Abstract
The activity degradation of hydrogen-fed proton exchange membrane fuel cells (H2-PEMFCs) in the presence of even trace amounts of carbon monoxide (CO) in the H2 fuel is among the major drawbacks currently hindering their commercialization. Although significant progress has been made, the development of a practical anode electrocatalyst with both high CO tolerance and stability has still not occurred. Currently, efforts are being devoted to Pt-based electrocatalysts, including (i) alloys developed via novel synthesis methods, (ii) Pt combinations with metal oxides, (iii) core–shell structures, and (iv) surface-modified Pt/C catalysts. Additionally, the prospect of substituting the conventional carbon black support with advanced carbonaceous materials or metal oxides and carbides has been widely explored. In the present review, we provide a brief introduction to the fundamental aspects of CO tolerance, followed by a comprehensive presentation and thorough discussion of the recent strategies applied to enhance the CO tolerance and stability of anode electrocatalysts. The aim is to determine the progress made so far, highlight the most promising state-of-the-art CO-tolerant electrocatalysts, and identify the contributions of the novel strategies and the future challenges.
Highlights
In the transition to the hydrogen economy era, hydrogen-fed proton exchange membrane fuel cells (H2 -PEMFCs) are expected to play a prominent role in automotive and portable applications, due to their high efficiency, high power density, quick startup, low weight, and silent operation [1,2]
FTIR spectra showed that several carbonyl, alcohol, and phenol compounds were present on the surface of multiwalled carbon nanotubes (MWCNTs) due to OH species anchoring after functionalization (Figure 9g)
In order to distinguish the most promising and up-to-date carbon monoxide (CO)-tolerant anodes, in Figure 13 we summarize the results regarding CO poisoning of the anodes tested in single PEMFCs
Summary
In the transition to the hydrogen economy era, hydrogen-fed proton exchange membrane fuel cells (H2 -PEMFCs) are expected to play a prominent role in automotive and portable applications, due to their high efficiency, high power density, quick startup, low weight, and silent operation [1,2]. The purification cycles required to achieve such low CO concentrations prohibitively increase the costs Alternative methods, such as on-board preferential CO oxidation [10] or operando oxygen bleeding [12], have been thoroughly investigated for mitigating CO poisoning. The oxygen can be supplied either externally, together with the hydrogen feed, or internally via the permeation of oxygen from the cathode through the membrane after applying a pressure difference between the anode and cathode feed Both methods have failed so far to eliminate CO poisoning, while they present important disadvantages, such as high costs and fuel cell potential oscillations, respectively [10,12]. Developing an anode electrocatalyst with both high CO tolerance and stability is a challenging task, due to the vulnerability of non-noble metals to dissolution under the acidic environment of PEMFCs [7,16]. Our discussion aims at providing a fundamental understanding of how the regulation of the structural and morphological features of materials, through the applied approaches, favors the enhancement of CO tolerance
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