TY - JOUR
T1 - Electrochemistry of oxygen in concentrated NaOH solutions
T2 - Solubility, diffusion coefficients, and superoxide formation
AU - Zhang, Cunzhong
AU - Fan, Fu Ren F.
AU - Bard, Allen J.
PY - 2009/1/14
Y1 - 2009/1/14
N2 - The diffusion coefficient (Do 2), solubility (Co 2), and electrochemical behavior of oxygen eduction were investigated by cyclic voltammetry and transient amperometry on a Pt ultramicroelectrode in aqueous solutions containing various concentrations of NaOH (1-12 M). The results show that both Do 2 and Co 2 decrease as the solution viscosity (η) increases significantly with increasing concentration of NaOH. The Stokes-Einstein relationship (Do 2 vs 1/η) is followed, yielding a radius for the O 2 molecule, 2.8 A7ring;, that does not change over the concentration range of NaOH studied. From results reported previously for Co 2 in more dilute NaOH solutions and the new results here, the number of electrons, n, involved in the first step of the oxygen reduction reaction (ORR) was found to change with the concentration of NaOH, from n = 2 at low NaOH concentrations (1-2 M) to n = 1 at high concentrations (>6 M), in line with the changing water activity. Scanning electrochemical microscopy (SECM) was employed as a sensitive tool to investigate the electrochemical behavior of the product of the ORR in 10 M NaOH solution, O 2 -, as a function of potential. The SECM approach curves depend on the substrate bias and state of the Pt substrate surface, and the apparent rate constant for the redox couple of O 2/O 2 - is determined to be about 2.6 × 10 -1 cm/s in this solution.
AB - The diffusion coefficient (Do 2), solubility (Co 2), and electrochemical behavior of oxygen eduction were investigated by cyclic voltammetry and transient amperometry on a Pt ultramicroelectrode in aqueous solutions containing various concentrations of NaOH (1-12 M). The results show that both Do 2 and Co 2 decrease as the solution viscosity (η) increases significantly with increasing concentration of NaOH. The Stokes-Einstein relationship (Do 2 vs 1/η) is followed, yielding a radius for the O 2 molecule, 2.8 A7ring;, that does not change over the concentration range of NaOH studied. From results reported previously for Co 2 in more dilute NaOH solutions and the new results here, the number of electrons, n, involved in the first step of the oxygen reduction reaction (ORR) was found to change with the concentration of NaOH, from n = 2 at low NaOH concentrations (1-2 M) to n = 1 at high concentrations (>6 M), in line with the changing water activity. Scanning electrochemical microscopy (SECM) was employed as a sensitive tool to investigate the electrochemical behavior of the product of the ORR in 10 M NaOH solution, O 2 -, as a function of potential. The SECM approach curves depend on the substrate bias and state of the Pt substrate surface, and the apparent rate constant for the redox couple of O 2/O 2 - is determined to be about 2.6 × 10 -1 cm/s in this solution.
UR - http://www.scopus.com/inward/record.url?scp=67849128254&partnerID=8YFLogxK
U2 - 10.1021/ja8064254
DO - 10.1021/ja8064254
M3 - Article
AN - SCOPUS:67849128254
SN - 0002-7863
VL - 131
SP - 177
EP - 181
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 1
ER -