Constructing NiCo/Fe3O4 Heteroparticles within MOF-74 for Efficient Oxygen Evolution Reactions

General Synthesis of Mixed Semiconducting Metal Oxide Hollow Spheres with Tunable Compositions for Low-Temperature Chemiresistive Sensing

Metal oxide hollow spheres (MOHSs) with multicomponent metal elements exhibit intriguing properties due to the synergistic effects of different components. However, it remains a great challenge to develop a general method to synthesize multicomponent MOHSs due to the different hydrolysis and condensation rates of precursors for different metal oxides. Herein, we demonstrate a general strategy for the controllable synthesis of MOHSs with up to five metal elements by decomposition of metal-phenolic coordination polymers (MPCPs), which are prepared by chelation of tannic acid with various metal ions. After calcination to burn out the organic component and induce heterogeneous contraction of MPCPs, a series of MOHSs with multishell structure, high specific surface area (55-171 m²/g), and crystalline mesoporous framework are synthesized, including binary (Fe-Co, Ni-Zn, and Ni-Co oxides), ternary (Ni-Co-Mn and Ni-Co-Zn oxides), and quinary (Ni-Co-Fe-Cu-Zn oxides) MOHSs. The gas sensing nanodevices based on quinary MOHSs show much higher response (10.91) than those based on single component toward 50 ppm of ethanol at 80 °C with the response/recovery time of 85/160 s. The quinary oxides sensor also displays high selectivity toward ethanol against other interfering gases (e.g., methanol, formadehyde, toluene, methane, and hydrogen) and long-term stability (∼94.0% after 4 weeks), which are extremely favorable for practical applications.

Regulation of the Ni2+ Content in a Hierarchical Urchin-Like MOF for High-Performance Electrocatalytic Oxygen Evolution

The exploitation of efficient non-precious electrocatalysts for the oxygen evolution reaction is extremely important but remains tremendously challenging. Here, we prepared a series of hierarchical urchin-like bimetallic Ni/Zn metal-organic framework nanomaterials that served as high-performance electrocatalysts, by regulating the Ni²⁺/Zn²⁺ ratio and using a facile one-step hydrothermal method for the application of the oxygen evolution reaction. The structure of the hierarchical urchin-like microspheres could improve the utilization efficiency of the active species by facilitating the diffusion of gas and reducing the transport resistance of ions, due to its features of a large interfacial area and convenient diffusion channels. In addition, we found that the higher the Ni ratio was, the better the electrocatalytic performance of these bimetallic metal-organic framework nanomaterials.

Synthesis of Bimetallic Conductive 2D Metal-Organic Framework (Cox Niy -CAT) and Its Mass Production: Enhanced Electrochemical Oxygen Reduction Activity

The development of new electrocatalysts for electrochemical oxygen reduction to replace expensive and rare platinum-based catalysts is an important issue in energy storage and conversion research. In this context, conductive and porous metal-organic frameworks (MOFs) are considered promising materials for the oxygen reduction reaction (ORR) due to not only their high surface area and well-developed pores but also versatile structural features and chemical compositions. Herein, the preparation of bimetallic conductive 2D MOFs (Co_x Ni_y -CATs) are reported for use as catalysts in the ORR. The ratio of the two metal ions (Co²⁺ and Ni²⁺ ) in the bimetallic Co_x Ni_y -CATs is rationally controlled to determine the optimal composition of Co_x Ni_y -CAT for efficient performance in the ORR. Indeed, bimetallic MOFs display enhanced ORR activity compared to their monometallic counterparts (Co-CAT or Ni-CAT). During the ORR, bimetallic Co_x Ni_y -CATs retain an advantageous characteristic of Co-CAT in relation to its high diffusion-limiting current density, as well as a key advantage of Ni-CAT in relation to its high onset potential. Moreover, the ORR-active bimetallic Co_x Ni_y -CAT with excellent ORR activity is prepared at a large scale via a convenient method using a ball-mill reactor.

Ammonia borane dehydrogenation and selective hydrogenation of functionalized nitroarene over a porous nickel–cobalt bimetallic catalyst

The hydrolysis of ammonia borane is a promising strategy for hydrogen energy exploration and exploitation. The in situ produced hydrogen could be directly utilized in hydrogenation reactions. In this work, a bimetallic nickel–cobalt material with porous structure was developed through the pyrolysis of ZIF-67 incorporated with Ni ions. Through the introduction of Ni(NO₃)₂ as an etching agent, the ZIF-67 polyhedrons were transformed into hollow nanospheres, and further evolved into irregular nanosheets. The bimetallic NiCo phase was formed after pyrolysis in a nitrogen atmosphere at high temperature, with the decomposition and release of organic ligands as gaseous molecules under flowing nitrogen. The obtained bimetallic NiCo porous materials show superior catalytic performance towards hydrolytic dehydrogenation of ammonia borane, thereby nitrobenzene with reducible functional groups can be reduced with high selectivity to the corresponding aniline.

Porous nickel–cobalt bimetallic catalyst realizes selective hydrogenation of nitrobenzene with in situ produced hydrogen through hydrolysis of ammonia borane.

In situ synthesis of a Fe3S4/MIL-53(Fe) hybrid catalyst for an efficient electrocatalytic hydrogen evolution reaction

By modulating the Fe₃S₄/MIL-53(Fe) ratio with a controlled partial sulfurization strategy, the Fe₃S₄(52.1 wt%)/MIL-53 hybrid catalyst with an ideal hierarchical nanostructure and composition exhibited high HER activity.

Carbon-incorporated NiO/Co3O4 concave surface microcubes derived from a MOF precursor for overall water splitting

Carbon-incorporated NiO/Co₃O₄ concave surface microcubes (denoted as NCMC) are successfully developed from a precursor of Ni₃[Co(CN)₆]₂ for the first time.

Optimized Co2+(Td)–O–Fe3+(Oh) electronic states in a spinel electrocatalyst for highly efficient oxygen evolution reaction performance

The introduction of iron into Co₃O₄ can induce a change in the electronic states of Co³⁺, which is an effective means to regulate the oxygen evolution reaction activity.

In situ growth of Fe(ii)-MOF-74 nanoarrays on nickel foam as an efficient electrocatalytic electrode for water oxidation: a mechanistic study on valence engineering

DFT results first demonstrate that varying the metal valence can tune the stable intrinsic electronic structure of MOF, different valence Fe(ii) and Fe(iii)-MOF-74 nanoarrrays on nickel foam are further synthesized as electrode for water oxidation.