An electrochemical actuator based on reversible changes in volume of poly(acrylic acid) gel induced by quinone redox

An actuator consisting of poly(acrylic acid) gel in contact with p-hydroquinone (QH2)/p-benzoquinone (BQ), which was immobilized on a Au-coated conductive film electrode, was developed. The driving force of the actuator was changes in volume of the gel induced by pH change resulting from redox reaction of quinone. The pH decreased upon oxidation of QH2, which gives rise to collapse of the gel, whereas it increased upon reduction of Q, which results in expansion. The actuator stretched upon oxidation of QH2 at +1.0 V vs. Ag/AgCl in a 10 mM quinone solution containing 1 × 10−4 M NaClO4. It bent at open circuit likely due to diffusion of protons to a bulk solution caused by concentration gradient, but the bending rate increased upon reduction of Q at −0.3 V which consumes protons. The actuator showed repeated stretching/bending at least 9 cycles with increasing its working distance upon successive potential switch between +1.0 and −0.3 V. Energy conversion efficiency was evaluated to be 10−3%.