Cobalt-based Metal Organic Framework Derived Heteroatom-doped Carbon Nanomaterials And Its Application In Oxygen Reduction Reaction

In order to achieve the goal of environmental protection and sustainable development,it is particularly urgent to develop the clean and renewable energy or energy conversion devices.Among many energy conversion technologies,fuel cells is considered to be a very attractive new energy conversion device owing to its clean and efficient characteristics.However,the efficiency of fuel cells is limited by the slow kinetics during the cathodic oxygen reduction?ORR?process.Therefore,the high efficient catalysts are needed to increase the reaction efficiency.At present,Pt-based catalysts are still the most effective ORR catalysts,but Pt-based catalysts have high costs,low reserves,easy CO poisoning and poor stability,which seriously hinder the large-scale commercial application of fuel cells.Therefore,it is necessary to explore cheap,efficient and highly stable Pt-based catalyst substitutes.Heteroatom-doped carbon materials derived from MOFs materials have proved to be one of the most promising noble metal catalyst alternatives due to the unique characteristics of simple preparation,low price,high stability and good methanol tolerance.In this study,based on Co-based MOF,two high-efficiency oxygen reduction catalysts were prepared by complexing with graphene oxide?GO?and co-doping heteroatoms,the details are as follows:?1?A series of GO-doped Co-MOF-GO?m?precursors were synthesized with hydrothermal method by using cobalt nitrate hexahydrate,GO,terephthalic acid,triethylenediamine,and urea as raw materials.Urea were introduced into the channels of Co-MOF-GO?m?to obtain a series of Co-MOF-GO?m?/Urea?n?template materials.Then a series of black Co-GO?m?-C/N?n?catalysts were synthesized by calcining these Co-MOF-GO?m?/Urea?n?materials at high temperature in a closed circumstance.The optimal Co-GO?50?-C/N?2.5?catalyst with a high degree of graphitization,an appropriate amount of nitrogen content,and a plentiful pore structure exhibits excellent ORR performance in alkaline media,the onset potential and half-wave potential are 0.934 V and 0.832 V?vs RHE?,respectively,which is very close to that of the commercial 20 wt%Pt/C catalyst.Moreover the Co-GO?50?-C/N?2.5?catalyst also exhibits a better fuel molecule tolerance and better stability than the commercial Pt/C catalyst.?2?A facile and repeatable pathway has been developed to synthesize the non-noble metal nanoparticles and N,P co-doped carbon material as high efficient ORR catalyst.First,a novel larger ligand was constructed by utilizing the interaction between N-ligands and P-source,and then construct a series of N,P-containing Co-based MOFs?P-ZIF?by employing the parallel feed-in method with the novel N,P-containing ligand and 2-methylimidazole as mixed linkers.With the P-ZIF materials as templates,the Co-Co₂P@NC-P composites can be obtained by simply calcining them in an airtight circumstance at high temperatures.The onset potential and half-wave potential of the optimal Co-Co₂P@NC-P₃-700 catalyst is 0.981 V and 0.840 V?vs RHE?,which is higher than that of commercial 20 wt%Pt/C catalysts for 27 mV and 10 mV,respectively,and also superior to the pristine ZIF-67 derived Co@NC-700 catalysts for 46 mV and 36 mV,respectively.In addition,Co-Co₂P@NC-P₃-700 catalysts has better fuel molecule tolerance and stability than commercial Pt/C catalysts.