A Hybrid Mineral Battery: Energy Storage and Dissolution Behavior of CuFeS 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 CuFeS (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 H SO ) and catholyte (0.5 m Fe in 0.2 m H SO with or without 0.1 m Cu ) were circulated in the cell. The electrochemical activity of the Fe /Fe redox couple over graphite felt significantly improved after the addition of Cu in the catholyte. Ultimately, in the CuFeS ∥Fe /Cu (CFeCu) FBFC system, the specific capacity increased continuously to 26.4 mAh g in 500 galvanostatic charge-discharge (GCD) cycles, compared to the CuFeS ∥Fe (CFe) system (13.9 mAh g ). Interestingly, the specific discharge energy gradually increased to 3.6 Wh kg in 500 GCD cycles for the CFeCu system compared to 3.29 Wh kg 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.