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A mesh-type dimensionally stable anode (DSA) consisting of ruthenium and iridium with low catalyst loading was prepared as an oxygen evolution reaction catalyst in acidic and alkaline media. The electrodeposition (ED) conditions, i.e., applied current density and total cycle number, and ED solutions with different precursor ratios of ruthenium to iridium are examined to fabricate various DSAs with a uniform thickness, and the effect of the iridium content on the catalytic activity is investigated. Among various DSA electrodes, the DSA electrode without iridium exhibits the highest activity and stability in the acidic medium owing to the high ratio of ruthenium. Conversely, the DSA electrode obtained using the ED solution with the ratio of 8:2 exhibits the highest performance in the alkaline medium. This is because the DSA electrode without iridium showed low stability, which is attributed to the dissolution of ruthenium oxide in the alkaline medium. In addition, two large-scale DSA electrodes optimized in the acidic and alkaline electrolytes show excellent performance, indicating the feasibility of the application of this electrode in practical electrolysis.

Formic acid is a chemical with a simple molecular structure containing hydrogen. This liquid at room temperature is easy to handle and has a low toxicity, and is thus in the spotlight as a fuel. In particular, formic acid is an excellent fuel candidate because it can be operated at low temperatures when applied as a fuel in fuel cells with a high theoretical open-circuit voltage (1.48 V). However, it has a drawback in that the electrode catalyst is deactivated due to the generation of CO intermediates when formic acid is oxidized during cell operation. Therefore, to prevent this, an irreversibly adsorbed Bi on Pt catalyst is applied to a direct formic acid fuel cell (DFAFC) anode because it is easy to synthesize and economical. Physical analyses such as transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were conducted, and electrochemical evaluations were performed through half-cell and single-cell level tests. The results revealed that the formic acid oxidation reaction activity of the Bi-modified Pt/C was 13 times higher than that of the conventional catalyst at 0.58 V. Further, a DFAFC stack was fabricated using the Bi-modified Pt/C, which yielded a power of 300 W. These results suggest that a simple synthesis method can be applied to fabricating industrially available DFAFC stacks.

In this study, we developed high-performance anion-exchange membrane water electrolysis (AEMWE) by investigating various parameters. To enhance AEMWE performance, the effects of the membrane-electrode assembly (MEA) fabrication method, operating conditions, and MEA parameters were examined. As a result of the optimization and the use of FAA-3-50 and FAA-3-Br as the AEM and anion-exchange ionomer, respectively, AEMWE showed the highest performance reported thus far. Single-cell tests and electrochemical impedance spectroscopy results indicate that optimized AEMWE minimized the ohmic, charge-transfer, and mass transport resistances. Overall, by examining the AEMWE parameters, we were able to improve the electrochemical reactions, namely, the oxygen evolution reaction and hydrogen evolution reaction, and achieved outstanding performance.

Graphitic carbon nitride-carbon nanofiber (g-CN-CNF) was synthesized as a bifunctional catalyst in an anion-exchange membrane water electrolyzer (AEMWE), and primary and rechargeable Zn–air cells. The g-CN-CNF catalyst shows high catalytic activity for oxygen reduction reaction and oxygen evolution reaction in half-cell, with low overpotentials and low Tafel slopes. The high activity is attributed to the synergistic effect of abundant active sites and the electrical conductivity following the pyrolysis of g-CN and CNF. As a result, AEMWE with the g-CN-CNF anode, the first application of a carbon-based catalyst, exhibits outstanding performance that is the highest record in the literature for AEMWE using a non-noble metal catalyst. In addition, the performance and durability of Zn-air cells with g-CN-CNF cathode outperform those fabricated with commercial platinum.