Powder samples of hydrogen molybdenum bronzes (HxMoO3) were effectively stabilized by the addition of 30 mass% polyethylene powder, pressing and a following thermal treatment. :The composite material does not degrade in 0.05 mol l(-1) H2SO4, so that cyclic voltammetry could be carried out in 0.05 mol l(-1) H2SO4 to give reproducible waves and peak potentials. Extrapolation to the scan rate v = 0 yields the following redox potentials (all versus the SHE) : +277 +/- 7 mV for phase II in its maximum reduction degree (x(max)), +67 +/- 7 mV for phase III (x(min)), -91 +/- 10 mV for phase III (x(max)), -204 +/- 1 mV for phase IV and -358 +/- 10 mV for hydrogen at phase IV. In 0.5 mol l(-1) H2SO4 the bronze is partially soluble, which leads to a strong decrease of the electrochemical activity.