Carbon nanotube-encapsulated Co/Co3Fe7 heterojunctions as a highly-efficient bifunctional electrocatalyst for rechargeable zinc-air batteries

In oxygen electrocatalysis, how to rationally design low-cost catalysts with reasonable structure and long-term stability is a crucial issue. Here, an in-situ growth strategy is used to construct a shaped structure encapsulating a uniformly-dispersed Co/Co3Fe7 heterojunction in nitrogen-doped carbon nanotubes (Co/Co3Fe7@NCNTs). Hollow CoFe layered-double-hydroxide prisms act as sacrifices for in-situ growth of Co/Co3Fe7 nanoparticles, which also catalyze the growth of bamboo-like NCNTs. Tubular structure not only accelerates the charge transfer through the interactions between Co and Co3Fe7, but also limits the aggregation of the particles, thereby promoting the 4e- oxygen reduction/evolution reactions (ORR/OER) kinetics and stabilizing the bifunctional activity. Co/Co3Fe7@NCNTs-800 (pyrolyzed at 800 °C) shows exceptional ORR activity (half-wave potential of 0.89 V) and methanol tolerance. Meanwhile, Co/Co3Fe7@NCNTs-800 shows a small OER overpotential of 280 mV, which increases by only 9 mV after 1000 cyclic voltammetry (CV) cycles. The outstanding bifunctionality (potential gap of 0.62 V) is ascribed to the electronic structure modulation at the Co/Co3Fe7 heterointerface. Notably, it also has a high performance as an air-cathode for rechargeable zinc-air battery, showing high power density (165 mW cm-2) and specific capacity (770.5 m Ah kg-1). This work provides a new reference for promoting the development of alloy catalysts with heterogeneous interfaces.

Regulation of electron density redistribution for efficient alkaline hydrogen evolution reaction and overall water splitting

The rational design of morphology and heterogeneous interfaces for non-precious metal electrocatalysts is crucial in electrochemical water decomposition. In this paper, a bifunctional electrocatalyst (Ni/NiFe LDH), which coupling nickel with nickel-iron layer double hydroxide (NiFe LDH), is synthesized on carbon cloth. At current density of 10 mA cm-2, the Ni/NiFe LDH exhibits a low hydrogen evolution reaction (HER) overpotential of only 36 mV due to the accelerated electrolyte penetration, which is caused by superhydrophilic interface. Moreover, an alkaline electrolyzer is formed and provide a current density of 10 mA cm-2 with a voltage of only 1.49 V. It is confirmed by the density functional theory (DFT) that electron from the Ni layer is transferred to NiFe LDH layer, redistributing the local electron density around the heterogeneous phase interface. Thus, the Gibbs free energy for hydrogen adsorption is optimized. This work provides a promising strategy for the rational regulation of electrons at heterogeneous interfaces and the synthesis of flexible electrocatalysts.

Reversible crowdedness of pH-responsive and host-guest active polymersomes: Mimicking µm-sized cell structures

The structure-function characteristics of isolated artificial organelles (AOs) in protocells are mainly known, but there are few reports on clustered or aggregated AOs. To imitate µm-sized complex and heterogeneous cell structures, approaches are needed that enable reversible changes in the aggregation state of colloidal structures in response to chemical, biological, and external stimuli. To construct adaptive organelle-like or cell-like reorganization characteristics, we present an advanced crosslinking strategy to fabricate clustered polymersomes as a platform based on host-guest interactions between azobenzene-containing polymersomes (Azo-Psomes) and a β-cyclodextrin-modified polymer (β-CD polymer) as a crosslinker. First, the reversible (dis)assembly of clustered Azo-Psomes is carried out by the alternating input of crosslinker and adamantane-PEG3000 as a decrosslinker. Moreover, cluster size dependence is demonstrated by environmental pH. These offer the controlled fabrication of various homogeneous and heterogeneous Azo-Psomes structures, including the size regulation and visualization of clustered AOs through a fluorescent enzymatic cascade reaction. Finally, a temperature-sensitive crosslinking agent with β-CD units can promote the coaggregation of Azo-Psomes mediated by temperature changes. Overall, these (co-)clustered Azo-Psomes and their successful transformation in AOs may provide new features for modelling biological systems for eukaryotic cells and systems biology.

