Search Results (10)

Utilizing renewable energy for green hydrogen production via electrolyzed seawater is a promising technology for the future. However, undesired chlorine evolution and the corrosive nature of seawater are crucial challenges for direct seawater splitting technology. In this work, heterojunctions of CoS₂/FeS₂ encapsulated in N-doped carbon nanocubes (denoted as CoS₂/FeS₂@NC) were designed by proposing the synchronous pyrolysis and vulcanization of polydopamine-coated coordination polymers. Such a synthetic strategy was demonstrated to be effective in increasing the favorable exposure of active sites, moderately regulating electronic structure, and remarkably facilitating charge transfer due to the controllable generation of unique core–shell structures with suitable carbon shells, leading to the excellent bifunctional electrocatalytic performance and enhanced stability of electrocatalysts. As a result, CoS₂/FeS₂@NC can be revealed as a superior water splitting catalyst, possessing a small voltage of 1.75 V and requiring 100.0 mA cm⁻² in 1 M KOH alkaline solution and 1.80 V for alkaline seawater media, with satisfactory long-term stability. This work presents fresh strategies for designing core–shell heterostructures and developing green technology for hydrogen production. Full article

The very slow anodic oxygen evolution reaction (OER) greatly limits the development of large-scale hydrogen production via water electrolysis. By replacing OER with an easier urea oxidation reaction (UOR), developing an HER/UOR coupling electrolysis system for hydrogen production could save a significant amount of energy and money. An Al-doped cobalt ferrocyanide (Al-Co₂Fe(CN)₆) nanocube array was in situ grown on nickel foam (Al-Co₂Fe(CN)₆/NF). Due to the unique nanocube array structure and regulated electronic structure of Al-Co₂Fe(CN)₆, the as-prepared Al-Co₂Fe(CN)₆/NF electrode exhibited outstanding catalytic activities and long-term stability to both UOR and HER. The Al-Co₂Fe(CN)₆/NF electrode needed potentials of 0.169 V and 1.118 V (vs. a reversible hydrogen electrode) to drive 10 mA cm⁻² for HER and UOR, respectively, in alkaline conditions. Applying the Al-Co₂Fe(CN)₆/NF to a whole-urea electrolysis system, 10 mA cm⁻² was achieved at a cell voltage of 1.357 V, which saved 11.2% electricity energy compared to that of traditional water splitting. Density functional theory calculations demonstrated that the boosted UOR activity comes from Co sites with Al-doped electronic environments. This promoted and balanced the adsorption/desorption of the main intermediates in the UOR process. This work indicates that Co-based materials as efficient catalysts have great prospects for application in urea electrolysis systems and are expected to achieve low-cost and energy-saving H₂ production. Full article

This study presents the synthesis of graphitic carbon nitride (g-C₃N₄) and its nanostructures with cobalt ferrite (CoFe₂O₄) and silver nanocubes (Ag) when using the combined pyrolysis of melamine and the polyol method. The resulted nanostructures were tested as electrocatalysts for hydrogen and oxygen evolution reactions in alkaline media. It was found that Ag@CoFe₂O₄/g-C₃N₄ showed the highest current density and gave the lowest overpotential of −259 mV for HER to reach a current density of 10 mA cm⁻² in a 1 M KOH. The overpotentials for reaching the current density of 10 mA·cm⁻² for OER were 370.2 mV and 382.7 mV for Ag@CoFe₂O₄/g-C₃N₄ and CoFe₂O₄/g-C₃N₄, respectively. The above results demonstrated that CoFe₂O₄/g-C₃N₄ and Ag@CoFe₂O₄/g-C₃N₄ materials could act as bifunctional catalysts due to their notable performances and high stabilities toward hydrogen and oxygen evolution reactions (HER and OER). Total water splitting in practical applications is a promising alternative to noble-metal-based electrocatalysts. Full article

Copper and iron are the basic metal elements that have attracted much attention in industry. Prussian blue (PB) is a significant class of metal–organic frameworks (MOFs); however, the lack of such linkages between the structure and properties, as well as properties differences, limits their potential applications. In this paper, the Cu-based Prussian blue nanocubes with and without Fe doping were synthesized. With the increasing reaction time, the morphology of the Cu-based Prussian blue nanocubes without Fe doping (PB:Cu NCs) changes from cuboidal to circular, and finally grows back to cuboidal. However, Cu-based Prussian blue nanocubes with Fe doping (PB: CuFe NCs) grow directly from the cube and eventually collapse. The nanocubes show a notable red shift with the tunable spectra from 400 nm to 700 nm. Compared with PB: Cu NCs, the PB: CuFe NCs have higher temperature rise under 808 nm irradiation and better photothermal efficacy. The catalytic efficiency of PB: CuFe NCs changes with the pH and reaches its maximum value of 1.021 mM with a pH of 5.5. The enhanced catalytic reaction by the near-infrared radiation plasmonic photothermal effect is also confirmed. This work highlights the potential of the developed PB: Cu and PB: CuFe NCs for photothermal-enhanced co-catalysis nanomaterials. Full article

