Periodic Reporting for period 3 - CREATE (Critical Raw materials Elimination by a top-down Approach To hydrogen and Electricity generation)
Reporting period: 2019-07-01 to 2020-12-31
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 world’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 world’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.
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.
Novel catalyst for the anode reaction in water electrolysis were developped during the first periodi. Libraries of multimetallic oxides of Earth-abundant metals where evaluated. Novel catalysts for the cathode of fuel cells were also developped, and an iron-based catalyst reached the internal target of CREATE. Regarding development of catalysts for the hydrogen evolution and hydrogen oxidation reactions, two approaches have been pursued, one without any PGM elements , and another with low PGM content. In the frame of this project, sufficient electrocatalytic activity was reached only with catalysts based on low-platinum content.
In the work package on ionomer and membrane preparation, a novel ex-situ durability protocol was established that highlighted the importance of water. Novel ionomer morphologies were also investigated, that showed high performance in electrochemical cells compared to the previously existing morphologies.
During the second period, two important milestones were achieved, MS1, anion exchange membrane with alkaline stability at 60°C > 400 h and anion exchange ionomer conductivity > 3 S m-1, and MS2, Novel bipolar membrane designed for electrolyzer with resistivity < 0.3 Ω cm2 and improved water transport to the anion-cation junction.
The second period saw also the successful replacement of iridium at the anode of anion - exchange membrane electrolyzers by Ni-Fe, and replacement of Pt at the cathode of fuel cell by Fe.
During the last period of the project, the fabrication of membrane-electrode-assembly and operating conditions of the electrochemical cells were optimized . Anion Exchange Membrane Fuel Cell (AEMFC) with a Fe-N-C cathode free of Critical Raw Materials (CRM) and paired with an anode with low loading of Platinum Group Metals (PGM) was developed. The optimized AEMFC achieved a cell voltage of 0.69 V at 0.5 A·cm-2 with air feed at the cathode, with a total PGM content of only 125 µg cm-2.This performance is only 10 mV below the challenging cell voltage targeted in the project under those condiitons. This result is above the 2021 state-of-the-art in the field, with anode PGM loading of typically 0.6 mg cm-2 used for achieving similar performance.
AEM electrolyzer (AEMEL) with NiFe oxide CRM-free anode and low-CRM cathode was developed. The optimized AEMEL-1 achieved a cell voltage of 1.85 V at 0.5 A·cm-2 at 45 °C, with a total PGM content of only 34 µg PtRu cm-2. A second optimized electrolyser cell (AEMEL-2) with slightly higher PGM content of 90 ug PtRu cm-2 at the cathode reached 1.76 V cell voltage at 0.5 A·cm-2, only 60 mV above the challenging cell voltage targeted.
The results obtained in CREATE have led to more than 50 peer-reviewed publications, and an international workshop on fuel cells and electorlyzers was organized in 2019 (www.efcd2019.eu). Three newsletters were disseminated, and numerous oral presentations given by the project partners.
Overall, the demonstration of substitutes to CRM-based catalysts in fuel cell or electrolyzer devices has been achieved, with high initial performance demonstrated when substituting Ir or Ru from AEMEL anode with Ni-Fe anode, while Pt was substituted by Fe at the cathode of AEMFC.
In the work package on ionomer and membrane preparation, a novel ex-situ durability protocol was established that highlighted the importance of water. Novel ionomer morphologies were also investigated, that showed high performance in electrochemical cells compared to the previously existing morphologies.
During the second period, two important milestones were achieved, MS1, anion exchange membrane with alkaline stability at 60°C > 400 h and anion exchange ionomer conductivity > 3 S m-1, and MS2, Novel bipolar membrane designed for electrolyzer with resistivity < 0.3 Ω cm2 and improved water transport to the anion-cation junction.
The second period saw also the successful replacement of iridium at the anode of anion - exchange membrane electrolyzers by Ni-Fe, and replacement of Pt at the cathode of fuel cell by Fe.
During the last period of the project, the fabrication of membrane-electrode-assembly and operating conditions of the electrochemical cells were optimized . Anion Exchange Membrane Fuel Cell (AEMFC) with a Fe-N-C cathode free of Critical Raw Materials (CRM) and paired with an anode with low loading of Platinum Group Metals (PGM) was developed. The optimized AEMFC achieved a cell voltage of 0.69 V at 0.5 A·cm-2 with air feed at the cathode, with a total PGM content of only 125 µg cm-2.This performance is only 10 mV below the challenging cell voltage targeted in the project under those condiitons. This result is above the 2021 state-of-the-art in the field, with anode PGM loading of typically 0.6 mg cm-2 used for achieving similar performance.
AEM electrolyzer (AEMEL) with NiFe oxide CRM-free anode and low-CRM cathode was developed. The optimized AEMEL-1 achieved a cell voltage of 1.85 V at 0.5 A·cm-2 at 45 °C, with a total PGM content of only 34 µg PtRu cm-2. A second optimized electrolyser cell (AEMEL-2) with slightly higher PGM content of 90 ug PtRu cm-2 at the cathode reached 1.76 V cell voltage at 0.5 A·cm-2, only 60 mV above the challenging cell voltage targeted.
The results obtained in CREATE have led to more than 50 peer-reviewed publications, and an international workshop on fuel cells and electorlyzers was organized in 2019 (www.efcd2019.eu). Three newsletters were disseminated, and numerous oral presentations given by the project partners.
Overall, the demonstration of substitutes to CRM-based catalysts in fuel cell or electrolyzer devices has been achieved, with high initial performance demonstrated when substituting Ir or Ru from AEMEL anode with Ni-Fe anode, while Pt was substituted by Fe at the cathode of AEMFC.
The novel electrolyser and fuel cell devices that were developped in CREATE have lead to a reduction by a factor of 15 (in electrolyzer) and by a factor 3 (in fuel cell) 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.
Durability of these novel electrohemical cells is a key issue for their industrial application, which is the next developmental stage. If high initial performance and durability can be simultaneously met in the future, such devices could find application in distributed stationary energy devices (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).
Complete elimination of CRMs in these devices while maintaining high performance will however require the development of highly active CRM-free catalysts for the hydrogen oxidation and evolution in alkaline medium, and intensification of R&D activities on these topics will certainly be witnessed in the coming years .
Bipolar membranes with improved properties were also developped during the project, and those may find industrial application in electrochemical energy conversion devices in the near future, especially in the frame of CO2 electrolysis and its conversion to high-value chemicals.
Durability of these novel electrohemical cells is a key issue for their industrial application, which is the next developmental stage. If high initial performance and durability can be simultaneously met in the future, such devices could find application in distributed stationary energy devices (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).
Complete elimination of CRMs in these devices while maintaining high performance will however require the development of highly active CRM-free catalysts for the hydrogen oxidation and evolution in alkaline medium, and intensification of R&D activities on these topics will certainly be witnessed in the coming years .
Bipolar membranes with improved properties were also developped during the project, and those may find industrial application in electrochemical energy conversion devices in the near future, especially in the frame of CO2 electrolysis and its conversion to high-value chemicals.