Effect of bismuth on hydrogen evolution reaction on lead in sulfuric acid solution

The effect of bismuth on hydrogen evolution on lead in sulfuric acid solution is investigated by linear potential sweep, alternating current (ac) impedance, X-ray diffraction (XRD) and hydrogen-collection experiments. First, hydrogen evolution behaviour on commercial lead with and without bismuth and on pure bismuth is compared. It is found that the hydrogen evolution reaction takes place more easily on bismuth than on lead, but that the commercial lead with 50 ppm bismuth has a slower hydrogen evolution than the commercial lead without bismuth. Next, the effect of bismuth is studied. Bismuth is added to lead at 0-7.33 wt.% to make lead-bismuth alloys, or is deposited chemically on the surface of lead to form a bismuth-containing lead. The results from X-ray diffraction show that the prepared lead-bismuth alloys have the same crystal structure as pure lead, i.e., the added bismuth enters into the lead crystals. Apparently, chemically-deposited bismuth does not enter into the lead crystals, but is independent of but contact electronically with the lead. The results, obtained from linear potential sweep, ac impedance and hydrogen evolution volume measurements, show that the rate of hydrogen evolution depends on the amount of bismuth in or on the lead. It is concluded that bismuth accelerates the hydrogen evolution reaction on lead, irrespective of whether it enters the lead crystals or not. By contrast, the hydrogen evolution reaction is less dependent on bismuth in lead-bismuth alloys than on bismuth that is chemically deposited on lead and the effect of bismuth can be neglected if the alloy electrode is not taken to a very negative potential.