Enhancement of Electrocatalytic Oxygen Reduction Reaction and Oxygen Evolution Reaction by Introducing Lanthanum Species in the Carbon Shell.

The development of cost-effective non-noble metal electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) opens up the possibility for sustainable energy systems. Herein, we report a surface overcoating strategy with lanthanum organic complex (La-OC) as the precursor to prepare lanthanum species (La-SPc) encapsulated in nitrogen, fluorine, and sulfur self-doped porous carbon (NFS-PC) composites (La-SPc@NFS-PC) for efficient ORR and OER. The La-SPc is introduced not only as a promoter to increase the electrochemical stability of the La-SPc@NFS-PC catalysts but also to tailor the electronic structure of NFS-PC due to the unique electrochemical properties of La-SPc. In addition, the integration of La-SPc and NFS-PC can improve the electronic conductivity of composites by inducing electron redistribution and lowering the band gap, which is advantageous in enhancing the kinetics of charge transfer. Simultaneously, benefiting from the optimized porous structure and positive cooperation of La-SPc with NFS-PC shells, the obtained La-SPc@NFS-PC-3 delivers robust bifunctional ORR/OER activities and stabilities. More importantly, the Zn-air battery (ZAB) assembled with La-SPc@NFS-PC-3 demonstrates an outstanding power density (181.1 mW cm-2) and long cycling life, outperforming the commercial Pt/C. This work offers a rational approach to preparing high-efficiency rare-earth-based catalysts and provides potential applications in ZABs.

Correction: Fabrication and behaviors of CdS on Bi2MoO6 thin film photoanodes.

[This corrects the article DOI: 10.1039/C6RA28323C.].

Nitrogen-incorporation activates NiFeOx catalysts for efficiently boosting oxygen evolution activity and stability of BiVO4 photoanodes.

Developing low-cost and highly efficient catalysts toward the efficient oxygen evolution reaction (OER) is highly desirable for photoelectrochemical (PEC) water splitting. Herein, we demonstrated that N-incorporation could efficiently activate NiFeOx catalysts for significantly enhancing the oxygen evolution activity and stability of BiVO4 photoanodes, and the photocurrent density has been achieved up to 6.4 mA cm-2 at 1.23 V (vs. reversible hydrogen electrode (RHE), AM 1.5 G). Systematic studies indicate that the partial substitution of O sites in NiFeOx catalysts by low electronegative N atoms enriched the electron densities in both Fe and Ni sites. The electron-enriched Ni sites conversely donated electrons to V sites of BiVO4 for restraining V5+ dissolution and improving the PEC stability, while the enhanced hole-attracting ability of Fe sites significantly promotes the oxygen-evolution activity. This work provides a promising strategy for optimizing OER catalysts to construct highly efficient and stable PEC water splitting devices.

Unveiling the Activity and Stability Origin of BiVO4 Photoanodes with FeNi Oxyhydroxides for Oxygen Evolution.

Understanding the origin of formation and active sites of oxygen evolution reaction (OER) cocatalysts is highly required for solar photoelectrochemical (PEC) devices that generate hydrogen efficiently from water. Herein, we employed a simple pH-modulated method for in situ growth of FeNi oxyhydroxide ultrathin layers on BiVO4 photoanodes, resulting in one of the highest currently known PEC activities of 5.8 mA cm-2 (1.23 VRHE , AM 1.5 G) accompanied with an excellent stability. More importantly, both comparative experiments and density functional theory (DFT) studies clearly reveal that the selective formation of Bi-O-Fe interfacial bonds mainly contributes the enhanced OER activities, while the construction of V-O-Ni interfacial bonds effectively restrains the dissolution of V5+ ions and promotes the OER stability. Thereby, the synergy between iron and nickel of FeNi oxyhydroxides significantly improved the PEC water oxidation properties of BiVO4 photoanodes.

Photocorrosion inhibition of CdS-based catalysts for photocatalytic overall water splitting.

The urgent need for clean and renewable energy drives the exploration of effective strategies to produce hydrogen. Semiconductor-based photocatalytic hydrogen production technology is one of the ideal processes for direct solar energy conversion and storage that has been widely studied. The development of highly efficient photocatalysts is essential for the cost-effective and large-scale production of hydrogen. CdS-based semiconductor photocatalysts have attracted significant attention due to their unique advantages, including strong visible light absorption capacity, suitable band edge levels and excellent electronic charge transfer. However, unlike TiO2 with good photostability, the intrinsic drawback of photocorrosion of CdS-based semiconductors significantly challenges their durable application in photocatalysis. This review focuses on recent advances in material design and strategies for improving the anti-photocorrosion of CdS-based photocatalysts for applications in photocatalytic overall water splitting to produce hydrogen. Moreover, brief prospective development and challenges in the synthesis of anti-corrosion CdS-based photocatalysts are also presented.

