Panpan Zhang

Stimulus-Responsive Micro-Supercapacitors with Ultrahigh Energy Density and Reversible Electrochromic Window

Stimulus-responsive micro-supercapacitors (SR-MSCs) with ultrahigh volumetric energy density and reversible electrochromic effect are successfully fabricated by employing a vanadium pentoxide and electrochemical exfoliated graphene-based hybrid nanopaper and viologen as electrode and stimulus-responsive material, respectively. The fabricated high-performance SR-MSCs offer new opportunities for intuitively observing the working state of energy devices without the aid of extra equipment and techniques.

Scalable Fabrication and Integration of Graphene Microsupercapacitors through Full Inkjet Printing

A simple full-inkjet-printing technique is developed for the scalable fabrication of graphene-based microsupercapacitors (MSCs) on various substrates. High-performance graphene inks are formulated by integrating the electrochemically exfoliated graphene with a solvent exchange technique to reliably print graphene interdigitated electrodes with tunable geometry and thickness. Along with the printed polyelectrolyte, poly(4-styrenesulfonic acid), the fully printed graphene-based MSCs attain the highest areal capacitance of ∼0.7 mF/cm2, substantially advancing the state-of-art of all-solid-state MSCs with printed graphene electrodes. The full printing solution enables scalable fabrication of MSCs and effective connection of them in parallel and/or in series at various scales. Remarkably, more than 100 devices have been connected to form large-scale MSC arrays as power banks on both silicon wafers and Kapton. Without any extra protection or encapsulation, the MSC arrays can be reliably charged up to 12 V and retain the performance even 8 months after fabrication.

Dual‐Graphene Rechargeable Sodium Battery

Sodium (Na) ion batteries are attracting increasing attention for use in various electrical applications. However, the electrochemical behaviors, particularly the working voltages, of Na ion batteries are substantially lower than those of lithium (Li) ion batteries. Worse, the state-of-the-art Na ion battery cannot meet the demand of miniaturized in modern electronics. Here, we demonstrate that electrochemically exfoliated graphene (EG) nanosheets can reversibly store (PF6- ) anions, yielding high charging and discharging voltages of 4.7 and 4.3 V vs. Na+ /Na, respectively. The dual-graphene rechargeable Na battery fabricated using EG as both the positive and negative electrodes provided the highest operating voltage among all Na ion full cells reported to date, together with a maximum energy density of 250 Wh kg-1 . Notably, the dual-graphene rechargeable Na microbattery exhibited an areal capacity of 35 μAh cm-2 with stable cycling behavior. This study offers an efficient option for the development of novel rechargeable microbatteries with ultra-high operating voltage and high energy density.

Ruthenium/nitrogen-doped carbon as an electrocatalyst for efficient hydrogen evolution in alkaline solution

For all electrocatalysts (even Pt), the kinetics of the hydrogen evolution reaction (HER) in alkaline environments are more sluggish by a factor of two to three compared to those in acidic solutions. Here, we demonstrated the preparation of a novel ruthenium/nitrogen-doped carbon (Ru/NC) electrocatalyst supported by graphite foam, in which abundant, singly dispersed Ru atoms were chelated to a nitrogen-doped carbon matrix. In a 1 M KOH aqueous solution, the resultant Ru/NC electrocatalyst exhibited excellent electrocatalytic HER activity with an extremely low overpotential of only 21 mV at 10 mA cm−2 and an excellent mass current density as high as 8 A mgRu−1 at 100 mV, which is superior to the values for reported electrocatalysts (overpotentials of >50 mV at 10 mA cm−2), even Pt catalysts (overpotential of ∼36 mV at 10 mA cm−2). Importantly, the inherent turnover frequency (TOF) value (per Ru atom) of the Ru/NC electrocatalyst reaches 4.55 s−1, which is 3.2 times higher than that of the Pt catalyst (1.41 s−1). Electrochemical analyses and structural characterization revealed that atomically dispersed Ru is responsible for the outstanding HER activity of the Ru/NC electrocatalyst because of a substantially accelerated Volmer step. The outstanding HER performance gives the Ru/NC electrocatalyst promising potential for practical hydrogen production applications.

A Dual‐Stimuli‐Responsive Sodium‐Bromine Battery with Ultrahigh Energy Density

Stimuli-responsive energy storage devices have emerged for the fast-growing popularity of intelligent electronics. However, all previously reported stimuli-responsive energy storage devices have rather low energy densities (<250 Wh kg-1 ) and single stimuli-response, which seriously limit their application scopes in intelligent electronics. Herein, a dual-stimuli-responsive sodium-bromine (Na//Br2 ) battery featuring ultrahigh energy density, electrochromic effect, and fast thermal response is demonstrated. Remarkably, the fabricated Na//Br2 battery exhibits a large operating voltage of 3.3 V and an energy density up to 760 Wh kg-1 , which outperforms those for the state-of-the-art stimuli-responsive electrochemical energy storage devices. This work offers a promising approach for designing multi-stimuli-responsive and high-energy rechargeable batteries without sacrificing the electrochemical performance.

