Laser ablation in air and its application in catalytic water splitting and Li-ion battery

Smart integration of cold plasma stream and surface discharge with ns laser ablation for composite nanomaterial

In this paper, smart integration of cold dielectric barrier discharge (DBD) plasma in various geometrical arrangements with laser ablation at atmospheric pressure for nanomaterial was described. A composite Co:ZnO target was ablated in an airflow by a nanosecond (ns) laser (wavelength: 1064 nm, pulse duration: 30 ns) using fluence of 5 J-cm-2 at a repetition rate of 10 Hz. The nanomaterial produced under vertical and oblique plasma streams, surface discharge and gas flow, were compared. Utilization surface discharge markedly improved the material adhesion by altering surface intrinsic behavior, inducing anticipated surface energy activation, chemical changes, and the formation of a densely packed solid structure. Under all conditions, the material consistently retained its crystalline nature, elemental composition, and ultraviolet emission characteristics. These preliminary findings hold promise for additional research, suggesting avenues for making complex materials in a flexible environment. Such new advancements could facilitate applications in the biomedical, catalysis, pharmaceutical, and surgical device domains.

Laser Ablation Nanoarchitectonics of Au-Cu Alloys Deposited on TiO2 Photocatalyst Films for Switchable Hydrogen Evolution from Formic Acid Dehydrogenation

The regulation of H₂ evolution from formic acid dehydrogenation using recyclable photocatalyst films is an essential approach for on-demand H₂ production. We have successfully generated Au-Cu nanoalloys using a laser ablation method and deposited them on TiO₂ photocatalyst films (Au _x Cu_100-x /TiO₂). The Au-Cu/TiO₂ films were employed as photocatalysts for H₂ production from formic acid dehydrogenation under light-emitting diode (LED) irradiation (365 nm). The highest H₂ evolution rate for Au₂₀Cu₈₀/TiO₂ is archived to 62,500 μmol h^-1 g^-1 per photocatalyst weight. The remarkable performance of Au₂₀Cu₈₀/TiO₂ may account for the formation of Au-rich surfaces and the effect of Au alloying that enables Cu to sustain the metallic form on its surface. The metallic Au-Cu surface on TiO₂ is vital to supply the photoexcited electrons of TiO₂ to its surface for H₂ evolution. The rate-determining step (RDS) is identified as the reaction of a surface-active species with protons. The results establish a practical preparation of metal alloy deposited on photocatalyst films using laser ablation to develop efficient photocatalysts.

Cobalt, Ferrum Co-Doped Ni3Se4 Nano-Flake Array: An Efficient Electrocatalyst for the Alkaline Hydrogen Evolution and Overall Water Splitting

Herein, Co, Fe co-doped Ni3Se4 nano-flake array (Ni0.62Co0.35Fe0.03)3Se4) was prepared on conductive carbon cloth by a two-step hydrothermal method. XRD and EDX analysis show that the nanosheets are monoclinic Ni3Se4, and Co, and Fe were doped into the lattice of Ni3Se4. Electrochemical tests showed that Co, Fe co-doping can effectively improve the hydrogen evolution activity of Ni3Se4 in acidic and alkaline environment. When the current density of (Ni0.62Co0.35Fe0.03)3Se4/CC is 10 mA/cm2 in 1 M KOH solution, the overpotentials of hydrogen evolution and oxygen evolution are 87 mV and 53.9 mV, respectively, and the Tafel slopes are 122.6 and 262 mV/dec. The electrochemical active area test (ECSA) and the polarization curve test further show that (Ni0.62Co0.35Fe0.03)3Se4/CC has a larger electrochemical active area (34.8 mF/cm2), lower electrolytic potential (0.9 V at 10 mA/cm2) and better stability. Therefore, the novel bifunctional catalyst synthesized by a simple method is a promising candidate for large-scale industrial water electrolysis.

Brookite, a sometimes under evaluated TiO2 polymorph

Brookite positively affects solar photocatalysis, electrocatalysis and electrochemical applications by stabilizing photogenerated e−/h+ pairs. Brookite-related heterojunctions, cus Ti atoms, surface acidity and redox behaviour are crucial aspects.

