Formation of Disordered High-Entropy-Alloy Nanoparticles for Highly Efficient Hydrogen Electrocatalysis.

Nanoparticles composed of high-entropy alloys (HEA NPs) exhibit remarkable performance in electrocatalytic processes such as hydrogen evolution and oxidations. In this study, two types of quinary HEA NPs of PtRhPdIrRu, are synthesized, featuring disordered and crystallized nanostructures, both with and without a boiling mixture. The disordered HEA NPs (d-HEA NPs) with a size of 3.5 nm is synthesized under intense boiling conditions, attributed to improved heat and mass transfer during reduction of precursors and particle growth. The disordered HEA NPs displayed an exceptionally high turnover frequency of 33.1 s-1 at an overpotential of 50 mV, surpassing commercial Pt NPs in acidic electrolytes by 5.4 times. Additionally, d-HEA NPs exhibited superior stability at a constant electrolyzing current of 50 mA cm-2 compared to commercial Pt NPs. When employed as the anodic catalyst in an H2-O2 fuel cell, d-HEA NPs demonstrated a remarkable high current power density of 15.3 kW per gram of noble metal. Consequently, these findings highlight the potential of d-HEA NPs in electrochemical applications involving hydrogen.

Electric Field-Assisted Uptake of Hexavalent Chromium Ions with In Situ Regeneration of Carbon Monolith Adsorbents.

The uptake of hexavalent chromium (Cr(VI)) ions from wastewater is of great significance for environmental remediation and resource utilization. In this study, a self-designed instrument equipped with an oxidized mesoporous carbon monolith (o-MCM) as an electro-adsorbent is developed. o-MCM with a super hydrophilic surface displayed a high specific surface area (up to 686.5 m2  g-1 ). With the assistance of an electric field (0.5 V), the removal capacity of Cr(VI) ions is as high as 126.6 mg g-1 , much higher than that without an electric field (49.5 mg g-1 ). During this process, no reduction reaction of Cr(VI) to Cr(III) ions is observed. After adsorption, the reverse electrode with 10 V is used to efficiently desorb the ions on the carbon surface. Meanwhile, the in situ regeneration of carbon adsorbents can be obtained even after ten recycles. On this basis, the enrichment of Cr(VI) ions in a special solution is achieved with the assistance of an electric field. This work lays a foundation for the uptake of heavy metal ions from wastewater with the assistance of the electric field.

Configuration Sensitivity of Electrocatalytic Oxygen Reduction Reaction on Nitrogen-Doped Graphene.

As one of the most promising nonprecious metal catalysts for the oxygen reduction reaction (ORR), the structure of the active site on nitrogen-doped carbon materials is still under debate. Here, we report that the sensitivity of the ORR on the local configuration of multiple nitrogen dopants may be overlooked. Combining global structure searching with density functional theory calculations, we established the structure-activity relationship for 19 and 298 possible configurations of graphitic nitrogen-doped graphene with N content of 2 and 3%, respectively. It was revealed that the stability cannot be a screener to determine the major contributor to the activity. 77.5% of current density is contributed by the active configuration with 4.59% population on the graphene containing 3% nitrogen. It unambiguously demonstrates the configuration sensitivity of N-doped graphene for ORR and opens a new window to identifying the optimal structure of N-doped carbons for various applications.

Oxygen Doping in Graphitic Carbon Nitride for Enhanced Photocatalytic Hydrogen Evolution.

The incorporation of oxygenic groups could remarkably enhance the light absorption and charge separation of graphitic carbon nitride (g-C3 N4 ). The intrinsic role of oxygenic species on photocatalytic activity in g-C3 N4 has been intensively studied, but it is still not fully explored. Herein, the essential relationships between oxygenic functionalities and the catalytic performance are revealed. Results demonstrate that C-O-C functionality as an electron trap could help to increase the resistance of conduction transfer (Rct ) by limiting electrons transfer in CNx. In contrast, N-C-O functionality between different tri-s-triazine unites could promote the electrons transfer, leading to a reduced Rct in CNx. The best H2 production rate (3.70 mmol h-1 g-1 , 12.76-fold higher than that of CN) is obtained over CN3, because of the highest N-C-O ratio (rN-C-O ). The apparent quantum efficiency (AQE) of CN3 at 405 nm, 420 nm, 450 nm, 500 nm and 550 nm is 33.90 %, 20.88 %, 8.25 %, 3.66 % and 1.01 %, respectively.

Intrinsic acid resistance and high removal performance from the incorporation of nickel nanoparticles into nitrogen doped tubular carbons for environmental remediation.

