Excellent Electrocatalytic Activity For Hydrogen Evolution Reaction Research Articles

Fluorine-doped CoP/Ni2P nanowires for enhanced hydrogen evolution activity

Doping hetero-atoms into non-noble metal phosphides is an important strategy for enhancement of hydrogen evolution reaction (HER) performance. Herein, we prepare a self-supported F-doped CoP/Ni2P nanowire arrays grown on Ni foam by using a strategy with three steps including hydrothermal reaction, fluorination, and low-temperature phosphorization. The F-CoP/Ni2P nanowire consists of a well-defined crystalline core and a thin amorphous surface layer. The F-doping and amorphous surface layers effectively expose a large number of active sites, optimize the electronic configuration of Ni, Co and P on the surface, and promote the electron transport performance. As a result, the prepared F-CoP/Ni2P@NF-II exhibits excellent electrocatalytic activity for HER in alkaline electrolyte with a lower overpotential of 75 mV at 10 mA cm−2, a small Tafel slope of 54.8 mV dec−1, and good durability. This work provides a simple method for developing transition metal phosphate-based catalysts towards hydrogen evolution reaction.

CdS@Au micro-spheres as an active and durable bifunctional catalyst for the urea-assisted H2 evolution reaction

Hydrogen evolution reaction (HER) and urea oxidation reaction (UOR) limit the efficiency of overall water splitting and urea oxidation for hydrogen generation, respectively. In this paper, we synthesize CdS@Au catalysts with excellent electrocatalytic activity for HER and UOR by a simple condensate reflux method. Using urea oxidation as an alternative anode reaction, the anodic oxidation potential decreased significantly to 286.4 mV@10 mA cm−2. With CdS@Au as the anode, the cell voltage drops to 1.34 V@10 mA cm−2. By discussing the Au content, it was shown that Au has a strong Lewis acidity and electronegativity, favoring hydrogen evolution.

Controllable N Doped in Carbon Nanolayers@Mo2C Nanodots as Electrocatalyst Boosts High‐Efficient Hydrogen Production

AbstractMo2C is one of the promising alternatives to the precious metal catalyst for hydrogen evolution reaction (HER). However, it is still challenging to prepare highly dispersed Mo2C and prevent nanoparticles (NPs) from sintering during high‐temperature carbonization. Herein, a strategy is proposed to realize dual purposes that confine the coalescence of Mo2C NPs and redistribute charge density by regulating N‐doped contents. As‐synthesized molybdenum carbide nanodots are well dispersed on the N‐doped carbon nanolayers, and the size of Mo2C is uniform and less than 5 nm. The HER tests reveal that as‐prepared Mo2C nanodots exhibit excellent electrocatalytic activity for HER and long‐term stability. Theory calculation proves that optimizing N doping amount can tune hydrogen adsorption free energies and redistribute charge density. The present study provides insight into the impact of nitrogen doped in C/Mo2C and also a synthetic route to achieve heteroatom doping and size control for the synthesis of nanocatalysts beyond Mo2C.

Hollow Co9S8@NiFe-LDH nanoarrays supported by nickel foam for boosting the overall water-splitting performance

Rational design of efficient, low-cost, and durable electrocatalyst for water-splitting is of great importance in the utilization of renewable energy. In this work, we report a facile heterostructure of nickel foam supporting hollow Co9S8 nanoarrays wrapped by NiFe-layered double-hydroxide (Co9S8@NiFe-LDH/NF) as the electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) to improve the water-splitting efficiency. By the structural design, the strong electronic interaction among each component could offer more actives sites, higher charge transfer capability and better durability. As a result, excellent electrocatalytic activity for HER and OER are obtained. In 1 M KOH solution, the Co9S8@NiFe-LDH/NF exhibits low overpotentials of 287 mV for OER and 280 mV for HER to achieve catalytic current density of 50 mA cm−2. This work offers a new avenue to construct efficient and low-cost electrocatalyst for water-splitting.

