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Synthesis of mixed transition metal nitrides often leads to the formation of more than one phases in the final product. A control over molar ratio of metals (Fe:Ni) along with synthetic strategy is used to form phase pure product (Fe 3 Ni 7 N@C). The synthesized material is used as an efficient and cost-effective electrocatalyst for oxygen evolution reaction (OER). Fe 3 Ni 7 N@C requires a low overpotential of 290 mV to achieve a catalytic current density of 10 mA cm−2 which holds Tafel slope of 40 mV dec−1 superior to the noble metal benchmark catalysts. The physicochemical integrity of Fe 3 Ni 7 N@C is maintained up to 12 h activity as evident from post catalytic characterization. Fe3Ni7N@C nanoparticles for oxygen evolution reaction. [Display omitted] • A control over molar ratio of metals (Fe:Ni) is used to form phase pure product (Fe 0.3 Ni 0.7 N@C). • Fe 0.3 Ni 0.7 N@C is used as an efficient electrocatalyst for oxygen evolution reaction (OER). • Fe 0.3 Ni 0.7 N@C requires a low overpotential of 290 mV to achieve a catalytic current density of 10 mA cm−2. • The physicochemical integrity of Fe 0.3 Ni 0.7 N@C is maintained up to 12 h activity. [ABSTRACT FROM AUTHOR]

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]

Efficient and noble metal-free electrocatalyst could enhance conceivably fuel cell's affordable commercialization. In this esteem, we developed CoO embedded N-doped CNTs from zeolitic imidazolate framework (ZIF-12) by single step inert atmosphere calcination, to be used as oxygen reduction reaction (ORR) electrocatalyst. In the electrochemical studies performed, the CoO/N-CNTs has demonstrated an onset potential of 0.83 V vs. RHE, very close to the commercial Pt catalyst value, electron transfer number of 3.5 which approaches the theoretical value of 4 and current density of 3.35 mA cm − 2 at 2500 rmp. The excellent activity of the electrocatalyst is to be attributed to its waved-tubular structure casing CoO particles and to its high surface area as it was proved by TEM and gas adsorption analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Transition metal nitrides (TMNs) have gained substantial interest to catalyse water splitting reaction. • Iron and nickel based TMNs are considered as ideal electrocatalysts because of the abundance, low cost, and high catalytic activity. • Single phase TMNs have unsatisfactory performance due to inadequate M−H/M−OH bond strength. • Recent developments pertaining to Fe and Ni-based TMNs are presented for electrochemical water splitting. Transition metal nitrides (TMNs) have gained substantial interest to generate hydrogen from direct dissociation of water via catalytic strategy. Due to the unique noble metal like structure, high electric conductivity, corrosion resistance, broad pH stability and probable structural modifications TMNs are gauged as efficient hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and overall water splitting (OWS) electrocatalysts. Iron and nickel based TMNs are considered as ideal electrocatalysts because of the abundance, low cost and high catalytic activity as compared to the expensive benchmark catalysts. However, the single phase TMNs have unsatisfactory performance due to inadequate M−H/M−OH bond strength. Most researchers have focused in designing advanced heterostructures by doping other metals, metallic compounds, and conductive substrates to improve catalytic performance due to the tailored electronic structure to modify M−H/M−OH bond strength, boost electrochemical stability and synergistic effects. In this review, we highlight the recent developments pertaining to Fe and Ni-based TMNs from the stance of advanced nanoarchitecture electrocatalysts for electrochemical water splitting. The key challenges and future perspectives confronting expansion of water splitting catalysts are critiqued. [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]

Transition metal oxyhydroxides have been used as promising electrocatalysts for water splitting however, their catalytic activity is restricted due to low surface area and poor conductivity. Herein, we report novel composite FeOOH@ZIF-12/graphene composite as electrocatalyst for water oxidation, whereby ZIF-12 provide extra surface for the FeOOH dispersion whilst graphene act as excellent electron mediator. The composite shows a low overpotential value of 291 mV to attain a current density of 10 mA cm−2 and a low Tafel slope value of 78 mV dec−1. The catalyst offers a maximum current density of 101 mA cm−2, while it gives a turnover frequency (TOF) value of 0.031 s−1 at an overpotential of 291 mV only. The excellent activity and remarkable stability of composite is attributed to highly conductive and porous support. [Display omitted] • FeOOH nanoparticles are incorporated in ZIF-12/graphene matrix. • The synthesized composite is utilized as electrocatalyst for water oxidation. • The composite shows a low overpotential value of 291 mV @ 10 mA cm−2. • The catalyst offers a maximum current density of 101 mA cm−2 with a TOF value of 0.031 s−1. [ABSTRACT FROM AUTHOR]