Facile generation of CeO2 nanoparticles on multiphased NiSx nanoplatelet arrays as a free-standing electrode for efficient overall water splitting

Constructing nanostructured electrocatalysts with heterointerface and finetuning their electronic properties are essential for high-efficient overall water splitting. Here, we prepared a well-designed nano-flower-like multiphase and hybrid material of NiS/NiS2/CeO2/NF (NiSx/CeO2/NF) with rich heterointerfaces and abundant active sites through solvothermal reaction and post-annealing treatment. The as-fabricated NiSx/CeO2/NF exhibits exceptional catalytic performance for OER and HER. Specifically, in 1 M KOH solution, it requires the low overpotentials of 326 and 92 mV to achieve the current density of 200 and 10 mA cm-2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. More satisfactorily, when NiSx/CeO2/NF is used as the bifunctional catalyst, a low voltage of only 1.53 V is required to achieve a current density of 10 mA cm-2 for overall water splitting. The excellent catalytic performance should be attributed to its special heterogeneous structure and the synergy effect between NiSx and CeO2. This work emphasizes the important significance of constructing efficient bifunctional electrocatalysts by reasonably designing heterostructures and multiphase components for overall water splitting.

Electrochemical surface reconstruction of Prussian blue-modified nickel sulfide to form iron-nickel bilayer hydroxyl oxides for efficient and stable oxygen evolution reaction processes

The oxygen evolution reaction (OER) is an important semi-reaction in the electrocatalytic water splitting for hydrogen energy production, and the development of efficient and low-cost electrocatalysts to solve the problem of slow 4-electron transport kinetics in the OER process is key. In this work, a pre-electrocatalyst with the heterogeneous interfacial structure, Prussian blue-modified nickel sulfide with sulfur vacancies (PB/NS-Sv), was designed and then converted to iron-nickel bilayer hydroxyl oxides in oxygen-rich vacancies (FeOOH/NiOOH-Ov@NS) through electrochemical oxidative reconstruction to obtain a truly stable and efficient active material. The study utilized in situ Raman to observe the transition from PB/NS-Sv to FeOOH/NiOOH-Ov@NS during the reaction. The electronic density of states in FeOOH/NiOOH-Ov@NS is regulated by the bilayer hydroxyl metal oxide synergistic effect and the abundant oxygen defect of Mental-OOH-Ov, which significantly improves OER catalytic performance. FeOOH/NiOOH-Ov@NS requires a low overpotential of only 257 mV in 1 mol/L KOH at 100 mA cm-2 current density, has a small Tafel slope of 35.2 mV dec-1 and has excellent stability for 150 h at 100 mA cm-2 current density, making it a promising candidate for industrial applications.

Polymer self-assembly guided heterogeneous structure engineering towards high-performance low-frequency electromagnetic wave absorption

Magnetic-dielectric synergy is currently regarded as among the most effective approaches to achieve low-frequency electromagnetic wave absorption (EMA). However, designing and fabricating EMA materials with tunable magnetic-dielectric balance towards high-performance low-frequency EMA remains challenging. Herein, a polymer self-assembly guided heterogeneous structure engineering strategy is proposed to fabricate hierarchical magnetic-dielectric nanocomposite. Polymer assemblies not only can be employed as intermediates to encapsulate metal-organic frameworks and load metal hydroxide, but also that they play a crucial role for the in-situ formation of polycrystalline FeCo/Co composite nanoparticles. As a result, the minimum reflection loss (RLmin) can reach -59.61 dB at 5.4 GHz (4.8 mm) with a 20 wt% filler loading, while the effective absorption bandwidth (EAB, RLmin ≤ -10 dB) is 2.16 GHz, exhibiting excellent low-frequency EMA performance. Systematic investigations demonstrate that hierarchical mesoporous carbon matrix that supports FeCo/Co composite nanoparticles is beneficial for optimizing impedance matching and increasing attenuation capacity. In general, this study opens up new prospects for developing magnetic-dielectric EMA materials using a polymer self-assembly guided heterogeneous structure engineering strategy, which may receive significant attention in future research.

