Figure 3. Voltammetric data for hydrogen evolution in various types of water with H₂SO₄ as the supporting electrolyte and a planar Pt electrode.

(a) Cyclic voltammograms of the second, 10^th and 20^th scans in 0.5 M H₂SO₄ at a scan rate of 0.5 V s⁻¹; the insert shows the 10^th scans for experiments performed on DI water and the blank (light-free) for comparison. (b) Linear sweep voltammograms (LSVs) in different concentrations of H₂SO₄ at a scan rate of 0.05 V s⁻¹; the insert shows the hydrogen evolution currents at −0.4 V vs Ag/AgCl in various waters with different concentrations of H₂SO₄. (c) Currents of hydrogen evolution at −0.4 V vs Ag/AgCl in various types of water, after its preparation for 0, 1, 3, 5, and 7 days (in 0.5 M H₂SO₄ at a scan rate of 0.05 V s⁻¹). Hydrogen evolution reaction performed at an inert-catalytic electrode (ITO) and photocatalytic (g-C₃N₄/ITO) electrodes. (d) LSVs for hydrogen evolution in DI water and HRHBW containing 0.5 M H₂SO₄ based on the ITO electrode. (e) The increased efficiency of HER based on HRHBW with the applied potential shown in Fig. 3d. (f) LSV for hydrogen evolution reactions performed in DI water and HRHBW containing 0.5 M Na₂SO₄ based on g-C₃N₄/ITO electrode with and without illumination of white-light LED.