The high surface area per unit volume and large mass-transfer rates offered by three-dimensional porous electrodes have resulted in their use in a wide variety of electrochemical processes.^1-4 Several types of porous electrodes are commercially available, including carbon paper, graphite felt, reticulated vitreous carbon (RVC), metal mesh, and metal foam. Metal foam offers relatively high conductivity (1.5x10^-5 ohm m) but low specific surface area (<4x10⁴ m^-1),⁵ whereas carbon paper has one of the highest specific surface areas (up to 1.6x10⁵ m^-1) but lower conductivity (4.7x10^-5 ohm m).⁶ An improved flow-through electrode would have the electrical conductivity of metals, a surface area greater than carbon paper, and a hydraulic permeability comparable to carbon paper.

This presentation will describe the characteristics of a Cu nanowire electrode that has 15 times more surface area (2.4x10⁶ m^­-1) and is 32 times more conductive (1.4x10^-6 ohm m) than carbon paper. The improvement in surface area is due to the small diameter of the nanowires relative to carbon fibers. The higher conductivity is due to the intrinsically higher conductivity of Cu, and the fact that the metal nanowires can be sintered together. The porosity of the nanowire electrode is 0.94, but its hydraulic permeability was 89 times lower than carbon paper. For Cu ion reduction, the Cu nanowire electrode can achieve the same single-pass conversion as carbon paper at flow rates up to 1000 times greater under mass transport-limited conditions, and 10 times greater under kinetically limited conditions. We will also report results for the hydrogenation of furfural and for water oxidation. Future work will focus on improving the hydraulic permeability of flow-through electrodes while maintaining a >10x increase in surface area relative to carbon paper.

References:

1. J. Newman, and W. Tiedemann, AIche J., 21, 25 (1975).
2. R. Alkire, and P.K. Ng, J. Electrochem. Soc., 124, 1220 (1977).
3. J.M. Friedrich, C. Ponce-De-Leon, G.W. Reade, and F.C. Walsh, J. Electroanal. Chem., 561, 203 (2004).
4. S. Porada, L. Weinstein, R. Dash, A. van der Wal, M. Bryjak, Y. Gogotsi, and P. M. Biesheuvel, ACS Appl. Mater. Interfaces, 4, 1194 (2012).
5. S. Langlois, and F. Coeuret, J. Appl. Electrochem., 19, 43 (1989).
6. S.C. Barton, Y. Sun, B. Chandra, S. White, and J. Hone, Electrochem. Solid-State Lett., 10, B96 (2007).

Figure 1. Images for Cu nanowire-based electrode and carbon paper.