triple phase boundary
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2021 ◽  
Author(s):  
Junnan Li ◽  
Nikolay Kornienko

<p>Electrosynthetic techniques are gaining prominence across the fields of chemistry, engineering and energy science. However, most works within the direction of synthetic heterogeneous electrocatalysis focus on water electrolysis and CO<sub>2</sub> reduction. In this work, we moved to expand the scope of this technology by developing a synthetic scheme which couples CO<sub>2</sub> and NH<sub>3</sub> at a gas-liquid-solid triple-phase boundary to produce species with C-N bonds. Specifically, by bringing in CO<sub>2</sub> from the gas phase and NH<sub>3</sub> from the liquid phase together over solid copper catalysts, we have succeeded in forming formamide and acetamide products for the first time. In a subsequent complementary step, we have combined electrochemical analysis and a newly developed <i>operando </i>spectroelectrochemical method, capable of probing the aforementioned triple phase boundary, to extract an initial level of mechanistic analysis regarding the reaction pathways of these reactions and the current system’s limitations. We believe that the development and understanding of this set of reaction pathways will play an exceptionally significant role in expanding the community’s understanding of on-surface electrosynthetic reactions as well as push this set of inherently sustainable technologies towards widespread applicability. </p>


Catalysts ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1065
Author(s):  
Oliver Lorenz ◽  
Alexander Kühne ◽  
Martin Rudolph ◽  
Wahyu Diyatmika ◽  
Andrea Prager ◽  
...  

Understanding the reaction pathways for the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) is the key to design electrodes for solid acid fuel cells (SAFCs). In general, electrochemical reactions of a fuel cell are considered to occur at the triple-phase boundary where an electrocatalyst, electrolyte and gas phase are in contact. In this concept, diffusion processes of reaction intermediates from the catalyst to the electrolyte remain unconsidered. Here, we unravel the reaction pathways for open-structured Pt electrodes with various electrode thicknesses from 15 to 240 nm. These electrodes are characterized by a triple-phase boundary length and a thickness-depending double-phase boundary area. We reveal that the double-phase boundary is the active catalytic interface for the HOR. For Pt layers ≤ 60 nm, the HOR rate is rate-limited by the processes at the gas/catalyst and/or the catalyst/electrolyte interface while the hydrogen surface diffusion step is fast. For thicker layers (>60 nm), the diffusion of reaction intermediates on the surface of Pt becomes the limiting process. For the ORR, the predominant reaction pathway is via the triple-phase boundary. The double-phase boundary contributes additionally with a diffusion length of a few nanometers. Based on our results, we propose that the molecular reaction mechanism at the electrode interfaces based upon the triple-phase boundary concept may need to be extended to an effective area near the triple-phase boundary length to include all catalytically relevant diffusion processes of the reaction intermediates.


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