Cu single-atom catalysts could be promising non-noble catalysts towards oxygen reduction for fuel cell applications.
including sustainable fuel cells and next-generation metal-air batteries. [1][2][3][4][5][6] Unfortunately, the complex reaction pathways and intrinsically sluggish reaction kinetics of the ORR predominantly limit the overall efficiency of energy conversion. Although platinum (Pt) and its alloys have been recognized as the most efficient ORR electrocatalysts to date, some critical issues, including the ever-increasing cost, scarce reserve, fuel crossover, and unsatisfactory durability of Pt, pose a severe challenge toward the widespread commercialization for these electrochemical energy devices. [7][8][9][10][11][12] In this regard, it is of great significance and highly imperative to explore Pt-free alternative electrocatalysts with superior activity and excellent durability, as well as low cost. Fortunately, the less expensive and more abundant palladium (Pd) nanostructures represent a class of promising and reliable ORR electrocatalysts with comparable or even superior electrocatalytic performances than Pt-based catalysts. [13][14][15][16][17][18][19] Moreover, incorporation of Pd with a secondary earth-abundant 3d-transition metal (TM) to form Pd-TM bimetallic alloy can not only further reduce the consumption of precious Pd, but also effectively modify the electronic structure of Pd, which often leads to extraordinary electrocatalytic properties, such as enhanced superior activity, high selectivity, and sufficient stability, which are inaccessible by the monometallic counterparts or physical mixture. [14,15,20,21] Among various 3d-transition metals, Ni has been identified as a promising candidate to form Pd-Ni alloys with excellent catalytic performances due to its relatively cheap price and the elaborate synergy between Ni and Pd. [14,[22][23][24] As such, PdNi bimetallic nanoalloys are considered to be a highly economical and efficient ORR electrocatalyst.On the other hand, construction of 3D networked nanostructures with hierarchical porosity, i.e., mesopores connected with macropores, also provides an effective strategy to improve the utilization efficiency of noble metal atoms and structural robustness of a noble metal-based nanocatalyst. Such unique structural feature could endow the catalyst with several fantastic properties which are distinct from the solid counterparts, including high surface area, low density, metallic backbone, excellent molecular accessibility, minimized mass diffusive Cost-effective electrocatalysts for the oxygen reduction reaction (ORR) play pivotal roles in energy conversion and storage processes. Designing a 3D networked bimetallic nanostructure with hierarchical porosity represents a reliable and effective strategy for the advancement of electrocatalysts with greatly improved activity and stability. However, it still remains a tremendous challenge in fabricating such fantastic nanostructure via a feasible and economical approach. Herein, a facile cyanogel-bridged synthetic strategy is demonstrated to fabricate PdNi 3D nanocorals with hierarchical porosity. The elaborate inte...
The chemical composition and architecture of catalytic layers significantly affect the performance of membrane electrode assemblies in proton exchange membrane fuel cells. In this work, a novel catalytic layer with hierarchical proton transport pathways has been designed by simultaneously employing Nafion nanofibers and Nafion ionomers. A H2/O2 fuel cell based on the hierarchical catalytic layer shows an increase of 32.3% on power output in comparison with the conventional fuel cell at 70 °C and 100% relative humidity. That is attributed to unique roles of Nafion nanofibers in the hierarchical catalytic layer. First, the addition of Nafion nanofibers significantly increases the proton conductivity of the catalytic layer up to 8.3 × 10–1 S cm–1 at 70 °C and 100% relative humidity, which is 15.7 times higher than that of the catalytic layer where the Nafion nanofibers are replaced by the same content of Nafion ionomers. That is confirmed by the accumulated proton transportation of a single Nafion nanofiber in the Nafion-nanofiber-based catalytic layer by a simulated model. Second, the porosity of the catalytic layer is increased due to the introduction of a Nafion nanofiber, leading to enhancement of mass transfer. Third, the Pt/C nanoparticles are homogeneously anchored on the surface of the Nafion nanofibers, which improves the electrochemical surface area and the utilization of the Pt catalyst.
It is of great significance to reduce the amount of platinum for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells. In this work, a copper single atom coordinated by nitrogen doped carbon nanotubes is employed as a support for the deposition of platinum nanoparticles (Pt/Cu-SAC), according to the prediction of the density functional theory calculation, which reveals the ORR activity of Pt/Cu-SAC should be improved in comparison to that of Pt/C due to the weaker adsorption of oxygen. The prepared Pt/Cu-SAC exhibits more promising ORR activity than the commercial Pt/C due to the synergetic effect of Cu-SAC on the Pt particles. Furthermore, the fuel cell based on Pt/Cu-SAC with a cathode Pt loading of 0.025 mg cm −2 exhibits a peak power density of 526 mW cm −2 , which is quite similar to that obtained with the commercial Pt/C with a cathode Pt loading of 0.1 mg cm −2 . The Pt/Cu-SAC paves the way to design low-Pt cathode catalysts for the polymer electrolyte membrane fuel cells.
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