Epitaxial growth of hexahedral Fe2O3@SnO2 nano-heterostructure for improved lithium-ion batteries.

Fe2O3 is one of the most important lithium storage materials and has attracted increasing interest owing to its good capacity in theory, abundant reserves, and better security. The utilization of Fe2O3 materials is hampered by their inferior cycle performance, low rate performance, and restricted composite variety. Herein, the heterostructure of Fe2O3@SnO2 with hexahedral structure was manufactured by two- step hydrothermal strategy, while the SnO2 nanopillars were epitaxially grown in six faces, not in the twelve edges of hexahedral Fe2O3 cubes, which comes from maximizing lattice matching on the six surfaces of Fe2O3. Furthermore, the experimental results prove that the hexahedral Fe2O3@SnO2 heterostructure exhibits remarkably enhanced electrochemical reversibility and reaction kinetics and delivers an impressive initial discharge capacity (1742 mA h g-1 at 4 A g-1), great rate performance (565 mA h g-1 at 5 A g-1), and stable long-term durability (661 mA h g-1 after 4000 cycles at 4 A g-1) as an anode for LIBs. The result of the finite element mechanical simulation further indicates that the SnO2 nanopillars grow on the six surfaces but not on the twelve edges of the hexahedral Fe2O3 cube, which would provide great rate performance and long-term stability. This study underlines the merits of the heterostructure and offers a useful design routine for superior electrode materials in LIBs.

Photothermal CO-PROX reaction over ternary CuCoMnOx spinel oxide catalysts: the effect of the copper dopant and thermal treatment.

The purification of carbon monoxide in H2-rich streams is an urgent problem for the practical application of fuel cells, and requires the development of efficient and economical catalysts for the preferential oxidation of CO (CO-PROX). In the present work, a facile solid phase synthesis method followed by an impregnation method were adopted to prepare a ternary CuCoMnOx spinel oxide, which shows superior catalytic performance with CO conversion of 90% for photothermal CO-PROX at 250 mW cm-2. The dopant of copper species leads to the incorporation of Cu ions into the CoMnOx spinel lattice forming a ternary CuCoMnOx spinel oxide. The appropriate calcination temperature (300 °C) contributes to the generation of abundant oxygen vacancies and strong synergetic Cu-Co-Mn interactions, which are conducive to the mobility of oxygen species to participate in CO oxidation reactions. On the other hand, the highest photocurrent response of CuCoMnOx-300 also promotes the photo-oxidation activity of CO due to the high carrier concentration and efficient carrier separation. In addition, the in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirmed that doping copper species could enhance the CO adsorption capacity of the catalyst due to the generation of Cu+ species, which significantly increased the CO oxidation activity of the CuCoMnOx spinel oxide. The present work provides a promising and eco-friendly solution to remove the trace CO in H2-rich gas over CuCoMnOx ternary spinel oxide with solar light as the only energy source.

From amorphous to crystalline: a universal strategy for structure regulation of high-entropy transition metal oxides.

High-entropy materials (HEMs) exhibit extensive application potential owing to their unique structural characteristics. Structure regulation is an effective strategy for enhancing material performance. However, the fabrication of HEMs by integrating five metal elements into a single crystalline phase remains a grand challenge, not to mention their structure regulation. Herein, an amorphous-to-crystalline transformation route is proposed to simultaneously achieve the synthesis and structure regulation of high-entropy metal oxides (HEMOs). Through a facile hydrothermal technique, five metal sources are uniformly integrated into amorphous carbon spheres, which are transformed to crystalline HEMOs after calcination. Importantly, by controlling ion diffusion and oxidation rates, HEMOs with different structures can be controllably achieved. As an example, HEMO of the five first-row transition metals CrMnFeCoNiO is synthesized through the amorphous-to-crystalline transformation route, and structure regulation from solid spheres to core-shell spheres, and then to hollow spheres, is successfully realized. Among the structures, the core-shell CrMnFeCoNiO exhibits enhanced lithium storage performance due to the component and structural advantages. Our work expands the synthesis methods for HEMs and provides a rational route for structure regulation, which brings them great potential as high-performance materials in energy storage and conversion.

Robust hollow Bowl-like α-Fe2O3 nanostructures with enhanced electrochemical lithium storage performance.

