Synergistic Phase and Disorder Engineering in 1T‐MoSe2 Nanosheets for Enhanced Hydrogen‐Evolution Reaction

MoSe₂ is a promising earth‐abundant electrocatalyst for the hydrogen‐evolution reaction (HER), even though it has received much less attention among the layered dichalcogenide (MX₂) materials than MoS₂ so far. Here, a novel hydrothermal‐synthesis strategy is presented to achieve simultaneous and synergistic modulation of crystal phase and disorder in partially crystallized 1T‐MoSe₂ nanosheets to dramatically enhance their HER catalytic activity. Careful structural characterization and defect characterization using positron annihilation lifetime spectroscopy correlated with electrochemical measurements show that the formation of the 1T phase under a large excess of the NaBH₄ reductant during synthesis can effectively improve the intrinsic activity and conductivity, and the disordered structure from a lower reaction temperature can provide abundant unsaturated defects as active sites. Such synergistic effects lead to superior HER catalytic activity with an overpotential of 152 mV versus reversible hydrogen electrode (RHE) for the electrocatalytic current density of j = ?10 mA cm^?2, and a Tafel slope of 52 mV dec^?1. This work paves a new pathway for improving the catalytic activity of MoSe₂ and generally MX₂‐based electrocatalysts via a synergistic modulation strategy.     

Phase Modulation of (1T‐2H)‐MoSe2/TiC‐C Shell/Core Arrays via Nitrogen Doping for Highly Efficient Hydrogen Evolution Reaction

Tailoring molybdenum selenide electrocatalysts with tunable phase and morphology is of great importance for advancement of hydrogen evolution reaction (HER). In this work, phase‐ and morphology‐modulated N‐doped MoSe₂/TiC‐C shell/core arrays through a facile hydrothermal and postannealing treatment strategy are reported. Highly conductive TiC‐C nanorod arrays serve as the backbone for MoSe₂ nanosheets to form high‐quality MoSe₂/TiC‐C shell/core arrays. Impressively, continuous phase modulation of MoSe₂ is realized on the MoSe₂/TiC‐C arrays. Except for the pure 1T‐MoSe₂ and 2H‐MoSe₂, mixed (1T‐2H)‐MoSe₂ nanosheets are achieved in the N‐MoSe₂ by N doping and demonstrated by spherical aberration electron microscope. Plausible mechanism of phase transformation and different doping sites of N atom are proposed via theoretical calculation. The much smaller energy barrier, longer H? Se bond length, and diminished bandgap endow N‐MoSe₂/TiC‐C arrays with substantially superior HER performance compared to 1T and 2H phase counterparts. Impressively, the designed N‐MoSe₂/TiC‐C arrays exhibit a low overpotential of 137 mV at a large current density of 100 mA cm^?2, and a small Tafel slope of 32 mV dec^?1. Our results pave the way to unravel the enhancement mechanism of HER on 2D transition metal dichalcogenides by N doping.     

Bionanofiber Assisted Decoration of Few‐Layered MoSe2 Nanosheets on 3D Conductive Networks for Efficient Hydrogen Evolution

Molybdenum diselenide (MoSe₂) has emerged as a promising electrocatalyst for hydrogen evolution reaction (HER). However, its properties are still confined due to the limited active sites and poor conductivity. Thus, it remains a great challenge to synergistically achieve structural and electronic modulations for MoSe₂‐based HER catalysts because of the contradictory relationship between these two characteristics. Herein, bacterial cellulose‐derived carbon nanofibers are used to assist the uniform growth of few‐layered MoSe₂ nanosheets, which effectively increase the active sites of MoSe₂ for hydrogen atom adsorption. Meanwhile, carbonized bacterial cellulose (CBC) nanofibers provide a 3D network for electrolyte penetration into the inner space and accelerate electron transfer as well, thus leading to the dramatically increased HER activity. In acidic media, the CBC/MoSe₂ hybrid catalyst exhibits fast hydrogen evolution kinetics with onset overpotential of 91 mV and Tafel slope of 55 mV dec^?1, which is much more outstanding than both bulk MoSe₂ aggregates and CBC nanofibers. Furthermore, the fast HER kinetics are well supported by theoretical calculations of density‐functional‐theory analysis with a low activation barrier of 0.08 eV for H₂ generation. Hence, this work highlights an efficient solution to develop high‐performance HER catalysts by incorporating biotemplate materials, to simultaneously achieve increased active sites and conductivity.     

