Development of correlative microscopy for studying solid/liquid interfaces

We are currently developing correlative multimodal approaches to better understand the elementary processes at solid/liquid interfaces during electrocatalytic reactions or battery cycling. For example, we recently combined scanning electron microscopy/electron backscatter diffraction (SEM/EBSD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and atom probe tomography (APT) with electrochemical measurements to reveal the oxidation state, structure, morphology and composition of in situ generated surface species formed on a cobalt microelectrode and how grain orientation affects the formation of surface species (see workflow below).

Publication:

C. Luan, M. Corva, U. Hagemann, H. Wang, M. Heidelmann, K. Tschulik, T. Li; Atomic-Scale Insights into Morphological, Structural, and Compositional Evolution of CoOOH during Oxygen Evolution Reaction, ACS Catalysis, 13(2) (2023) 1400-1411. 

We have also developed an approach to directly examine the oxidation state and surface composition of nanosized Ir electrodes after oxygen evolution reaction (OER). APT reveals compositional changes in the topmost surface and subsurface on various Ir planes during OER. Our approach provides atomic-scale insights into surface changes during electrochemical reactions (see image below).

Publication:

A. BalaKrishnan, N. Balnc, U. Hagemann, P. Gemagami, K. Wonner, K. Tschulik, T. Li; Direct Detection of Surface Species Formed on Iridium Electrocatalysts during the Oxygen Evolution Reaction, Angewandte Chemie International Edition 60(39) (2021) 21369-21403. 

I am also interested in pushing the boundaries of APT applications. For example, MOFs are a novel family of hybrid organic-inorganic materials whose high porosity, tunable pore functionality and versatile pore architecture/compositions make them potentially useful in storing fuel gases such as H2, and for the capture of CO2. Mixing metal-containing secondary building units (SBUs) into a single crystal has been demonstrated to lead to heterogeneous crystalline materials. Tuning the structure towards the desired property in a controlled manner requires a sufficient understanding of the structure-synthesis-perfomance-relationships. However, revealing the sequencing of metal-containing SBUs, i.e. metallic ions, remains a notorious challenge. Here, we have succesfully prepared the APT specimens of MOF-74 (see figure below, a), characterized by APT and revealed that the Co,Cd-MOF-74 prepared at 120°C (Co,Cd, 120°C) has a random structure (b,c).

Publication:

J. Zhe, T. Li*, O.M. Yaghi*; Sequencing metals in multivariate metal-organic frameworks, Science, 369 (2020), 674-780. (*corresponding authors)