In-situ construction of N-doped carbon nanosnakes encapsulated FeCoSe nanoparticles as efficient bifunctional electrocatalyst for overall water splitting

The development of bifunctional electrocatalysts with high activity and stability for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial for efficient overall water splitting but still challenging. Herein, we propose a facile and effective polymerization–pyrolysis–selenization (PPS) strategy for in-situ synthesis of N-doped carbon nanosnakes (NCNSs) encapsulated Fe-doped CoSe nanoparticles (NPs) derived from predesigned trimetallic Zn/Fe/Co polyphthalocyanine conjugated polymer networks. Benefiting from the synergistic effect between the regulation of Fe atoms and CoSe NPs as well as the confinement effect of in situ formed porous conductive carbon nanosnakes, the FeCoSe@NCNSs catalyst exhibited the excellent electrocatalytic activity for HER with small overpotentials (142 and 99 mV in 0.5 M H2SO4 and 1 M KOH) and OER (320 mV in 1 M KOH) at the current density of 10 mA cm−2. Particularly, it also can be used as an efficient bifunctional electrocatalyst with a cell voltage of 1.66 V to achieve a current density of 10 mA cm−2 and superior stability for overall water splitting. Density functional theory study reveals that the doping of Fe atoms on CoSe enhanced the splitting and delocalization of metal-d orbitals close Fermi level, and modifies the distribution of Se-p orbitals close Fermi level, which improved the flexibility of electron donor-acceptor system and the hydrogen adsorption free energy change on metal-metal bridge sites in FeCoSe@NCNSs. Additionally, beneficial from the accepting of Fe-Se bridge site, the overpotential of OER which following intramolecular oxygen coupling mechanism is also decreased, thus accelerating the electrocatalytic performance. This work presents a novel strategy to regulate the activity and stability of transition metal selenides and facilitating the rational design of bifunctional electrocatalysts for overall water splitting applications.

Highly Dispersed Mo2 C Nanodots in Carbon Nanocages Derived from Mo-Based Xerogel: Efficient Electrocatalysts for Hydrogen Evolution.

The production of hydrogen via electrochemical water splitting has the potential to enable the utilization of hydrogen-powered fuel cells on a large scale. However, to realize this technology, inexpensive, noble metal-free electrocatalysts possessing high performances for the hydrogen evolution reaction (HER) are needed. Mo2 C nanoparticles recently receive much attention as alternative noble metal-free electrocatalysts because their electronic structures are akin to that of Pt. However, the synthesis of Mo2 C at nanoscale with high catalytic activity for HER remains a great challenge. Moreover, although efforts have been made to prevent their aggregation, the particles coalesce during high temperature carbonization, which is typically used to produce such transition metal carbides. Here, the synthesis of Mo2 C nanodots that are well-dispersed within 3D cage-like carbon microparticles using rationally designed Mo-based xerogels, which are prepared via the sol-gel process as precursors, is reported. During their pyrolysis, the xerogels maintain their structures while the Mo species in them transform into well-dispersed Mo2 C nanodots in situ. The as-synthesized Mo2 C nanodots exhibit excellent electrocatalytic activity for HER, in both alkaline and acidic media, while remaining largely stable. The work also demonstrates a promising synthetic route and procedure to other well-dispersed yet stable nanocatalysts.

High-valent bimetal Ni3S2/Co3S4 induced by Cu doping for bifunctional electrocatalytic water splitting

Rational design of low-cost and efficient electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is imperative for renewable energy conversion. Herein, for the first time, a facile strategy is developed to synthesize M (M = Fe, Cu, Zn, Mo) doped bimetallic sulfide heterostructure Ni3S2/Co3S4 electrocatalysts. The as-prepared bifunctional Cu-Ni3S2/Co3S4 electrode exhibits excellent electrocatalytic activity for HER and OER in 1 M KOH electrolyte, and it requires only an overpotential of 79 mV (150 mV) to deliver 10 mA cm−2 (20 mA cm-2) current density for HER process. Moreover, it shows a considerable low cell voltage of 1.49 V at the current density of 10 mA cm-2 in a two-electrode configuration which is far surpassing most of the reported bifunctional metal sulfides. Meanwhile, besides increasing the specific surface area of the electrocatalyst by optimizing the microstructure, the introduction of Cu cation could also stimulate the formation of high-valent Ni/Co sites, which can be verified by XPS technique. Density function theory calculations demonstrate that the Cu-doping boosts the formation of high valent Co sites and enhances the charge transfer performance of Ni and Co species, thus promotes intrinsic catalytic activity through modulating the d-band center of Co and reducing the adsorption energy of H and O-containing intermediates (H*, OH*, OOH*) on the surface of the catalyst. This work suggests the importance of exploitation of transition metal ion-doping for promoting the electrocatalytic activity of bimetallic sulfides.

