Conventional solid ion channel systems relying on single one- or two-dimensional confined nanochannels enabled selective and ultrafast convective ion transport. However, due to intrinsic solid channel stacking, these systems often face pore–pore polarization and ion concentration blockage, thereby restricting their efficiency in macroscale ion transport. Here, we constructed a soft heterolayer-gel system that integrated an ion-selective hydrogel layer with a water-barrier organogel layer, achieving ultrahigh cation selectivity and flux and effectively providing high-efficiency gradient energy conversion on a macroscale order of magnitude. Specifically, the hydrogel layer featured an unconfined 3D network, where the fluctuations of highly hydrated polyelectrolyte chains driven by thermal dynamics enhanced cation selectivity and mitigated transfer energy barriers. Such chain fluctuation mechanisms facilitated ion-cluster internal transmission, thereby enhancing ion concentration hopping for more efficient ion-selective transport. Compared to the existing rigid nanochannel-based gradient energy conversion systems, such a heterogel-based power generator exhibited a record power density of 192.90 and 1.07 W/m2 at the square micrometer scale and square centimeter scale, respectively (under a 500-fold artificial solution). We anticipate that such heterolayer gels would be a promising candidate for energy separation and storage applications.
Recently developed asymmetric heterogeneous moisture-driven electricity generators (AHMEGs) are advantageous for harvesting energy from ubiquitous moisture due to their superior output performance and possible flexibility. However, the regeneration of AHMEG has seldom been explored. Here, we report the fabrication of flexible AHMEGs with regeneration ability simply by asymmetrically incorporating carbon nanotubes into a bilayer-structured gel with heterogeneities of both hygroscopicity and charge. The bilayered gel consists of a Na+-containing macroporous aerogel and a highly hygroscopic Cl–-containing hydrogel. After assembly, the resulting flexible AHMEG unit shows excellent output performance, with a stable voltage of 1.03 V, a current density of 23.8 μA cm–2, a power density of up to 9.12 μW cm–2 and a high stability over 7 days, resulting from a synergistic effect between hygroscopicity and charge heterogeneities of the bilayered gel. The regeneration of the AHMEGs has been realized via light irradiation of the aerogel containing carbon nanotubes, and the regeneration can be repeated for at least 30 cycles, significantly expanding the lifecycle of moisture-driven electricity generators. Regeneration imposed by carbon nanotubes, combined with flexibility, simple preparation, and excellent electrical performance, enables the AHMEGs to be excellent moisture-driven electricity generators for advantageous applications.
Polymer network gels usually exhibit spatial heterogeneity of local defects and cross-link density, which can affect their elasticity on the microscopic scale differently. The ability to evaluate the formation and distribution of these heterogeneities is important for guiding the application of gels in biology, medicine, and separation science. Previously, it has been reported that single-particle tracking based microrheology could provide local properties of gel networks with high resolution; however, the particle probes have been limited to spherical micro/nanotracers undergoing translational motions. In this work, we used single gold nanorods (AuNRs) as rotational microrheology probes to study the polyacrylamide gelation process by dual-channel polarization dark-field microscopy. The AuNRs were in Brownian motion during the initial stages of the gelation. As the reaction continues, individual AuNRs are confined locally and almost lost translational motion, but still maintained rotational motion. As the reaction proceeded further, the rotation state of the AuNRs gradually changed from free rotation in 3D to restricted rotation in 2D and eventually stopped completely. The appearance of the intermediate 2D plane indicated the existence of localized anisotropic compression of the gel during the heterogeneous gelation process. Our method can be further applied to investigate the formation of different polymer gels and a wide variety of heterogeneous biophysical and soft material systems.
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