Yibing Li

Fabrication of Nanoporous Nickel–Iron Hydroxylphosphate Composite as Bifunctional and Reversible Catalyst for Highly Efficient Intermittent Water Splitting

Global-scale application of water-splitting technology for hydrogen fuel production and storage of intermittent renewable energy sources has called for the development of oxygen- and hydrogen-evolution catalysts that are inexpensive, efficient, robust, and can withstand frequent power interruptions and shutdowns. Here, we report the controlled electrodeposition of porous nickel-iron hydroxylphosphate (NiFe-OH-PO4) nanobelts onto the surface of macroporous nickel foams (NF) as a bifunctional electrocatalyst for efficient whole-cell water electrolysis. The NiFe-OH-PO4/NF electrode shows both high water oxidation and water reduction catalytic activity in alkaline solutions and is able to deliver current densities of 20 and 800 mA cm-2 at overpotentials of merely 249 and 326 mV for oxygen-evolution reaction, current densities of 20 and 300 mA cm-2 at overpotentials of only 135 and 208 mV for hydrogen-evolution reaction. Further, in a two-electrode water electrolytic cell, the bifunctional NiFe-OH-PO4/NF electrodes can obtain the current densities of 20 and 100 mA cm-2 at an overall cell potential of only 1.68 and 1.91 V, respectively. Remarkably, the NiFe-OH-PO4/NF catalyst also represents prolonged stability under both continuous and intermittent electrolysis and can be used for oxygen evolution and hydrogen evolution reversibly without degradation.

Microwave-Assisted Synthesis of Nitrogen-Doped Multi-Layer Graphene Quantum Dots with Oxygen-Rich Functional Groups

Strong green-luminescent nitrogen-doped multi-layer graphene quantum dots (N-GQDs) have been prepared via a microwave-assisted hydrothermal method using glucose and urea as the starting materials. The fabricated N-GQDs show a highly crystalline structure and consist of ~3–10 graphene layers with an N/C atomic ratio 5.7 %. The wavelength-dependent luminescence emission behaviour is observed with a photoluminescence quantum yield of 5.2 %. The combination of the unique optical properties introduced by nitrogen doping with the high solubility in aqueous medium offered by the surface oxygen-rich functional groups in N-GQDs provides additional advantages for their potential applications in biolabelling and bioimaging.

NiFeCr Hydroxide Holey Nanosheet as Advanced Electrocatalyst for Water Oxidation

By introducing chromium into a nickel-iron layered double hydroxide (LDH), a nickel iron chromium hydroxide nanomesh catalyst has been achieved on nickel foam substrate via electrodeposition followed by partial etching of chromium. The electrodeposited chromium acts as a sacrificial template to introduce holes in the LDH to increase the electrochemically active surface area, and the remaining chromium synergistically modulates the electronic structure of the composite. The obtained electrode shows extraordinary performance for oxygen evolution reaction and excellent electrochemical stability. The onset potential of the as-prepared electrode in 1 M KOH is only 1.43 V vs RHE, and the overpotential to achieve a high current density of 100 mA·cm-2 is only 255 mV, outperforming benchmark nonprecious NiFe hydroxide composite electrode in alkaline media.

Three-Dimensional Branched and Faceted Gold-Ruthenium Nanoparticles: Using Nanostructure to Improve Stability in Oxygen Evolution Electrocatalysis

Achieving stability with highly active Ru nanoparticles for electrocatalysis is a major challenge for the oxygen evolution reaction. As improved stability of Ru catalysts has been shown for bulk surfaces with low-index facets, there is an opportunity to incorporate these stable facets into Ru nanoparticles. Now, a new solution synthesis is presented in which hexagonal close-packed structured Ru is grown on Au to form nanoparticles with 3D branches. Exposing low-index facets on these 3D branches creates stable reaction kinetics to achieve high activity and the highest stability observed for Ru nanoparticle oxygen evolution reaction catalysts. These design principles provide a synthetic strategy to achieve stable and active electrocatalysts.

Low-Temperature Synthesis of Cuboid Silver Tetrathiotungstate (Ag2WS4) as Electrocatalyst for Hydrogen Evolution Reaction

Ternary bimetallic sulfide silver tetrathiotungstate (Ag2WS4) was prepared by a simple low-temperature precipitation method. The structure of Ag2WS4 was determined using the data from powder X-ray diffraction, which is in space group I4̅2 m (I-phase) with a tetragonal unit cell of a = b = 5.950 71 Å and c = 9.562 65 Å, containing layers of edge-sharing AgS4 and WS4 tetrahedra. The Ag2WS4 was also used as an electrocatalyst for the hydrogen evolution reaction (HER) in acid electrolyte. The results demonstrated that, attributed to its unique composition, large electrochemical active surface area, and high electric conductivity, the Ag2WS4 exhibited superior electrocatalytic activity for HER, in comparison with the ternary counterparts of WS2 and Ag2S with a low onset potential and small Tafel slope. The Ag2WS4 also presented superior stability and maintained the electrocatalytic activity of HER for at least 24 h in 0.5 M H2SO4.