates tunability in light absorption, charge transfer kinetics, and material stability. The optimized heterostructure (SnS₂ -Ce₂ S₃ -CeO₂ ) exhibits an incredibly strong light absorption ranging from deep UV to infrared light. Significantly, it also shows superior hydrogen generation with the rate of 240 µmol g^-1 h^-1 under the illumination of simulated sunlight with a very good stability.

Bromide Photo-oxidation Sensitized to Visible Light in Consecutive Ion Pairs

The titration of bromide into a [Ru(deeb)(bpz)₂]²⁺ (Ru²⁺, deeb = 4,4'-diethylester-2,2'-bipyridine; bpz = 2,2'-bipyrazine) dichloromethane solution led to the formation of two consecutive ion-paired species, [Ru²⁺, Br^-]⁺ and [Ru²⁺, 2Br^-], each with distinct photophysical and electron-transfer properties. Formation of the first ion pair was stoichiometric, K_eq 1 > 10⁶ M^-1, and the second ion-pair equilibrium was estimated to be K_eq 2 = (2.4 ± 0.4) × 10⁵ M^-1. The ¹H NMR spectra recorded in deuterated dichloromethane indicated the presence of contact ion pairs and provided insights into their structures and were complimented by density functional theory calculations. Static quenching of the [Ru(deeb)(bpz)₂]^2+* photoluminescence intensity (PLI) by bromide was observed, and [Ru²⁺, Br^-]^+* was found to be nonluminescent, τ < 10 ns. Further addition of bromide resulted in partial recovery of the PLI, and [Ru²⁺, 2Br^-]* was found to be luminescent with an excited-state lifetime of τ = 65 ± 5 ns. Electron-transfer products were identified as the reduced complex, [Ru(deeb)(bpz)₂]⁺, and dibromide, Br₂^•-. The bromine atom, Br^•, was determined to be the primary excited-state electron-transfer product and was an intermediate in Br₂^•- formation, Br^• + Br^- → Br₂^•-, with a second-order rate constant, k = (5.4 ± 1) × 10⁸ M^-1 s^-1. The unusual enhancement in PLI for [Ru²⁺, 2Br^-]* relative to [Ru²⁺, Br^-]^+* was due to a less favorable Gibbs free energy change for electron transfer that resulted in a smaller rate constant, k_et = (1.5 ± 0.2) × 10⁷ s^-1, in the second ion pair. Natural atomic charge analysis provided estimates of the Coulombic work terms associated with ion pairing, ΔG_w, that were directly correlated with the measured change in rate constants.

Ethanol surface chemistry on MBE-grown GaN(0001), GaOx/GaN(0001), and Ga2O3(2¯01)

In this work, ethanol is used as a chemical probe to study the passivation of molecular beam epitaxy-grown GaN(0001) by surface oxidation. With a high degree of oxidation, no reaction from ethanol to acetaldehyde in temperature-programmed desorption experiments is observed. The acetaldehyde formation is attributed to a mechanism based on α-H abstraction from the dissociatively bound alcohol molecule. The reactivity is related to negatively charged surface states, which are removed upon oxidation of the GaN(0001) surface. This is compared with the Ga₂O₃(2¯01) single crystal surface, which is found to be inert for the acetaldehyde production. These results offer a toolbox to explore the surface chemistry of nitrides and oxynitrides on an atomic scale and relate their intrinsic activity to systems under ambient atmosphere.

High Electrocatalytic Response of a Mechanically Enhanced NbC Nanocomposite Electrode Toward Hydrogen Evolution Reaction

Resistant and efficient electrocatalysts for hydrogen evolution reaction (HER) are desired to replace scarce and commercially expensive platinum electrodes. Thin-film electrodes of metal carbides are a promising alternative due to their reduced price and similar catalytic properties. However, most of the studied structures neglect long-lasting chemical and structural stability, focusing only on electrochemical efficiency. Herein we report on a new approach to easily deposit and control the micro/nanostructure of thin-film electrodes based on niobium carbide (NbC) and their electrocatalytic response. We will show that, by improving the mechanical properties of the NbC electrodes, microstructure and mechanical resilience can be obtained while maintaining high electrocatalytic response. We also address the influence of other parameters such as conductivity and chemical composition on the overall performance of the thin-film electrodes. Finally, we show that nanocomposite NbC electrodes are promising candidates toward HER and, furthermore, that the methodology presented here is suitable to produce other transition-metal carbides with improved catalytic and mechanical properties.

Comprehensive Study of All-Solid-State Z-Scheme Photocatalytic Systems of ZnO/Pt/CdZnS

We have investigated a Z-scheme based on a ZnO/Pt/CdZnS photocatalyst, active in the presence of a complex medium composed of acetic acid and benzyl alcohol, the effects of which on the catalyst stability and performance are studied. Transmission electron microscopy images showed uniformly dispersed sub-nanometer Pt particles. Inductively coupled plasma and X-ray photoelectron spectroscopy analyses suggested that Pt is sandwiched between ZnO and CdZnS. An apparent quantum yield (AQY) of 34% was obtained over the [ZnO]₄/1 wt %Pt/CdZnS system at 360 nm, 2.5-fold higher than that of 1%Pt/CdZnS (14%). Furthermore, an AQY of 16% was observed using [ZnO]₄/1 wt %Pt/CdZnS, which was comparable to that of 1 wt %Pt/CdZnS (10%) at 460 nm. On the basis of these results, we proposed a charge transfer mechanism, which was confirmed through femtosecond transient absorption spectroscopy. Finally, we identified the two main factors that affected the stability of the catalyst, which were the sacrificial reagent and the acidic pH.

