Magnetite/zeolite nanocomposite-modified cathode for enhancing methane generation in microbial electrochemical systems

Abstract

• Magnetite/zeolite (MZ) was synthesized as novel cathode catalyst in MES. • Electrochemical analyses proved superior catalytic activity of MZ for methanation. • Current generation, substrate and VFAs removal rate were promoted in MES-MZ. • MZ catalyst facilitated electron transfer by lowering cathode overpotential losses. In this study, magnetite/zeolite (MZ) was successfully synthesized to use as a feasible and cost-effective cathode catalyst for enhancing methane generation in a microbial electrochemical system (MES). The novel MZ catalyst consists of hydrophilic zeolite cores and conductive magnetite nanoparticles for enhanced electroactive biofilm development on the cathode by facilitating micro-channels for nutrient diffusion, increased surface area, and reduced charge transfer resistance. The MES using an MZ cathode (MES-MZ) achieved a maximum methane yield of 0.38 ± 0.010 LCH 4 /gCOD, which was significantly higher than that of the control operation without a catalyst (0.33 ± 0.008 LCH 4 /gCOD). The methane production rate was increased by almost 21% from 196 mL/(L.d) in the control MES to 238 mL/(L.d) in the MES-MZ, along with an improvement in the methane percentage from 73% to 79%. In addition, the maximum current generation was recorded using the MES-MZ at 9.29 ± 0.16 mA, which was about 16% higher than that of 8.0 ± 0.13 mA observed in the control reactor and is consistent with about a 36.2% improvement of the Coulombic efficiency. The CV and EIS analyses revealed that MZ lowered the overpotential losses during the electron transfer process, and revealed a more positive cathode potential with the MES-MZ (−0.48 V vs. Ag/AgCl), which possibly suggests direct electron transfer for the dominant pathway for the conversion of carbon dioxide to methane.