Improvement of the froth flotation of LiAlO2 and melilite solid solution via pre-functionalization

In this work froth flotation studies with LiAlO₂ (lithium-containing phase) and Melilite solid solution (gangue phase) are presented. The system was optimized with standard collectors and with compounds so far not applied as collectors. Furthermore, the principle of self-assembled monolayers was introduced to a froth flotation process for the first time resulting in excellent yields and selectivities.

Controllable Morphology of Sea-Urchin-like Nickel-Cobalt Carbonate Hydroxide as a Supercapacitor Electrode with Battery-like Behavior

Nickel-cobalt carbonate hydroxide with a three-dimensional (3D) sea-urchin-like structure was successfully developed by the hydrothermal process. The obtained structure enables the enhancement of charge/ion diffusion for the high-performance supercapacitor electrodes. The mole ratio of nickel to cobalt plays a vital role in the densely packed sea-urchin-like structure formation and electrochemical properties. At optimized nickel/cobalt mole ratio (1:2), the highest specific capacitance of 950.2 F g^-1 at 1 A g^-1 and the excellent cycling stability of 178.3% after 3000 charging/discharging cycles at 40 mV s^-1 are achieved. This nickel-cobalt carbonate hydroxide electrode yields an energy density in the range of 42.9-15.8 Wh kg^-1, with power density in the range of 285.0-2849.9 W kg^-1. The charge/discharge mechanism at the atomic level as monitored by time-resolved X-ray absorption spectroscopy (TR-XAS) indicates that the high capacitance behavior in a nickel-cobalt carbonate hydroxide is mainly dominated by cobalt carbonate hydroxide.

Influence of Temperature on ZnO/Co3O4 Nanocomposites for High Energy Storage Supercapacitors

We developed a two-step chemical bath deposition method followed by calcination for the production of ZnO/Co₃O₄ nanocomposites. In aqueous reactions, ZnO nanotubes were first densely grown on Ni foam, and then flat nanosheets of Co₃O₄ developed and formed a porous film. The aspect ratio and conductivity of the Co₃O₄ nanosheets were improved by the existence of the ZnO nanotubes, while the bath deposition from a mixture of Zn/Co precursors (one-step method) resulted in a wrinkled plate of Zn/Co oxides. As a supercapacitor electrode, the ZnO/Co₃O₄ nanosheets formed by the two-step method exhibited a high capacitance, and after being calcined at 450 °C, these nanosheets attained the highest specific capacitance (940 F g^-1) at a scan rate of 5 mV s^-1 in the cyclic voltammetry analysis. This value was significantly higher than those of single-component electrodes, Co₃O₄ (785 F g^-1) and ZnO (200 F g^-1); therefore, the presence of a synergistic effect was suggested. From the charge/discharge curves, the specific capacitance of ZnO/Co₃O₄ calcined at 450 °C was calculated to be 740 F g^-1 at a current density of 0.75 A g^-1, and 85.7% of the initial capacitance was retained after 1000 cycles. A symmetrical configuration exhibited a good cycling stability (Coulombic efficiency of 99.6% over 1000 cycles) and satisfied both the energy density (36.6 Wh kg^-1) and the power density (356 W kg^-1). Thus, the ZnO/Co₃O₄ nanocomposite prepared by this simple two-step chemical bath deposition and subsequent calcination at 450 °C is a promising material for pseudocapacitors. Furthermore, this approach can be applied to other metal oxide nanocomposites with intricate structures to extend the design possibility of active materials for electrochemical devices.

PtSe2 /Pt Heterointerface with Reduced Coordination for Boosted Hydrogen Evolution Reaction

PtSe₂ is a typical noble metal dichalcogenide (NMD) that holds promising possibility for next-generation electronics and photonics. However, when applied in hydrogen evolution reaction (HER), it exhibits sluggish kinetics due to the insufficient capability of absorbing active species. Here, we construct PtSe₂ /Pt heterointerface to boost the reaction dynamics of PtSe₂ , enabled by an in situ electrochemical method. It is found that Se vacancies are induced around the heterointerface, reducing the coordination environment. Correspondingly, the exposed Pt atoms at the very vicinity of Se vacancies are activated, with enhanced overlap with H 1s orbital. The adsorption of H^. intermediate is thus strengthened, achieving near thermoneutral free energy change. Consequently, the as-prepared PtSe₂ /Pt exhibits extraordinary HER activity even superior to Pt/C, with an overpotential of 42 mV at 10 mA cm^-2 and a Tafel slope of 53 mV dec^-1 . This work raises attention on NMDs toward HER and provides insights for the rational construction of novel heterointerfaces.

