Preparation Of Carbon Supported Copper-Based Materials And Study Of Oxygen Reduction Reaction Properties

Oxygen reduction reaction?ORR?with slow kinetic process is a rate control step for fuel cells.It requires catalysts to reduce its overpotential.At present,commercial platinum carbon?Pt/C?as a fuel cell cathode catalyst shows excellent oxygen reduction performance.But the large scale commercial application in fuel cells has been limited due to its susceptibility to CO poisoning and high cost as well as other shortages.Therefore,it is of great significance to seek an efficient,stable and inexpensive non-precious metal oxygen reduction catalyst as a substitute of Pt/C.In recent years,copper?Cu?has been widely used in various catalytic reactions due to its wide source,high electrical conductivity,and stable properties.Simultaneously,Cu has very excellent oxygen reduction activity in theoretical calculations,but it is difficult to achieve expectations in experiments.In order to prepare electrocatalysts with higher oxygen reduction activity,this paper mainly focuses on the carbon-supported monometallic Cu,bimetallic Cu-Zn and Cu-Ni composite catalysts.The design and preparation of catalyst precursors,the carbonization temperature of precursor,the structure and morphology of the catalyst and the ORR catalytic performance of the catalyst,etc.were systematically studied to clarify the possible active sites of the catalyst and the ORR catalytic mechanism.The main research contents and results are as follows:?1?The N/C supported bimetallic Cu-Zn catalysts?Cu-Zn-N/C?with high N content were synthesized via a simple metal-organic framework?MOFs?-derived method.The as-prepared Cu-Zn-N/C catalyst presents superior catalytic activity toward ORR with an onset potential of 0.90 V,a half-wave potential of 0.79 V and a diffusion limiting current density of 5.82 mA cm^-22 in 0.1 M KOH electrolyte.It is found that Cu exists in three forms in the Cu-Zn-N/C catalysts:Cu particles,Cu high valent single atoms and Cu zero valent single atoms that embedded in the carbon substrate.The electrocatalytic performance of N/C supported bimetallic Cu-Zn catalysts were attributed to the synergistic effect of multiple factors,such as high N content,the different Cu forms,the pore structure and high surface area created by the Zn evaporation,etc.In addition,as an efficient Cu-based catalyst for many applications,we found that the as-prepared catalyst can selectively oxidize1,2-propanediol to lactic acid with 75.7%selectivity at 82.8%conversion.?2?A simple and efficient method was developed to prepare copper-carbon?Cu-C?catalyst with high ORR activity via direct pyrolysis of the mixture of metal salts?Cu?NO₃?₂·3H₂O and Zn?CH₃COO?₂?and 1,3,5-benzenetricarbocylic acid.Cu-C catalyst exhibits superior catalytic activity toward ORR with a half-wave potential of0.81 V and the four-electron transfer pathway in 0.1 M KOH electrolyte.Generally,it is known that N plays an important role for the high ORR catalytic activities of nonprecious metal doped carbon materials.Herein,we found that N is not required for the superior catalytic activity of Cu-C materials.Both the Cu particles and the embedded Cu atoms in the carbon substrate are suggested to provide the ORR active sites.Despite the fact that the Zn is removed during the pyrolysis,the adding of Zn salt in the precursor is important for the enhanced catalytic activity.The evaporation of Zn during the pyrolysis results in large surface area of the catalyst,which is beneficial to the mass transfer during the catalytic process.Moreover,a large number of carbon defects can be created via the removal of Zn atoms that facilitated the ORR.?3?N/C supported bimetallic Cu-Ni composite catalyst?CuNi-N/C?was prepared by liquid phase synthesis.The prepared CuNi-N/C catalyst exhibited excellent electrocatalytic performance in 0.1 M KOH electrolyte with an onset potential of 0.87 V,a half-wave potential of 0.78 V and a Tafel slope of 49 mV dec^-1.Ni in CuNi-N/C catalyst can refine the particle size and improve the electrochemical active area of the catalyst,while Cu can effectively increase the content of N in the catalyst.The oxygen reduction performance of bimetallic CuNi-N/C catalyst was superior to that of single-metal Cu-N/C and Ni-N/C catalysts.