Preparation of High‐Percentage 1T‐Phase Transition Metal Dichalcogenide Nanodots for Electrochemical Hydrogen Evolution

Nanostructured transition metal dichalcogenides (TMDs) are proven to be efficient and robust earth‐abundant electrocatalysts to potentially replace precious platinum‐based catalysts for the hydrogen evolution reaction (HER). However, the catalytic efficiency of reported TMD catalysts is still limited by their low‐density active sites, low conductivity, and/or uncleaned surface. Herein, a general and facile method is reported for high‐yield, large‐scale production of water‐dispersed, ultrasmall‐sized, high‐percentage 1T‐phase, single‐layer TMD nanodots with high‐density active edge sites and clean surface, including MoS₂, WS₂, MoSe₂, Mo_0.5W_0.5S₂, and MoSSe, which exhibit much enhanced electrochemical HER performances as compared to their corresponding nanosheets. Impressively, the obtained MoSSe nanodots achieve a low overpotential of ?140 mV at current density of 10 mA cm^?2, a Tafel slope of 40 mV dec^?1, and excellent long‐term durability. The experimental and theoretical results suggest that the excellent catalytic activity of MoSSe nanodots is attributed to the high‐density active edge sites, high‐percentage metallic 1T phase, alloying effect and basal‐plane Se‐vacancy. This work provides a universal and effective way toward the synthesis of TMD nanostructures with abundant active sites for electrocatalysis, which can also be used for other applications such as batteries, sensors, and bioimaging.     

Directional Construction of Vertical Nitrogen‐Doped 1T‐2H MoSe2/Graphene Shell/Core Nanoflake Arrays for Efficient Hydrogen Evolution Reaction

The low utilization of active sites and sluggish reaction kinetics of MoSe₂ severely impede its commercial application as electrocatalyst for hydrogen evolution reaction (HER). To address these two issues, the first example of introducing 1T MoSe₂ and N dopant into vertical 2H MoSe₂/graphene shell/core nanoflake arrays that remarkably boost their HER activity is herein described. By means of the improved conductivity, rich catalytic active sites and highly accessible surface area as a result of the introduction of 1T MoSe₂ and N doping as well as the unique structural features, the N‐doped 1T‐2H MoSe₂/graphene (N‐MoSe₂/VG) shell/core nanoflake arrays show substantially enhanced HER activity. Remarkably, the N‐MoSe₂/VG nanoflakes exhibit a relatively low onset potential of 45 mV and overpotential of 98 mV (vs RHE) at 10 mA cm^?2 with excellent long‐term stability (no decay after 20 000 cycles), outperforming most of the recently reported Mo‐based electrocatalysts. The success of improving the electrochemical performance via the introduction of 1T phase and N dopant offers new opportunities in the development of high‐performance MoSe₂‐based electrodes for other energy‐related applications.     

Edge‐Riched MoSe2/MoO2 Hybrid Electrocatalyst for Efficient Hydrogen Evolution Reaction

Molybdenum diselenide (MoSe₂) is widely considered as one of the most promising catalysts for the hydrogen evolution reaction (HER). However, the absence of active sites and poor conductivity of MoSe₂ severely restrict its HER performance. By introducing a layer of MoO₂ on Mo foil, MoSe₂/MoO₂ hybrid nanosheets with an abundant edge and high electrical conductivity can be synthesized on the surface of Mo foil. Metallic MoO₂ can improve the charge transport efficiency of MoSe₂/MoO₂, thereby enhancing the overall HER performance. MoSe₂/MoO₂ exhibits fast hydrogen evolution kinetics with a small overpotential of 142 mV versus RHE at a current density of 10 mA cm^?2 and Tafel slope of 48.9 mV dec^?1.     

