Abstract
Achieving and sustaining net-zero greenhouse-gas emissions will require the long-term deployment of green hydrogen. Proton exchange membrane water electrolysers (PEMWEs) are attractive for variable renewable electricity (VRE) because of their fast dynamic response; however, they rely on iridium (Ir) anode catalysts, and Ir supply is severely constrained. Here, a Japan-specific dynamic material flow analysis (DMFA) model is developed for 2025-2100 to quantify Ir circularity in PEMWE deployment under a backcasting-oriented hydrogen production pathway. The model tracks Ir in anode catalysts only and represents: (i) Ir demand for new capacity additions and replacements, (ii) end-of-life (EoL) outflows governed by a Weibull lifetime distribution, and (iii) closed-loop recycling characterised by an overall recycling rate across collection, separation/pre-processing, and refining. Sensitivity analyses show that long-term primary Ir requirements are governed by the coupled effects of catalyst durability and recycling performance. Although lowering Ir loading reduces initial Ir intensity, accelerated degradation can increase replacement frequency and cumulative primary Ir demand unless recycling rate improves concurrently. Importantly, conclusions depend on the analysis horizon: Ir loading dominates cumulative demand up to 2050, whereas recycling becomes increasingly decisive toward 2100. These results highlight that Ir-thrifting catalyst designs must be evaluated jointly with durability under dynamic operation and recyclability to ensure scalable and continuous PEMWE deployment.