image: In HT-PEMFCs, hydrogen is oxidized at the anode to generate protons, which are transported to the cathode through the proton conductor phosphoric acid in the high-temperature proton exchange membrane. The SiO2 in the cathode CNT@SiO2-Pt catalyst can induce the transfer of phosphoric acid from the active site of Pt to the adjacent SiO2. The specific adsorption and immobilization of phosphoric acid on the SiO2 form an efficient proton hopping transport network in the catalytic layer, and successfully achieves a power density of more than 1 W cm-2 for high-temperature proton exchange membrane fuel cells. view more
Credit: ©Science China Press
High-temperature proton exchange membrane fuel cells (HT-PEMFCs) have the advantages of simple hydrothermal management systems, strong tolerance to fuel impurities (CO, H2S), and are expected to be applied to fuel cell vehicles and other vehicles. HT-PEMFCs generally use Pt-based materials as the cathode catalyst and phosphoric acid as the proton conductor. However, the random distribution of phosphoric acid in the catalytic layer and the strong adsorption on the Pt sites make the oxygen reduction active sites unable to be exposed, so the performance of HT-PEMFCs is usually only half of that of low-temperature proton exchange membrane fuel cells. Earlier research found that the alloy composition, morphology, size, surface and interface of platinum-based catalysts can be adjusted to expose more active sites to alleviate the poisoning effect of phosphoric acid. However, these studies are still in the solution electrochemical stage, and the effectiveness of the catalyst under the actual working conditions of HT-PEMFCs has not been confirmed. In HT-PEMFCs, if phosphoric acid can be fixed in the vicinity of the active site of Pt, the loss of phosphoric acid in the catalytic layer and the poisoning of Pt by phosphoric acid can be reduced and local protons can be efficiently provided. The rapid proton coupling electron process will promote oxygen reduction reaction, thereby improving the performance of HT-PEMFCs. Studies have shown that SiO2 has a strong hydrogen bonding ability with acids. Therefore, the introduction of SiO2 into the catalyst design of HT-PEMFCs will help prevent the loss of phosphoric acid and improve stability.
Recently, Wang et al. prepared CNT@SiO2-Pt cathode catalysts by modifying carbon nanotubes with SiO2 and further loading with Pt nanoparticles. Solution electrochemical testing, HT-PEMFCs performance research, physical characterizations and theoretical calculations show that the SiO2 of CNT@SiO2-Pt has a stronger phosphate ion adsorption capacity than that of adjacent Pt, which greatly inhibits the poisoning effect of phosphoric acid on the active Pt site of the oxygen reduction catalyst. At the same time, the immobilization of SiO2 on the phosphoric acid promotes the uniform distribution of phosphoric acid in the catalytic layer of HT-PEMFCs, constructs an efficient and fast proton hopping transport network. At the same time, the rapid proton coupling electron process promotes the occurrence of oxygen reduction reactions, thereby improving the performance of HT-PEMFCs. HT-PEMFCs with CNT@SiO2-Pt as the cathode catalyst exhibit 765 mW cm-2 (H2/O2) and 486 mW cm-2 (H2/Air) performance at 160℃, and power density of 1061 mW cm-2 at 220℃ (dry H2/O2, no back pressure). The introduction of SiO2 provides a high-speed path for the oxygen reduction process of proton-coupled electrons, thereby achieving high power density of HT-PEMFCs.
See the article:
Silica-Facilitated Proton Transfer for High-Temperature Proton Exchange Membrane Fuel Cells
https://doi.org/10.1007/s11426-021-1142-x
Journal
Science China Chemistry