Thermoswitchable on-chip microsupercapacitors: one potential self-protection solution for electronic devices

Efficient thermal protection is of great significance for electronic devices. Herein, we demonstrate a novel thermoswitchable microsupercapacitor (TS-MSC) with the self-protection function utilizing the thermodynamic behavior of a smart electrolyte, a lithium salt–dissolved polymer sol, poly(N-isopropylacrylamide)-g-methylcellulose. Benefiting from the reversibility of ionic conductivity, the TS-MSC exhibited a broad temperature window (30–80 °C) and totally switch-off behavior at 80 °C, as well as excellent cycling stability upon heating/cooling cycles. In addition, the thermal protection of on-chip integrated MSCs in series or parallel was achieved by controlling a single TS-MSC connected with a computer CPU under different working conditions. Therefore, TS-MSCs are promising components in the thermal protection of practical on-chip electronic devices.

A Delamination Strategy for Thinly Layered Defect‐Free High‐Mobility Black Phosphorus Flakes

Extraordinary electronic and photonic features render black phosphorus (BP) an important material for the development of novel electronics and optoelectronics. Despite recent progress in the preparation of thinly layered BP flakes, scalable synthesis of large-size, pristine BP flakes remains a major challenge. An electrochemical delamination strategy is demonstrated that involves intercalation of diverse cations in non-aqueous electrolytes, thereby peeling off bulk BP crystals into defect-free flakes comprising only a few layers. The interplay between tetra-n-butylammonium cations and bisulfate anions promotes a high exfoliation yield up to 78 % and large BP flakes up to 20.6 μm. Bottom-gate and bottom-contact field-effect transistors, comprising single BP flakes only a few layers thick, exhibit a high hole mobility of 252±18 cm2  V-1  s-1 and a remarkable on/off ratio of (1.2±0.15)×105 at 143 K under vacuum. This efficient and scalable delamination method holds great promise for development of BP-based composites and optoelectronic devices.

Fluoride-Free Synthesis of Two-Dimensional Titanium Carbide (MXene) Using A Binary Aqueous System

Two-dimensional (2D) titanium carbide (Ti3 C2 ) is emerging as an important member of the MXene family. However, fluoride-based synthetic procedures remain an impediment to the practical applications of this promising class of materials. Here we demonstrate an efficient fluoride-free etching method based on the anodic corrosion of titanium aluminium carbide (Ti3 AlC2 ) in a binary aqueous electrolyte. The dissolution of aluminium followed by in situ intercalation of ammonium hydroxide results in the extraction of carbide flakes (Ti3 C2 Tx , T=O, OH) with sizes up to 18.6 μm and high yield (over 90 %) of mono- and bilayers. All-solid-state supercapacitor based on exfoliated sheets exhibits high areal and volumetric capacitances of 220 mF cm-2 and 439 F cm-3 , respectively, at a scan rate of 10 mV s-1 , superior to those of LiF/HCl-etched MXenes. Our strategy paves a safe way to the scalable synthesis and application of MXene materials.

Polarity‐Switchable Symmetric Graphite Batteries with High Energy and High Power Densities

Multifunctional batteries with enhanced safety performance have received considerable attention for their applications at extreme conditions. However, few batteries can endure a mix-up of battery polarity during charging, a common wrong operation of rechargeable batteries. Herein, a polarity-switchable battery based on the switchable intercalation feature of graphite is demonstrated. The unique redox-amphoteric intercalation behavior of graphite allows a reversible switching of graphite between anode and cathode, thus enabling polarity-switchable symmetric graphite batteries. The large potential gap between anion and cation intercalation delivers a high midpoint device voltage (≈average voltage) of ≈4.5 V. Further, both the graphite anode and cathode are kinetically activated during the polarity switching. Consequently, polarity-switchable symmetric graphite batteries exhibit a remarkable cycling stability (96% capacity retention after 500 cycles), a high power density of 8.66 kW kg-1 , and a high energy density of 227 Wh kg-1 (calculated based on the total weight of active materials in both anode and cathode), which are superior to other symmetric batteries and recently reported dual-graphite or dual-carbon batteries. This work will inspire the development of new multifunctional energy-storage devices based on novel materials and electrolyte systems.