Tris(trifluoromethylsulfonyl)methide-doped polypyrrole as a conducting polymer actuator with large electrochemical strain

A free-standing polypyrrole (PPy) film actuator, prepared electrochemically from a methyl benzoate solution of 1,2-dimethyl-3-propylimidazolium tris(trifluoromethylsulfonyl)methide (DMPIMe), exhibited up to 36.7% electrochemical strain in a propylene carbonate (PC)/water solution of lithium bis(nonafluorobutylsulfonyl)imide, Li(C4F9SO2)2N (LiNFSI). The maximum electrochemical strain of Me-doped PPy film depended on the electrolyte used for driving the Me-doped PPy actuator. When a PC/water mixed solution of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was used as the driving electrolyte, the maximum electrochemical strain, measured by cycling between −0.9 and +0.7 V versus Ag/Ag+ at 2 mV s−1, was 24.2%, smaller than that (30.0%) driven with LiNFSI. When a PC/water suspension of DMPIMe was used as the driving electrolyte, the maximum electrochemical strain was 31.9%. However, the response speed of Me-doped PPy actuator driven with DMPIMe was slower than those driven with Li(CnF2n+1SO2)2N, due presumably to the size and shape of the anions. The addition of CF3COOH in electrolytic solutions for electropolymerization increased the maximum electrochemical strains (36.7% and 36.6%) of Me-doped PPy actuator driven by using a PC/water solution of LiNFSI and a PC solution of DMPIMe, respectively.