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[Display omitted] • Highly porous carbon network was derived from zeolitic-imidazole frameworks. • Co-deposition on porous carbon enhanced the catalytic activity. • Co on carbon was electrochemically stable as cathode material during 520 h cycling. Porous carbon wrapped on cobalt catalyst is one of the promising candidates to replace noble metal-based catalysts for ORR. Herein, a porous carbon network (PCN) was obtained by synthesis of zeolitic-imidazole frameworks (ZIF-8) followed by pyrolysis at 1050 ℃ under a nitrogenous atmosphere and the cobalt (Co) was deposited on PCN to obtain Co-PCN by sequential reduction method. The PCN showed a relatively high specific surface area of 806.43 m2/g and decreases to 329.4 m2/g with the introduction of Co contents in PCN. The Co-PCN reveals excellent performance having a current density of 350 mA cm−2 for the ORR at 0.5 V after 20th cycles as a cathode material in rechargeable zinc-air batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fabrication of nickel-cobalt nanocage for oxygen evolution reactions. • Excellent oxygen evolution reaction performance with overpotential of 350 mV. • Synergic effect of cobalt-nickel catalyst improves the conductivity and charge transfer. The development of efficient, eco-friendly, and inexpensive electrocatalysts has become crucial and significant in water-splitting applications. Herein, we developed a nickel-cobalt nanocage (Ni/Co-NC) electrocatalyst via the solvothermal method which can boost the performances towards oxygen evolution reactions (OER) and hydrogen evolution reactions (HER). The Ni/Co-NC reveals significant performance at an onset potential of 350 mV for the OER at a delivered current density of 10 mA cm−2. The significant amount of oxygen vacancies generated by the addition of nickel in cobalt has been verified by XPS and the nanocage structure revealed by TEM and SEM images helps in effective performance for OER/HER. Furthermore, the synergistic effect between various Ni3+/Ni2+ and Co2+ could optimize the performance resulting in a smaller Tafel slope of 70 mV dec−1 for Ni/Co-NC. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanosized Ag@Co 3 O 4 nanoflower were synthesized by chemical deposition. • Small crystallite size and silver deposition enhanced electrochemical performance. • Highly stability upto 500 h with lower overpotential. The studies of core–shell nanoparticles have gained significant interests due to the high stability and probable template to form a core–shell complex by coating on them with organic or inorganic substances. The silica nanoparticle covered with cobalt is especially important because it has a chemically stable core. Co 3 O 4 -NF was synthesized by the calcination of Co(OH) 2 @SiO 2 under atmospheric air for oxygen reduction and evolution reactions. After calcination, Ag deposition was performed to produce Ag@Co 3 O 4 -NF and their surface area reduces from 125.68 to 108.12 m2/g. The crystallanity and morphological features were observed by the X-ray diffraction (XRD) and scanning electron microscopy (SEM). Furthermore, Ag@Co 3 O 4 -NF catalysts exhibited superior electrochemical performance as a cathode material for Zinc-air batteries. The cyclic test for charging and discharging was performed for 500 h revealing Ag@Co 3 O 4 -NF a potential catalyst, having splendid stability for the OER and ORR. [ABSTRACT FROM AUTHOR]

The wide structural versatility of the Metal-Organic Framework (MOF) is considered to be potential catalysts. In this work, [Mn (BDC). nDMF] n was synthesized by the reaction of 1,4-benzene dicarboxylic acid (1,4-BDC) with Manganese (II) nitrate using a solvothermal method. The [Mn (BDC). nDMF] n crystals were calcined for 2 h to produce Mn-MOF derived catalysts (C@MnO catalysts). The formation of MnO crystals was investigated by the X-ray diffraction (XRD) and the Raman Spectroscopy analyzed the graphitization. The resulting catalysts, C@MnO are highly porous with a high specific surface area of 291.62 m2/g at 700 °C. After calcination, Ni deposition was performed, to produce Ni@C@MnO on which Ni-atoms are deposited on the surface of MnO. The surface area reduces to 214.09 m2/g at 700 °C and the structure is distorted due to deposition. Numerous characterization techniques, including XRD, SEM, EDS, TGA, and Raman, strongly support the effective incorporation of Mn and Ni into the material frameworks. When applied as a cathode for Zinc-air battery, the Ni@C@MnO electrode delivered a high current density of 0.206 Acm−2 for the OER. The cyclic test for charging-discharging was performed for 152 cycles revealing a potential catalyst, having splendid stability for the OER and ORR. Unlabelled Image • Fabrication of carbon-coated manganese (C@MnO) catalysts by solvothermal method • Nickel deposition on C@MnO catalysts • Improved catalytic performance for the oxygen reduction and evolution reactions [ABSTRACT FROM AUTHOR]

