Liquid-Phase Electron Microscopy for Probing Electrocatalytic Material Interfaces

The oxygen evolution half-reaction (OER) is responsible for the limited efficiency of water splitting devices for storing clean energy. A holistic understanding of the fundamental processes taking place during operation of catalysts in solution can be gained by using advanced operando techniques that can complement characterization pre and post operation. In particular, electrochemical liquid-phase transmission electron microscopy (TEM) can provide morphological, structural, and chemical information for these catalysts.<br/>As an example, I will focus on OER oxide-based catalysts studied using liquid-phase TEM to investigate the solid-liquid interface in an alkaline solution [1]. The potential-dependent variation of the local contrast was associated to the modification of the alkaline liquid electrolyte and its wettability at the Co-oxide surfaces. At low applied potential, the hydrophobic character of the oxides was found to reduce due to electrowetting induced by OH^- accumulation at the interface. A distinct transition towards hydrophilicity was probed at the potential associated with the redox Co²⁺/Co³⁺ reaction, which alters the interfacial capacitance. This leads to a relatively stable wetting character at intermediate potentials prior to the OER region where the oxide surfaces catalyse the adsorbed hydroxide ions at the solid-liquid interface to form molecular oxygen. Further operando measurements using electron energy loss spectroscopy (EELS) provided direct evidence of the evolution of molecular oxygen. Finally, similar experiments on IrO₂ particles reveal the possibility of facet-dependent production detections using EELS [2].<br/>Overall, advanced electron diagnostics and characterization applied to electrocatalyst structures can provide valuable insights into solid/liquid/gas interfaces and can guide development of efficient devices.<br/><br/><br/>References<br/>[1] T.-H. Shen, L. Spillane, J. Peng, Y. Shao-Horn, V. Tileli, Nature Catalysis, 5 (2022), pp. 30-36.<br/>[1] T.-H. Shen, R. Girod, J. Vavra, V. Tileli, The Journal of the Electrochemical Society, 170 (2023), pp. 056502.