Electrochemically grown MnO2 nanowires for supercapacitor and electrocatalysis applications

Abstract

In this study, MnO₂ nanowires are electrochemically grown over a 3D nickel foam (NF) substrate using cyclic-voltammetry at 27°C; furthermore, their potential for applications in supercapacitors and oxygen evolution reactions (OERs) is explored. The as-obtained MnO₂@NF nanowire-type electrode has demonstrated a specific capacitance (SC) of 641 F g⁻¹ and a capacitance retention of 97%. The as-assembled MnO₂//MnO₂ symmetric supercapacitor device has endowed a maximum energy density of 25 W h kg⁻¹ at power and current densities of 588 W kg⁻¹ and 2 A g⁻¹, respectively, which has successfully activated three different-colored LEDs with moderate light intensity. Furthermore, a small overpotential of 260 mV is obtained when the MnO₂ electrode was used for OERs, highlighting its potential as an efficient catalyst. The use of MnO₂ nanowires in supercapacitors and OERs has several advantages, such as (a) accessibility of several active sites, (b) easy charge transfer with reduced diffusion resistance, and (c) smooth and fast percolation of electrolyte ions responsible for optimum redox reactions. Therefore, the design of a hybrid system, containing both energy storage and water splitting applications, can be featured using only the MnO₂ electrode material.