Synergistic Interactions of Bulk Polarization and Built-In Electric Field Inducing 2D/2D S-Scheme Homojunction Toward Enhanced Photocatalytic Performance.

The rational design of S-scheme photocatalysts, achieved by serially integrating two different semiconductors, represents a promising strategy for efficient charge separation and amplified photocatalytic performance, yet it remains a challenge. Herein, ZnIn2S4 (ZIS) and oxygen-doped ZnIn2S4 (O-ZIS) nanosheets are chosen to construct a homojunction catalyst architecture. Theoretical simulations alongside comprehensive in situ and ex situ characterizations confirm that ZIS and O-ZIS with noncentrosymmetric layered structures can generate a polarization-induced bulk-internal electric field (IEF) within the crystal. A robust interface-IEF is also created by the strong interfacial interaction between O-ZIS and ZIS with different work functions. Owing to these features, the O-ZIS/ZIS homojunction adopts an S-scheme directional charge transfer route, wherein photoexcited electrons in ZIS and holes in O-ZIS concurrently migrate to their interface and subsequently recombine. This enables spatial charge separation and provides a high driving force for both reduction and oxidation reactions simultaneously. Consequently, such photocatalyst exhibits an H2 evolution rate up to 142.9 µmol h-1 without any cocatalysts, which is 4.6- and 3.4-fold higher than that of pristine ZIS and O-ZIS, respectively. Benzaldehyde is also produced as a value-added oxidation product with a rate of 146.9 µmol h-1. This work offers a new perspective on the design of S-scheme systems.

Band Structure Tuning via Pt Single Atom Induced Rapid Hydroxyl Radical Generation toward Efficient Photocatalytic Reforming of Lignocellulose into H2.

Photocatalytic lignocellulose reforming for H2 production presents a compelling solution to solve environmental and energy issues. However, achieving scalable conversion under benign conditions faces consistent challenges including insufficient active sites for H2 evolution reaction (HER) and inefficient lignocellulose oxidation directly by photogenerated holes. Herein, it is found that Pt single atom-loaded CdS nanosheet (PtSA-CdS) would be an active photocatalyst for lignocellulose-to-H2 conversion. Theoretical and experimental analyses confirm that the valence band of CdS shifts downward after depositing isolated Pt atoms, and the slope of valence band potential on pH for PtSA-CdS is more positive than Nernstian equation. These characteristics allow PtSA-CdS to generate large amounts of •OH radicals even at pH 14, while the capacity is lacking with CdS alone. The employment of •OH/OH- redox shuttle succeeds in relaying photoexcited holes from the surface of photocatalyst, and the •OH radicals can diffuse away to decompose lignocellulose efficiently. Simultaneously, surface Pt atoms, featured with a thermoneutral Δ G H ∗ $\Delta G_{\mathrm{H}}^{\mathrm{*}}$ , would collect electrons to expedite HER. Consequently, PtSA-CdS performs a H2 evolution rate of 10.14 µmol h-1 in 1 m KOH aqueous solution, showcasing a remarkable 37.1-fold enhancement compared to CdS. This work provides a feasible approach to transform waste biomass into valuable sources.

Enhanced durability of Pd/CeO2-C via metal-support interaction for oxygen reduction reaction.

It is a challenge to improve the long-term durability of Pd-based electrocatalysts for oxygen reduction reaction (ORR) in fuel cells. Herein, Pd/CeO2-C-T (T= 800 °C, 900 °C and 1000 °C) hybrid catalysts with metal-support interaction are prepared from Ce-based metal organic framework precursor. Abundant tiny CeO2nanoclusters are produced to form nanorod structures with uniformly distributed carbon through a calcination process. Meanwhile, both carbon and CeO2nanoclusters have good contact with the following deposited surfactant-free Pd nanoclusters. Benefited from the large specific surface area, good conductivity and structure integrity, Pd/CeO2-C-900 exhibits the best electrocatalytic ORR performance: onset potential of 0.968 V and half-wave potential of 0.857 V, outperforming those obtained on Pd/C counterpart. In addition, the half-wave potential only shifts 7 mV after 6000 cycles of accelerated durability testing, demonstrating robust durability.

Defect-Induced Atomic Arrangement in CoFe Bimetallic Heterostructures with Boosted Oxygen Evolution Activity.

