Oxygen and activation energy 1. The suitable choice

Oxygen evolution reaction (OER) is the obstacle to overall water splitting due to its slow kinetics reaction, high overpotential and activation energy 1. The suitable choice of materials with less overpotential and high electrocatalytic activity is accomplished by decreases in the overpotential. Platinum (Pt) is the most efficient electrocatalyst for OER and almost near zero overpotential in acid and alkaline media with significant rate, and it used as electrode makes the process too expensive for practical application. In this regard, researchers to search for alternative catalyst to Pt, which have cost-effective, high OER activity and no corrosion problem with long lifetime. Moreover profuse researchers have been investigated a variety of spinel ferrites (AB2O4; where, A & B are a bivalent & trivalent transition metal ions) electrocatalysts. Among them Co, Zn, Mo, Ni and etc. spinel-type structures are considered the most promising and are extensively studied 2. Spinel established an important class of ferrite shows abroad kind of interesting applications viz.

energy storage and conversion 3, supercapacitor 4, lithium-ion batteries 5, sensors 6, photocatalysts 7 and medical applications 8. Such type of spinel 9 has its own significant electrocatalytic activity and stability in high pH but its low electrical conductivity restricts its application as a catalyst. Spinel-type iron cobalt oxide (Fe-Co-O-NF) was developed on Ni-foam with help of chemical bath deposition method and these composite electrodes show improved catalytic activity at low overpotential for HER (205mV) and OER (244mV) at 10mAcm-2 10.

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CoFe2O4 nanoparticles synthesized using a facile hydrothermal growth scheme and their attachment to 3D carbon fiber papers samples acting as a bifunctional electrocatalyst for efficient and durable OER and HER 11. Notably cobalt ferrite can be a promising electrocatalyst due to its unique properties. The fabrication of Co3O4 and FexCo3–xO4 nanoparticles using vapor-fed flame aerosol synthesis, the catalysts exhibit stable OER overpotential of 295 mV at 10 mA/cm-2 and Tafel slopes down to 38 mVdec-1 12.

Li et al. 13 synthesized ultrathin Co3O4 nano-meshes (Co-UNMs) by employing the CoCl2/K3Co-(CN)6 cyanogen as reaction precursor by an etch-free one-step process. These synthesized Co-UNMs with 1.5 nm thickness and abundant pores own the high surface area and numerous defected atoms, resulting in enhanced OER activity (?= 307mV, Tafel slope of 76 mVdec?1) in the alkaline media. Chakrapani et al.14 reported that the spinel-type of CoV2-xFexO4 (0 ? x ? 2) nanoparticles was used as a bi-functional catalysts for OER and ORR in alkaline electrolyte. These catalyst shows an overpotential for OER (300 mV with low Tafel slope of 38 mVdec-1). Li et al.

15 synthesized 3-D flower-like nanostructure by hydrothermal method of a high specific surface area, high conductivity and the synergic effect of metal ions are as-synthesized (Co0.5Ni0.5)3(PO4)2 /Ni reveals excellent OER activity in KOH electrolyte. Alshehri et al. 16 prepared the CoFe2O4-NC using chicken egg white/albumin after pyrolysis at 700oC, 800oC, 900oC and 1000oC. The catalyst prepared at 900oC, N/CF-EC-900 exhibit superior catalytic activity as well as the superior stability than that of other nanocomposites prepared and other commercial catalyst (Pt/C, RuO2) for water splitting. Maruthapandian et al. 17 synthesized a Ni2+ and Co2+ substituted MxNi1-xFe2O4 (x = 0 to 1) through the sol-gel auto combustion method.

In order to investigate the role of Co2+ substitution in the spinel system was studied for OER in alkaline media. Among these investigated catalysts, bare nickel ferrite showed better catalytic activity with ? = 381mV, a Tafel slope of 46.4mVdec?1. Sun et al. 18, stable mesoporous spinel ZnFe2O4 with large surface area and smaller particle size was successfully prepared via a surface binding strategy as an efficient catalyst for electrochemical hydrogen generation in acidic water.


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