Carbon-Based Non-Precious Metal Catalyst For Fuel Cell Cathode

Increasing energy crisis and environmental pollution have stimulated extensive researchs on alternative and sustainable energy conversion systems.Fuel cells,which could transform the chemical energy of fuels into electric energy directly and efficiently,have been one of the researching hotspots currently.What’s more,fuel cells,with the features of simple system structure,low running temperature and high conversion efficiency,have widespread implementation prospects for fixed power stations,transportation,and military power and so on.Currently,design and preparation the oxygen reduction reaction（ORR）catalysts with remarkable catalytic activity and long-term stability has been one of the tough bottlenecks of electrochemistry,which could be used as the potential substitutes for Pt-based catalysts.In this thesis,the modern spectroscopy microscopy and electrochemical methods were conducted to elucidate the structure-activity relationship for carbon-based non-precious metal catalysts.The main research results are as follows:（1）MnCo_xO₄/NCNT hybrid was synthesized through a facile hydrothermal route.It can be seen from the physical characterizations that the nanoparticle of MnCo_xO₄,with a particle size of 5-10 nm,was consist of Co2MnO4 and（Co,Mn）[Mn,Co]2O4 and supported on the surface of MWCNTs with sencondary aggregation.The electrochemical measurements show that the obtained MnCo_xO₄/NCNT catalyst with superior ORR catalytic activity with the positive half-wave potential（only 22 mV negative than commercial 20 wt.% Pt/C catalyst）.After 2400 s chronoamperometric measurements at-0.4 V with 1600 rpm,the current density of MnCo_xO₄/NCNT catalyst decreases by 1.7%,this is better than that of 17% for commercial Pt/C catalyst.（2）The N/S-Kb catalyst was prepared simply by pyrolyzing thiourea and ketjenblack（Kb）in the presence of FeCl₃·6H₂O.Physical characterization revealed that the N/S-Kb catalyst featured with the three-dimensional network structure while the active pyridinic N and thiophene S（32.7 at.% and 84.3 at.%）were homogeneously incorporated into the nanostructure of Kb to provide high-efficient active sites.The N/S-Kb catalyst could facilitate the ORR via high efficient 4 electron process,with an onset potential of 0.08 V at 0.1 mA cm-2,which is 20 m V more positive than that of commercial 20 wt.% Pt/C catalyst.After the 10000 s chronoamperometric measurement and the 8000 cycles accelerated aging test,no changes were observed for the catalytic activity,indicating the excellect stability for N/S-Kb catalyst.（3）The Fe-N/S/B-C catalyst was prepared simply by pyrolyzing thiourea and boric acid with the catalysis of Fe Cl3·6H₂O.Physical characterizations revealed that the Fe species of Fe-N/S/B-C catalyst were encased by carbon layers.Furthermore,the heteroatoms including N,S and B bave been introduced into the carbon matrix by a heat-treatment method to boost the ORR activity of Fe-N/S/B-C catalyst with the help of active pyridinic N,thiophene S and B-C.The electrochemical measurements show that the half-wave potential of obtained Fe-N/S/B-C catalyst was positive than that of 20 wt.% Pt/C catalyst（-0.1 V vs-0.131 V）,indicating the remarkable activity of Fe-N/S/B-C catalyst.Further accelerated aging test and chronoamperometric measurement confirmed the superior stability for Fe-N/S/B-C catalyst（half-wave potential negative shift 8 mV and the current density with 98.6% retention）.