Jingjing Duan

Three‐Dimensional N‐Doped Graphene Hydrogel/NiCo Double Hydroxide Electrocatalysts for Highly Efficient Oxygen Evolution

A highly hydrated structure was fabricated for catalyzing the oxygen evolution reaction (OER), which demonstrated significantly enhanced catalytic activity, favorable kinetics, and strong durability. The enhanced performance is correlated with the dual-active-site mechanism, and high hydrophilicity of the electrode can dramatically expedite the process of water oxidation into molecular oxygen.

Nitrogen and oxygen dual-doped carbon hydrogel film as a substrate-free electrode for highly efficient oxygen evolution reaction

A three-dimensional (3D) electrode composed of nitrogen, oxygen dualdoped graphene-carbon nanotube hydrogel film is fabricated, which greatly favors the transport and access of gas and reaction intermediates, and shows a remarkable oxygen-evolution catalytic performance in both alkaline and acidic solutions.

Porous C3N4 Nanolayers@N-Graphene Films as Catalyst Electrodes for Highly Efficient Hydrogen Evolution

Pt-free electrocatalysts for hydrogen evolution reaction (HER) with high activity and low price are desirable for many state-of-the-art renewable energy devices, such as water electrolysis and photoelectrochemical water splitting cells. However, the design and fabrication of such materials remain a significant challenge. This work reports the preparation of a flexible three-dimensional (3D) film by integrating porous C3N4 nanolayers with nitrogen-doped graphene sheets, which can be directly utilized as HER catalyst electrodes without substrates. This nonmetal electrocatalyst has displayed an unbeatable HER performance with a very positive onset-potential close to that of commercial Pt (8 mV vs 0 mV of Pt/C, vs RHE @ 0.5 mA cm(-2)), high exchange current density of 0.43 mA cm(-2), and remarkable durability (seldom activity loss >5000 cycles). The extraordinary HER performance stems from strong synergistic effect originating from (i) highly exposed active sites generated by introduction of in-plane pores into C3N4 and exfoliation of C3N4 into nanosheets, (ii) hierarchical porous structure of the hybrid film, and (iii) 3D conductive graphene network.

3D WS2 Nanolayers@Heteroatom‐Doped Graphene Films as Hydrogen Evolution Catalyst Electrodes

A 3D catalyst electrode is fabricated by layer-by-layer assembly of 2D WS nanolayers and P, N, O-doped graphene sheets into a heterostructured film. The film exhibits remarkable hydrogen evolution performance, benefitting from the utmost exposed active centers on 2D nanolayers, highly expanded surface, and continuous conductive network, as well as strong synergistic effects between the components.

Nanostructured morphology control for efficient supercapacitor electrodes

The fast growing interest in portable electronic devices and electric vehicles has stimulated extensive research in high performance energy storage devices, such as supercapacitors. Nanostructured electrodes can achieve high electrochemical performances in supercapacitors owing to their high surface atom ratio, tuneable texture and unique size-dependent properties that can afford effective electrolyte diffusion and improved charge transportation and storage during charging–discharging. This review reports on the recent progress in designing and fabricating different kinds of nanostructured electrodes, including electrical double layer based electrodes such as porous carbons and graphene, and Faradic reaction based electrodes such as metal oxides/hydroxides and conductive polymers. Furthermore, the review also summarizes the advances of hybrid electrodes, which store charges by both mechanisms, such as porous carbons–metal oxides/hydroxides, porous carbons–conductive polymers, graphene–metal oxides/hydroxides, and graphene–conductive polymers. Finally, we provide some perspectives as to the future directions of this intriguing field.

Mesoporous hybrid material composed of Mn3O4 nanoparticles on nitrogen-doped graphene for highly efficient oxygen reduction reaction

The hybrid material composed of Mn3O4 nanoparticles on nitrogen-doped graphene was prepared via a solvothermal process and investigated for the first time as a catalyst for oxygen reduction reaction (ORR). Its high ORR activity, excellent durability and tolerance to methanol make this hybrid material a promising candidate for highly efficient ORR in fuel cells and metal-air batteries.

Hybrid Hydrogels of Porous Graphene and Nickel Hydroxide as Advanced Supercapacitor Materials

Graphene-based hydrogels can be used as supercapacitor electrodes because of their excellent conductivity, their large surface area and their high compatibility with electrolytes. Nevertheless, the large aspect ratio of graphene sheets limits the kinetics of processes occurring in the electrode of supercapacitors. In this study, we have introduced in-plane and out-of-plane pores into a graphene-nickel hydroxide (Ni(OH)2) hybrid hydrogel, which facilitates charge and ion transport in the electrode. Due to its optimised chemistry and architecture, the hybrid electrode demonstrates excellent electrochemical properties with a combination of high charge storage capacitance, fast rate capability and stable cycling performance. Remarkably, the Ni(OH)2 in the hybrid contributes a capacitance as high as 3138.5 F g(-1), which is comparable to its theoretical capacitance, suggesting that such structure facilitates effectively charge-transfer reactions in electrodes. This work provides a facile pathway for tailoring the porosity of graphene-based materials for improved performances. Moreover, this work has also furthered our understanding in the effect of pore and hydrogel structures on the electrochemical properties of materials.

Anion and Cation Modulation in Metal Compounds for Bifunctional Overall Water Splitting

As substitutes for precious cathodic Pt/C and anodic IrO2 in electrolytic water splitting cells, a bifunctional catalyst electrode (Fe- and O-doped Co2P grown on nickel foam) has been fabricated by manipulating the cations and anions of metal compounds. The modified catalyst electrode exhibits both superior HER and OER performances with high activity, favorable kinetics, and outstanding durability. The overall ability toward water splitting is especially extraordinary, requiring a small overpotential of 333.5 mV to gain a 10 mA cm(-2) current density. A study on the electrocatalytic mechanism reveals that the atomic modulation between cation and anion plays an important role in optimizing the electrocatalytic activity, which greatly expands the active sites in the electrocatalyst. Further, the three-dimensional conductive porous network is highly advantageous for the exposure of active species, the transport of bubble products, and the transfer of electrons and charges, which substantially boosts reaction kinetics and structure stability.

A graphene–MnO2 framework as a new generation of three-dimensional oxygen evolution promoter

A three-dimensional framework promoter of graphene-MnO2 was fabricated to enhance the catalytic properties of NiCo2O4. The as-resultant graphene-MnO2-NiCo2O4 hybrid material features a number of remarkable structural properties such as well-developed pores, 3D conductive networks and strong coupling synergistic effects, rendering it an outstanding catalyst for electrocatalytic oxygen evolution.

Size Fractionation of Two-Dimensional Sub-Nanometer Thin Manganese Dioxide Crystals towards Superior Urea Electrocatalytic Conversion.

A universal technique has been proposed to sort two-dimensional (2D) sub-nanometer thin crystals (manganese dioxide MnO2 and molybdenum disulfide MoS2 ) according to their lateral dimensions. This technique is based on tuning the zeta potential of their aqueous dispersions which induces the selective sedimentation of large-sized 2D crystals and leaves the small-sized counterparts in suspension. The electrocatalytic properties of as-obtained 2D ultrathin crystals are strongly dependent on their lateral size. As a proof-of-concept study, the small-sized MnO2 nanocrystals were tested as the electrocatalysts for the urea-oxidation reaction (UOR), which showed outstanding performance in both half reaction and full electrolytic cell. A mechanism study reveals the enhanced performance is associated with the remarkable structural properties of MnO2 including ultrathin (ca. 0.95 nm), laterally small-sized (50-200 nm), and highly exposed active centers.