Computational and experimental approach to the electromechanical and electrochemical behavior of Pt-reduced IPMC

Ionomeric polymer–metal composites (IPMCs) are advanced smart materials with an ionic-conducting polymer membrane coated with noble metal electrodes. When subjected to an electrical stimulus, an electric field is generated between the electrodes, causing solvated ions to migrate through the polymer membrane and create an internal pressure gradient, which results in the composite bending. However, the high cost of noble metals, such as gold and platinum, and the toxic waste generated during deposition are significant drawbacks. This study compares the electromechanical performance of a Nafion®-based IPMC with a reduced platinum (PR-IPMC) layer to that of a reference IPMC (R-IPMC). Tests were conducted under controlled relative humidity (RH), and blocking force and current response were used to assess performance. Scanning electron microscopy (SEM) was employed to examine the morphology of the platinum layer. The devices demonstrated optimal performance at 90% relative humidity (RH), with the PR-IPMC exhibiting a 60% thinner platinum layer. However, it displayed a 40% reduction in blocking force compared to the R-IPMC. The reduced platinum content results in cost savings and reduced waste production while still providing satisfactory mechanical performance. Theoretical analysis using molecular dynamics and finite element method (FEM) simulations revealed the stress distribution (S_Pt) in the platinum layers as a function of their thickness (δ_Pt). Interestingly, S_Pt remained independent of the ionomer’s hydration condition (λ), showing that thinner platinum layers are more efficient at storing stress relative to their thickness. Despite having only 40% of the platinum thickness, the PR-IPMC retained 57.6% of the stress compared to the reference IPMC. This relatively increased stress concentration explains why the decrease in blocking force is less than expected based on the reduction in platinum thickness. FEM simulations, aligned with experimental results, provide a useful tool for predicting device behavior under various conditions and guiding the development of future IPMC devices.

Graphical abstract