Probing Individual Cuprous Oxide Microcrystals towards Carbon Dioxide Reduction by using In Situ Raman‐coupled Scanning Electrochemical Microscopy

Abstract

In this work, the simultaneous investigation of a single cuprous oxide microcrystal towards CO2 electroreduction (CRR, CO2 reduction reaction) by using Raman microscopy and scanning electrochemical microscopy (SECM) is shown. Cu2O microcrystals were electrochemically crystallized on an indium‐doped tin oxide‐substrate (ITO). Structural changes of the Cu2O microcrystal are observed in situ by Raman microcopy, which indicates their fast conversion into elemental Cu at low overpotentials. Simultaneously, detection of products of the CO2 reduction is carried out electrochemically using the sample‐generation tip‐collection mode (SG/TC) of SECM and formate ions are the main product of CRR, as detected by a 10 μm Pt ultramicroelectrode (UME). Thus, with our approach, the very beginning of the CRR (onset potential), potential‐dependent product formation as well as structural changes in the catalyst can be precisely investigated.

Operando Scanning Electrochemical Probe Microscopy during Electrocatalysis

“…SECM was also coupled to Raman spectroscopy to analyze the changes in chemical properties while modulating electrochemical processes on the surface. − The operando SECM-Raman analysis was recently applied to interrogate a self-assembled monolayer with high structural-pH sensitivity . The local pH was modulated by the HER on the SECM tip and the Raman analysis registered changes of the protonated state of a modified self-assembled monolayer on the surface.…”

“…The ITO electrode had no relevant contribution to the CO 2 RR and as such can be a useful substrate material although its application as a transparent electrode material for optical probing was limited to potential values above −1 V vs Ag/ AgCl/KCl sat . 186 SECM in the SG-TC mode has been the most employed SEPM methodology for the operando investigation of CO 2 RR. Nevertheless, EC-STM was also used to study the interfacial dynamics of electrocatalysts.…”

“…(j) Setup of the Raman-coupled scanning electrochemical microscope, (k,l) selected cyclic voltammograms of the Pt UME in 10 μm tip-to-sample distance to the Cu 2 O microcrystal at various substrate potentials ( E substrate from −0.1 to −1.05 V); the arrows in (k) indicate the decrease of currents with decreasing substrate potential, whereas in (l), the curve progression is indicated for −1 V, (m) selected corresponding in situ Raman spectra, the asterisk indicates a peak from the quartz substrate. Reproduced with permission from ref ( 186 ). Copyright 2022 John Wiley and Sons.…”

“…Recently, Steimecke et al 186 combined SECM with Raman microscopy to investigate the activity of a single cuprous oxide microcrystal electrochemically deposited on a transparent ITO substrate (Cu 2 O/ITO) toward CO 2 RR. Figure 7 j is a scheme of the Raman-coupled SECM setup that allowed Raman measurements from the backside of the ITO electrode while the SG-TC-SECM mode was run simultaneously.…”

“…The ITO electrode had no relevant contribution to the CO 2 RR and as such can be a useful substrate material although its application as a transparent electrode material for optical probing was limited to potential values above −1 V vs Ag/AgCl/KCl sat . 186 …”