Stable and Efficient CuO Based Photocathode through Oxygen-Rich Composition and Au-Pd Nanostructure Incorporation for Solar-Hydrogen Production

Enhancing stability against photocorrosion and improving photocurrent response are the main challenges toward the development of cupric oxide (CuO) based photocathodes for solar-driven hydrogen production. In this paper, stable and efficient CuO-photocathodes have been developed using in situ materials engineering and through gold-palladium (Au-Pd) nanoparticles deposition on the CuO surface. The CuO photocathode exhibits a photocurrent generation of ∼3 mA/cm² at 0 V v/s RHE. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis and X-ray spectroscopy (XPS) confirm the formation of oxygen-rich (O-rich) CuO film which demonstrates a highly stable photocathode with retained photocurrent of ∼90% for 20 min. The influence of chemical composition on the photocathode performance and stability has been discussed in detail. In addition, O-rich CuO photocathodes deposited with Au-Pd nanostructures have shown enhanced photoelectrochemical performance. Linear scan voltammetry characteristic shows ∼25% enhancement in photocurrent after Au-Pd deposition and reaches ∼4 mA/cm² at "0" V v/s RHE. Hydrogen evolution rate significantly depends on the elemental composition of CuO and metal nanostructure. The present work has demonstrated a stable photocathode with high photocurrent for visible-light-driven water splitting and hydrogen production.

Molybdenum-doped ZnS sheets with dominant {111} facets for enhanced visible light photocatalytic activities

ZnS is widely used as a semiconductor photocatalyst in photo-electrochemical water splitting and photodegradation under ultraviolet (UV)-light irradiation. In this work, Molybdenum (Mo)-doped ZnS sheets with dominant {111} facets are developed using a hydrothermal method with Mo ions as precursors to realize non-visible-light photocatalytic activity and reduce the recombination rate of photoexcited carriers in ZnS. Mo ions are found to play a key role in the growth process of the sheet-like structure. Mo-dopants in the ZnS sheets introduce the acceptor energy levels among the bandgaps. The light absorption range of Mo-doped ZnS sheets covers the entire visible light and even extends to the near-infrared light region. The p-type Mo-doped ZnS sheets exhibit enhanced photocatalytic activities under visible light irradiation, which is promising for the photo-electrochemistry and photo-oxidation applications.

Impact of Photosensitizing Multilayered Structure on Ruthenium(II)-Dye-Sensitized TiO2-Nanoparticle Photocatalysts

To improve the efficiency of photoinduced charge separation on the surface of dye-sensitized TiO₂ nanoparticles, we synthesized the Ru(II)-photosensitizer-immobilized, Pt-cocatalyst-loaded TiO₂ nanoparticles RuCP ² @Pt-TiO₂, RuCP ² -Zr-RuP ⁶ @Pt-TiO₂, and RuCP ² -Zr-RuP ⁴ -Zr-RuP ⁶ @Pt-TiO₂ (RuCP ² = [Ru(bpy)₂(mpbpy)]^2-, RuP ⁴ = [Ru(bpy)(pbpy)₂]^6-, RuP ⁶ = [Ru(pbpy)₃]^10-, H₄mpbpy = 2,2'-bipyridine-4,4'-bis(methanephosphonic acid), and H₄pbpy = 2,2'-bipyridine-4,4'-bis(phosphonic acid)) using phosphonate linkers with bridging Zr⁴⁺ ions. X-ray fluorescence and ultraviolet-visible absorption spectra revealed that a layered molecular structure composed of Ru(II) photosensitizers and Zr⁴⁺ ions (i.e., RuCP ² -Zr-RuP ⁶ and RuCP ² -Zr-RuP ⁴ -Zr-RuP ⁶ ) was successfully formed on the surface of Pt-TiO₂ nanoparticles, which increased the surface coverage from 0.113 nmol/cm² for singly layered RuCP ² @Pt-TiO₂ to 0.330 nmol/cm² for triply layered RuCP ² -Zr-RuP ⁴ -Zr-RuP ⁶ @Pt-TiO₂. The photocatalytic H₂ evolution activity of the doubly layered RuCP ² -Zr-RuP ⁶ @Pt-TiO₂ was three times higher than that of the singly layered RuCP ² @Pt-TiO₂, whereas the activity of triply layered RuCP ² -Zr-RuP ⁴ -Zr-RuP ⁶ @Pt-TiO₂ was less than half of that for RuCP ² @Pt-TiO₂. The photosensitizing efficiencies of these Ru(II)-photosensitizer-immobilized nanoparticles for the O₂ evolution reaction catalyzed by the Co(II)-containing Prussian blue analogue [Co^II(H₂O)₂]_1.31[{Co^III(CN)₆}_0.63{Pt^II(CN)₄}_0.37] decreased as the number of Ru(II)-photosensitizing layers increased. Thus, crucial aspects of the energy- and electron-transfer mechanism for the photocatalytic H₂ and O₂ evolution reactions involve not only the Ru(II)-complex-TiO₂ interface but also the multilayered structure of the Ru(II)-photosensitizers on the Pt-TiO₂ surface.

