Abstract
Systems consisting of a bright platinum plate, hydrogen gas, and oxyanions, such as brómate, iodate, and chlorite, in aqueous sulfuric acid solution are found to exhibit two different stable steady states under some sets of identical experimental conditions, whereas under other conditions sustained oscillations appear at room temperature and in the absence of any external current. In the platinum-catalyzed oxidation of hydrogen by potassium brómate these oscillations are observed at concentrations of 0.03-0.1 M for brómate and 0.6-1.5 M for sulfuric acid in unstirred solutions or at higher acidity (2.0 M) if the solution is stirred gently. In the presence of one-electron redox couples, such as Ce(IV)/Ce(III), Mn(III)/Mn(II), V(V)/V(IV), Fe(III)/Fe(II), and Ag(I)/Ag, the oscillation can be maintained even under strong mechanical stirring. Under certain conditions, where the reaction fails to oscillate, bistability may appear. The iodate-hydrogen-acid-platinum system shows bistability as well, and some experiments suggest that oscillation may also occur. Chlorite gives rise to bistability at slightly lower acidity than brómate and iodate, and shows oscillation at significantly higher pH. In these systems, the oscillations and bistability are a surface rather than a bulk phenomenon. The essential role of such physical parameters as surface area, speed of stirring, etc., in giving rise to these phenomena is noted. A plausible explanation for the oscillation is suggested. Efforts to produce oscillation or bistability with chlorate, bichromate, and permanganate ions were unsuccessful.