Key challenges to the acceptance of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) for automobiles are the cost reduction and its improvement in power density for compactness. In order to get the solutions for these issues, further improvement in the cell performance is required with high current density operation. In this study, the impacts of heat and water transport on the cell performance under high current density were investigated by experimental evaluation of liquid water distribution and numerical validation. Liquid water distribution in-plane direction was evaluated by neutron radiography. Furthermore, electrochemical reaction distribution was also evaluated by using inserted metal wires at anode, and then the experimental results were qualitatively validated by the numerical model. The experimental and numerical validation results revealed that significant increase in mass and ohmic loss was induced by temperature, liquid water, and electrochemical reaction distribution in-plane direction.

Near-field radiation that has a high intensity of electric field was applied to enhance conversion from thermal energy to electricity in a wavelength range less than 1.1 μm or 1.8 μm. A commercial Si-photovoltaic cell and a thermophotovoltaic cell made of GaSb semiconductors were used to confirm that the near-field radiation effect (the evanescent wave effect) can be applied to enhance generation of electricity. As a result, an increase in output power generation of electricity by the evanescent wave effect was detected and the short-circuit current density increased about 1.3 times for the Si-PV cell and 3.0 times for the GaSb-TPV cell as larger than those obtained by the conventional propagating-wave radiation.

In Polymer electrolyte membrane fuel cells (PEFCs), freezing of produced water induces the extreme deterioration of cell performance below zero. This phenomenon is a serious problem in cold regions and is needed to be solved to achieve the practical use of PEFCs. In this study, we investigated ice distribution at the cold start in a PEFC using an optical microscope and a CRYO-SEM to clarify the freezing mechanism. The observation results showed that the cold start at −10°C makes ice at the interface between the cathode catalyst layer (CL) and the micro porous layer of gas diffusion layer. Little ice was, however, observed in the cold start at −20°C, which indicated the ice formation inside the CL. The CRYO-SEM observation was conducted at −20°C to investigate the ice formation inside the CL, and this identified the effects of the current density and the cathode gas species on the ice distribution.

In order to prevent membrane dryout in polymer electrolyte fuel cells (PEFCs) during low humidity operation, it is essential to understand the fundamental phenomena of the water transport and reaction distribution at the anode side in an operating fuel cell. In this study, the water vapor distribution along the anode flow channel of a PEFC under low humidity conditions was quantitatively evaluated by using humidity test paper (HTP), and the effects of flow configuration and inlet humidification on the water distribution in the anode were investigated. HTP is a test paper for detecting water vapor of 20–90% RH, which is coated with a blue surface. This test paper was inserted between the anode electrode and separator in the transparent fuel cell, and the discoloration of HTP was directly visualized using a digital CCD camera. Furthermore, the temperature and current distributions in the anode electrode were measured using IR thermography and segmented cell structure concept. It was found that the water vapor concentration on the anode side increases immediately after the startup because of the back diffusion of the product water from the cathode to anode. In the case of the co-flow configuration with the dry anode and cathode inlets, the water vapor concentration increases monotonically along the anode flow channel. In addition, the anode water distribution affects the temperature and current distributions in the fuel cell largely. The local temperature and current density at the dry anode inlet are lower than those in the downstream region because of the membrane dehydration and low proton conductivity. On the other hand, in the case of the counter-flow pattern, the distributions of water concentration, temperature and current density have the maximum points in the midstream region. The counter-flow configuration is effective in improving the membrane hydration and alleviating the anode dryout.

In order to improve the power generation performance of polymer electrolyte fuel cells (PEFC), it is necessary to maintain high current density over the whole area of the membrane electrode assembly (MEA) that includes the additional Pt-carbon particles loaded on the Polymer Electrolyte Membrane (PEM) as an electrocatalyst layer. However, the current density generated at the MEA is distributed unevenly due to a lack of hydrogen, flooding, and so on. Therefore, achieving a higher current density in a PEFC requires monitoring the local current density. The local current density in a PEFC can be measured by the frequency shift of the NMR signal received from planar surface coils inserted into the PEFC as sensors. This method is based on the relationship that the spatial gradient of the frequency shifts in NMR signals along the MEA is proportional to the magnetic field strength induced by local current density. In this study, two kinds of MEA were used. One MEA was with the platinum catalyst applied to an area of 50 mm * 50 mm. The other MEA was with platinum catalyst over half this area. The distributions of the frequency shift of NMR signals in PEFCs using these two MEAs were measured. These measured distributions of the spatial gradients were in agreement with those obtained by the theoretical-analysis of magnetic fields in PEFC. The spatial distributions of current density generated in PEFCs were obtained from the spatial gradients and theoretical result.

This paper reports the temperature and irradiance dependence of dye-sensitized solar cells (DSSCs) with acetonitrile-based electrolytes. The prototyped DSSCs had nanocrystalline titanium dioxide photoanodes and platinum thin film cathode. The photoanodes were sensitized with N-749 dye. The current-voltage characteristics of the DSSCs were measured at temperatures from 5 to 50 °C and under 500, 1000, and 1500 W m −2 irradiance. The open circuit voltage, V OC , decreased linearly with increasing temperature and had positive, logarithmic relation with irradiance. At temperatures lower than 15 °C, short circuit current density, J SC , was limited by the diffusion of I 3 − in the electrolyte and increased with increasing temperature. At higher temperatures the recombination of electrons injected into the TiO 2 conduction band was dominant over diffusion and J SC decreased with increasing temperature. Moreover, J SC increaed linearly with increasing irradiance. The DSSC photoconversion efficiency did not vary appreciably at temperatures lower than 15 °C but decreased with increasing temperature. Finally, the efficiency increased with increasing irradiance.