Mass Transport in Porous Electrodes Studied by Scanning Electrochemical Microscopy: Example of Nanoporous Gold

Abstract

Scanning electrochemical microscopy (SECM) approach curves were measured above different samples of nanoporous gold (NPG) using ascorbic acid as an irreversible redox mediator. Under these circumstances, the microelectrode current is informative in terms of the diffusive mass transport inside the network of pores in the sample, because mediator regeneration at NPG is not possible for an irreversible mediator. The reaction–transport problem was solved by finite element simulation for a wide variety of working distances, film thicknesses, and microelectrode geometries. The Bruggeman equation was used to relate transport properties and porosity. The simulation leads to an analytical expression that allows the determination of porosity values corrected by the tortuosity of insulating and conducting materials. The validity of the approach was demonstrated by applying it to NPG samples for which structural parameters can be varied by the particular dealloying protocol. This procedure is potentially applicable for following coarsening processes in porous electrodes and other materials, because the SECM procedure avoids emersion from electrolyte solution for those determinations.

Mass Transport in Nanoporous Gold and Correlation with Surface Pores for EC1 Mechanism: Case of Ascorbic Acid

“…electrochemical processes on NPG films with small pore size has already been reported. [29][30] Interestingly, a different behavior was noticed in similar plots obtained for the AA electrode process for NPG films prepared at a fixed E D (-4 V) but for varying t D (in the range of 50 to 600 s) (Figure 7). At the shorter t D value (50 s), E 1/2 is reported instead of E p because the voltammogram recorded with this electrode presented a steady-state feature instead of a peak-shaped profile.…”

“…[29] Therefore, a trade-off between mass transport limitation and ECSA is always noticed to improve the electroanalytical performance of NPG-based platforms. [30] This balance depends on two important factors: the kinetics and mechanism of the electrode reactions, and the pore size in the NPG films. At first, electrode reactions with slower kinetics are expected to have lower mass transport limitations because the analyte would have a longer time to travel deeper in the film before getting oxidized/reduced.…”

From Chip Size to Wafer-Scale Nanoporous Gold Reliable Fabrication Using Low Currents Electrochemical Etching

“…It is worth mentioning here that the porous counterpart has higher current feedback zones because of the fact that many of the features formed during the process are suitable for the reduction of [FcMeOH] + . Moreover, the ligaments and the micropores enable a large surface area that drastically inhibits mass transfer of educts and products [ 50 ], which translates into a drop of feedback current as the tip scans over the surface. At the same time, the slow mass transfer on the overall reactivity of the ligaments and micropores makes the nanoporous gold substrate very attractive to many electrochemical applications.…”

Local electrochemical impedance spectroscopy: A window into heterogeneous interfaces

“…The study of the electrochemical interface by means of local measurements is a subject that remains in constant evolution, and is accelerated by the numerous technical developments involving probe size reduction (used to sense the interface reactivity) or the development of more advanced associated electronics for data acquisition. In fact, the versatility offered by local electrochemical techniques benefits a large panel of research topics as different as the local catalytic or photocatalytic activity of materials [1][2][3], the production of redox species in living cells [4,5], corrosion processes on various interfaces [6][7][8][9] or complex kinetics mechanism [10][11][12].…”