The design and synthesis of hollow-nanostructured transition metal oxide-based anodes is of great importance for long-term operation of lithium ion batteries (LIBs). Herein, a special hollow bowl-like α-Fe2O3 nanostructure is controllably synthesized through a facile hydrothermal technique and exhibits great electrochemical lithium storage performance when used as LIBs anode. Under a facile hydrothermal condition, α-Fe2O3 nanostructures evolve from solid pie-like structure to hollow bowl-like structure and finally α-Fe2O3 nanorings through the regulation of HPO4- derived from ionized Na3PO4·12H2O and Ostwald ripening process. The designed hollow bowl-like α-Fe2O3 nanostructure not only has the merits of hollow structure, which can accelerate the diffusion of lithium ions and electrons, but also shows great mechanical strength to disperse stress when compared to solid pie-like and ring-like α-Fe2O3 nanostructures, which would avoid collapse during charge/discharge process. As a result, the as-synthesized hollow bowl-like α-Fe2O3 nanostructure displays an initial reversible capacity of 1616 mAh g-1 at a current density of 1 A g-1, an excellent cycling performance with a reversible capacity of 1018 mAh g-1 after 500 cycles and an outstanding rate capability (68.1% capacity retention at current densities from 100 to 2000 mA g-1). This work provides not only a novel hollow bowl-like α-Fe2O3 nanostructure with high specific surface area and stable structure as potential electrode materials for energy storage, but also a facile self-templated strategy free of any surfactants and templates for hollow nanostructures.

In-situ generation of In2O3 nanoparticles inside In[Co(CN)6] quasi-metal-organic-framework nanocubes for efficient electroreduction of CO2 to formate.

Three-dimensional (3D) network structure of metal-organic framework (MOF) can accommodate outstanding electrocatalysis performances, but always collapse during the conversion to active materials or applications process. How to maintain the 3D network when producing active species is of great importance for full application of MOF. Herein, a new MOF material, In[Co(CN)6] (In-Co PBA) nanocubes, are firstly synthesized. Through a controlled low-temperature deligandation process, the In-Co PBA nanocubes are transformed to a novel In2O3@In-Co PBA quasi-MOF nanocubes, which basically retain the 3D porous structure of PBA but with in situ generated In2O3 nanoparticles inside. When used as CO2RR electrocatalyst, such a novel cubic composite structure exhibits excellent performances with faradaic efficiency of 85% for formate at a potential of -0.96 V and with current density of 31.5 mA·cm-2 at -1.32 V, surpassing most of the reported indium-based catalysts. The excellent performance can be attributed to the special composite structure, which provides not only active sites by In2O3 nanoparticles to catalyze CO2RR, but also the 3D porous framework by quasi-MOF to accelerate gaseous exchange and electrolyte permeation and prevent the electrode choking. This work offers a new strategy for the design of post-transition metal catalysts and the structure design of quasi-MOF.

Intrinsic activity modulation and structural design of NiFe alloy catalysts for an efficient oxygen evolution reaction.

NiFe alloy catalysts have received increasing attention due to their low cost, easy availability, and excellent oxygen evolution reaction (OER) catalytic activity. Although it is considered that the co-existence of Ni and Fe is essential for the high catalytic activity, the identification of active sites and the mechanism of OER in NiFe alloy catalysts have been controversial for a long time. This review focuses on the catalytic centers of NiFe alloys and the related mechanism in the alkaline water oxidation process from the perspective of crystal structure/composition modulation and structural design. Briefly, amorphous structures, metastable phases, heteroatom doping and in situ formation of oxyhydroxides are encouraged to optimize the chemical configurations of active sites toward intrinsically boosted OER kinetics. Furthermore, the construction of dual-metal single atoms, specific nanostructures, carbon material supports and composite structures are introduced to increase the abundance of active sites and promote mass transportation. Finally, a perspective on the future development of NiFe alloy electrocatalysts is offered. The overall aim of this review is to shed light on the exploration of novel electrocatalysts in the field of energy.

One-pot synthesis of mesoporous palladium/C nanodendrites as high-performance oxygen reduction eletrocatalysts through a facile dual surface protecting agent-assisted strategy.

Palladium (Pd) is regarded as a potential non-platinum electrocatalyst to drive oxygen reduction in fuel cells. The development of Pd-based electrocatalysts with high performances through structural engineering is still highly desirable. Herein, a facile one-pot synthesis strategy with the assistance of dual surface protecting agents was developed to fabricate carbon-supported Pd (Pd/C) nanodendrites with high mesoporosity. The mesoporous spherical Pd/C nanodendrites are built with connected nanoparticles with a small size of several nanometers and coated by simultaneously formed carbon layers. The used dual protecting agents, glycine and oleylamine, exhibit synergistic effects to engineer Pd growth to form the unique mesoporous dendritic structure. Benefiting from the mesoporous feature, small size, defect-rich surface and carbon coating, the obtained mesoporous Pd/C nanodendrites exhibit great electrocatalytic performance toward the oxygen reduction reaction (ORR).

A Universal Strategy for Carbon-Supported Transition Metal Phosphides as High-Performance Bifunctional Electrocatalysts towards Efficient Overall Water Splitting.

