Electroactive Area from Porous Oxide Films Loaded with Silver Nanoparticles: Electrochemical and Electron Tomography Observations

Abstract

Electrochemical studies of nanomaterial-based electrodes have been widely developed for catalyst and energy-harvesting applications. The evolution of these electrodes over time and their efficiency have been extensively studied and analyzed in order to optimize their performance. However, the electrochemical responses of electrodes are rarely studied in terms of the position of the active species within these electrodes. In this paper, we highlight that the spatial location of silver nanoparticles (NPs) embedded inside semiconductive porous films, TiO 2 or Fe 2 O 3 , is crucial for the electrochemical response. In fact, by using cycling voltammetry and electron tomography experiments, we show the existence of an "electroactive area", corresponding to a reduced thickness of the sample in close vicinity to a fluorine-doped tin oxide substrate where most of the electrochemical responses originate. Our results demonstrate that, for a film thickness of several hundred nanometers, only less than 30 nm close to the substrate responds electrochemically. However, cyclic voltammetry empties the electroactive area of silver NPs. Therefore, application of chronoamperometry coupled to irradiation allowed regeneration of this area thanks to an increased diffusion of silver species. In this paper, we also show the significant diffusion of silver species within the film during electrochemical experiments, a phenomenon even increased by irradiation. These results are therefore an important step that shows the importance of the localization of active species within a porous film and help in understanding and increasing the durability of nanomaterial-based electrodes.

Electrochemical Properties of Silver Nanoparticles in Mesoporous Silica and Titania Films: Specific Behavior of Titania Composite

“…The films were aged under ambient conditions (T = 23 °C, RH = 30–40%) for 24 h and then calcined at 350 °C for 2 h, with a heating ramp of 1 °C·min –1 . These films are about 200 nm thick and have a mesoporous volume equal to 0.25 cm 3 ·g –1 , provided by pores of 11 nm average diameter …”

“…These films are about 200 nm thick and have a mesoporous volume equal to 0.25 cm 3 .g -1 , provided by pores of 11 nm average diameter. 61 In order to form silver NPs inside the porous oxide films, the titania films were immersed in a silver nitrate solution (50 mM). Silver NPs were formed by coulometry by imposing in general on the working electrode constitut-ed by the mesoporous film deposited on FTO a current of -10 μA for 180 s. The amount of silver introduced corresponds to a load of -1.8 mC.…”