(544ch) Exploring the Effect of Chloride-Ion Exposure on CNx and Fe-N-C Catalysts for Application As Oxygen Depolarized Cathodes in Chlorine Production

Electrolysis of hydrochloric acid is a widely used process for manufacture of chlorine gas, which is an essential chemical in majority of processes that produce many indispensable products including polymers like polyvinyl chloride, polyurethanes and chloroaromatics. Traditional HCl electrolysis suffers from its high energy requirements, however, significant amount of energy can be conserved by replacing the traditional H₂-evolving electrode by an oxygen depolarized cathode (ODC) where O₂ is reduced instead of protons¹. Successful operation of this technology therefore depends on the oxygen reduction reaction (ORR) activity and stability of ODC catalysts, along with high resistance to poisoning in the presence of chloride anions². State-of-the-art catalysts used for ORR are Pt-based and are highly susceptible to poisoning in the presence of Cl^- ions. Rhodium sulfide based materials have also been used as catalysts for ODCs³. However, the use of highly toxic H₂S gas in the synthesis of Rh_xS_y/C and the exorbitant cost of Rh limits the viability of ODC technology². In this work, we have evaluated the use of nitrogen-doped carbon nanostructures (CN_x) and iron-nitrogen coordinated carbon-supported materials (FeNC) as ODC catalysts in Cl₂ manufacturing process. These catalysts have been shown to demonstrate good ORR performance in acidic media^4-5. Our current focus is to further investigate their resistance to poisoning in the presence of chloride anions.

The ORR electrocatalytic activity of FeNC catalysts was observed to reduce after exposure to chloride anions, while CN_x catalysts showed an enhancement in ORR activity after chloride-ion exposure². X-ray photoelectron spectroscopy (XPS), Raman and infrared spectroscopy, temperature programmed desorption (TPD) and near edge X-ray absorption fine structure measurements were used to shed light on the chlorine species incorporated in CN_x that contribute to improved ORR activity⁶. FeNC catalysts, which exhibit irreversible poisoning in the presence of Cl^- ions, were characterized using X-ray absorption spectroscopy to study the change in co-ordination environment of Fe centers after Cl^- exposure. These observations further re-emphasize the difference in nature of ORR active sites in FeNC and CN_x catalysts⁴.

References

1. Federico, F.; Martelli, G.; Pinter, D. In Gas-diffusion electrodes for chlorine-related (production) technologies, Modern Chlor-Alkali Technology, Proceedings of the 2000 London International Chlorine Symposium Organized by SCI’s Electrochemical Technology Group, London, 2008; pp 114-127.
2. Mamtani, K.; Jain, D.; Ozkan, U. S., Investigation of Chloride Poisoning Resistance for Nitrogen-Doped Carbon Nanostructures as Oxygen Depolarized Cathode Catalysts in Acidic Media. Catal. Lett. 2017, 1-7.
3. Gullá, A. F.; Gancs, L.; Allen, R. J.; Mukerjee, S., Carbon-supported low-loading rhodium sulfide electrocatalysts for oxygen depolarized cathode applications. Appl. Catal. A-Gen. 2007, 326 (2), 227-235.
4. Mamtani, K.; Ozkan, U. S., Heteroatom-doped carbon nanostructures as oxygen reduction reaction catalysts in acidic media: An overview". Catal. Lett. 2015, 145, 436-450.
5. Lefevre, M.; Proietti, E.; Jaouen, F.; Dodelet, J. P., Iron-based catalysts with improved oxygen reduction activity in polymer electrolyte fuel cells. Science 2009, 324, 71-74.
6. Jain, D.; Mamtani, K.; Gustin, V.; Gunduz, S.; Celik, G.; Waluyo, I.; Hunt, A.; Co, A. C.; Ozkan, U. S., Enhancement in Oxygen Reduction Reaction Activity of CNx in Acidic Media through Chloride-ion Exposure. ChemElectroChem 2018, Accepted.