Scalable, Eco-Friendly Fabrication and Physical Characterization of a Sodium-Rich Prussian Blue Cathode for Aqueous Sodium-Ion Batteries

A water-based synthesis and electrode fabrication protocol for sodium-rich Prussian blue (Na–PB) cathodes designed for sustainable aqueous sodium-ion batteries was adopted. Using a citric-acid-assisted co-precipitation method followed by aqueous Na⁺ ion exchange, the process consistently yielded 3.113 g of high-quality Na–PB per 400 mL batch under mild conditions (<80 °C). Electrodes were fabricated via doctor-blade coating onto aluminium foil using a biodegradable carboxymethyl cellulose (CMC) binder and conductive additive, completely eliminating toxic organic solvents. X-ray diffraction confirmed a highly crystalline cubic (slightly rhombohedral-distorted) phase with low [Fe(CN)₆] vacancy content (<10%), while scanning electron microscopy revealed uniform cubic particles ranging from 200 to 800 nm. Brunauer–Emmett–Teller analysis indicated moderate specific surface areas (12–18 m² g⁻¹) with mesoporous characteristics. The results demonstrate that structurally optimized Na–PB cathodes can be produced through an environmentally benign and scalable approach, and future work should incorporate electrochemical performance evaluation and long-term cycling studies to support practical battery applications.