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Developing effective and robust electrocatalysts that are applicable for different pH conditions is promising for variable industrial hydrogen evolution reaction (HER), whereas it remains challenging for designing proper materials and protocols. Herein, we have developed a two-step electrodeposition-hydrothermal strategy to construct heterostructured binary Ni-W sulfides nanosheets based on carbon fiber (NiWS/CF). The electrodeposited nickel oxides film on CF in the first step is sulfurized and concurrently incorporated with tungsten disulfide in the following hydrothermal process. Benefiting from synergistic advantages of bimetallic sulfides as well as interwoven nanosheets for efficient mass/charge transport, the NiWS/CF electrode shows excellent HER performances over a broad pH range from acidic (pH = 0), neutral (pH = 7) to alkaline (pH = 14) media. The NiWS/CF electrode also presents stability in long-term electrolysis in wide PH range for at least 12 h, and its interlaced nanosheets structure are well maintained. Our work may provide general and promising strategies to obtain inexpensive and efficient electrocatalysts for pH-universal hydrogen production. [ABSTRACT FROM AUTHOR]

Designing mixed transition metal oxides with advantageous nanostructure is efficient access to highly-efficient electrocatalysts for hydrogen evolution reaction (HER) in water electrolysis due to more exposed active sites and synergistic effects in mixed metals. A hierarchically three-level nanostructure combining two types of mixed transition metal oxides on nickel foam (Ni 3 (VO 4 ) 2 @NiCo 2 O 4 /NF) has been synthesized through a two-step hydrothermal process. The hierarchically three level nanostructure comprises porous nickel foam as robust and conductive substrate in the bottom, vertical and uniform NiCo 2 O 4 nanowires arrays in the intermediate, and top-coated Ni 3 (VO 4 ) 2 nanoparticles in 10 nm. The triple hierarchical nanostructure of Ni 3 (VO 4 ) 2 @NiCo 2 O 4 /NF is favorable for enlarging surface areas, exposing more active sites, promoting mass and charge transfer and accelerating HER process. Ni 3 (VO 4 ) 2 @NiCo 2 O 4 /NF electrode can afford a current density of 10 mA cm −2 at a moderate overpotential of 113 mV with robust stability for at least 12 h. It may provide a new strategy to design triple hierarchical nanostructures based on earth-abundant transition metals to achieve large-scale production of hydrogen through water electrolysis in alkaline. [ABSTRACT FROM AUTHOR]

Highly efficient and metal-free electrocatalysts hold promising in industrial water electrolysis with low cost, environmental friendliness and structural stability in wide pH electrolyte. Herein, N and O dual-doped carbon fiber (CF-O-N) has been hydrothermally synthesized as a three-dimensional (3D) electrocatalyst for oxygen evolution reaction (OER). The co-doping of N and O atoms acts as dual-active-site to improve OER properties, while the rough surface and large pores in CF-O-N electrode may expose abundant active sites and sufficient contacting in catalyst/electrolyte interfaces. CF-O-N electrode behaves excellently for OER with only 130 and 590 mV to generate 10 mA cm −2 and 100 mA cm −2 , respectively. The superior OER property of CF-O-N electrode than single N- or O-doped CF implies the synergistic effect between N and O dopants that may further enhance OER activities. More importantly, dual-doped CF-O-N electrode displays roust stability in 10,000 cycles of cyclic voltammogram (CV) and 12 h chronoamperometry test with unchangeable structures proved by post physical characterizations. It may provide a facile and rational design of self-supported and metal-free materials with excellent activities for water oxidation and holds promising for further industrialization. [ABSTRACT FROM AUTHOR]

A facile sulfurization process has been utilized to synthesize WS 2 /WO 3 heterostructure using WO 3 square nanosheets as support. The thin WO 3 nanosheets synthesized by hydrothermal method may provide large surface area with homogeneous dispersion, which is favorable for exposing active sites and fast charge transfer for hydrogen evolution reaction (HER). SEM and TEM images show that the thin square nanosheets of as-prepared WS 2 /WO 3 heterostructure are well kept after sulfurization process. The formation of WS 2 on the surface of heterostructured nanosheets may greatly enhance the intrinsic HER activity and conductivity. The electrochemical measurements demonstrate the obviously enhanced HER activity of WS 2 /WO 3 heterostructured nanosheets compared with pure WO 3 or bulk WS 2 , illustrating that the synergistic effect derived from heterostructured WS 2 /WO 3 may be a key to enhance HER performances of WO 3 . Therefore, designing heterostructure of transition metal sulfides/oxides may be a promising strategy to prepare efficient electrocatalysts for HER. [ABSTRACT FROM AUTHOR]

