Nitrogen-doped carbon and cobalt selenide electrocatalysts for oxygen reduction reaction

• Main Authors: Yu-Hsuan Chao, 趙余亘
• Other Authors: Dah-Shyang Tsai
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/5erfuj

碩士 === 國立臺灣科技大學 === 化學工程系 === 99 === Proton exchange membrane fuel cell (PEMFC), a high energy efficient and environmentally friendly system, is considered to be a future power supplier. The major barriers for PEMFC commercialization are high cost and insufficient cycle life, which mainly arise from the platinum-based catalysts of limited supply. N-doped carbon and non-noble metal chalcogenides are potentially substitutes for platinum catalysts, although their activities are less than platinum. In this investigation, we attempt to promote the activity of cobalt selenide with N-doped carbon. We coated cobalt and iron doped ethylenediamine–formaldehyde chelate complexes on Vulcan support. The N-doped carbon catalyst was subsequently synthesized by heat treatment and wet ball-mill to break down aggregations.The optimal catalyst of N-doped carbon demonstrates an onset potential 0.831 V (vs. NHE), half-wave potential (E1/2) 0.667 V (vs. NHE) when reducing saturated oxygen in 0.5 M H2SO4, measured with the rotating disk voltammetry. It has excellent stability, showing only 0.031V E1/2 decay after 1000 cycles. It also generated less than 3.7% H2O2, accompanying oxygen reduction. This N-doped carbon catalyst contains 5.09 wt% nitrogen, measured with elemental analysis. XPS analysis reveals four types of nitrogen sites. Among them, the pyridinic-N site occupies 40.28%, the pyrrolic-N site takes up 24.80%, and the quarternary-N and pyridinic oxide make up the rest. Raman results indicate a moderate distortion of the graphitized edge, with ID/IG 1.05. TEM shows the morphology of the catalyst. The catalyst activity is improved when cobalt selenium (CoSe2) is integrated with N-doped carbon properly, even though the activity improvement and the stability of this compound catalyst are much less than the catalyst of RuSe2 and N-doped carbon that our group synthesized previously. One salient feature of CoSe2 and N-doped carbon is its relatively low material cost.The best compound catalyst exhibits an onset potential 0.792 V (vs. NHE), half-wave potential (E1/2) 0.711 V (vs. NHE) on oxygen reduction. However, CoSe2 seems unable to withstand the 1000 CV cycles of stability test, the compound catalyst shows a 0.067 V E1/2 decay after 1000 cycles. It also shows a higher H2O2 yield 6.4%. Two crystalline phases are found in CoSe2 catalyst, including the 21 nm particles of orthorhombic phase and the 28-29 nm particles of cubic phase.