Two-Dimensional Effects of Ni-Based Metal–Organic Framework Materials on Electrochemical Actuators

The performance of electrochemical actuators is mainly based on the migration path of the electron/ion, the ion storage space, and the mechanical strength. Despite many studies devoted to developing elaborate hierarchical architectures of electrode materials to achieve a better actuation effect, the underlying relationship between the dimensions of materials and the actuation properties has been seldom investigated. Herein, three different dimensions of Ni-1,4-benzenedicarboxylic acid microstructures sharing the same composition and crystal phase were introduced into the PEDOT:PSS electrode layer. By comparing their conductivity, capacitance, and the mechanical properties, the two-dimensional Ni-1,4-benzenedicarboxylic acid sample exhibited the best electrical conductivity (175.1 S cm –1 ), ion conductivity (1.07 × 10 –4 S cm –1 ), charge transfer resistance (3.48 Ω), capacitance (12.64 mF cm –2 ), response speed (1.02 mm s –1 ), Young’s modulus (34.89 MPa), and stress (0.195 mN). Under low-voltage testing conditions of ±3 V, the deflection displacement reached 17.6 mm, which is four times higher than that of the pure PEDOT:PSS electrode (4.2 mm). The driving strain was as high as 0.57% (PEDOT:PSS’s driving strain was 0.2%), and the electromechanical conversion efficiency was 2.78%, attributed to two-dimensional nanostructures providing a large surface area and abundant active sites for electrochemical reaction. The unique two-dimensional layer promotes a faster diffusion and accumulation of ions on the entire electrode and shortens the diffusion distance of ions in the electrochemical reaction process.