MoS x as a promising electrocatalyst for hydrogen evolution reaction (HER) has the active sites of rims and edges and inert sites of basal plane. A strategy to activate MoS x is to produce more unsaturated S or S vacancies on the inert plane by designing unique nanostructure. Herein, we report a facile electrodeposition assisted by liquid crystal template (LCT) to prepare MoS x film on ITO substrate (MoS x (LCT)). XPS confirms the state of Mo and S of the obtained MoS x film. SEM shows that there are many uniform disk bulges with the diameter of about 100 nm on the surface of MoS x (LCT), which may provide more rims and edges of MoS x . While the electrodeposited MoS x film in water (MoS x (H 2 O)) is a smooth plane structure. The electrochemical measurements show MoS x (LCT) exhibits an ultrahigh activity for HER with the small onsetpotential very close to that of Pt/C, which may be due to not only the uniform disk bulges but also the more unsaturated S atoms of MoS x (LCT). The electrodeposition assisted by LCT may be a novel strategy to prepare novel nanostructure and activate MoS x -based electrocatalysts for HER. [ABSTRACT FROM AUTHOR]

To maximum the activity of transition metal sulfides for hydrogen evolution reaction (HER), two strategies usually have been adopted including designing unique nanostructures and integrating other metal element. Herein, Co x S y /WS 2 nanosheets supported on carbon cloth (Co x S y /WS 2 /CC) have been fabricated via a facile hydrothermal process. The cross-linked structures composed of Co x S y /WS 2 nanosheets uniformly cover on the surface of CC, which may expose abundant active sites for HER and accelerate charge transfer rate. The molar ratio of Co x S y -incorporating has been investigated in detail. The molar ratio of W/Co = 1/3 (noted as Co x S y /WS 2 /CC-3) has been proved to have unique spherical Co x S y /WS 2 nanostructure, which may further expose more active sites for HER. Electrochemical measurements demonstrate that Co x S y -incorporating can enhance HER activity and conductivity compared with WS 2 /CC. In addition, Co x S y /WS 2 /CC-3 exhibits the best HER activity, smallest charge transfer resistance and excellent stability than the counterparts, implying that the degree of Co x S y -incorporating may impact the HER activity of WS 2 . The mechanisms of Co x S y -incorporating on enhancing HER activity of WS 2 have been discussed. It may offer a promising way to design transition metal sulfides-based electrocatalysts for HER by non-precious metal incorporating. [ABSTRACT FROM AUTHOR]

The efficiency of electrochemical water splitting is greatly hindered by the thermodynamic uphill reaction of oxygen evolution reaction (OER). Thus, it is important to synthesize an active OER electrocatalysts with abundant active sites, favorable conductivity and good durability. Herein, a facile reduction method using NaBH 4 as readily available reductant has been developed to fabricate the reduced CoFe 2 O 4 nanosheets (NS). The obtained reduced CoFe 2 O 4 NS are rich in oxygen deficient sites, leading to more active sites as well as the enhanced conductivity than the pristine CoFe 2 O 4 hollow nanosphere, which reaches the current density of 10 mA cm −2 at the overpotential of 320 mV in 1 M KOH. Meanwhile, CoFe 2 O 4 samples with three different morphology nanostructures including hollow nanospheres, bulk and nanoparticles have been provided to study the effect of different morphology on NaBH 4 reduction efficiency. As expected, after NaBH 4 reduction, CoFe 2 O 4 hollow nanosphere with relatively higher surface area exhibits most obvious improvement for OER activity and also its corresponding reduced CoFe 2 O 4 NS showed best OER performance than the reduced CoFe 2 O 4 bulk as well as the reduced CoFe 2 O 4 nanoparticles, implying the hollow nanospheres feature more accessible surface area than bulk and nanoparticles samples, thus greatly facilitate efficiency of NaBH 4 reduction treatment. [ABSTRACT FROM AUTHOR]

Oxidized carbon fiber (oCF) as support successfully realizes the vertical growth of uniform WS 2 nanosheets arrays for efficient hydrogen evolution reaction (HER) via a facile hydrothermal process. Thanks to oxygen functional groups on oCF, vertical WS 2 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 WS 2 and WS 2 nanosheets on bare carbon fiber (CF) fabricated at the same condition. The electrochemical measurements confirmed that WS 2 /oCF possesses better HER activity than bulk WS 2 and WS 2 /CF. Especially, the 10-h stability with unchanged vertical WS 2 nanosheets morphology further demonstrate the positive effect of oxygen functional groups on the enhanced vertical structure and close combination between WS 2 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. [ABSTRACT FROM AUTHOR]