ZIF-8-derived ZnS–Ni3Fe–Ni co-loaded N-doped porous carbon for efficient hydrogen evolution reaction catalysis

Abstract Herein, N-doped porous carbon (NC) decorated with ZnS, Ni3Fe, and metallic Ni, and denoted as ZnFeNiS/NC, was fabricated via the direct carbonization of a zeolitic imidazolate framework (ZIF-8), that is, a Zn-based metal–organic framework, combined with absorption and sulfurization processes. The synthesized material was used as an electrocatalyst for the hydrogen evolution reaction (HER) in alkaline solutions. Compared with Zn/NC, ZnFe/NC, and ZnFeNi/NC, ZnFeNiS/NC exhibited excellent HER activity with the lowest potential (162.57 mV) and Tafel slope (65.48 mV decade−1) at a current density of 10 mA cm−2. This better performance can be attributed to the synergistic effects of the ZnS, Ni3Fe, and Ni dopants; the ZnS, Ni3Fe, and Ni nanoparticles embedded in NC not only provided many active reaction sites but also ensured long-term stability in alkaline media. The new method presented here could allow the fabrication of non-noble-metal electrocatalysts with excellent electrocatalytic activity for HER.

Facile preparation of Ni, Co - Alloys supported on porous carbon spheres for supercapacitors and hydrogen evolution reaction application

Carbon nanomaterials that are electrochemically bifunctional and active in supercapacitor and hydrogen-evolution-reaction (HER) applications have attracted recent research attention. We have prepared porous carbon spheres - doped Ni, Co - alloys by using a hydrothermal method with melamine and pectin as precursors and with the addition of nickel nitrate and cobalt nitrate. The corresponding materials exhibit good electrochemical performance and excellent electrocatalytic activity for HER. The overpotential (OP) of the as-prepared materials can achieve 240 mV keeping a Tafel slope (TS) of 55 mV dec−1 at 10 mA cm−2 in an acid (0.5 M H2SO4) solution. The corresponding samples maintain stability after 24 h and 5000 cycles in the chronovoltage and cyclic voltammetry methods, respectively. When the as-prepared materials are oxidized by 30% H2O2 for 12 h, the corresponding as-prepared oxidation samples exhibit excellent electrochemical performance in a supercapacitor application. The specific capacitance (SC) of the as-obtained materials reaches 312 F g−1 at 1 A g−1 with decent rate capability and cyclic stability. This work provides new applications for bifunctional electrochemically active materials.

Transition Metal Phosphides Fabricated through a Codeposition-Annealing Technique As Electrocatalysts for Hydrogen Evolution Reaction

