Seung Jun Hwang

Electrodeposited Ni dendrites with high activity and durability for hydrogen evolution reaction in alkaline water electrolysis

Different shapes of various nickel structures, including dendrite, particle and film are fabricated by electrodeposition under various conditions. The shape of nickel structures is definitely dependent on the deposition potential, leading to different electrochemical surface area and edge facets. The nickel particle which has a polycrystalline center and edge is obtained at high negative potential. On the other hand, the nickel dendrite deposited by relatively low negative potential exhibits large electrochemical surface area and a particularly active facet for hydrogen evolution reaction (HER) in alkaline water electrolysis. In fact the nickel dendrite shows the highest catalytic activity and stability for HER among the various nickel structures.

Effect of morphology of electrodeposited Ni catalysts on the behavior of bubbles generated during the oxygen evolution reaction in alkaline water electrolysis

We have investigated the release of active sites blocked by bubbles attached on the surface of catalysts during the oxygen evolution reaction (OER) in alkaline water electrolysis, via the modulation of the wetting properties of the four different morphologies of a nickel catalyst.

Facile preparation of carbon-supported PtNi hollow nanoparticles with high electrochemical performance

To design Pt-based materials with a hollow structure via a galvanic reaction would be one of the effective ways to prepare electro- catalysts with high activity. The galvanic reaction between Pt ions and metal template is usually conducted under limited conditions, which makes the preparation of Pt hollow nanoparticles laborious. Here, we introduce a one-step and one-pot synthetic approach for the preparation of carbon-supported PtNi alloy hollow nanoparticles with a narrow size distribution. Prepared PtNi alloys were characterized by a nonporous shell consisting of a Pt-enriched surface layer and an inner alloy layer of Pt and Ni. Due to its unique structural advantages, this material showed excellent electrocatalytic performance for oxygen reduction (3.3- and 7.8-fold enhanced mass and specific activities compared to those of a commercial carbon-supported Pt nanoparticle). A possible mechanism for the formation of PtNi hollow structure is suggested.

Promoting effects of La for improved oxygen reduction activity and high stability of Pt on Pt–La alloy electrodes

The design of polymer electrolyte fuel cell electrocatalysts depends on two equally important fundamental principles: the optimization of electrocatalytic activities as well as the long-term stability under operating conditions (e.g., pH 0.8 V). Pt-based alloys with transition metals (i.e., Pt–La) address both of these key issues. The oxygen reduction kinetics depends on the alloy composition which, in turn, is related to the d-band center position. The stability of the oxygen reduction reaction is predictable by correlation of the d-band fillings and vacancies of Pt–M (M = Ti, Fe, Zr and La).

Supported core@shell electrocatalysts for fuel cells: close encounter with reality.

Core@shell electrocatalysts for fuel cells have the advantages of a high utilization of Pt and the modification of its electronic structures toward enhancement of the activities. In this study, we suggest both a theoretical background for the design of highly active and stable core@shell/C and a novel facile synthetic strategy for their preparation. Using density functional theory calculations guided by the oxygen adsorption energy and vacancy formation energy, Pd3Cu1@Pt/C was selected as the most suitable candidate for the oxygen reduction reaction in terms of its activity and stability. These predictions were experimentally verified by the surfactant-free synthesis of Pd3Cu1/C cores and the selective Pt shell formation using a Hantzsch ester as a reducing agent. In a similar fashion, Pd@Pd4Ir6/C catalyst was also designed and synthesized for the hydrogen oxidation reaction. The developed catalysts exhibited high activity, high selectivity, and 4,000 h of long-term durability at the single-cell level.

Binaphthyl-based molecular barrier materials for phosphoric acid poisoning in high-temperature proton exchange membrane fuel cells

In this study, thiol-functionalized binaphthyl barrier molecules were designed and synthesized for eliminating phosphoric acid (PA)-poisoning on Pt catalysts in oxygen reduction reactions (ORRs). In high-temperature proton exchange membrane fuel cell, the ORR activity of Pt catalysts significantly decreases because of the PA poisoning. The binaphthyl thiol (BNSH) molecules with a tweezer-like structure can self-assemble on the Pt surface, thereby blocking the adsorption of PA, while permitting the approach of smaller oxygen molecules. After the treatment of Pt surfaces with BNSHs, the ORR activities were tested in the presence of PA, and the results were compared with respect to the molecular structures of BNSHs. Even in the presence of PA, the ORR activity of BNSH-treated Pt catalysts appeared to restore significantly up to the level of the pristine Pt without PA (kinetic current density at 0.8 V from 12 to 20.4 mA cm−2). This enhanced activity was attributed to the physical blocking of PA molecules on Pt surface and was affected by the molecular structures such as tweezer backbone, length of alkyl chains, and the type and number of functional groups.

Electrochemical Reduction of Carbon Dioxide Using a Proton Exchange Membrane

Electrochemical reduction of carbon dioxide has been widely studied by many sci- entists and researchers. Recently, the production of formic acid, which is expensive but highly useful liquid material, is receiving a great attention. However, difficulties in the electrochemical reduction process and analyzing methods impede the researches. Therefore, it is important to design an adequate system, develop the reduction process and establish the analyzing methods for carbon dioxide reduction to formic acid. In this study, the production of formic acid through electrochemical reduction of carbon dioxide was performed and concentration of the product has been analyzed. Large scale batch cell with proton exchange membrane was used in the experiment. The electrochemical experiment has been performed using a series of metal cata- lysts. Linear sweep voltammetry (LSV) and chronoamperometry were performed for carbon dioxide reduction and electrochemical analysis using silver chloride and platinum electrode as a reference electrode and counter electrode, respectively. The concentration of formic acid generated