Acid-engineered carbon electrodes for microbial electrochemical energy systems: Mapping synergies and trade-offs via comprehensive abiotic analysis

In this study, three widely used carbon electrodes in bioelectrochemical systems, carbon cloth (CC), carbon felt (CF), and carbon paper (CP) were treated with HNO 3 , HCl, and H 2 SO 4 at various molar ratios (0.5–2 M) to investigate their electrochemical characteristics under abiotic conditions. The results demonstrate that the electrochemical response, including integrated voltammetric area (IVA), maximum currents, electrode resistance, electrochemical accessible surface area (ECSA), and specific capacitance (SC), is remarkably variable and highly dependent on electrode-specific features such as porosity, toughness, and morphology. Findings indicate that the performance of CC is primarily dictated by the type of acid rather than molarity, whereas CP consistently achieves optimal results at the highest molar ratio (2 M). Conversely, CF exhibits superior electrochemical performance at lower acid molarities (0.5 M). Notably, improvements in electrode resistance and ECSA were not always correlated with gains in IVA and maximum currents. Finally, to better understand the complex behaviour of electrodes under different treatment strategies, a capacitive-voltammetric divergence plot to highlight the synergies and trade-offs based on the type of electrodes, acids, and molar ratios was mapped to illustrate the interactions of these parameters in a broader context toward rational treatment of carbon electrodes.