Carbon-supported ultra-high loading Pt nanoparticle catalyst by controlled overgrowth of Pt: Improvement of Pt utilization leads to enhanced direct methanol fuel cell performance

Carbon-supported Pt nanoparticle catalysts with ultra-high loading up to 85% are prepared by multi-step reduction (Pt/C-nR), in which additional Pt precursors are reduced upon a preformed Pt/C catalyst (Pt/C-1R). Transmission electron microscopy images show that the Pt/C-nR catalysts are composed of multilayers of Pt nanoparticles. The multiply stacked morphology in the Pt/C-nR catalysts may originate from the local overgrowth of additionally reduced Pt nanoparticles on the pre-existing Pt nanoparticles in the Pt/C-1R catalyst rather than conformal growth. The electrochemical characterizations by cyclic voltammograms in HClO4 solution reveal that Pt/C-2R catalyst exhibits an increased Pt utilization over the Pt/C-1R catalyst of the same Pt loading on the carbon support where a significant portion of catalytically active surfaces are buried within micropores of carbons. Furthermore, a direct methanol fuel cell (DMFC) single cell employing Pt/C-2R catalyst exhibits an enhanced DMFC performance compared to a single cell using the Pt/C-1R catalyst, demonstrating the importance of morphological control of Pt nanoparticles that can improve the catalyst utilization.

► The particle size of Pt/C (76 wt.% loading) can be kept less than 4 nm. ► Pt/C by multi-step reduction is composed of multilayers of Pt nanoparticles. ► Pt/C shows a higher Pt utilization in multi-step than in single step reduction. ► Pt/C in multi-step reduction results in an enhancement of DMFC performance.