• Energy Research

Abstract Within this contribution an experimental analysis of a 50 cm long single-channel polymer electrolyte membrane water electrolysis cell is presented. The current density and the temperature distribution along the channel coordinate is measured with a printed circuit board setup that enables a very fine resolution of 252 independent measurement segments. After first cell testings in a steady state mode, effects of changed amounts of feed water flux on the cell voltage, the distribution of current density and the temperature profile were investigated. Although the water feed did not significantly influence the current density distribution over a wide range of water fluxes, very low water fluxes lead to a massive drop in the current density in the rear part of the active area and a moderate increase at the inlet. This growing heterogeneity influenced the temperature distribution as well as the cell voltage.

Abstract Within this contribution an experimental analysis of a 50 cm long single-channel polymer electrolyte membrane water electrolysis cell is presented. The current density and the temperature distribution along the channel coordinate is measured with a printed circuit board setup that enables a very fine resolution of 252 independent measurement segments. After first cell testings in a steady state mode, effects of changed amounts of feed water flux on the cell voltage, the distribution of current density and the temperature profile were investigated. Although the water feed did not significantly influence the current density distribution over a wide range of water fluxes, very low water fluxes lead to a massive drop in the current density in the rear part of the active area and a moderate increase at the inlet. This growing heterogeneity influenced the temperature distribution as well as the cell voltage.

Nafion membrane was studied as a potential electrolyte for a polymer electrolyte membrane (PEM) reactor operating at temperatures in the range of 100-160°C. An attempt was made to avoid the well known problem of the decrease in the conductivity of Nafion at elevated temperatures caused by its insufficient humidification. Elevated pressure was applied. In the first instance the influence of elevated temperature and pressure on the ion exchange capacity of a Nafion membrane, one of the main characteristics, was tested in selected environments. One environment tested was 14.7 M H 3 PO 4 used nowadays generally for the high temperature proton conducting polymer electrolytes. 0.5 M H 2 SO 4 , demineralized water and an open atmosphere represent the remaining environments under study. The most significant deterioration of the ion exchange capacity of the membrane was observed in 0.5 M H 2 SO 4 . In contrast to this, 14.7 M H 3 PO 4 and an open air atmosphere left the membrane properties almost unchanged. Subsequently Nafion's conductivity was determined in the temperature range of 110-150°C at pressure up to 0.65 MPa. As anticipated, it was found that Nafion also exhibits sufficient conductivity above 100°C at 100% relative humidity of the environment. The conductivity decrease was observed during prolonged experiments. Surprisingly enough, no related changes in the structure of Nafion were indicated by IR spectroscopy, one exception being the sample stored in an autoclave for a prolonged time in 0.5 M H 2 SO 4 .

Nafion membrane was studied as a potential electrolyte for a polymer electrolyte membrane (PEM) reactor operating at temperatures in the range of 100-160°C. An attempt was made to avoid the well known problem of the decrease in the conductivity of Nafion at elevated temperatures caused by its insufficient humidification. Elevated pressure was applied. In the first instance the influence of elevated temperature and pressure on the ion exchange capacity of a Nafion membrane, one of the main characteristics, was tested in selected environments. One environment tested was 14.7 M H 3 PO 4 used nowadays generally for the high temperature proton conducting polymer electrolytes. 0.5 M H 2 SO 4 , demineralized water and an open atmosphere represent the remaining environments under study. The most significant deterioration of the ion exchange capacity of the membrane was observed in 0.5 M H 2 SO 4 . In contrast to this, 14.7 M H 3 PO 4 and an open air atmosphere left the membrane properties almost unchanged. Subsequently Nafion's conductivity was determined in the temperature range of 110-150°C at pressure up to 0.65 MPa. As anticipated, it was found that Nafion also exhibits sufficient conductivity above 100°C at 100% relative humidity of the environment. The conductivity decrease was observed during prolonged experiments. Surprisingly enough, no related changes in the structure of Nafion were indicated by IR spectroscopy, one exception being the sample stored in an autoclave for a prolonged time in 0.5 M H 2 SO 4 .

