Transition-metal oxides as faradaic charge-storage intermediates sandwiched between conductor and electrolyte are key components to store/deliver high-density energy in microsupercapacitors for many applications in miniaturized portable electronics and microelectromechanical systems. While the conductor facilitating their electron transports, they generally suffer from a switch of rate-determining step to their sluggish redox reactions in pseudocapacitive energy storage, during which poor cation accessibility and diffusion leads to high internal resistances and lowers volumetric capacitance and rate performance. Here it is shown that the faradaic processes in a model system of MnO₂ can be radically boosted by tuning crystallographic structures from cryptomelane (α-MnO₂) to birnessite (δ-MnO₂). As a result of greatly enhanced Na⁺ accessibility and diffusion, 3D layered crystalline δ-MnO₂ microelectrodes exhibit volumetric capacitance as high as ≈922 F cm⁻³ (≈1.5-fold higher than α-MnO₂, ≈617 F cm⁻³) and excellent rate performance. This enlists δ-MnO₂ microsupercapacitor to deliver ultrahigh stack electrical powers (up to ≈295 W cm⁻³) while maintaining volumetric energy density much higher than that of thin-film lithium battery.

Nanostructured transition-metal oxides can store high-density energy in fast surface redox reactions, but their poor conductivity causes remarkable reductions in the energy storage of most pseudocapacitors at high power delivery (fast charge/discharge rates). Here it is shown that electron-correlated oxide hybrid electrodes made of nanocrystalline vanadium sesquioxide and manganese dioxide with 3D and bicontinuous nanoporous architecture (NP V₂O₃/MnO₂) have enhanced conductivity because of metallization of electron-correlated V₂O₃ skeleton via insulator-to-metal transition. The conductive V₂O₃ skeleton at ambient temperature enables fast electron and ion transports in the entire electrode and facilitates charge transfer at abundant V₂O₃/MnO₂ interface. These merits significantly improve the pseudocapacitive behavior and rate capability of the constituent MnO₂. Symmetric pseudocapacitors assembled with binder-free NP V₂O₃/MnO₂ electrodes deliver ultrahigh electrical powers (up to ≈422 W cm²³) while maintaining the high volumetric energy of thin-film lithium battery with excellent stability.

The safe and efficient storage and release of hydrogen are widely recognized as the main challenges for the establishment of a fuel-cell-based hydrogen economy. Formic acid (FA) has great potential as a safe and convenient source of hydrogen for fuel cells. Despite tremendous efforts, the development of heterogeneous catalysts with high activity and relatively low cost remains a major challenge. The synthesis of AuPd–MnO_x nanocomposite immobilized on ZIF-8–reduced-graphene-oxide (ZIF-8–rGO) bi-support by a wet-chemical method is reported here. Interestingly, the resultant AuPd–MnO_x/ZIF-8–rGO shows excellent catalytic activity for the generation of hydrogen from FA, and the initial turnover frequency (TOF) reaches a highest value of 382.1 mol H₂ mol catalyst⁻¹ h⁻¹ without any additive at 298 K. This good performance of AuPd–MnO_x/ZIF-8–rGO results from the modified electronic structure of Pd in the AuPd–MnO_x/ZIF-8–rGO composite, the small size and high dispersion of the AuPd–MnO_x nanocomposite, and also the strong metal-support interaction between the AuPd–MnO_x and ZIF-8–rGO bi-support.

Alloying techniques show genuine potential to develop more effective catalysts than Pt for oxygen reduction reaction (ORR), which is the key challenge in many important electrochemical energy conversion and storage devices, such as fuel cells and metal-air batteries. Tremendous efforts have been made to improve ORR activity by designing bimetallic nanocatalysts, which have been limited to only alloys of platinum and transition metals (TMs). The Pt-TM alloys suffer from critical durability in acid-media fuel cells. Here a new class of mesostructured Pt–Al catalysts is reported, consisting of atomic-layer-thick Pt skin and Pt₃Al or Pt₅Al intermetallic compound skeletons for the enhanced ORR performance. As a result of strong Pt–Al bonds that inhibit the evolution of Pt skin and produce ligand and compressive strain effects, the Pt₃Al and Pt₅Al mesoporous catalysts are exceptionally durable and ≈6.3- and ≈5.0-fold more active than the state-of-the-art Pt/C catalyst at 0.90 V, respectively. The high performance makes them promising candidates as cathode nanocatalysts in next-generation fuel cells.