Three CoFe-bimetallic oxides with different compositions (termed as CoFeOx -A/N/H) are prepared by thermally treating metal-organic-framework (MOF) precursors under different atmospheres (air, N2, and NaBH4 /N2 ), respectively. With the aid of vast oxygen vacancies (Ov ), cobalt at tetrahedral sites (Co2+ (Th)) in spinel Co3 O4 is diffused into interstitial octahedral sites (Oh) to form rocksalt CoO and ternary oxide CoFe2 O4 has been induced to give the unique defective CoO/CoFe2 O4 heterostructure. The resultant CoFeOx -H exhibits superb electrocatalytic activity toward water oxidation: overpotential at 10 mA cm-2 is 192 mV, which is 122 mV smaller than that of CoFeOx -A. The smaller Tafel slope (42.53 mV dec-1 ) and higher turnover frequency (785.5 h-1 ) suggest fast reaction kinetics. X-ray absorption spectroscopy, ex situ characterizations, and theoretical calculations reveal that defect engineering effectively tunes the electronic configuration to a more active state, resulting in the greatly decreased binding energy of oxo intermediates, and consequently much lower catalytic overpotential. Moreover, the construction of hetero-interface in CoFeOx -H can provide rich active sites and promote efficient electron transfer. This work may shed light on a comprehensive understanding of the modulation of electron configuration of bimetallic oxides and inspire the smart design of high-performance electrocatalysts.

Cooperative effect of bimetallic MOF-derived CoNi(OH)2@NiCo2S4nanocomposite electrocatalysts with boosted oxygen evolution activity.

Highly efficient and inexpensive electrocatalysts for oxygen evolution reaction (OER) are extensively studied for water splitting. Herein, a unique bimetallic nanocomposite CoNi(OH)2@NiCo2S4nanosheet arrays derived from metal-organic-frameworks (MOFs, CoNi-ZIF) is simply fabricated on Ni foam, endowing large specific surface area and outstanding electrical conductivity. Compared with their single-metallic counterparts, the bimetallic composite displays dramatically low overpotential and small Tafel slope as well as outstanding catalytic stability. The overpoptential at 20 mA cm-2for CoNi(OH)2@NiCo2S4is only 230 mV in comparison with Ni(OH)2@Ni3S2(266 mV), Co(OH)2@Co3S4(294 mV) and RuO2(η = 302 mV). First-principle calculations based on density functional theory (DFT) are carried out and reveal that the introduction of Ni in Co(OH)2helps lowered the energy difference of ΔGOOH*-ΔGO*, and thereby boosting the OER reactivity. This study provides an effective approach for the rational construction of low-cost metal hybrids.

Dramatic Responsivity Enhancement Through Concentrated H2 SO4 Treatment on PEDOT:PSS/TiO2 Heterojunction Fibrous Photodetectors.

In order to satisfy the growing requirements of wearable electronic devices, 1D fiber-shaped devices with outstanding sensitivity, flexibility, and stability are urgently needed. In this study, a novel inorganic-organic heterojunction fibrous photodetector (FPD) based on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and highly ordered TiO2 nanotube array is fabricated, which endows a high responsivity, large external quantum efficiency, and fast response speed at 3 V bias. To further ameliorate its performance in the self-powered mode, a facile acid treatment is adopted and the assembled H-PEDOT:PSS/TiO2 FPD demonstrates outstanding self-powered properties with ≈3000% responsivity enhancement (161 mA W-1 at 0 V under 365 nm irradiation, photocurrent enhancement of ≈50 times) compared with the untreated device. It is found that the concentrated H2 SO4 post-treatment helps decrease the tube wall thickness of TiO2 and partially removes the insulated PSS component in PEDOT:PSS, leading to enhanced conductivity and facilitated charge transportation, and thereby superb responsivity/photocurrent enhancement of self-powered H-PEDOT:PSS/TiO2 FPD. This low-cost and high-performance self-powered FPD shows high potential for applications in wearable electronic devices.

Novel UV-Visible Photodetector in Photovoltaic Mode with Fast Response and Ultrahigh Photosensitivity Employing Se/TiO2 Nanotubes Heterojunction.

A feasible strategy for hybrid photodetector by integrating an array of self-ordered TiO2 nanotubes (NTs) and selenium is demonstrated to break the compromise between the responsivity and response speed. Novel heterojunction between the TiO2 NTs and Se in combination with the surface trap states at TiO2 help regulate the electron transport and facilitate the separation of photogenerated electron-hole pairs under photovoltaic mode (at zero bias), leading to a high responsivity of ≈100 mA W-1 at 620 nm light illumination and the ultrashort rise/decay time (1.4/7.8 ms). The implanting of intrinsic p-type Se into TiO2 NTs broadens the detection range to UV-visible (280-700 nm) with a large detectivity of over 1012 Jones and a high linear dynamic range of over 80 dB. In addition, a maximum photocurrent of ≈107 A is achieved at 450 nm light illumination and an ultrahigh photosensitivity (on/off ratio up to 104 ) under zero bias upon UV and visible light illumination is readily achieved. The concept of employing novel heterojunction geometry holds great potential to pave a new way to realize high performance and energy-efficient optoelectronic devices for practical applications.