Engineering the highly efficient heterogeneous catalyst based on PdCu nanoalloy and nitrogen-doped Ti(3)C(2)T(x) MXene for ethanol electrooxidation

Improving the electrocatalytic performance by modulating the surface and interface electronic structure of noble metals is still a research hotspot in electrocatalysis. Herein, we prepared the heterogeneous catalyst based on the well-dispersed PdCu nanoalloy and the N-doped Ti₃C₂T_x MXene support (PdCu/N-Ti₃C₂T_x) via in situ growth of PdCu nanoparticles on the fantastic N-Ti₃C₂T_x sheets. By exploring the electrocatalytic properties of ethanol oxidation reaction (EOR), the composition optimized Pd₁Cu₁/N-Ti₃C₂T_x delivers higher mass activity/specific activity/intrinsic activity (2200.7 mA mg_Pd^-1/13.1 mA cm^-2/2.2 s^-1), anti-poisoning ability and stability than those of Pd/N-Ti₃C₂T_x, Pd₁Cu₁/Ti₃C₂T_x and commercial Pd/C, which can be attributed to the modified surface electronic features of Pd by the participation of Cu atoms and N-Ti₃C₂T_x MXene, as well as the "metal-carrier" effect between the PdCu nanoalloy and N-Ti₃C₂T_x heterogeneous interface. Furthermore, the conductivity of N-Ti₃C₂T_x MXene can be improved by N-doping, and the abundant terminal groups (-O, -OH, -F and N) on the N-Ti₃C₂T_x surface can promote the electron exchange between PdCu and N-Ti₃C₂T_x. This work provides an effective strategy for engineering heterogeneous electrocatalysts for enhanced electrocatalytic EOR by adjusting the interfacial electronic structure of noble metals.

Coupling heterostructured CoP-NiCoP nanopin arrays with MXene (Ti(3)C(2)T(x)) as an efficient bifunctional electrocatalyst for overall water splitting

Developing a highly effective bifunctional electrocatalyst for alkaline-condition electrochemical water splitting is both essential and challenging. The work presented here successfully synthesizes and employs a heterostructured CoP-NiCoP ultra-long nanopin array in situ growing on MXene (Ti₃C₂T_x) as a stable bifunctional electrocatalyst for electrochemical water-splitting. The heterogeneous structure formed by CoP nanoparticles and NiCoP nanopins provides extra active sites for water-splitting. Also, Ti₃C₂T_x works as a support substrate during electrochemical operations, accelerating mass transfer, ion transport, and rapid gas product diffusion. Meanwhile, throughout the catalytic process, the dense nanopin arrays shield Ti₃C₂T_x from further oxidation. At a result, the CoP-NiCoP-Ti₃C₂T_x (denoted as CP-NCP-T) demonstrated excellent catalytic activity, with overpotentials of just 46 mV for hydrogen evolution at 10 mA cm^-2 and 281 mV for oxygen evolution at 50 mA cm^-2. Furthermore, in 1.0 M KOH solution, the outstanding bifunctional electrode (CP-NCP-T || CP-NCP-T) exhibits efficient electrochemical water splitting activity (1.54 V@10 mA cm^-2) and outperforms the comparable device Pt/C || IrO₂ (1.62 V@10 mA cm^-2).

