Spatially Resolved Probing of Electrochemical Reactions via Energy Discovery Platforms

Abstract

The electrochemical reactivity of solid surfaces underpins functionality of a broad spectrum of materials and devices ranging from energy storage and conversion, to sensors and catalytic devices. The surface electrochemistry is, however, a complex process, controlled by the interplay of charge generation, field-controlled and diffusion-controlled transport. Here we explore the fundamental mechanisms of electrochemical reactivity on nanocrystalline ceria, using the synergy of nanofabricated devices and time-resolved Kelvin probe force microscopy (tr-KPFM), an approach we refer to as energy discovery platform. Through tr-KPFM, the surface potential mapping in both the space and time domains and current variation over time are obtained, enabling analysis of local ionic and electronic transport and their dynamic behavior on the 10 ms to 10 s scale. Based on their different responses in the time domain, conduction mechanisms can be separated and identified in a variety of environmental conditions, such as humidity and temperature. The theoretical modeling of ion transport through finite element method allows for creation of a minimal model consistent with observed phenomena, and establishing of the dynamic characteristics of the process, including mobility and diffusivity of charged species. The future potential of the energy discovery platforms is also discussed.

Pressure-induced switching in ferroelectrics: Phase-field modeling, electrochemistry, flexoelectric effect, and bulk vacancy dynamics

“…As an example we turned on all the aforementioned effects (surface charge, flexoelectricity and bulk vacancy dynamics) to study the mechanical switching behavior in a 20nm PZT thin film subjected to 4μN tip load. Figure 10 85,86 ) and by transport from gas phase to the film surface. And the Vegard strain effect is limited by the oxygen vacancy diffusivity, which is normally very slow in solids under room temperature, but becomes much faster once the local electric bias and mechanical load overcome the activation energy barrier of vacancies.…”

Solid-state electrochemistry on the nanometer and atomic scales: the scanning probe microscopy approach

“…For instance, for the CeO 2 sample in Ref. 133 the RC constant was ca. 100 s – too slow to be detected in the timeframe of 10 s used for tr-KPFM.…”

“…Proton generation takes place at the triple-phase boundary (platinum electrode, air and ceria) due to splitting of adsorbed water (Eq. (2)) 133 The injected protons then, electromigrate and diffuse in the adsorbed water layers by Grotthuss mechanism: 134 …”

“…Deconvolution of this complexity is possible by considering coupling between the transport, reaction and electrostatics equations: 133 …”

“…133, 134 As the surface potential evolution strongly depends on temperature and ambient gas humidity, the extracted parameters can be plotted in the form of phase diagrams, whose shapes will reflect the differences in parameter contributions to the overall potential under different conditions, as they have distinct temperature and humidity dependencies.…”