| Oxygen reduction reaction(ORR)describes the process of oxygen molecules receiving electrons forming products.This reaction is the cornerstone of many important energy conversion devices,such as fuel cells and metal-air batteries.In these applications,fuel cells have a remarkable prospect of being a future energy device.Fuel cells are considered to be the most effective and clean energy conversion device where fuels react with oxygen by a mild electrochemical method,not burning,and the overall fuel conversion efficiency is not constrained by the Carnot cycle.At room temperature,the ideal thermodynamic efficiency of hydrogen-oxygen fuel cell reaches 83%.However,in low-temperature fuel cells,due to the slow kinetic process of its cathodic oxygen reduction reaction,a large number of platinum-based catalysts are needed to accelerate the reaction process.However,Platinum(Pt)is an expensive metal,with limited reserves(only 66000 t),resulting in high cost of fuel cells,severely hampering the widespread use of fuel cells.In addition,the Pt in the actual operation condition is poor stability and the weak ability to resist methanol is also a very challenging problem.Therefore,the design of low-cost non-noble metal catalysts with high oxygen reduction activity,strong stability and good resistance toward methanol has become one core of fuel cell research.Among them,carbon-based catalyst has been widely concerned by researchers.Its research has become one of the most important topics in the field of fuel cells.The M/N/C catalyst has been the most promising non-noble metal oxygen reduction catalyst with the above advantages.In this paper,the Fe/N/C material is the object of study and was optimized and upgraded systematically through heteroatom doping and nanostructuring,which showed excellent activity for ORR both in acidic and alkaline conditions.Well,this paper contains following two parts:(1)Many theoretical and experimental reports confirm that heteroatom doping is an important strategy to promote the ORR catalytic performance of the carbon material.So the work of S doping to improve ORR performance of Fe/N/C is available.In this work,an efficient and simple method was developed for the first time to successfully prepare in situ S-doped Fe/N/C(S-Fe/N/C)by pyrolysis of acetic acid ferrous and thiourea,while the doping volume of S atom reaching 4.76%(atomic ratio).S-Fe/N/C demonstrated excellent ORR electro-catalytic performance,whether in alkaline or acidic solutions and its catalytic performance was comparable to the high price of commercial platinum carbon(Pt/C,mass ratio 20%)and obviously better than the non-doped Fe/N/C.Compared with commercial platinum carbon,S-Fe/N/C has better stability and tolerance to methanol,and it catalyzed ORR following a highly efficient 4e path.The S-Fe/N/C catalyst prepared in this paper shows the ability to become a good substitute of commercial Pt/C and its unlimited potential for application in fuel cell and related fields.(2)With ferrous acetate,melamine and 1,2-ethylene phosphonic acid(EDPA)as precursors,a novel compound type ORR electrocatalyst was prepared by "one-pot" method,Iron Phosphide/N,P-doped Carbon Nanosheets.In the process of preparation,EDPA is as P source while plays a role like soft template.For the catalyst,carbon-coated iron phosphide,Fe-N and N,P-doped carbon are synergistically enhancing ORR catalytic activity.Iron phosphide/N,P-doped carbon nanosheets have a high specific surface area and exhibit excellent ORR electrocatalytic performance in basic,acidic and neutral media.It is of great significance to show excellent performance for ORR under acidic and neutral conditions,because there are fewer non-noble catalysts of high performance in acidic and neutral conditions.In addition,it has excellent performance stability and tolerance toward methanol.The composite catalyst of Iron phosphide/N,P-doped carbon nanosheets has good application foreground in the field of energy conversion and related fields. |
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