Electrodeposits of MoSx on FTO electrodes and their application in the electrochemical redution of N 2 Mauricio Isaacs , Elias Leiva, Rodrigo del Río, Esteban Landaeta Pontificia Universidad Católica de Chile, Chile The Haber-Bosch process is currently the most efficient method of obtaining ammonia at industrial level, with the disadvantage that it requires extreme operating conditions, and involves a large production of greenhouse gases. As a result of the above, the present work seeks the use of compounds based on transition metal dichalcogenides (TMD's) and modifications on them, as active materials for the electroreduction of N 2 (NRR), since the process allows obtaining NH 3 under more moderate conditions. The obtaining of these catalysts is carried out by the procedures described by Hu et. al. 1 electrodepositing mainly MoS 2 -MoS 3 on Fluorine Doped Tin Oxide (FTO) electrodes. For this purpose, electrodeposition of [MoS 4 ] 2- anion was performed by cyclic voltammetry (CV) in a potential range from 0.1 to -1 V (vs Ag/AgCl), obtaining fine dark crimson-colored particles on the electrodic surface. The characterization of these films was performed by physical methods, directly on the FTO substrate. UV-visible, IR-ATR, Raman spectroscopy (see figure 1), and SEM-EDX studies were performed, obtaining in all cases consistent signals with the presence of MoSx and MoOy in the films, in agreement with literature 2,3,4 . Electrochemical tests were also carried out to determine the activity of the films formed against NRR, indicating that the films show favorable activity for this reaction (see Fig.2). Electrolysis was carried out at different potentials, obtaining an ammonia production peak determined by the indophenol method at -0.6 V vs. Ag/AgCl, with a calculated faradaic efficiency of 4.6 %. Further research is focused on determining selectivity improvements of the modified electrodes towards NRR instead of favoring HER
Fig 1. (left) 2D Raman, taken using filter at 414 cm-1. The image was taken in a 10x10 µm section. The applied filter corresponds to a signal associated with the E 1 2g band of molybdenum sulfide, corresponding to Mo-S interactions in layers of the electrodeposit. (right) Average Raman spectrum of MoSx films on FTO electrode. The signals near 400 cm-1 correspond to the E 1 2g band associated with Mo-S interactions in the electrodeposit, there are also two signals at about 589 and 650 cm-1 associated with 2E 1g and D bands respectively, these signals are implied to correspond to interlayer S-Mo-S bond vibrations and Mo=S signals in nanoparticulate structures.
Figure 2. polarization curve recorded in 0.25 M LiClO 4 at 1 mVs -1 , the inset graph shows an approach of the zone between 0 and -0.7 V. A decrease in overpotential for NRR was observed, indicating that the electrodes show favorable activity for this reaction. References
1. Chem. Sci., 2011, 2, 1262ACS Appl. Mater. Interfaces 2019, 11, 32879−32886 2. ACS Appl. Mater. Interfaces 2017, 9, 18675−18681Langmuir 2017, 33, 9354−9360
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