New Oscillatory Electrocatalytic Oxidation of Amino Compounds on a Nanoporous Film Electrode of Electrodeposited Nickel Hydroxide Nanoflakes

Systematic investigations have been carried out on the electrocatalytic oxidation of several amino compounds in alkaline solutions on a nanoporous thin-film electrode of electrodeposited nickel hydroxide nanoflakes (NHNFs). The amino compounds studied here include two amines (ethylamine and propylamine), five amino acids (β-alanine, alanine, lysine, glycine, serine, and arginine), and one dipeptide (glycylglycine). Potential-dependent, time- and space-resolved in situ Raman spectra, together with electrochemical measurements, have been employed to reveal the electrocatalytic processes at the molecular level for the first time. Experimental results show that (i) the NHNFs act as an effective electron mediator with high electrocatalytic activity toward these amino compounds; (ii) the amino group is converted into a nitrile group, and decarboxylation occurs simultaneously for the α-amino acids; and (iii) the electrooxidation reaction rate of amino compounds is diffusion-controlled. Moreover, oscillations in both potential and current were observed for the first time during the electrocatalytic oxidation of these amino compounds on the film electrode of NHNFs. Periodic oxygen evolution plays a key role in the oscillations. It is initiated and terminated, respectively, when the surface concentration of amino compounds decreases to zero by diffusion-limited oxidation and is replenished by convection-enhanced flow from the gas release.