Engineering cobalt molybdate nanosheet arrays with phosphorus-modified nickel as heterogeneous electrodes for highly-active energy-saving water splitting

Electrochemical urea electrolysis has been regarded as a promising strategy to replace traditional water-splitting technology to achieve hydrogen fuel due to its cost savings and high energy efficiency. Designing efficient bifunctional electrocatalysts easily is important but still faces significant challenges. Herein, an interface engineering strategy is used to construct a hybrid material by coupling cobalt molybdate (CoMoO₄) nanosheet arrays with phosphorus-modified nickel (P-Ni) particles on copper foam (P-Ni@CoMoO₄/CF) through the hydrothermal and in-situ electrodeposition process. Benefiting from the abundant catalytic active sites, low charge transfer resistance, and synergistic coupling effect, the optimal P-Ni@CoMoO₄/CF electrocatalyst presents a superior bifunctional activity for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). In detail, a small overpotential of 125 mV and a low potential of 1.36 V is required to attain the current density of 100 mA cm^-2 for HER and UOR, respectively. In the process of urea electrolysis, the P-Ni@CoMoO₄/CF-based electrolyzer provides a current density of 100 mA cm^-2 with an overall voltage of 1.50 V, about 170 mV less than that in a traditional water electrolyzer. The high performance of P-Ni@CoMoO₄/CF outperforms many recently reported electrodes, suggesting its promising application in energy-saving hydrogen production. Our work proposes a novel idea for the rational design and exploitation of low-cost and robust bifunctional electrodes for electrocatalysis.

Fiber-like ZnO with highly dispersed Pt nanoparticles for enhanced photocatalytic CO2 reduction

Utilizing solar energy to convert carbon dioxide (CO₂) into chemical fuels could simultaneously mitigate the greenhouse effect and fossil fuel crisis. Herein, a heterogeneous photocatalyst of ZnO nanofiber deposited by Pt nanoparticles was successfully synthesized toward photocatalytic CO₂ reduction via radio-frequency thermal plasma and photo-deposition method. The Pt nanoparticles were introduced on the surface of ZnO nanofibers to broaden the light absorption and utilization, increase the additional reaction active sites and facilitate the separation of photo-generated electron/hole pairs. Combined with the natural advantages of short transfer path of charge carriers and self-support effecting in humid reaction environment for nanofibers, the Pt/ZnO hetero-junction nanocomposites displayed superior photocatalytic activity for CO₂ reduction with respect to bare ZnO nanofibers, affording a CO-production rate as high as 45.76 μmol g^-1 h^-1 under 300 W Xe lamp irradiation within a gas-solid reaction system. Furthermore, in-suit Fourier transform infrared (FTIR) spectra were applied to unveil the details during photocatalytic CO₂ reduction. This work presents a hetero-junction nanocomposite photocatalyst based on eco-friendly semiconductor and metal materials.

Molybdenum disulfide loading on a Z-scheme graphitic carbon nitride and lanthanum nickelate heterojunction for enhanced photocatalysis: Interfacial charge transfer and mechanistic insights

Interfacial design and the co-catalyst effect are considered to be effective to achieve separation and transport of photogenerated carriers in composite photocatalysts. In this study, a Z-scheme heterojunction was successfully combined with a co-catalyst to achieve a highly efficient LaNiO₃/g-C₃N₄/MoS₂ photocatalyst. MoS₂ flakes were loaded on a hybrid material surface, which was formed by LaNiO₃ nanocubes embedded on layered g-C₃N₄, and a good heterostructure with multiple attachment sites was obtained. Experimental studies confirmed that the Z-scheme heterojunction completely preserves the strong redox ability of the photogenerated electrons and holes. As a cocatalyst, MoS₂ further promoted interfacial charge separation and transport. The synergistic effect of the Z-scheme heterojunction and co-catalyst effectively realized the transfer of photogenerated carriers from "slow transfer" to "high transfer" and promoted water decomposition and pollutant degradation. Results revealed that under simulated sunlight irradiation, LaNiO₃/g-C₃N₄/MoS₂ composites exhibit superior hydrogen evolution of 45.1 μmol h^-1, which is 19.1 times that of g-C₃N₄ and 4.9 times that of LaNiO₃/g-C₃N₄, respectively. Moreover, the LaNiO₃/g-C₃N₄/MoS₂ Z-scheme photocatalyst exhibited excellent photocatalytic performance for antibiotic degradation and heavy-metal ion reduction under visible light. This study might provide some insights into the development of photocatalysts for solar energy conversion and environmental remediation.