CNT-rGO Hydrogel-Integrated Fabric Composite Synthesized via an Interfacial Gelation Process for Wearable Supercapacitor Electrodes

We demonstrate a flexible and stretchable supercapacitor assembled via straightforward interfacial gelation of reduced graphene oxide (rGO) with carbon nanotube (CNT) on a stretchable fabric surface. The difference between the redox potential of aqueous graphene oxide (GO) dispersion, prepared using a modified Hummers' method, and of a solid Zn plate, which was used as an external stimulus, induces a spontaneous reduction of GO flakes forming porous CNT-rGO hydrogel at the liquid-solid interface. With the aid of Zn, a macroporous and flexible CNT-rGO hydrogel was fabricated on a stretchable fabric platform using a facile fabrication method, and the CNT-rGO fabric composite was assembled into a supercapacitor to demonstrate its feasibility as a wearable electrode. The porous structure of the as-formed CNT-rGO fabric composite allows excellent electrolyte accessibility and ion transport that result in a fast charge/discharge rate up to 100 mV/s and a large areal capacity of 10.13 mF/cm² at a discharge rate of 0.5 mA (0.1 mA/cm²). The inclusion of one-dimensional CNT as conductive bridges allows an excellent capacity retention of 95.2% after complete folding of the electrode and a capacity retention of 93.3% after 1000 bending cycles. Additional stretching test displayed a high capacity retention of 90.0% even at an applied strain as high as 50%, overcoming previous limitations of brittle graphene-based electrodes. This low-cost, lightweight, easy to synthesize, stretchable supercapacitor holds promise for next-generation wearable electronics and energy storage applications.

A three-dimensional nano-network WO3/F-TiO2-{001} heterojunction constructed with OH-TiOF2 as the precursor and its efficient degradation of methylene blue

In this study, three-dimensional nested WO₃/F-TiO₂-{001} photocatalysts with different WO₃ loadings were prepared by a hydrothermal process and used to degrade methylene blue (MB). The photocatalysts with various ratios of WO₃ to OH-TiOF₂ can be transformed into a three-dimensional network WO₃/F-TiO₂ hetero-structure with {001} surface exposure. The results showed that the composite catalyst with 5% WO₃, denoted as FWT5, had the best comprehensive degradation effect. FWT5 has a limited band gap of 2.9 eV, which can be used as an advanced photocatalyst to respond to sunlight and degrade MB. The average pore diameter of the composite catalyst is 10.3 nm, and the multi-point specific surface area is 56 m² g⁻¹. Compared with pure TiOF₂, the average pore size of the composite catalyst decreased by 8.44 nm and the specific surface area increased by 51.2 m² g⁻¹, which provides a larger contact space for the catalytic components and pollutants. Moreover, TiO₂ on the {001} surface has higher photocatalytic activity and methylene blue can be better degraded. Under the irradiation of 0.03 g FWT5 composite catalyst with a simulated solar light source for 2 h, the degradation rate of 10 mg L⁻¹ methylene blue can reach 82.9%. The trapping experiment showed that photo-generated holes were the principal functional component of WO₃/F-TiO₂-{001} photo-catalysis, which could capture OH⁻ and form hydroxyl radical (˙OH) and improved the photocatalytic degradation performance. Kinetic studies show that the photocatalytic degradation of MB fits with the quasi-first order kinetic model.

A new type of WO₃/F-TiO₂-{001} heterostructure semiconductor material with a three-dimensional network structure was successfully prepared by the hydrothermal method.

