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Cobalt sulfides have drawn enormous attention as earth-abundant alternatives to precious-metal electrocatalysts capable of catalyzing oxygen evolution reaction (OER) in alkaline medium. Although significant progresses have been realized in the development of various composite modulation to improve their properties for oxygen evolution, to boost their poor catalytic activity for oxygen evolution reaction is still challenging, which unambiguously limits the wide utilization of cobalt sulfides. Here, we present the facile growth of metal-doping (Fe, Ni) into Co9S8 supported on nickle foam (NF) through a one-step simple hydrothermal process. The effect of (Fe, Ni)-doping on the morphology and the catalytic activity of Co9S8 has been thoroughly investigated. Fe-Co9S8 nano-microspheres supported on NF (Fe-Co9S8 NM/NF) have been obtained with the remarkable electrocatalytic activity, which only requires a lower overpotential of 270 mV to reach a current density of 10 mA cm−2 and exhibits the smaller Tafel slope of 70 mV dec−1 as well as robust stability. The excellent OER performance of Fe-Co9S8 NM/NF could be attributed to the synergistic interaction of Fe dopants with Co9S8 nano-microspheres and faster charge transfer rate derived from NF support. This work provides a new and effective way to design metal-doped Co9S8-based heterostructures supported on conductive support as efficient OER electrocatalysts.

Mixed first-row transition metal-based sulfides with specific nanostructure hold the promising performances for oxygen evolution reaction (OER). Herein, based on the optimum Ni/Fe/Co ratio (8/1/1) in electrolyte for electrodeposition on nickel foam (NiFeCo/NF), ripple-like sNiFeCo/NF has been prepared as efficient electrode for water oxidation through solvothermal sulfurization. The unique ripple-like structures contain many pores and voids with many wrinkles and distortions, which may enlarge the surface area and expose more active sites, improving the contacting of catalyst/electrolyte interfaces and facilitate electron transfer. sNiFeCo/NF shows better OER activity than NiFeCo/NF, requiring overpotential of 180 mV to deliver 100 mA cm −2 and a low Tafel slope of 50.4 mV dec −1 . In order to further overcome the poor stability of sNiFeCo/NF, Fe hydroxide film has been electrodeposited on the surface of sNiFeCo/NF (sNiFeCo-Fe/NF), which leads to enhanced stability at the sacrifice of partial activity loss of sNiFeCo/NF. The electrodeposited Fe is supposed to protect NiFeCo-based sulfides from severe corrosion in alkaline and ensure the OER activity in long-term water oxidation. It implies a balance between activity and durability of NiFeCo sulfides. This work may provide a facile routine to fabricate ternary Ni-Fe-Co sulfides as efficient electrocatalyst for water oxidation.

Adjusting the hydrogen-binding free energy (ΔGH*) of two dimensional (2D) MoS2 by changing the interlayer distance has been an effective strategy to improve the intrinsic activity for hydrogen evolution reaction (HER). Herein, a facile solvothermal access via various ratio of N, N-dimethylformamide (DMF)/H2O has been used to modulate interlayer distance of nanostructured MoS2. With increasing of DMF, the interlayer distance of MoS2 can be expanded to 9.4 A with smaller sizes, which may be derived from intercalation effect of DMF. The certain ratio of DMF/H2O (volume ratio of 19/1, MoS2-D19H1) leads to the largest interlayer distances of 10.0 A and the smallest size of nanospheres with less stacking than counterparts synthesized at other ratios of DMF/H2O. The expanded interlayer distance of MoS2-D19H1 may change electronic structure of active sites for HER, implying the improved ΔGH* and the intrinsic activity of MoS2. The smallest size also suggests the more exposure of active sites for HER. The electrochemical measurements demonstrate that MoS2-D19H1 shows the best electrocatalytic performances than MoS2 samples synthesized at other ratio of DMF/H2O. This work may provide a promising strategy to tune the interlayer distance of 2D-layered transition metal dichalcogenide for efficient HER.

Oxidized carbon fiber (oCF) as support successfully realizes the vertical growth of uniform WS2 nanosheets arrays for efficient hydrogen evolution reaction (HER) via a facile hydrothermal process. Thanks to oxygen functional groups on oCF, vertical WS2 nanosheets structures have grown more easily on oCF, which can provide better dispersion, short charge transfer distance and more exposed active sites for HER in comparison with bulk WS2 and WS2 nanosheets on bare carbon fiber (CF) fabricated at the same condition. The electrochemical measurements confirmed that WS2/oCF possesses better HER activity than bulk WS2 and WS2/CF. Especially, the 10-h stability with unchanged vertical WS2 nanosheets morphology further demonstrate the positive effect of oxygen functional groups on the enhanced vertical structure and close combination between WS2 and oCF. It may offer a facile way to realize more exposed active sites from stable electrocatalyst hybrids of transition metal sulfides by surface oxidization of carbon supports.

