A Hybrid Mineral Battery: Energy Storage and Dissolution Behavior of CuFeS 2 in a Fixed Bed Flow Cell.

The development of a hybrid system capable of storing energy and the additional benefit of Cu extraction is discussed in this work. A fixed bed flow cell (FBFC) was used in which a composite negative electrode containing CuFeS2 (80 wt %) and carbon black (20 wt %) in graphite felt was separated from a positive (graphite felt) electrode by a proton-exchange membrane. The anolyte (0.2 m H2 SO4 ) and catholyte (0.5 m Fe2+ in 0.2 m H2 SO4 with or without 0.1 m Cu2+ ) were circulated in the cell. The electrochemical activity of the Fe2+ /Fe3+ redox couple over graphite felt significantly improved after the addition of Cu2+ in the catholyte. Ultimately, in the CuFeS2 ∥Fe2+ /Cu2+ (CFeCu) FBFC system, the specific capacity increased continuously to 26.4 mAh g-1 in 500 galvanostatic charge-discharge (GCD) cycles, compared to the CuFeS2 ∥Fe2+ (CFe) system (13.9 mAh g-1 ). Interestingly, the specific discharge energy gradually increased to 3.6 Wh kg-1 in 500 GCD cycles for the CFeCu system compared to 3.29 Wh kg-1 for the CFe system in 150 cycles. In addition to energy storage, 10.75 % Cu was also extracted from the mineral, which is an important feature of the CFeCu system as it would allow Cu extraction and recovery through hydrometallurgical methods.