Zhen-Feng Huang

Hollow Cobalt-Based Bimetallic Sulfide Polyhedra for Efficient All-pH-Value Electrochemical and Photocatalytic Hydrogen Evolution

The development of highly active, universal, and stable inexpensive electrocatalysts/cocatalysts for hydrogen evolution reaction (HER) by morphology and structure modulations remains a great challenge. Herein, a simple self-template strategy was developed to synthesize hollow Co-based bimetallic sulfide (MxCo3-xS4, M = Zn, Ni, and Cu) polyhedra with superior HER activity and stability. Homogenous bimetallic metal-organic frameworks are transformed to hollow bimetallic sulfides by solvothermal sulfidation and thermal annealing. Electrochemical measurements and density functional theory computations show that the combination of hollow structure and homoincorporation of a second metal significantly enhances the HER activity of Co3S4. Specifically, the homogeneous doping in Co3S4 lattice optimizes the Gibbs free energy for H* adsorption and improves the electrical conductivity. Impressively, hollow Zn0.30Co2.70S4 exhibits electrocatalytic HER activity better than most of the reported nobel-metal-free electrocatalysts over a wide pH range, with overpotentials of 80, 90, and 85 mV at 10 mA cm(-2) and 129, 144, and 136 mV at 100 mA cm(-2) in 0.5 M H2SO4, 0.1 M phosphate buffer, and 1 M KOH, respectively. It also exhibits photocatalytic HER activity comparable to that of Pt cocatalyst when working with organic photosensitizer (Eosin Y) or semiconductors (TiO2 and C3N4). Furthermore, this catalyst shows excellent stability in the electrochemical and photocatalytic reactions. The strategy developed here, i.e., homogeneous doping and self-templated hollow structure, provides a way to synthesize transition metal sulfides for catalysis and energy conversion.

Tungsten Oxides for Photocatalysis, Electrochemistry, and Phototherapy.

The conversion, storage, and utilization of renewable energy have all become more important than ever before as a response to ever-growing energy and environment concerns. The performance of energy-related technologies strongly relies on the structure and property of the material used. The earth-abundant family of tungsten oxides (WOx ≤3 ) receives considerable attention in photocatalysis, electrochemistry, and phototherapy due to their highly tunable structures and unique physicochemical properties. Great breakthroughs have been made in enhancing the optical absorption, charge separation, redox capability, and electrical conductivity of WOx ≤3 through control of the composition, crystal structure, morphology, and construction of composite structures with other materials, which significantly promotes the efficiency of processes and devices based on this material. Herein, the properties and synthesis of WOx ≤3 family are reviewed, and then their energy-related applications are highlighted, including solar-light-driven water splitting, CO2 reduction, and pollutant removal, electrochromism, supercapacitors, lithium batteries, solar and fuel cells, non-volatile memory devices, gas sensors, and cancer therapy, from the aspect of function-oriented structure design and control.

Efficient water oxidation through strongly coupled graphitic C3N4 coated cobalt hydroxide nanowires

The development of low cost and durable electrocatalysts for the oxygen evolution reaction (OER) for water splitting remains a great challenge. Here, we developed strongly coupled hybrid nanowires (NWs) of anion (Cl− and CO−) doped cobalt hydroxide coated with nanosheets of graphitic carbon nitride (Co(OH)2@g-C3N4) through an in situ hydrothermal method. With 5% g-C3N4 added in the synthesis, we obtained perfectly coated Co(OH)2 by g-C3N4 nanosheets with an overall diameter of ∼110 nm and a coating layer of ∼10 nm. The structural and compositional analyses confirm the strong interaction between g-C3N4 and Co(OH)2 that makes the hybrid highly effective for the OER. As a result Co(OH)2@g-C3N4 NWs exhibit an excellent over-potential of 0.32 V at 10 mA cm−2 as well as extraordinary stability, which are better than those of the state-of-the-art noble metals (IrO2 and RuO2) and most reported Co- and C3N4-based electrocatalysts although both Co(OH)2 and g-C3N4 separately display very fair performance. Furthermore, a combination of Co(OH)2@g-C3N4 and Pt/C delivers a current density of 80 mA cm−2 at 1.9 V for overall water splitting.