Highly Efficient Photocatalytic Z-Scheme Hydrogen Production over Oxygen-Deficient WO3-x Nanorods supported Zn0.3Cd0.7S Heterostructure

The demand for clean renewable energy is increasing due to depleting fossil fuels and environmental concerns. Photocatalytic hydrogen production through water splitting is one such promising route to meet global energy demands with carbon free technology. Alternative photocatalysts avoiding noble metals are highly demanded. Herein, we fabricated heterostructure consist of oxygen-deficient WO_3–x nanorods with Zn_0.3Cd_0.7S nanoparticles for an efficient Z-Scheme photocatalytic system. Our as obtained heterostructure showed photocatalytic H₂ evolution rate of 352.1 μmol h⁻¹ with apparent quantum efficiency (AQY) of 7.3% at λ = 420 nm. The photocatalytic hydrogen production reaches up to 1746.8 μmol after 5 hours process in repeatable manner. The UV-Visible diffuse reflectance spectra show strong absorption in the visible region which greatly favors the photocatalytic performance. Moreover, the efficient charge separation suggested by electrochemical impedance spectroscopy and photocurrent response curves exhibit enhancement in H₂ evolution rate. The strong interface contact between WO_3–x nanorods and Zn_0.3Cd_0.7S nanoparticles ascertained from HRTEM images also play an important role for the emigration of electron. Our findings provide possibilities for the design and development of new Z-scheme photocatalysts for highly efficient hydrogen production.

Enhanced Photocarrier Separation in Hierarchical Graphitic-C3N4-Supported CuInS2 for Noble-Metal-Free Z-Scheme Photocatalytic Water Splitting

The effective separation of photogenerated electrons and holes in photocatalysts is a prerequisite for efficient photocatalytic water splitting. CuInS₂ (CIS) is a widely used light absorber that works properly in photovoltaics but only shows limited performance in solar-driven hydrogen evolution due to its intrinsically severe charge recombination. Here, we prepare hierarchical graphitic C₃N₄-supported CuInS₂ (denoted as GsC) by an in situ growth of CIS directly on exfoliated thin graphitic C₃N₄ nanosheets (g-C₃N₄ NS) and demonstrate efficient separation of photoinduced charge carriers in the GsC by forming the Z-scheme system for the first time in CIS-catalyzed water splitting. Under visible light illumination, the GsC features an enhanced hydrogen evolution rate up to 1290 μmol g^-1 h^-1, which is 3.3 and 6.1 times higher than that of g-C₃N₄ NS and bare-CIS, respectively, thus setting a new performance benchmark for CIS-based water-splitting photocatalysts.

Combining photocatalytic hydrogen generation and capsule storage in graphene based sandwich structures

The challenge of safe hydrogen storage has limited the practical application of solar-driven photocatalytic water splitting. It is hard to isolate hydrogen from oxygen products during water splitting to avoid unwanted reverse reaction or explosion. Here we propose a multi-layer structure where a carbon nitride is sandwiched between two graphene sheets modified by different functional groups. First-principles simulations demonstrate that such a system can harvest light and deliver photo-generated holes to the outer graphene-based sheets for water splitting and proton generation. Driven by electrostatic attraction, protons penetrate through graphene to react with electrons on the inner carbon nitride to generate hydrogen molecule. The produced hydrogen is completely isolated and stored with a high-density level within the sandwich, as no molecules could migrate through graphene. The ability of integrating photocatalytic hydrogen generation and safe capsule storage has made the sandwich system an exciting candidate for realistic solar and hydrogen energy utilization.

Enhanced Solar-to-Hydrogen Generation with Broadband Epsilon-Near-Zero Nanostructured Photocatalysts

The direct conversion of solar energy into fuels or feedstock is an attractive approach to address increasing demand of renewable energy sources. Photocatalytic systems relying on the direct photoexcitation of metals have been explored to this end, a strategy that exploits the decay of plasmonic resonances into hot carriers. An efficient hot carrier generation and collection requires, ideally, their generation to be enclosed within few tens of nanometers at the metal interface, but it is challenging to achieve this across the broadband solar spectrum. Here the authors demonstrate a new photocatalyst for hydrogen evolution based on metal epsilon-near-zero metamaterials. The authors have designed these to achieve broadband strong light confinement at the metal interface across the entire solar spectrum. Using electron energy loss spectroscopy, the authors prove that hot carriers are generated in a broadband fashion within 10 nm in this system. The resulting photocatalyst achieves a hydrogen production rate of 9.5 µmol h^-1  cm^-2 that exceeds, by a factor of 3.2, that of the best previously reported plasmonic-based photocatalysts for the dissociation of H₂ with 50 h stable operation.