Gu-Gon Park

Ordered mesoporous porphyrinic carbons with very high electrocatalytic activity for the oxygen reduction reaction

The high cost of the platinum-based cathode catalysts for the oxygen reduction reaction (ORR) has impeded the widespread application of polymer electrolyte fuel cells. We report on a new family of non-precious metal catalysts based on ordered mesoporous porphyrinic carbons (M-OMPC; M = Fe, Co, or FeCo) with high surface areas and tunable pore structures, which were prepared by nanocasting mesoporous silica templates with metalloporphyrin precursors. The FeCo-OMPC catalyst exhibited an excellent ORR activity in an acidic medium, higher than other non-precious metal catalysts. It showed higher kinetic current at 0.9 V than Pt/C catalysts, as well as superior long-term durability and MeOH-tolerance. Density functional theory calculations in combination with extended X-ray absorption fine structure analysis revealed a weakening of the interaction between oxygen atom and FeCo-OMPC compared to Pt/C. This effect and high surface area of FeCo-OMPC appear responsible for its significantly high ORR activity.

Pore size effect of the DMFC catalyst supported on porous materials

Abstract Activated carbons were employed for the support material of catalyst in the direct methanol fuel cell (DMFC). Until now, most of the papers related to the catalyst of fuel cells reported carbon blacks as catalyst support materials. In the present study, an activated carbon was re-activated by chemical activation method with NaOH at the various temperatures for the development of meso or/and macro pores. By using these pretreated activated carbons, Pt–Ru catalysts on the activated carbons (Pt–Ru/AC) which have various surface areas and porosities were prepared for the anode catalyst of DMFC. Surface areas and the crystal sizes of active metals were measured by N 2 adsorption and XRD, respectively. The performance of prepared Pt–Ru/AC catalysts has been evaluated by using the typical I – V curve of air breathing-type DMFC single cell. By this study, the optimum conditions of catalyst were suggested by correlating the catalyst reactivity with surface areas, pore sizes, metal sizes and distances between active metals.

Carbon Nanotubes/Heteroatom‐Doped Carbon Core–Sheath Nanostructures as Highly Active, Metal‐Free Oxygen Reduction Electrocatalysts for Alkaline Fuel Cells

A facile, scalable route to new nanocomposites that are based on carbon nanotubes/heteroatom-doped carbon (CNT/HDC) core-sheath nanostructures is reported. These nanostructures were prepared by the adsorption of heteroatom-containing ionic liquids on the walls of CNTs, followed by carbonization. The design of the CNT/HDC composite allows for combining the electrical conductivity of the CNTs with the catalytic activity of the heteroatom-containing HDC sheath layers. The CNT/HDC nanostructures are highly active electrocatalysts for the oxygen reduction reaction and displayed one of the best performances among heteroatom-doped nanocarbon catalysts in terms of half-wave potential and kinetic current density. The four-electron selectivity and the exchange current density of the CNT/HDC nanostructures are comparable with those of a Pt/C catalyst, and the CNT/HDC composites were superior to Pt/C in terms of long-term durability and poison tolerance. Furthermore, an alkaline fuel cell that employs a CNT/HDC nanostructure as the cathode catalyst shows very high current and power densities, which sheds light on the practical applicability of these new nanocomposites.

Current distribution in a single cell of PEMFC

Abstract Understanding of current and temperature distributions along with the variation of gas composition in the cell of PEMFC is crucial for designing cell components such as the flow field plate and the membrane–electrode assembly. Current distribution in the single cell was experimentally measured by using a specially designed single cell which was composed of 81 compartments. Each compartment was electronically insulated from the neighboring compartments. Current distribution was measured by using Hall effect sensors that were connected to the corresponding compartments. The influences of flooding and stoichiometry variation of the feed gas were discussed in terms of the rate of electrochemical reaction, from the measured distributions of local currents in a segmented single cell.

Effect of pore structure of catalyst layer in a PEMFC on its performance

Influence of pore structure of the cathode catalytic layer in a PEMFC in its performance has been studied. Membrane–electrode assemblies were prepared to have various kinds of porosities and pore structures using spray-drying method. From the I–V characteristics of catalytic layers, pore structure seems to be an important factor determining the cell performance. Addition of thermoplastic agent seems to indeed enhance the structural stability and performance of the catalytic layer. Pore forming agent is considered to assist the transport of oxygen through the catalytic layer.

