Elevating Platinum to Volumetric Capacitance: High Surface Area Electrodes through Reactive Pt Sputtering

Platinum is the most widespread electrode material used for implantable biomedical and neuroelectronic devices, motivating exploring ways to improve its performance and understand its fundamental properties. Using reactive magnetron sputtering, PtO_x is prepared, which upon partial reduction yields a porous thin-film form of platinum with favorable properties, notably record-low impedance values outcompeting other reports for platinum-based electrodes. It is established that its high electrochemical capacitance scales with thickness, in the way of volumetric capacitor materials like IrO_x and poly(3,4-ethylenedioxythiophene), PEDOT. Unlike these two well-known analogs, however, it is found that PtO_x capacitance is not caused by reversible pseudofaradaic reactions but rather due to high surface area. In contrast to IrO_x, PtO_x is not a reversible valence-change oxide, but rather a porous form of platinum. The findings show that this oxygen-containing form of Pt can place Pt electrodes on a level competitive with IrO_x and PEDOT. Due to its relatively low cost and ease of preparation, PtO_x can be a good choice for microfabricated bioelectronic devices.