Stable and inexpensive electrodes for the hydrogen evolution reaction

Abstract

The HER activities of Raney–Ni electrodes obtained by partial leaching of Al in a Ni–Al–Fe alloy doped with Mo, Cr or Pd were studied in 28% KOH. PTFE bonded Gas Diffusion Electrodes (GDEs) were prepared by the rolling method before sintering at 300 °C under N2. Ni in alkaline electrolyte has a lower intrinsic HER activity than Pt in acid. However, the spongy and highly porous character of Raney–Ni greatly enhances HER resulting in a cheap material with outstanding catalytic performance. The polarization behavior of GDEs consisting mainly of Raney–Ni catalysts with optional addition of co-catalyst or conductivity enhancing powders, such as carbonyl iron, carbonyl nickel, copper and molybdenum oxide are studied as a function of temperature and time in order to determine activities, behavior in the high current density regime, and long term stability in view of potential exploitation in industrial electrolysis. Cr and Pd-doped Raney–Ni initially achieve outstanding performances with unusually low “Tafel slopes”. After weeks long cathodic treatments, these GDEs eventually attain inferior but stable activities due to an apparently irreversible aging of Raney–Ni. The aging of Mo-doped Raney–Ni is less conspicuous, and relevant performances are sometimes improved by additives. A clear picture is emerging of the mechanisms controlling polarization and aging behavior of Raney–Ni GDEs. From this picture, suggestions are put forward on how to improve stability and performances of full electrode assemblies and make them suitable for use in advanced alkaline electrolyzers.