A multi-layer structured cathode for the PEMFC

Multi-layer structured cathodes for PEMFC were prepared by a spray-drying method to provide more efficient oxygen reduction in the cathode. The catalytic layer is, in general, composed of electrolyte for proton conduction and of Pt/C for both the electrochemical reaction and electron conduction. Although the presence of electrolyte is essential for proton conduction, the electrolyte phase retards the electron conduction through the catalytic layer because the electrolyte is electronically insulating. For the Pt/C part, vice versa is valid. In an attempt to develop a cathode possessing superior properties both in the proton and electron conduction, double catalytic electrolyte-rich and -poor layers were coated on the polymer electrolyte membrane (PEM). Performances of the double layered cathodes were evaluated from the current–voltage (I–V) characteristics of single cells. In addition, pressure drops across the fabricated cathodes were determined by using permeability measuring apparatus. From the experimental results, the rate of electrochemical reaction in the cathode was discussed in terms of proton transport and electronic conduction along with oxygen transport.

Self-Supported Mesostructured Pt-Based Bimetallic Nanospheres Containing an Intermetallic Phase as Ultrastable Oxygen Reduction Electrocatalysts

Developing highly active and stable cathode catalysts is of pivotal importance for proton exchange membrane fuel cells (PEMFCs). While carbon-supported nanostructured Pt-based catalysts have so far been the most active cathode catalysts, their durability and single-cell performance are yet to be improved. Herein, self-supported mesostructured Pt-based bimetallic (Meso-PtM; M = Ni, Fe, Co, Cu) nanospheres containing an intermetallic phase are reported, which can combine the beneficial effects of transition metals (M), an intermetallic phase, a 3D interconnected framework, and a mesoporous structure. Meso-PtM nanospheres show enhanced oxygen reduction reaction (ORR) activity, compared to Pt black and Pt/C catalysts. Notably, Meso-PtNi containing an intermetallic phase exhibits ultrahigh stability, showing enhanced ORR activity even after 50 000 potential cycles, whereas Pt black and Pt/C undergo dramatic degradation. Importantly, Meso-PtNi with an intermetallic phase also demonstrated superior activity and durability when used in a PEMFC single-cell, with record-high initial mass and specific activities.

Enhanced Oxygen Reduction Activity of IrCu Core Platinum Monolayer Shell Nano-electrocatalysts

Designing novel cathode materials for a proton exchange membrane fuel cell with high activity for the oxygen reduction reaction, low Pt loading, and enhanced long-term stability is imperative for its sustainability. To date, Pt monolayer based electrocatalysts deposited on a metallic core substrate have shown promising possibilities. In this study, we synthesized bimetallic IrCu nanoparticles and used them as a core for Pt monolayer electrocatalysts. It was found that the de-alloyed IrCu nanoparticle surfaces increased both the mass and specific activities of the resulting Pt monolayer catalyst. In addition, we demonstrated that Pt monolayer electrocatalysts with a de-alloyed IrCu core have a better stability than those using a non-dealloyed core based on a 5,000 potential cycling test. These data describe a new simple synthesis of a high-performance catalyst suitable for practical applications.

Performance Improvement of Electrode for Polymer Electrolyte Membrane Fuel Cell

The very high power density output available from polymer electrolyte membrane fuel cells combined with low cost has high potential for commercialization. Such high power densities are attained via better utilization of Pt crystallites in the reaction layer. This enhanced performance can be achieved by making a thin catalyst layer on the membrane surface. The robustness in the front surface catalysts is essential to minimize the coagulation of Pt particles when the fuel cells are subjected to long-term operation. This robustness of the catalyst structure depends on the manufacturing processes and also the organic solvents used to make the slurry. In this work, five different electrodes were fabricated by using different fabrication procedures, and the poison effect of CO was investigated at the anode interface.

A new evaluation method of anode/cathode used for polymer electrolyte membrane fuel cell

Abstract A new evaluation method of anode/cathode used for polymer electrolyte membrane fuel cell (PEMFC) was developed by using membrane/electrode assembly combined with a gold wire. The gold wire was centered in the polymer electrolyte by the concurrent pressing of two Nafion sheets, gold wire and 10% Nafion solution. Using this new evaluation method, the magnitude of polarization in each side of the anode and cathode was simultaneously obtained with the I–V curve of PEMFC. The cathodic overpotential under oxygen or air and the anodic overpotential under hydrogen containing various CO contents were measured as a function of the current density. This evaluation method is more conveniently employed to analyze quantitatively the anodic and cathodic polarization of PEMFC.