Our target is to achieve 1.80 V of cell voltage at 0.4 A/cm2, 80℃ and over 99.9% hydrogen purity. Many separators were screened. A separator of diaphragm type showed good performance for AWE. The evaluation of separator was carried out by using different sizes of cells such as 0.2, 1.0 and 16 dm2depending on the aim of evaluation. The structure of each test cell is based on zero-gap concept to reduce gas effect in the electrolysis.
The cell voltage of 16 dm2 bench cell was 1.81 V at current density 0.4 A/cm2, temperature 80℃ and hydrogen purity 99.95% and 1.94 V at current density 0.6 A/cm2, temperature 80℃ and hydrogen purity 99.96%. It was confirmed that only single side feeding to cathode is available for the cell operation without any serious problems under Δ300 mmH2O differential pressure (between anode chamber <low pressure> and cathode chamber<high pressure>). The result indicates that cathode electrolyte can easily pass through the diaphragm from cathode side to anode side.
The cell equipped with diaphragm without hydrophilic treatment showed a large fluctuation in cell voltage. It suggests that hydrophilic treatment of membrane is very important factor to get steady operation in the actual large-scale plant. The flow rate of electrolyte (0.3 to 0.45 mL/min-cm2) does not dominate the purity of hydrogen gas produced. It was also confirmed that the diffusion amounts of gas through the diaphragm as gas (bubble) and solved species (gas) in the electrolyte are on the same level (H2 gas: dissolved H2 gas = 1:1.25).