Phasing out Critical metals in Membrane Fuel Cells: Evaluating the environmental impact and risk of Pt substitution towards optimized cathode performance

Platinum (Pt) has unique chemical and catalytic properties, making it indispensable for several key industrial applications, such as Renewable Energy or Electric Mobility. However, due to its high price and scarcity, reliance on import from sources outside Europe, and lack of effective substitutes for Pt, it is categorized as a Critical Raw Material (CRM). To address this, several attempts have been made to (partially) replace Pt with more inexpensive and abundant metals, such as Iron, Molybdenum or Cobalt. Nevertheless, prevous reports on Pt substitution often focus only on the catalyst’s properties during optimization at the laboratory scale, while criteria of Safety and Sustainability are often overlooked.

According to the Safe and Sustainable by Design (SSbD) framework, safety and sustainability considerations should be integrated into the early stages of development for new materials, by iteratively applying the assessment phase and the re-design phase of the framework at each scale of development. Specific operations or substances can be identified as hotspots during the assessment phase at early stages of development, and targeted for substitution / minimization during the re-design phase, before technology lock-ins occur.

Previous sustainability assessments have revealed that the Pt catalyst in Membrane Fuel Cells (MFCs) is a major contributor to the environmental impacts. Here, the (partial) substitution of Pt by Nickel-based coatings is addressed, as a cathode catalyst for MFC applications. Core-shell nanoparticles are prepared with a range of Pt loadings between 0.01-0.2 mg/cm² and tested as catalysts for oxygen reduction reaction in acidic conditions typical for MFC. A comparative Life Cycle Assessment (LCA) and Chemical Risk Assessment (CRA) of different catalyst compositions with varying Pt content is performed, to establish a correlation between the catalyst performance, safety and sustainability criteria, and quantify the trade-off between the catalyst performance and sustainability when increasing Pt loading. The outcomes of the assessments are used to select an optimal Pt content for upscaling and characterization at the demonstrator scale. Finally, the outcomes are used to establish Re-Design indicators and SSbD Criteria for CRM substitution, which can contribute to SSbD assessments on MFC applications beyond the pilot scale.

Funded by the European Union under Grant Agreement No. 101058076. Views and opinions expressed are however those of the author(s) only and not necessarily reflect those of the European Union or HADEA. Neither the European Union nor HADEA can be held responsible for them.