Effects of Ion Energy and Density on the Plasma Etching‐Induced Surface Area,Edge Electrical Field,and Multivacancies in MoSe2 Nanosheets for Enhancement of the Hydrogen Evolution Reaction

Plasma functionalization can increase the efficiency of MoSe₂ in the hydrogen evolution reaction (HER) by providing multiple species but the interactions between the plasma and catalyst are not well understood. In this work, the effects of the ion energy and plasma density on the catalytic properties of MoSe₂ nanosheets are studied. The through‐holes resulting from plasma etching and multi‐vacancies induced by plasma‐induced damage enhance the HER efficiency as exemplified by a small overpotential of 148 mV at 10 mA cm^–2 and Tafel slope of 51.6 mV dec^–1 after the plasma treatment using a power of 20 W. The interactions between the plasma and catalyst during etching and vacancies generation are evaluated by plasma simulation. Finite element and first‐principles density functional theory calculations are also conducted and the results are consistent with the experimental results, indicating that the improved HER catalytic activity stems from the enhanced electric field and more active sites on the catalyst, and reduced bandgap and adsorption energy arising from the etched through‐holes and vacancies, respectively. The results convey new fundamental knowledge about the plasma effects and means to enhance the efficiency of catalysts in water splitting as well insights into the design of high‐performance HER catalysts.     

Surface Engineering of MoS2 via Laser‐Induced Exfoliation in Protic Solvents

With excellent performance in the hydrogen evolution reaction (HER), molybdenum disulfide (MoS₂) is considered a promising nonprecious candidate to substitute Pt‐based catalysts. Herein, pulsed laser irradiation in liquid is used to realize one‐step exfoliation of bulk 2H‐MoS₂ to ultrastable few‐layer MoS₂ nanosheets. Such prepared MoS₂ nanosheets are rich in S vacancies and metallic 1T phase, which significantly contribute to the boosted catalytic HER activity. Protic solvents play a pivotal role in the production of S vacancies and 2H‐to‐1T phase transition under laser irradiation. MoS₂ exfoliated in an optimal solvent of formic acid exhibits outstanding HER activity with an overpotential of 180 mV at 10 mA cm^?2 and Tafel slope of 54 mV dec^?1.     

Construction of Defect‐Rich Ni‐Fe‐Doped K0.23MnO2 Cubic Nanoflowers via Etching Prussian Blue Analogue for Efficient Overall Water Splitting

Designing elaborate nanostructures and engineering defects have been promising approaches to fabricate cost‐efficient electrocatalysts toward overall water splitting. In this work, a controllable Prussian‐blue‐analogue‐sacrificed strategy followed by an annealing process to harvest defect‐rich Ni‐Fe‐doped K_0.23MnO₂ cubic nanoflowers (Ni‐Fe‐K_0.23MnO₂ CNFs‐300) as highly active bifunctional catalysts for oxygen and hydrogen evolution reactions (OER and HER) is reported. Benefiting from many merits, including unique morphology, abundant defects, and doping effect, Ni‐Fe‐K_0.23MnO₂ CNFs‐300 shows the best electrocatalytic performances among currently reported Mn oxide‐based electrocatalysts. This catalyst affords low overpotentials of 270 (320) mV at 10 (100) mA cm^?2 for OER with a small Tafel slope of 42.3 mV dec^?1, while requiring overpotentials of 116 and 243 mV to attain 10 and 100 mA cm^?2 for HER respectively. Moreover, Ni‐Fe‐K_0.23MnO₂ CNFs‐300 applied to overall water splitting exhibits a low cell voltage of 1.62 V at 10 mA cm^?2 and excellent durability, even superior to the Pt/C||IrO₂ cell at large current density. Density functional theory calculations further confirm that doping Ni and Fe into the crystal lattice of δ‐MnO₂ can not only reinforce the conductivity but also reduces the adsorption free‐energy barriers on the active sites during OER and HER.     

