Zi-You Yu

Flexible all-solid-state high-power supercapacitor fabricated with nitrogen-doped carbon nanofiber electrode material derived from bacterial cellulose

To meet the pressing demands for portable and flexible equipment in contemporary society, it is strongly required to develop next-generation inexpensive, flexible, lightweight, and sustainable supercapacitor systems with large power densities, long cycle life, and good operational safety. Here, we fabricate a flexible all-solid-state supercapacitor device with nitrogen-doped pyrolyzed bacterial cellulose (p-BC–N) as the electrode material via a low-cost, eco-friendly, low-temperature, and scalable fabrication hydrothermal synthesis. The pliable device can reversibly deliver a maximum power density of 390.53 kW kg−1 and exhibits a good cycling durability with ∼95.9% specific capacitance retained after 5000 cycles. Therefore, this nitrogen-doped carbon nanofiber electrode material holds significant promise as a flexible, efficient electrode material.

Growth of NiFe2O4 nanoparticles on carbon cloth for high performance flexible supercapacitors

In this paper, we report that NiFe2O4 nanoparticles can be directly grown on a flexible carbon cloth substrate by a facile surfactant-assisted hydrothermal method. The produced carbon cloth/NiFe2O4 (CC/NiFe2O4) electrodes with a loading density of 1.55 mg cm−2 exhibited excellent electrochemical performances in both 6 M KOH and 1 M H2SO4 aqueous electrolytes in a two-electrode system. The carbon cloth substrate provided the conductive three-dimensional network, efficient ion diffusion path, and high surface area for NiFe2O4 nanoparticles, resulting in the enhancement in the specific capacitances of CC/NiFe2O4. The specific capacitances of CC/NiFe2O4 (based on the mass of NiFe2O4) were as high as 1135.5 F g−1 (in H2SO4) and 922.6 F g−1 (in KOH) at a current density of 2 mA cm−2. After the current density was increased to 100 mA cm−2, the rate retentions in both electrolytes were greater than 80%, which exceeded most of the reported electrode materials. The assembled all-solid-state symmetric supercapacitor cell showed a voltage window of 2 V using poly(vinyl alcohol) (PVA)–H2SO4 as the gel electrolyte, offering a high energy density of 2.07 mW h cm−3 at a current density of 2 mA cm−2. These remarkable results have demonstrated that the CC/NiFe2O4 electrodes may provide us a new opportunity for designing high performance flexible supercapacitors.

Sustainable Hydrothermal Carbonization Synthesis of Iron/Nitrogen-Doped Carbon Nanofiber Aerogels as Electrocatalysts for Oxygen Reduction.

It is urgent to develop new kinds of low-cost and high-performance nonprecious metal (NPM) catalysts as alternatives to Pt-based catalysts for oxygen reduction reaction (ORR) in fuel cells and metal-air batteries, which have been proved to be efficient to meet the challenge of increase of global energy demand and CO2 emissions. Here, an economical and sustainable method is developed for the synthesis of Fe, N codoped carbon nanofibers (Fe-N/CNFs) aerogels as efficient NPM catalysts for ORR via a mild template-directed hydrothermal carbonization (HTC) process, where cost-effective biomass-derived d(+)-glucosamine hydrochloride and ferrous gluconate are used as precursors and recyclable ultrathin tellurium nanowires are used as templates. The prepared Fe/N-CNFs catalysts display outstanding ORR activity, i.e., onset potential of 0.88 V and half-wave potential of 0.78 V versus reversible hydrogen electrode in an alkaline medium, which is highly comparable to that of commercial Pt/C (20 wt% Pt) catalyst. Furthermore, the Fe/N-CNFs catalysts exhibit superior long-term stability and better tolerance to the methanol crossover effect than the Pt/C catalyst in both alkaline and acidic electrolytes. This work suggests the great promise of developing new families of NPM ORR catalysts by the economical and sustainable HTC process.

Ni-Mo-O nanorod-derived composite catalysts for efficient alkaline water-to-hydrogen conversion via urea electrolysis

Photo/electrochemical splitting of water to hydrogen (H2) fuel is a sustainable way of meeting our energy demands at no environmental cost, but significant challenges remain: for example, the sluggish anodic reaction imposes a considerable overpotential requirement. By contrast, urea electrolysis offers the prospect of energy-saving H2 production together with urea-rich wastewater purification, whereas the lack of inexpensive and efficient urea oxidation reaction (UOR) catalysts places constraints on the development of this technique. Here we report a porous rod-like NiMoO4 with high oxidation states of the metal elements enabling highly efficient UOR electrocatalysis, which can be readily produced through annealing solid NiMoO4·xH2O as a starting precursor in Ar. This precursor gives the derived Ni/NiO/MoOx nanocomposite when switching the shielding gas from Ar to H2/Ar, exhibiting platinum-like activity for the hydrogen evolution reaction (HER) in alkaline electrolytes. Assembling an electrolytic cell using our developed UOR and HER catalysts as the anode and cathode can provide a current density of 10 milliamperes per square centimeter at a cell voltage of mere 1.38 volts, as well as remarkable operational stability, representing the best yet reported noble-metal-free urea electrolyser. Our results demonstrate the potential of nickel–molybdenum-based materials as efficient electrode catalysts for urea electrolysers that promises cost-effective and energy-saving H2 production.

Wood-Derived Ultrathin Carbon Nanofiber Aerogels

Carbon aerogels with 3D networks of interconnected nanometer-sized particles exhibit fascinating physical properties and show great application potential. Efficient and sustainable methods are required to produce high-performance carbon aerogels on a large scale to boost their practical applications. An economical and sustainable method is now developed for the synthesis of ultrathin carbon nanofiber (CNF) aerogels from the wood-based nanofibrillated cellulose (NFC) aerogels via a catalytic pyrolysis process, which guarantees high carbon residual and well maintenance of the nanofibrous morphology during thermal decomposition of the NFC aerogels. The wood-derived CNF aerogels exhibit excellent electrical conductivity, a large surface area, and potential as a binder-free electrode material for supercapacitors. The results suggest great promise in developing new families of carbon aerogels based on the controlled pyrolysis of economical and sustainable nanostructured precursors.