Self-supporting graphitized palm-branch anodes for enhanced electricity generation from sewage wastewater in membrane-less microbial fuel cells

Abstract

A simple strategy was developed to fabricate self-supporting bioanodes from graphitized palm-tree-branch powder for application in membrane-less microbial fuel cells (MFCs). Palm tree branches were graphitized at 900°C, 1000°C and 1100°C, ground into fine powder, blended with bitumen and starch, compression-moulded and thermally treated to produce robust anodes. The resulting electrodes were evaluated in an air-cathode, single-chamber MFC using raw sewage wastewater without external microbial inoculation or nutrient addition. Structural and electrochemical analyses showed that the prepared anodes possessed rough porous surfaces, stable carbon-dominated electrochemical behaviour and improved conductivity compared with an activated-carbon-based anode. Among the investigated samples, the anode prepared from palm branches graphitized at 1000°C exhibited the best overall performance. In sewage containing 5g l−1 sodium acetate, this anode delivered a maximum power density of about 1300 mW m−2, which was nearly 25 times higher than that of the activated-carbon-based anode (approx. 52 mW m−2). Even under electrolyte-free conditions, the same anode generated a maximum power density of about 400 mW m−2, indicating that intrinsically retained inorganic species, particularly KCl, may contribute to sustaining MFC operation without external electrolyte addition. In contrast, NaCl showed a much weaker promoting effect than sodium acetate. Electrochemical impedance spectroscopy confirmed relatively low ohmic and charge-transfer resistances under the optimum condition.