In Situ/Operando Characterization Techniques of Electrochemical CO₂ Reduction

Abstract

Electrocatalytic conversion of carbon dioxide to valuable chemicals and fuels driven by renewable energy plays a crucial role in achieving net-zero carbon emissions. Understanding the structure–activity relationship and the reaction mechanism is significant for tuning electrocatalyst selectivity. Therefore, characterizing catalyst dynamic evolution and reaction intermediates under reaction conditions is necessary but still challenging. We first summarize the most recent progress in mechanistic understanding of heterogeneous CO2/CO reduction using in situ/operando techniques, including surface-enhanced vibrational spectroscopies, X-ray- and electron-based techniques, and mass spectroscopy, along with discussing remaining limitations. We then offer insights and perspectives to accelerate the future development of in situ/operando techniques. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 14 is June 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Photocatalytic CO2 Reduction with Dissolved Carbonates and Near-Zero CO2(aq) by Employing Long-Range Proton Transport

“…These results clearly showed two contrasting scenarios of sufficient and insufficient CO 2 adsorption with and without a CO 2 -producing proton transport flux, respectively, indicating that CO 2 R is indeed enhanced by designing the arrangement of proton-producing sites in nano-to-mesoscale proximity to the CO 2 R sites. Our study also complements Raman spectroscopy of bare Ag nanoparticles, showing the comparable behavior of Ag-catalyzed CO 2 R with and without a porous oxide modification layer . We found no unknown peaks within 500–1250 cm –1 to indicate a new phase formed at Ag/CrO x interfaces.…”

“…Our study also complements Raman spectroscopy of bare Ag nanoparticles, showing the comparable behavior of Ag-catalyzed CO 2 R with and without a porous oxide modification layer. 46 We found no unknown peaks within 500−1250 cm −1 to indicate a new phase formed at Ag/CrO x interfaces. However, the effect of the porous modification layer for its effect on catalysis and spectroscopy under potential control requires enhanced Raman signals and well-defined Ag active sites 47,48 and is subject to further study.…”

Well-defined surface catalytic sites for solar CO2reduction: heterogenized molecular catalysts and single atom catalysts

“…Furthermore, elucidating the unique advantages of heterogenized molecular catalysts and SACs in photocatalysis requires mechanistic studies using ultrafast spectroscopies and in situ/ operando techniques. [168][169][170][171] As mentioned earlier, results obtained using transient absorption spectroscopy revealed underlying reasons for observed enhancement in the CO 2reduction activity of Re-bpy upon heterogenization on TiO 2 surfaces. 52,53 In this sense, one advantage of photocatalysts containing well-defined surface sites lies in the fact that they could utilize techniques from both homogeneous catalysis and heterogenous catalysis.…”

In-situ Studies of Copper-based CO2 Reduction Electrocatalysts by Scanning Transmission Soft X-ray Microscopy

“…This has motivated the development and application of in-situ/operando spectroscopy, microscopy and spectro-microscopy techniques to provide real-time and same-position characterization of working catalysts under electrochemical reaction conditions. [17][18] In this work, we have used in-situ soft X-ray scanning transmission X-ray microscopy (STXM) [19][20][21][22][23][24][25][26][27][28] to characterize Cu electrocatalysts in a micro-chip electrochemical cell designed to achieve electrolyte flow under applied electrochemical potentials which closely resemble the conditions experienced by Cu particles in a laboratory-scale CO2R reactor. STXM is a synchrotron-based spectro-microscopic technique that can simultaneously provide microscopic imaging of catalyst morphologies alongside spatially resolved (sub-50 nm spatial resolution) [29,30] spectroscopic characterization through near edge X-ray absorption fine structure (NEXAFS) spectroscopy [29] to enable quantitative, chemically selective imaging.…”