Theoretical Study On Design And Performances Of Electrocatalysts For Oxygen Reduction Reaction

Proton exchange membrane fuel cells?PEMFCs?are regarded as a clear,efficient and environmentally friendly energy storage device.The oxygen reduction reaction?ORR?at the cathode is a kinetically slow reaction process,requiring being accelerated by high-performance catalysts.The most commonly used catalysts in such process are Pt and Pt-based ones,but the poor durability and high cost have limited their commercially application.it is becoming urgent and important to develop new and low-cost catalysts for oxygen reduction reaction.But it takes long time to synthesis a new catalyst in the lab and it is difficult to accurately observe the reaction process.Theoretical calculation has been proved to be effective in evaluating the performances for oxygen reduction reaction.In this work,we designed three kinds of catalysts for oxygen reduction reaction.And Density Functional Theory was employed to evaluate and characterize their performances.This work will help to provide some theoretical guidance for the selection and synthesis of oxygen reduction reaction catalysts in the future.The research contents and corresponding results are summarized as follows:1.Introduction.In this section,we introduced the type and basic principle for fuel cells,the basic principle for oxygen reduction reaction,commonly used catalyst and the basic principle and development of density functional theory.2.The catalyzed oxygen reduction reaction of Pt-doped oxide graphene in acidic medium.Based on graphene,we designed the catalysts of Pt-doped graphene and Pt-doped oxide graphene for oxygen reduction reaction.Density functional theory?DFT?is conducted to study the oxygen reduction reaction?ORR?mechanisms on Pt-doped graphene oxide systems?-COOH,-OH,-O-,-MIX and-MIX2?and perfect graphene electrocatalyst in acidic medium.The adsorptive property of the ORR intermediates?O₂,O,OOH,OH,H₂O and H₂O₂?are calculated.Meanwhile,the reaction pathways during the ORR process are simulated and the energy of each reaction is observed.The results show that graphene oxide is superior to perfect graphene in O2 activation,intermediate adsorption,doping difficulty?defect formation energy?,band gap and relative energy reduction in the reaction.The Pt-OH-Gand Pt-O-G are considered to be the better catalysts.And their limiting potential were 1.4V and 2.34V,respectively according to the results of the Gibbs free energy calculation.3.The influence of the ligand on the activity of porphyrin-catalyzed for oxygen reduction reaction.The effect of electron-donating groups and electron-withdrawing groups on the activity of porphyrin catalyzed oxygen reduction was studied.The calculation results showed that the ligand groups can significantly Increasethe oxygen reduction activity of porphyrin molecules.Compared to the donor ligand,electron-absorbing ligands have higher catalytic activity in coordination with porphyrins.The highest activity of donor electron ligands can be achieved when the porphyrins are tetrad–coordinated with them.Among designed electron-donor ligand catalysts,TrOPPand PNPP can provide the limiting potential of about 2.4V.When the electron-withdrawing groups are coordinated,there is only one catalyst that reacts through the2e^-path,others react through the 4e^-path and provide about 2.4V of the limiting potential.4.The influence of the electron-withdrawing ligand on the activity of corrole-catalyzed for oxygen reduction reaction.Based on the resultsabove section,the influence of the ligand by changing the macrocyclic compounds was further investigated.We selected the best performedligand of trifluoromethyl aniline to design five kinds of corrole-catalyst.The calculation results indicated that the introduction of ligands can obviously enhance the catalytic performances of oxygen reduction,transfer the originally uncatalyzed oxygen reduction reaction into excellent oxygen reduction electrocatalyst.Finally,three kinds of catalyst named CL1?CL2 and CL3 were obtained,whichcould provide the limiting potential of about 1.8 V.