Cathode oxygen reduction reaction (ORR) and anodic hydrogen oxidation reaction (HOR) are two extremely important electrochemical reactions in proton exchange membrane fuel cells (PEMFC) and metal air batteries. Among them, due to the sluggish reaction kinetics of ORR, electrocatalysts with high catalytic activity are needed to promote the rapid progress of the reaction. Currently, the mainstream ORR catalyst is still based on carbon-supported platinum (Pt/C) catalyst. However, under actual harsh electrochemical conditions, Pt/C catalysts have poor durability, and platinum nanoparticles often dissolve, migrate, mature, and grow. Therefore, the performance of the PEMFC device is significantly reduced.
Based on this, Nanchang UniversityProfessor Chen Yiwang, Professor Yuan Kai collaborated with Central China Normal UniversityProfessor Qiu Ming, and reported that uses strong interactions with metal carriers to adjust the electronic structure of Pt in PtCu alloys to increase catalytic activity and improve the durability of electrocatalysts. The related work was published in "CCS Chemistry" as "Arranging Electronic Localization of PtCu Nanoalloys to Stimulate Improved Oxygen Electroreduction for High-Performance Fuel Cells". The first author of this article is Wu Bing, a master's student in at Nanchang University.
First, the author used the molten salt method to prepare a carbon carrier with nitrogen-doped carbon nanosheets supporting Cu nanoparticles, and then used a high-temperature thermal reduction method to prepare a nitrogen-doped carbon nanosheet-loaded PtCu alloy catalyst. The successful preparation of the PtCu alloy catalyst can be seen from the scanning transmission electron microscope (STEM) images and element mapping images.
Figure 1. Synthesis diagram and corresponding morphology and structure characterization of PtCuNC-700.
From the XRD spectrum, it can be observed that the diffraction peak of PtCuNC-700 has shifted significantly, which once again proves that the PtCu nanoalloy was successfully prepared. From X-ray photoelectron spectroscopy (XPS), it can be observed that the binding energy of Pt in PtCuNC-700 is significantly shifted compared with PtCuC-700 and PtNC-700, proving that Cu in the PtCu alloy and N in the carbon support work together to adjust the electronic structure of Pt.
Figure 2. XRD and XPS characterization of PtCuNC-700 and comparison samples.
used X-ray adsorption fine structure technology (XAFS) to characterize the electronic structure and coordination environment information of Pt atoms in PtCuNC-700, proving that the electronic structure of Pt in PtCuNC-700 is jointly adjusted by Cu and N, and that the PtCu alloy forms a stable Pt-N bond with the carbon carrier, confirming that there is a strong interaction between the PtCu nanoalloy and the nitrogen-doped carbon carrier.
Figure 3. Synchrotron radiation structural characterization of PtCuNC-700 and comparison samples.
PtCuNC-700 catalyst exhibits a more positive half-wave potential than Pt/C catalyst in acidic environment (ΔE1/2= 48 mV). At the same time, PtCuNC-700 has smaller Tafel slope, better four-electron selectivity, and higher mass activity and specific activity. Under acidic conditions, after 30,000 cycles, PtCuNC-700 shows better cycling stability than Pt/C. The PtCuNC-700 catalyst was further used as the cathode catalytic layer of H2-air PEMFC. The device showed excellent power density (929.7 mW cm−2) and better durability, indicating that it has good application prospects.
Figure 4. Half-cell electrochemical performance of PtCuNC-700 and comparison samples and performance characterization of H2-air PEMFC device.
Finally, the author used theoretical calculations to reveal that the Cu and N introduced into PtCu-NC significantly optimized the electronic configuration of the Pt site, causing it to change the energy barrier of the reaction rate-determining step in oxygen reduction, and adjusted the d-band center of Pt, reducing its binding strength with oxygen intermediates, thereby accelerating the oxygen reduction reaction kinetics.
Figure 5. Theoretical calculation analysis of PtCu-NC model.
This work proposes the use of doped carbon supports to modulate the electronic structure of PtCu nanoalloys to stimulate their oxygen reduction properties, which not only deepens the understanding of the strong interaction between Pt-based nanoalloys and doped carbon supports, but also provides a reliable method for designing efficient and durable low-platinum electrocatalysts for PEMFC.
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paper link:
https://doi.org/10.31635/ccschem.022.202202552
Source: Frontiers of Polymer Science
