Facets or anions?
How do the electrochemical properties of neighbouring grains, grain boundaries and facets of a polycrystalline surface differ, and how do they correlate with crystal orientation?
The control curve at polycrystalline Pt in 0.05 M H₂SO₄ shows two closely spaced inflection points at ≈ 595 and 620 mV vs. RHE. They may originate from two anions (HSO₄⁻/SO₄²⁻) or from different facets.
The 5 µm microdisc averages over a few grains and cannot decide this question on its own. A grain-resolved measurement on the same surface can.
Grain-resolved voltammetry and control curve on the same Pt surface
- EBSD of the end face of the microdisc: grain orientations and grain boundaries.
- SECCM mapping of the same or an identically prepared surface in 0.05 M H₂SO₄.
- EFCE at the microdisc; comparison of the inflection points with the grain-specific voltammograms.
Outcome A · grain-dependent
The two inflection points can be assigned to specific grain orientations. The doublet is a facet effect.
Outcome B · the same on all grains
The doublet is independent of grain orientation. It is due to the two anion species.
- The electrolyte conditions in the SECCM meniscus must correspond to those in the EFCE cell.
- The pretreatment (conditioning) of both surfaces must be comparable.
- A measurement on a Pt(111) single crystal is suitable as an independent control.