Potassium-modified graphitic carbon nitride (K-g-C₃N₄) nanosheets are synthesized by a facile KCl-template method that holds the advantage of easy removal of residual template. A combination of XRD, X-ray photoelectron spectroscopy, and inductively coupled plasma analyses are utilized to characterize the obtained resultant K-g-C₃N₄ architectures, which are composed of nanosheets of variable thickness (<10 nm). Photocatalytic hydrogen evolution experiments under visible light irradiation showed that K-g-C₃N₄ nanosheets have high photocatalytic activities (up to about thirteen times higher than that of pure g-C₃N₄) as well as good stability (no reduction in activity within 16 h); both features emanate from their unique structural characteristics. These results illustrate the viability of this methodology for the facile synthesis of efficient heterogeneous photocatalysts for potential commercial applications.

By using a size-dependent cohesive energy formula for two-dimensional coordination materials, the bandgap openings of ideal graphene quantum dots (GQDs) and nanoribbons (GNRs) have been investigated systematically regarding dimension, edge geometry, and magnetic interaction. Results demonstrate that the bandgap openings in GQDs can be dominated by the change of atomic cohesive energy. Relative to zigzag GQDs, the openings in the armchair ones are more substantial, attributed to its edge instability. The change of cohesive energy can also lead to bandgap openings in zigzag and armchair GNRs. The contribution from the interedge magnetic interaction in zigzag GNRs is negligible, while the cohesive-energy induced openings in armchair GNRs can oscillate according to the so-called full-wavelength effect, depending on the width. The model prediction provides physicochemical insight into the bandgap openings in graphene.

An Ag₂O–ZnO nanohybrid is synthesized for the first time through a facile, basic coprecipitation-assisted hydrothermal strategy. This novel method endows the Ag₂O–ZnO nanohybrid (Ag₂O/ZnO=0.3:0.7) with small particle size and strong electronic synergistic effects owing to the uniform distribution of the constituents. The as-synthesized nanohybrid shows excellent photocatalytic properties for degradation of rhodamine B, even under visible light irradiation. This effect is much better than pure or physical mixtures of Ag₂O and ZnO, as well as the traditional homogenous Fenton catalyst (Fe³⁺/H₂O₂).

The quantum confinement and electronic properties of silicon nanowires (SiNWs) under an external strain field ε and an electric field E—as well as both (ε plus E)—are systematically investigated using density functional theory. These two fields exist in working environments of integrated circuits. It is found that both ε and E lead to a drop of the band gap E_g(ε,E) of the SiNWs. If both fields coexist, the interaction between ε and E causes that E_g(ε,E) becomes orientation-dependent, which results from variations of both the conduction-band minimum and the valence-band maximum. The interaction is further illustrated by the density of states near the Fermi level and the eigenvalue of the highest occupied molecular orbital.

Adsorption ability and reaction rate are two essential parameters that define the efficiency of a catalyst. Herein, we implement density functional theory (DFT) and report that CO can be oxidized by a pyramidal Cu cluster with an associated reaction barrier E_b=1.317 eV. In this case, our transition state calculations reveal that the barrier can be significantly lowered after superimposing a negative electric field. Moreover, when the field intensity corresponds to F=−0.010 au, the magnitude of E_b=0.698 eV is equivalent to—or lower than—those of typical catalysts such as Pt, Rh, and Pd. The superimposition of a positive field is found to enhance the release of the nascent CO₂ molecule. Our study demonstrates that small Cu clusters have better adsorption ability than the corresponding flat surface while the field can be used to enhance the purification of the exhaust gas.

Based on a model for the size-dependent bandgap energy of low-dimensional semiconductor compounds, the alloying effect on the bandgap of nanoscale semiconductors is modeled without any adjustable parameter. The model predicts not only a trend of increasing bandgap with decreasing nanocrystal size but also Végard¢s relationship between the bandgap and the alloy composition when the size drops close to twice that of the critical size for the nanocrystals. The model predictions agree with available experimental results for bandgap changes of pseudo-binary IIB–VIB chalcogenide semiconductor nanocrystals.

The non-CO-involved oxidation of methanol (NCOIOM) on a Pt(111) surface is investigated by using density functional theory. Relative energy diagrams for the NCOIOM are established in which the reaction mechanisms for a catalytic cycle—including the associated barriers, the reactive energies, the intermediates, and the transient states—are shown. The results indicate that the reaction proceeds via the kinetically favored pathways: A) HCOHHC(OH)₂HCOOHHCOO- [-COOH]CO₂ and B) CHOHCOOHHCOO- [-COOH]CO₂, with OH playing a key role in the entire process. The vibrational frequencies of the intermediate states derived from the calculations are in agreement with the experimental measurements.