Preparation of gradually componential metal electrode on solution-casted Nafion™ membrane

Abstract

A typical ionic polymer–metal composite consists of a thin perfluorinated ionomer membrane and noble metal electrodes plated on both surfaces. It undergoes a large bending motion when an electric field is applied hence exhibits deformation by a certain amount of cation. With proper arrangement and package, a great number of “smart devices” are anticipated. In this study, a solution-cast route was used to prepare the electro-active polymer membrane and platinum electrodes were fabricated onto the membrane through electro-less plating. The ionic polymer used is the commercial Nafion™, the perfluoro-sulfonated ionomer membrane, developed by DuPont Co. Nafion™ membrane was cast by the solution-casting route and then loaded with different weights simultaneously. The optimized processing conditions, membrane properties and electrodes behaviors were investigated. The results of shift in WAXD peaks showed that weights delineated the crystallinity of the solution-cast membranes. The number and size of the crystalline domains of solution-cast membrane decrease as studied by SAXS. The Young's modulus of solution-cast membrane decreases as increasing weight because of the loss of crystallinity (180–140 MPa). A finely dispersed platinum particle deeper and gradient penetrating within the near-boundary region with a smaller average particle size and more uniform distribution could be obtained through a reverse electro-less plating. Its surface roughness is 3 nm comparing to 52 nm of a typical process. But its surface resistance is too high (3.5 Ω) to activate the bending motion. To solve this problem, we coated the second Pt electrodes by a typical electro-less plating, and the resistance decreased to 0.7 Ω. The results depicted that the fabricated IPMC shows longer bending lifetime than typical IPMC. In a 0.09% NaCl solution, the device was able to vibrate for 8 h under a 5 V, 0.1 Hz actuation.