Fig. 2: Reduced bispyridinium compounds, their performance characteristics and dimerization propensity.

a, Radical concentration profiles for 10, 11 and 13 during charge derived from spin counting based on the EPR data shown in Extended Data Fig. 1. b, Spectroelectrochemical data for 10, 11 and 13 at a concentration of 1 mM. Bands assigned to bispyridinium singly reduced and π-dimeric species^40,41 are shown. c, Voltage versus discharge capacity over five full charge–discharge cycles for 10 mM 10, 11 and 13 in 100 mM NaCl and 20 mM 4-hydroxy-TEMPO in 100 mM NaCl full cells. A current of 2 mA cm⁻² was used in all cases. For compound 11, voltage versus discharge capacity data over five full charge–discharge cycles for 5 mM and 1 mM 11 full cells are overlaid. The 5 mM 11 in 100 mM NaCl and 10 mM 4-hydroxy-TEMPO in 100 mM NaCl full cell was cycled at a current of 1 mA cm⁻². The 1 mM 11 in 100 mM NaCl and 2 mM 4-hydroxy-TEMPO in 100 mM NaCl full cell was cycled at a current of 0.2 mA cm⁻². Cut-off voltages of 0.5 V (10, 11 and 13), 1.90 V (10), 1.95 V (11) and 2.00 V (13) were used with 1 h potential holds being applied at the respective cut-off values. d, Discharge capacity versus cycle number for 11 at 10 mM, 5 mM and 1 mM concentrations. e, Normalized discharge capacity versus cycle number for 10, 11 and 13 at 10 mM concentration.