Chaos in the oxidation of formaldehyde and/or methanol

The appearance of chaos is studied with a platinum electrode in acidic solutions of formaldehyde, methanol, and their mixtures at 43 degrees C under galvanostatic conditions. The oscillation mode changes with time, and chaos is found after the period-doubling bifurcation for formaldehyde alone, methanol alone, and their mixtures. Two types of alternating periodic and chaotic sequence are observed depending on the current value: descending and ascending orders respectively at currents lower and higher than approximately 0.5 mA cm(-2) at 43 degrees C. The former is usually seen in the oxidation of formaldehyde and the mixtures of formaldehyde with a small molar fraction of methanol. The latter is ordinarily recognized for methanol and the mixtures of formaldehyde with a large fraction of methanol. Around 0.5 mA cm(-2), the oscillation pattern does not show the alternating sequence but rather a disordered periodic one. We identify aperiodic patterns as chaos by the presence of the period-doubling cascade and by the shape of the Lorenz map. We discuss the difference in the order of the alternating sequence in terms of the platinum surface state. Because oscillation occurs at even less than 0.6 V (rhe), we think adsorbed water is an important reactant with adsorbed carbon monoxide. We also think the nonuniformity of chaos shown in the Lorenz map prevails in a natural system and plays an essential role in the system.