Hierarchical-Porous Hollow Nitrogen-Doped Carbon-Supported Pt Alloy Catalysts with a Controllable Triheterointerface for Methanol Electrooxidation

Carbon-supported Pt-based catalysts are the most effective catalysts for direct methanol fuel cells (DMFCs). However, challenges such as high Pt loading, cost, and susceptibility to CO poisoning severely hinder the development of DMFCs. In this paper, CoFe₂O₄@polymer@ZIF-67 is prepared successfully through sequential solution polymerization and in situ growth with modified CoFe₂O₄ as the core. Subsequently, a hierarchical-porous hollow nitrogen-doped carbon-confined controllable triheterointerface catalyst, PtCoFe-CoFeO_x@N-HHCS, was successfully prepared via a strategy involving high-temperature-induced phase migration and in situ chemical replacement. Under the optimal conditions, the mass activity of PtCoFe-CoFeO_x@N-HHCS reached 1054 mA mg_Pt^-1, which is 4.1 and 2.1 times higher than those of commercial Pt/C and commercial PtRu/C, respectively. The peak potential of the CO electrooxidation of the PtCoFe-CoFeO_x@N-HHCS shifts negatively by 70 mV compared with commercial Pt/C. The high methanol oxidation performance is attributed to the highly dispersed triheterointerface, hierarchical-porous hollow structure, and nitrogen-doped ultrathin carbon layer. The highly dispersed triheterointerface of PtCoFe-CoFeO_x@N-HHCS promotes the release of Pt and enhances the electron transfer rate through interfacial interaction, significantly improving the catalyst activity. The confinement effect of the nitrogen-doped ultrathin carbon layer prevents Pt dissolution and enhances the stability of the catalyst. The hierarchical-porous hollow structure provides rapid mass transfer channels for the methanol oxidation reaction, enhancing the reaction rate. The synergistic effect of multiple approaches endows PtCoFe-CoFeO_x@N-HHCS with good methanol oxidation performance. This work provides important prospects for preparing highly active, stable, and low-loading Pt catalysts.