Yue Dong

Hydrogen is the energy carrier with the highest energy density and is critical to the development of renewable energy. Efficient hydrogen storage is essential to realize the transition to renewable energy sources. Electrochemical hydrogen storage technology has a promising application due to its mild hydrogen storage conditions. However, research on the most efficient electrochemical hydrogen storage materials that satisfy the goals of the U.S. Department of Energy remain open questions. All of the above require strategies for designing new hydrogen storage materials. This review provides a brief overview of hydrogen preparation, hydrogen storage, and details the development of electrochemical hydrogen storage materials. We summarize the electrochemical hydrogen storage capabilities of alloys and metal compounds, carbonaceous materials, metal oxides, mixed metal oxides, metal–organic frameworks, MXenes, and polymer-based materials. It was observed that mixed metal oxides exhibit superior discharge capacity and cycling stability. The review indicates that it is vital to create novel materials with large surface area, active-conductive profiles, and low cost. We describe the challenges, gaps, and future perspectives of electrochemical hydrogen storage materials, and hope that the review could draw more attention to the development of electrochemical hydrogen storage materials with high hydrogen storage capacity, high safety, high cycle stability, and low cost and promoting their practical applications.

Abstract Improving the capacitance of carbon materials for supercapacitors without sacrificing their rate performance, especially volumetric capacitance at high mass loadings, is a big challenge because of the limited assessable surface area and sluggish electrochemical kinetics of the pseudocapacitive reactions. Here, it is demonstrated that “self‐doping” defects in carbon materials can contribute to additional capacitance with an electrical double‐layer behavior, thus promoting a significant increase in the specific capacitance. As an exemplification, a novel defect‐enriched graphene block with a low specific surface area of 29.7 m 2 g −1 and high packing density of 0.917 g cm −3 performs high gravimetric, volumetric, and areal capacitances of 235 F g −1 , 215 F cm −3 , and 3.95 F cm −2 (mass loading of 22 mg cm −2 ) at 1 A g −1 , respectively, as well as outstanding rate performance. The resulting specific areal capacitance reaches an ultrahigh value of 7.91 F m −2 including a “self‐doping” defect contribution of 4.81 F m −2 , which is dramatically higher than the theoretical capacitance of graphene (0.21 F m −2 ) and most of the reported carbon‐based materials. Therefore, the defect engineering route broadens the avenue to further improve the capacitive performance of carbon materials, especially for compact energy storage under limited surface areas.

Untethered small actuators have various applications in multiple fields. However, existing small-scale actuators are very limited in their intractability with their surroundings, respond to only a single type of stimulus and are unable to achieve programmable structural changes under different stimuli. Here, we present a multiresponsive patternable actuator that can respond to humidity, temperature and light, via programmable structural changes. This capability is uniquely achieved by a fast and facile method that was used to fabricate a smart actuator with precise patterning on a graphene oxide film by hydrogel microstamping. The programmable actuator can mimic the claw of a hawk to grab a block, crawl like an inchworm, and twine around and grab the rachis of a flower based on their geometry. Similar to the large- and small-scale robots that are used to study locomotion mechanics, these small-scale actuators can be employed to study movement and biological and living organisms.

Intelligent magnetic soft robots capable of programmable structural changes and multifunctionality modalities depend on material architectures and methods for controlling magnetization profiles. While some efforts have been made, there are still key challenges in achieving programmable magnetization profile and creating heterogeneous architectures. Here, we directly embed programmed magnetization patterns (magnetization modules) into the adhesive sticker layers to construct soft robots with programmable magnetization profiles and geometries and then integrate spatially distributed functional modules. Functional modules including temperature and ultraviolet light sensing particles, pH sensing sheets, oil sensing foams, positioning electronic component, circuit foils, and therapy patch films are integrated into soft robots. These test beds are used to explore multimodal robot locomotion and various applications related to environmental sensing and detection, circuit repairing, and gastric ulcer coating, respectively. This proposed approach to engineering modular soft material systems has the potential to expand the functionality, versatility, and adaptability of soft robots.