Charge storage capacity of electromethanogenic biocathodes

Methanogenic biocathodes (MB) can convert CO2 and electricity into methane. This feature, that allows them to potentially be used for long-term electrical energy storage, has aroused great interest during the past 10 years. MB can also operate as biological supercapacitors, a characteristic that can be exploited for short-term energy storage and that has received much less attention. In this study, we investigate the electrical charge storage capabilities of carbon-felt-based MB modified with graphene oxide. The charge-discharge experiments revealed that the potential of the electrode plays an important role during the discharging period: low potentials (-1.2 V vs Ag/AgCl) created an inrush of faradaic current that masked any capacitive current. At more positive potentials (-0.8 V vs Ag/AgCl), the biological electrodes were outperformed by the abiotic electrodes, and only when the potential was set at -1.0 V vs Ag/AgCl the graphene-modified biological electrode showed its superior charge storage capacity. Overall, results indicated that the graphene modification is crucial to obtain bioelectrodes with improved capacitance: untreated bioelectrodes showed a charge storage capacity inferior to that measured in the abiotic electrodes.

Automated summary

Methanogenic biocathodes have the potential to convert CO2 and electricity into methane, making them suitable for long-term electrical energy storage. They can also function as biological supercapacitors for short-term energy storage, although this aspect has received less attention. In this study, carbon-felt-based MB modified with graphene oxide were investigated for their electrical charge storage capabilities. Results showed that the potential of the electrode during discharging plays a significant role in determining the charge storage capacity.