Acidic PEM fuel cell

The stability and durability of Pt alloys, especially those involving a >d transition metal, are the major hurdles preventing them from commercial fuel cell applications. "" The transition metals in these alloys are not thermodynamically stable and may leach out in the acidic PEM fuel cell environment. Transition metal atoms at the surface of the alloy particles leach out faster than those under the surface of Pt atom layers." The metal cations of the leaching products can replace the protons of ionomers in the membrane and lead to reduced ionic conductivity, which in turn increases the resistance loss and activation overpotential loss. Gasteiger et al. showed that preleached Pt alloys displayed improved chemical stability and reduced ORR overpotential loss (in the mass transport region), but their long-term stability has not been demonstrated. " These alloys experienced rapid activity loss after a few hundred hours of fuel cell tests, which was attributed to changes in their surface composition and structure." ... 

Fuel cell CLs are the key components in the entire fuel cell device because the reactions such as hydrogen—oxidation reaction (HOR) at anode and the ORR at cathode occur inside the CLs. Particularly, in order to carry out the ORR, the catalyst particles inside the cathode CL must be in contact with each other for electrical conductivity and also in contact with protonic conducting (in acidic PEM fuel cells), or hydroxide conducting (in alkaline PEM fuel cells) ionomer for ionic conductivity. In addition, there must be some channels within the CL for transporting the reactants and the products. In other words, the catalyst particles must be in close contact with each other, with the electrolyte, and also with the adjacent diffusion medium (DM). Moreover, the reactants gas O2) and the produced water travel mainly through the voids, so the CL must be porous enough to allow gas to diffuse to the reaction sites and liquid water to wick out. 

High Temperature Phosphoric Acid PEM Fuel Cells... 

Oezaslan M, Hasche F, Strasser P (2012) Oxygen electroreduction on PtCos, PtCo and PtsCo alloy nanoparticles for alkaline and acidic PEM fuel cells. J Electrochem Soc 159(4) B394-B405... 

In general, the activation energy is also affected by the complexity of the reaction, with more complex mechanisms inciuring much greater activation losses than for more simplistic ones. For this reason, the ORR is much slower than the very facile HOR and usually contributes the majority of the activation losses in an acidic PEM fuel cell (Figure 2.4). 

Most of the discussion so far has pertained to acidic PEM fuel cells as they have been the main focus of low-temperature fuel cell research for the last 20 years... 

The kinetics of the hydrogen oxidation reaction in acidic PEM fuel cells above room temperature are often so fast that they contribute a negligible voltage to the overall activation overpotential, which is therefore often assumed to be wholly attributable to the ORR [41]. This allows catalyst loadings on the anode to be as low as 0.05mgptcm without affecting overall fuel cell performance significantly [42] and means that catalyst development is mainly focused on the cathode. However, in alkaline media, the HOR on polycrystalline Pt has been... 

In summary, solid alkaline fuel cells using hydrogen as a fuel represent a potential improvement in performance and reduction of cost over acidic PEM fuel cells. The technology is in the early stages of development, shown by the lack of studies to date and the variation in techniques and results in these studies, and requires further research with bespoke methods applied to the alkaline case (as opposed to trying to apply acid PEM principles to what might be a very different technology) to attain the performance levels achieved from state-of-the-art PEM fuel cells. 

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