Ultramicrotomed samples were prepared from the slurry-coated sheets used for XAS. An acute triangle (approximately 7 mm long side, approximately 2 mm short side) was cut from each sheet and embedded in slow-curing, low-viscosity resin (EpoFix) within a silicone mat (Ted Pella). The epoxy was allowed to cure for 24 hours. Using a Leica Ultramicrotome UC7, embedded samples were first trimmed to a rectangular block face with side length on the order of 100 µm using a diamond trimming tool (Diatome), then sectioned with a custom diamond knife created specifically for dry sectioning of electrodes (Diatome) as described elsewhere. 49 Samples were sectioned with nominal thickness of 80 nm, 100 nm, or 150 nm.