Natural solar intermittent-powered electromethanogenesis towards green carbon reduction.

[Display omitted] • Solar intermittent-powered electromethanogenesis achieved efficient CO 2 reduction. • Higher bicarbonate loading promoted the redox activity of electrode biofilms. • Increased HCO 3 − facilitated electron transfer and lowered charge transfer resistance. • More functional mcrA genes were upregulated with elevated bicarbonates. • Basophilic Methanobacterium alcaliphilum occupied predominated at the biocathode. Microbial electromethanogenesis (EM), as a sustainable bioderived carbon-neutrality catalyzing platform, can be accelerated and regulated by weak power input for carbon fixation into value-added bioenergy. Solar electricity as a day-night intermittent renewable resource has been verified to effectively drive microbes to capture carbon dioxide (CO 2). However, understanding the influence mechanisms of higher CO 2 loading on EM is of intrinsic significance yet lacking. Herein, natural solar-powered bioelectrocatalytic CO 2 reduction to methane (CH 4) under increasing bicarbonate concentrations was investigated. CH 4 recovery for the long-term measurement showed that CH 4 production rate positively responded to improved bicarbonate concentrations from 2.5 to 10.0 g HCO 3 −·L−1, exhibiting a robust and potent competence in CH 4 yield compared to reported EM. Whereas exceed bicarbonate mainly contributed to raised pH in the solution resulting in the proton limitation despite the intermittent driven-mode could mitigate pH shock. Electrochemistry results demonstrated that higher bicarbonate concentrations promoted the redox activity of electrode biofilm and lowered the system resistances, especially the charge transfer resistance. Adequately improving CO 2 loading can dynamically optimize the structure of anodic electroactive microorganisms and facilitate electron transfer. Furthermore, more functional cathodic mcrA genes were upregulated with elevated bicarbonates and the species of basophilic Methanobacterium alcaliphilum occupied predominated at the cathode. These findings open up a perspective avenue to carbon reduction using natural solar intermittent-powered EM. [ABSTRACT FROM AUTHOR]