Oxygen reduction reaction mechanism on nitrogen-doped graphene: A density functional theory study

Nitrogen-doped graphene (N-graphene) was reported to exhibit a good activity experimentally as an electrocatalyst of oxygen reduction reaction (ORR) on the cathode of fuel cells under the condition of electropotential of ∼0.04 V (vs. NHE) and pH of 14. This material is promising to replace or partially replace the conventionally used Pt. In order to understand the experimental results, ORR catalyzed by N-graphene is studied using density functional theory (DFT) calculations under experimental conditions taking the solvent, surface adsorbates, and coverages into consideration. Two mechanisms, i.e., dissociative and associative mechanisms, over different N-doping configurations are investigated. The results show that N-graphene surface is covered by O with 1/6 monolayer, which is used for reactions in this work. The transition state of each elementary step was identified using four different approaches, which give rise to a similar chemistry. A full energy profile including all the reaction barriers shows that the associative mechanism is more energetically favored than the dissociative one and the removal of O species from the surface is the rate-determining step.

The electrocatalytic reduction of oxygen on nitrogen-doped graphene in alkaline solution follows an associative mechanism which is energetically more favorable than the dissociative mechanism. The rate-limiting step of the reaction is the O(ads) removal from the surface. The formation of peroxide is energetically unfavored.Figure optionsDownload high-quality image (73 K)Download as PowerPoint slideHighlights
► The reaction kinetics of oxygen reduction reaction (ORR) on nitrogen-doped graphene is illuminated.
► The water effect, bias effect, pH, surface coverages, and charges on electrode under experimental conditions are considered.
► The full energy profile of ORR including all barriers is presented.
► Effect of charges on activation barriers is investigated.