A Chemical Traveling Wave Arising from the Electrochemical Peroxydisulfate-Oxalate Autocatalytic Reaction

Autocatalytic reactions commonly display reaction-diffusion behavior that can give rise to spatial patterns, oscillations, and wavefronts. Herein, we present experimental demonstrations and computational analyses of a new chemical traveling wave originating from the electrochemical S2O82–/C2O42– autocatalytic reaction. Following a brief electrochemical initiation step, the S2O82–/C2O42– chemical traveling wave propagates through the solution away from the electrode surface and is imaged using a colorimetric method based on a pH change induced by CO2 generation at the wavefront. Following mediated initiation using the Ru(NH3)63+/2+ redox couple, a chemical traveling wave with an initial velocity of ∼8 μm/s propagates through the solution. Finite element simulations based on a reaction-diffusion model demonstrate that the experimentally observed chemical traveling wave behavior originates from the autocatalytic reaction between S2O82– and C2O42–. However, the chemical traveling wave displays nonideal reaction-diffusion behavior as indicated by a decrease in wave velocity after ∼3 min and an approach to purely diffusional mass transfer within ∼10 min. Simulated concentration profiles are consistent with a declining SO4·– concentration with time due to quenching by Cl– and phenol red, resulting in a gradual dissipation of the chemical traveling wave. Lastly, the colorimetric method used to analyze the chemical traveling wave may be generally useful in monitoring the concentration distribution of dissolved CO2 in real time.