Enhancing electricity generation and CO2 fixation in photosynthetic algal microbial fuel cells via bioelectrochemical coupling of cathode modification and electron-acceptor regulation.

The sluggish cathode oxygen reduction reaction (ORR) kinetics and insufficient supply of electron acceptors are the critical bottlenecks limiting the power generation performance of microbial fuel cells (MFCs), particularly photosynthetic algal microbial fuel cells (PAMFCs). This study constructed a cathode optimization strategy integration of polypyrrole (PPy) modification and electron acceptor regulation, aiming to elucidate the working mechanism of bioelectrochemical coupling in biocathodes. The performance of PPy-modified carbon felt cathodes was systematically investigated in both conventional MFC and PAMFC systems, and the cathode electron acceptor supply levels were modulated via the dosage of ammonium chloride (NH4Cl) and sodium nitrate (NaNO3). The results indicated that an optimal PPy loading effectively enhanced electrode conductivity and upgraded ORR activity. Notably, the optimal PPy loading in the PAMFC shifted compared to that in the conventional MFC. This shift demonstrated that the performance of the algal biocathode is not dictated solely by the electrocatalytic activity of the electrode, but is co-regulated by the dynamic matching between biological oxygen evolution and electrochemical oxygen consumption. Further evaluation of electron acceptor supplementation revealed that NaNO3 exerted a more pronounced promotion effect than NH4Cl, with a maximum power density of 422.5 mW/m2 achieved at 2.0 g/L NaNO3. This enhancement was attributed not only to the provision of auxiliary electron acceptors but also to the stimulation of algal nitrogen metabolism, which bolstered photosynthetic oxygen evolution and effectively mitigated the oxygen consumption pressure imposed by the biocathode reaction. The bioelectrochemical coupling developed in this study enhances PAMFC power generation and carbon sequestration potential.