Youngkook Kwon

A Stable and Cost-Effective Anode Catalyst Structure for Formic Acid Fuel Cells†

The high energy density, fast oxidation kinetics, and convenience of use of liquid formic acid (HCOOH), as well as the simplicity of power-system integration make direct formic acid fuel cells (DFAFCs) a promising power source for portable device applications. Considerable progress in aspects of DFAFC research and engineering has been achieved in recent years, which has enabled the fuel-cell technology to be implemented in practical devices. However, large-scale practical commercialization has been limited by several challenging issues such as high anode overpotential, excessive fuel and water permeability of the polymer electrolyte membrane, and questionable long-term durability of the fuel cells. The issue of high overpotential for anode catalysts is associated with the formation of poisons on the catalyst surface and also with the large amount of catalyst loading. To date, despite the problem of being strongly poisoned by intermediate species, Pt is the best-known anode catalyst for the oxidation of small organic molecules. Besides Pt, Pd catalysts have recently shown superior performances compared to platinum-based catalysts in the oxidation ultrapure HCOOH in DFAFCs, because of the great initial activity of Pd, even at low temperature. However, Pd catalysts have a significant drawback; their high performance is not sustained for extended time periods, largely because of the vulnerability of these catalysts towards uncharacterized intermediate species and the potential for the dissolution of Pd in acidic solutions. 12] To enhance the power performance as well as the durability of the catalyst, we have recently demonstrated that irreversible modification of the Pt metal surface with foreign metal adatoms such as Bi, 13, 14] Pb , and Sb 16] is a powerful method to drive a practical DFAFC system. In addition, an effective anode structure that alleviates mass transport of HCOOH in the membrane electrode assembly (MEA) enabled us to reduce the amount of Pt loading and extend the range of the HCOOH concentration windows. Herein, we report a novel approach for the fabrication of more stable and cost-effective anode catalysts for DFAFC by using a three-step electrochemical process. The newly developed catalyst, which contains Pt modified with Bi, is directly applied to the fuel cell to evaluate its catalytic activity and performance. The PtBi catalyst was fabricated in three consecutive electrochemical steps, namely: 1) electrochemical oxidation of carbon paper to form the adequate catalyst support, followed by 2) Pt electrodeposition, and 3) underpotential deposition (UPD) of Bi onto the Pt. The conceptual design of the final electrode is illustrated schematically in Figure 1 and

Electrocatalytic Recycling of CO2 and Small Organic Molecules

As global warming directly affects the ecosystems and humankind in the 21st century, attention and efforts are continuously being made to reduce the emission of greenhouse gases, especially carbon dioxide (CO2). In addition, there have been numerous efforts to electrochemically convert CO2 gas to small organic molecules (SOMs) and vice versa. Herein, we highlight recent advances made in the electrocatalytic recycling of CO2 and SOMs including (i) the overall trend of research activities made in this area, (ii) the relations between reduction conditions and products in the aqueous phase, (iii) the challenges in the use of gas diffusion electrodes for the continuous gas phase CO2 reduction, as well as (iv) the development of state of the art hybrid techniques for industrial applications. Perspectives geared to fully exploit the potential of zero-gap cells for CO2 reduction in the gaseous phase and the high applicability on a large scale are also presented. We envision that the hybrid system for CO2 reduction supported by sustainable solar, wind, and geothermal energies and waste heat will provide a long term reduction of greenhouse gas emissions and will allow for continued use of the abundant fossil fuels by industries and/or power plants but with zero emissions.

Autonomous interfacial creation of nanostructured lead oxide

We first established a process for the autonomous creation of PbO nanostructures consisting of a simple three-step procedure for both the formation of Pb nanoparticles and their oxidation. Oxygen contacting aqueous media results in an autonomous conversion from electrodeposited Pb particles to PbO nanostructures; i) flower-like PbO structures are placed at the interface of water and oxygen, ii) the growth/burst of PbO nanowires in various directions is observed in the middle of water media, and iii) ultra-thin PbO nano-platelets are dominantly placed onto the substrate. A new mechanistic origin was also proposed based on experimental observations and further suggests that major requirements are essential for the autonomous creation of PbO nanostructures.

Electrochemical Characteristics of Home-Made Bipolar Plate and Its Relationship with Fuel Cell Performance

The effect of physico-electrochemical properties of carbon bipolar plate(BPP) on hydrogen and formic acid fuel cell performance has been investigated. BPP made of conventional graphite and carbon fiber composite were compared with the factors of interfacial contact resistance (ICR), corrosion behaviours, and hydrophobicity. Among them, the ICR of carbon fiber composite BPP has 50% higher than conventional graphite and the surface of carbon fiber composite BPP became rougher due to weaker corrosion resistance. Fuel cell performance was strongly dependent of ICR value of carbon bipolar plate.