Anal. Chem. 1993, 65, 2300-2303
2300
Carbon Aerogel Composite Electrodes Joseph Wang,’ Lucio Angnes,?and Haim Tobias$ Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003
Rebecca A. Roesner,l Keith C. Hong, Robert S. Glass, Fung Ming Kong, and Richard W. Pekala Lawrence Livermore National Laboratory, Livermore, California 94551
The electrochemical behavior and analytical performance of new vitreous carbonaerogel composite electrodes are described. These new composite electrodes rely on the unique open-cell nanostructure of aerogel materials, including their interconnectedporosity, ultrafine pore sizes ( 4 0 nm), and huge surface area. Transmission and scanning electron microscopies are used to shed useful insights into the carbon network. The enhanced diffusional flux results in a sigmoidal voltammetric response and nonlinear i vs t1I2 chronoamperometricplots. The potential window is broad, and the background currents are low. Square-waveanodic stripping voltammetry at the mercury-coated carbon aerogel composite electrode is demonstrated for the quantitationof trace metals at the microgram per liter level using short deposition periods. These carbon aerogels and other aerogels present new opportunities for a wide range of electrode materials.
INTRODUCTION Considerable effort has been devoted to the development and characterizationof new electrodematerials with improved analytical performance.1 In particular, composite carbon electrodes, consisting of an ordered or random arrangement of conductor regions, separated by an insulator, offer many potential analytical advantages compared to continuous electrodes.2 Such improvements are attributed to the enhanced diffusional flux, which leads to higher current densities, lower detection limits, and reduced dependence on convectivetransport. The exact distribution of the conductor and insulator within the material (and hence on the surface) plays a major role in obtaining the desired enhancement in the current density. Such edge effect enhancements become very significant upon increasing the perimeter-to-area ratio of the conductor sites.3 A number of carbon-based composite materials have thus been used to prepare solid electrodes for voltammetry. These include carbon paste electrodes: Kel-F graphite (Kelgraf) surfaces,5 Teflon/graphite electrodes?
* Corresponding author.
+ Present address: Instituto de Quimica da USP, SHo Paulo, Brazil. 8 Present address: Dept. of Analytical Chemistry,NRCN, P.O. Box 9001, Beer Sheva, 84190 Israel. t Present address: Department of Chemistry, University of Kansas, Lawrence, KS. (1) Kissinger, P. T., Heineman, W. R., Eds. Laboratory Techniques in Electroanalytical Chemistry; Dekker: New York, 1984. (2) Tallman, D. E.; Petereen, S.L. Electroanalysis 1990,2, 499. (3) Cope, D. K.; Tallman, D. E. J. Electroanal. Chem. 1985,188,21. (4)Adams, R. N. Anal. Chem. 1958,30, 1576. (5) Weisshaax, D. E.; Tallman, D. E. Anal. Chem. 1983,55, 1146. (6) Klatt, L. N.; Connell, D. R.; Adams, R. E.; Honigberg, I.; Price, J. Anal. Chem. 1978,50, 1051.
0003-2700/93/0365-2300$04.0010
carbon foam composites,’** or epoxy-impregnated reticulated vitreous carbon.9 Precious metal composite electrodes have also been reported (e.g., ref 10). In this paper, we describe the electrochemical behavior and electroanalyticalperformance of anew compositematerial based on carbon aerogels. Carbon aerogels, developed at LawrenceLivermore National Laboratory,”-14 are synthesized by the sol-gel polycondensation of resorcinol and formaldehyde (in a slightly basic medium), followed by supercritical drying and pyrolysis (in an inert atmosphere). This fabrication process results in unique open-cell carbon foams that have high porosity, high surface area (4W1000 m2/g), ultrafiie cell/poresizes (
