| Fossil energy is a non-renewable energy,and the increasingly depletion of resources and environmental problems caused by its combustion products have become increasingly prominent,so the research and development of new energy and its application are extremely urgent.Among all kinds of new energy sources,zero carbon emission hydrogen energy has attracted great attention.With the development of hydrogen production and hydrogen storage technology,hydrogen fuel cells which convert hydrogen energy into electric energy have a broad market prospect.At present,the slow cathodic oxygen reduction reaction(ORR)is one of the important factors limiting the large-scale application of hydrogen fuel cells.Traditional platinum-based catalytic materials are expensive due to resource scarcity.At the same time,platinum element is easy to accumulate on the carrier and even fall off,causing inactivation.Therefore,it is of great significance to develop new ORR catalytic materials,among which the low dimensional carbon nanomaterials containing doped elements have the advantages of diverse forms,rich sources,good stability and low cost,and are a very promising electro-catalytic materials.In this paper,ORR activity of phosphorus/nitrogen doped graphene nanoribons was studied by density functional theory(DFT).The main contents are as follows:First,the edge of armchair p-doped graphene nanoribbons(PGNR)were studied.PGNR has good adsorption performance,P atom is the active site,and has positive charge density value and electron spin density value.The ORR path of PGNR is relatively complex and may produce ~*OOH configuration,but this configuration exists for a very short time,so the ORR does not produce hydrogen peroxide.In addition,the calculation results of reaction barrier and free energy show that ORR cannot be carried out to the end.Although PGNR has good adsorption performance and ORR does not produce hydrogen peroxide,it is very difficult to obtain better ORR performance by adjusting the energy of this complex reaction.Based on ORR activity of P doped graphene nanoribbons containing O,it was found that the active site of the substrate was C atom adjacent to P atom.Since the active site cannot directly adsorb oxygen,ORR under the weak adsorption mechanism is considered.The calculation shows that the energy released by other hydrogenation steps is similar except that the adsorption reaction is endothermic,indicating that the catalytic performance of The C atomic site is better.The ORR mechanism of P-doped graphene nanoribbons(PD-GNR)with edge defects was studied,and it was found that PD-GNR has good adsorption performance.The ORR of PD-GNR is the dissociation mechanism,because the first step of hydrogenation to form ~*OOH configuration will increase the system energy by 0.12 eV.In addition,the heat release in each step of hydrogenation reaction is relatively close,making PD-GNR have an overpotential of about 0.52 eV.Considering the modification of substrate by changing doped elements,N-doped graphene nanoribons(ND-GNR)with edge defects were studied.The ORR of ND-GNR tends to dissociate,so ~*OOH configuration does not form.And the ORR overpotential of ND-GNR is 0.36 V,lower than that of Pt as 0.45 V.Finally,the active sites and their distribution were qualitatively analyzed through the change of the base resonance energy,revealing that the width of the nanoribbon could adjust the adsorption energy and overpotential of n-doped graphene nanoribbon containing edge defects. |
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