Preparation Of Doped Carbon-base Catalysts For Oxygen Reduction Reaction And Their Electrocatalytic Properties

Energy consumption and production dependent on fossil fuels are extremely detrimental to the development of the world economy and ecology.At present,researchers are working on the development of green and efficient new energy sources.Oxygen reduction reaction(ORR)is one of the essential electrochemical reaction processes in metal-air cells and fuel cells of new energy utilization devices.However,due to the high cost and low durability of platinum-based catalysts used in the ORR,the commercial application is seriously hindered.Hence,in view of the problems faced by commercial fuel cells,it is very important to develop cheap and efficient non-precious metal ORR catalysts,which is the key to determine the further market-oriented application of commercial fuel cells.Based on this,three new ORR catalysts based on functionalized carbon materials were designed and synthesized from the development of alternative platinum-based non-noble metal catalysts.(1)A sheet-like nitrogen-doped graphene/porous carbon composite(NPGC)was prepared by using cheap glucose as carbon source and melamine as nitrogen source after high temperature carbonization and activation.The morphology and structure of the prepared materials were analyzed by means of SEM,XRD,Raman and XPS,and the electrochemical properties of the composites were analyzed by instruments such as rotating disk electrodes ORR used.The study showed that the limit current density of the NPGC was 4.7 mA·cm-2,showing ORR activity comparable to commercial Pt/C(20 wt%)in alkaline electrolyte.Its average number of transferred electrons is 3.8,which is a nearly 4 electrons reaction pathway in the oxygen reduction reaction.The composite exhibits good stability compared to commercial platinum-based catalysts.After 6 h of continuous testing,the initial current density retention efficiency of the NPGC can reach 86%.In addition,NPGC has good resistance to CH3OH cross-border effects" and its current density does not change significantly after methanol injection.(2)The Fe3O4 nanocrystals were mechanically anchored on the reduced graphene oxide surface by low temperature pyrolysis using mechanical stirring method using FeCl3·6H2O and GO as raw materials to obtain Fe3O4/rGO composites.Its worth noting that Fe3O4 nanoparticles are directly embedded into the rGO,without the use of any molecular binder or linker.The morphology and structure of the prepared materials were analyzed by means of SEM,TEM,XRD,Raman and XPS.The ORR performance of Fe3O4/rGO as oxygen reduction catalyst under alkaline conditions was tested.The study shows that the catalyst has remarkable activity for ORR,in which the limiting current density can reach 4.5 mA·cm-2,and the Tafel slope is close to the commercial Pt based catalyst.The RDE and the RRDE test calculations mutually confirm that the reaction of oxygen in this catalyst material is a four-electron reaction pathway with low H2O2 yield.Moreover,compared with commercial platinum-based catalysts,Fe3O4/rGO have better long-term stability and methanol resistance.In the case of continuous testing for 6 h,the initial current density retention can be as high as 91%,which is expected to be due in actual production.(3)The ZIF-67@ZIF-8 of core-shell structure was used as the precursor for the preparation of carbon materials.The Co,N codoped hierarchical porous carbon composites(Co-N@PC)were prepared by one-pot method after high temperature carbonization.The morphology and structure of the prepared materials were analyzed by means of SEM,XRD,Raman and XPS,and the electrochemical properties of the composites were analyzed using ORR rotating disk electrode equipment.The study shows that the limit current density of Co-N@PC is close to Pt/C in alkaline electrolyte,especially its half-wave potential is 0.831 V,which has excellent ORR performance.The average number of electrons transferred during the ORR reaction is 3.9,which is dominated by 4 electron paths.The excellent oxygen reduction performance is attributed to the accelerated electron transfer of the material by fractional porous carbon during the testing process.This method is simple and controllable,which provides a new idea for the preparation of non-noble metal catalysts.