Atomic Diffusion Rate Dominated Fabrication of High Entropy Phosphide with Heterogeneous Aggregation for Oxygen Evolution Reaction.

The synthesis of high-entropy phosphide (HEP) remains a great challenge owing to the different migration rates of different metallic atoms. Herein, a new metal organic gel (MOG) precursor strategy is proposed for HEP synthesis by controlling the migration rate of different atoms in an organic gel. The MOG precursor with five kinds of metal and phosphor species homogeneously dispersing is formed through a facile solvothermal method, which is calcined at 900 °C to obtain carbon-supported HEP FeCoNiMnCdP (MPC-5). The difference in the atom radius and the influence of MOG on the migration rate result in heterogeneous aggregation of different atoms in the product, which increases the defects in the product to a certain extent. In addition, the presence of carbon and nitrogen in the gel simultaneously realizes carbon coating and nitrogen doping. Combining the above advantages, the MPC-5 shows excellent oxygen evolution reaction (OER) catalytic performance with an overpotential of 250 mV at 10 mA·cm-2, superior to many recently reported OER electrocatalysts. This work provides a new strategy to solve the differences in the migration rates of different metals to obtain pure phase high-entropy phosphides, which is conducive to the further development of high-entropy materials and their applications in the energy and catalysis fields.

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.

One-Step Phase Separation for Core-Shell Carbon@Indium Oxide@Bismuth Microspheres with Enhanced Activity for CO2 Electroreduction to Formate.

It is a substantial challenge to construct electrocatalysts with high activity, good selectivity, and long-term stability for electrocatalytic reduction of carbon dioxide to formic acid. Herein, bismuth and indium species are innovatively integrated into a uniform heterogeneous spherical structure by a neoteric quasi-microemulsion method, and a novel C@In2 O3 @Bi50 core-shell structure is constructed through a subsequent one-step phase separation strategy due to melting point difference and Kirkendall effect with the nano-limiting effect of the carbon structure. This core-shell C@In2 O3 @Bi50 catalyst can selectively reduce CO2 to formate with high selectivity (≈90% faradaic efficiency), large partial current density (24.53 mA cm-2 at -1.36 V), and long-term stability (up to 14.5 h), superior to most of the Bi-based catalysts. The hybrid Bi/In2 O3 interfaces of core-shell C@In2 O3 @Bi will stabilize the key intermediate HCOO* and suppress CO poisoning, benefiting the CO2 RR selectivity and stability, while the internal cavity of core-shell structure will improve the reaction kinetics because of the large specific surface area and the enhancement of ion shuttle and electron transfer. Furthermore, the nano-limited domain effect of outmost carbon prevent active components from oxidation and agglomeration, helpful for stabilizing the catalyst. This work offers valuable insights into core-shell structure engineering to promote practical CO2 conversion technology.

Crystal Face Dominated Fabrication of Prussian Blue Analogue with Oriented Growth and Naturally Nonpreferred Unsaturated Coordination Center.

Defects, such as unsaturated coordination centers and vacancies, can fundamentally change materials' inherent properties and growth habits. The development of defect engineering has promoted the application of many technologies, but it is still a great challenge to selectively manufacture defect sites in existing material systems. It is shown here that in situ site-directed tailoring of metal sites in Prussian blue analogs (PBA) can be achieved according to the reducibility differences of different metal atoms, forming naturally nonpreferred unsaturated coordination centers. Meanwhile, the in situ capture of small reducing molecule can realize site-directed tailoring of crystal facets during crystal growth and results in oriented 1D growth. As an oxygen evolution reaction catalyst, the resulted PBA with the nonpreferred unsaturated coordination centers shows a low overpotential of 239 mV at 10 mA cm-2 in alkali, superior to the original PBAs and the previously reported defective PBA derivatives, which can be ascribed to the unsaturated coordination active center and the unique 1D structure. This work opens up opportunities for producing naturally nonpreferred unsaturated coordination center in nanomaterials for broad applications.

Two-Dimensional Imide-Based Covalent Organic Frameworks with Tailored Pore Functionality as Separators for High-Performance Li-S Batteries.

Modifying the separator of lithium-sulfur batteries (LSBs) is considered to be one of the most effective strategies for relieving the notorious polysulfide shuttle effect. Constructing a stable, lightweight, and effective LSB separator is still a big challenge but highly desirable. Herein, a stable and lightweight imide-based covalent organic framework (COF-TpPa) is facilely fabricated on reduced graphene oxide (rGO) through an oxygen-free solvothermal technique. With the directing effect of rGO and changing the side functional group of the monomer, the morphology and the pore tailoring of COF-TpPa can be simultaneously achieved and two-dimensional (2D) COF nanosheets with different functionalities (such as -SO3H and -Cl) are successfully constructed on rGO films. The specific functional groups inside the COF's pore channels and the narrowed pore size result in efficient absorption and restriction of Li2Sn for weakening the "shuttle effect". Meanwhile, the 2D COF nanosheets on the rGO is a favorable morphology for better exploiting pores inside the COF materials. As a result, the COF-SO3H-modified separator, consisting of rGO and COF-TpPa-SO3H, exhibits a high specific capacity (1163.4 mA h/g at 0.2 C) and a desirable cyclic performance (60.2% retention rate after 1000 cycles at 2.0 C) for LSBs. Our study provides a feasible strategy to rationally design functional COFs and boosts their applications in various energy storage systems.