Synthesis And Electrocatalytic Activity Of Low Platinum/Non-Platinum Cathode Catalysts For Fuel Cells

As an energy conversion device,proton exchange membrane fuel cell?PEMFC?can convert chemical energy into electricity directly without generating any harmful substances at room temperature.PEMFC has the advantages of high energy conversion efficiency,environmental friendliness and instant-on capacity at low temperature,so it is regarded as the next generation of energy technology to break the bottleneck of solving the problem of fossil fuel exhaustion and environmental pollution.However,the sluggish kinetics of cathodic oxygen reduction reaction?ORR?severely restricts the development of PEMFC and becomes a critical technical challenge.The commercial catalyst Pt/C with the best performance at present,however,owned the expensive and limited characters in the same time.And that makes the PEMFC difficult to widely commercialize.Therefore,it is necessary to develop new low platinum/non-platinum oxygen reduction catalysts to achieve high performance and afforable price to promote the development of PEMFC.In this paper,the research mainly focuses on adjusting the electronic structure and morphology of the catalyst by various means to prepare an efficient and stable inexpensive electrocatalyst.Firstly,we develop a facile and green method to selectively deposit pseudomorphological Pt shell on Ni core by spontaneous chemical displacement reaction under mild conditions.Thus,Pt can inherit the crystalline lattice features from the underneath Ni core.Ni_x@Pt/C catalysts with different atomic ratios can be obtained by adjusting the number of reductions.Further electrochemical tests show that the Ni₆@Pt/C catalyst exhibits an excellent onset potential?1.05 V vs.RHE?and half-wave potential?0.90 V vs.RHE?with the electrochemical surface area?ECSA?of 84.68 m²/g,which is superior to commercial Pt/C catalysts.Besides,the catalyst has an extraordinary stability with negligible degradation even after 5000-cycle potential scanning.This experiment provided a simple and efficient method to prepare platinum-based core-shell catalysts,and successfully introduced compression strain to regulate the electronic structure of Pt and reduce the d-band center.Next,a facile high-temperature molten salt bath method was developed to effectively dope sulfur into carbon skeleton.Molten potassium sulfide acts as a high-concentration sulfur source and provides an immersion bath,thus,favoring sulfur doping.SC-950 shows an exceptionally high sulfur content of 1.84 at.%and the best performance?onset potential increased by 40 mV?.All SC-x catalysts have a certain increase in ORR catalytic activity compared to pure VC72-x.This work proves the feasibility and superiority of doping heteroatoms in high temperature molten salt bath and manifests S atom's favorable effect on catalyzing the oxygen reduction reaction.Finally,based on the study of the morphology evolution of ZIF-67 crystals at different carbonization times.Here,SiO₂ microspheres modified with amino group were used to induce ZIF-67 growth along the surface of SiO₂ microspheres by using the interaction between amino group and Co²⁺.After further carbonization,ZIF-67 derived carbon catalyst with ordered pore structure was obtained by removing template.Preliminary electrochemical investigation proved that the porous structure improved the catalytic activity of the ZIF-67 derived carbon catalyst.