A Hybrid Mineral Battery: Energy Storage and Dissolution Behavior of CuFeS₂ 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.