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Non-noble metal containing catalysts for oxygen reduction reaction (ORR) are being targeted due to their low cost and availability. The rarity, high-cost, and self-poisoning of noble metals are the main drawbacks for the large-scale applications. Herein, a facile and simple synthetic strategy is adopted to prepare non-noble metal-based nitrogen doped carbon nanotubes (N-CNTs). The cobalt oxides (CoOx) nanoparticles are in-situ encapsulated inside these N-CNTs which are then treated with acid (HCl) and phosphidized to obtain CoOx-CoP/N-CNTs. High resolution transmission electron spectroscopy (HR-TEM) results reveal that the ends of N-CNTs are closed with nanoparticles. X-ray photoelectron spectroscopy (XPS) confirms the presence of cobalt oxide and cobalt phosphide nanoparticles. The catalyst CoOx-CoP/N-CNTs2 demonstrated E onset and E 1/2 of 0.96 V and 0.81 V, respectively in alkaline environment which is very much comparable to the state of art catalyst (20 wt% Pt/C). Acid treatment significantly enhances the electrocatalytic activity for ORR in comparison to material synthesized without prior treatment with acid. The catalyst exhibits excellent durability over 10,000 cycles and methanol tolerance to 0.5 M methanol addition. The enhanced ORR activity is attributed to synergistic effect of carbon matrix and encapsulated nanoparticles. • Cobalt oxides (CoOx) nanoparticles are in-situ encapsulated inside N-CNTs. • CoOx/N-CNTs treated with acid (HCl) and phosphidized to obtain CoOx-CoP/N-CNTs. • High resolution transmission electron spectroscopy results reveal that the ends of N-CNTs are closed with nanoparticles. • CoOx-CoP/N-CNTs2 demonstrated E onset and E 1/2 of 0.96 V and 0.81 V, respectively in alkaline environment. • The catalyst exhibited excellent durability over 10,000 cycles and methanol tolerance to 0.5 M methanol addition. [ABSTRACT FROM AUTHOR]

[Display omitted] • The oxygen evolution reaction (OER) is a crucial electrochemical reaction of water-splitting system. • Cobalt-based bimetallic zeolitic imidazole frameworks (ZIFs) and their derivatives are extensively utilized. • Only cobalt-based bimetallic ZIFs used as electrocatalysts during OER are discussed. • Future prospects for bimetallic ZIF-derived carbon-based materials for OER electrocatalysis are discussed. Oxygen evolution reaction (OER) is a crucial electrochemical reaction in metal-air batteries and water-splitting system. It is of utmost importance for these devices to achieve highly efficient clean energy production and storage. The zeolitic imidazolate frameworks (ZIFs) have received a lot of attention as a new type of crystalline porous materials due to their large surface area, high porosity, large pore volume, and easy functionalization as well as promising precursors to produce carbon-based electrocatalysts with high electrical conductivity. Cobalt-based bimetallic ZIFs with two distinct metal ions hold specific synergistic effects that demonstrate water oxidation performance and stability better than those of individual monometallic ZIFs. This review focuses on cobalt based bimetallic ZIFs; their advantages, synthesis and modification methods, derived compounds, synergistic effects, and activity of electrocatalysts during OER. We have summed up the application of bimetallic ZIFs and their derivatives in oxygen evolution reaction for the first time, that has sparked a lot of interest in this field. Finally, the future prospective of bimetallic ZIF-derived carbon-based materials for OER electrocatalysis is briefly discussed. [ABSTRACT FROM AUTHOR]

Research on water splitting reaction is on priority to explore an alternative source of energy with little to no carbon emissions. Among the two half reactions of electrochemical water splitting, oxygen evolution reaction (OER) is highly desirable yet challenging to prepare a cost effective and viable electrocatalyst to boost the OER activity. Herein, we have prepared a novel electrocatalyst, CoO x -CoP/N-CNTs, by the phosphidization of cobalt oxides (CoO x) encapsulated N- doped carbon nanotubes (CoO x /N-CNTs). The CoO x /N-CNTs composite is derived via pyrolysis of cobalt based zeolitic imidazole framework (ZIF-12) at 950 °C under argon atmosphere. The CoO x /N-CNTs is phosphidized at various temperatures ranging from 320 °C to 400 °C. The optimized temperature to attain the best catalytic activity is 380 °C. The phosphatized material, CoO x -CoP/N-CNTs, shows superior performance towards OER with an overpotential of 250 mV @ 20 mAcm−2 vs 532 mV @ 20 mAcm−2 of un-phosphidized material, CoO x /N-CNTs, which shows significant effect of phosphidization. The maximum current density of 160 mAcm−2 in 1 M KOH solution is achieved. • A novel electrocatalyst, CoO x -CoP/N-CNTs, is fabricated. • The phosphatized material, CoO x -CoP/N-CNTs, shows superior performance towards OER. • During OER activity, an overpotential of 250 mV at 20 mAcm−2 and current density of 160 mAcm−2 is observed. • The electrochemical activity remarkably greater than the un-phosphatized material. [ABSTRACT FROM AUTHOR]