Final Report Summary - SUSHGEN (Sustainable Hydrogen Generation)
SUSHGEN—Sustainable Hydrogen Generation
Marie Curie Actions—Networks for Initial Training (ITN) FP7-PEOPLE-ITN-2008
Coordinator: University of Newcastle, UK., Professor Keith Scott
(website: http://research.ncl.ac.uk/sushgen)
Summary
Polymer Electrolyte Membrane Water Electrolysis (PEMWE) has gained increasing interest over the last decade and represents a viable alternative for production of very pure hydrogen and oxygen from renewable energy sources, making them carbon neutral. However, the main drawback with water electrolysis is a considerable energy consumption, which can be partly resolved by increasing the operating temperature of the system.
To achieve progress in the electrolyser field, this project investigated new materials for the membranes and the electrocatalysts that form the electrolyser cell. Membranes based on PBI derivatives and new pyridine-containing aromatic polyethers (TPS) have been produced that have the required conductivity above 150 °C. Also double functionality proton conducting membranes incorporating both phosphonic and sulfonic acid have been developed for operation at up to 120 oC. Composite membranes of with the short side chain perfluorosulfonic acid ionomer, Aquivion have been produced.
Thin film proton conducting composite membranes have been produced of all of the above membrane systems. Evaluation of acid-doped PBI based membranes has been performed but performance is not as good as required for PEMWE. Composite membranes based on solid acids have been prepared and characterised. Composite Aquivion composite membranes have high conductivity and good performance under water electrolysis conditions at temperatures up to140 °C.
Anode electrocatalyst materials, for oxygen evolution, made from Ru/Ir operating at high temperatures were investigated. The catalysts were prepared by precipitation of the hydroxides from aqueous solution of the corresponding chlorides, followed by heat treatment to form the oxides. Ruthenium oxide catalysts were shown not to be stable under cell operating conditions at high temperatures. IrO2 catalyst has been fabricated and tested in solutions of CsH2PO4 H2SO4, H3PO4, TFMSA and data indicates that such iridium oxide catalyst should be stable under electrolysis operation at high temperatures.
To enhance catalyst stability different supporting materials were investigated. One-dimensional nanomaterials of nanofibre oxide electrocatalyst supports were fabricated. Nanofibre doped titanium oxide, and nanofibre and nanotubular doped ruthenium oxide supported on tin oxide have been prepared by electrospinning, and characterised for their structural, surface and electrical properties.
Alternative cathode electrocatalysts to Pt catalyst such as Co3O4, Zr&Y&Ce, Ti+Zr&Ce&Y have been fabricated and characterised. The use of niobium doped titania substrates as supports for cathode catalyst was also investigated as an alternative to carbon nano-powders.
Thin film electrodes, based on iridium oxides and ruthenium oxides, have been fabricated onto PEMs, using acid-doped PBI, Aquivion PFSA, sPBI-OO and other polymer membranes. Tests of the thin film electrodes in electrolysers have been performed, with very good results indicating the promise of the electrolyser technology at the lower range of intermediate temperatures. Investigations of cell performance and stability behaviour during the electrolysis of water (at high pressure) and steam have provided promising results at temperatures up to 140 °C. Using sulfonated polybenzimidazole, an in-house prepared IrO2 anode, and a commercial Pt/C cathode for example, the cell voltages at 1 and 2 A/cm2 were 1.64 and 1.75 V respectively, at 120 °C (3 bara).
A PEM water electrolysis test unit (Tmax. = 80-250 °C and Pmax. = 8-50 bars, respectively) and test cell (16 cm2 geometric area) has been built for membrane electrode assembly evaluation. High temperature steam electrolyser for temperatures up to 300 oC has been tested to evaluate MEAs based on composite membranes based on solid acids. Performance of the cell was modest and voltages need to be reduced through electrode layer optimisation.
The SUSHGEN ITN consists of 7 partners from six EU member states. Ten researchers underwent training in the ITN SUSHGEN. The SUSHGEN consortium organised three workshops, one summer school, one spring school and were involved in the 2nd CARISMA international conference (on progress in MEA materials for medium and high temperature polymer electrolyte fuel cells) which were attended by both SUSHGEN ESRs and ERs and external participants. The last event focused on High Temperature Electrolysers and was a joint dissemination event with the EU project Electrohypem.