Preparation of Nafion Membranes for Reproducible Ammonia Quantification in Nitrogen Reduction Reaction Experiments

• Published in: Angewandte Chemie International Edition Vol. 59; no. 51; pp. 22938 - 22942
• Main Authors: Hanifpour, Fatemeh, Sveinbjörnsson, Arnar, Canales, Camila Pía, Skúlason, Egill, Flosadóttir, Helga Dögg
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 14-12-2020
• Edition: International ed. in English
• Subjects: Air pollution; Ammonia; Ammonia - analysis; Ammonium; Catalysis; Chemical reduction; Contamination; Electrochemical Techniques; Electrochemistry; Experiments; Fertilizers; Fluorocarbon Polymers - chemistry; Membranes; Nafion; Nitrogen; Nitrogen - chemistry; nitrogen reduction reaction; Oxidation-Reduction; Pollution sources; Pretreatment; pretreatment methods; Temperature; Wind direction; ammonia; Nafion; pretreatment methods; nitrogen reduction reaction; contamination
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202007998

This study highlights the importance of following a strict protocol for Nafion membrane pretreatment for electrochemical nitrogen reduction reaction experiments. Atmospheric ammonia pollution can be introduced to the experimental setup through membranes and interpreted falsely as catalysis product from N2. The sources of ammonia contamination vary drastically between locations worldwide and even within the same location between days depending on temperature, wind direction, fertilizer use, and manure accumulation in its vicinity. The study shows that significant amounts of ammonium is accumulated in the membranes after commonly practiced pretreatment methods, where the amount depends on the ammonia concentration in the surrounding of the experiment. Therefore, we introduce a new pretreatment method which removes all the ammonium in the membrane. The membranes can be stored for several days but a short final step in the method needs to be carried out right before NRR experiments.
A utilizable method of Nafion pretreatment for the nitrogen reduction reaction (NRR) is proposed. This method rules out a critical source of false positive results in NRR experiments. Failing to follow these steps can introduce variable amounts of atmospheric ammonia to the setup, which may be interpreted falsely as catalysis product. This observation questions previous results reported in this field.