Ki Rak Lee

Combinatorial screening of highly active Pd binary catalysts for electrochemical oxygen reduction.

Electro-catalysts omitting platinum are of interest to reduce the cost of fuel cells. The development of non-Pt alloys for this purpose would require a large number of experiments. Palladium-based bimetallic electro-catalysts using eight different metals were computationally evaluated for the oxygen reduction reaction (ORR) and were made and tested in acidic media using combinatorial methods. A Pd-Co alloy showed the closest oxygen adsorption energy to platinum in simple theoretical model calculations, suggesting the highest ORR activity. This prediction was confirmed experimentally, suggesting that the single parameter of oxygen adsorption energy can be a useful guide to developing non-Pt oxygen reduction catalysts in the future.

Enhancement in electro-oxidation of methanol over PtRu black catalyst through strong interaction with iron oxide nanocluster.

One of the major issues in direct methanol fuel cell research is to develop a new catalyst for methanol electro-oxidation reaction (MOR) with high activity and low cost. In this study, a new, simple, and economic way was introduced to improve the catalytic activity of commercial PtRu black catalyst for the MOR. A nanocomposite electrode was fabricated by mixing the PtRu catalyst with Fe(2)O(3) nanoclusters. When 10 wt % of the PtRu catalyst was replaced by the Fe(2)O(3) nanoclusters, mass activity (A/g(Pt)) increased by 80% compared to that of the pure PtRu catalyst. Specific activity of the mixed catalyst was 100% higher than that of the pure PtRu catalyst. The nanocomposite catalysts were also applied to single cells. Although the amount of the PtRu catalyst was reduced by 10 wt %, 10% higher potential was observed in the nanocomposite catalysts at a current density of 100 mA/cm(2).

A direct ammonium carbonate fuel cell with an anion exchange membrane

Direct ammonium carbonate- and ammonia-based fuel cells with an anion exchange membrane (AEM) and Pt/C catalyst have been constructed and their performance has been evaluated. Ammonium carbonate, which has never been used as a fuel, can become massively available when CO2 is captured with ammonia as a non-recyclable, single-use adsorbent. It is a solid at ambient conditions and thus as a fuel option, has the advantages of volumetric energy density, ease of transportation, and storage safety. In this paper, the oxidative activities of the Pt/C catalyst on ammonium carbonate, along with ammonia, were evaluated by means of a half-cell test. Ammonium carbonate exhibited approximately 75% of the oxidation activity of ammonia; this reduced activity was likely attributable to the existence of the carbonate. This was also observed in a single cell test: the direct ammonium carbonate fuel cell generated approximately 50% lower maximum power density than that of an ammonia-based counterpart. Although its performance is seemingly inferior, it turns out that the energy power is comparable to pure ammonia or at least in the same order of magnitude. We showed that ammonium carbonate has enough potential as a fuel in low temperature polymer fuel cells.

Optimum concentration gradient of the electrocatalyst, Nafion® and poly(tetrafluoroethylene) in a membrane-electrode-assembly for enhanced performance of direct methanol fuel cells

A combinatorial library of membrane-electrode-assemblies (MEAs) which consisted of 27 different compositions was fabricated to optimize the multilayer structure of direct methanol fuel cells. Each spot consisted of three layers of ink and a gradient was generated by employing different concentrations of the three components (Pt catalyst, Nafion® and polytetrafluoroethylene (PTFE)) of each layer. For quick evaluation of the library, a high-throughput optical screening technique was employed for methanol electro-oxidation reaction (MOR) activity. The screening results revealed that gradient layers could lead to higher MOR activity than uniform layers. It was found that the MOR activity was higher when the concentrations of Pt catalyst and Nafion ionomer decreased downward from the top layer to the bottom layer. On the other hand, higher MOR activity was observed when PTFE concentration increased downward from the top to the bottom layer.

Quaternary Pt2Ru1Fe1M1/C (M=Ni, Mo, or W) catalysts for methanol electro-oxidation reaction

Quaternary Pt2Ru1Fe1Ni1/C (M=Ni, Mo, or W) catalysts were investigated for the methanol electro-oxidation reaction (MOR). Electrocatalytic activities of the quaternary catalysts for CO electro-oxidation were studied via CO stripping experiments, and the Pt2Ru1Fe1Ni1/C and Pt2Ru1Fe1W1/C catalysts exhibited lowered on-set potential compared to that of a commercial PtRu/C catalyst. MOR activities of the quaternary catalysts were determined by linear sweep voltammetry (LSV) experiments, and the Pt2Ru1Fe1Ni1/C catalyst outperformed the commercial PtRu/C catalyst by 170 and 150% for the mass and specific activities, respectively. X-ray photoelectron spectroscopy (XPS) was employed to analyze surface oxidation states of constituent atoms, and it was identified that the structure of the synthesized catalysts are close to a nano-composite of Pt and constituent metal hydroxides and oxides. In addition, the XPS results suggested that the bi-functional mechanism accounts for the improved performance of the Pt2Ru1Fe1Ni1/C and Pt2Ru1 Fe1W1/C catalysts.

Performance improvement of direct methanol fuel cells via anodic treatment using various organic acids

Performance improvement of direct methanol fuel cells (DMFCs) was achieved via an anodic treatment technique. Previously, anodic treatment was performed using sulfuric acid as acidic media, but various organic acids including formic, acetic, oxalic, and citric acids were employed in this study to avoid the use of toxic sulfuric acid. By replacing sulfuric acid to organic acids, a potential damage to catalyst layers and other components such as polymer electrolyte membrane and bipolar plates are expected to be minimized. The anodic treatment was performed by applying 0.7 V (vs. reversible hydrogen electrode) at the anode of DMFCs flowing the organic acid solutions for 30min. After the anodic treatment, peak power densities of DMFCs were increased by +7, +32, +23, and −2.6% when formic, acetic, oxalic, and citric acid solutions were employed, respectively. The enhanced catalytic activity of the DMFCs in the acetic and oxalic acid solutions was confirmed by analyzing electrochemical impedance spectroscopy data.