Nitrogen doped tubular magnetic carbons embedded with nickel nanoparticles (Ni@NTMCs) were prepared via a simple pyrolysis process and employed as the effective adsorbents for the Cr(VI) removal. Ni@NTMCs with as high as 10.63 at.% N doping exhibited the excellent Cr(VI) removal capacities of 24.4 and 250 mg g-1 in neutral and acidic solution, respectively. Adsorption kinetics and isotherm study revealed that the monolayer chemical adsorption was the rate-controlling step for the Cr(VI) removal. The high removal performance can be ascribed to the combination of adsorption and reduction reaction between Cr(VI) ions, and Ni nanoparticles. N dopant and edge carbons acted as the Cr(VI) adsorption site. The surface Ni nanoparticles mainly made contributions to the reduction process. The embedded Ni nanoparticles steadily provided magnetism for the separation and helpful for the recycles stability, showing a high acid corrosion resistance in this study.

Electronic synergism of pyridinic- and graphitic-nitrogen on N-doped carbons for the oxygen reduction reaction.

Nitrogen-doped carbon materials (NCs) are extensively studied for the oxygen reduction reaction (ORR). However, the nature of active sites of pyridinic nitrogen (NP) or graphitic nitrogen (NG) on NCs is still under debate. Herein, we demonstrated that the ORR activity of NCs in alkaline media depended on the electronic synergism between NP and NG, rather than any single type of N. We measured the transferable electrons of NCs by absorption spectroscopy using 7'7'8'8-tetracyanoquinodimethane as an electron acceptor. The transferable electron amount of NCs is relevant to either NP or NG, leading to the [NP] : [NG] ratio as an electron transfer descriptor of NCs in a reverse volcano curve manner across nineteen NCs. The similar dependence of ORR activity on the [NP] : [NG] ratio of NCs was also discovered, demonstrating the synergistic effect of NP and NG. These results provide a new angle to understand the nature of ORR activity of NCs and optimize the ORR catalyst.

Superoxide Decay Pathways in Oxygen Reduction Reaction on Carbon-Based Catalysts Evidenced by Theoretical Calculations.

Superoxide decay behavior is evaluated by contrastive potential energy surface analyses from theoretical calculations. The presence of carbon surfaces enhances the superoxide decay through disproportionation instead of electroreduction, which is a non-electrochemical reaction that impedes the increase in energy efficiency for relevant energy conversion applications. Nitrogen doping of carbon effectively retards the disproportionation by influencing the oxygen stretching vibration and changing the proton-coupled electron transfer trend.

Unraveling the intrinsic enhancement of fluorine doping in the dual-doped magnetic carbon adsorbent for the environmental remediation.

Heteroatom doping endows magnetic carbons with unique electronic features and rich surface chemistry, significantly enhancing their adsorption performances for the environmental remediation. In this work, fluorine and nitrogen co-doped magnetic nanocarbon fibers (FN-MCFs) were prepared via a facile carbonization method combined with electrospinning procedure. FN-MCFs were used as adsorbents for Cr(VI) removal, displaying a remarkable activity with as high as 153.61 mg/g and 0.58 mg/m2 of the Cr(VI) removal ability. F and N co-doping in magnetic nanocarbon fibers offered a higher specific surface area and disorder degree in graphite layer, therefore providing more active sites on the adsorbents surface. The electrostatic adsorption and reduction reaction between the Fe0, Fe2+ nanoparticles or edge carbons and Cr(VI) ions played significant roles in the adsorption process, which was believed to be facilitated by F and N co-doping. It was found that chemical adsorption was the main process in this work. Moreover, the adsorption capacity of FN-MCFs was majorly influenced by the doping level or doping type. F doping was found to be more important than N doping for the Cr(VI) removal in the dual-doping system. In addition, the excellent reusability of the FN-MCFs was observed.

Monodisperse light color nanoparticle ink toward chromatic electrophoretic displays.

The facile synthesis of nanoparticles for precise image control and fast response of chromatic electrophoretic displays (EPDs) is a challenge. Herein, we report a general method to prepare pink, blue, and yellow nanoparticles with low density and a tunable size of 230-310 nm. The monodispersity is down to 0.02 and surface charges are up to 666e. Importantly, our work highlights the feasibility of chromatic nanoparticles as cost-effective candidates for electrophoretic displays.

Comparatively Thermal and Crystalline Study of Poly(methyl-methacrylate)/Polyacrylonitrile Hybrids: Core-Shell Hollow Fibers, Porous Fibers, and Thin Films.

The polyacrylonitrile/polymethyl-methacrylate (PMMA/PAN) porous fibers, core-shell hollow fibers, and porous thin films are prepared by coaxial electrospinning, single electrospinning, and spin-coating technologies, respectively. The different morphologies arising from different processes display great influences on their thermal and crystalline properties. The adding of PMMA causes porous structure due to the microphase-separation structure of immiscible PMMA and PAN phases. The lower weight loss, higher degradation temperature, and glass-transition temperatures of porous thin films than those of porous fibers and core-shell hollow fibers are obtained, evidencing that the polymer morphologies produced from the different process can efficiently influence their physical properties. The orthorhombic structure of PAN crystals are found in the PMMA/PAN porous thin films, but the rotational disorder PAN crystals due to intermolecular packing are observed in the PMMA/PAN porous fibers and core-shell hollow fibers, indicating that different processes cause different types of PAN crystals.