ORIGINAL PAPER Simple chemical route for nanorod-like cobalt oxide films for electrochemical energy storage applications Assumpta C Nwanya 1 & Daniel Obi 2 & Rose U. Osuji 1,3 & R. Bucher 3 & Malik Maaza 3,4 & Fabian I. Ezema 1,3,4 Received: 20 September 2016 /Revised: 20 December 2016 /Accepted: 25 January 2017 # Springer-Verlag Berlin Heidelberg 2017 Abstract We used a simple chemical synthesis route to de- posit nanorod-like cobalt oxide thin films on different sub- strates such as stainless steel (ss), indium tin oxide (ITO), and microscopic glass slides. The morphology of the films show that the films were uniformly spread having a nanorod-like structure with the length of the nanorods short- ened on ss substrates. The electrochemical properties of the films deposited at different time intervals were studied using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). The film deposited after 20 cycles on ss gave the highest specific capacity of 67.6 mAh g −1 and volumetric capacity of 123 mAh cm −3 at a scan rate 5 mV s −1 in comparison to 62.0 mAh g −1 and 113 mAh cm −3 obtained, respectively, for its counterpart on ITO. The film electrode deposited after 20 cycles on ITO gave the best rate capability and excellent cyclability with no depreciation after 2000 charge–discharge cycles. Keywords Cobalt oxide . Specific capacitance . Nanorod-like . SILAR . Stainless steel Introduction Among the transition metal oxides, cobalt oxide has three well-known polymorphs; monoxide or cobaltous oxide (CoO), cobaltic oxide (Co 2 O 3 ), and cobaltosic oxide or cobalt cobaltite (Co 3 O 4 ). Pure CoO is not stable in the air and readily takes up oxygen even at room temperature to reform to a higher oxide; hence, it is difficult to obtain, while Co 2 O 3 is completely converted into Co 3 O 4 at a temperature of about 538 K [1]. Among the cobalt oxides, Co 3 O 4 is the most stable and our focus is on this oxide of cobalt. Co 3 O 4 is a black antiferromagnetic, thermostable p-type semiconductor with a band gap of ∼2.0 eV and density of 6.11 g cm −3 [2]. Co 3 O 4 gives excellent electrochemical reac- tivity and redox reversibility, high capacity (the theoretical capacity of lithium-ion battery for Co 3 O 4 is 890 mAh g −1 while the theoretical specific capacitance is ≈3560 F g −1 ) [3]. These properties make this oxide of cobalt attractive for electrochemical applications after the pioneering works of Tarascon’s group and Conway et al. [4, 5]. Cobaltosic oxide is extensively used in lithium-ion batteries [ 6 , 7 ], supercapacitors [8, 9], catalysis [10], etc. Numerous nanostructured Co 3 O 4 such as nanowires, nanoflakes, nanocage, nanorods, nanoparticles, nanobowls, and nanospheres have been prepared by different synthesis routes and for various applications. For example, Reddy et al. [6] used the urea combustion method to prepare nano- rods of Co 3 O 4 . The films were used as anode materials in lithium-ion batteries and four Li 2 O and three Co formed dur- ing the discharge cycle giving a theoretical capacity of 890 mAh g −1 while showing negligible capacity fading. * Assumpta C Nwanya chinwe.nwanya@unn.edu.ng * Fabian I. Ezema fabian.ezema@unn.edu.ng 1 Department of Physics and Astronomy, University of Nigeria Nsukka, Nsukka, Nigeria 2 INRS Centre for Energy, Materials and Telecommunications and UNESCO Chair in Materials and Technologies for Energy Conversion, Saving and Storage, 1650, Boulevard Lionel-Boulet, Varennes, QC J3X 1S2, Canada 3 Nanosciences African Network (NANOAFNET), iThemba LABS-National Research, Cape Town, South Africa 4 UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, College of Graduate Studies, University of South Africa (UNISA), Muckleneuk ridge, P.O. Box 392, Pretoria, South Africa J Solid State Electrochem DOI 10.1007/s10008-017-3520-8