Preparation Of Tuber Crops-derived Porous Carbon Materials And Exploration Of Their Oxygen Reduction Electrocatalytic Properties

Carbon materials converted from plant-based biomasses are considered as one of the most promising carbon-based catalysts for oxygen reduction reaction(ORR),due to their wide sources,renewable nature,well-developed pore structure and abundant heteroatoms.Tuber crops have the large amount of spherical starch granules and abundant protein and metal elements,so they can futher form in-situ nitrogen doping,high graphitization degree and high porosity on the basis of preparation of spherical carbon materials.Thus,this plant is an excellent precursor for synthesizing nitrogen-doped porous carbon-based catalysts for the ORR.In this paper,tuber crops are used as raw material to prepare nitrogen-doped porous carbons,and their structures and electrochemical properties were explored,which provides a new direction for exploring efficient and inexpensive carbon-based electrocatalysts.The main outcomes are as follows:(1)Firstly,using potato as an example,spherical carbon with high specific surface area(1250.74 m2 g-1),degree of graphitization and nitrogen doping content(4.74%,N/C),was prepared via hydrothermal carbonization and activation treatment.It exhibits better ORR activity(half-wave potential,0.89 V vs.RHE),stability and methanol resistance than the commercial Pt/C in alkaline media,and also exhibits good activity in acidic solution.At the same time,zinc-air battery test has demonstrated that the sample have a maximum power density(116 mW cm-2)exceeding the Pt/C.Therefore,this method opens up a new way of preparing high-activity tuber crops-derived carbons.(2)Based on the above preparation method,tuber crops such as potato,yam and sweet potato were systematically studied.By analyzing their morphologies,pore structures,compositions and electrochemical properties,it has been confirmed that the three kinds of tuber crops-derived materials are all nitrogen-doped porous carbons with spherical morphology,and they exhibit high electrocatalytic performances.In addition,three kinds of rod-shaped tuber crops-derived carbons with excellent properties were prepared via changing the hydrothermal carbonization conditions.From the computational DFT,the pyridinic-N promotes the adsorption and reduction of O2,which is the origin of ORR activities of the tuber crops-derived carbons.(3)In order to design more excellent catalytic active centers,the tuber crops-derived carbons are further modified by copper doping.The copper-ammine complexation and solid migration methods have both been used to obtain high-content and atomically dispersed copper doped carbons,which exhibit enhanced ORR activities.The XAFS and other tests have proved that Cu atoms are doped in the forms of Cu?-N2 and Cu?-N4,thus providing more ORR active sites,and the catalytic mechanisms of two Cu-N coordination structures are also proposed.