In the present work, transition metal phosphides were fabricated through a facile codeposition-annealing process. Pure red phosphorous particles were electrolytically codeposited with amorphous phosphorus containing alloys of general structure Me-P (with Me being a transition metal). A subsequent annealing step was applied to promote the formation of intermetallics and the interdiffusion between pure phosphorus particles and the metallic matrix. The main advantage of this approach is the possibility to easily obtain metal phosphides characterized by a very high P content, well beyond the limit typical of normal electrochemical processes involving induced codeposition of P [1, 2]. Another interesting benefit of the technique presented is the confinement of elemental P inside the coating during the annealing step. This strongly limits the presence of gaseous phosphorus, which is typical of different phosphorization processes used in literature to obtain metal phosphides [3]. Avoiding gaseous P is advantageous, since in specific conditions the formation of the highly dangerous white allotrope can take place. The use of P particles confined inside the coating is preferable also to phosphorization methods involving phosphine, an extremely poisonous gas commonly employed at lab level. The codeposition-annealing route described in the present work can be in principle applied to a number of transition metals for many different applications. One of the most attractive application for metal phosphides, however, is electrocatalysis for water splitting [4]. In this context, the codeposition-annealing technique was applied to the fabrication of Ni and Co phosphides, which can be used as catalytic substrates for Hydrogen Evolution Reaction (HER). These two materials present remarkable advantages over commonly used Pt based catalysts: lower cost, comparable performances and ease of manufacturing. Operatively, amorphous Ni-P and Co-P alloys were codeposited with P particles and subsequently annealed. As a result, different phase pure metal phosphides like Ni2P, Ni12P5, Co2P, Cu3P etc. were obtained after annealing. Characterization techniques like XRD, SEM (EDS), cross-sectional analysis and XPS were used to determine phase composition of the materials obtained and to characterize their morphology. Effect of annealing temperature and duration on phase composition were investigated as well. The electrocatalytic HER activity and stability of the different transition metal phosphides were tested in 0.5 M H2SO4. In all the cases, remarkable results were obtained, which matched up well with present existing literature where similar electrocatalysts have been fabricated through different methods [5]. For example, a Co2P electrocatalyst plated on copper and annealed at 290 °C exhibited excellent electrocatalytic activity for HER, showing a low overpotential of 62 mV at a current density of 10 mA/cm2 in 0.5M H2SO4 solution. [1] R. L. Zeller and U. Landau; J. Electrochem. Soc. 139 (12), 3464-3469 (1992) [2] A. Brenner; Electrodeposition of Alloys: Principles and Practice, Elsevier (2013) [3] X. Wang et al.; Angew. Chem. 54 (28), 8188-8192 (2015) [4] P. Xiao et al.; Adv. Energy Mater. 5 (24), 1500985 (2015) [5] Z.Pu et al.; Chem.Mater. 26 (15), 4326-4329 (2014)

Porous NiCu alloy cathode with oriented pore structure for hydrogen evolution reaction by freeze casting

Porous NiCu alloy with oriented pore structure was successfully prepared by freeze casting method with Ni powders and Cu powders as the source materials, and water as the solvent. The pore structure of porous NiCu alloy was analyzed, finding that the porous NiCu alloy frozen at lower temperature having thinner wall thickness and narrower pore width. The electrocatalytic performance for hydrogen evolution reaction (HER) in 6 M KOH at room temperature was evaluated by cyclic voltammetry, linear sweep voltammetry and electrochemical impedance spectroscopy techniques. Results show that porous NiCu alloy frozen at − 50 °C exhibits the most excellent electrocatalytic activity for 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 H2 SO4 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.

In-situ Selenization of Co-based Metal-Organic Frameworks as a Highly Efficient Electrocatalyst for Hydrogen Evolution Reaction

Metal-organic frameworks (MOFs) derived cobalt diselenide (MOF-CoSe2) constructed with CoSe2 nanoparticles anchored into nitrogen-doped (N-doped) graphitic carbon has been synthesized through in-situ selenization of Co-based MOFs. The obtained MOF-CoSe2 exhibits excellent hydrogen evolution reaction (HER) performance: it shows a small Tafel slope of 42mVdec−1, a low onset potential of 150mV; it delivers a high current density and excellent long-term stability. Such enhancement can be attributed to the unique N-doped MOFs derived architecture with high conductivity, which can not only provide abundant active reaction sites, but also ensure robust contact between the CoSe2 nanoparticles and N-doped carbon matrix, leading to outstanding electrocatalytic activity for HER. This study provides a route to prepared non-noble-metal catalyst with high efficiency and excellent electrocatalytic activity for HER.

Mo‐Based Ultrasmall Nanoparticles on Hierarchical Carbon Nanosheets for Superior Lithium Ion Storage and Hydrogen Generation Catalysis

Constructing 3D hierarchical architecture consisting of 2D hybrid nanosheets is very critical to achieve uppermost and stable electrochemical performance for both lithium‐ion batteries (LIBs) and hydrogen evolution reaction (HER). Herein, a simple synthesis of uniform 3D microspheres assembled from carbon nanosheets with the incorporated MoO2 nanoclusters is demonstrated. The MoO2 nanoclusters can be readily converted into the molybdenum carbide (Mo2C) nanocrystals by using high temperature treatment. Such assembling architecture is highly particular for preventing Mo‐based ultrasmall nanoparticles from coalescing or oxidizing and endowing them with rapid electron transfer. Consequently, the MoO2/C hybrids as LIB anode materials deliver a specific capacity of 625 mA h g−1 at 1600 mA g−1 even after 1000 cycles, which is among the best reported values for MoO2‐based electrode materials. Moreover, the Mo2C/C hybrids also exhibit excellent electrocatalytic activity for HER with small overpotential and robust durability in both acid and alkaline media. The present work highlights the importance of designing 3D structure and controlling ultrasmall Mo‐based nanoparticles for enhancing electrochemical energy conversion and storage applications.

