Fig. 4: Three-electrode characterization of nanofibrillar PEDOT-coated bricks.

a Nanofibrillar PEDOT-coated type 1 brick (1 cm × 0.5 cm × 0.28 cm) is connected to a Pt current lead using polyimide tape that exposes a 1 cm × 0.5 cm face to the electrolyte. b Cyclic voltammogram at 2 mV s⁻¹ shows a quasi-rectangular shape stemming from PEDOT’s capacitive behavior with Fe³⁺/Fe²⁺ redox pair peaks at 0.37 and 0.49 V (vs. Ag/AgCl). c The Fe³⁺/Fe²⁺ redox peaks disappear when scan rate increases to 25 mV s⁻¹. d The electrode shows a smaller curve area for 1 M Na₂SO₄ electrolyte compared to 1 M H₂SO₄, indicating lower capacitance. e Nyquist plots collected using different electrolytes (inset shows equivalent circuit diagram) show fitted (solid lines) versus experimental data (segregated points). f Powder X-ray diffraction shows identical patterns for pristine type 1 brick vs. PEDOT-coated type 1 brick after cycling in 1 M H₂SO₄ between −0.2 and 0.8 V (vs. Ag/AgCl) at scan rates of 2, 5, 10, 25, 50, and 100 mV s⁻¹ (10 cycles each).