Nanocomposites and nanomaterials

Bifunctional Co-N-C nanoelectrocatalysts derived from poly-5-aminoindole for overall water splitting
Mazur D.O., Pariiska O.O., Kurys Ya.I., Koshechko V.G., Pokhodenko V.D.
L. V. Pysarzhevsky Institute of Physical Chemistry of the NAS of Ukraine. 
Prospect Nauki, 31, Kyiv-03028, Ukraine. 
E-mail: mazur.denis.olegovich@gmail.com

New Co-N-C nanoelectrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were successfully prepared via heat treatment of a nitrogen containing monomer (5-aminoindole) with oxidant (ammonium persulfate), Co(NO3)2 and carbon nanomaterial (carbon black – CB or N-doped multilayer graphene – NMLG [1]). In the high-temperature treatment conditions, the presence of (NH4)2SO4 in the reaction mixture, as a by-product of oxidative polymerization of 5-aminoindole, causes the formation of cobalt sulfides in the carbonized matrix, that are identified as a cubic densely packed Co9S8. 
The obtained Co-N-CCB and Со-N-CNMLG nanoelectrocatalysts have a bifunctional nature (showing high activity in HER and OER) and can be used for overall water splitting in alkaline media (fig. 1 a). In 1.0 M NaOH, the voltage difference between HER and OER at current density 10 mA/cm2 for Со-N-CNMLG and Co-N-CCB composites are 1923 and 1900 mV, respectively. Also, we demonstrated high activity of obtained nanocomposites toward HER in acid electrolyte (fig. 1 b) – HER overpotential at current density 10 mA/cm2 are ~ 200 mV (vs. RHE) for Со-N-CNMLG and ~ 250 mV for Co-N-CCB.

Fig. 1. HER/OER polarization curves in 1.0M NaOH (a) and HER polarization curves in 0.5M H2SO4 (b) for Со-N-CNMLG (–) and Co-N-CCB (--).

1.	Ustavytska O., Kurys Ya., Koshechko V., Pokhodenko V. One-Step Electrochemical Preparation of Multilayer Graphene Functionalized with Nitrogen // Nanoscale Res. Lett. – 2017. – 12: 175.