Modulating the Nitrogen Species of N-Doped Graphene—A Step Forward Towards Improving the Selectivity of Electrochemical Reactions

Global challenges such as alternative clean energy sources and environmental remediation issues can find some options with electrochemical reactions. Nitrogen doped (N-doped) graphitic nanostructures have been emerging as promising candidates to overcome precious metal electrocatalysts drawbacks such as increasing costs and scarcity and even some corrosion effects by side-products, due to the Earth-abundant availability of carbon and their chemical stability.<br/>The N-doping of graphitic nanostructures commonly includes different nitrogen species such as pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen. Each of such different nitrogen species sites present different properties and therefore electrochemical activity and they could even dictate different reaction pathway. For instance, for the Oxygen reduction reaction, it has been shown that pyridinic nitrogen favors the 4-electron pathway while the graphitic nitrogen favor the 2-electron pathway [1-2]. Then, to be able to modulate the proportion of nitrogen species in N-doped Graphene becomes a challenge of paramount importance in order to improve its selectivity as electrocatalyst for important electrochemical reactions.<br/>Here, we will start showing some evidence in the selectivity dependence on different nitrogen species for the Oxygen reduction reaction (ORR) and the Iodide reduction reaction (IRR) for N-doped graphitic carbon nanostructures. Then, we will describe experimental and DFT calculations results on the understanding of the N-doping process by post-synthesis treatments using graphene oxide as precursor; this results show the feasibility of two different approaches for modulating the nitrogen species proportions in N-doped graphene. Following, we will show the effect of this nitrogen species proportion modulation on the ORR selectivity for N-doped graphene as the electrocatalyst. We will end up discussing alternative N-doping approaches with a special emphasis on nitrogen species proportion modulation.<br/><br/>Acknowledgements: We thank financial support from the DGAPA-UNAM through PAPIIT project IN111223 and IN105722. Calculations were performed in the DGTIC-UNAM Supercomputing Center projects LANCAD-UNAM-DGTIC-051 and LANCAD-UNAM-DGTIC-382. We thank Francisco Ruiz, Eduardo Murillo, David Dominguez, Lazaro Huerta, Eloisa Aparicio, Israel Gradilla, Jesus Diaz and Jaime Mendoza for technical support. Similarly, we are very thankful to all the AG&P groupmates for fruitful discussions.<br/><br/>References:<br/>[1] Contreras E. et al. Nanoscale 11: 2829 (2019).<br/>[2] Fernandez-Escamilla H.N. et al. Adv. Ener. Mater. 11: 2002459 (2021).