Porous monolithic carbon-nanocomposite electrodes based on carbonized wood/ MOF as a free-standing cathode for sediment microbial fuel cells

Carbon materials bearing advantages such as chemical and thermal stability, electrical conductivity, high specific surface area, and high porosity are widely used in electrode materials. Although the utilization of wood-based carbon materials in electrochemical energy storage devices has good capacitive behavior and it increases charge storage, wood does not show sufficient electrical conductivity due to the inadequate electrical conductivity as a carbon electrode. In order to boost its performance, composites of carbon materials have been synthesized with other conductive materials. In this study, the physicochemical and electrochemical properties of nanocomposite electrodes based on carbonized wood/ Mn-MOF, prepared by the in-situ synthesis method, were assessed. Furthermore, the Performance of these electrodes as the cathode in sediment microbial fuel cells was investigated. Its performance was compared with control wood-based and commercial carbon felt electrodes, too. The sapwood blocks of Platanus orientalis as lignocellulosic precursor were pyrolyzed at a temperature of 700 °C and a heating rate of 5 °C min-1 in the argon atmosphere with a constant flow of 100 mLmin-1 and a retention time of 1 h. After pyrolysis, the carbonized wood samples were washed with distilled water and dried in an oven. Then, to synthesize composite electrodes of CW/ Mn-MOF, manganese (II) acetate tetrahydrate, and 1,3,5-benzene tricarboxylic acid ligand were used. Finally, the samples were washed with ethanol and dried in the oven. Secondary pyrolysis was performed at 900 °C for 2 h in an argon atmosphere and a heating rate of 5 °C min-1. The results of this study showed that after wood pyrolysis, morphologically, the porous structure and its connected and direct channels were preserved. In addition, in-situ synthesis of Mn-MOF on carbonized wood was successfully performed. According to Raman spectra, the increase in the degree of disordering in the structure of prepared nanocomposite electrodes compared to control carbonized woods was observed. Furthermore, XRD patterns indicate the presence of amorphous and graphitic carbon in graphitic crystals of carbon. In addition, carbon electrodes doped with Mn-MOF showed the lowest impedance and the highest maximum power density compared to control and carbon felt electrodes. According to the results, high-temperature carbonization causes graphitization of wood material and yields electrical conductivity. Doping of carbon electrodes and fabrication of carbon-nanocomposite electrodes based on carbonized wood/ Mn-MOF promoted the electrochemical performance of the cathode in sediment microbial fuel cells. The synergistic effect between the pseudocapacitive behavior of Mn-MOF and the electrical double-layer capacitance behavior of carbon material improved the performance of the whole SMFC setup.