Probing ions at the platinum-electrolyte interface using soft XAS

Alfred Larsson^a, Lucas de Kam^a, Hassan Javed Nagra^a, Robert Temperton^b, Andrey Shavorskiy^b, Katharina Doblhoff-Dier^a, Marc Koper^a, Rik Mom^a

^aLeiden Institute of Chemistry, Leiden University, the Netherlands

^bMAX IV, Laboratory, Fotongatan 2, Lund 224 84, Sweden

Proceedings of MATSUS Spring 2026 Conference (MATSUSSpring26)

G4 In situ/operando characterization of energy-related materials with synchrotron X-ray techniques

Barcelona, Spain, 2026 March 23rd - 27th

Organizers: Carlos Escudero and Juan Jesús Velasco Vélez

Oral, Alfred Larsson, presentation 236
Publication date: 15th December 2025

Electrocatalysis is crucial to numerous technologies supporting the green energy transition. The efficiency of the devices is governed by the properties of the electrode–electrolyte interface, the heart of any electrochemical device, where catalytic conversion occurs. Traditionally, efforts have focused on tailoring electrode surfaces to optimize the adsorption energies of reaction intermediates [1]. However, recent pioneering studies have shown that the electrolyte side of the interface also strongly affects activity and selectivity via ion-electrode interactions [2-4]. However, the exact mechanisms by which ions influence the reactions are not known, partly due to the lack of experimental tools suitable for directly probing ions at the electrochemical interface.

In this contribution, I will demonstrate how we utilize soft X-ray absorption spectroscopy (XAS) to experimentally detect interfacial ions. For this, we use mesoporous platinum, with a large ratio between the interfacial and bulk electrolyte in the pores. This allows the otherwise bulk-sensitive technique to provide quantitative data on the concentration and degree of hydration of Na ions at the platinum electrolyte interface. We study three distinct surface adsorbate structures, H-covered, OH-covered, and oxide-covered platinum by varying the potential vs RHE, at pH values ranging from 1 to 13 at varying and fixed Na bulk concentrations. For a fixed adsorbate structure, we find that the interfacial cation concentration is strongly dependent on the distance to the potential of zero charge (PZC), which varies with pH. We also find that at pH 13, the Na concentration increased when adsorbates changed from H (-0.05 V_RHE) to OH (0.5 V_RHE) and oxide (1 V_RHE), counterintuitive to capacitor models, which predict cation repulsion at higher potentials. This shows how adsorbates reshape surface charge and the ions attracted, altering the local reaction environment. The link between EDL structure and catalysis will also be discussed.

References:

[1] Vojislav R. Stamenkovic et al. ,Improved Oxygen Reduction Activity on Pt3Ni(111) via Increased Surface Site Availability.Science315,493-497(2007)

[2] Strmcnik, D., Kodama, K., van der Vliet, D. et al. The role of non-covalent interactions in electrocatalytic fuel-cell reactions on platinum. Nature Chem 1, 466–472 (2009)

[3] Monteiro, M.C.O., Dattila, F., Hagedoorn, B. et al. Absence of CO2 electroreduction on copper, gold and silver electrodes without metal cations in solution. Nat Catal 4, 654–662 (2021).

[4] Shah, A.H., Zhang, Z., Huang, Z. et al. The role of alkali metal cations and platinum-surface hydroxyl in the alkaline hydrogen evolution reaction. Nat Catal 5, 923–933 (2022).

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