3D flower-like CoNi2S4/polyaniline with high performance for glycerol electrooxidation in an alkaline medium

Abstract

Herein, a 3D flower-like CoNi₂S₄ and leaf-like polyaniline (CoNi₂S₄/PANI) hybrid was designed and prepared using a hydrothermal method and physical grinding method for the electrocatalytic oxidation of glycerol. The as-prepared materials were first screened and optimized, and then, a series of characterizations and electrochemical measurements of modified electrodes towards glycerol were performed. The characterization results showed that the 3D flower-like CoNi₂S₄ displayed distinct mesoporous structures and large specific surface area. Moreover, based on the X-ray photoelectron spectroscopy results, its nickel and cobalt species mainly contain Ni²⁺ and Ni³⁺ and Co²⁺ and Co³⁺, respectively. When the mass ratio of CoNi₂S₄ : PANI was 1 : 1, the material exhibited highest catalytic activity towards the oxidation of glycerol in 1.0 mol L⁻¹ NaOH containing a 1.0 mol L⁻¹ C₃H₈O₃ solution. The electrochemical impedance spectroscopy test shows that the CoNi₂S₄/PANI (1 : 1) composite presents lower R_ct value and larger slope value, indicating that the composite has excellent electrochemical activity. The lower Tafel slope for the CoNi₂S₄/PANI (1 : 1) composite most likely indicates the increased glycerol oxidation; chronoamperometry has proved that the CoNi₂S₄/PANI (1 : 1) composite possesses higher stability and better poison resistance as compared to commercial Pt/C (20 wt%); the possible mechanism for the enhanced performance of CoNi₂S₄/PANI (1 : 1) is attributed to its unique structure with larger specific area, including 3D flower-like CoNi₂S₄, highly conductive PANI with a leaf shape, and a stable 3D architecture of CoNi₂S₄/PANI. This pioneering study should be conducive to improving the electro-oxidation of glycerol in the field of direct alcohol fuel cells.