Novel Structure for High Performance UV Photodetector Based on BiOCl/ZnO Hybrid Film.

A novel type of high performance ultraviolet (UV) photodetector (PD) based on a ZnO film has been prepared by incorporating a BiOCl nanostructure into the film. The responsivity of the BiOCl/ZnO hybrid film PD in UV region can reach 182.87 mA W-1 , which is about 2.72 and 6.87 times for that of TiO2 /ZnO hybrid film PD and pure ZnO film PD. The rise/decay time of BiOCl/ZnO hybrid film PD is 25.83/11.25 s, which is much shorter than that of TiO2 /ZnO hybrid film PD (51.94/26.05 s) and pure ZnO film PD (69.34/>120 s). The BiOCl nanostructure can inject photogenerated electrons into the ZnO film under UV light illumination, leading to the increase of photocurrent, and forms barriers to block the straight transmission of electrons between electrodes, resulting in the decrease of decay time. The results of control experiment show that the transfer path of photogenerated electrons formed by p-n junction will be cut off after depositing gold nanoparticles on the film surface, which means this hybrid film is a unique and novel structure to improve the optoelectronic performance of photodetectors. This novel BiOCl/ZnO hybrid structure paves new route for the development of film PDs based on ZnO film.

Wavelength-Tunable Electroluminescent Light Sources from Individual Ga-Doped ZnO Microwires.

Electrically driven wavelength-tunable light emission from biased individual Ga-doped ZnO microwires (ZnO:Ga MWs) is demonstrated. Single crystalline ZnO:Ga MWs with different Ga-doping concentrations have been synthesized using a one-step chemical vapor deposition method. Strong electrically driven light emission from individual ZnO:Ga MW based devices is realized with tunable colors, and the emission region is localized toward the center of the wires. Increasing Ga-doping concentration in the MWs can lead to the redshift of electroluminescent emissions in the visible range. Interestingly, owing to the lack of rectification characteristics, relevant electrical measurement results show that the alternating current-driven light emission functions excellently on the ZnO:Ga MWs. Consequently, individual ZnO:Ga MWs, which can be analogous to incandescent sources, offer unique possibilities for future electroluminescence light sources. This typical multicolor emitter can be used to rival and complement other conventional semiconductor devices in displays and lighting.

Hierarchical MoS2 Nanosheet@TiO2 Nanotube Array Composites with Enhanced Photocatalytic and Photocurrent Performances.

A novel type of hierarchical nanocomposites consisted of MoS2 nanosheet coating on the self-ordered TiO2 nanotube arrays is successfully prepared by a facile combination of anodization and hydrothermal methods. The MoS2 nanosheets are uniformly decorated on the tube top surface and the intertubular voids with film appearance changing from brown to black color. Anatase TiO2 nanotube arrays (NTAs) with clean top surfaces and the appropriate amount of MoS2 precursors are key to the growth of perfect compositing TiO2 @MoS2 hybrids with significantly enhanced photocatalytic activity and photocurrent response. These results reveal that the strategy provides a flexible and straightforward route for design and preparation nanocomposites based on functional semiconducting nanostructures with 1D self-ordered TiO2 NTAs, promising for new opportunities in energy/environment applications, including photocatalysts and other photovoltaic devices.

Ultrasensitive Self-Powered Solar-Blind Deep-Ultraviolet Photodetector Based on All-Solid-State Polyaniline/MgZnO Bilayer.

A high sensitivity self-powered solar-blind photodetector is successfully constructed based on the polyaniline/MgZnO bilayer. The maximum responsivity of the photodetector is 160 µA W-1 at 250 nm under 0 V bias. The device also exhibits a high on/off ratio of ≈104 under 250 nm illumination at a relatively weak light intensity of 130 µW cm-2 without any power.

Formation of mesoporous heterostructured BiVO4/Bi2S3 hollow discoids with enhanced photoactivity.