Ligand design is an important aspect of the surface engineering on the quantum dots. Organic ligands with three types of widely used function groups (-SH, -NH2, -COOH) are chosen to investigate the bonding behavior and electronic properties modification on ZnS ( 10 1 ¯ 0 ) based on first-principles calculations. The thermodynamic studies of ( 10 1 ¯ 0 ) ligands suggest that -SH and -COOH are prone to undergo a proton dissociation when binding on the surface, while -NH2 remains molecular adsorption on the 2-coordinated Zn atom. The binding strengths of these ligands exhibits the order of -SH > -COOH > -NH2, which is consistent with their ligand exchange ability in experiments. The gap states of ZnS ( 10 1 ¯ 0 ) mainly come from 2-coordinated S/Zn, and the passivation effect of -NH2 ligand is inferior to the other two due to the absence of dissociated H which covers the 2-coordinated S. The change of ligand structures shows that ligand length has slight influence on the binding energies, while branched ligands bind more strongly on the surface than those linear ones with the same number of carbon atoms. As for the surface vacancies that cause severe trap states, the ligands tend to be located at bridge sites between two 2-coordinated Zn rather than filling the vacancies. Our study provides an insight into the bonding behavior and passivation mechanism of typical ligands on II-VI QDs at the atomic level and gives helpful guidance for surface engineering aimed at improving QD performance.

The first-principles calculations are employed to investigate the electrical properties of (0 0 1) epitaxial LaGaO3/SrTiO3 heterostructure. It is found that the interface remains metallic and the atomic displacements occur mostly in the SrTiO3 side after atomic relaxation. The interface crystal field induces the Ti t2g orbitals to split into the nondegenerate dxy and two-fold degenerate dxz/yz orbitals. The partly filled nondegenerate dxy orbitals are the origin of two-dimensional electron gas at the interface of LaGaO3/SrTiO3 (0 0 1).

Aiming to enhance the stability of noble metal nanoparticles that are anchored on the surface of colloidal carbon spheres (CCSs), we designed and prepared a new kind of sandwich-structured ZIF-8@Pd-CCS microsphere. Typically, uniform CCSs were first synthesized by the aromatization and carbonization of glucose under hydrothermal conditions. Subsequently, noble metal nanoparticles, herein Pd nanoparticles, were attached to the surface of CCSs via self-reduction route, followed by in situ assembly of a thin layer of ZIF-8 over the Pd nanoparticles to form the sandwich-type ZIF-8@Pd-CCS microspheres. X-ray diffraction (XRD) patterns and Fourier transform infrared spectroscopy (FTIR) spectra confirmed the presence of crystalline ZIF-8, while TEM analysis revealed that the ZIF-8 shells were closely bound to the Pd-loaded CCSs. The shell thickness could be tuned by varying the ZIF-8 assembly cycles. Further, liquid-phase hydrogenation of 1-hexene as the probe reaction was carried out over the ZIF-8@Pd-CCS microspheres and results showed that the prepared microspheres exhibited excellent agglomeration-resistant and leach-proof properties for the Pd nanoparticles, thus leading to the good reusability of the ZIF-8@Pd-CCS microspheres.

Herein, a reverse microemulsion route was developed to synthesize bismuth oxyiodide (BiOI) nanocrystals and reduced graphene oxide (RGO) nanocomposites as a highly efficient photocatalyst, and both the formation of BiOI and the reduction of RGO were achieved in situ in microemulsions simultaneously at low temperature (60 °C). The uniform nanocrystal size and structure were indicated by XRD, TEM, and the reduction of GO by ascorbic acid was evidenced by FTIR, XPS, and Raman spectra techniques. The enhanced photoactivity of RGO/BiOI nanocomposites under visible light was attributed to improved light absorption and efficient charge separation and transportation.

Reverse microemulsions, consisting of n-hexanol, Triton X-100, Cyclohexane and aqueous salt solutions, were used to synthesize BiOI, TiO2 and BiOI/TiO2 hybrid nanoparticles at room temperature. The particles had been characterized by X-ray powder diffraction, FT-IR spectra, TG-DSC analysis, nitrogen sorption, electron microscopy, and UV–vis diffuse reflectance spectroscopy. The photocatalytic properties of those particles were evaluated by degradation of methyl orange under visible light irradiation. The BiOI/TiO2 composites showed about 5 times higher photocatalytic performances than BiOI when the mole ratio of BiOI to TiO2 was 75%. The remarkable enhancement in the visible light photocatalytic activities of the BiOI/TiO2 heterostructures could be first attributed to the effective electron–hole separations at the interfaces of the two semiconductors, which facilitated the transfer of the photoinduced carriers. Meanwhile, the heterojunction formed between BiOI and TiO2 would further retard the recombination of photoinduced carriers. In addition, high degree of crystallization, bimodal porous structure, relative large specific surface area, and appropriate energy band gap have great contribution to the enhancement of photocatalytic performance.