Local probe investigation of electrocatalytic activity.

As the world energy crisis remains a long-term challenge, development and access to renewable energy sources are crucial for a sustainable modern society. Electrochemical energy conversion devices are a promising option for green energy supply, although the challenge associated with electrocatalysis have caused increasing complexity in the materials and systems, demanding further research and insights. In this field, scanning probe microscopy (SPM) represents a specific source of knowledge and understanding. Thus, our aim is to present recent findings on electrocatalysts for electrolysers and fuel cells, acquired mainly through scanning electrochemical microscopy (SECM) and other related scanning probe techniques. This review begins with an introduction to the principles of several SPM techniques and then proceeds to the research done on various energy-related reactions, by emphasizing the progress on non-noble electrocatalytic materials.

Forced convection during feedback approach curve measurements in scanning electrochemical microscopy: maximal displacement velocity with a microdisk.

In scanning electrochemical microscopy (SECM), an approach curve performed in feedback mode involves the downward displacement of a microelectrode toward a substrate while applying a bias to detect dissolved electroactive species at a diffusion-limited rate. The resulting measured current is said to be at steady state. In order to reduce the required measurement time, the approach velocity can be increased. In this paper, we investigate experimentally and theoretically the combination of diffusion and convection processes related to a moving microdisk electrode during feedback approaches. Transient modeling and numerical simulations with moving boundaries are performed, and the results are compared to the experimental approach curves obtained in aqueous solution. The geometry and misalignment of the microelectrode influence the experimental approach curves recorded at high approach velocities. The effects are discussed through the decomposition of the current into transient diffusional, radial convectional, and axial convectional contributions. Finally a ready-to-use expression is provided to rapidly evaluate the maximal approach velocity for steady state measurements as a function of the microelectrode geometry and the physical properties of the media. This expression holds for the more restrictive case of negative feedback as well as other modes, such as SECM approach curves performed at substrates displaying first order kinetics.