Ni3S2/carbon nanotube nanocomposite as electrode material for hydrogen evolution reaction in alkaline electrolyte and enzyme-free glucose detection

Abstract In this study, the nanocomposite of Ni 3 S 2 and multi-walled carbon nanotubes (MWCNTs) with the high catalytic activities toward hydrogen evolution reaction (HER) and glucose oxidation was synthesized using glucose-assisted hydrothermal method. Ni 3 S 2 nanoparticles with the diameters ranging from 10 to 80 nm were highly dispersed over conductive MWCNT surface. A series of linear polarization measurements suggested that the HER activity of nanocomposite of Ni 3 S 2 and MWCNTs was increased with decreasing the loading amount of Ni 3 S 2 on MWCNTs and the optimal Ni 3 S 2 loading on MWCNTs was 55 wt%. Furthermore, the immersion of the composite catalyst in a concentrated KOH solution induced the morphological change of the Ni 3 S 2 nanoparticles on MWCNTs, which increases the active surface area of the composite electrode. As a result, the KOH-treated composite electrode showed a higher HER activity than other electrodes. For example, the value of exchange current density of the KOH-treated composite electrode was ca. 395 times and 1.6 times larger than that of Ni 3 S 2 electrode and as-synthesized composite, respectively. Furthermore, the impedance measurements showed the KOH-treated composite electrode had the smaller charge transfer resistance of the HER than Ni 3 S 2 electrode. Based on the slopes obtained from Arrhenius curves of the electrodes, the estimated HER activation energy (71.8 kJ/mol) of KOH-treated composite electrode was only one-third of that of the pure Ni 3 S 2 electrode. The high catalytic activity of the KOH-treated composite electrode was stemmed from the synergistic effect of the large active surface area of Ni 3 S 2 nanoparticles and the excellent electrical coupling to the conductive MWCNT network. More importantly, the current density of KOH-treated composite electrode showed no sign of degradation after the continuous 1000 cycling in a 1 M KOH solution at the temperature of 323 K. On the other hand, the nanocomposite of Ni 3 S 2 and MWCNTs was proposed for the first time as an enzyme-free sensor for glucose. The Ni 3 S 2 nanoparticles on MWCNTs exhibited high electrocatalytic activity toward glucose oxidation and were insensitive to uric acid and ascorbic acid. Furthermore, the composite electrode exhibited that its catalytic current was linearly dependent on the concentration of glucose in the range from 30 to 500 μM and its sensitivity was as high as 3345 μA/mM. The present work suggested that the nanocomposite of Ni 3 S 2 and MWCNTs not only served as an inexpensive, highly active and stable electrode material for alkaline water electrolysis, but also showed a great potential application as a highly sensitive and selective biosensor for glucose.