PEMFC中Pt-Co核壳催化剂衰减规律研究

In this work, aiming to reveal the intricate structural evolution and comprehensive performance degradation mechanisms of Pt₃Co core-shell catalysts at the cathode of proton exchange membrane fuel cells (PEMFCs), a sophisticated one-dimensional degradation model was meticulously constructed and rigorously validated. The multi-physics model elegantly integrates numerous interconnected physicochemical processes, including electrochemical redox reactions of the protective Pt shell, progressive Co dissolution kinetics, and the Ostwald ripening phenomenon, with the primary objective of quantitatively analyzing the dynamic temporal changes in catalyst particle size distribution, critical Pt shell thickness (with a definitive threshold value of 2.25 Å, precisely corresponding to a single atomic layer of protective Pt shell), and the evolving Pt/Co atomic ratio throughout the electrochemical aging process of the nanoscale catalyst structures. The extensive research findings unequivocally demonstrate that the structural integrity and continuity of the Pt shell play a fundamentally decisive role in maintaining the long-term stability of Co atoms within the catalyst core. When the protective Pt shell thickness is progressively thinned below the crucial single atomic layer threshold due to electrochemical dissolution mechanisms, it inevitably leads to the detrimental exposure of underlying Co atoms, subsequently triggering a substantial Co mass loss of up to 70.6% at the cathode catalyst layer/membrane (CCL/MEM) interfacial region. This significant degradation value is considerably higher than that observed at the gas diffusion layer/catalyst layer (GDL/CL) interface, thereby revealing the pronounced spatial inhomogeneity and location-dependent nature of the complex degradation processes throughout the electrode structure. Various operational parameters also exhibit a profound and measurable impact on the catalyst degradation rate and mechanisms. In accelerated stress tests involving potential cycling protocols, when the upper voltage limit (UPL) surpasses the critical threshold of 0.95 V, the decay rate of the electrochemical active surface area (ECSA) accelerates dramatically and irreversibly. Furthermore, systematic increases in operating temperature not only substantially intensify the cumulative mass loss of Co within the functional catalyst layer but also significantly exacerbate the inhomogeneity of its spatial distribution along the thickness direction of the catalyst layer, creating localized regions of accelerated degradation. The comprehensive model successfully elucidates the multifaceted degradation evolution pathways of Pt₃Co core-shell nanostructured catalysts: small-sized catalyst particles experience premature Co exposure and consequent deactivation primarily due to preferential dissolution of their protective Pt shell layers, while larger-sized particles simultaneously undergo progressive coarsening predominantly through the thermodynamically-driven Ostwald ripening effect, thereby continuously reducing the total electrochemically active surface area available for oxygen reduction reactions. This study provides crucial theoretical foundations and quantitative guidance for optimizing the design of alloy catalysts and regulating the operating conditions of PEMFCs, contributing to the improvement of their long-term durability and performance stability.