Development of high-performance silver-based gas-diffusion electrodes for chlor-alkali electrolysis with oxygen depolarized cathodes

Silver-based gas-diffusion electrodes were prepared, characterized and tested during chlor-alkali electrolysis with oxygen depolarized cathodes. Spraying of aqueous suspensions containing silver catalyst particles, a PTFE suspension, a surfactant and an organic thickening agent on nickel nets followed by drying, hot-pressing and sintering allowed for the preparation of highly active electrodes. Electrodes obtained from the most suitable catalyst SF9ED (Ferro) were systematically investigated. The best electrodes contain 97-98 wt.% silver and 2-3 wt.% PTFE, are hot-pressed at ca. 130 degrees C with moderate pressure and subsequently sintered at temperatures around 340 degrees C. For these electrodes, half cell potentials of ca. 650 mV vs. RHE corresponding to electrolysis cell voltages of ca. 2.17V at current densities of 4 kA/m(2) were obtained. Both half cell and electrolysis cell voltages were found to be reproducible within about +/- 30 mV during repeated measurements using electrodes from different batches. While the Ag/PTFE loading had little influence on the observed voltages in the range studied (100-300 mg/cm(2)), loadings of at least 200 mg/cm(2) are recommended to prevent leakage of NaOH electrolyte and to allow for operation under oxygen overpressures of more than 100 mbar without breakthrough of gas to the electrolyte. (C) 2011 Elsevier B.V. All rights reserved.