The development of pseudocapacitive materials for energy‐oriented applications has stimulated considerable interest in recent years due to their high energy‐storing capacity with high power outputs. Nevertheless, the utilization of nanosized active materials in batteries leads to fast redox kinetics due to the improved surface area and short diffusion pathways, which shifts their electrochemical signatures from battery‐like to the pseudocapacitive‐like behavior. As a result, it becomes challenging to distinguish “pseudocapacitive” and “battery” materials. Such misconceptions have further impacted on the final device configurations. This Review is an earnest effort to clarify the confusion between the battery and pseudocapacitive materials by providing their true meanings and correct performance metrics. A method to distinguish battery‐type and pseudocapacitive materials using the electrochemical signatures and quantitative kinetics analysis is outlined. Taking solid‐state supercapacitors (SSCs, only polymer gel electrolytes) as an example, the distinction between asymmetric and hybrid supercapacitors is discussed. The state‐of‐the‐art progress in the engineering of active materials is summarized, which will guide for the development of real‐pseudocapacitive energy storage systems.

This study elucidates the role of each class of nanopore by in-depth electrochemical analysis of three types of ZIF-8-derived carbons. Also, engineered co-doping of Fe and N is found essential to selectively form Fe–Nx sites in the carbon matrix.

This study investigated how to control the rate of photoreduction of metastable AuCl2(-) at the solid-solution interface of large ZnO nanoparticles (NPs) (50-100 nm size). Band-gap photoexcitation of electronic charge in ZnO by 370 nm UV light yielded Au NP deposition and the formation of ZnO-Au NP hybrids. Au NP growth was observed to be nonepitaxial, and the patterns of Au photodeposition onto ZnO NPs observed by high-resolution transmission electron microscopy were consistent with reduction of AuCl2(-) at ZnO facet edges and corner sites. Au NP photodeposition was effective in the presence of labile oleylamine ligands attached to the ZnO surface; however, when a strong-binding dodecanethiol ligand coated the surface, photodeposition was quenched. Rates of interfacial electron transfer at the ZnO-solution interface were adjusted by changing the solvent, and these rates were observed to strongly depend on the solvent's permittivity (ε) and viscosity. From measurements of electron transfer from ZnO to the organic dye toluidine blue at the ZnO-solution interface, it was confirmed that low ε solvent mixtures (ε ≈ 9.5) possessed markedly higher rates of photocatalytic interfacial electron transfer (∼3.2 × 10(4) electrons·particle(-1)·s(-1)) compared to solvent mixtures with high ε (ε = 29.9, ∼1.9 × 10(4) electrons·particle(-1)·s(-1)). Dissolved oxygen content in the solvent and the exposure time of ZnO to band-gap, near-UV photoexcitation were also identified as factors that strongly affected Au photodeposition behavior. Production of Au clusters was favored under conditions that caused electron accumulation in the ZnO-Au NP hybrid. Under conditions where electron discharge was rapid (such as in low ε solvents), AuCl2(-) precursor ions photoreduced at ZnO surfaces in less than 5 s, leading to deposition of several small, isolated ∼6 nm Au NP on the ZnO host instead.

Two-dimensional transition metal carbides, that is, MXenes and especially Ti3C2, attract attention due to their excellent combination of properties. Ti3C2 nanosheets could be the material of choice for future flexible electronics, energy storage, and electromechanical nanodevices. There has been limited information available on the mechanical properties of Ti3C2, which is essential for their utilization. We have fabricated Ti3C2 nanosheets and studied their mechanical properties using direct in situ tensile tests inside a transmission electron microscope, quantitative nanomechanical mapping, and theoretical calculations employing machine-learning derived potentials. Young’s modulus in the direction perpendicular to the Ti3C2 basal plane was found to be 80–100 GPa. The tensile strength of Ti3C2 nanosheets reached up to 670 MPa for ∼40 nm thin nanoflakes, while a strong dependence of tensile strength on nanosheet thickness was demonstrated. Theoretical calculations allowed us to study mechanical characteristics of Ti3C2 as a function of nanosheet geometrical parameters and structural defect concentration.

replacing gasoline, diesel, or other types of fuels with electricity, it is expected that our world will become more environmentally friendly by storing energy directly from sustainable sources, such as solar, wind, geothermal, bioenergy, and the ocean. Even Australia, as a country with abundant energy resources, has identified energy as one of the key scientific research priorities. It is clear that the efficiency of energy harvesting and consumption must be improved, emissions must be reduced, and the integration of various energy sources into the electricity grid and chemical storage must be implemented. A desirable outlook is one with a variety of energy sources and mechanisms that significantly reduces carbon emissions and is economical for consumers and society. Recent fast-growing research should boost the development of reliable, highly efficient, low-cost, and sustainable energy materials that are effective for new technologies and that satisfy the growing demand for energy storage and climate change solutions.The progress in energy materials is indeed significant, however, as the expectations of energy materials research are always quite high, it is not sufficient. Particularly, the material performances are always theoretically predicted but are limited by the underlying mechanisms in real applications. As a wellknown example, silicon is expected to deliver a high theoretical capacity of 4200 mAh g −1 in the form of Li 4.4 Si, and is thought to replace the currently commercial graphite with a capacity of 372 mAh g −1 . However, in real applications, it is found that Si exhibits more than 360% of volume expansion during lithiation, which leads to battery anode failure. In the last few years, TEM, especially in situ TEM, has provided exceptional advantages in investigating the lithiation process of silicon anodes: direct imaging, full crystallography information, and real-time recording have all become possible. By directly observing the charge/discharge processes of Si anodes, the dynamics of expansion have been well understood. The research has then been focused on structural designs of composites containing Si to overcome the expansion. The Si composites (for instance, carbon-wrapped Si nanoparticles with different sizes) were directly analyzed by in situ TEM to determine the best structural design. [12] From 2012, in situ TEM became an essential tool to review and evaluate structural designs for high-capacity anodes with significant volume expansions. The same scenarios apply to similar research topics. In situ transmission electron microscopy (TEM) is one of the most powerfulapproaches for revealing physical and chemical process dynamics at atomic resolutions. The most recent developments for in situ TEM techniques are summarized; in particular, how they enable visualization of various events, measure properties, and solve problems in the field of energy by revealing detailed mechanisms at the nanoscale. Related applications include rechargeable batteries such as Li-ion, Na-ion, Li-O 2 , Na-O 2 , Li...