Experimental study on the degradation mechanism of LaCoO3-based symmetric supercapacitors

In this paper, LaCoO₃ powders were prepared by the urea combustion method and used as electrode materials for supercapacitors. The effect of the potential window and the current density on the performance degradation of LaCoO₃ electrodes during the cycling test was analyzed. The degradation mechanism of LaCoO₃-based symmetric supercapacitors was discussed. The results of the cycling test show that: with the increase in potential window and current density, the performance degradation in the cycling test becomes more intense. The results of cyclic voltammetry tests, galvanostatic charge–discharge tests, X-ray photoelectron spectroscopy tests and KOH electrolyte concentration measurements before and after the cycling test show that the degradation of the supercapacitors is mainly caused by the occurrence and accumulation of irreversible redox reactions during the charge and discharge process, which reduces the ratio of Co²⁺/Co³⁺ and the number of oxygen vacancies.

Cycling tests for LaCoO₃-based symmetric supercapacitors were carried out. The change in the valence state of Co in the electrode surface active material, LaCoO₃, before and after the cycling test was investigated by X-ray photoelectron spectroscopy.

Particle Size Effect of Lanthanum-Modified Bismuth Titanate Ceramics on Ferroelectric Effect for Energy Harvesting

Piezoelectric nanogenerators (PNGs) have been studied as renewable energy sources. PNGs consisting of organic piezoelectric materials such as poly(vinylidene fluoride) (PVDF) containing oxide complex powder have attracted much attention for their stretchable and high-performance energy conversion. In this study, we prepared a PNG combined with PVDF and lanthanum-modified bismuth titanate (Bi_4-XLa_XTi₃O₁₂, BLT) ceramics as representative ferroelectric materials. The inserted BLT powder was treated by high-speed ball milling and its particle size reduced to the nanoscale. We also investigated the effect of particle size on the energy-harvesting performance of PNG without polling. As a result, nano-sized powder has a much larger surface area than micro-sized powder and is uniformly distributed inside the PNG. Moreover, nano-sized powder-mixed PNG generated higher power energy (> 4 times) than the PNG inserted micro-sized powder.

Construction of a novel step-scheme CdS/Pt/Bi2MoO6 photocatalyst for efficient photocatalytic fuel denitrification

Construction of step-scheme (S-scheme) heterojunction (HJ) structures is an excellent strategy to achieve efficient photogenerated carrier separation and retain strong redox ability. Recently, the development of efficient S-scheme HJ photocatalysts for the degradation of environmental organic pollutants has attracted considerable attention. In this work, a novel S-scheme CdS/Pt/Bi₂MoO₆ (CPB) photocatalyst was prepared for the first time by sonochemical and solvothermal methods. By anchoring Pt nanoparticles (NPs) at the interface between CdS nanorods (NRs) and Bi₂MoO₆ nanosheets (NSs), the migration of photogenerated electron–hole pairs along the stepped path was achieved. The ternary CPB samples were characterized by various analytical techniques, and their photocatalytic performance was investigated by conducting simulated fuel denitrification under visible-light irradiation. It was found that the CPB-4 composites exhibited the highest pyridine degradation activity, which reached 94% after 4 h of visible-light irradiation. The superior photocatalytic performance of the CPB-4 composite could be attributed to the synergistic effect of the Pt NPs and Bi₂MoO₆ NRs on the photocatalytic degradation as well as to the introduction of Pt and Bi₂MoO₆, which led to an excellent response and large specific surface area of the CPB-4 composite. Lastly, the bridging role of the Pt NPs introduced into the S-scheme system was also notable, as it effectively improved the separation and transfer of the CdS/Bi₂MoO₆ interfaces for the photogenerated electron–hole pairs while retaining strong redox ability.

The S-scheme heterojunction in which Pt nanoparticles were anchored between CdS and Bi₂MoO₆ as ‘bridges’ enhanced the utilization of visible light and efficient separation of photogenerated electron–hole pairs.

