N-doped carbon encapsulated nickel nanoparticles: rational fabrication and ultra-high performance for ethanol oxidation

N-doped carbon encapsulated nickel nanoparticles (NiNC) are prepared from mixtures of nickel salt, glucose and urea by a simple heating protocol. A higher viscosity of the mixture inhibits the migration of Ni species such that highly dispersed and very small Ni nanoparticles form during heat treatment. The sizes of the Ni nanoparticles can be controlled by adjusting the composition of the raw mixtures. The optimized sample of NiNC-4 contains Ni nanoparticles of 2.02 nm in size which afford a large metal surface area of 400.7 m(2) g (1) and a high nitrogen content of 7.21 at%. An ultra-high current density of 327 mA cm (2) is achieved in 0.1 M NaOH electrolyte containing 1 M ethanol using NiNC-4 as the electrocatalyst. NiNC-4 electrodes also exhibit a good long-term cycling stability. After 500 cycles, 89% of the initial current density is sustained in 0.1 M NaOH electrolyte containing 0.5 M ethanol. 96.8% of the initial current density is retained by moving the NiNC-4 electrode into fresh 0.1 M NaOH solution with 0.5 M ethanol after 500 cycles. The excellent electrocatalytic properties of NiNC-4 for ethanol oxidation stem from the synergistic effect of the porous carbon substrate, abundant N-containing groups and the small nickel nanoparticle size. (C) 2017 Elsevier Ltd. All rights reserved.