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Abstract Electrochemical nitrate reduction reaction (NO3RR) has garnered increasing attention as a pathway for converting a harmful pollutant (nitrate) into a value‐added product (ammonia). However, high selectivity toward ammonia (NH3) is imperative for process viability. Optimizing proton availability near the catalyst is important for achieving selective NH3production. Here, the aim is to systematically examine the impacts of proton availability on NO3RR selectivity in a bipolar membrane (BPM)‐based membrane electrode assembly (MEA) system. The BPM generates a proton flux from the membrane toward the catalyst during electrolysis. Thus, the BPM‐MEA system can modulate the proton flux during operation. The impact of interposer layers, proton scavenging electrolytes (CO32−), and catalyst configurations are also examined to identify which local microenvironments favor ammonia formation. It is found that a moderate proton supply allows for an increase in ammonia yield by 576% when compared to the standard MEA setup. This also results in a high selectivity of 26 (NH3over NO2−) at an applied current density of 200 mA cm−2.
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Tuning the Selectivity of Nitrate Reduction via Fine Composition Control of RuPdNP Catalysts
Abstract Herein, aqueous nitrate (NO3−) reduction is used to explore composition‐selectivity relationships of randomly alloyed ruthenium‐palladium nanoparticle catalysts to provide insights into the factors affecting selectivity during this and other industrially relevant catalytic reactions. NO3−reduction proceeds through nitrite (NO2−) and then nitric oxide (NO), before diverging to form either dinitrogen (N2) or ammonium (NH4+) as final products, with N2preferred in potable water treatment but NH4+preferred for nitrogen recovery. It is shown that the NO3−and NO starting feedstocks favor NH4+formation using Ru‐rich catalysts, while Pd‐rich catalysts favor N2formation. Conversely, a NO2−starting feedstock favors NH4+at ≈50 atomic‐% Ru and selectivity decreases with higher Ru content. Mechanistic differences have been probed using density functional theory (DFT). Results show that, for NO3−and NO feedstocks, the thermodynamics of the competing pathways for N–H and N–N formation lead to preferential NH4+ or N2production, respectively, while Ru‐rich surfaces are susceptible to poisoning by NO2−feedstock, which displaces H atoms. This leads to a decrease in overall reduction activity and an increase in selectivity toward N2production. Together, these results demonstrate the importance of tailoring both the reaction pathway thermodynamics and initial reactant binding energies to control overall reaction selectivity.
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- Award ID(s):
- 1922504
- PAR ID:
- 10517831
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small
- Volume:
- 20
- Issue:
- 26
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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