Preparation Of Nitrogen-doped Porous Carbon-based Electrocatalytic Materials And Thier Activity Regulation

Oxygen reduction reaction(ORR)has always been considered as an important electrochemical reactions involved in the energy storage and conversion.However,due to its sluggish kinetic process,to investigate the cost-effective catalysts toward the ORR are essentially required to achieve practical utilization.Since N-doped porous carbons have exhibited superior catalytic activity and stability,as well as their wide sources and low cost,these carbons are believed to be one of the most likely ORR catalysts,alternative to the commercial Pt/C.Biomasses,especially the plants,are ideal templates to prepare N-doped porous carbons,because they contain rich carbon and nitrogen,but more importantly,have the channel of nutrient transport.Therefore,to prepare the biomass-based N-doped porous carbons is meaningful for the development of the cost-effctive ORR catalysts.The main research results are as follows.Firstly,the pomelo peel-based N-doped porous carbons have been prepared through the hypersaline impregnation treatment(the ultrasaturated solutions containing NaCl,ZnCl2 and FeCl3)at the room temperature,followed by the megathermal carbonization(700?)and ammonia activation(900?).As a result,the best synthetic conditions are determined by the analyses to the morphology,structure and the electrocatalytic activity of the carbons.The carbon obtained under the hypersaline treatment exhibits the high specific surface area(3092.26 m2g-1)and nitrogen content(2.81%N/C).Moreover,the carbon displays superior ORR electrocatalytic activity(half-wave potential,0.86V vs RHE;Jk,10.40 mA cm-2)to the Pt/C,as well as outstanding stability and methanol tolerance.The advanced activity of the carbon may be arised from enlarged specific surface area and high graphitic degree,as well as increased nitrogen content in the carbon.Secondly,the N-doped porous carbons derived from radish are prepared with the similar method of hypersaline treatment,carbonization and activation.The obtained radish-based carbons exhibit unique hexagonal pores,the large specific surface area with 1595.42 m2g-1 as well as the nitrogen content with 2.92%.Importantly,the carbon offer outstanding catalytic activity to ORR,which is superior to the pomelo peel-based carbons and the Pt/C.The excellent ORR activity can be attributed to its unique hexagonal porous structure.Thirdly,the carbon supported lanthanum oxides have been prepared using the carbon black(Vulcan XC-72),the pomelo peel-based carbon,and the radish-based carbon as the supports.Therein,the radish-based carbon supported lanthanum oxide displays the most positive ORR activity,which has the half-wave potential with 0.90V vs RHE.The remarkably superior ORR activity is attributed to the C-O-La bonds between the carbon and La2O3.The formed C-O-La covalent bonds have a good effect on the electron transfer from the carbon(? electron)to the La2O3,filling the unoccupied eg orbital splited by the La 5d orbital of La2O3.Such eg greatly promotes adsorption of active oxygen and desorption of the hydroxide(OH-ad)on the oxide surface,therefore enhancing the ORR catalytic activity.Preparing biomass-based porous carbons and carbon supported lanthanum oxides may open a new way to develop nonprecious metal-based materials as ORR catalysts.