An Aqueous Electrochemical System Based on Prussian Blue, Wheat-Grain-Derived Biochar, and MnO2 and FeS2 Additives

This study investigates a model aqueous electrochemical system based on Prussian blue, wheat-grain-derived biochar, and MnO2 or FeS2 additives. A sodium alginate/Na2SO4 aqueous matrix was used, and the effects of glycerol and halloysite as system modifiers were evaluated. The electrochemical behavior was investigated using galvanostatic charge–discharge measurements, cyclic voltammetry, polarization curves, electrochemical impedance spectroscopy, and FT-IR spectroscopy. Among the investigated formulations, the FeS2-containing system without glycerol or halloysite exhibited the highest measured discharge capacity, reaching approximately 0.157 mAh, compared with approximately 0.081 mAh for the corresponding MnO2 system, representing an approximately 94% higher maximum discharge capacity under the investigated conditions. The FeS2 system retained approximately 0.148 mAh after 21 cycles. However, the mean Coulombic efficiencies of all investigated formulations remained below 10%, indicating substantial irreversible and/or parasitic electrochemical processes. Glycerol-containing formulations exhibited increased charging voltage, reduced electrochemical response, and pronounced capacity loss. Halloysite was associated with a more stable charging voltage profile in the FeS2 system but also with reduced discharge capacity and increased low-frequency impedance. Wheat-grain-derived biochar was successfully incorporated as a carbonaceous component of the composite anode. The present study should therefore be regarded as a laboratory-scale proof of concept, and further work is required to establish reversible energy-storage performance, optimize electrode composition and electrolyte formulation, and evaluate long-term cycling stability.