Electroprecipitation of Nanometer-Thick Films of Ln(OH)3 [Ln = La, Ce, and Lu] at Pt Microelectrodes and Their Effect on Electron-Transfer Reactions

Tunable High Entropy Lanthanide Oxide Microspheres via Confined Electroprecipitation in Emulsion Droplet Scaffolds

Emergent high entropy nanomaterials and their associated complex surface structure hold promise to unlock unique catalytic intermediate pathways and photonic/plasmonic interactions; however, synthetic strategies to tune the size, morphological, and stoichiometric properties remain limited. This work demonstrates a confined electro-precipitation mechanism for the formation of tunable, high-entropy oxide microspheres within emulsion droplet scaffolds. This mechanism complements a traditional confined electrodeposition mechanism and explains the previously observed anomalous formation of thermodynamically unfavorable particles, including lanthanide species. Mass transfer studies reveal that microsphere coverage over a surface may be tuned and modeled by using a time-dependent modified Levich equation. Additionally, morphological tuning was demonstrated as a function of experimental conditions, such as rotation rate and precursor concentration. Finally, extension to multimetallic species permitted the generation of high-entropy lanthanide oxide microspheres, which were confirmed to have equimolar stoichiometries via energy dispersive spectroscopy and inductively coupled plasma mass spectrometry. This novel method promises to generate tunable, complex oxides with applications to thermal catalysis, optics, and applications yet unknown.

Operando Scanning Electrochemical Probe Microscopy during Electrocatalysis

Scanning electrochemical probe microscopy (SEPM) techniques can disclose the local electrochemical reactivity of interfaces in single-entity and sub-entity studies. Operando SEPM measurements consist of using a SEPM tip to investigate the performance of electrocatalysts, while the reactivity of the interface is simultaneously modulated. This powerful combination can correlate electrochemical activity with changes in surface properties, e.g., topography and structure, as well as provide insight into reaction mechanisms. The focus of this review is to reveal the recent progress in local SEPM measurements of the catalytic activity of a surface toward the reduction and evolution of O₂ and H₂ and electrochemical conversion of CO₂. The capabilities of SEPMs are showcased, and the possibility of coupling other techniques to SEPMs is presented. Emphasis is given to scanning electrochemical microscopy (SECM), scanning ion conductance microscopy (SICM), electrochemical scanning tunneling microscopy (EC-STM), and scanning electrochemical cell microscopy (SECCM).