Sustained voltammetric responses, with periods 2-12 times longer than
the period of the cycling potential, were found in application of cycl
ic voltammetry to the oxidation of methanol at a rotating platinum dis
k in alkaline solution. Experiments were conducted in which a control
parameter (the upper potential limit of the potential cycle) was varie
d. The results demonstrate that the periodic states are ordered in the
same way as dynamical states with the same symbolic representations a
re ordered in a combined forward and reverse U-sequence. Between range
s of the bifurcation parameter for which periodic states were observed
, aperiodic behavior was found that possessed properties that are char
acteristic of deterministic chaos. High-order periodic responses were
also obtained in experiments in which the system was allowed to relax
under fixed conditions following the transfer of the Pt electrode to t
he methanol solution. These results provide evidence that the high-ord
er periodic states do not arise from a slow aging process but, instead
, are a consequence of the electrochemical mechanism for the voltammet
ric oxidation of methanol.