The effect of chloride ion complexation on reversibility and redox potential of the Cu(II)/Cu(I) couple for use in redox flow batteries

► Complexation with chlorides improves the chemical stability of soluble Cu(I) species. ► Reversibility of the Cu(II)/Cu(I) couple is improved in concentrated chloride media. ► The observed potential of Cu(II)/Cu(I) couple allows its use as catholyte for RFB.