Toward a Comprehensive Understanding of Cation Effects in Proton Exchange Membrane Fuel Cells

Abstract

Metal alloy catalysts (e.g., Pt–Co) are widely used in fuel cells for improving the oxygen reduction reaction kinetics. Despite the promise, the leaching of the alloying element contaminates the ionomer/membrane, leading to poor durability. However, the underlying mechanisms by which cation contamination affects fuel cell performance remain poorly understood. Here, we provide a comprehensive understanding of cation contamination effects through the controlled doping of electrodes. We couple electrochemical testing results with membrane conductivity/water uptake measurements and impedance modeling to pinpoint where and how the losses in performance occur. We identify that (1) ∼44% of Co 2+ exchange of the ionomer can be tolerated in the electrode, (2) loss in performance is predominantly induced by O 2 and proton transport losses, and (3) Co 2+ preferentially resides in the electrode under wet operating conditions. Our results provide a first-of-its-kind mechanistic explanation for cation effects and inform strategies for mitigating these undesired effects when using alloy catalysts.

Regulating Catalytic Properties and Thermal Stability of Pt and PtCo Intermetallic Fuel-Cell Catalysts via Strong Coupling Effects between Single-Metal Site-Rich Carbon and Pt

“…The voltage loss (40 mV, 6%) at 0.8 A cm −2 was still larger than the challenging DOE target of 30 mV (Table S4). 12,31 The slightly inferior stability compared to RDE results is likely due to the contamination or damage of the ionomer caused by dissolved Co ions, 53,54 which is discussed in the following section.…”

Catalyst Stability in Aqueous Electrochemistry

“…Usually, the initial leaching of the non-noble metal, the so-called dealloying, results in a shell of the more noble metal, here platinum. The dissolution of non-noble metals can cause ion exchange with the polymer electrolyte, decreasing proton transport conductivity and O 2 permeability, all of which are secondary degradation effects stemming from the initial instability against dissolution. − Another salient example of the importance of an ordered chemical environment is the dependence of crystallinity and dissolution in oxides. Highly coordinated metal atoms and a high degree of saturated bonds lead to higher stability in comparison to that of amorphous oxide phases.…”

Multigram-Scale Synthesis of High-Pt-Content PtCo Intermetallic Catalysts for Proton Exchange Membrane Fuel Cells

“…The dissolution of Co not only causes a decrease in the catalyst activity but also induces the contamination of the membrane and ionomer, leading to increased mass transport resistance in the catalyst layer. 8,9 To mitigate the leaching of Co, researchers in this field have put forward an effective strategy by tailoring the atomic arrangement of PtCo alloys into ordered configurations, known as intermetallic compounds (IMCs). 10,11 The enhanced bond strength between Pt and Co atoms within IMCs 12−14 is considered the key factor that favors the alleviation of Co leaching.…”

“…Prior efforts have found significant promise in carbon-supported PtCo alloy nanoparticles as candidates for highly efficient cathode catalysts. − However, the alloy structure introduces an additional hurdle concerning catalyst durability due to the leaching of Co during the PEMFC operation. The dissolution of Co not only causes a decrease in the catalyst activity but also induces the contamination of the membrane and ionomer, leading to increased mass transport resistance in the catalyst layer. , To mitigate the leaching of Co, researchers in this field have put forward an effective strategy by tailoring the atomic arrangement of PtCo alloys into ordered configurations, known as intermetallic compounds (IMCs). , The enhanced bond strength between Pt and Co atoms within IMCs − is considered the key factor that favors the alleviation of Co leaching. Moreover, a recent study suggested that ordered intermetallic structures may possess higher Co diffusion barriers relative to disordered alloys.…”