New insights into high-valence state Mo in molybdenum carbide nanobelts for hydrogen evolution reaction

Hydrogen evolution reaction (HER) is considered to be one of the most promising strategies to create hydrogen. Recently, searching high-efficient, stable, and earth-abundant electrocatalysts to replace precious metals for practical utilizations of HER is attracting more and more attentions. Herein, novel molybdenum carbide nanobelts containing Mo of high-valence state derived from MoO3-ethylenediamine inorganic/organic hybrid precursors are successfully synthesized via a facile one-pot pyrolysis method. The molybdenum carbide nanobelts are characterized using XRD, SEM, TEM and XPS. Moreover, the high-valence state Mo and their relative content in the molybdenum carbide nanobelts can be identified by XPS. The high-resolution XPS spectra of Mo 3d indicates in the molybdenum carbide nanobelts the proportion of high-valence state Mo in active Mo components is 51.3%. More importantly, the as-synthesized products exhibit excellent electrocatalytic activity for HER with a low onset overpotential of 50 mV and a small Tafel slope of 49.6 mV dec−1 in acidic medium (0.5 M H2SO4). Besides, the catalysts require only overpotentials of 143 and 234 mV to achieve current densities of 10 and 220 mA cm−2, respectively. Furthermore, they also exhibit good durability after 2000 cycles and constant current density test. Such excellent electrocatalytic HER performance can be ascribed to the high intrinsic activity of high-valence state Mo in Molybdenum Carbide. Synthesizing molybdenum carbide with high-valence state Mo electrocatalysts for HER will open up an exciting alternative avenue to acquire outstanding HER electrocatalytic activity.

Tungsten-molybdenum oxide nanowires/reduced graphene oxide nanocomposite with enhanced and durable performance for electrocatalytic hydrogen evolution reaction

Hydrogen has attracted huge interest globally as a durable, environmentally safe and renewable fuel. Electrocatalytic hydrogen evolution reaction (HER) is one of the most promising methods for large scale hydrogen production, but the high cost of Pt-based materials which exhibit the highest activity for HER forced researchers to find alternative electro-catalyst. In this study, we report noble metal free a 3D hybrid composite of tungsten-molybdenum oxide and reduced graphene oxide (GO) prepared by a simple one step hydrothermal method for HER. Benefitting from the synergistic effect between tungsten-molybdenum oxide nanowires and reduced graphene oxide, the obtained W-Mo-O/rGO nanocomposite showed excellent electro-catalytic activity for HER with onset potential 50 mV, a Tafel slope of 46 mV decade−1 and a large cathodic current, while the tungsten-molybdenum oxide nanowires itself is not as efficient HER catalyst. Additionally, W-Mo-O/rGO composite also demonstrated good durability up to 2000 cycles in acidic medium. The enhanced and durable hydrogen evolution reaction activity stemmed from the synergistic effect broadens noble metal free catalysts for HER and provides an insight into the design and synthesis of low-cost and environment friendly catalysts in electrochemical hydrogen production.

One-Step Electrodeposition of Co/CoP Film on Ni Foam for Efficient Hydrogen Evolution in Alkaline Solution.

The development of high-efficiency catalysts for hydrogen evolution via water splitting has been an effective strategy to solve the energy environmental problems and energy crisis. The abundant-reserving transition metals and their phosphides are becoming attractive Pt alternatives for hydrogen evolution reaction (HER). Herein, a crystalline/amorphous Co/CoP film was facilely prepared on nickel foam (NF) by a one-step electrodeposition technique at room temperature, named Co/CoP-NF. The as-prepared Co/CoP-NF electrocatalyst exhibits excellent electrocatalytic activity for HER, on par with Pt/C, showing a low overpotential of 35 mV at a current density of 10 mA·cm-2 and small Tafel slope of 71 mV·dec-1 in 1.0 M NaOH solution. More importantly, the Co/CoP-NF catalyst presents good long-term durability at an overpotential of 60 mV. Moreover, the influence of the electrodeposition parameters on the catalytic performance of the catalyst was discussed. This study offers an effective strategy to develop a non-noble-metal HER catalyst for industrial production of hydrogen.

