Kan-Lin Hsueh

On the Accelerating Degradation of DMFC at Highly Anodic Potential

A convenient method of investigating the degradation of a direct methanol fuel cell (DMFC) was carried out at highly anodic potential (i.e., 0.8 V). Accelerating degradation of a DMFC was investigated by electrochemical methods, X-ray diffraction (XRD), transmission electron microscopy (TEM), electron probe microanalysis (EPMA), and X-ray photoelectron spectroscopy (XPS). The degradation was preliminarily diagnosed and predicted with electrochemical impedance spectroscopy and verified with microscopic examination. The EPMA and XPS results showed that the sulfonic acid vanished in the broken anodic layer compared to the original one, which results in an increase of internal resistance (Rs). The increase of interfacial (R if ) and electrochemical reaction resistance (R rxn ) in the degraded cell might be a result from catalytic degradation. Ru dissolves from the anodic catalyst to decrease the catalytic activity then reduced near the cathode. The evidence for Ru dissolution was determined by CO stripping combined with EPMA and XPS analyses. Its reduction near the cathode was observed through TEM and EPMA. The catalysts in both the anode and cathode aggregated to decrease the catalytic activity in the degradation process by XRD and TEM. On the basis of the electrochemical study and related analysis, we proposed a mechanism for this accelerating degradation of DMFC.

Effect of Hygroscopic Platinum/Titanium Dioxide Particles in the Anode Catalyst Layer on the PEMFC Performance

This study investigates the feasibility of adding platinum (Pt)/titanium dioxide (TiO 2 ) particles into the anode catalyst layer to improve the performance of proton exchange membrane fuel cells. The effects of adding Pt/TiO 2 in the catalyst layer on three critical factors, namely, the wettability, the electrical resistance, and the loading of Pt/TiO 2 particles, were also evaluated. It was observed that the water contact angles of these catalyst layers were decreased as the weight percentage of Pt/TiO 2 particles increased. Similarly, the electrochemically active surface areas prepared by these catalyst inks were decreased with the increase in Pt/TiO 2 addition. Single cell performance with various amounts of Pt/TiO 2 particles in the anode catalyst layer was investigated under different temperatures of anode humidifier. The cell with 5% Pt/TiO 2 particle addition in the anode catalyst layer revealed the best performance at anode humidifier temperatures ranging from 25 to 75°C.

Effect of Ethanol on the Photoelectrochemical Fabrication of Macroporous n-Si(100) in HF Solution

The effect of ethanol on the photoelectrochemical fabrication of macroporous n-type Si(100) (pore diameter > 50 nm) in 2.0 M hydrofluoric acid was investigated. A cross-sectional scanning electron microscope examination revealed the formation of rough bigger pores (diameter ≈ 7-8 μm) in the absence of ethanol but smooth smaller ones (diameter ≈ 3-4 μm) in the presence of ethanol when the silicon was etched at 0.250 V (vs saturated calomel electrode) under 50 W illumination for 3 h. Characteristic electrochemical properties, such as limiting current density (i limit ), half-wave current density (i 1/2 ), transition potential (E trans ), and half-wave potential (E p/2 ) were derived from dc polarization. Electrochemical impedance spectroscopy conducted at E trans and E p/2 was helpful to illustrate the kinetics of the photoelectrochemical reaction. An additional inductive loop in the Nyquist plot occasioned at low frequencies in the presence of ethanol was attributed to the relaxation of the adsorption of ethanol in the pores. Addition of ethanol in the etching solution led to a decrease of contact angle between the solution and the silicon. Wetting behavior of ethanol plays an important role in the formation of smooth and small macropores.

Effect of Addition of AB2-Type Hydrogen Storage Alloy into the Anode Catalyst Layer on the PEMFC Performance

Transition-metal oxides had been utilized as a water adsorbent to improve the wettability of the anode in proton exchange membrane fuel cells (PEMFCs) for many years. Nevertheless, the high electrical resistance of the metal oxides limits the content that can be added to the electrode. In this study, the feasibility of adding an AB 2 -type hydrogen storage alloy (HSA) into the anode catalyst layer to improve the cell performance of PEMFCs was investigated. The wettability of the catalyst layer upon adding the AB 2 -type HSA to the anode and the internal resistance of single cell were also evaluated. The experimental results indicate that the wettability of the catalyst layers with ground AB 2 -type HSA addition was superior to that with as-received AB 2 -type HSA, reflected from the water contact angle of the catalyst layers that decreases as the weight fraction of the AB 2 -type HSA increases. The cell with 10% ground AB 2 -type HSA addition in the anode catalyst layer exhibits the best performance in which the anode humidifier temperature ranges from 30 to 70°C.

Reduction of the Electrode Overpotential of the Oxygen Evolution Reaction by Electrode Surface Modification

Metal–air batteries exhibit high potential for grid-scale energy storage because of their high theoretical energy density, their abundance in the earth’s crust, and their low cost. In these batteries, the oxygen evolution reaction (OER) occurs on the air electrode during charging. This study proposes a method for improving the OER electrode performance. The method involves sequentially depositing a Ni underlayer, Sn whiskers, and a Ni protection layer on the metal mesh. Small and uniform gas bubbles form on the Ni/Sn/Ni mesh, leading to low overpotential and a decrease in the overall resistance of the OER electrode. The results of a simulated life cycle test indicate that the Ni/Sn/Ni mesh has a life cycle longer than 1,300 cycles when it is used as the OER electrode in 6 M KOH.