Prussian blue analogs are promising cathode materials in aqueous ion batteries that have attracted increasing attention, but their low specific capacity and limited cycling stability remain to be further improved. Effective strategies to optimize the electrochemical performance of Prussian blue cathode materials are the aspects of electrolyte and structure modification. In this work, Na₂MnFe(CN)₆@PPy nanocubes were prepared by a simple co-precipitation method with PPy coating. Compared with the uncoated electrode material, the discharged capacity of the Na₂MnFe(CN)₆@PPy cathode material is raised from 25.2 to 55.0 mAh g⁻¹ after 10 cycles in the Na-Zn hybrid electrolyte, while the capacity retention is improved from 63.5% to 86.5% after 150 cycles, indicating higher capacity and better stability. This work also investigates the electrochemical performances of Na₂MnFe(CN)₆@PPy cathode material in hybrid electrolyte of Li-Zn and K-Zn adjusted via different mixed ion solutions. The relevant results provide an innovative way to optimize advanced aqueous hybrid batteries from the perspective of cycling stability. Full article

Exploring bifunctional electrocatalysts to lower the activation energy barriers for sluggish electrochemical reactions for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are of great importance in achieving lower energy consumption and higher conversion efficiency for future energy conversion and storage system. Despite the excellent performance of precious metal-based electrocatalysts for OER and ORR, their high cost and scarcity hamper their large-scale industrial application. As alternatives to precious metal-based electrocatalysts, the development of earth-abundant and efficient catalysts with excellent electrocatalytic performance in both the OER and the ORR is urgently required. Herein, we report a core–shell CoFeS₂@CoS₂ heterostructure entangled with carbon nanotubes as an efficient bifunctional electrocatalyst for both the OER and the ORR. The CoFeS₂@CoS₂ nanocubes entangled with carbon nanotubes show superior electrochemical performance for both the OER and the ORR: a potential of 1.5 V (vs. RHE) at a current density of 10 mA cm⁻² for the OER in alkaline medium and an onset potential of 0.976 V for the ORR. This work suggests a processing methodology for the development of the core–shell heterostructures with enhanced bifunctional performance for both the OER and the ORR. Full article

The electrochemical carbon dioxide reduction reaction (CO₂RR) to C₂ chemicals has received great attention. Here, we report the cuprous oxide (Cu₂O) nanocubes cooperated with silver (Ag) nanoparticles via the replacement reaction for a synergetic CO₂RR. The Cu₂O-Ag tandem catalyst exhibits an impressive Faradaic efficiency (FE) of 72.85% for C₂ products with a partial current density of 243.32 mA·cm⁻². The electrochemical experiments and density functional theory (DFT) calculations reveal that the introduction of Ag improves the intermediate CO concentration on the catalyst surface and meanwhile reduces the C-C coupling reaction barrier energy, which is favorable for the synthesis of C₂ products. Full article

Nanocubic pyrite (FeS₂) crystals with exposed (100) crystal faces and sizes of 100–200 nm were successfully synthesized via a facile hydrothermal method using greigite (Fe₃S₄) as the iron precursor and thiourea (NH₂CSNH₂) as the sulfur source. When the concentration of thiourea was 40 mmol/L, both pyrite and hematite were observed in the as-prepared sample, indicating incomplete conversion of greigite into pyrite. With an increased thiourea concentration to 80 mmol/L, pyrite was found to be the only crystalline phase in the synthesized samples. All greigite could be transformed to pyrite within 24 h via the hydrothermal method, while further prolonging the hydrothermal time had insignificant effect on the crystal phase composition, crystallinity, and morphologies of the prepared nanocubic pyrite crystals. In contrast, when a mixture of Na₂S and S powder was used to replace the thiourea as the sulfur source, tetragonal, orthorhombic, cubic, and irregular pyrite crystal particles with sizes of 100 nm–1 μm were found to co-exist in the prepared samples. These results demonstrate the critical influence of sulfur source on pyrite morphology. Furthermore, our hydrothermal process, using a combination of greigite and thiourea, is proved to be effective in preparing nanocubic pyrite crystals. Our findings can also provide new insight into the formation environments and pathways of nanocubic pyrite under hydrothermal conditions. Full article

Three-dimensional (3D) nanomagnetism, where spin configurations extend into the vertical direction of a substrate plane allow for more complex, hierarchical systems and the design of novel magnetic effects. As an important step towards this goal, we have recently demonstrated the direct-write fabrication of freestanding ferromagnetic 3D nano-architectures of ferromagnetic CoFe in shapes of nano-tree and nano-cube structures by means of focused electron beam induced deposition. Here, we present a comprehensive characterization of the magnetic properties of these structures by local stray-field measurements using a high-resolution micro-Hall magnetometer. Measurements in a wide range of temperatures and different angles of the externally applied magnetic field with respect to the surface plane of the sensor are supported by corresponding micromagnetic simulations, which explain the overall switching behavior of in part rather complex magnetization configurations remarkably well. In particular, the simulations yield coercive and switching fields that are in good quantitative correspondence with the measured coercive and switching fields assuming a bulk metal content of 100 at % consisting of bcc Co ${}_3$ Fe. We show that thermally-unstable magnetization states can be repetitively prepared and their lifetime controlled at will, a prerequisite to realizing dynamic and thermally-active magnetic configurations if the building blocks are to be used in lattice structures. Full article

Polydopamine-coated FeCo nanocubes (PDFCs) were successfully synthesized and tested under microwave irradiation of 2.45 GHz frequency and 0.86 W/cm² power. These particles were found to be non-toxic in the absence of irradiation, but gained significant toxicity upon irradiation. Interestingly, no increase in relative heating rate was observed when the PDFCs were irradiated in solution, eliminating nanoparticle (NP)-induced thermal ablation as the source of toxicity. Based on these studies, we propose that microwave-induced redox processes generate the observed toxicity. Full article