Enantiomer-selective sensing and the light response of chiral molecules coated with a persistent luminescent material.

Pr3+:CaTiO3, a robust persistent luminescent material, was coupled with chiral molecules and Ag nanoparticles (NPs) to construct a Pr3+:CaTiO3@Ag@l-cysteine ternary material that can realize rapid enantiomer selective sensing of l- and d-arginine by making use of the chiral induced spin selectivity (CISS) effect. In addition, long-lifetime photoelectrons excited in the Pr3+:CaTiO3 matrix were effectively transported through a Ag NP "bridge" into the l-cysteine chiral monolayer, due to cooperation between each component in the ternary material.

Assembly of Ultra-Thin NiO Layer Over Zn1-x Cdx S for Stable Visible-Light Photocatalytic Overall Water Splitting.

Photocatalytic splitting of water into hydrogen and oxygen by using visible light is considered to be a clean, green, and renewable route for solar energy conversion and storage. Although the Zn1-x Cdx S catalysts show comparatively higher activity for photocatalytic hydrogen generation under visible-light irradiation, they suffer from serious photocorrosion during the photocatalytic reaction. The deposition of a protective layer over the Zn1-x Cdx S catalysts is believed to be an effective way to inhibit photocorrosion. However, only a few materials exhibit satisfactory catalytic properties for hydrogen evolution as well as a good protection ability. In this work, a new Zn1-x Cdx S photocatalyst was developed for water splitting under visible-light illumination by assembling an ultrathin NiO layer over Zn0.8 Cd0.2 S through an in situ photodeposition method. The as-prepared NiO/Zn0.8 Cd0.2 S showed significantly higher activity for overall water splitting compared with Pt/Zn0.8 Cd0.2 S under the same conditions without photocorrosion. An apparent quantum efficiency of 0.66 % was achieved for hydrogen evolution at 430 nm with an accomplished multicycle stability for up to 12 h without any significant decay. The strong electronic coupling between the NiO layer and Zn1-x Cdx S also promoted efficient charge separation and migration.

Oxidized multiwalled carbon nanotubes coated fibers for headspace solid-phase microextraction of amphetamine-type stimulants in human urine.

Carbon nanotubes (CNTs) have attracted a lot of attention as effective sorbents due to their strong sorption properties and several potential applications in many fields. In this work, the acid oxidized multiwalled carbon nanotubes (MWCNTs-COOH) was coated onto a stainless steel wire by a simple physical adhesion approach to develop solid-phase microextraction (SPME) fibers. By combination of the MWCNTs-COOH coated fiber-based headspace SPME and gas chromatography-mass spectrometry (GC-MS), the developed method demonstrates a good enhancement factor (288-651), low limits of detection (LODs, 0.2-1.3µg/L) for determination of amphetamine-type stimulant drugs (ATSs) in urine samples. The recoveries of the spiked ATSs (5, 50 and 500µg/L) were in the range of 88-107%, the calibration curve was linear for concentrations of analytes in the range from 0.5 to 1000µg/L (R=0.963-0.999). Furthermore, single fiber repeatability and fiber-to-fiber reproducibility were in the range of 2.3%-6.2% (n=6) and 5.7%-9.8% (n=3), respectively. The MWCNTs-COOH coated fiber is highly thermally stable and can be used over 150 times. The method was successfully applied to the forensic determination of amphetamine (AMP) and methamphetamine (MAMP) in human urine samples and satisfactory results were achieved.

Facile synthesis of -C[double bond, length as m-dash]N- linked covalent organic frameworks under ambient conditions.

We reported herein a facile approach for the synthesis of -C[double bond, length as m-dash]N- linked covalent organic frameworks under ambient conditions. Three known (COF-42, COF-43, and COF-LZU1) and one new (Pr-COF-42) COF materials were successfully synthesized using this method. Furthermore, this simple synthetic approach makes the large-scale synthesis of -C[double bond, length as m-dash]N- linked COFs feasible.

Fe/W Co-Doped BiVO4 Photoanodes with a Metal-Organic Framework Cocatalyst for Improved Photoelectrochemical Stability and Activity.