Exploring cost-effective and general approaches for highly active and stable bifunctional transition metal phosphide (TMP) electrocatalysts towards overall water splitting is greatly desirable and challenging. Herein, a general strategy combining sol-gel and a carbonization-assisted route was proposed to facilely fabricate a series of TMP nanoparticles, including CoP, MoP, FeP, Cu2P, Ni2P, PtP2, FeNiP, CoNiP, and FeCoNiP, coupled in an amorphous carbon matrix with one-step carbon composite formation. The resultant NiFeP@C exhibits excellent activities as a bifunctional electrocatalyst toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with low overpotentials of 260 and 160 mV, respectively, at 10 mA/cm2 in 1 M KOH solution. With the NiFeP@C electrocatalyst as both electrode materials, an integrated electrolyzer can deliver 47.0 mA/cm2 of current density at 1.60 V, better than the assembled Pt/C20∥IrO2 counterpart. The encapsulation of NiFeP nanoparticles in the carbon matrix effectively prevents their corrosion and leads to almost unfading catalytic activities for more than 20 h for either the HER, OER, or overall water splitting, outperforming recently reported bifunctional electrocatalysts. The coexistence of Ni, Fe, P, and C would have synergetic effects to accelerate charge transfer and promote electrocatalytic activity. This universal strategy for TMP-based composites opens up a new avenue to explore TMPs as multifunctional materials for various applications.

Agaric-derived N-doped carbon nanorod arrays@nanosheet networks coupled with molybdenum carbide nanoparticles as highly efficient pH-universal hydrogen evolution electrocatalysts.

Non-precious, stable and efficient catalysts for the pH-universal hydrogen evolution reaction (HER) are highly desirable to meet the vast energy demands. Herein, we report a facile and scalable strategy using agaric as a precursor to construct a Mo2C-based HER electrocatalyst consisting of ultrafine Mo2C nanoparticles embedded within biomass-derived 3D N-doped carbon nanorod arrays@nanosheet networks (Mo2C@N-CANs). This electrocatalyst is highly active for the pH-universal hydrogen evolution reaction and requires overpotentials of only 82 mV, 100 mV and 350 mV to drive a current density of -10 mA cm-2 in acidic, alkaline and neutral media, exhibiting stable operation for 3000 cycles and 24 h long-term stability. Theoretical calculations indicate that coupling Mo2C, N and CANs into a hybrid results in producing wrinkles on carbon nanolayers, which changes the direction of sp2 hybrid orbitals to push the Gibbs free energy toward zero. This result reinforces the presence of a synergy effect between Mo2C and N-CANs in Mo2C@N-CAN catalysts, which leads to their impressive HER performances.

Rapid solvent-evaporation strategy for three-dimensional cobalt-based complex hierarchical architectures as catalysts for water oxidation.

It is a challenging task to seek a highly-efficient electrocatalyst for oxygen evolution reaction (OER) of water splitting. Non-noble Co-based nanomaterials are considered as earth-abundant and effective catalysts to lower overpotential and increase polarization current density of OER. In this work, we reported, for the first time, a "rapid solvent-evaporation" strategy for the synthesis of three-dimensional (3D) cobalt complex hierarchical architectures constructed by two-dimensional (2D) nanosheets. The 3D structured cobalt complexes have excellent performances in catalyzing OER with lower onset potential, overpotential, Tafel slope and better stability than commercial IrO2. Superior electrochemical performances would be beneficial from the unique 3D structure. This extremely simple method for 3D Co complex with good OER activities makes the complex be promising commercial OER catalyst to replace earth-rare and expensive IrO2.

Micelle-template synthesis of hollow silica spheres for improving water vapor permeability of waterborne polyurethane membrane.

Hollow silica spheres (HSS) with special interior spaces, high specific surface area and excellent adsorption and permeability performance were synthesized via micelle-template method using cetyl trimethyl ammonium bromide (CTAB) micelles as soft template and tetraethoxysilane (TEOS) as silica precursor. SEM, TEM, FT-IR, XRD, DLS and BET-BJH were carried out to characterize the morphology and structure of as-obtained samples. The results demonstrated that the samples were amorphous with a hollow structure and huge specific surface area. The growth of HSS was an inward-growth mechanism along template. Notably, we have provided a new and interesting fundamental principle for HSS materials by precisely controlling the ethanol-to-water volume ratio. In addition, the as-obtained HSS were mixed with waterborne polyurethane (WPU) to prepare WPU/HSS composite membrane. Various characterizations (SEM, TEM, FT-IR and TGA) revealed the morphology, polydispersity and adherence between HSS and WPU. Performance tests showed that the introduction of HSS can improve the water vapor permeability of composite membrane, promoting its water resistance and mechanical performance at the same time.