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

• The Ni3S2/CNT nanocomposite can be easily synthesized using hydrothermal method.
• The HER performance of Ni3S2/CNT nanocomposite is activated by base treatment.
• The HER activity of nanocomposite is correlated to Ni3S2 morphology on CNTs.
• Ni3S2 and conductive CNTs impart high HER activity and stability to the catalyst.
• The composite electrode exhibits high catalytic activity toward glucose oxidation.

In this study, the nanocomposite of Ni3S2 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. Ni3S2 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 Ni3S2 and MWCNTs was increased with decreasing the loading amount of Ni3S2 on MWCNTs and the optimal Ni3S2 loading on MWCNTs was 55 wt%. Furthermore, the immersion of the composite catalyst in a concentrated KOH solution induced the morphological change of the Ni3S2 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 Ni3S2 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 Ni3S2 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 Ni3S2 electrode. The high catalytic activity of the KOH-treated composite electrode was stemmed from the synergistic effect of the large active surface area of Ni3S2 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 Ni3S2 and MWCNTs was proposed for the first time as an enzyme-free sensor for glucose. The Ni3S2 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 Ni3S2 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.

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