Nanostructured platinum (platinum black / gray / fractal)

Platinum and platinum-iridium are the classic biocompatible electrode metals, but a smooth platinum surface has limited charge capacity. Nanostructuring it, as porous platinum black, platinum gray, or fractal/dendritic electrodeposits, raises the real surface area by one to two orders of magnitude, lowering impedance and increasing charge-injection capacity while retaining platinum's proven chronic biocompatibility and manufacturability.

Platinum gray was developed specifically for high-charge stimulation, for example in retinal prostheses, because classic platinum black, though extremely high in area, is mechanically fragile and sheds particles. The general lesson recurs across materials: mechanical durability of a nanostructured surface, not peak surface area measured on day one, governs chronic performance.