Hyung-Suk Oh

Preparation of carbon-supported nanosegregated Pt alloy catalysts for the oxygen reduction reaction using a silica encapsulation process to inhibit the sintering effect during heat treatment

The heat treatment of alloy nanoparticles to improve their catalytic properties generally results in severe sintering. In this study, we report a new synthetic process of silica encapsulation to inhibit the sintering of Pt3Co1 alloy particles during heat treatment at high temperature. The silica layer acts as a physical barrier to prevent sintering; thus, the carbon-supported Pt3Co1 alloy nanoparticles retained their small particle size after heat treatment. The heat treatment allows the atoms to rearrange themselves, which results in a Pt-rich surface of the alloy nanoparticles. As a result, catalytic activity and stability were improved significantly.

Modification of electrodes using Al2O3 to reduce phosphoric acid loss and increase the performance of high-temperature proton exchange membrane fuel cells

The addition of a small amount of Al2O3 (6 wt%) to the catalyst layer of high temperature-polymer electrolyte membrane fuel cells (HT-PEMFCs) using phosphoric acid-doped membranes was proved to be an effective way to increase durability and performance. It was confirmed from the XRD study that Al2O3 reacts with phosphoric acid diffusing from the membrane to the electrode and produces aluminum dihydrophosphate (Al(H2PO4)3), which has proton conductivity. As a result, the formation of Al(H2PO4)3 not only reduces the loss of phosphoric acid and the resistance in fuel cells but also enhances the electrochemical surface area of catalysts.

Preparation of Pt/C catalyst using alcohol reduction and a polyol process in the presence of urea for oxygen reduction reaction

The effect of urea hydrolysis was studied on the preparation and properties of Pt/C catalyst. The hydrolysis of urea provided hydroxyl ions in a controlled manner that prevented the localized pH change in the solution and only surface precipitation is resulted in a particle growth. From rotating ring disk electrode (RRDE) experiments, the Pt/C prepared in the presence of urea showed better exchange current density toward the oxygen reduction reaction. The rate of H2O2 formation was reduced when urea was used in the alcohol reduction process and it was further decreased in the Pt/C catalyst prepared by the polyol process combined with urea.

Effect of Graphitized Carbon Supports on Electrochemical Carbon Corrosion in Polymer Electrolyte Membrane Fuel Cells

The influence of graphitization of carbon support on the electrochemical corrosion of carbon and sintering of Pt particles are investigated by measuring emission at a constant potential of 1.4 V for 30 min using on-line mass spectrometry and cyclic voltammogram. In comparison to commercial Pt/C (from Johnson Matthey), highly graphitized carbon nanofiber (CNF) supported Pt catalyst exhibits lower performance degradation and emission. As the more carbon corrosion occurred, the more prominent changes were detected in electrochemical characteristics of fuel cell. This indicates that the carbon corrosion affects significantly the fuel cell durability. From the observed results, CNF is considered to be more corrosion resistant material as a catalyst support. However, CNF shows higher aggregation of Pt particles under repeated cyclic voltammetry between 0 and 0.8 V where the carbon corrosion is not initiated.

Effect of Acid Treatment of Graphitized Carbon on Carbon Corrosion in Polymer Electrolyte Membrane Fuel Cells

Pt catalyst was adsorbed on Carbon nanofiber (CNF) by modified polyol method after acid treatment of the carbon support with and . As the time for acid treatment increases, more oxygen functional groups on carbon surface were produced which improve the loading amount and dispersion of Pt catalyst on carbon supports. In order to inspect the effect of CNF acid treatment time on electrochemical corrosion, constant potential of 1.4 V was applied to a single cell for 30 min and the amount of emitted was monitored with on-line mass spectrometry. According to the results of our experiment, more was produced with Pt/ oxidized-CNF catalyst in compared to that with unoxidized-CNF. Increasing acid treatment time also induces the more emission. Besides, performance degradation after corrosion test expanded with severer carbon corrosion. From the observed results, it can be concluded that the acid treatment of CNF is beneficial to catalyst loading, but it also is a significant factor declining the fuel cell durability by accelerating electrochemical oxidation of carbon support.