BiVO4 has been identified as one of the excellent visible light responsive photoanodes for use in photoelectrochemical (PEC) water splitting. However, pristine BiVO4 usually exhibits relative low photocatalytic properties owing to insufficient charge separation and transport characteristics. Although the marginal n-type doping of higher valence ions can obviously raise the photocurrent value, it by no means improves the PEC stability. In this work, we successfully enhanced the PEC stability of BiVO4 by doping Fe ions in substitution of Bi. Density functional theory calculations have illustrated that Fe-doping would result in an impurity band in the forbidden gap, and thus narrow its energy gap. More importantly, Fe-doping can synergize with other means to further improve the PEC activities of BiVO4 . Therefore, we fabricated a nanoporous Fe/W co-doped BiVO4 photoelectrode, and then loaded the metal-organic framework (MOF) MIL-100(Fe) as cocatalyst to further promote the separation of charge carriers. To the best of our knowledge, MOFs have not yet been utilized as a cocatalyst to facilitate the charge separation, which could increase the photocurrent density of Fe/W co-doped BiVO4 .

Fabrication of Low Adsorption Energy Ni-Mo Cluster Cocatalyst in Metal-Organic Frameworks for Visible Photocatalytic Hydrogen Evolution.

An effective cocatalyst is crucial for enhancing the visible photocatalytic performance of the hydrogen generation reaction. By using density-functional theory (DFT) and frontier molecular orbital (FMO) theory calculation analysis, the hydrogen adsorption free energy (ΔGH) of Ni-Mo alloy (458 kJ·mol(-1)) is found to be lower than that of Ni itself (537 kJ·mol(-1)). Inspired by these results, the novel, highly efficient cocatalyst NiMo@MIL-101 for photocatalysis of the hydrogen evolution reaction (HER) was fabricated using the double solvents method (DSM). In contrast with Ni@MIL-101 and Mo@MIL-101, NiMo@MIL-101 exhibited an excellent photocatalytic performance (740.2 µmol·h(-1) for HER), stability, and high apparent quantum efficiency (75.7%) under 520 nm illumination at pH 7. The NiMo@MIL-101 catalyst also showed a higher transient photocurrent, lower overpotential (-0.51 V), and longer fluorescence lifetime (1.57 ns). The results uncover the dependence of the photocatalytic activity of HER on the ΔGH of Ni-Mo (MoNi4) alloy nanoclusters, i.e., lower ΔGH corresponding to higher HER activity for the first time. The NiMo@MIL-101 catalyst could be a promising candidate to replace precious-metal catalysts of the HER.

Direct Observation of Charge Separation on Anatase TiO2 Crystals with Selectively Etched {001} Facets.

Synchronous illumination X-ray photoelectron spectroscopy (SIXPS) was employed for the first time to directly identify the photogenerated charge separation and transfer on anatase TiO2 single-crystals with selectively etched {001} facets. More specifically, for the TiO2 crystals with intact {001} and {101} facets, most of photogenerated charge carriers rapidly recombined, and no evident electron-hole separation was detected. With selectively etching on {001} facets, high efficient charge separation via hole transfer to titanium and electron to oxygen was clearly observed. However, when the {001} facets were completely etched into a hollow structure, the recombination for photogenerated electron-hole pairs would dominate again. These demonstrations clearly reveal that the appropriate corrosion on {001} facets could facilitate more efficient electron-hole separation and transfer. As expected, the optimized TiO2 microcrystals with etched {001} facets could achieve a hydrogen generation rate of 74.3 µmol/h/g, which is nearly 7 times higher than the intact-TiO2 crystals.

Intrinsic magnetic characteristics-dependent charge transfer and visible photo-catalytic H2 evolution reaction (HER) properties of a Fe3O4@PPy@Pt catalyst.

A ternary nano-architectural photocatalyst has been designed to investigate whether the intrinsic magnetic property of photo-catalysts has an effect on the charge transfer and its photo-catalytic H2 evolution reaction (HER) properties under visible light irradiation. The electron transfer and visible-light-driven hydrogen evolution were remarkably enhanced by regulating the electromagnetic interaction between the magnetic catalysts and the photo-generated electrons.

Surface texture and physicochemical characterization of mesoporous carbon--wrapped Pd-Fe catalysts for low-temperature CO catalytic oxidation.

