Peihua Yang

Low-Cost High-Performance Solid-State Asymmetric Supercapacitors Based on MnO2 Nanowires and Fe2O3 Nanotubes

A low-cost high-performance solid-state flexible asymmetric supercapacitor (ASC) with α-MnO2 nanowires and amorphous Fe2O3 nanotubes grown on flexible carbon fabric is first designed and fabricated. The assembled novel flexible ASC device with an extended operating voltage window of 1.6 V exhibits excellent performance such as a high energy density of 0.55 mWh/cm(3) and good rate capability. The ASC devices can find numerous applications as effective power sources, such as powering color-switchable sun glasses and smart windows.

Hydrogenated ZnO Core–Shell Nanocables for Flexible Supercapacitors and Self-Powered Systems

Although MnO2 is a promising material for supercapacitors (SCs) due to its excellent electrochemical performance and natural abundance, its wide application is limited by poor electrical conductivity. Inspired by our results that the electrochemical activity and electrical conductivity of ZnO nanowires were greatly improved after hydrogenation, we designed and fabricated hydrogenated single-crystal ZnO@amorphous ZnO-doped MnO2 core-shell nanocables (HZM) on carbon cloth as SC electrodes, showing excellent performance such as areal capacitance of 138.7 mF/cm(2) and specific capacitance of 1260.9 F/g. Highly flexible all-solid-state SCs were subsequently assembled with these novel HZM electrodes using polyvinyl alcohol/LiCl electrolyte. The working devices achieved very high total areal capacitance of 26 mF/cm(2) and retained 87.5% of the original capacitance even after 10 000 charge/discharge cycles. An integrated power pack incorporating series-wound SCs and dye-sensitized solar cells was demonstrated for stand-alone self-powered systems.

Fiber-Based All-Solid-State Flexible Supercapacitors for Self-Powered Systems

All-solid-state flexible supercapacitors based on a carbon/MnO(2) (C/M) core-shell fiber structure were fabricated with high electrochemical performance such as high rate capability with a scan rate up to 20 V s(-1), high volume capacitance of 2.5 F cm(-3), and an energy density of 2.2 × 10(-4) Wh cm(-3). By integrating with a triboelectric generator, supercapacitors could be charged and power commercial electronic devices, such as a liquid crystal display or a light-emitting-diode, demonstrating feasibility as an efficient storage component and self-powered micro/nanosystems.

Array of nanosheets render ultrafast and high-capacity Na-ion storage by tunable pseudocapacitance

Sodium-ion batteries are a potentially low-cost and safe alternative to the prevailing lithium-ion battery technology. However, it is a great challenge to achieve fast charging and high power density for most sodium-ion electrodes because of the sluggish sodiation kinetics. Here we demonstrate a high-capacity and high-rate sodium-ion anode based on ultrathin layered tin(II) sulfide nanostructures, in which a maximized extrinsic pseudocapacitance contribution is identified and verified by kinetics analysis. The graphene foam supported tin(II) sulfide nanoarray anode delivers a high reversible capacity of ∼1,100 mAh g−1 at 30 mA g−1 and ∼420 mAh g−1 at 30 A g−1, which even outperforms its lithium-ion storage performance. The surface-dominated redox reaction rendered by our tailored ultrathin tin(II) sulfide nanostructures may also work in other layered materials for high-performance sodium-ion storage.

All Metal Nitrides Solid‐State Asymmetric Supercapacitors

Two metal nitrides, TiN porous layers and Fe2 N nanoparticles, are grown uniformly with the assistance of atomic layer deposition on vertically aligned graphene nanosheets and used as the cathode and anode for solid-state supercapacitors, respectively. Full cells are constructed and show good flexibility, high-rate capability, and 98% capacitance retention after 20,000 cycles.

Large‐Scale Fabrication of Pseudocapacitive Glass Windows that Combine Electrochromism and Energy Storage

Multifunctional glass windows that combine energy storage and electrochromism have been obtained by facile thermal evaporation and electrodeposition methods. For example, WO3 films that had been deposited on fluorine-doped tin oxide (FTO) glass exhibited a high specific capacitance of 639.8 F g(-1). Their color changed from transparent to deep blue with an abrupt decrease in optical transmittance from 91.3% to 15.1% at a wavelength of 633 nm when a voltage of -0.6 V (vs. Ag/AgCl) was applied, demonstrating its excellent energy-storage and electrochromism properties. As a second example, a polyaniline-based pseudocapacitive glass was also developed, and its color can change from green to blue. A large-scale pseudocapacitive WO3-based glass window (15×15 cm(2)) was fabricated as a prototype. Such smart pseudocapacitive glass windows show great potential in functioning as electrochromic windows and concurrently powering electronic devices, such as mobile phones or laptops.

