V.I. Vigdorovich, L.E. Tsygankova, I.E. Gladysheva
Kinetics of hydrogen evolution reaction (HER) on the pressed micro graphite electrodes containing up to 8 wt. % multi-walled carbon nanotubes (MWNTs) has been studied. Aqueous and ethylene glycol solutions containing Х М НС1 + (1-Х) М МеСl with constant ionic strength equal to 1 have been used. Me is Na in aqueous medium and Li – in the ethylene glycol ones containing 0,1 and 10 wt. % H2O. MWNTs have been obtained by catalytic pyrolysis of propane – butane mixture at 625 ± 25о С on Ni/Mg catalyst and have been activated by 2 hours acid treatment at 106о C in the mixture of concentrated НNО3 and Н2SО4 (1 : 3). Inner diameter of MWNTs is equal to 20…60 nm, the length is equal up to 2 mm, the specific surface is equal to 144 m2g-1. The electrodes have been prepared by pressing of micro graphite containing up to 8 wt. % MWNTs at pressure equal to 6000 kg/cm2.
A character of the cathodic polarization curves does not depend on a nature and composition of a solvent. Direct and backward polarization course without removal of an electrode from a solution forms a wide hysteresis loop conditioned by a reduction of the surface functional groups on carbon base (direct course). The kinetic parameters values of the linear sections of the polarization curves observed in E, lgic coordinates (ic is cathodic current density) and corresponding to hydrogen evolution reaction proceeding have been calculated. The dE/dlgic and dE/dlgCH+ kinetic parameters values essentially exceed the values demanded by the HER kinetics at the slow discharge or the slow Tafel reaction or Heyrovsky one. The dlgic/dlgCH+ value is in 0,5 – 1,0 range. HER proceeds at the mixed kinetics with a considerable contribution of a diffusion component. It is conditioned with a predominant proceeding of the cathodic reactions in the pores of the pressed electrode. A growth of the MWNTs concentration in the composite increases HER rate with the order from 0,2 to 0,6. In hole such composites can be considered as the systems perspective for hydrogen accumulation.