Non-Pt Electrocatalysts For Oxygen Reduction Reaction

Fuel cell as clean and sustainable energy device shows various advantages,such as high energy conversion efficiency,virtually no environmental pollution,and unlimited sources of reactants.It can gradually replace the decreasing fossil fuel.Therefore,fuel cell is promising to come into widespread commercial use in the areas of transportation,stationary,and portable power generation,and thus will help solve the global problems of energy supply and clean environment.However,at the most cathode of fuel cell,the reaction kinetics of oxygen reduction reaction(ORR)is slμggish.Even on the best Pt-based catalyst,to achieve a desirable fuel cell performance,the required Pt loading is much higher(～0.4 mg cm-2).Pt is a scarce and expensive metal,thus hinder its large-scale applications in fuel cells.Therefore,effective catalysts for ORR are pivotal for improving the performance of fuel cells whilst reducting cost.Thus,efforts are needed to investigate the alternative catalysts that are easily available,lower cost,while show comparable even better catalytic effects than Pt for cathodic ORR in fuel cells.This paper focus on developing non-platinum ORR electrocatalysts including advanced carbon-based non-noble metal catalysts,Pdbased catalysts,metal oxides,and chalcogenides.Detailed contents are summarized as follows:1.Synthesis of Two Dimensional Nanosheets(MoS2,BN,C3N4)/Palladium Composites and Their Electrocatalytic Activity for Oxygen Reduction Reaction and Anodic Oxidation ReactionThe preparation of high active electrocatalysts with good durability and low cost is a great challenge for developing high performance fuel cells.Here we synthesized two dimensional(2D)(MoS2,BN,C3N4)nanosheets supported palladium composites(MoS2/Pd,BN/Pd,C3N4/Pd)via a general and convenient sonochemical approach.We have systematically studied the electrocatalytic performance of as-prepared catalysts.The results demonstrate the three catalysts all possess excellent catalytic activity and stability for oxygen reduction reaction(ORR)in alkaline media.Encouragingly,the BN/Pd and C3N4/Pd catalysts exhibit the excellent electrocatalytic activity for formic acid oxidation(FAO)and methanol oxidation reaction(MOR)in both acidic and alkaline media,respectively,even better than the performance of the commercial Pt/C catalyst.The excellent electrocatalytic performance of the 2D(MoS2,BN,C3N4)/Pd composites roots in their strong interaction between the ultrathin substrate material with large surface area and excellent dispersion of palladium nanoparticles.This study demonstrated that sonochemical method opens up a new avenue for the preparation of electrocatalysts for fuel cells.The synthesized materials are promising in a broad range of applications,for example,fuel cells,solar cells,batteries and other electrochemical analysis.2.Synthesis of Porous MnO2 and Its Electrocatalytic Activity for Oxygen Reduction ReactionPorous MnO2,a non-noble metal oxygen reduction reaction(ORR)electrocatalyst,was prepared via a simple sonochemical route.The as-prepared porous MnO2 exhibited higher electrocatalytic activity,superior stability and better methanol tolerance than commercial Pt/C catalyst in alkaline media.Furthermore,the ORR proceeded via a nearly four-electron pathway.Cyclic voltammetry(CV)and rotating-disk electrode(RDE)measurements verified that the ORR enhancement was attributed to the porous structure and good dispersity,which facilitated sufficient transport of ions,electrons,O2 and other reactants in the process of ORR.The results indicated that a facile and feasible sonochemical route could be used to prepare highly active porous MnO2 electrocatalyst for ORR,which might be promising for direct methanol fuel cells.3.Synthesis of Nitrogen Self-Doped Porous Graphitic Carbon Nanosheets for Efficient Oxygen Reduction ReactionThe demand on the highly efficient and low-cost cathodic electrocatalysts for commercialization of fuel cells is rapidly increasing.One smart route for obtaining ideal electrocatalysts is extracting active carbon materials from natural and cheap biomass waste.Here,we prepared a novel nitrogen self-doped porous graphitic carbon nanosheets(NPGCNs-NaCl)derived from a nitrogen-rich pruning of Lycium barbarum L.using NaCl crystal as intercalation agent.The as-obtained NPGCNs-NaCl possessed porous structure,large surface area,increased content of nitrogen and high graphitic carbon,and thus endowing it with high electrocatalytic activity for oxygen reduction reaction(ORR).Most importantly,significantly enhanced stability and tolerance against methanol were observed compared with commercialized Pt/C catalyst in alkaline solution.This work is believed to open a new avenue for manufacturing advanced and low-cost ORR electrocatalysts in fuel cells from biomass waste.