The Journal of
Physical Chemistry
0 Copyright, 1982, by the American Chemical Society
VOLUME 86, NUMBER 11
MAY 27, 1982
LETTERS Electrochemical Production of H202and O2 at an Anthracene/H,O Interface Martin Pope" and Kenneth Siotnick Chemistry Department and Radiation and Solid State Laboratory, New York University, New Yo&, New York 10003 (Received: January 5, 1982; In Final Form: March 8, 1982)
The discharge of electrochemicallygenerated holes at an anthracene crystal/water interface produces mainly oxidation products of anthracene. A t high current densities (-400 pA cm-,), H202and 0,are produced. The efficiency of 0,production is -3%.
It has previously been shown' that an electric current can be passed through an anthracene crystal provided with electrolytic contacts. Since the flow of current through the crystal occurs by electron movement, and ions carry the current in the aqueous phase, it follows that chemical oxidation and reduction of water must take place at the crystal/water interface. Jarnagin et al., studied the chemical reactions that took place at this interface and found, paradoxically, that, at least for the discharge of the positive hole, not only was oxygen not produced, it was consumed. In this paper, we show for the first time that at sufficiently high current density, H202 and 0,are produced at the crystal anode. The experimental setup is shown in Figure 1. Anthracene single crystals were graciously donated by G. J. Sloan of DuPont Laboratories. In a typical experiment, the crystal was -500 pm thick, -0.48 cm2in effective area, and presented its ab plane to the aqueous contacting electrode. Holes were injected into the crystal at the cathode side of the crystal, using a 0.28 M Ce4+solution in 12 M H2S04. The holes were forced across the crystal (1) H.Kallmann and M. Pope, J. Chem. Phys., 32, 300 (1960). (2) R. C. Jarnagin, J. Gilliland, Jr., J. S.Kim, and M. Silver, J. Chem. Phys., 39,573 (1963).
under a field of 1 X lo4 to 5 X lo4 V cm-' (300-1500 V), producing current densities of up to 430 pA cm-,; the current density was kept contant within a factor of two during an experiment. The anode side of the crystal was in contact with 500 pL of HPLC grade H20, previously to rebubbled with ultrahigh purity N2 (
