Proton exchange membrane fuel cells (PEMFC) are widely recognized as a viable option for the transition to sustainable energy and play a key role in the hydrogen economy plan. Although significant progress has been made in the research of PEMFC cathode oxygen reduction reaction (ORR) catalysts in the past few decades, the development of catalysts with excellent activity and good durability remains a major challenge. PT-M (M=transition metal element) alloys exhibit better ORR activity than PT C, but most PT-M alloy catalysts suffer significant structural degradation due to metal leaching under PEMFC's harsh operating conditions, resulting in insufficient stability.
Previous studies on the corrosion of metal alloys have shown that the introduction of some valence elements such as V, CR and NB into the alloy can effectively improve the corrosion resistance of PT-M. In principle, these valence metals, with their weak electron affinity and strong tendency to ionize, can act as buffers for receiving or donating electrons, thereby facilitating electron transport in metal alloys, which helps to evenly distribute electron densities and reduce local charge imbalances and polarization. Inspired by this phenomenon, the introduction of electronic buffers into the PT-M alloy ORR electrocatalyst is expected to effectively reduce the surface oxidation and polarization of the PT shell when operating at high potential in an acidic environment.
Based on this,Li Jing, Huazhong University of Science and TechnologyThe research group introduced electronic buffers (variable valence metal elements, i.e., M= Ti, V, Cr and Nb) to enhance the structural stability of the intermetallic PT alloy ORR catalyst. Among them, L10-Cr-PTFE C had the best ORR activity and stability. In 054~0.In the voltage range of 90 VRHE, the in-situ X-ray absorption spectroscopy (XAS) test results show that compared with L10-PTFE, the introduction of CR can effectively act as an electronic buffer, inhibit the surface polarization of the PT shell by reducing the valence state and weakening the tensile strain, thereby stabilizing the structure of the catalyst and preventing the dissolution of PT Fe.
In proton exchange membrane fuel cells (PEMFC), the total cathode PT load is 0075 and 0125 mgpt cm-2 (anode loading of 0.)025 mgPT cm-2), the initial mass activity (mA) of L10-Cr-PTFE C was 1., respectively41 and 102 a mgpt-1 (0.90 V), the rated power is 140 and 92 w mgpt-1。In addition, after 60,000 ADT cycles, L10-Cr-PTFE C has a MA retention of 71% and a power density rating of 79 w mgpt-1 (0.99 W cm-2), as well as at 0The potential loss at 8 A cm-2 is only 20 mV, which is one of the best-performing PT-based alloy cathodes reported in the literature.
The results of density functional theory (DFT) calculations show that the introduction of CR optimizes the center of the D-band and the surface strain of PT, thereby improving the ORR activity. The introduction of CR increases the electron enrichment of the PT shell and improves the kinetic barrier of PT detachment and Fe diffusion, thereby improving the long-term stability of the ORR. Therefore, the strategy proposed in this study is expected to promote the development of durable catalysts in harsh electrochemical environments, and can be extended to other electrochemical energy conversion technology applications.
introducing electron buffers into intermetallic pt alloys against surface polarization for high-performing fuel cells. journal of the american chemical society, 2024. doi: 10.1021/jacs.3c10681