A novel porous polymeric microsphere for the selective adsorption and isolation of conalbumin

Porous polymeric microspheres, poly(styrene-divinyl benzene, PSDVB)-poly(ethylene glycol monoallyl ether, PEGMAE), termed as PSDVB-PEGMAE, are prepared via double emulsion interfacial polymerization strategy. PSDVB-PEGMAE microspheres exhibit a mean diameter of 2.98 μm, and possess heterogeneous porous structure with a pore volume of 0.354 cm³ g^-1 and a pore size of 34.3 nm. PEGMAE moiety is identified on the external surface of the microspheres, while both PSDVB and PEGMAE moieties are found in the interior pores. The PSDVB-PEGMAE microspheres possess favorable selectivity towards the adsorption of conalbumin (ConA) through hydrogen-bonding and hydrophobic interactions, via surface and inter-pore adsorption. At pH 6, an adsorption capacity of 171.9 mg g^-1 is achieved for ConA. The captured ConA may be readily recovered by stripping with a cetane trimethyl ammonium bromide (CTAB) solution (0.1%, m/v). The microspheres are further used for the isolation of ConA from egg white, deriving high purity ConA as demonstrated by SDS-PAGE assay.

Nedis-Serpent simulation of a neutron source assembly with complex internal heterogeneous structure

The hybrid use of Nedis-2m and Serpent 2.1.30 codes to predict the radiation characteristics (i.e., neutron yield and energy spectrum) of an Am-Be source with a fine-grained mixture of americium dioxide (AmO₂) and beryllium (Be) core was studied with a focus on the grain size influence on the simulation results. The study showed that the fine-grained structure of the source core would decrease the number of alpha particles participating in the nuclear reactions with ^17,18O and ⁹Be nuclei, which softened the neutron energy spectrum and reduced the neutron yield. The simulations also confirmed that the source core made of the stable crystals of AmBe₁₃ intermetallic alloy would improve the neutron yield to maximum 50% compared to the core made of AmO₂. Moreover, a source with a variable neutron yield was proposed with a heterogeneous core of AmO₂ rods embedded in Be. The neutron energy spectrum of heterogeneous source resembled the energy spectrum of Deuterium-Tritium (D-T) neutrons which were generated in a long magnetic trap with high-temperature plasma. The subcritical irradiation facility assembled from the nth number of heterogeneous Am-Be source can be used to study the properties of materials and the equipment operating in the epithermal and fast neutron spectra. The use of a heterogeneous Am-Be assembly, as a basic element of an irradiation installation, simplifies the handling and operation procedures because it is easily disabled by removing the Be layer, or by inserting a sheet of the appropriate size and material between the Be and Am rod.

Platinum-based heterogeneous nanomaterials via wet-chemistry approaches toward electrocatalytic applications

The heterogeneously structured nanomaterials usually exhibit enhanced catalytic properties in comparison with each one of the constituent materials due to the synergistic effect among their different domains. Within the last decade, the development of wet-chemistry methods leads to the blossom of research in materials with heterogeneous nanostructures, which creates great opportunities also a tremendous challenge to apply these materials for highly efficient energy conversion. We herein would systematically introduce the latest research developments in Pt-based nanomaterials with heterogeneous structures, e.g. core-shell, hollow interiors, stellated/dendritic morphologies, dimeric, or composite construction, and their potential applications as electrocatalysts toward direct methanol fuel cell reactions, including methanol oxidation reaction and oxygen reduction reaction in acidic conditions, aiming at the summarization of the fundamentals and technical approaches in synthesis, fabrication and processing of heterogeneous nanomaterials so as to provide the readers a systematic and coherent picture of the filed. This review will focus on the intrinsic relationship between the catalytic properties and the physical or/and chemical effects in the heterogeneous nanomaterials, providing for technical bases for effectively developing novel electrocatalyts with low cost, enhanced activity and high selectivity.