Natural solar intermittent-powered electromethanogenesis towards green carbon reduction

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 directly drive microbes to capture CO₂. However, understanding the influence mechanisms of higher CO₂ loading on EM is of intrinsic significance yet lacking. Herein, natural solar-powered bioelectrocatalytic CO₂ reduction to CH₄ under increasing bicarbonate concentrations was investigated. CH₄ recovery for the long-term measurement showed that CH₄ production rate positively responded to improved bicarbonate concentrations from 2.5 to 10 g HCO₃^-·L^-1, exhibiting a robust and potent competence in CH₄ 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 CO₂ 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.