Hidrophobic Fe-Mo electrodes as electrocatalist for nitrogen Electroreduction Rodrigo del Rio 1 , Mauricio Isaacs 1 , Daniel Correa-Encalada 1,2 , Macarena Kroff 1,2 , Galo Ramirez 1 , Enrique Dalchiele 2 , Samuel Hevia 1,2 1 Pontificia Universidad Católica de Chile, Chile, 2 Instituto de Física, Uruguay Carbon dioxide, which in 2020 reached approximately 35,000 million metric tons in emissions 1 and Ammonia production by the Haber-Bosh process may part of the problem, in 2010, out of 157.3 million metric tons of NH 3 produced, there was a total of 451 million metric tons of CO 2 emissions 2 . The electrocatalytic nitrogen reduction reaction (NRR) to obtain ammonia is a promising alternative to getting this raw material with lower greenhouse gas emissions 3, 4 . For this reason, this work shows the fabrication of Fe-Mo electrodes and their application in the electrocatalytic obtention of ammonia [4, 5]. The electrodes were prepared by applying a fixed potential on a copper electrode in FeSO 4 x7H 2 O y Na 2 MoO 4 x2H 2 O aqueous solution. The electrodes were characterized by X-Ray diffraction, FESEM microscopy and after that they were covered with Zeolitic Imidazolate Framework (ZIF-71), PVDF and PTFE films by spin coating. Different electrodes were prepared by electrolysis and tested for electrocatalysis of NRR. The best activity was found for the electrode with a 1:1 Fe:Mo composition. This electrode was characterized by FESEM and a homogeneous distribution of Fe and Mo was observed (figure 1).
These electrodes were assayed as electrocatalysts to the NRR recording polarization curves on Ar and N 2 saturated atmosphere, where the electrode with a composition of 1:1 Fe-Mo, showed a greater reduction current compared with the same experiment in absence of N 2 (Figure 2). This electrode showed a current density 40 % greater at 1.0 V. In electrolysis at 1,2 V, this electrode shows a faradaic efficiency of around 10 %. This electrode was covered with different hydrophobic films, Zeolitic Imidazolate Framework (ZIF-71), PDVF, and PTFE. The hydrophobic behavior of the modified surfaces was similar as evaluated by their contact angle. The polarization curves using the modified electrodes were evaluated by comparing the current density at -1.0 V vs Ag/AgCl and PTFE showed the best electrocatalytic behavior showing the greater difference in the current in N 2 versus Ar. This difference was 2 times at -1,0 V and 4,7 times at -1,2 V, showing that this modifier increases the hydrophobicity and avoids the interference of the hydrogen reduction.
References 1. Solution, C. o. C. a. E. Global Emissions. https://www.c2es.org/content/international-emissions/. 2. Boerner, L. K. https://cen.acs.org/environment/green-chemistry/Industrial-ammonia-production-emits-CO2/97/i24 3. Hu, L., Khaniya, A., Wang, J., Chen, G., Kaden,W.E., Feng , X., ACS Catal. 2018, 8, 9312−9319. 4. Xue Zhao, Guangzhi Hu, Gao-Feng Chen, Haibo Zhang, Shusheng Zhang, Haihui Wang Adv. Mater. 2021, 33, 2007650. 5. Lu,K.,Xia, F.,Li,B.,Liu, Y.,Razak, I.,Gao, S.,Kaelin, J.,Brown, D.E.,Cheng, Y., ACS Nano 2021, 15, 16887−16895.
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