have been explored to this end [ 7,8 ] and in particular cobalt-based oxides and their binary oxides with nickel are reported to be potential candidates. [ 9 ] For a favorable OER, the M OH bond strength should be moderate enough as per the Sabatier's principle of balanced intermediate adsorption in catalysis. [ 4,10,11 ] Cobalt in Co 3 O 4 spinel occupies two different sites, tetrahedral for Co 2+ and both tetrahedral and octahedral for Co 3+ . [ 12 ] Incorporation of nickel in the Co 3 O 4 spinel structure results in the octahedral substitution, which is reported to improve the electronic conductivity and effective surface area and add benefi cial effect on oxygen evolution kinetics. [ 13,14 ] Additionally, nickel-based oxides and hydroxides that are prepared by wet chemical routes are found to produce hierarchical nanostructures, and as a consequence provide high surface area for catalytic reactions. [ 15,16 ] Microstructuring of materials into thin fi lms, [ 17 ] 3D cages, [ 18 ] nanorod, [ 19 ] wires, [ 20 ] and porous structures [ 21 ] are known to enhance the active surface area. The oxygen vacancies and nonstoichiometry introduced during fabrication and annealing processes can further improve the conductivity and lower the hydroxyl adsorption energy. [ 22,23 ] Rational design of morphology is a promising approach to promote material's performance. Building hierarchical hollow structures thus holds promise for more effi cient electrocatalyst which can render large surface area, better electronic conductivity and porosity for electrochemical processes. [ 14,24 ] Great efforts have been devoted to develop such porous and hollow nanostructure, which can not only enhance the desired activity, but also impart new functionalities. [ 24,25 ] Recently, metal-organic framework (MOF) has been demonstrated as excellent precursors and templates for fabrication of 3D structures of metal oxides for highly effi cient supercapacitors, Li ion batteries, and oxygen reduction reactions. [ 26 ] Following similar fabrication methodology, MOF derived coreshell structured NiCo 2 O 4 -Co 3 O 4 has been prepared and used to study supercapacitor and catalytic oxygen evolution behavior. [ 18 ] There is, however, a need for systematic investigations to arrive at an optimum nickel-cobalt oxide for OER based on this fabrication route. Such investigations assume importance in realizing a competitive OER catalyst of this class for use in solar to hydrogen conversion devices.In this paper, we report a simple template based fabrication route for non-stoichiometric Ni Co metal oxide nanocages with mesoporous structure, and rich in Ni and Co redox centers, and Nonstoichiometric Ni x Co 3− x O 4− y 3D nanocages are fabricated through metalorganic framework template route and their electrocatalytic oxygen evolution reaction (OER) characteristics have been investigated. Substitution of Ni in Co 3 O 4 spinel structure improves the intrinsic catalytic activity. Enhanced OER activity stems from the presence of nonstoichiometry and low co...