In this paper, mesoporous carbon (meso-C) with three-dimensional mesoporous channels was synthesized through a nanocasting route using three-dimensional mesoporous silica KIT-6 as the template. Mesoporous carbon wrapped Pd-Fe nanocomposite catalysts were synthesized by the co-precipitation method. The effects of the experimental conditions, such as pH value, Fe loading content and calcination temperature, on CO oxidation were studied in detail. The prepared Pd-Fe/meso-C catalysts showed excellent catalytic activity after optimizing the experimental conditions. The surface tetravalent Pd content, existing forms of Fe species, surface chemical adsorbed oxygen concentration, and pore channels of mesoporous carbon played vital roles in achieving the highest performance for the Pd-Fe/meso-C catalyst. The reaction pathway was conjectured according to the XPS analysis of the Pd-Fe/meso-C catalysts for CO oxidation, which maybe adhered to the Langmuir-Hinshelwood + redox mechanism. The effect of moisture on CO conversion was investigated, and the superior Pd-Fe/meso-C catalyst could maintain its activity beyond 12 h. This catalyst also showed excellent activity compared to the reported values in the existing literature.

Controllable Synthesis and Photocatalytic Properties Study of Na2Ti3O7 and H2Ti3O7 Nanotubes with High Exposed Facet (010).

The role of replacing Na+ with H+ of titanate in promoting photocatalytic performance was investigated. The experimental results showed that H2Ti3O7 and Na2Ti3O7 catalysts with the same high exposed (010) facet had the similar light absorption capacity, TiO6 octahedral structure, and specific surface area. By comparing to Na2Ti3O7, H2Ti3O7 had longer lifetime and higher separation efficiency of the photo-generated electron-hole pairs, and also had higher density of surface oxygen vacancies, which resulted in the excellent performances for photocatalytic hydrogen production and dye degradation reactions.

Super-paramagnetic nano-Fe3O4/graphene for visible-light-driven hydrogen evolution.

A super-paramagnetic nano-architecture, which could be separated and re-dispersed easily for reuse, was designed for effective dye-sensitized H2 evolution. By the enhancement of electron-transfer and surface-repair ability of graphene, the visible-light-driven hydrogen evolution rate over the exposed Pt(111) facet loaded Fe3O4/GO catalyst was remarkably enhanced.

Catalytic wet oxidation of aqueous methylamine: comparative study on the catalytic performance of platinum-ruthenium, platinum, and ruthenium catalysts supported on titania.

Promotion of the dispersion of Ru species supported on TiO2 was achieved by introduction of Pt component and the role of Pt in enhancing the catalytic performances of Pt-Ru was investigated with catalytic wet air oxidation of methylamine used as a probing reaction. It was found that Pt-Ru/TiO2 displayed a much better catalytic performance compared with Pt/TiO2 and Ru/TiO2 catalysts due to having the highest dispersion of active species. Both high total organic carbon conversion and nitrogen selectivity (∼100%) over Pt-Ru/TiO2 catalyst were achieved at low temperature (200 °C). X-ray photoelectron spectroscopy characterization indicated that there were strong interactions between metal particles and the support, which may increase the catalytic performance of catalysts.

Electric field-directed growth and photoelectrochemical properties of cross-linked Au-ZnO hetero-nanowire arrays.

We demonstrate a simple and effective strategy for vertically growing Au nanowires over ZnO nanowire arrays to construct a cross-linked hierarchical architecture under the synergistic effects of the electric field direction and photoreduction, which exhibit excellent photoelectrochemical performances under visible light irradiation.

Enhancing catalytic activity and stability for CO2 methanation on Ni@MOF-5 via control of active species dispersion.

A novel, highly active catalyst Ni@MOF-5 showed unexpected activity at low temperature for CO2 methanation. The characterization results indicated that Ni was uniformly and highly dispersed over MOF-5. This catalyst showed high stability and almost no deactivation in long term stability tests up to 100 h.

BiAg alloy nanospheres: a new photocatalyst for H2 evolution from water splitting.

We demonstrate for the first time that Bi and BiAg alloy nanospheres, fabricated with a facile hydrothermal method, display evident photocatalytic H2 production activities. Element Bi can serve as an active photocatalyst for both water splitting and photoelectrochemical applications. More interestingly, these activities of Bi can be greatly enhanced by introducing Ag to form BiAg alloy nanoparticles, which may be ascribed to the improved charge separation and enlarged carrier concentration. The constituent of the BiAg alloy can be rationally tuned by varying the amount of Ag nanowires, and it is found that Bi0.7Ag0.3 exhibits the highest photoelectrochemical property.