Simultaneous bioelectricity generation and selective copper recovery via controlled two-step discharge strategy in a two-chamber microbial fuel cell using an unbuffered copper catholyte

• Cu(II) was removed via cathodic reduction in a two-chamber microbial fuel cell. • Discharge profiles revealed a two-step pathway: Cu(II) → Cu 2 O and Cu 2 O → Cu(0). • The unbuffered catholyte pH increased from 4.8 to 8.0 during operation. • Cu(II) removal reached up to 99% with a peak power density of 549 mW/m 2 . • Cathode deposits contained both Cu(0) and Cu 2 O. Microbial fuel cells (MFCs) are bioelectrochemical systems that generate electricity through the microbial oxidation of organic substrates and offer potential for concurrent pollutant remediation. The anode potentials associated with common substrates are typically near − 0.3 V (vs. standard hydrogen electrode (SHE) at pH 7.0), making electricity generation feasible when paired with a cathodic reaction exhibiting a sufficiently positive potential. In this study, we developed two-chamber MFCs that simultaneously generate electricity and remove dissolved cupric ion (Cu(II)) from unbuffered copper catholyte. At an initial Cu(II) concentration of 10.0 mM, the system achieved 99.0% dissolved Cu(II) removal, and the cathodic coulombic efficiency (cathodic CE) reached 85.0%. Conversely, lower initial Cu(II) concentrations (5.0 and 2.5 mM) resulted in lower cathodic CEs (57.7% and 69.6%, respectively), which is consistent with a less-developed secondary discharge stage. The open-circuit voltage was ∼ 640.0 mV, and the maximum power density reached 553.1 mW/m 2 when 10 mM Cu(II) catholyte was used. During operation, the catholyte pH increased from 4.8 to 8.0, indicating dissolved Cu(II) removal. Scannig electron microscope (SEM)/energy Dispersive X-ray Spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses revealed the presence of deposits containing both Cu(0) and Cu 2 O, supporting a two-step reduction process wherein Cu 2 O forms during the primary discharge stage and is further reduced to Cu(0) during the secondary stage.