Controlled engineering of nickel carbide induced N-enriched carbon nanotubes for hydrogen and oxygen evolution reactions in wide pH range

The design of cost-effective and competent electrochemical water splitting module that is functional in a wide pH range is still a formidable challenge for viable H₂ production. Herein, we report control synthesis of Ni/Ni₃C nanoparticles (NPs) induced engineering of the nitrogen-enriched carbon-nanotubes (NCNT) of three different sizes/morphologies by the pyrolysis of melamine with Ni(NO₃)·6H₂O at various stoichiometric ratios (0.5-wt%, 2-wt% and 4-wt% of Ni). The catalytic potential and structural integrity of the in-situ self-assembled hybrid material was explored and found very effective to catalyse both OER and HER in a broad pH range (0-14). Promisingly, the nanostructuring of the Ni/Ni₃C NPs and subsequently the diameter of the NCNT hold the catalytic potential, where 0.5-Ni/Ni₃C@NCNT (average size ≈ 15–20 nm) showed remarkable activity for OER (ƞ_{10-base/acid/neutral} = 280/400/600 mV, Tafel slope_base = 42 mV/dec) and HER (ƞ_{10-acid/base/neutral} = 210/290/370 mV, Tafel slope_acid = 40 mV/dec). It is anticipated, that favourable electronic modulation of Ni/Ni₃C, structural strain of NCNT, and possible concerted synergistic effect of the hybrid/doped nanocarbons with metal-carbide hold a great potential in this regard, and such modular strategies tailoring the structural-performance relationship may provide the guidance towards the designing of commercially viable electrocatalysts in this regard.