An etched nanoporous Ge anode in a novel metal-air energy conversion cell.

We first report the successful synthesis of porous germanium with ordered hierarchical structures, via controlled etching, and show its performance as an anode in a new metal-air battery. Our experimental results demonstrate the potential use of porous germanium in a high power density Ge-air energy conversion cell, showing a stable long-term discharge profile at various current drains.

On the origin of reactive Pd catalysts for an electrooxidation of formic acid.

We investigated the origin of the reactive surface of Pd catalysts during the electrocatalytic oxidation of formic acid. XPS analysis was the primary tool adapted to characterize the surface changes in Pd catalysts arising from interactions with formic acid. Pd catalysts showed fast deactivation, though their activity could be simply recovered by applying a reduction potential at which hydrogen evolution reaction can occur. XPS analysis revealed that the surface of Pd catalysts is significantly affected by interaction with formic acid, thus confirming that the surface coverage of oxygen species plays an important role in formic acid electrooxidation on the Pd catalysts. At the same time, mass transfer of formic acid also has an effect on the deactivation of Pd catalysts.

Understanding underlying processes in formic acid fuel cells.

A basic understanding of electrode structure and the characteristics of its components can be powerfully utilized in fuel cell applications such as direct formic acid fuel cell (DFAFC) system integration and HCOOH concentration controlled systems. There have been, thus, tremendous efforts made to elucidate theoretical aspects of electrochemical processes involving new anode catalysts and put them into practical effect on formic acid fuel cells. Herein, we highlight recent studies for better understanding of the underlying processes in DFAFC: (i) a systematic approach for developing cost-effective and stable anode catalysts and electrode structures that incorporate mass transport characteristics of HCOOH; (ii) a clear evaluation of the HCOOH crossover rate based on its physicochemical properties; and (iii) a theoretical assessment process of individual electrodes and related components during DFAFC operation using electrochemical impedance spectroscopy and a reversible hydrogen reference electrode, which can potentially detect subtle changes in the DFAFC mechanism and provide useful information pertaining to rate-limiting processes.

Enhancement of methanol tolerance in DMFC cathode: addition of chloride ions.

In the operation of a direct methanol fuel cell, the modification by chloride ions on the surface of a Pt cathode can facilitate the extraordinary increase of power performance and long-term stability. Analyzing the results of cyclic voltammograms and electrochemical impedance spectroscopy, the positive shift of Pt oxidation onset potential and the depression of oxidation current are observed, which results from the role of chloride as surface inhibitor. In addition, O(2) temperature-programmed desorption and X-ray photoelectron spectroscopy also reveal that the suppression of Pt surface oxide can be best understood in terms of lower binding of oxygen species by the alteration of electronic state of Pt atoms. Such a reduced surface oxide formation not only provides more efficient proton adsorption sites with high selectivity but also decreases the mixed potential by crossover methanol, resulting in higher performance and stability even under high voltage long-term operation.