Electrified, decentralised upcycling of Platinum-Group Metals from spent automotive catalysts into functional electrocatalysts

Abstract

Securing platinum-group metals (PGMs) for low-carbon technologies requires recycling routes that are both efficient and deployable near the source of waste. We report a fully electrified, modular flowsheet that couples microwave-assisted leaching (MWAL) with gas-diffusion electrocrystallization (GDEx) to recover and upcycle PGMs from spent automotive catalysts. Using 1.5 M HCl + 1.5 M NaCl at up to 200 °C and L/S ≤ 10, MWAL achieves ≥90% PGM leaching while suppressing matrix dissolution at lower L/S. The resulting multielement leachates are treated at room temperature by GDEx (10–200 mA cm-2), which selectively converts dissolved PGMs into ~5 nm alloy nanoparticles of ~83-91 wt% purity with >95% metal conversion. The as-recovered nanoparticles act directly as electrocatalysts for the methanol oxidation reaction, delivering MA = 241.7 mA mgPt-1, SA = 0.42 mA cm-2, and ~85% activity retention after 1000 cycles. Closed-loop leachate reuse between GDEx and MWAL preserves PGM extraction while progressively reducing matrix co-leaching. Life-cycle assessment identifies MWAL electricity as the primary hotspot (~half of the average impacts), followed by GDEx effluent neutralisation. A 30% heat recovery in MWAL and low-carbon electricity reduces burdens (up to 60% in Climate Change). A techno-economic assessment at 50 L h-1 treatment capacity indicates robust viability (operating margin 13.9%, NPV = 9.08 M€, IRR = 45.1%, 4-year payback), with further gains from scale-up and valorising the nanoparticle product. The MWAL–GDEx route thus offers a scalable, decentralisation-ready, electrified pathway that recovers PGMs with high efficiency and directly upgrades them into functional catalysts.