Nickel@Nitrogen‐Doped Carbon@MoS2 Nanosheets: An Efficient Electrocatalyst for Hydrogen Evolution Reaction

Developing cheap, abundant, and easily available electrocatalysts to drive the hydrogen evolution reaction (HER) at small overpotentials is an urgent demand of hydrogen production from water splitting. Molybdenum disulfide (MoS₂) based composites have emerged as competitive electrocatalysts for HER in recent years. Herein, nickel@nitrogen‐doped carbon@MoS₂ nanosheets (Ni@NC@MoS₂) hybrid sub‐microspheres are presented as HER catalyst. MoS₂ nanosheets with expanded interlayer spacings are vertically grown on nickel@nitrogen‐doped carbon (Ni@NC) substrate to form Ni@NC@MoS₂ hierarchical sub‐microspheres by a simple hydrothermal process. The formed Ni@NC@MoS₂ composites display excellent electrocatalytic activity for HER with an onset overpotential of 18 mV, a low overpotential of 82 mV at 10 mA cm^?2, a small Tafel slope of 47.5 mV dec^?1, and high durability in 0.5 H₂SO₄ solution. The outstanding HER performance of the Ni@NC@MoS₂ catalyst can be ascribed to the synergistic effect of dense catalytic sites on MoS₂ nanosheets with exposed edges and expanded interlayer spacings, and the rapid electron transfer from Ni@NC substrate to MoS₂ nanosheets. The excellent Ni@NC@MoS₂ electrocatalyst promises potential application in practical hydrogen production, and the strategy reported here can also be extended to grow MoS₂ on other nitrogen‐doped carbon encapsulated metal species for various applications.     

Synergistic Interlayer and Defect Engineering in VS2 Nanosheets toward Efficient Electrocatalytic Hydrogen Evolution Reaction

A simple one‐pot solvothermal method is reported to synthesize VS₂ nanosheets featuring rich defects and an expanded (001) interlayer spacing as large as 1.00 nm, which is a ≈74% expansion as relative to that (0.575 nm) of the pristine counterpart. The interlayer‐expanded VS₂ nanosheets show extraordinary kinetic metrics for electrocatalytic hydrogen evolution reaction (HER), exhibiting a low overpotential of 43 mV at a geometric current density of 10 mA cm^?2, a small Tafel slope of 36 mV dec^?1, and long‐term stability of 60 h without any current fading. The performance is much better than that of the pristine VS₂ with a normal interlayer spacing, and even comparable to that of the commercial Pt/C electrocatalyst. The outstanding electrocatalytic activity is attributed to the expanded interlayer distance and the generated rich defects. Increased numbers of exposed active sites and modified electronic structures are achieved, resulting in an optimal free energy of hydrogen adsorption (?G_H) from density functional theory calculations. This work opens up a new door for developing transition‐metal dichalcogenide nanosheets as high active HER electrocatalysts by interlayer and defect engineering.     

Coupled Biphase (1T‐2H)‐MoSe2 on Mold Spore Carbon for Advanced Hydrogen Evolution Reaction

