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Herein, we investigate the effects of catholyte feed method and anode binder content on the characteristics of anion exchange membrane water electrolysis (AEMWE) to construct a high-performance electrolyzer, revealing that the initial AEMWE performance is significantly improved by pre-feeding 0.5 M aqueous KOH to the cathode. The highest long-term activity during repeated voltage cycling is observed for AEMWE operation in the dry cathode mode, for which the best long-term performance among membrane electrode assemblies (MEAs) featuring polytetrafluoroethylene (PTFE) binder–impregnated (5–20 wt%) anodes is detected for a PTFE content of 20 wt%. MEAs with low PTFE content (5 and 9 wt%) demonstrate high initial performance, rapid performance decay, and significant catalyst loss from the electrode during long-term operation, whereas the MEA with 20 wt% PTFE allows stable water electrolysis for over 1600 voltage cycles. Optimization of cell operating conditions (i.e., operation in dry cathode mode at an optimum anode binder content following an initial solution feed) achieves an enhanced water splitting current density (1.07 A cm−2 at 1.8 V) and stable long-term AEMWE performance (0.01% current density reduction per voltage cycle).

Precise monitoring of electrolyte leaching in high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) devices during lifetime tests is helpful in making a diagnosis of their quality changes and analyzing their electrochemical performance degradation. Here, we investigate electrolyte leaching in the performance degradation of phosphoric acid (PA)-doped polybenzimidazole (PBI) membrane-based HT-PEMFCs. We first perform quantitative analyses to measure PA leakage during cell operation by spectrophotometric means, and a higher PA leakage rate is detected when the current density is elevated in the cell. Second, long-term degradation tests under various current densities of the cells and electrochemical impedance spectroscopy (EIS) analysis are performed to examine the influence of PA loss on the membrane and electrodes during cell performance degradation. The combined results indicate that PA leakage affect cell performance durability, mostly due to an increase in charge transfer resistance and a decrease in the electrochemical surface area (ECSA) of the electrodes. Additionally, a three-dimensional (3-D) HT-PEMFC model is applied to a real-scale experimental cell, and is successfully validated against the polarization curves measured during various long-term experiments. The simulation results highlight that the PA loss from the cathode catalyst layer (CL) is a significant contributor to overall performance degradation.

To improve the cell performance for alkaline anion exchange membrane water electrolysis (AEMWE), the effects of the amount of polytetrafluoroethylene (PTFE) non-ionomeric binder in the anode and the hot-pressing conditions during the fabrication of the membrane electrode assemblies (MEAs) on cell performances are studied. The electrochemical impedance data indicates that hot-pressing at 50 °C for 1 min during MEA construction can reduce the polarization resistance of AEMWE by ∼12%, and increase the initial water electrolysis current density at 1.8 V (from 195 to 243 mA cm −2 ). The electrochemical polarization and impedance results also suggest that the AEMWE performance is significantly affected by the content of PTFE binder in the anode electrode, and the optimal content is found to be 9 wt% between 5 and 20 wt%. The AEMWE device fabricated with the optimized parameters exhibits good water splitting performance (299 mA cm −2 at 1.8 V) without noticeable degradation in voltage cycling operations.

Efficient water management is considered a prerequisite to advance the commercialization of anion exchange membrane fuel cells because water imbalance not only results in flooding and drying issues in the electrodes, but also leads to performance degradation. Herein, strategic electrode structures to achieve desirable water behavior during operation are reported. Carbon supports are employed as reservoirs to store the produced water and as carbon-supported catalysts with poly(N-isopropylacrylamide), possessing hydrophobic characteristics at the operating temperatures, as the polymer entangles by itself. This polymer is preferentially functionalized on the carbon surface before the reduction of the precursors to minimize the blocking of the catalyst active sites. X-ray photoelectron spectroscopy and electrochemical analyses support that the electronic structures of the catalysts are not significantly affected even when the polymer is functionalized. Furthermore, the synergistic effect of the reservoir and thermo-responsive polymer is demonstrated in a real device exhibiting performance enhancement. The resulting electrode shows 11.9% increase in the current density at 0.6 V and 21.3% increase in the maximum power density compared to those observed with the conventional electrodes. This phenomenon is attributed to favorable water distribution, as confirmed by in-situ visualization via synchrotron X-ray imaging.

