Comparison of NiCo2O4, CoNiAl-LDH, and CoNiAl-LDH@NiCo2O4 performances as ORR catalysts in MFC cathode

Abstract In this study, the performances of NiCo2O4, CoNiAl-LDH, and CoNiAl-LDH@NiCo2O4 were investigated as the catalysts of cathodic reaction in an MFC, for the first time. The synthesized catalysts were characterized by FESEM, XRD, EDX, and DLS techniques. The electrophoretic deposition method was used to immobilize the catalysts on the graphite electrode. The modified electrodes were applied as the cathode of an MFC to compare their output voltage and maximum power density. CoNiAl-LDH electrode had the highest maximum voltage (411.6 mV) and power density (87.91 mW m−2). CoNiAl-LDH@NiCo2O4-modified electrode showed similar results for maximum voltage (405.6 mV) and power density (85.28 mW m−2), however, it had a stable period of maximum voltage equal to 93.66 h. Cyclic Voltammetry results showed that CoNiAl-LDH@NiCo2O4-modified graphite was more electroactive than the others as it produced the highest current density of the redox peaks. Nyquist plots were used to find the equivalent circuit. They showed that the charge transfer and the diffusion resistances of all the modified electrodes significantly decreased compared with the bare graphite.