Electrodepositing Polyvinyl Ferrocene Films to Enhance Oxyanion Recovery and Electrode Longevity

Rhenium, a critical high-value mineral, naturally occurs as perrhenate (ReO4–) and is difficult to separate from competing anions. Polyvinyl ferrocene (PVF) coated electrodes have exhibited selective adsorption of transition metal oxyanions, but performance degradation with cycling is poorly understood. This study examines the impact of two PVF film fabrication strategies (electrodeposition (ED) and dip-coating (DC)) on (i) rhenium uptake capacity and selectivity, (ii) electrode regeneration and performance longevity, and (iii) lifecycle cost of Re recovery. Electrodeposited PVF films exhibited nearly twice the rhenium uptake (351 ± 82.1 mg Re/g coating) of dip-coating PVF films (158 ± 32.7 mg Re/g coating). Additionally, after 15,000 charge/discharge cycles, Re uptake remained 69.1 ± 11.3% for ED but only 28.0 ± 12.3% for DC films, indicating improved PVF attachment to carbon scaffolds. Operational conditions significantly affected rhenium release after adsorption, with regeneration of 82.6 ± 9.4% at −0.8 V vs Ag/AgCl compared to 30.78 ± 6.2% at 0 V vs Ag/AgCl, due to reduction of both Fe and Re which promoted electrode regeneration at −0.8 V vs Ag/AgCl. A preliminary technoeconomic analysis indicates the high selectivity and longevity of PVF-ED electrodes could facilitate Re recovery at ∼5% of the current market price.