N-doped carbon confined CoFe@Pt nanoparticles with robust catalytic performance for the methanol oxidation reaction

Pt-based electrocatalysts are essential to direct methanol fuel cells (DMFCs), but their sluggish reaction kinetics, poor stability, inefficient Pt utilization and susceptibility to CO poisoning hamper the widespread application of DMFCs. Herein, 3.28 nm CoFe@Pt nanoparticles were encapsulated into N-doped carbon shells (CoFe@Pt-NCs) via pyrolysis of polydopamine-coated CoFe₂O₄ nanoparticles followed by a galvanic displacement reaction. The structures (thickness of NCs, reduction degree, and Pt content) in the CoFe@Pt-NCs were modified by varying the experimental parameters (amount of polydopamine, pyrolysis temperature, and time of the galvanic displacement reaction), to establish a structure-activity relationship between the CoFe@Pt-NCs and the methanol oxidation reaction (MOR) performance. Under optimal conditions, the mass activity (914.80 mA mg_Pt⁻¹) and specific activity (0.98 mA cm_Pt⁻²) of CoFe@Pt-NCs (Pt, 4.39 wt%) were 3.3 and 2.6 times higher than those of Pt/C, respectively. Moreover, the peak potential of the CO electrooxidation was negatively shifted by 104 mV compared with Pt/C. After carrying out chronoamperometry measurements, the current density of the CoFe@Pt-NCs was 3.3 times greater than that of Pt/C. The prominent MOR performance of the CoFe@Pt-NCs is attributed to the confinement and anchoring effects, as well as to the ion/electron transport of the three-dimensional porous NCs and the modulation effects of CoFe on Pt in conjunction with the high dispersion of Pt (small particle size, low Pt content). Our work might pave the way for a controllable and facile strategy that involves the integration of multiple strategies to improve the performance of Pt-based electrocatalysts for the MOR.