Figure 1.

a) Crystal structure of {XW₁₂O₄₀} (phosphorous, grey; silicon, orange; zinc, blue; tungsten, cerulean; oxygen, red) and the corresponding cyclic voltammograms (CVs) of 100 mm H_nXW₁₂O₄₀ (X=P⁵⁺, Si⁴⁺, and Zn²⁺) solution on glassy carbon electrode at a scan rate of 50 mV s⁻¹. b) pH changing during the reduction process of 100 mm H_nXW₁₂O₄₀ (X=P⁵⁺, Si⁴⁺, and Zn²⁺) solution. c) CVs of a 1 mm H_nXW₁₂O₄₀ (X=P⁵⁺, Si⁴⁺, and Zn²⁺) under different pH buffer solutions at a scan rate of 50 mV s^−1. For more details, see the Supporting Information, Sections SI‐3, SI‐4, and SI‐5.