Beyond pure precursors: Towards oxygen reduction reaction activity enhancement in PEM fuel cells from recycled mining waste

Clean energy is essential to achieving the United Nations' Sustainable Development Goals and targets. Proton Exchange Membrane Fuel Cells (PEMFCs) are one of the leading technologies for implementing the "hydrogen economy" and contributing to a sustainable energy supply. PEMFC development requires high-performing, durable electrocatalysts (ECs) whose synthesis is as facile and inexpensive as possible. This work demonstrates that it is feasible to synthesize viable ECs for PEMFCs from platinum mining residues obtained in Colombia. This Pt source is hardly exploited and, in perspective, could offer a lower-cost alternative to more established precursors for the preparation of ECs for PEMFCs. In particular, the ECs considered in this work are intended to promote the oxygen reduction reaction (ORR), a key bottleneck in PEMFC operation. The precursors from mining residues were characterized by micro-Raman, ATR-FTIR, XRD, TGA, and SEM/EDS to clarify their chemical composition and identify the coordination complexes present therein. Two synthetic methods are considered: (i) the microemulsion method; and (ii) the polyol method. A statistical Design of Experiments (DoE) is implemented to determine the optimal experimental conditions for each synthetic method. The physicochemical properties of the resulting Pt/C ECs are elucidated by SEM, TEM/STEM-EDS, XRD, and XPS. Finally, it is found that the "ex-situ" ORR performance determined by the CV-TF-RRDE method of the Pt/C ECs presented in this work compares favorably to that of a state-of-the-art Pt/C EC benchmark for the ORR.