Highly active nitrogen – doped carbon nanostructures as electrocatalysts for bromine evolution reaction: A combined experimental and DFT study

Electrocatalytic bromine evolution reaction (BER) is significant for bromine production, energy storage, and wastewater treatment applications. Previously reported electrocatalysts for BER either include unstable graphite anodes or precious metal-containing materials. To overcome their disadvantages, this work has proposed, for the first time, the use of nitrogen-doped carbon nanostructures (CNx) as anode catalysts for BER in acidic medium. In terms of BER activity, CNx outperforms both Vulcan Carbon and commercial 10 % Pt/C at bromide concentration as low as 0.025 M. CNx also exhibits high BER selectivity and remarkable stability at highly oxidizing potentials. Tafel slope was measured to be ∼ 120 mV/dec supporting a first electron transfer limiting step for BER on CNx. The high activity and stability of CNx is attributed to several nitrogen-doped carbon sites in its graphitic matrix, which have been examined using DFT. The inclusion of oxygen evolution reaction (OER) intermediates is critical to identify BER active sites accurately, as the most active sites (zigzag pyridinic, zigzag oxide, and pyrrolic oxide) proceed via a OH*-mediated Volmer-Heyrovsky mechanism. For these sites, DFT predicts that the potential determining step is the first electron transfer to form Br* in agreement with the experimental Tafel slope. Comparison to post-reaction XPS shows good agreement between DFT predicted Br* structures. This work thus provides a direction for the rational design of CNx electrocatalysts for BER.