Aqueous electrolytes comprising fluorenone/fluorenol derivatives are disclosed. The electrolyte may be an anolyte for an aqueous redox flow battery. In some embodiments, the compound, or salt thereof, has a structure according to any one of formulas I-III where Q1-Q4 independently are CH, C(R1) or N, wherein 0, 1, or 2 of Q1-Q4 are N; Q5-Q8 independently are CH, C(R2), or N, wherein 0, 1, or 2 of Q5-Q8 are N; Y is C═O or C(H)OH; R1 and R2 independently are an electron withdrawing group; n is an integer >1; and x and y independently are 0, 1, 2, 3, or 4, where at least one of x and y is not 0.