Metal oxide nanoparticles (NPs) provide a large surface area and short diffusion pathways for ions in supercapacitor electrode materials. However, binders and conductive additives used for tight connections with current collectors and improved conductivity hamper these benefits. In this work, we successfully fix manganese oxide (Mn3O4) NPs onto ITO current collectors by a simple 1,2-ethanedithiol (EDT) treatment without using any binders or conductive additives. As compared to the electrode fabricated using binder-mixed Mn3O4 NPs, the EDT-treated electrode shows significantly improved specific capacitance of 403 F g(-1) at a scan rate of 10 mV s(-1). The EDT-treatment is more effective at higher scan rates. The specific capacitances, 278 F g(-1) at 100 mV s(-1) and 202 F g(-1) at 200 mV s(-1), are larger than those reported so far at scan rates >= 100 mV s(-1) . The deconvolution of capacitive elements indicates that these improved capacitive properties are attributed to large insertion elements of the binder-free NP electrodes. Furthermore, this additive-free electrode is highly transparent and can be easily fabricated by simple spray-coating on various substrates including polymer films, implying that this new method is promising for the fabrication of large-area, transparent and flexible electrodes for next-generation supercapacitors. (C) 2015 Elsevier B.V. All rights reserved.