Research ArticleMATERIALS SCIENCE

Giant electrochemical actuation in a nanoporous silicon-polypyrrole hybrid material

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Science Advances  30 Sep 2020:
Vol. 6, no. 40, eaba1483
DOI: 10.1126/sciadv.aba1483
  • Fig. 1 Synthesis of a nanoporous PPy-silicon material.

    (A) High-angle annular dark-field scanning TEM top view on a nanoporous silicon membrane filled by electropolymerization with pyrrole. The green and red color codes indicate the N and Si concentration resulting from EDX detection measurements, respectively. (B) Voltage-time recording during galvanostatic electropolymerization of pyrrole in nanoporous silicon, with mean pore diameter d and thickness t. Characteristic regimes are indicated and discussed in the main text.

  • Fig. 2 Electrochemical actuation experiments.

    (A) Schematics of the electroactuation experiments on the pSi membrane (gray) filled with PPy (green) immersed in an aqueous electrolyte [HClO4 (blue and red) and H2O (red and white) molecules]. The dimensions of the as-fabricated membrane, on the left, are length l0, width w, and thickness t. The middle part illustrates the case where a voltage of 0.4 V is applied and the ClO4 anions are expelled from the PPy, resulting in the contraction of the sample. Vice versa, in the right part, a voltage of 0.9 V is applied, and the anions are incorporated, followed by the subsequent expansion of the sample. The change in length is indicated by Δl. (B) The graph depicts an exemplary cyclic voltammetry of a pSi-PPy membrane in 1 M HClO4 electrolyte. The current j is plotted against the applied potential E measured versus the SHE. The potential sweep rate is 10 mV/s. (C) The graph depicts the mean values for the maximal current density of j plotted against varying potential sweep rates dE/dt from 10 to 50 mV/s. The dashed line indicates a linear regression of the data points, which yields the capacitance c* as the slope. Depicted on the right are (D) five representative potential cycles E, (E) the resulting volumetric charge qV, and (F) the introduced effective strain ε of the nanoporous membrane.

  • Fig. 3 Static and dynamic electrochemical performance parameters.

    (A) Strain ε versus deposited volumetric charge qV. (B) Step coulombmetry to determine the electroactuation kinetics. The applied potential E is changed in a step-like fashion from 0.4 to 0.8 V and backward, while the thereby incorporated volumetric charge qV and the caused strain ε are measured versus time. (C) Operating voltage U needed to achieve a strain amplitude of ε = 0.05% for the sample length of l = 0.626 mm for the pSi-PPy sample in comparison with high-performance piezoelectric lead-free (22) and lead-containing [lead zirconate titanate (PZT)] ceramics (21).

  • Fig. 4 Young’s modulus of the empty and PPy-filled pSi membrane.

    Values are predicted as function of the grayscale threshold value. The black curve corresponds to the empty pSi membrane, and the blue curve is predicted for the PPy-filled pSi membrane. Calibration of the pSi membrane to the measured macroscopic Young’s modulus of E = 10 GPa yields a grayscale threshold of 123.

  • Fig. 5 Micromechanical analysis of electrochemical actuation.

    Results of numerical simulations at maximum swelling strain: (A) von Mises stress distribution in the pSi walls, (B) pressure distribution in the PPy-infiltrated pores, and (C) von Mises stress distribution in the pores—red colored areas exceed the 2-MPa yield stress of PPy.

Supplementary Materials

  • Supplementary Materials

    Giant electrochemical actuation in a nanoporous silicon-polypyrrole hybrid material

    Manuel Brinker, Guido Dittrich, Claudia Richert, Pirmin Lakner, Tobias Krekeler, Thomas F. Keller, Norbert Huber, Patrick Huber

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