Hierarchical MoS2@MoP core-shell heterojunction electrocatalysts for efficient hydrogen evolution reaction over a broad pH range.

A low-cost catalyst for the hydrogen evolution reaction (HER) over a broad pH range is highly desired to meet the practical needs in different areas. In this study, hierarchical flower-like MoS2@MoP core-shell heterojunctions (HF-MoSP) are designed as a promising catalyst for HER over a broad pH range. The materials are obtained by the controllable phosphidation of the hierarchical MoS2 flower (HF-MoS2) composed of thin silk belt-like sheets. The phosphidation degree, P/S ratio and work function (WF) of HF-MoSP can be tuned easily over broad range by changing the phosphidation temperature. Under optimized condition, HF-MoSP exhibits excellent electrocatalytic activity for HER with a low onset overpotential of 29 mV and η of 108 mV at 10 mA cm(-2) in 0.5 M H2SO4 and retains its good activity for 30 h. In addition, the catalyst shows excellent activity in 1 M KOH with an onset overpotential of 42 mV and η of 119 mV at 10 mA cm(-2). The catalysts also exhibit obvious activity in neutral, weak acid and weak alkaline conditions. The good performance is relative to the synergy of the MoP shell and MoS2 core and the high WF of HF-MoSP close to Pt, and the large SBET of HF-MoSP benefited from the hierarchical structure. This study represents the construction of the core-shell heterojunction and provides a new way to provide the low-cost and high-performance catalyst for HER.

Nitrogen-Doped Carbon Nanofiber/Molybdenum Disulfide Nanocomposites Derived from Bacterial Cellulose for High-Efficiency Electrocatalytic Hydrogen Evolution Reaction.

To remit energy crisis and environmental deterioration, non-noble metal nanocomposites have attracted extensive attention, acting as a fresh kind of cost-effective electrocatalysts for hydrogen evolution reaction (HER). In this work, hierarchically organized nitrogen-doped carbon nanofiber/molybdenum disulfide (pBC-N/MoS2) nanocomposites were successfully prepared via the combination of in situ polymerization, high-temperature carbonization process, and hydrothermal reaction. Attributing to the uniform coating of polyaniline on the surface of bacterial cellulose, the nitrogen-doped carbon nanofiber network acts as an excellent three-dimensional template for hydrothermal growth of MoS2 nanosheets. The obtained hierarchical pBC-N/MoS2 nanocomposites exhibit excellent electrocatalytic activity for HER with small overpotential of 108 mV, high current density of 8.7 mA cm(-2) at η = 200 mV, low Tafel slope of 61 mV dec(-1), and even excellent stability. The greatly improved performance is benefiting from the highly exposed active edge sites of MoS2 nanosheets, the intimate connection between MoS2 nanosheets and the highly conductive nitrogen-doped carbon nanofibers and the three-dimensional networks thus formed. Therefore, this work provides a novel strategy for design and application of bacterial cellulose and MoS2-based nanocomposites as cost-effective HER eletrocatalysts.

Polymorphic CoSe2 with mixed orthorhombic and cubic phases for highly efficient hydrogen evolution reaction.

We report polymorphic CoSe2 (p-CoSe2) with mixed orthorhombic and cubic phases as a highly active electrocatalyst toward hydrogen evolution reaction (HER). The p-CoSe2 is obtained by calcining CoSex via electrodeposition at 300 °C. The results of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) demonstrated the crystal structure of p-CoSe2. The p-CoSe2 exhibits excellent electrocatalytic activity for HER with a low onset overpotential of -70 mV and a small Tafel slope of ∼30 mV/decade, which are basically state-of-the-art performance of earth-abundant electrocatalysts. The HER performance of p-CoSe2 was much higher than that of amorphous CoSex, cubic CoSe2, and CoSe. This study offers a competitive electrocatalyst for HER and opens up a new strategy to the synthesis of catalysts for energy conversion.