Semiconductor heterostructures are of great interest in a wide range of applications. In this work, we design and synthesize a novel heteronanostructure with controlled relative composition, i.e., BiVO4/Bi2S3 hollow discoid-like particles with mesoporous shell. The synthesis involves a facile anion exchange process by reacting pre-synthesized BiVO4 discoid-like particles with Na2S in an aqueous solution. Benefiting from the unique structural features and the formation of heterostructure, the as-prepared BiVO4/Bi2S3 hollow discoids exhibit significantly enhanced photoelectrochemical current response and photocatalytic activity for reduction of Cr(VI) under visible-light illumination.

Selective removal of the outer shells of anodic TiO2 nanotubes.

A facile electrochemical method to selectively remove the outer walls of anodic TiO(2) nanotubes by leaving the as-anodized nanotubes in the same electrolyte and applying an electric field parallel to the anodic film for several minutes is reported. The better-separated single-walled TiO(2) nanotubes thus obtained show significantly improved photocatalytic efficiency compared with their non-etched counterparts.

High-Valence Mo Doping and Oxygen Vacancy Engineering to Promote Morphological Evolution and Oxygen Evolution Reaction Activity.

The rational design of high-efficiency, low-cost electrocatalysts for electrochemical water oxidation in alkaline media remains a huge challenge. Herein, combined strategies of metal doping and vacancy engineering are employed to develop unique Mo-doped cobalt oxide nanosheet arrays. The Mo dopants exist in the form of high-valence Mo6+, and the doping amount has a significant effect on the structure morphology, which transforms from 1D nanowires/nanobelts to 2D nanosheets and finally 3D nanoflowers. In addition, the introduction of vast oxygen vacancies helps to modulate the electronic states and increase the electronic conductivity. The optimal catalyst MoCoO-3 exhibits greatly increased active sites and enhanced reaction kinetics. It gives a dramatically lower overpotential at 50 mA cm-2 (288 mV), much smaller than that of the undoped counterpart (418 mV) and comparable to those of the recently reported electrocatalysts. Density functional theory results further verify that the increased electronic conductivity and optimized adsorption energy toward oxygen evolution reaction intermediates are mainly responsible for the enhanced catalytic activity. Moreover, the assembled two-electrode electrolyzer (MoCoO-3||Pt/C) exhibits superior performance with the cell potential decreased by 233 mV to reach a current density of 50 mA cm-2 with respect to the benchmark counterpart catalysts (RuO2||Pt/C). This work might contribute to the rational design of effective, low-cost electrocatalyst materials by combining multiple strategies.

Porous metal-based multilayers for selective thermal emitters.

We report the numerical study of a selective thermal emitter based on a metallic multilayered structure consisting of a graded antireflection top layer, a middle layer with uniform porosity (i.e., volume fraction of voids), and a nonporous substrate layer. Simulation results show that the proposed emitters feature an emission edge in near-IR where the emissivity drops from over 0.9 to below 0.1, for both the TE and TM polarizations. Moreover, these desired emission characteristics persist for a wide range of emission angles with the emission edge nearly nonshifted, making the proposed emitters promising for achieving isotropic thermal emission. The designed emitters are particularly attractive for the thermal-photovoltaic applications by suppressing emission below the photovoltaic material bandgap, which is normally in near-IR.

Assessment of recycling methods and processes for lithium-ion batteries.

This review discusses physical, chemical, and direct lithium-ion battery recycling methods to have an outlook on future recovery routes. Physical and chemical processes are employed to treat cathode active materials which are the greatest cost contributor in the production of lithium batteries. Direct recycling processes maintain the original chemical structure and process value of battery materials by recovering and reusing them directly. Mechanical separation is essential to liberate cathode materials that are concentrated in the finer size region. However, currently, the cathode active materials are being concentrated at a cut point that is considerably greater than the actual size found in spent batteries. Effective physical methods reduce the cost of subsequent chemical treatment and thereafter re-lithiation successfully reintroduces lithium into spent cathodes. Some of the current challenges are the difficulty in controlling impurities in recovered products and ensuring that the entire recycling process is more sustainable.

TiO2@PDA inorganic-organic core-shell skeleton supported Pd nanodots for enhanced electrocatalytic hydrodechlorination.