• Fabrication of efficient bimetallic catalysts for OER. • Nickel decoration was performed on bimetallic CNT/CoNi. • Ni/CNT/CoNi exhibited excellent electrochemical performance and cycling stability. The fabrication of efficient catalysts for the oxygen evolution reactions (OER) that are required to accelerate the sluggish kinetics of metal-air batteries has attracted significant attention for application in energy conversion devices. Metal-organic frameworks (MOFs) have been recognized as potential candidates for the formation of promising catalysts. In this study, we report the formation of Ni/CNT/CoNi using bimetallic-ZIF (CoNi-ZIF) as a precursor. Bimetallic CoNi encapsulated in carbon nanotubes (CNTs) was obtained by calcinating CoNi-ZIF-67 to yield CNT/CoNi. The resulting CNT/CoNi was highly porous with a significant specific surface area of 242 m2/g. After calcination, Ni deposition on the CNT was performed and the surface area was reduced to 168.7 m2/g. Ni/CNT/CoNi was applied as a cathode material in zinc-air batteries, exhibiting excellent electrochemical performance and cycling stability. [ABSTRACT FROM AUTHOR]

• Nickel deposited catalysts using Zeolitic-Imidazolate Frameworks-67 as a precursor were synthesized. • The catalysts exhibited higher catalytic activities for oxygen reduction and evolution reactions. • The catalysts show low overpotential and high stability. Zeolitic imidazolate framework containing cobalt and nickel (Co- and Ni-ZIF-67) were used as a precursor to perform Ni deposition, in order to obtain enhanced catalytic activity and nanocatalysts. Co or Ni embedded in the carbon nanotubes (CNTs) were obtained by the heat treatment of Co- or Ni-ZIF-67. On Co or Ni embedded CNTs, Ni-deposition was performed to obtain the Ni-deposited catalysts, Ni-CNT-(Co or Ni), which have a higher surface area of 136.7 and 259 m2/g, respectively. These catalysts exhibit superior performance, low overpotential, and high stability for both oxygen reduction and evolution reactions. The superior performance is attributed to metal deposition, which creates highly active catalytic sites and has potential application as a catalyst for the rechargeable zinc-air battery. [ABSTRACT FROM AUTHOR]

• Synthesis and characterization of Co 3 O 4 -NFs by the calcination of Co(OH) 2 @SiO 2. • Fabrication of Ni@Co 3 O 4 -NFs by chemical deposition of nickel nanoparticles. • Higher catalytic activity for the OER and ORR. • Higher stability and longer life cycles. Co 3 O 4 nanoflowers (NFs) were obtained from cobalt hydroxide coated on silica, Co(OH) 2 @SiO 2 , prepared from a homogenous mixture of urea and cobalt nitrate in an aqueous solution. The Co 3 O 4 @SiO 2 was obtained by calcining Co(OH) 2 @SiO 2 under atmospheric air for 3 h and then immersing in sodium hydroxide to yield Co 3 O 4 -NFs. The Ni-deposited Co 3 O 4 NFs (Ni@Co 3 O 4 -NFs) were synthesized by chemical deposition of nickel nanoparticles onto Co 3 O 4 -NF by a reducing agent, NaBH 4. The physical characterization of Co 3 O 4 -NFs and Ni@Co 3 O 4 -NFs was performed by Brunauer-Emmett-Teller analysis, scanning electron microscopy and X-ray diffraction. The electrochemical properties of Co 3 O 4 -NFs and Ni@Co 3 O 4 -NFs for the oxygen reduction and evolution reaction were determined in an 8 M KOH solution. Ni@Co 3 O 4 -NF showed a better cell performance than that of Co 3 O 4 -NF. Moreover, Ni@Co 3 O 4 -NF exhibited a higher stability and longer life cycles at 20 mA cm−2 at a 2 h charging and discharging rate as compared to Co 3 O 4 -NF. Therefore, Co 3 O 4 -NF and Ni@Co 3 O 4 -NF could be used as a cathode material for Zn-air rechargeable batteries. [ABSTRACT FROM AUTHOR]