Manufacture and characterization of ionic polymer transducers employing non-precious metal electrodes

Abstract

Ionic polymer membranes are commonly used in fuel cell power generation, water electrolysis and desalinization, chlorine generation, and other niche applications. Since the early 1990s ionic polymer membranes have also shown promise as distributed electromechanical actuators and sensors. The cost of these materials is very high because of the expensive noble metals that are used as the electrodes in these applications, however. Currently, high cost of these devices has prevented them from experiencing widespread use. The goal of the current research project is to study new methods of plating metal electrodes onto ionic polymer membranes in order to reduce the cost of these materials and open the door for potential industrial, aerospace, and biomedical applications.At this time ionic polymer actuators are only made using gold or platinum as the electrode in a lengthy and labor-intensive process. The current research focuses on using less costly metals and revising the metal deposition process. Several new methods allowing for faster deposition of metals onto ionic polymer membranes are developed and evaluated including sputter-coating, electroless plating, and impregnation/reduction. Using these methods, metal electrodes have been plated onto ionic polymer membranes in processes resulting in a purely surface deposition and in processes resulting in interpenetration of the metal into the polymer. This work shows that electromechanical coupling is present with all of these processes, although results indicate that interpenetration of the electrode is important for good adhesion of the metal and good performance of the transducers.Also studied were different metals; X-ray photoelectron spectroscopy (XPS) testing shows that the use of non-noble metals as the electrodes results in oxidation of the metal and corresponding loss of performance in the actuator. Noble metals are found to not experience the oxidation problem. Further work shows that non-noble metals can be effectively employed as electrodes if alloyed with noble metals by using a co-reduction technique. Also ii studied is the use of protective coatings of noble metal to stabilize the non-noble metal electrodes. Using these approaches, a new plating method is developed and the stability of the electrodes made using this method is studied. These results indicate that samples made using this new process may be actauted continuously for over 150,000 cycles with very little degredation in their performance.Using this new plating method, ionic polymer membrane transducers can be made in less than five hours. Characterization of these new devices shows that they have a mass energy density of 4-20 mJ/kg in the cantilevered mode. This compares well with a baseline material, which is found to have a mass energy density of 3-12 mJ/kg. Composition and morphology of the electrodes made using the new method are investigated using scanning electron microscopy (SEM) and the density and tensile modulus are measured. The density of the new material is found to be app...

Thickness dependence of curvature, strain, and response time in ionic electroactive polymer actuators fabricated via layer-by-layer assembly

“…11 Bennet et al embedded precious and nonprecious metals via electroless plating into CNCs and have shown that both categories of metals can be used in forming CNC layers; yet precious metals, primarily gold or platinum, are advantageous as they eliminate the oxidation problem and do not require further processing steps such as a co-reduction process or deposition of an ultra-thin protective layer. 12 Use of aqueous electrolytes limits the operating voltage of actuators to values below the voltage of water hydrolysis. Bennett et al have shown that use of ionic liquids can eliminate this issue.…”

Characterization of the solvent-induced nonlinear response of ionic polymer actuators

“…Each sample has Nafion r -117 as the base ionomer, sodium as the cation, and platinumgold electrodes. 19 The difference between the samples is that the first sample has water as the solvent, while the second sample has been solvated with the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf). While differing in dimensions, they do maintain a 4:1 length-to-width ratio (water: 8x2mm; EMI-Tf: 16x4mm).…”

Ionic electroactive polymer metal composites: Fabricating, modeling, and applications of postsilicon smart devices

“…45 Nevertheless, considering the high cost of noble metals some authors 46 developed a co-reduction process for plating ionic polymer materials that gives noble and non-noble metal alloy electrodes, with a resulting reduction in the consumption of expensive precious metals such as platinum and gold.…”

“…Though the concept of co-reduction is not a new one, [47][48][49] Bennett and Leo 46 developed a new process to reduce simultaneously a noble (Pt) and a non-noble metal (Cu) on the Nafion surface and to form an alloy sublayer consisting of two metal phases that appear to be homogeneously mixed.…”

“…In particular, results in Ref. 46 showed that Nafion V R membrane has a much higher preference for the tetra-ammine platinum ion than for the copper ion. A plausible explanation for this phenomenon may be that the copper ion is more solvated, and thus the platinum ions should be preferred by the polymer.…”