Screening of CO2 electroreduction catalysts

The electroreduction of carbon dioxide is an important reaction in view of fuels for both fuel cells and redox flow batteries as well as towards a carbon neutral energy cycle. Hence the reaction has been intensively studied and a range of different catalyst materials have been presented.

In today’s paper “Scanning electrochemical microscopy screening of CO2 electroreduction activities and product selectivities of catalyst arrays” by Francis D. Mayer et al. Sn/SnOx catalysts are investigated using SECM. The final goal of this approach is to obtain a high-throughput screening procedure with the ability of spatial resolution to evaluate local activity changes in the catalysts.

Here, the authors show the capability of SECM for CO2 electroreduction catalyst screenings by comparing three different Sn/SnOx materials towards the production of H2, COad and HCOOand their selectivity. In contrast to traditional SECM experiments where the microelectrode is biased at a constant potenial while moving across the surface, the products are detected in a CV cycle as shown below. This allows for a simultaneous detection of all three relevant reaction products in one experiment.

Presentation of A CV at a Pt microelectrode for the simultaneous detection of H2, COad and HCOO-.
Fig. 1: Cyclic voltammograms indicating the different redox processes during CO2 electroreduction. Image taken from Mayer, F.D., et al. Commun Chem 3, 155 (2020). https://doi.org/10.1038/s42004-020-00399-6.

The screening of the Sn/SnOx catalyst array was performed by conducting and analysing a fast CV (1 V/s) at the Pt microelectrode at each measuring point of the 8750 x 1250 µm map. The Potmaster software of the ElProScan allows to perform matrix scans where advanced protocols can be executed and analyzed which made these experiments possible.

SECM maps created from the analysis of fast CV scans at each point of the map.
Fig. 2: Resulting maps of the catalyst array for each product as analyzed in the CV scans. Image taken from Mayer, F.D., et al. Commun Chem 3, 155 (2020). https://doi.org/10.1038/s42004-020-00399-6.

The analysis showed indeed differences in the product selectivities and shows the great potential of using the combined SECM-CV approach for larger catalyst arrays.

Read the full paper here: Mayer, F.D., Hosseini-Benhangi, P., Sánchez-Sánchez, C.M. et al. Scanning electrochemical microscopy screening of CO2 electroreduction activities and product selectivities of catalyst arrays. Commun Chem 3, 155 (2020). https://doi.org/10.1038/s42004-020-00399-6

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Combining SECCM with Microspectroscopy for Evaluation of ROS Generation at non-Pt Fuel Cell Catalysts

Scanning electrochemical cell microscopy (SECCM) is the only technique which allows the study of a material using well-established bulk electrochemical techniques with a resolution of a few micrometer down to the nanometer regime. The measurement takes place in a nano- or microdroplet formed at the end of a nano- or micropipette in contact with the surface of interest. This allows e.g. study of single nanoparticle agglomerates or generally spatially resolved analysis of the sample. The analysis of the data is equivalent to the bulk experiment and often straightforward.

In this paper “Mapping Localized Peroxyl Radical Generation on a PEM Fuel Cell Catalyst Using Integrated Scanning Electrochemical Cell Microspectroscopy” by J. Edgecomb et al. SECCM using a HEKA ElProScan platform was combined with adsorption and fluorescence microscopy allowing the recording of spectra within a 10 µm wetted sample area. A fluorescent dye 6CFL was used to detect the generation of peroxyl radicals during the ORR at the non-Pt catalyst TaTiOx on a Nafion membrane which were indeed formed.

The measurements using this integrated SECCM setup were validated by RRDE bulk measurements and can further be applied to novel fuel cell catalysts.

Edgecomb J, Xie X, Shao Y, El-Khoury PZ, Johnson GE and Prabhakaran V (2020) Mapping Localized Peroxyl Radical Generation on a PEM Fuel Cell Catalyst Using Integrated Scanning Electrochemical Cell Microspectroscopy.
Front. Chem. 8:572563. doi: 10.3389/fchem.2020.572563

Scheme of the SECCM setup with integrated spectrometer for adsorption and fluorescence microspectroscopy in the droplet (left), fluorescence spectra within the droplet of a Nafion membrane with a layer of fluorescence dye 6CFL and active catalyst (middle) and fluorescence intensity during ORR at the active catalyst (right). Reproduced from J. Edgecomb et al. (2020) Front. Chem. 8:572563. Copyright by © 2020 Edgecomb, Xie, Shao, El-Khoury, Johnson and Prabhakaran.