Speaker
Description
Platinum on high-surface-area carbon supports remains the benchmark oxygen-reduction-reaction (ORR) catalyst in proton-exchange-membrane fuel cells (PEMFCs) and a leading cathode for the hydrogen-evolution reaction (HER). The mesoporous N-doped carbon (MPNC) is used as a tunable platform to control dispersion and metal, support interactions, not as a field-wide state-of-the-art. The working catalyst is dynamic: entity size distributions (single atoms (SA), sub-nanometer clusters, nanoparticles (NP)), oxidation state, and coordination evolve under bias and mass-transport stress. Pt L₃-edge X-ray absorption spectroscopy (XAS), interpreted via X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), including wavelet-domain views, enables quantitative speciation linking structure to durability and performance. We present a unified program following Pt/MPNC across synthesis, baseline characterization, stress evolution, and operation: (i) ex-situ baselining with synthesis control, (ii) accelerated-stress-test (AST)-resolved XAS with electrochemical readouts, and (iii) in-situ electrochemical XAS (EC-XAS) capturing CO-stripping transients and steady-state HER/ORR. In-situ EC-XAS then captures electrocatalyst dynamics under working conditions by tracking the spectroscopic response while co-recording the electrochemical CO-stripping signal, thereby directly correlating structural signatures with electrochemical performance.1,2
Modulating synthesis on Pt-MPNC electrocatalyst and tracking with XAS tunes the SA/cluster/NP ensemble, then advances to operando to interrogate interfacial chemistry during CO-stripping voltammetry, providing predictive baselines for durability. To complete the picture of the MPNC support and Pt–support interactions, we extend beyond absorption to hard X-ray Raman scattering (XRS) of the C/N (and O) K-edges delivers bulk-sensitive soft-edge information in Pt/MPNC, while valence-to-core X-ray emission spectroscopy (XES; Pt Lβ₂) reports on ligand field and covalency around Pt. These datasets, together with aberration-corrected high-resolution transmission electron microscopy (ac-HRTEM), scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy (STEM-EDX), and TEM tomography, corroborate speciation assignments and spatial heterogeneity at the nanoscale. Overall, the continuous Pt-L₃ XAS program, augmented by XRS/XES and correlative EM, yields design rules linking initial dispersion and interfacial chemistry to operando dynamics and durability in Pt/MPNC catalysts for PEMFC ORR and HER.
References:
(1) Küspert, S.; Campbell, I. E.; Zeng, Z.; Balaghi, S. E.; Ortlieb, N.; Thomann, R.; Knäbbeler-Buß, M.; Allen, C. S.; Mohney, S. E.; Fischer, A. Small 2024, 20 (34), 2311260.
(2) Zeng, Z.; Küspert, S.; Balaghi, S. E.; Hussein, H. E. M.; Ortlieb, N.; Knäbbeler-Buß, M.; Hügenell, P.; Pollitt, S.; Hug, N.; Melke, J.; Fischer, A. Small 2023, 19 (29), 2205885.
