(532cg) Investigation of Active Sites for Electrochemical Bromine Evolution Using Nitrogen-Doped Carbon Nanostructures | AIChE

(532cg) Investigation of Active Sites for Electrochemical Bromine Evolution Using Nitrogen-Doped Carbon Nanostructures


Hightower, J., University of Pittsburgh
Jain, D., Clariant Corporation
Co, A., The Ohio State University
Asthagiri, A., The Ohio State University
Ozkan, U., The Ohio State University
Bromine (Br2) is widely used to produce brominated flame retardants, which are ubiquitous in the electronics and plastics industries. The U.S. and Israel account for 80% of the global Br2 production. Despite its ever-increasing demand, conventional Br2 manufacturing employs outdated techniques requiring hazardous chlorine gas as the bromide oxidizing agent or expensive Platinum (Pt) based electrodes for hydrogen evolution reaction (HER) on the cathode (while the Br2 evolution reaction (BER) takes place on the anode). We proposed a novel approach for more economical Br2 production, by replacing HER with oxygen reduction reaction (ORR) on the cathode, using nitrogen doped carbon nanostructures (CNx) on both electrodes.

Recently, we reported CNx as a robust BER catalyst in comparison to commercial Pt/C. CNx is also a promising ORR catalyst and several chemical probes have been used previously to provide insights into its active sites for ORR. In particular, the phosphate anion (PO4-), was found to be the sole probe that poisoned CNx for ORR. In this work PO4- has been used to distinguish the sites responsible for ORR and BER over CNx. It was found, that while the ORR performance degraded with increasing PO4- concentration, the BER performance remained unaffected. Pyridinic nitrogen or the positively charged carbon atom adjacent to it, is widely reported to be correlated with ORR activity. Previously we have shown that the pyridinic nitrogen concentration of CNx decreased with PO4- adsorption. However, the lack of PO4- poisoning in case of BER in conjunction with density functional theory (DFT) calculations, show that BER active sites differ from ORR active sites. Additionally, post reaction characterization using X-ray photoelectron spectroscopy, further elucidated the nature of BER active sites. This work aids in the rational design of inexpensive catalysts for sustainable electrochemical Br2 generation at low temperature, eliminating the need for hazardous reactants.