Tailored microcells for probing real-time electrocatalytic reactions in TEM

Session

PST.6 - In-situ and in-operando microscopy

Authors

Mr. Tzu-Hsien Shen (1), Prof. Yang Shao-Horn (2), Prof. Vasiliki Tileli (1)

Affiliations

1. EPFL
2. MIT

Keywords

Electrocatalysis, Functional oxides, and Operando liquid-phase TEM

Abstract text

Understanding the interaction between surface and aqueous solutions is key to enhancing the performance and activity of electrocatalysts for water splitting (H₂O → 2H₂ + O₂). Recently, electrochemical liquid-phase transmission electron microscopy (TEM) has been applied to study reactions in solutions such as metal deposition, fuel cells, and batteries [1–3]. For the operation of electrochemical liquid-phase TEM, electrochemical MEMS chips with ultra-thin membranes and thin-film electrodes are needed. However, to interpret the electrochemical response in such a confined system, tailored micro-cell configurations for targeted electrocatalytic reactions are needed. 

Herein, we describe the optimized microfabrication of MEMS-based chips designed for the oxygen evolution reaction. Electrode configurations including material selection, thickness and design were prepared in-house. The imaging was performed in zero-loss energy-filtering mode to enhance the image contrast by removing inelastic scattering and additional aberrations caused by the liquid layer. A direct electron camera with high sensitivity and temporal resolution was used to minimize electron-beam effects and record in real-time the surface catalytic reactions. 

The optimized system was tested on three different oxide catalysts, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF), CoO and Co₃O₄ for the anodic oxygen evolution reaction in 0.1 M KOH. Unlike the other oxides, BSCF exhibited significant shrinkage at the beginning of cyclic voltammetry (CV) measurements that is attributed to Ba/Sr secondary phase dissolution. Interestingly, a change in the wetting behavior and associated surface functionalization of the BSCF particles was demonstrated at 1.1 V vs. RHE during cathodic scans. The wettability of oxides catalysts has been previously related to their electronic structure which is linked to the OER catalytic properties [4,5]. Thus, the ability to perform tailored operando measurements for electrocatalytic applications in a TEM has provided unprecedented insights into surface catalytic reactions of Co-based oxides.

References

[1] V Beermann et al, Energy & Environmental Science 12 (2019), p. 2476.

[2] E R White et al, ACS Nano 6 (2012), p. 6308.

[3] A J Leenheer et al, ACS Nano 10 (2016), p. 5670. 

[4] J Suntivich et al, Science 334 (2011), p. 1383.

[5] K A Stoerzinger et al, Journal of  Physical Chemistry C 119 (2015), p. 18504.

[6] The work was supported by the Swiss National Research Foundation (SNF) under award no. 200021_175711.