Fig. 3: Structural and electro-active investigations.

a³¹P NMR of different reduced states of 3Na-PW₁₂ (0.1 mol l⁻¹) anolyte in the charging process. b The acid-base titration curves of different reduced states of H-PW₁₂ (room temperature). c³¹P NMR of 3Na-PW₁₂ anolyte (0.1 mol l⁻¹) before charging (blue line) and after discharging (red line) at pH 1.3. d CV curves of H-PW₁₂ and 3Na-PW₁₂ (0.1 mol l⁻¹) at pH 7 and (e) at pH 11 (scan rate 100 mV s⁻¹, room temperature without iR-correction).