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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - CREATE (Critical Raw materials Elimination by a top-down Approach To hydrogen and Electricity generation)

Teaser

Summary

The increasing demand for energy combined with targets for reducing carbon dioxide emissions to curtail global climate change call for alternative ways of producing energy. The vast majority of the worldâ€™s energy production relies today on oil, natural gas and coal. The current consumption rate of these fuels is much higher than what can be regenerated by nature, and it can be expected that fossil fuels will be significantly depleted during this century if the energy production system is not modified. Solar and wind energy are two renewable energy sources that are being contemplated for replacing fossil fuels. They hold the promise to satisfy the worldâ€™s energy demand in a sustainable way, without emission of greenhouse gases.

While producing electricity from sunlight or wind is one important aspect to consider when switching to renewable energy, another aspect is electricity storage. Due to a mismatch existing between the moment at which renewable electricity is mostly produced and the moment at which it is needed, a significant amount of electricity must be reversibly stored. One way to do this is to convert it to hydrogen first, via water electrolysis, and to reconvert, when necessary, the hydrogen into electricity and water in fuel cells. The overall loop is a closed system, with as much water being produced in fuel cells as consumed during electrolysis. The energy efficiency of water electrolysis and fuel cells in converting electricity to hydrogen and vice versa, respectively, must be high in order to be economic. To this end, catalysts have been developped to accelerate the four reactions occurring in such devices. For the best performing devices based on proton-conducting polymer electrolytes (an acidic medium), state-of-art catalysts are based on precious metals, namely platinum and iridium.

The overall objective of CREATE is to develop novel membrane-electrode-assemblies for fuel cells and electrolysers, comprising no or a much reduced amount of precious metals (at large, comprising no critical raw materials stamped with risk of supply). This will be achieved by developing novel catalysts and novel polymer electrolytes that conduct negatively-charged ions (equivalent to high pH value), a medium in which a broad range of non-precious-metal catalysts are stable.

Work performed

During the first reporting period, activities were initiated in all technical work packages. Technical specifications were identified for catalysts and membranes, with key functional properties established. Harmonized testing protocols were established and are used by the various partners developing catalysts and membranes.

Novel catalyst for the anode reaction in water electrolysis were developped. Libraries of multimetallic oxides of Earth-abundant metals where evaluated. The best catalyst passed the activity and stability criteria and was transferred in a water electrolyser. Novel catalysts for the cathode of fuel cells were also developped, and an iron-based catalyst reached the internal activity and stability criteria of CREATE. Regarding development of catalysts for the hydrogen evolution and oxidation reactions (the cathode and anode of an electrolyser and a fuel cell, respectively), two approaches have been pursued. Presently, sufficient activity has only been reached with catalysts based on low-platinum content. Novel catalysts with few % of platinum nanoparticles were deposited on carbon nanotubes and best catalysts reached internal activity and stability criteria of CREATE. One such catalyst was tested at the cathode of an electrolyzer and showed promising results.

In the work package on ionomer and membrane preparation, a novel ex-situ durability protocol was established that highlighted the importance of water. This will help us better predicting the stability of novel ionomeric materials when operated in devices. A series of novel functional groups for anion-exchange ionomers was prepared and tested for stability using the novel ex-situ method. In a specific approach for novel bipolar membranes (with one side characterised with acidic properties and the other side with basic properties), a range of amphoteric ionomers was prepared and transferred for bipolar-membrane preparation.

In the work package on cell testing, commercial catalysts (containing precious metals) and commercial anion-conducting membranes have been benchmarked in a laboratory-size electrolyser. Best initial performance closely approaching the project target was achieved, but with platinum and iridium catalysts at the cathode and anode, respectively.

During the second period, two important milestones were achieved, MS1, anion exchange membrane with alkaline stability at 60Â°C > 400 h and anion exchange ionomer conductivity > 3 S m-1, and MS2, Novel bipolar membrane designed for electrolyzer with resistivity < 0.3 Î© cm2 and improved water transport to the anion-cation junction, while MS3, First generation polymer based fuel cells achieving 0.5 W cm-2 initial peak power with total platinum group metal content â‰¤ 80 Âµg cm-2, was reached in terms of performance with a cathode catalyst free of Critical raw material (CRM),but with slightly higher loading of PGM at the anode than targeted.

The reporting period 2 was particularly successful for the work package on cell testing, with the replacement of iridium oxide at the anode of anion - exchange membrane electrolyzers by CRM-free metal oxide catalysts. Work on fuel cell testing has led to high peak power density up to 1.3 W/cm2 with pure H2/O2 feeds and with 0.6 mg of PGM (platinum and ruthenium) per cm2 at the anode, but with an iron-based cathode. In the work package on ionomer and membrane preparation, a breakthrough was achieved toward lowered through-plane resistance of bipolar membranes, while novel ionomers with appropriate morphologies for fuel cell electrodes were developped and successfully tested in fuel cell.

Final results

The novel electrolyser and fuel cell devices that are being developped in CREATE are expected to lead to at least a reduction by a factor of 5 in the amount of precious metal and critical raw material amounts, as compared to the existing technologies based on proton-conductive polymer-electrolyte electrolyzer and fuel cell. Due to the significant cost related to precious metals in existing acidic-type devices, only a fraction (circa 50% based on an internal assessment) of the power performance needs being achieved without precious metals, for novels cells being developped in CREATE to be economically viable. Durability of these novel cells is a key issue for their industrial application. If performance and durability can be simultaneously met and be competitive relative to proton-conductive devices, such devices could find application in the short- or medium-term in distributed stationary energy devices (1-100 kW size, on-site H2 production for H2 refueling stations, in parallel with the deployment of H2-fed vehicles, or combined electrolyzer and fuel cell for electricity storage). The proposed devices could also be applied in the portable electronic sector. The expected benefits are comparable or improved balance between performance and cost compared to existing technology. Beside the pure technical and economic aspects, the demonstration of an existing path for fuel cell and electrolyser that contain no or only a minimum amount of precious metals is important for the public acceptance of all hydrogen-related technologies.