An efficient electrochemical urea oxidation reaction (UOR) could be used in energy production technology. Metallic nickel nano-particles (Ni NPs) are incorporated in cobalt hydroxide layered material to form Ni/Co(OH) 2. The synthesized material is utilized as an electrocatalyst in UOR. It has been revealed that the incorporation of Ni NPs into cobalt hydroxide significantly enhances their electrocatalytic activity toward UOR. Ni/Co(OH) 2 catalyzes UOR at a very low anodic potential of 1.15 V vs RHE with a peak current density of 14.2 mAcm−2 and Tafel slope of 75 mVdec−1. The current work is a step ahead towards use of transition metal hydroxide (TMH) as support in the electrocatalytic oxidation applications especially UOR. [ABSTRACT FROM AUTHOR]

Abstract The development of efficient and cost-effective electrocatalysts for oxygen evolution reaction is a priority research area. Metal-organic frameworks (MOFs) have recently captured attention as heterogeneous water oxidation catalysts. In spite of their robustness and stability under specific pH conditions, the relatively low current density achieved is their main drawback. Herein, we explored a cobalt based framework [Co(bpy)(fa)] n (DMF) 0.25 (bpy) 0.25 (1) {bpy = 4,4ʹ-bipyridine, fa = fumarate, DMF = dimethylformamide} as an efficient electrocatalyst for the water oxidation reaction. Compound 1 exhibits excellent activity in a neutral phosphate buffer solution. Chronoamperometric studies show that 1 offers a current density of 10 mA cm−2 at only η = 382 mV. Onset over-potential of 248 mV is observed which holds a Tafel slope value of 84 mV dec−1. The catalyst showed a turnover frequency (TOF) of 2 × 10−3 s−1 for oxygen evolution reaction (OER) at 289 mV. Detailed electrochemical studies, including long-term electrolysis, indicates the potential of compound 1 to be utilized as heterogeneous catalyst toward the oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • The polymeric compound [{NiII(4,4ʹ-dipy) 4 }{Ni(CN) 4 }] n (1) is presented as electrocatalyst towards water oxidation. • 1 has showed ca. 28 times enhanced surface concentration (Γ = 39.5 nmol/cm2), compared to the reported CoFe(CN) 6 (Γ = 1.4 ± 0.2 nmol/cm2). • The overpotential of merely 315 mV is required to produce a current density of 1 mA/cm2. • The development is designing the noble metal (Pt/Ru/Ir) free, efficient electrocatalysts for water oxidation reaction. The search of proficient, copious, economical and robust electrocatalyst is of prime prerequisite. Recently, the usage of cyanometallate based coordination polymers as electrocatalysts for water oxidation has acquired an expanding measure of attraction attributable to their high surface area and stability. In this study, a homo-metallic Ni based cyanometallate coordination polymer [{NiII(4,4ʹ-dipy) 4 }{Ni(CN) 4 }] n ·(4,4ʹ-dipy)·3H 2 O·C 2 H 6 O 2 (1) (4,4ʹ-dipy = 1,3-di(4-pyridyl)propane) is presented as an efficacious and robust electrocatalyst towards water oxidation reaction at pH = 13. The inimitable 3-D zig-zag topology of 1 has directed to ~28 times enhanced surface concentration (Γ) i.e. 39.5 nmol/cm2 as compared to the reported CoFe(CN) 6 (Γ = 1.4 ± 0.2 nmol/cm2). The 1 presents a TOF of 0.25 s−1 at an overpotential (η) of 381 mV (vs. RHE) which is much larger than those reported for other cyanide bridged and Ni based coordination polymers for instance: CoFe(CN) 6 (TOF = 2 × 10−3 s−1, η = 300 mV), CoFe(CN) 5 -PVP (TOF = 2 × 10−3 s−1, η = 284 mV), Codca2 (TOF = 2 × 10−3 s−1, η = 358 mV), Ni-UMOFNs (TOF = 0.18 s−1, η = 300 mV), bulk NiCo-MOFs (TOF = 0.15 s−1, η = 300 mV) and Ni-MOF/NF (TOF = 0.25 s−1, η = 400 mV). The overpotential (η) of of 315 mV is required to produce a current density (J) of 1 mA/cm2. Controlled potential electrolysis (CPE), PXRD and FT-IR experiments confirm that 1 remains active and chemically integrate over a 36,000 s test reaction. The outcomes of the comprehensive electrochemical investigations are prophesied to direct the imminent development in designing noble metal free, efficient and low-priced electrocatalysts for oxygen evolution reaction. [ABSTRACT FROM AUTHOR]