The effect of temperature and pressure, and diffusion layer thickness is assessed on performance of a proton exchange membrane water electrolyzers (PEMWEs) with an ultralow iridium oxide (IrO 2 ) loading (0.1 mg cm −2 ) anode prepared by electrodeposition and a Pt/C catalyzed cathode with a Pt loading of 0.4 mg cm −2 . Increasing pressure to 2.5 bar at 120 °C enhances the water electrolysis current, so the anode electrodeposited with 0.1 mg cm −2 IrO 2 gives a current density of 1.79 A cm −2 at 1.6 V, which is comparable to the conventional powder-type IrO 2 electrode with 2.0 mg cm −2 at a temperature of 120 °C and pressure of 2.5 bar. The major factors for cell performances are rationalized in terms of overpotentials, water flow rates and thickness of diffusion layers, based on polarization behavior and ac-impedance response.

A simple and precise colorimetric method for analyzing phosphoric acid leakage in phosphoric acid-doped polybenzimidazole membrane fuel cells is described. The developed method is based on the colorimetric determination from a rapid formation of molybdenum blue color by the reduction reaction of molybdate ions in the presence of phosphoric acid in the acidic medium. The color is stable up to a few months and can be used for the sensitive and accurate detection of phosphoric acid electrolyte which is discharged from the fuel cell during operation. Tests with a wide concentration range of phosphate compounds showed that it permits determination of phosphoric acid up to nanogram quantities. The developed detection method assists monitoring the phosphoric acid contents and developing stable operation strategies of fuel cells.

For carbon-supported Pt-enriched Pt3Au nanoparticles (Pt3Au/C), the effect of oleylamine (OA) concentration during nanoparticle synthesis is investigated. When the OA concentration is increased from 0.12 mM to 1.2 mM, the particle size of Pt3Au gradually decreased from 5.1 nm to 3.3 nm, whereas the crystal structure and surface Pt concentration are not significantly influenced. With higher OA concentration, the oxygen reduction reaction activity of the Pt3Au/C is largely enhanced, which can be explained by the combined effect of increased specific activity and electrochemical surface area of Pt. It is experimentally confirmed using a bulk CO-oxidation technique that smaller particle size (larger OA concentration) leads to decreased OH adsorption strength, which originates from the double layer overlapping effect of closely adjacent nanoparticles.

Polymer electrolyte membrane fuel cell (PEMFC) stacks in a fuel cell vehicle can be inevitably exposed to harsh environments such as cold weather in winter, causing water flooding by the direct flow of condensed water to the electrodes. In this study, anode flooding was experimentally investigated with condensed water generated by cooling the anode gas line during a long-term operation (∼1600 h). The results showed that the performance of the PEMFC was considerably degraded. After the long-term experiment, the thickness of the anode decreased, and the ratio of Pt to carbon in the anode increased. Moreover, repeated fuel starvation of the half-cell severely oxidized the carbon surface due to the high induced potential (>1.5 VRHE). The cyclic voltammogram of the anode in the half-cell experiments indicated that the characteristic feature of the oxidized carbon surface was similar to that of the anode in the single cell under anode flooding conditions during the long-term experiment. Therefore, repeated fuel starvation by anode flooding caused severe carbon corrosion in the anode because the electrode potential locally increased to >1.0 VRHE. Consequently, the density of the tri-phase boundary decreased due to the corrosion of carbons supporting the Pt nanoparticles in the anode.

The application field of the fuel cell system has recently expanded to portable devices and unmanned aircraft systems, which require development of high performance fuel cell systems that function in versatile environments including near-dry operation conditions. In such low relative humidity condition, hydration of membrane electrode assembly in the fuel cell system is essential in prevention of performance degradation caused by decreased ion conductivity of the Nafion® membrane. Herein, we successfully improved the device performance of the membrane electrode assembly in low relative humidity condition by depositing a functional carbon-covering layer onto the catalyst layer on the cathode side. The carbon-covering layer plays an effective role of retaining generated water in the membrane electrode assembly without interfering with the electrochemical reaction of the catalyst as confirmed by the electrochemical impedance spectroscopy and cyclic voltammograms. Moreover, we have investigated the optimized Nafion® ionomer loading and the thickness of the carbon-covering layer.