Performance breakthrough of MoSe₂‐based hydrogen evolution reaction (HER) electrocatalysts largely relies on sophisticated phase modulation and judicious innovation on conductive matrix/support. In this work the controllable synthesis of phosphate ion (PO₄^3?) intercalation induced‐MoSe₂ (P‐MoSe₂) nanosheets on N‐doped mold spore carbon (N‐MSC) forming P‐MoSe₂/N‐MSC composite electrocatalysts is realized. Impressively, a novel conductive N‐MSC matrix is constructed by a facile mold fermentation method. Furthermore, the phase of MoSe₂ can be modulated by a simple phosphorization strategy to realize the conversion from 2H‐MoSe₂ to 1T‐MoSe₂ to produce biphase‐coexisted (1T‐2H)‐MoSe₂ by PO₄^3‐ intercalation (namely, P‐MoSe₂), confirmed by synchrotron radiation technology and spherical aberration‐corrected TEM (SACTEM). Notably, higher conductivity, lower bandgap and adsorption energy of H⁺ are verified for the P‐MoSe₂/N‐MSC with the help of density functional theory (DFT) calculation. Benefiting from these unique advantages, the P‐MoSe₂/N‐MSC composites show superior HER performance with a low Tafel slope (≈51 mV dec^‐1) and overpotential (≈126 mV at 10 mA cm^‐1) and excellent electrochemical stability, better than 2H‐MoSe₂/N‐MSC and MoSe₂/carbon nanosphere (MoSe₂/CNS) counterparts. This work demonstrates a new kind of carbon material via biological cultivation, and simultaneously unravels the phase transformation mechanism of MoSe₂ by PO₄^3‐ intercalation.     

Nitrogen‐Doped Graphene‐Encapsulated Nickel–Copper Alloy Nanoflower for Highly Efficient Electrochemical Hydrogen Evolution Reaction

Development of high‐performance and low‐cost nonprecious metal electrocatalysts is critical for eco‐friendly hydrogen production through electrolysis. Herein, a novel nanoflower‐like electrocatalyst comprising few‐layer nitrogen‐doped graphene‐encapsulated nickel–copper alloy directly on a porous nitrogen‐doped graphic carbon framework (denoted as Ni_x Cu_y @ NG‐NC) is successfully synthesized using a facile and scalable method through calcinating the carbon, copper, and nickel hydroxy carbonate composite under inert atmosphere. The introduction of Cu can effectively modulate the morphologies and hydrogen evolution reaction (HER) performance. Moreover, the calcination temperature is an important factor to tune the thickness of graphene layers of the Ni_x Cu_y @ NG‐NC composites and the associated electrocatalytic performance. Due to the collective effects including unique porous flowered architecture and the synergetic effect between the bimetallic alloy core and graphene shell, the Ni₃Cu₁@ NG‐NC electrocatalyst obtained under optimized conditions exhibits highly efficient and ultrastable activity toward HER in harsh environments, i.e., a low overpotential of 122 mV to achieve a current density of 10 mA cm^?2 with a low Tafel slope of 84.2 mV dec^?1 in alkaline media, and a low overpotential of 95 mV to achieve a current density of 10 mA cm^?2 with a low Tafel slope of 77.1 mV dec^?1 in acidic electrolyte.     

Hydrogen‐Etched Bifunctional Sulfur‐Defect‐Rich ReS2/CC Electrocatalyst for Highly Efficient HER and OER

The design on synthesizing a sturdy, low‐cost, clean, and sustainable electrocatalyst, as well as achieving high performance with low overpotential and good durability toward water splitting, is fairly vital in environmental and energy‐related subject. Herein, for the first time the growth of sulfur (S) defect engineered self‐supporting array electrode composed of metallic Re and ReS₂ nanosheets on carbon cloth (referred as Re/ReS₂/CC) via a facile hydrothermal method and the following thermal treatment with H₂/N₂ flow is reported. It is expected that, for example, the as‐prepared Re/ReS₂‐7H/CC for the electrocatalytic hydrogen evolution reaction (HER) under acidic medium affords a quite low overpotential of 42 mV to achieve a current density of 10 mA cm^?2 and a very small Tafel slope of 36 mV decade^?1, which are comparable to some of the promising HER catalysts. Furthermore, in the two‐electrode system, a small cell voltage of 1.30 V is recorded under alkaline condition. Characterizations and density functional theory results expound that the introduced S defects in Re/ReS₂‐7H/CC can offer abundant active sites to advantageously capture electron, enhance the electron transport capacity, and weaken the adsorption free energy of H* at the active sites, being responsible for its superior electrocatalytic performance.     

