Direct methanol fuel cells (DMFCs) are a kind of electrochemical energy-conversion device which converts the chemical energy of methanol directly into electric energy. Due to methanol’s high energy density, abundant source, low price, safety of storage and transportation, DMFCs have a great application potential in national defense, communication, electric appliances and sensing devices. Although appealing, the commercialization process of DMFCs is significantly hindered by their high cost, resulting from the employment of large amounts of Pt-based catalysts. Thus, to develop new catalysts to replace Pt-based catalyst is one of the most important research on DMFCs. For anode of DMFCs, the complexity and sluggish kinetics of methanol oxidization reaction (MOR) makes it difficult...[ Read more ]

Direct methanol fuel cells (DMFCs) are a kind of electrochemical energy-conversion device which converts the chemical energy of methanol directly into electric energy. Due to methanol’s high energy density, abundant source, low price, safety of storage and transportation, DMFCs have a great application potential in national defense, communication, electric appliances and sensing devices. Although appealing, the commercialization process of DMFCs is significantly hindered by their high cost, resulting from the employment of large amounts of Pt-based catalysts. Thus, to develop new catalysts to replace Pt-based catalyst is one of the most important research on DMFCs. For anode of DMFCs, the complexity and sluggish kinetics of methanol oxidization reaction (MOR) makes it difficult to develop non-Pt catalysts with comparable performance. The focus of developing alternative catalysts is on cathode catalyst for oxygen reduction reaction (ORR). Among the reported catalysts, heteroatom-doped carbons are one of the most promising catalysts for ORR for their low cost and excellent durability. However, the mechanism for ORR is still undecided.

In this thesis, heteroatom-doped carbons are prepared and the mechanism for ORR are investigated by a combination of experimental and DFT calculation. Firstly, the impact of carbon precursors on P-doped carbons for ORR is investigated by using PF-resin and glucose as carbon precursors. Ratios of P-O bonds and P-C bonds are influenced because of different carbon precursors used, leading to their discrepancy performance on ORR, implying the different effect of P-O bonds and P-C bonds on ORR. Secondly, the role of P on N, P dual-doped carbons for ORR is studied by modifying the doping order of N and P. Experimental proves the first doped P has an orientation effect on the doped N by increasing the ratio of graphitic-N, leading to the improved ORR performance, which is also confirmed by DFT calculation. Thirdly, a ternary-doped porous carbons with B, P, and N is developed with excellent electrocatalysis not only for ORR, but also for oxygen evolution reaction (OER), showing great potential to be a bifunctional catalyst with low cost.

Although progress has been achieved on heteroatom-doped carbons, Pt catalyst is still regarded as the best ORR electrocatalyst for its superior activity. Thus, research on improving the utilization of Pt catalyst is another focus of this thesis. Firstly, by using ordered mesoporous carbons (OMCs) as support materials, the impact of pore size OMCs is investigated by preparing OMCs with different pore sizes. Pt catalyst supported on OMCs with a pore size of 6.5 nm delivers the best activity on ORR and single cell performance, because of a combination effects of Pt particle size and electric conductivity. Secondly, a OMC/TiC composite is synthesized by forming TiC in the skeleton of OMCs. Pt catalyst supported on the as-prepared OMC/TiC composite performs enhanced activities on ORR and MOR, compared to that of commercial Pt/C. Lastly, a novel electrode is proposed with decreasing amount of catalyst in the flow direction. Compared with traditional electrode, the total amount of catalyst in novel electrode reduces, while keep the performance in the same level by improving the utilization of Pt catalyst.

Keywords: Direct methanol fuel cell; Ordered Mesoporous carbons; Heteroatom-doped; Oxygen reduction reaction