Brummer S B, Robblee L S, Hambrecht F T
Ann N Y Acad Sci. 1983;405:159-71. doi: 10.1111/j.1749-6632.1983.tb31628.x.
Smaller, more charge-intensive electrodes are needed for "safe" stimulation of the nervous system. In this paper we review critical concepts and the state of the art in electrodes. Control of charge density and charge balance are essential to avoid tissue electrolysis. Chemical criteria for "safe" stimulation are reviewed ("safe" is equated with "chemically reversible"). An example of a safe, but generally impractical, charge-injection process is double-layer charging. The limit here is the onset of irreversible faradaic processes. More charge can be safely injected with so-called "capacitor" electrodes, such as porous intermixtures of Ta/Ta2O5. BaTiO3 has excellent dielectric properties and may provide a new generation of capacitor electrodes. Faradaic charge injection is usually partially irreversible since some of the products escape into the solution. With Pt, up to 400 muc/cm2 real area can be absorbed by faradaic reactions of surface-adsorbed species, but a small part is lost due to metal dissolution. The surface of "activated" Ir is covered with a multilayer hydrated oxide. Charge injection occurs via rapid valence change within this oxide. Little or no metal dissolution is observed, and gassing limits are not exceeded even under stringent conditions.
为实现对神经系统的“安全”刺激，需要尺寸更小、电荷密度更高的电极。在本文中，我们回顾了电极方面的关键概念和最新技术。控制电荷密度和电荷平衡对于避免组织电解至关重要。本文还回顾了“安全”刺激的化学标准（“安全”等同于“化学可逆”）。双层充电是一种安全但通常不实用的电荷注入过程示例。这里的限制是不可逆法拉第过程的开始。使用所谓的“电容器”电极，如Ta/Ta2O5的多孔混合物，可以更安全地注入更多电荷。钛酸钡具有优异的介电性能，可能会提供新一代的电容器电极。由于一些产物逸出到溶液中，法拉第电荷注入通常部分不可逆。对于铂，表面吸附物种的法拉第反应可吸收高达400μC/cm²的真实面积，但由于金属溶解会损失一小部分。“活化”铱的表面覆盖着多层水合氧化物。电荷注入通过该氧化物内的快速价态变化发生。几乎没有观察到金属溶解，即使在严格条件下也不会超过放气极限。