Molybdenum Carbide‐Decorated Metallic Cobalt@Nitrogen‐Doped Carbon Polyhedrons for Enhanced Electrocatalytic Hydrogen Evolution

Electrocatalytic hydrogen evolution reaction (HER) based on water splitting holds great promise for clean energy technologies, in which the key issue is exploring cost‐effective materials to replace noble metal catalysts. Here, a sequential chemical etching and pyrolysis strategy are developed to prepare molybdenum carbide‐decorated metallic cobalt@nitrogen‐doped porous carbon polyhedrons (denoted as Mo/Co@N–C) hybrids for enhanced electrocatalytic hydrogen evolution. The obtained metallic Co nanoparticles are coated by N‐doped carbon thin layers while the formed molybdenum carbide nanoparticles are well‐dispersed in the whole Co@N–C frames. Benefiting from the additionally implanted molybdenum carbide active sites, the HER performance of Mo/Co@N–C hybrids is significantly promoted compared with the single Co@N–C that is derived from the pristine ZIF‐67 both in alkaline and acidic media. As a result, the as‐synthesized Mo/Co@N–C hybrids exhibit superior HER electrocatalytic activity, and only very low overpotentials of 157 and 187 mV are needed at 10 mA cm^?2 in 1 m KOH and 0.5 m H₂SO₄, respectively, opening a door for rational design and fabrication of novel low‐cost electrocatalysts with hierarchical structures toward electrochemical energy storage and conversion.     

Structure Engineering of MoS2 via Simultaneous Oxygen and Phosphorus Incorporation for Improved Hydrogen Evolution

Oxygen and phosphorus dual‐doped MoS₂ nanosheets (O,P‐MoS₂) with porous structure and continuous conductive network are fabricated using a one‐pot NaH₂PO₂‐assisted hydrothermal approach. By simply changing the precursor solution, the chemical composition and resulting structure can be effectively controlled to obtain desired properties toward the hydrogen evolution reaction (HER). Thanks to the beneficial structure and strong synergistic effects between the incorporated oxygen and phosphorus, the optimal O,P‐MoS₂ exhibit superior electrocatalytic performances compared with those of oxygen single‐doped MoS₂ nanosheets (O‐MoS₂). Specifically, a low HER onset overpotential of 150 mV with a small Tafel slope of 53 mV dec^?1, excellent conductivity, and long‐term durability are achieved by the structural engineering of MoS₂ via O and P co‐doping, making it an efficient HER electrocatalyst for water electrocatalysis. This work provides an alternative strategy to manipulate transition metal dichalcogenides as advanced materials for electrocatalytic and related energy applications.     

Unveiling the Interfacial Effects for Enhanced Hydrogen Evolution Reaction on MoS2/WTe2 Hybrid Structures

Using the MoS₂‐WTe₂ heterostructure as a model system combined with electrochemical microreactors and density function theory calculations, it is shown that heterostructured contacts enhance the hydrogen evolution reaction (HER) activity of monolayer MoS₂. Two possible mechanisms are suggested to explain this enhancement: efficient charge injection through large‐area heterojunctions between MoS₂ and WTe₂ and effective screening of mirror charges due to the semimetallic nature of WTe₂. The dielectric screening effect is proven minor, probed by measuring the HER activity of monolayer MoS₂ on various support substrates with dielectric constants ranging from 4 to 300. Thus, the enhanced HER is attributed to the increased charge injection into MoS₂ through large‐area heterojunctions. Based on this understanding, a MoS₂/WTe₂ hybrid catalyst is fabricated with an HER overpotential of ?140 mV at 10 mA cm^?2, a Tafel slope of 40 mV dec^?1, and long stability. These results demonstrate the importance of interfacial design in transition metal dichalcogenide HER catalysts. The microreactor platform presents an unambiguous approach to probe interfacial effects in various electrocatalytic reactions.     

