Surface fluorinated nickel-graphene nanocomposites for high-efficiency methanol electrooxidation

Abstract

Transition metal electrocatalysts with high activity and long durability are desired for methanol oxidation reaction (MOR). Here, the surface fluorinated nickel-graphene nanocomposites (F–Ni–G) are synthesized via the reduction of Si–H bonds produced by silicon and ammonium fluoride in hydrothermal condition. During this process, ionic nickel-F bonds and semi-ionic C–F bonds are introduced to the catalysts as confirmed by X-ray photoelectron spectroscopy. When F–Ni–G nanocomposites are employed as MOR catalysts, the surface fluorination is contributed to the formation of nickelic, which can increase the activity and kinetics for MOR. The onset oxidation potential of F–Ni–G-2 for methanol oxidation is 53 mV lower than that of the Ni/G catalyst without fluorine. The mass activity of F–Ni–G-2 (2493.3 A g−1) is 3.90 folds than that of Ni/G (638.5 A g−1). In addition, the density functional theory calculation indicates that the modified fluorine in graphene results in the decreased reaction energy barrier from ∗CO to ∗COOH step in MOR. The strong electronegativity of F atom makes intermediates easier to attract OH− groups and repel protons, which is conductive to decrease the reaction energy barrier for MOR. Such a facile method for the fabrication of the surface fluorinated catalytic system may be extended to the preparation of other transition metal electrocatalysts.