ORIGINAL PAPER Surfactant tuned morphology of mesoporous β-Co(OH) 2 /CMC nanoflakes: a prospective candidate for supercapacitors I. Manohara Babu 1 & J. Johnson William 1 & G. Muralidharan 1 Received: 12 December 2018 /Revised: 15 February 2019 /Accepted: 16 February 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Innovative electrode materials are the need of the hour towards the fabrication of electrochemical energy storage systems with superior performance. In the objective of designing flexible high power supercapacitors, herein, we have synthesized β-cobalt hydroxide/carboxymethyl cellulose nanoflakes via a facile route using anionic, cationic, and non-ionic structure directing agents. When tested as a supercapacitor electrode, β-cobalt hydroxide/carboxymethyl cellulose nanoflakes prepared using cationic surfactant (cetyltrimethylammonium chloride) exhibit better electrochemical behaviour including specific capacitance (306 C g -1 at a scan rate of 2 mV s -1 ), excellent cycle life (89% capacitance retention even after 5000 repeated charge/ discharge cycles) in an aqueous alkaline solution. Furthermore, we have designed an asymmetric supercapacitor utilizing β- cobalt hydroxide/carboxymethyl cellulose and activated carbon as electrodes which is capable of delivering an energy density of 29.7 W h kg -1 with the power density of 695 W kg -1 . The notable features of this device open pathways for the new electrode materials in supercapacitors. Keywords Carboxymethyl cellulose . Precipitation . Nanoflakes . Supercapacitor Introduction Two-dimensional (2D) materials with significant features have attracted the attention of researchers in various domains owing to their porous nature, layered structure, and so on [1–3]. In particular, 2D layered cobalt hydroxide has found place in extensive applications ranging from catalysts, adsor- bents, hydrogen and oxygen evolution (HER & OER) studies, alkaline secondary batteries, supercapacitors (SC’s) etc., [4–6]. In recent years, supercapacitors, a special class of elec- tricity storage devices, endowed with desirable parameters such as (i) excellent rate capacity (ii) high power (10 3 kW g -1 ), (iii) fast charge-discharge rate, (iv) extended cycle life (orders of million cycles), and (iv) maintenance free [7–9]. Supercapacitors store charges either by ion adsorption/ desorption (electric double layer capacitor-EDLC) or surface redox reactions (pseudocapacitor). In the case of EDLCs, car- bonaceous materials are employed as electrode materials while transition metal oxides/hydroxides and conducting polymers (TMO/TMH/CP) act as electrode materials in the case of pseudocapacitors [10–13]. Presently, TMHs-based SC electrode materials hold supe- rior physicochemical properties like tunable interlayer spac- ing, multilayered structure, and good electrochemical activity that provides excellent ion mobility on continuous charging and discharging [14]. Among different TMHs, cobalt hydrox- ide is considered as a better candidate (battery type electrode material) for energy storage/conversion systems owing to its unique qualities such as diverse redox states (Co 2+ , Co 3+ , Co 4+ ), high theoretical capacity (1420 C g -1 ), and eco- friendly nature [15–23]. A vital aspect in layered hydroxide material is phase transformation. It is familiar that layered cobalt hydroxide has two polymorphs: (i) Hydrotalcite phase Highlights • Using carboxymethyl cellulose as carbon source, β- Co(OH) 2 /CMC nanoflakes were synthesized by facile and simple chemistry route. • CTAC-assisted Co (OH) 2 /CMC exhibits excellent electrochemical per- formance due to porous network and flaky structures. • Asymmetric supercapacitor provides a maximum power density of 1320 W kg –1 . Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10008-019-04223-7) contains supplementary material, which is available to authorized users. * G. Muralidharan muraligru@gmail.com 1 Department of Physics, The Gandhigram Rural Institute—Deemed to be University, Gandhigram, Tamilnadu 624302, India Journal of Solid State Electrochemistry https://doi.org/10.1007/s10008-019-04223-7