Bipolar plates represent a crucial component of the PEM fuel cell stack. Polymer–carbon composites are recognized as state-of-the-art materials for bipolar plate manufacturing, but their use involves a compromise between electrical and heat conductivity, mechanical strength and costs. Thus, all key parameters must be considered when selecting a suitable plate satisfying the demands of the desired application. However, data relevant to commercial materials for such selection are scarce in the open literature. To address this issue, 13 commercially available polymer–carbon composites are characterised in terms of the following parameters: through-plane conductivity, hydrogen permeability, mechanical strength, water uptake, density, water contact angle and chemical stability. None of the materials tested reached the DOE target for electrical conductivity, while five of the materials met the target for flexural strength. The overall best-performing material showed a conductivity value of 50.4 S·cm−1 and flexural strength of 40.1 MPa. The data collected provide important supporting information in selecting the materials most suitable for the desired application. In addition, the key parameters determined for each bipolar plate supply important input parameters for the mathematical modelling of fuel cells.

Bipolar plates represent a crucial component of the PEM fuel cell stack. Polymer–carbon composites are recognized as state-of-the-art materials for bipolar plate manufacturing, but their use involves a compromise between electrical and heat conductivity, mechanical strength and costs. Thus, all key parameters must be considered when selecting a suitable plate satisfying the demands of the desired application. However, data relevant to commercial materials for such selection are scarce in the open literature. To address this issue, 13 commercially available polymer–carbon composites are characterised in terms of the following parameters: through-plane conductivity, hydrogen permeability, mechanical strength, water uptake, density, water contact angle and chemical stability. None of the materials tested reached the DOE target for electrical conductivity, while five of the materials met the target for flexural strength. The overall best-performing material showed a conductivity value of 50.4 S·cm−1 and flexural strength of 40.1 MPa. The data collected provide important supporting information in selecting the materials most suitable for the desired application. In addition, the key parameters determined for each bipolar plate supply important input parameters for the mathematical modelling of fuel cells.

This study is an effort to cover and interconnect multiple aspects of the fabrication of the yttria-stabilized zirconia (YSZ) from powder preparation to a solid electrolyte suitable for utilization in solid oxide cells. Thus, a series of YSZ electrolytes was prepared, differing in the content of the Y2O3 dopant and in the method of preparation. Combustion synthesis along with the thermal decomposition of precursors was used for YSZ powder synthesis with a dopant content of 8 to 18 mol.%. Post-synthesis treatment of the powder was necessary for achieving satisfactory quality of the subsequent sintering step. The morphology analyses of the YSZ powders and sintered electrolytes produced proved that small particles with a uniform size distribution are essential for obtaining a dense electrolyte. Furthermore, the conductivity of YSZ electrolytes with different Y2O3 contents was examined in the temperature range of 400 to 800 °C. The lowest conductivity was found for the sample with the highest Y2O3 content. The obtained results enable the preparation methods, YSZ powder morphology, and composition to be connected to the mechanical and electrochemical properties of the YSZ electrolyte. Thus, this study links every step of YSZ electrolyte fabrication, which has not been sufficiently clearly described until now.

This study is an effort to cover and interconnect multiple aspects of the fabrication of the yttria-stabilized zirconia (YSZ) from powder preparation to a solid electrolyte suitable for utilization in solid oxide cells. Thus, a series of YSZ electrolytes was prepared, differing in the content of the Y2O3 dopant and in the method of preparation. Combustion synthesis along with the thermal decomposition of precursors was used for YSZ powder synthesis with a dopant content of 8 to 18 mol.%. Post-synthesis treatment of the powder was necessary for achieving satisfactory quality of the subsequent sintering step. The morphology analyses of the YSZ powders and sintered electrolytes produced proved that small particles with a uniform size distribution are essential for obtaining a dense electrolyte. Furthermore, the conductivity of YSZ electrolytes with different Y2O3 contents was examined in the temperature range of 400 to 800 °C. The lowest conductivity was found for the sample with the highest Y2O3 content. The obtained results enable the preparation methods, YSZ powder morphology, and composition to be connected to the mechanical and electrochemical properties of the YSZ electrolyte. Thus, this study links every step of YSZ electrolyte fabrication, which has not been sufficiently clearly described until now.