Preparation And Electrochemical Properties Of Carbon-based/transition Metal(Co And Cu)as Oxygen Reduction Reaction(ORR) Catalyst

Compared with the energy depletion and the environmental pollution caused by the high consumption of fossil fuels, more attentions and research are focused on the fuel cells due to the highly efficient energy conversion and wide market demand.In the field of fuel cells, the study of catalysts in the oxygen reduction reaction(ORR) is one of the most popular topics. Platinum-based catalysts are the most frequently applied catalysts for ORR due to its high catalytic activity and durability. However, the high cost and limited sources of Pt in nature restrict its actual application. Therefore, developing non-precious metal catalysts with comparable ORR activity to the Pt-based materials is thus of great importance.In this thesis, four kinds of composites, such as nitrogen-doped graphene/cobalt(NG/Co) nano composite, nitrogen-doped graphene/copper(NG/Cu) composite, porous carbon/cobalt sulfide(PC/Co S1.097) composite, and nitrogen-doped graphene/cobalt sulfide(NG/Co S) nano composite were prepared from the precursors of glucose, dicyandiamide(DCDA), Co(NO3)2·6H2O(or Cu(NO3)2·3H2O), and ZIF-9 in the nitrogen atmospheres. The structure and electrocatalysis properties of these catalysts was detected by X-ray diffractometer, thermogravimetric analysis, scanning electron microscopy, transmission electron microscope, N2 adsorption analysis, X-ray photoelectron spectroscopy in details and the results are described bellow.1. Nanocomposite of Co(or Cu) species supported on N-doped graphene was successfully prepared through a one-step pyrolysis of low-cost chemicals using glucose, dicyandiamide(DCDA) and Co(NO3)2·6H2O(or Cu(NO3)2·3H2O) as starting materials in N2 atmosphere. The investigations of NG/Co indicated that Co particles are deposited on the graphene with the nano size of 15-20 nm which is beneficial for the high electrocatalytic activities because the nano particles can enhance the effective area of the catalyst. The electrochemical tests show that the composite exhibits a peak potential with value of +0.866V(vs.RHE), which is more positive than that of 20 % Pt/C. The study of prepared NG/Cu material exhibited that the product has a porous structure which is helpful to ORR. The NG/Cu has a peak potential with value of +0.843V(vs.RHE), which is comparable to that of 20 % Pt/C. The i-t test presents the NG/Cu composite has high stability and tolerance to methanol poisoning effects in the alkaline media for ORR.2. A strategy was devised to produce Co S1.097 nanocomposite embedded in a porous carbon matrix via a one-step thermolytic cracking of Co based MOFs(ZIF-9) with sulfur powder together in an inert(N2) environment. The results showed that the composite had a large specific surface area and mesoporous structure which are helpful to ORR. The electrochemical test shows PC/Co S1.097 had excellent electrocatalytical activity with remarkable ability to immune methanol crossover, and superior durability in alkaline electrolyte.3. Nitrogen-doped graphene/Co S(NG/Co S) composite was prepared through heating the as-prepared N-doped graphene/Co in the presence of sulfur. And the study of electrochemical property of NG/Co S indicated that the peak potential is +0.851V(vs.RHE) which is similar to that of 20 % Pt/C(+0.857V(vs.RHE)). The electrochemical test shows NG/Co S had excellent electrocatalytical activity with remarkable ability to immune methanol crossover, and superior durability in alkaline electrolyte, which implies the nano composite is a superior ORR electrocatalyst for fuel cells.In this thesis, four kinds of composites, such as Nitrogen-doped graphene/Co, Nitrogen-doped graphene/Cu, porous carbon/Co S1.097, and Nitrogen-doped graphene/Co S had been prepared. The four non precious metal composites show superior ORR activities. The results provide valuable experimental data for the research and potential applications for the low-cost catalysts in the fields of fuel cells.