Is It Appropriate to Use the Nafion Membrane in Electrocatalytic N₂ Reduction?

Abstract

The electrocatalytic N2 reduction reaction (ENRR) to ammonia has attracted much attention due to the mild operating conditions, in which the Nafion membrane is generally adopted to separate the ammonia from the anode products. However, it has been mentioned that the Nafion membrane allows ammonia to pass through and traps the ammonia to some extent, but powerful confirmation experiments and effective solutions are still lacking. Herein, it is experimentally confirmed that the use of the Nafion membrane in the ENRR is inappropriate, based on the results that the ammonia can pass through the membrane, be adsorbed on the membrane, and interact with the membrane. This causes a measurement error and accelerates the membrane degradation process, which is unfavorable for ammonia quantification and the long‐term stability operation of the ENRR in practical application. Also, for the first time, a more accurate method to evaluate the activity of the ENRR electrocatalyst using a salt bridge to replace the Nafion membrane is presented.

Recent Advances in Electrochemical Synthesis of Ammonia through Nitrogen Reduction under Ambient Conditions

“…In 2018, Tao and co‐worker used density functional theory calculations to show that the Ru sites with oxygen vacancies are beneficial for N 2 adsorption . It is worth noting that Tao also pointed out that the addition of ZrO 2 increased the Faraday efficiency, which was due to the inhibitory effect of ZrO 2 on the HER, which is consistent with the calculation results of Nørskov …”

“…For the use of membrane, Qiu et al. confirm that Nafion membrane is inappropriate for N 2 reduction reaction because it allows NH 3 to pass through, and traps NH 3 to some extent …”

“…Nørskov and co‐workers pointed out that when the generated hydrogen or ammonia is desorbed, the re‐vacuum active center can be occupied by H (from the recombination of H + and an e − ) or N 2 . When there are enough electrons and protons around the active center, the HER will occupy the main position from the thermodynamic and kinetic points of view, and the NRR will be suppressed . Theoretically, if the number of protons around the active center is controlled and there is enough N 2 , then N 2 will be adsorbed by the active center, and the HER will be effectively inhibited.…”

Photocatalytic and Photoelectrochemical Systems: Similarities and Differences

“…Nevertheless, the possible physical and chemical interactions between the Nafion membrane and the redox products should be carefully avoided when designing the photoelectrochemical reactors. Very recently, Ren et al reported that the Nafion membrane allows ammonia to pass through and absorbs the ammonia to some extent, which may cause a measurement error up to around 30% . Similar considerations should be taken into the design of photoelectrochemical reactors for CO 2 conversion and pollutant degradation processes in the future.…”

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

“…[1,2,9] Ren and co-workers have concluded that the use of Nafion membranes in NRR experiments may be inappropriate, as ammonium can pass through the membrane, be adsorbed on the membrane or, even, interact with it, which is unfavorable for reliable and reproducible quantification of the product. [10] Although long-term application of Nafion (7-10 days) is not suitable owing to loss of conductivity, Nafion membranes are nevertheless widely used in short term (ca. 2 h) NRR experiments today and deserve further investigation on pretreatment protocols to obtain as reliable data as possible.…”