A catalyst-coated membrane (CCM) as used in the membrane electrode assembly (MEA) of a polymer electrolyte membrane fuel cell is treated by dilute sulfuric acid solution (0.5 M) at boiling temperature for 1 h. This treatment improves the single-cell performance of the CCM without further addition of Pt catalyst. The changed microstructure and electrochemical properties of the catalyst layer are investigated by field emission scanning electron microscopy with energy dispersive X-ray, mercury intrusion porosimetry, waterdrop contact angle measurement, Fourier transform-infrared spectrometry in attenuated total reflection mode, electrochemical impedance spectroscopy, and cyclic voltammetry. The results indicate that this pretreatment enhances MEA performance by changing the microstructure of the catalyst layer and thus changing the degree of hydration, and by modifying the Pt surface, thus enhancing the oxygen reduction reaction.

WO3 bilayer electrodes composed of WO3 top and bottom layers are designed for photoelectrochemical cells (PECs). The bottom layers are sputter-deposited at a high temperature (773 K) that leads to large grains and suitable electrical pathways for carrier collection. The top layer is deposited at a low temperature (573 K) and consists of small grains, which give rise to large electrochemical reaction sites. The bilayer electrodes give a significant enhancement in PEC performance compared with WO3 monolayer electrodes deposited at 573 or 773 K, because of a combination of favourable effects.

The polyol-reduction method is modified for both high metal loading and high dispersion of particles. The catalysts are post-treated with different atmospheres and temperatures. The post-treatment modifies the morphological and crystallographic structures of the catalysts which influence the methanol oxidation activities. The catalysts are characterized by using X-ray diffraction, transmission electron microscopy, and cyclic voltammetry. The post-treatment induces a change of surface areas and a phase separation of Pt and Ru that modify the surface structures along with the intrinsic and mass-specific activities of methanol oxidation. The activities modified by the post-treatment are investigated by using methanol oxidation at room temperature and at 60 °C. Comparison with single-cell performance is conducted, and the results are in accord with those for methanol oxidation at 60 °C. All synthesized catalysts exhibit higher single-cell performances than the commercial catalyst.

Pt nanocatalysts formed on a gas diffusion layer substrate for use in proton exchange membrane fuel cells were fabricated by using a high-pressure sputtering technique in a gaseous mixture of Ar and He. Rather than the dense film deposited by conventional sputtering techniques, the resulting structure was comprised of a porous Pt nanocatalyst layer with an average particle size of 8.9 nm. The porous Pt nanocatalysts were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray absorption near edge spectroscopy. Compared with the dense Pt catalyst layer, the electrochemical activated surface of the porous Pt nanocatalyst layer, measured using cyclic voltammetry, was enhanced about 250%. Polarization characteristics of the membrane electrode assembly, which utilized the porous Pt nanocatalyst layer in the proton exchange membrane fuel cells, showed that the maximum power density per unit area increased with an increase in the sputtering pressure. The high performance of Pt nanocatalysts fabricated at a sputtering pressure of 200 mTorr (Ar/He = 1) was due to miniaturization of the Pt particles and formation of the porous catalyst layer.

Tandem dye-sensitized solar cell (DSSC)-electrochromic (EC) devices were realized using two-faced transparent conducting oxide (TCO). To supply sufficient voltage to drive the EC devices, two series connected, semitransparent DSSCs were fabricated with 7 nm-thick, dye-adsorbed TiO2 and 4 nm-thick Pt layers. The two series connected, semitransparent DSSCs that were used had an open circuit voltage and short circuit current density of about 1.35 V and 3.96 mA cm−2, respectively, at 1-sun. The tandem DSSC-EC devices showed an optical density difference of 1.2 at 750 nm and reasonable response times of about 60 and 45 s during the coloring and bleaching processes, respectively, indicating that the two series-connected, semitransparent DSSCs could be used as the power sources in the tandem photovoltaic-powered EC devices.