Efficient recycling techniques of precious platinum (Pt) for polymer electrolyte fuel cells & electrolyzers (PEFC&E) are of considerable interest in the near future. In view of apparently different scientific field, some microorganisms are known to be capable of physiologically reducing various soluble metals and metalloids under ambient conditions. In particular, some microbial cells can accumulate Pt nanoparticles through microbiological processes, suggesting potential use of the cells for alternative Pt recovery techniques. However, immobilized Pt nanoparticles encapsulating bacterial cells have yet to be investigated for PEFC&E applications. Herein, we report electrochemical studies on recovered Pt nanoparticles from spent catalyst materials by metal-reducing bacteria, Shewanella sp. strain HN-41. The crystal structures and morphologies of cell-bound Pt nanoparticles were characterized by electron microscopy, X-ray diffraction and spectroscopy measurements. After optimized post-heating conditions for the cells covered by nanoparticles were investigated, their catalytic activities and electrochemical stabilities were compared with commercial Pt/C. Electrochemical characterization was performed using a standard three-electrode half-cell configuration with a rotating disk electrode (RDE) system in 0.1 M aqueous HClO₄ solution at 298 K, evaluating oxygen reduction reaction (ORR) activity in terms of linear sweep voltammetry (LSV) and cyclic voltammetry (CV). This study is of great importance to provide a green approach to revaluation of spent Pt-containing wastes into value-added and cost-competitive new catalyst materials.

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