The development of catalysts with high atom utilization and activity is the biggest challenge for electrocatalytic hydrodechlorination (EHDC) technology. Herein, a design strategy of TiO2@PDA inorganic-organic core-shell skeleton for loading lower dosage of noble palladium (Pd) with robust activity is reported. The self-supported TiO2@PDA nanorod arrays provides exposed surface area for anchoring Pd and PDA as interlayer controls the Pd nucleation to form nanodots with high dispersion, realizing high atom utilization. Moreover, the strong interaction between PDA and Pd realizes the coexistence of electron-rich and deficient Pd species with suitable proportion, which facilitate the H* formation and the C-Cl bond activation, respectively, resulting in the promoted activity. The optimal TiO2@PDA/Pd electrode exhibits a low dosage of Pd (0.093 mg cm-2) and excellent activity for 4-chlorophenol reduction with a mass activity (MA) of 23.96 min-1g-1, which is 3.31 times as high as that of TiO2/Pd. The design scheme with inorganic-organic core-shell skeleton as support is benefit for developing highly efficient and lower price elctrocatalysts for EHDC.

Machine Learning Guided Dopant Selection for Metal Oxide-Based Photoelectrochemical Water Splitting: The Case Study of Fe2 O3 and CuO.

Doping is an effective strategy for tuning metal oxide-based semiconductors for solar-driven photoelectrochemical (PEC) water splitting. Despite decades of extensive research effort, the dopant selection is still largely dependent on a trial-and-error approach. Machine learning (ML) is promising in providing predictable insights on the dopant selection for high-performing PEC systems because it can uncover correlations from the seemingly ambiguous linkages between vast features of dopants and the PEC performance of doped photoelectrodes. Herein, the authors successfully build ML model to predict the doping effect of 17 metal dopants into hematite (Fe2 O3 ), a prototype photoelectrode material. Their findings disclose the critical parameters from the 10 intrinsic features of each dopant. The model is further experimentally validated by the coherent prediction on Y and La dopants' behaviors. Further interpretation of the ML model suggests that the chemical state is the most significant selection criteria, meanwhile, dopants with higher metal-oxygen bond formation enthalpy and larger ionic radius are favored in improving the charge separation and transfer (CST) in the Fe2 O3 photoanodes. The generic feature of this ML guided selection criteria has been further extended to CuO-based photoelectrodes showing improved CST by alkaline metal ions doping.

Protruding Pt single-sites on hexagonal ZnIn2S4 to accelerate photocatalytic hydrogen evolution.

Single-site cocatalysts engineered on supports offer a cost-efficient pathway to utilize precious metals, yet improving the performance further with minimal catalyst loading is still highly desirable. Here we have conducted a photochemical reaction to stabilize ultralow Pt co-catalysts (0.26 wt%) onto the basal plane of hexagonal ZnIn2S4 nanosheets (PtSS-ZIS) to form a Pt-S3 protrusion tetrahedron coordination structure. Compared with the traditional defect-trapped Pt single-site counterparts, the protruding Pt single-sites on h-ZIS photocatalyst enhance the H2 evolution yield rate by a factor of 2.2, which could reach 17.5 mmol g-1 h-1 under visible light irradiation. Importantly, through simple drop-casting, a thin PtSS-ZIS film is prepared, and large amount of observable H2 bubbles are generated, providing great potential for practical solar-light-driven H2 production. The protruding single Pt atoms in PtSS-ZIS could inhibit the recombination of electron-hole pairs and cause a tip effect to optimize the adsorption/desorption behavior of H through effective proton mass transfer, which synergistically promote reaction thermodynamics and kinetics.

Pseudohomogeneous metallic catalyst based on tungstate-decorated amphiphilic carbon quantum dots for selective oxidative scission of alkenes to aldehyde.

Herein, we present an interesting role of tungstate-decorated amphiphilic carbon quantum dots (A-CQDs/W) in the selective oxidative cleavage of alkenes to aldehydes. In this work, for the first time, we disclose an unprecedented tungstate-based oxidative system incorporating A-CQDs as a bridge to the homogeneous catalyst for selective and efficient cleavage of a wide substrate scope of alkenes into aldehydes. The A-CQDs/W were synthesized via a one-step hydrothermal synthesis approach using 1-aminopropyl-3-methyl-imidazolium chloride and stearic acid for the surface modification, following by anion-exchange to immobilize WO4-2 to A-CQDs. The A-CQDs/W act as a pseudohomogeneous metallic catalyst (PMC) for selective oxidative scission of alkenes under phase transfer catalysts (PTC) free condition without over oxidation to acids, using water and H2O2 as a green oxidant. Thanks to the sub-nanometric size and novel engineered chemical structure, this PMC and reactants are in the same phase, besides they can be easily isolated from each other by extraction processes. The synthesized PMC exhibited excellent solubility and stability in various solvents. Interestingly, the system's high conversion efficiency was preserved even after eight catalytic cycles indicating the recyclability of the synthesized PMC. We believe that this study provides a significant and conceptually novel advance in oxidative cleavage chemistry.