Gel-like three-dimensional (3D) reduced graphene oxide (rGO) structure can be achieved upon connecting rGO sheets with divalent ions (Ca 2+ , Ni 2+ , or Co 2+ ) and water molecules via hydrothermal treatment. In this architecture, the rGO sheets, water molecules, and divalent ions play the role of skeleton, filler, and linker, respectively. The rGO sheets in the gel-like 3D rGO structure mainly exist as single or double layers by the isolation of the interlamellar water molecules. Since a large amount of water (∼99 wt %) facilitates the introduction of polyvinyl alcohol as a strengthening agent, hereby dried 3D rGO structure with micropores could be obtained after freeze drying.

Success in making artificial muscles that are faster and more powerful and that provide larger strokes would expand their applications. Electrochemical carbon nanotube yarn muscles are of special interest because of their relatively high energy conversion efficiencies. However, they are bipolar, meaning that they do not monotonically expand or contract over the available potential range. This limits muscle stroke and work capacity. Here, we describe unipolar stroke carbon nanotube yarn muscles in which muscle stroke changes between extreme potentials are additive and muscle stroke substantially increases with increasing potential scan rate. The normal decrease in stroke with increasing scan rate is overwhelmed by a notable increase in effective ion size. Enhanced muscle strokes, contractile work-per-cycle, contractile power densities, and energy conversion efficiencies are obtained for unipolar muscles.

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