Preparation of Bimetallic Conductive Metal-organic Framework Material Ni/Co-CAT for Electrocatalytic Oxygen Reduction

Abstract

Ni-catecholate and Ni-Co-catecholate (hereafter referred to as Ni-CAT and Ni-Co-CAT) were prepared by hydrothermal method using 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) as the organic ligand and Ni and Co as the metal centers, respectively. After characterization, a microbial fuel cell (MFC) was constructed in a single chamber reactor device. Single chamber air cathode microbial fuel cell reactors offer the advantages of both small reactor size and no aeration. Ni-CAT and Ni-Co-CAT were mixed with carbon black in a 3∶1 mass ratio and applied to the cathode of MFC to catalyze the oxygen reduction reaction (ORR). The experiments included the preparation of M-CAT (M＝Co or Ni), the preparation of air cathode and the assembly and operation of MFC. When preparing the catalytic layer of the air cathode, the conductive MOF and carbon black were mixed in a 3∶1 mass ratio to improve the catalytic effect. Furthermore, the air cathode was mixed with dispersant (isopropanol) and polytetrafluoroethylene (PTFE) to make it waterproof and breathable. The results showed that the MFC reactor catalyzed by Ni-Co-CAT had the best performance. This is due to the fact that bimetallic MOFs have stronger oxygen reduction activity compared to their monometallic counterparts. The MFC reactor catalyzed by Ni-Co-CAT had a maximum output voltage and power density of 310 mV and 190 mW/cm2, respectively, which were comparable to the performance of commercial Pt/C. The limiting current density of the MFC reactor catalyzed by Ni-Co-CAT was 2.84 mA/cm2, which was better than that of Ni-CAT (2.18 mA/cm2), indicating that the MFC power production efficiency was enhanced by the introduction of Co in the Ni-CAT structure. The main reason is that Ni-Co-CAT has a higher porosity and specific surface area when fully mixed with carbon black, and the metal sites M-O6 (M＝Ni or Co) on its structure provide more catalytic activity, which gives Ni-Co-CAT an optimal electrochemical catalytic performance.