Heteroatom Doped Carbon Materials As The Highly Efficient Electrocatalysts For Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is a crucial process that widely exists infuel cells and metal-air batteries. Owing to the slow kinetics of ORR, catalysts arerequired to increase the reaction rate and lower the overpotential on the cathode. Sofar, Pt and its alloys have been regarded as the most effective catalysts. However, thehigh cost, scarcity and poor durability have largely hindered its commercialization infuel cells.Recently, carbon materials doped with heteroatom (such as N, P, S, and B) havebeen discovered excellent catalytic activity toward ORR, and resistance to fuelcrossover and CO poisoning. In this paper, in one hand we developed a facile way toprepare highly efficient electrocatalysts for ORR by direct carbonization of naturalplants which containing N, P, S elements, on the other hand, we investigated thebehaviors of O-doped carbons as the oxygen reduction catalysts, and based on this westudied O, N co-doping for metal-free catalysts.1. Preparing highly efficient electrocatalysts for ORR by direct carbonization ofnatural plants. The carbon-based catalyst derived from the sponge material formedfrom ripened Luffa (cucumber family) showed a good ORR catalytic activity,enhanced stability and tolerance to alcohol crossover. Moreover, we found thatcarbon-based catalysts derived from other plants also showed good ORRelectrocatalytic activities. The good ORR catalytic activities of the studied catalystscould be attributed to the formation of heteroatom dopants originating from thenutrient elements of N, P and S. This study provides a simple and effective method forthe preparation of high efficient and low-cost ORR catalysts from the abundant andrenewable plant resources.2. Oxygen doped carbon nanoparticles as the catalysts for oxygen reductionreaction. It is widely reported that heteroatom (e.g. N, P, S and B) doped carbonmaterials could yield electrocatalytic activities towards the oxygen reduction reaction(ORR). In this part, we reported that oxygen doped carbon nanoparticles (O-CNPs)also exhibit electrocatalytic ORR activities in alkaline conditions. The O-CNPs weresimply synthesized by the incomplete combustion of hydrocarbons. Electrochemicalresults showed that the onset potential and peak current potential of the most optimal O-CNPs ORR catalyst was-0.12V and-0.24V vs. Ag/AgCl, respectively. Weproposed that the high ORR electrocatalytic activities of the O-CNPs could beattributed to semi-quinone groups that bonded to the edge of the graphitic carbonlayer.3. O, N co-doped melamine carbon foam as the oxygen reduction catalysts. Weprepared nitrogen-doped carbon foams (CFs) with different oxygen content bypyrolyzing the melamine foam, a nitrogen-rich polymer precursor. The oxygencontent in resulting carbons is deliberately modulated by control the atmosphereduring pyrolytic process. Our study showed that the N-doped carbons tend to be lowoxygen reduction activity in the absence of residual O2. When stepwise increase theoxygen content and the proportion of C=O, enhanced ORR catalytic activity wasobserved on the CFs. Ultimately, the CF catalysts co-doped with O and N iscomparable to commercial20%Pt/C. This study clearly revealed the essential role ofO atom in preparing high efficient N-doped catalysts.