Development of Highly Efficient Raney Nickel Electrodes for Alkaline Water Electrolysis

Kurzfassung

The increasing use of renewable energies such as wind power and solar energy requires storage capabilities since they are only intermittently available. The most attractive secondary energy carrier for large amounts of electrical energy which fulfills the requirements of storing electrical energy in an environmentally friendly way is hydrogen. Furthermore, power-to-gas technology can provide synthetic fuels for transportation in a future energy scenario by using renewable energy sources. Water electrolysis is the key technology for production of both hydrogen and fuels for a sustainable CO2-free energy supply. Among the different electrolysis technologies alkaline water electrolysis is the most advanced technique with long experience in high quantity hydrogen production. However, commercially available alkaline water electrolysers are still limited to low current densities and not optimised for intermittent operation. For cost-effective hydrogen production in respect of storage of gigawatt electrical energy coming from renewable energy sources, improved electrolysers in terms of higher efficiency as well as cost reduction of major components such as electrodes are required. The development of cost-effective and highly efficient electrodes reported here aims at achieving this goal. The energy efficiency of electrodes for alkaline water electrolysis for energy storage application can be significantly improved by developing electrocatalytically active electrode coatings showing long-term stability under intermittent operating conditions. Based on Raney nickel as electrocatalytically active material, DLR has developed electrode coatings for cathodes and anodes. For cathodic hydrogen evolution Mo containing Raney nickel alloy coatings and for the anodic oxygen evolution reaction pure Raney nickel or Raney nickel/oxide coatings have been developed by applying plasma spray technology. Initially vacuum plasma spraying (VPS) was applied for the electrode development but for cost reduction of the electrode production process also atmospheric plasma spraying (APS) has recently been used. The plasma spray processes including powder feedstock, the equipment used and the operating conditions for electrode manufacturing are presented. The electrocatalytic activity of the electrode coatings was investigated by performing polarisation curves on half cells and electrodes with 300 cm2 size and by cyclovoltammetry. The electrode coatings show an overvoltage reduction on the cathode side of 250-300 mV and on the anode side of 130-150 mV at a current density of 0.5 A/cm2 and 80 °C. Also excellent stability during 1100 on-off cycles could be demonstrated when 98% of the initial efficiency was retained. Cost-effective electrode coatings prepared by atmospheric plasma spraying which have recently been tested show promising electrochemical behaviour on the same performance level as VPS electrodes. The electrodes described will be implemented in a 300 kW electrolyser which will be attached to a 1 MW power-to-gas facility to be operated by the utility Energiedienst in Whylen, Germany, as a demonstration plant using electricity from hydropower. The concept of the power-to-gas plant will be briefly described.