Insight into the effect of electrolyte ions docked in subnanopores of metal-free carbon cathode on the ORR activity

M Florent and R Dupuis and K Ioannidou and RJM Pellenq and TJ Bandosz, CARBON, 239, 120324 (2025).

DOI: 10.1016/j.carbon.2025.120324

We combined electrocatalytic measurements to reactive dynamics and meta- dynamics simulations in voltage-polarized conditions to better understand the mechanism of metal-free nanoporous-carbon-assisted-O2 reduction reaction (ORR) in an aqueous alkaline electrolyte. We use a reactive constant voltage simulation framework to show that the surface in pores larger than 1 nm can be sufficiently polarized to induce O2 dissociation as experimentally observed. Simulations showed that at 0V, pH =13 reduces a free energy barrier for O2 adsorption inside sub- nanopores (pores less than 1 nm) and at 0.7V vs. RHE potential of a cathode O2 splitting occurs, leading to OH-formation in these pores and also in larger pores. ORR in these latter environments is induced by a strong and global surface electrostatic field that is the consequence of the ion docking in sub-nanopores. The applied voltage causes cations to enter the pores only partially hydrated or bare. Their docking increases the charge on carbon atoms, and when O2 is in their proximity it splits. Overall, combining the simulation results with experimental ones suggests that the extent of metal-free nanoporous-carbon-assisted O2 reduction is affected by the amount of sub-nanopores. Surface chemistry/some level of carbon hydrophilicity in larger pores is also important since it affects the electrolyte and oxygen transport to these subnanopores.

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