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RISS 인기검색어
- 검색키워드
- 저자 : Jahowa Islam (검색결과 1 건)
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Jahowa Islam University of Science & Technology 2022 국내박사
Fossil fuels are the world's most widely used energy source, but this source is limited and will be depleted over time. Attention is therefore being paid to renewable energy sources to reduce the dependence on fossil fuels. Energy storage and energy conversion technology play an essential role in the renewable energy sector. In particular, proton exchange membrane water electrolyzers (PEMWEs) and proton exchange membrane fuel cells (PEMFCs) are examples of energy storage and energy conversion technologies. Although these technologies offer several advantages over other technologies of renewable energy sectors, there are still some challenges that prevent the commercialization of PEMWE and PEMFC technologies. For PEMWEs, the main roadblock is the anodic oxygen evolution reaction (OER) catalyst, whereas for PEMFCs, it is the cathodic oxygen reduction reaction (ORR) catalyst. Electrocatalysts for the OER/ORR are an important area where many breakthroughs are needed to improve the slow kinetics of the OER/ORR and reduce the amount of precious metal loading. In this light, the aim of the present research is to develop electrocatalysts for the OER/ORR with promising activity and durability. In terms of the OER catalyst in a PEMWE, a series of boron carbide-supported iridium catalysts were prepared via the wet impregnation method using NaBH4 as a reducing agent. Boron carbide has good electrical conductivity and corrosion resistivity. Physical and electrochemical properties of the catalysts were controlled by changing the synthetic reduction temperature (30 °C–100 °C) and iridium content (10 wt%-60 wt%) on the boron carbide support. The prepared Ir/B4C catalyst is the most promising catalyst for the OER and was synthesized at 100°C reduction temperature. In addition, at 40% loading, Ir/B4C showed maximum OER catalytic performance. The 40%-Ir/B4C catalyst outperformed all synthesized catalysts as well as two commercial catalysts in both activity and durability. The improved performance of 40%-Ir/B4C can be correlated to three key factors: i) high electrochemical surface area, (ii) better electrical conductivity, and (iii) high concentration of Ir(III) on the surface. Controlling the synthetic reduction temperature and iridium content on the B4C support was found to help develop the interaction between iridium and B4C. This metal-support interaction prevents the oxidative dissolution and aggregation of iridium species. In a single cell test, Ir/B4C-40% showed outstanding cell performance of 1.61 V at 1.0 A/cm2 at 0.5 mg/cm2 loading. Using this catalyst in the anode of a PEMWE, the precious catalyst metal loading can be reduced by more than six orders. The Ir/B4C-40% catalyst also showed outstanding durability, e.g. only a small voltage increase of 11 mV during the durability test in MEA performance after operation for 48 hours at a constant current density of 2.0 A/cm2. In terms of the ORR catalyst in a PEMFC, a durable carbon-based electrocatalyst support was synthesized. Platelet-type carbon nanofiber (PCNF) and Vulcan carbon black (CB) were coated in a uniform and discrete manner with silica, followed by platinum deposition on it. Accelerated degradation testing of the silica-coated catalysts showed higher durability than non-silica-coated catalysts under potential cycling. The silica coating can reduce carbon corrosion during the potential cycling between 1.0 and 1.5 V by i) blocking the carbon support from direct contact with the oxygen source and ii) preventing the effect of oxygen spillover from the platinum to carbon. The results suggest the silica coating on a carbon support is an effective strategy to improve the durability of Pt-based electrocatalysts under potential cycling.
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