The mechanism of enhanced photocatalytic activity for water-splitting of ReS2 by strain and electric field engineering

To enhance the photocatalytic water splitting performance of 2D ReS₂, we theoretically propose a feasible strategy to engineer its band structure by applying strain or an electric field. Our calculated results show that the strains greatly tune the electronic structure of ReS₂ especially band gap and band edge positions, because the strains significantly alter the crystal structure and then cause rearrangement of the surface charge. However, electric fields have little influence on band gap but obviously affect the band edge positions. This is because the electric fields have little effect on the crystal structure of ReS₂ but easily produce an in-plane electric dipole moment. The shifts in band edge position mainly arise from competition between the surface charge and the in-plane electric dipole. For an applied strain, the shifts are dominated by rearrangement of surface charge; for an applied electric field, the shifts are determined by an induced electric dipole moment. Importantly, functionalized ReS₂ with a bi-axial strain of −4% or an electronic field of −0.1 V Å⁻¹ may be good candidates for water-splitting photocatalysts owing to their suitable band edge positions for water splitting, ideal band gaps, good stability, reduced electron–hole recombination and high carrier mobility. We hope our findings will stimulate experimental efforts to develop new photocatalysts based on functionalized ReS₂.

This work proposes applying the strain and electric filed to engineer the band structure of 2D ReS₂ and enhance its photocatalytic activity for hydrogen production through water-splitting.

Constructing NiSe2@MoS2 nano-heterostructures on a carbon fiber paper for electrocatalytic oxygen evolution

Although MoS₂ has shown its potential as an electro-catalyst for the oxygen evolution reaction (OER), its research is still insufficient. In this study, as a novel MoS₂-based heterostructure electro-catalyst for OER, namely NiSe₂@MoS₂ nano-heterostructure, was constructed on a carbon fiber paper (CFP) substrate by a simple approach, which includes electrochemical deposition of NiSe₂ film and hydrothermal processing of MoS₂ film. In addition to a series of observations on the material structure, electrocatalytic OER performance of NiSe₂@MoS₂ was fully evaluated and further compared with other MoS₂-based OER electro-catalysts. It exhibits an outstanding catalytic performance with an overpotential η₁₀ of 267 mV and a Tafel slope of 85 mV dec⁻¹. Only 6% loss of current density before and after 10 h indicates its excellent durability. The results indicate that the obtained NiSe₂@MoS₂ is an excellent OER electro-catalyst and worth exploring as a substitute for noble metal-based materials.

Although MoS₂ has shown its potential as an electro-catalyst for the oxygen evolution reaction (OER), its research is still insufficient.

Preparation of F-doped H2Ti3O7-{104} nanorods with oxygen vacancies using TiOF2 as precursor and its photocatalytic degradation activity

Photocatalytic degradation is an eco-friendly and sustainable method for the treatment of water pollutants especially tetracycline hydrochloride (TCH). Herein, we developed F-doped H₂Ti₃O₇-{104} nanorods with oxygen vacancies using TiOF₂ as a precursor by simple alkali hydrothermal and ion-exchange methods. The phase structure, surface composition, optical properties, specific surface areas and charge separation were analysed by a series of measurements. The effects of KOH concentration on the structure and properties of H₂Ti₃O₇ were investigated. It is confirmed that the TiOF₂/H₂Ti₃O₇ composite can be formed in low concentration KOH solution (1 mol L⁻¹), while the H₂Ti₃O₇ single phase can be formed in high concentration KOH solution (>3 mol L⁻¹). The prepared F-doped H₂Ti₃O₇-{104} nanorods provide a high specific surface area of 457 m² g⁻¹ and a macroporous volume of 0.69 cm³ g⁻¹. The appropriate mesoporous structure of the photocatalyst makes TCH have a stronger affinity on its surface, which is more conducive to the subsequent photodegradation. Moreover, a synergistic mechanism of photosensitization and ligand–metal charge transfer (LMCT) in the photocatalytic degradation of TCH was proposed. In addition, the prepared F-doped H₂Ti₃O₇-{104} nanorods showed excellent cycle stability and resistance to light corrosion. After five cycles of photodegradation, the degradation rate of TCH was only reduced from 92% to 83%. This low-cost strategy could be used for the mass production of efficient photocatalysts, which can be used for TCH clean-up in wastewater treatment.

Efficient photocatalytic degradation of tetracycline hydrochloride by F-doped H₂Ti₃O₇-{104} nanorods.