Synthesis of nickel-based layered double hydroxide (LDH) and their adsorption on carbon felt fibres: application as low cost cathode catalyst in microbial fuel cell (MFC)

Abstract

Following their successful utilization as novel bioanodes in Microbial Fuel Cells (MFCs), Layered Double Hydroxide (LDH) were tested in the present investigation, as promising cathodes to reduce electrons coming from oxidation of organic matter in the anode compartment, in the presence of oxygen used as successful oxidant. Therefore, the LDH samples Ni₃Al-LDH with the ionic ratio Ni²⁺/Al³⁺ equal to 3, were synthesized and added by adsorption to Carbon Felt (CF) fibres. They were then stored separately in three electrolyte solutions KCl, NiCl₂ and AlCl₃ used as catholytes in the MFCs. Effects of the active cationic sites located inside the Ni₃Al-LDH on these electrolytes, were discussed in terms of energies produced by these MFCs. The structure and morphology of the synthesized LDH, were studied by using the analytical techniques XRD, FTIRS and SEM, while the electrode performances of the LDH-electrodes were investigated with the electrochemical methods CV and EIS. It was revealed that the CF modified with Ni₃Al-LDH cathode and conditioned in the NiCl₂ electrolyte solution yielded the highest energy harvesting for the MFC (i.e. 3.2 µW/cm²). This power density output was similar to previous clean one-compartment MFC. However, it was less expensive than an Enzymatic Fuel Cell (45 µW/cm²), making in evidence the highest cost of the material. Thus, by taking into account these encouraging findings, the low cost materials used in MFCs held great promise for practical application in electrochemical power devices and therefore fruit waste treatment. Abbreviations: ACFC: Air Cathode Fuel Cell; ADEFC: Alkaline Direct Ethanol Fuel Cell; AFC: Alcaline Fuel Cell; BET: Brunauer-Emmett-Teller; BFC: Biological Fuel Cell; CF: Carbon Felt; CV: Cyclic Voltammetry; DGFC: Direct Glucose Fuel Cell; DMFC: Direct Methanol Fuel Cell; EFC: Enzymatic Fuel Cell; EIS: Electrochemical Impedance Spectroscopy; FC: Fuel Cell; FTIR: Fourier Transform Infra Red spectroscopy; LDH: Layered Double Hydroxide; MEC: Microbial Electrolysis Cell; MFC: Microbial Fuel Cell; Mg-Al- ${\mathrm{CO}}_3^2$ -LDH: Layered Double Hydroxide Magnesium-Aluminium-Carbonate; Ni-Al-LDH: Layered Double Hydroxide Nickel-Aluminium; OCP: Open Circuit Potential; SEM: Scanning Electron Microscope; TG/DTA: ThermoGravimetric and Differential Thermal Analysis; XRD: X-Ray Diffraction.

Keywords: Nickel-Aluminium layered double hydroxide synthesis; carbon cathode catalyst; fruit waste treatment; low cost energy; microbial fuel cell.