Worm-like amorphous MnO2 nanowires grown on textiles for high-performance flexible supercapacitors

A novel class of amorphous MnO2 nanowires with a worm-like (WL) nanostructure was prepared by electrodeposition and a possible formation mechanism was proposed. The specific capacitance of WL amorphous MnO2 was 2–3 times larger than that of its crystalline cotton-like MnO2 counterpart. The unique WL amorphous nanostructure is believed to significantly facilitate the electrochemical performance of MnO2. Flexible solid-state symmetric supercapacitors assembled with WL-MnO2 electrodes exhibited a high energy density of 6.3 W h kg−1. These results demonstrate that the amorphous WL nanostructure grown on carbon fabric can serve as a promising electrode material for flexible and portable energy storage devices.

Flexible supercapacitors based on carbon nanotube/MnO2 nanotube hybrid porous films for wearable electronic devices

To meet the requirement of clean and efficient energy storage system for practical applications, supercapacitors (SCs) to be promising candidates for the next-generation energy storage devices have received tremendous attentions. In fact, the SCs can have broader potential if they are designed as flexible power supplies for wearable electronic devices. Herein, we develop the first flexible, low-cost and high-performance hybrid electrode based on MnO2 nanotubes (NTs) and carbon nanotubes (CNTs) by employing a facile vacuum-filtering method. The superior mechanical and electrochemical performance of these flexible electrodes is attributed to: (1) the ultra-long one-dimensional nanotube morphology, (2) the synergistic effects between pseudocapacitive MnO2 NTs and conductive CNTs, (3) hierarchical porous structure of the freestanding film, and (4) high mass loading of MnO2 (4 mg cm−2). Subsequently, the as-synthesized freestanding CNT/MnO2 NT hybrid electrodes are assembled in the form of solid-state SC devices using polyvinyl alcohol (PVA)/LiCl as gel electrolyte. The device exhibits an excellent volumetric capacitance of 5.1 F cm−3 and a high energy density of 0.45 mW h cm−3 for the entire SC volume. Finally, these SCs are integrated in a flexible power band that can drive watches and LEDs. The solid-state SC devices with outstanding flexibility and stability clearly demonstrate their broad applications as flexible, low-cost, high-performance power supplies in wearable electronic devices.

Significantly Enhanced Photocatalytic Activities and Charge Separation Mechanism of Pd-Decorated ZnO–Graphene Oxide Nanocomposites

Electron-hole recombination is one of the major factors limiting the efficiency of ZnO-based photocatalysts. In this work, a 2-fold enhancement strategy was employed to suppress electron-hole recombination and boost photocatalytic efficiency. First, significantly enhanced photocatalytic activity of ZnO by introducing graphene oxide (GO) was systematically investigated. Hybrid photocatalysts with different weight ratios of ZnO to GO (from 0.95:0.05 to 0.70:0.30) were synthesized and characterized. The results indicated that when the proportion ratio of ZnO to GO reached 0.85:0.15, the as-synthesized ZnO-GO nanocomposite exhibited the maximum photocatalytic efficiency on methylene blue with an apparent rate constant κapp almost 10 times faster than that of pure ZnO under UV illumination. GO was suggested to enhance the photocatalytic activity of ZnO because of its great capability in dye adsorption and charge separation. Second, Pd nanoparticles were introduced to decorate ZnO-GO to produce generally better photocatalyst ZnO-GO-Pd nanocomposites. The junction between Pd and ZnO was believed to also effectively separate the photogenerated charges due to the metal-semiconductor diode effect. These two systems of ZnO-GO and ZnO-GO-Pd nanocomposites are expected to have a broad range of applications in environmental conservation.

Robust and Low-Cost Flame-Treated Wood for High-Performance Solar Steam Generation

Solar-enabled steam generation has attracted increasing interest in recent years because of its potential applications in power generation, desalination, and wastewater treatment, among others. Recent studies have reported many strategies for promoting the efficiency of steam generation by employing absorbers based on carbon materials or plasmonic metal nanoparticles with well-defined pores. In this work, we report that natural wood can be utilized as an ideal solar absorber after a simple flame treatment. With ultrahigh solar absorbance (∼99%), low thermal conductivity (0.33 W m-1 K-1), and good hydrophilicity, the flame-treated wood can localize the solar heating at the evaporation surface and enable a solar-thermal efficiency of ∼72% under a solar intensity of 1 kW m-2, and it thus represents a renewable, scalable, low-cost, and robust material for solar steam applications.