Development of Novel Hydrophobic Gas Diffusion Layer for High-Pressure Water Electrolysis using Water-Absorbing Porous Electrolyte

Hydrogen gas production can be used to produce electric power that will ensure a reduction in the overreliance in the fossil fuels, whose use being the major pollution cause. Water electrolysis is one of the methods for producing hydrogen gas, enabling its conversion to electrical power by fuel cells. However, higher performing water electrolysis cells have been developed to improve the efficiency of the existing methods. For example, polymer electrolyte water electrolysis (PEWE) comprises of dense polymer electrolyte, the gas diffusion layer and the electrocatalyst layer that ensures supplying water to the electrolyte layer for the electrolysis process.

However, just like PEWE, other hydrogen gas production methods also experience several limitations such as dehydration of the electrolyte layer, poor stability at higher temperatures and decomposition of the carbon supports at the electrodes. Electrolysis cells based on water-absorbing porous electrolyte have the potential of overcoming such limitations. The cell constitutes a hydrophobic gas diffusion layer (GDL), hydrophilic porous electrolyte and electrocatalyst layer. This ensures continuous water supply hence preventing dehydration during electrolysis, controlled pressure for production of pressurized hydrogen gas and reduction of the overvoltage concentration at the electrode.

Despite the cells showing significant improvements in hydrogen gas production, they are expensive to construct and difficult to achieve in complicated cell designs. Therefore, development of new hydrophobic GDLs is capable of achieving the full potential of water-absorbing porous electrolyte electrolysis cells such as gas permeability, high water support force and excellent electron conductivity.

Kyushu University scientists (Dr. Yuki Terayama, Dr. Yoshitsugu Sone, Dr. Masamichi Nishihara, Dr. Stephen M. Lyth) and led by Professor Hiroshige Matsumoto developed a bespoke gas diffusion layer constituting acetylene black (AB) and polytetrafluoroethylene (PTFE) composite films for application in water-absorbing porous electrolyte electrolysis cell. This was in a bid to examine the characteristics of the cell such as water support force, gas permeability and electrical resistance. High-performance uniform AB/PTFE slurry was prepared by ball-milling and transfer method which also aided the covering of the film. Also, the various condition favoring fabrication and composition of GDL was determined. The research work is published in the journal, International Journal of Hydrogen Energy.

The group of authors obtained AB/PTFE optimal composition of 1/2.5 from the evaluated weight ratios by testing the electrical resistance, and gas permeability. As a result, excellent performances such as low electrical resistance, preferable gas permeability, and water support force were achieved. Ball-milling and transfer method enabled the realization of uniform AB/PTFE slurry and covering the films thereby ensuring no crack development on the coated micro-porous layer.

According to the authors, fabrication of an optimized gas diffusion layer was also useful for the excellent performance of the designed cell. For instance, it prevented water injection through the electrolyte layer thereby acting as a gas-permeation layer for effective hydrogen gas generation during the electrolysis process. However, the present system still experiences the problem of limited hydrophobicity resulting in low hydrogen evolution rate and significantly high voltages. The former was about 70% while the latter was about 1.97 when compared to the theoretical values. Thus, the authors attribute future studies towards improving the hydrophobicity of these water-absorbing porous electrolyte electrolysis systems.