Co-precipitation synthesis control for sodium ion adsorption capacity and cycle life of copper hexacyanoferrate electrodes in battery electrode deionization

Prussian blue analogues are being explored as electrode materials for electrochemical desalination of saline water in battery-type deionization systems and hybrid capacitive due to their open framework crystal structure that provides selective adsorption multiple cations, high theoretical sodium capacities, low costs. However, poor electronic conductivity instability (dissolution) prevents the use these long-term applications. To understand how synthesis conditions might improve properties copper hexacyanoferrate (CuHCF) powders relative ion capacity cycle life, co-precipitation process was investigated using common strategies included addition chelators salts well different concentrations oxidation states precursors. Smaller crystallite sizes (<35 nm) lower structural contents increased initial removal 53.2 mAh/g from 40.4 (control), but also reduced cycling stability operation (20–55% retention over 100 cycles). The trade-off is thought be a consequence facilitating diffusion within material. Adding precursors led highly reversible CuII/CuI redox couple FeIII/FeII BDI performance (79.4%