Nanoscale Active Sites for the Hydrogen Evolution Reaction on Low Carbon Steel

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Abstract
To fully elucidate the structural controls on corrosion-related processes at metal surfaces, experimental measurements should correlate and compare directly structure and activity at the scale of surface heterogeneities (e.g., individual grains, grain boundaries, inclusions etc.). For example, the hydrogen evolution reaction (HER), which usually serves as the cathodic counterpart to anodic metal dissolution in acidic media, may be highly sensitive to surface microstructure, highlighting the need for nanoscale-resolution electrochemical techniques. In this study, we employ scanning electrochemical cell microscopy (SECCM) in conjunction with co-located scanning electron microscopy, electron backscatter diffraction, and energy dispersive X-ray spectroscopy to elucidate the relationship between surface structure/composition and HER activity on low carbon steel in aqueous sulfuric acid (pH ≈ 2.3). Through this correlative electrochemical multimicroscopy approach, we show that the HER activity of the low index grains (slightly) decreases in the order (100) > (111) > (101), with grain-dependent free energy of hydrogen adsorption (calculated for the low index planes of iron using density functional theory, DFT) proposed as a tentative explanation for this subtle structural-dependence. More significantly, we show that the HER is greatly facilitated by sub-micron surface defects, specifically grain boundaries and MnS inclusions, directly identifying these heterogeneities as potential “cathodic sites” during (atmospheric) corrosion. This study demonstrates the considerable attributes of correlative SECCM for identifying nanoscale active sites on surfaces, greatly aiding understanding of corrosion and electrocatalytic processes.
Funding Information
  • Engineering and Physical Sciences Research Council
  • H2020 Marie Skłodowska-Curie Actions (792948)
  • Wolfson Foundation (INF/R1/180026)
  • Ramsay Memorial Fellowships Trust, University College London

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