Oxygen Evolution on Mechanically Strained TiO2/NiTi: Implications of Compositional Heterogeneity at (Photo)Electrocatalytic Interfaces

Carvalho, O. Quinn [National Renewable Energy Lab., Golden, CO (United States)]; Dutta, Nikita [National Renewable Energy Lab., Golden, CO (United States)] (ORCID:0000000323014010); Ghoshal, Debjit [National Renewable Energy Lab., Golden, CO (United States)]; Harvey, Steven [National Renewable Energy Lab., Golden, CO (United States)] (ORCID:0000000161207062); Kerner, Ross [National Renewable Energy Lab., Golden, CO (United States)]; Li, Shuya [National Renewable Energy Lab., Golden, CO (United States)]; Schichtl, Zebulon [National Renewable Energy Lab., Golden, CO (United States)]; Walker, Patrick [National Renewable Energy Lab., Golden, CO (United States)]; Wilder, Logan [National Renewable Energy Lab., Golden, CO (United States)]; Girotto, Gustavo [Federal University of Rio Grande do Sul; Lawrence Berkeley National Laboratory]; Jaugstetter, Maximilian [Lawrence Berkeley National Laboratory]; Nemsak, Slavomir [Lawrence Berkeley National Laboratory; University of California, Davis]; Crumlin, Ethan [Lawrence Berkeley National Laboratory]; Miller, Elisa [National Renewable Energy Lab., Golden, CO (United States)]; Greenaway, Ann [National Renewable Energy Lab., Golden, CO (United States)]

doi:10.1021/acselectrochem.5c00228

DOE OSTI · 2583632

Oxygen Evolution on Mechanically Strained TiO2/NiTi: Implications of Compositional Heterogeneity at (Photo)Electrocatalytic Interfaces

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Abstract

The adsorption and activation energetics underpinning small molecule conversion on heterogeneous (photo)electrocatalysts are intrinsically tied to catalyst surface properties. Absent compositional characterization techniques with sufficient interface sensitivity, however, (photo)electrochemical performance can be misinterpreted in the context of bulk or near-surface material properties. Here we provide a fundamental investigation of the convoluting role of near-surface compositional heterogeneity in the interpretation of (photo)electrochemical alkaline oxygen evolution reaction (OER) activity, highlighting challenges in correlating composition measured by surface- and near-surface-sensitive probes. TiO2 thin films grown by air-annealing the superelastic alloy Nitinol (TiO2/NiTi) crack under tensile mechanical strain, increasing the number of electrochemically active Ni sites (Ni site density) that are probed via voltammetric features corresponding to Ni3+/Ni2+ redox events. (Photo)electrochemical OER kinetics trend with Ni site density, with overpotentials and Tafel slopes decreasing for Ni site densities < 1013 Ni/cm2geo and asymptotically approaching the performance of the base NiTi substrate for Ni site densities > 1013 Ni/cm2geo. Photoelectrochemical fill factors follow similar Ni site density dependent trends. When probing unstrained TiO2/NiTi, Ni site densities are two orders of magnitude higher when comparing near-surface-sensitive techniques (e.g., X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectrometry (TOF-SIMS), and scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS)) to surface-sensitive electrochemical measurements. This result highlights the challenge of correlating kinetic performance with intrinsic surface properties of electrochemical interfaces in the presence of near-surface compositional heterogeneity. Further, it reinforces the importance of fundamental investigations of surfaces with well-controlled composition and structure and the need for physically grounded and self-consistent interpretation of multiple near-surface characterization techniques.

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY electrochemistry heterogeneous electrocatalysis oxygen evolution reaction photoelectrochemistry surface characterization

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Carvalho, O. Quinn [National Renewable Energy Lab., Golden, CO (United States)], Dutta, Nikita [National Renewable Energy Lab., Golden, CO (United States)] (ORCID:0000000323014010), Ghoshal, Debjit [National Renewable Energy Lab., Golden, CO (United States)], Harvey, Steven [National Renewable Energy Lab., Golden, CO (United States)] (ORCID:0000000161207062), Kerner, Ross [National Renewable Energy Lab., Golden, CO (United States)], Li, Shuya [National Renewable Energy Lab., Golden, CO (United States)], Schichtl, Zebulon [National Renewable Energy Lab., Golden, CO (United States)], Walker, Patrick [National Renewable Energy Lab., Golden, CO (United States)], Wilder, Logan [National Renewable Energy Lab., Golden, CO (United States)], Girotto, Gustavo [Federal University of Rio Grande do Sul; Lawrence Berkeley National Laboratory], Jaugstetter, Maximilian [Lawrence Berkeley National Laboratory], Nemsak, Slavomir [Lawrence Berkeley National Laboratory; University of California, Davis], Crumlin, Ethan [Lawrence Berkeley National Laboratory], Miller, Elisa [National Renewable Energy Lab., Golden, CO (United States)], Greenaway, Ann [National Renewable Energy Lab., Golden, CO (United States)]. 2025-07-30. Oxygen Evolution on Mechanically Strained TiO2/NiTi: Implications of Compositional Heterogeneity at (Photo)Electrocatalytic Interfaces. https://doi.org/10.1021/acselectrochem.5c00228

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