Performance improvement strategies of a cobalt-based electrode for the electrooxidation of sodium borohydride

Abstract

Herein, cobalt (Co) nanoplates were firstly grown on nickel foam (NF) via a simple electrodeposition method. Subsequently, the component and structure of Co on NF were regulated and controlled through chemical etching using oxalic acid (H₂C₂O₄), and finally the surface of the obtained material was reduced using sodium borohydride (NaBH₄) to form an electrode (Co/NF-CoC₂O₄-Co) containing various Co-based composites (e.g., Co, CoC₂O₄, and Co oxides) with a three-dimensional (3D) porous nanoflower structure. The special structure of Co/NF-CoC₂O₄-Co provided abundant catalytically active sites during the electrochemical reaction and the synergistic effect of the various components in the electrode further improved its electrocatalytic performance. Besides, the metallic Co in the electrode provided fast electron transfer paths. The oxidation current density of Co/NF-CoC₂O₄-Co reached 315.85 mA cm⁻² at −0.58 V in 1.0 mol dm⁻³ NaOH and 0.1 mol dm⁻³ NaBH₄, which are much higher than that of Co/NF (59.96 mA cm⁻²) and Co/NF-CoC₂O₄ (264.55 mA cm⁻²). It is worth noting that Co/NF-CoC₂O₄-Co was further applied in a cylindrical rotating bed (CRB) to weaken the bubble effect and enhance the mass transfer during the electrooxidation of NaBH₄. The results demonstrated that the device exhibited a significantly improved electrochemical performance, which was 2.7 (electrode rotational speed of 112 rpm) and 3.9 (solution circulating flow rate of 400 mL min⁻¹) times that of the traditional stationary state, respectively.