Optimal stimulation of Houttuynia cordata herbal extract as electron shuttle for bioenergy extraction in microbial fuel cells.

• Τen herbal extracts were subjected to cyclic voltammetry for 100 times. • The Houttuynia cordata extract (HCE) possessed the highest CV area. • The supplement of HCE in MFC was found to have a PD value of 33.70 mW/m². • Τhe CV areas were positively correlated to the PD ratios in the MFC tests. This first-attempt study revealed electrochemically promising strategy to provide optimal herbal species of supplementation as electron shuttling stimulator to microbial fuel cells (MFCs). First, cyclic voltammetry (CV) was used to screen the feasible electron shuttle (ES) materials after serial testing of 100 cycles. The results indicated that Houttuynia cordata extract (HCE) possessed the highest CV area of closed-loop profile (i.e., the most appropriate ES). Alternanthera paronychioides exhibited a symmetrical peak in the oxidation and reduction profiles. All of the herb extracts were subjected to the Shewanella sp. WLP72-inoculated double-chamber MFC to compare their power density (PD) ratios. The optimal supplement of HCE in MFC was found to have a PD value of 33.70 mW/m², which was 2.67-fold higher than the blank control. It indicated that HCE could express the highest electrochemical characteristics as a potential ES. In addition, the CV areas were positively correlated to the PD ratios in the MFC tests. However, there were no correlations between CV areas to their total polyphenol contents (TPCs) and 2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity. This study showed that HCE contains polyphenolic compounds (e.g., kaempferol, chlorogenic acid, and quercitrin), indicating that HCE possesses highly promising ES characteristics for bioenergy extraction. [ABSTRACT FROM AUTHOR]