Pt/C electrocatalysts derived from recycled Pt/Re mixed solutions: synthesis, characterization, and electrochemical behaviour in fuel cells

Abstract

Utilizing critical metals such as platinum (Pt) and rhenium (Re) recycled from spent catalysts in energy conversion systems is a strategy to solve the problems of metal resource scarcity. A microwave-assisted polyol reduction method was developed to convert H₂PtCl₆·6H₂O (containing Re) into high-purity Pt/C electrocatalysts, leaving a small amount of Re in solution for further recovery. PtCl₆²⁻ can be selectively reduced to metallic Pt in an alkaline environment, whereas ReO₄⁻ cannot be reduced to metallic Re. Additionally, the optimum size distribution (2.03 nm) of Pt nanoparticles can be controlled by adjusting the molar ratio of NaOH to Pt. The M-50 electrocatalyst demonstrated mass and specific activities of 0.0890 A mg_Pt⁻¹ and 0.0810 mA cm⁻², respectively, towards the oxygen reduction reaction. When employed in a membrane electrode assembly (MEA) test, the highest power density of 0.80 W cm⁻² was achieved, which was competitive with that of TANAKA 20 wt% commercial Pt/C electrocatalysts. This microwave-assisted polyol reduction can convert H₂PtCl₆·6H₂O (containing Re) into high-purity Pt/C electrocatalysts, which solves the problem of insufficient purity of secondary resources brought on by the challenge of in-depth separation of Pt and Re during the hydrometallurgical process. This process provides a new idea for recycling critical metals in an economical, sustainable, and affordable manner.