Evaluation Of Novel Fuel Cell Catalysts With Ultra-low Platinum Contents-a Route Towards Electrochemical Catalysis

With the excessive consumption of fossil fuels and rising environmental issues,the harvesting,conversion,and storage technologies of sustainable energy have been extensively studied.Recently,fuel cells have become one of the most promising technologies by using more environment-friendly energetic vectors.Among various fuel cell types,proton exchange membrane fuel cells(PEMFCs)have attracted wide attention in the past few years.These possess desirable features such as high theoretical energy density,cheaper materials,and lower cost of manufacturing.The improvement of the PEMFC reactions is a critical point for its development.The oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)are two crucial reactions of these devices;however,sluggish kinetics severely limit their commercialization.Therefore,it is essential yet challenging to develop highly efficient ORR and OER bifunctional catalysts.Up to now,Pt-based catalysts still perform the most effective ORR activity but a poor OER activity.Conversely,IrO2,and RuO2 based electrocatalysts are the most excellent commercial OER electrocatalysts but possess a poor ORR property.Meanwhile,the large-scale applications of these noble electrocatalysts are limited due to their scarcity,high cost,and poor stability;even so,it is of significance to develop electrocatalysts with low noble metal contents and with high efficiencies and stabilities for both OER and ORR applications.This dissertation mainly contains three parts:in the first part,the investigation focuses on the development of support-less and ultra-low Pt contents based on nanostructured platinum copper(Pt-Cu)nanoparticles(NPs).The novelty of present work lies in the use of sustainable approaches for catalyst synthesis to support-free Pt-Cu NPs with lower Pt loadings(0.04-0.25 wt.%).The Pt0.25Cu with onset potential(Eo)0.98 V vs.RHE exhibits superior activity compared to all prepared catalysts as well commercial Pt/C(20 wt.%).The accelerating electrocatalyst durability tests(ADTs)show that Pt0.25Cu electrodes are much more stable than state-of-the-art Pt/C catalysts(20 wt.%)for ORR in alkaline solution.To the best of our knowledge,this is the first time we have used bimetallic Pt-Cu catalysts with ultra-low Pt contents for ORR in the alkaline solution with superior activity compare to commercial Pt/C(20 wt.%).The second part of this dissertation focuses on the utilization of metal-organic framework(MOF)as a host matrix for immobilizing metal nanoparticles(MNPs)and the use of fabricated MNP@MOF composites as bifunctional catalysts for ORR and OER.To the best of our knowledge,the possibility for the synthesis of CTAB-capped non-noble metal-based(Cu NPs),ultra-low noble metallic(Pt NPs),and bimetallic(Pt-Cu)alloy NPs successfully encapsulated in the pores of Zn-MOF-74 and pyrolyzed at 900 ?,was achieved for the first time.Among the prepared catalysts,Pt/Cu-NPC-900(Eo 1.01 V,E1/2 0.89 V,?E 0.59 V and overpotential 0.265 V vs.RHE)exhibited promising electrocatalytic activity and superior durability in alkaline solutions superior to the state-of-the-art Pt/C(Eo 0.96 V,E1/2 0.85 V,?E 0.96 V and overpotential 0.564 V vs.RHE)and RuO2(overpotential 0.272 V vs.RHE)electrocatalysts.The sample Pt/Cu/NPC-900 exhibits a very small ?E(0.59 V)compare to state-of-the-art bifunctional oxygen electrocatalysts,indicating excellent bifunctional electrocatalytic for both ORR and OER in alkaline electrolyte.These cutting-edge results show the highest catalytic activity for supported Pt,Cu,and Pt-Cu-based catalysts,that had been ever reported for ORR and OER.Thus,our effort in making state-of-the-art-catalyst has effectively proved to be the first landmark of its time.In the third part,we report the superiorly active and durable non-noble metal-based bifunctional electrocatalyst of CTAB-capped copper(Cu)nanoparticles doped on ZIF-67 and then pyrolyzed at different temperatures(500-900?)and named as Cu/Co-N-C-X(X=500,600,700,800 and 900?).The sample Cu/Co-NC-800 exhibits the superior ORR catalytic activity with Eo,and E1/2 of 0.98 V,0.84 V vs.RHE,respectively,these are superior compare to all prepared catalysts and commercial Pt/C(0.96 V,0.82 V vs.RHE),respectively.The Cu/Co-NC-800 exhibits the highest catalytic activity with lowest OER overpotential,lower Eo,and high current density(278 mV,1.50 V,and 51.98 mA cm-2),compared to all prepared catalysts as well commercial Pt/C(542 mV,1.77 V,and 0.31 mA cm-2)and RuO2(290 mV,1.52 V,and 39.07 mA cm-2),respectively.Considering the above results,the Cu/Co-NC-800 electrocatalyst demonstrates superior bifunctionality,that is superior to the commercial catalysts and a majority of the reported non-precious metal catalysts.To the best of our knowledge,the possibility for the synthesis of CTAB-capped non-noble metal-based nanoparticles(Cu NPs)and deposited on the ZIF-67 pores and py roly zed at different temperatures,was achieved for the first time.This research offers new insights into the construction of dual-function crystalline heterostructures.It opens the door to the design for renewable energy applications of high-performance transition metal-based oxygen catalysts.With the great variability of MOF compositions,pore structures,and coordination space for loading with dopants,this work shows the potential to design advanced oxide nanocomposite bifunctional catalysts as a replacement of expensive precious metals energy storage and conversion technologies.This work not only enables fundamental insights on the activity origin of the high-performance catalysts but also inspires a new point-of-view for designing and synthesizing more economical and efficient electrocatalysts.The ultra-low Pt loading with uniform distribution,superior catalytic activity,and durability indicates that our strategy is facile and cost-efficient,and it has great potential in developing high-performing electrocatalysts for PEMFCs.The research on bifunctional catalysts in on the early stage,thus,exploring cost-effective,efficient,non-precious or low precious metals based bifunctional oxygen electrocatalysts is of vital significance to further advance the fuel cells.