Superior Hydrogen Evolution Reaction Performance in 2H‐MoS2 to that of 1T Phase

In the hydrogen evolution reaction (HER), energy‐level matching is a prerequisite for excellent electrocatalytic activity. Conventional strategies such as chemical doping and the incorporation of defects underscore the complicated process of controlling the doping species and the defect concentration, which obstructs the understanding of the function of band structure in HER catalysis. Accordingly, 2H‐MoS₂ and 1T‐MoS₂ are used to create electrocatalytic nanodevices to address the function of band structure in HER catalysis. Interestingly, it is found that the 2H‐MoS₂ with modulated Fermi level under the application of a vertical electric field exhibits excellent electrocatalytic activity (as evidenced by an overpotential of 74 mV at 10 mA cm^?2 and a Tafel slope of 99 mV per decade), which is superior to 1T‐MoS₂. This unexpected excellent HER performance is ascribed to the fact that electrons are injected into the conduction band under the condition of back‐gate voltage, which leads to the increased Fermi level of 2H‐MoS₂ and a shorter Debye screen length. Hence, the required energy to drive electrons from the electrocatalyst surface to reactant will decrease, which activates the 2H‐MoS₂ thermodynamically.     

3D Nitrogen‐Anion‐Decorated Nickel Sulfides for Highly Efficient Overall Water Splitting

Developing non‐noble‐metal electrocatalysts with high activity and low cost for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of paramount importance for improving the generation of H₂ fuel by electrocatalytic water‐splitting. This study puts forward a new N‐anion‐decorated Ni₃S₂ material synthesized by a simple one‐step calcination route, acting as a superior bifunctional electrocatalyst for the OER/HER for the first time. The introduction of N anions significantly modifies the morphology and electronic structure of Ni₃S₂, bringing high surface active sites exposure, enhanced electrical conductivity, optimal HER Gibbs free‐energy (ΔG_H*), and water adsorption energy change (ΔG_H2O*). Remarkably, the obtained N‐Ni₃S₂/NF 3D electrode exhibits extremely low overpotentials of 330 and 110 mV to reach a current density of 100 and 10 mA cm^?2 for the OER and HER in 1.0 m KOH, respectively. Moreover, an overall water‐splitting device comprising this electrode delivers a current density of 10 mA cm^?2 at a very low cell voltage of 1.48 V. Our finding introduces a new way to design advanced bifunctional catalysts for water splitting.     

Ruthenium Nanoparticles on Cobalt‐Doped 1T′ Phase MoS2 Nanosheets for Overall Water Splitting

2D MoS₂ nanostructures have recently attracted considerable attention because of their outstanding electrocatalytic properties. The synthesis of unique Co–Ru–MoS₂ hybrid nanosheets with excellent catalytic activity toward overall water splitting in alkaline solution is reported. 1T′ phase MoS₂ nanosheets are doped homogeneously with Co atoms and decorated with Ru nanoparticles. The catalytic performance of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is characterized by low overpotentials of 52 and 308 mV at 10 mA cm^?2 and Tafel slopes of 55 and 50 mV decade^?1 in 1.0 m KOH, respectively. Analysis of X‐ray photoelectron and absorption spectra of the catalysts show that the MoS₂ well retained its metallic 1T′ phase, which guarantees good electrical conductivity during the reaction. The Gibbs free energy calculation for the reaction pathway in alkaline electrolyte confirms that the Ru nanoparticles on the Co‐doped MoS₂ greatly enhance the HER activity. Water adsorption and dissociation take place favorably on the Ru, and the doped Co further catalyzes HER by making the reaction intermediates more favorable. The high OER performance is attributed to the catalytically active RuO₂ nanoparticles that are produced via oxidation of Ru nanoparticles.