Polymer Electrolyte Membrane Fuel Cell (PEMFC) is an electrochemical energy conversion device, in which hydrogen reacts with oxygen, producing electricity and water as the only by-product. Due to the high energy density and conversion efficiency, PEMFC has particularly attracted considerable attenti...
Polymer Electrolyte Membrane Fuel Cell (PEMFC) is an electrochemical energy conversion device, in which hydrogen reacts with oxygen, producing electricity and water as the only by-product. Due to the high energy density and conversion efficiency, PEMFC has particularly attracted considerable attention as a primary power source of zero-emission electric vehicle. However, its widespread application is impeded by the high cost of electrocatalyst, in particular, for oxygen reduction reaction (ORR) at cathode. To make PEMFC more economically competitive to the combustion engine, therefore, currently employed Pt-based catalyst for ORR should be improved in terms of its activity and durability. In this work, two approaches have been applied to enhance ORR performance of Pt-based electrocatalyst. One is the modification of carbon support with transition metal oxide and the other is the morphology control of Pt-based alloy. A commercial carbon support was modified with TiO2 (C-TiO2-X; X represents wt% of TiO2), where the concentration of TiO2 was controlled from 10 to 30 wt% by adjusting the amount of TiO2 precursor during the preparation. All the C-TiO2 showed highly dispersed TiO2 with anatase crystalline phase, while the size of TiO2 slightly increased with increasing the amount of TiO2 precursor. The ORR activity of Pt supported on C-TiO2 (Pt/C-TiO2) was varied depending on the concentration of TiO2. The best ORR activity was obtained on Pt/C-TiO2-x. Although the initial activity of Pt/C-TiO2-x was lower than that of a commercial Pt/C, which resulted from low electrical conductivity of C-TiO2-x, the former catalyst showed higher electrocatalytic performance than the latter after accelerating durability test had been performed. In order to improve both the initial activity and durability, the C-TiO2 support was further modified with Nb oxide (C-NbTi-20/x; x represents wt% of NbTi). The ORR activity of Pt/C-NbTi-20/x was the highest among the catalysts tested. Compared to Pt/C, 1.5-fold increased kinetic current was achieved on the Pt/C-NbTi-20/x. The morphological control of Pt to have hollow structure has been highlighted as a strategy for the design of catalyst since the structural advantages induced by hollow interior have been proved to have a positive effect in ORR activity. The Pt-based hollow nanoparticles have been usually prepared through a transmetallation between the metal template with low reduction potential and Pt ions. However, several synthetic complications such as pre-formation of metal template and the use of surfactant under air-excluding condition make this method unsuitable for the large-scale production. In this study, PtNi alloy hollow nanoparticles (PtNi/C and PtNi/C AT; AT denote acidic synthesis condition) with a uniform size were formed on a carbon support through a one-step and one-pot process without the need of pre-formation of metal template, surfactant and air-excluding condition, which has not been reported previously. Hollow structure of PtNi/C and PtNi/C AT was confirmed by STEM images and TEM-EDX line profile. It was observed that the shell consisted of Pt-enriched surface layer and PtNi alloy inner layer. Contrary to Pt hollow nanoparticles prepared by a conventional method, the PtNi/C were observed to have non-porous shell structure. The electrochemical active surface areas of PtNi/C and PtNi/C AT were lower than that of a commercial carbon-supported Pt nanoparticle (Pt/C). However, largely enhanced ORR performance was obtained on the carbon-supported PtNi hollow catalysts, particularly, on PtNi/C, compared to Pt/C. The Pt mass-normalized activity of PtNi/C AT was 3.3 times higher than that of Pt/C, which exceeds activity target of fuel cell catalyst.
Polymer Electrolyte Membrane Fuel Cell (PEMFC) is an electrochemical energy conversion device, in which hydrogen reacts with oxygen, producing electricity and water as the only by-product. Due to the high energy density and conversion efficiency, PEMFC has particularly attracted considerable attention as a primary power source of zero-emission electric vehicle. However, its widespread application is impeded by the high cost of electrocatalyst, in particular, for oxygen reduction reaction (ORR) at cathode. To make PEMFC more economically competitive to the combustion engine, therefore, currently employed Pt-based catalyst for ORR should be improved in terms of its activity and durability. In this work, two approaches have been applied to enhance ORR performance of Pt-based electrocatalyst. One is the modification of carbon support with transition metal oxide and the other is the morphology control of Pt-based alloy. A commercial carbon support was modified with TiO2 (C-TiO2-X; X represents wt% of TiO2), where the concentration of TiO2 was controlled from 10 to 30 wt% by adjusting the amount of TiO2 precursor during the preparation. All the C-TiO2 showed highly dispersed TiO2 with anatase crystalline phase, while the size of TiO2 slightly increased with increasing the amount of TiO2 precursor. The ORR activity of Pt supported on C-TiO2 (Pt/C-TiO2) was varied depending on the concentration of TiO2. The best ORR activity was obtained on Pt/C-TiO2-x. Although the initial activity of Pt/C-TiO2-x was lower than that of a commercial Pt/C, which resulted from low electrical conductivity of C-TiO2-x, the former catalyst showed higher electrocatalytic performance than the latter after accelerating durability test had been performed. In order to improve both the initial activity and durability, the C-TiO2 support was further modified with Nb oxide (C-NbTi-20/x; x represents wt% of NbTi). The ORR activity of Pt/C-NbTi-20/x was the highest among the catalysts tested. Compared to Pt/C, 1.5-fold increased kinetic current was achieved on the Pt/C-NbTi-20/x. The morphological control of Pt to have hollow structure has been highlighted as a strategy for the design of catalyst since the structural advantages induced by hollow interior have been proved to have a positive effect in ORR activity. The Pt-based hollow nanoparticles have been usually prepared through a transmetallation between the metal template with low reduction potential and Pt ions. However, several synthetic complications such as pre-formation of metal template and the use of surfactant under air-excluding condition make this method unsuitable for the large-scale production. In this study, PtNi alloy hollow nanoparticles (PtNi/C and PtNi/C AT; AT denote acidic synthesis condition) with a uniform size were formed on a carbon support through a one-step and one-pot process without the need of pre-formation of metal template, surfactant and air-excluding condition, which has not been reported previously. Hollow structure of PtNi/C and PtNi/C AT was confirmed by STEM images and TEM-EDX line profile. It was observed that the shell consisted of Pt-enriched surface layer and PtNi alloy inner layer. Contrary to Pt hollow nanoparticles prepared by a conventional method, the PtNi/C were observed to have non-porous shell structure. The electrochemical active surface areas of PtNi/C and PtNi/C AT were lower than that of a commercial carbon-supported Pt nanoparticle (Pt/C). However, largely enhanced ORR performance was obtained on the carbon-supported PtNi hollow catalysts, particularly, on PtNi/C, compared to Pt/C. The Pt mass-normalized activity of PtNi/C AT was 3.3 times higher than that of Pt/C, which exceeds activity target of fuel cell catalyst.
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