Stability For Hydrogen Evolution Reaction Research Articles

Carbide Supported Phosphides Are Superior Electrocatalysts for Hydrogen Generation Than Nanocrystalline Phosphides

Phosphides such as hexagonal nickel phosphide (Ni2P) and carbides such as hexagonal Fe2N type molybdenum carbide (Mo2C) have been extensively explored as efficient and stable hydrogen evolution reaction (HER) catalysts in both acid and base electrolytes. To a lesser extent, they have also been investigated as oxygen evolution reaction (OER) catalysts in alkaline medium in recent years. Molybdenum carbide has been shown to exhibit superior enhancement in the electrochemical activity compared to carbon materials as support for noble metal catalysts such as platinum. It has also been shown that carbon support deposited phosphides show enhanced HER and OER activities compared to nanocrystalline phosphide powders. Thus, a carbide supported nickel phosphide should show relatively enhanced electrocatalytic activities than carbon supported material as well as unsupported crystalline powders. While the two families of materials have been investigated individually, to our knowledge, there is not a report of a composite material of phosphide and carbide. Since both phosphide and carbides can form hexagonal crystal structure there is likelihood that some phosphides can be deposited on molybdenum carbide surfaces. The electrocatalytic activities of phosphides and carbides depend on the optimal adsorption and desorption energies of hydrogen and hydrogen ion species for the reaction to proceed efficiently. Formation of composite electrocatalysts is postulated to give rise to superior catalyst sites. This presentation will investigate the structural and catalytic activities of transition metal phosphide deposited on carbothermic reduction derived molybdenum carbide. Additionally, intermetallic interactions and electrochemical stabilities of the composite catalysts will be discussed.

3D multi-structural porous NiAg films with nanoarchitecture walls: high catalytic activity and stability for hydrogen evolution reaction

The design of efficient and stable electrocatalysts for hydrogen evolution reaction (HER) is essential to the sustainable hydrogen production by water electrolysis. The catalytic activity of electrocatalysts can be significantly improved by increasing the effective active area. The 3D multi-structural micro/nanoporous NiAg films with nanoarchitecture walls were directly electrodeposited by hydrogen bubble template method. The catalytic activity and durability of NiAg films for HER were studied in 6M KOH solution based on the adjustment of the surface roughness and the wettability. It was found that the walls of porous NiAg films were composed of nanoparticles and nanochannels. However, the closely arranged microparticles were only observed in the pore walls of Ni films. The thicknesses of NiAg films (>20μm) were much larger than those of Ni (7μm) and Ag film (4μm). The 3D multi-structural porous NiAg films exhibited better catalytic activity than Ni or Ag film. HER on all films was controlled by the electrochemical adsorption step of hydrogen atoms (H) to form MHads. The surface roughness of NiAg films was up to 4352 and much higher than those (32 and 273) of Ni and Ag films. Therefore, the effective active areas for H adsorption on NiAg films increased, which led to the improvement of HER activity. In addition, NiAg films possessed good long-term durability. The cell voltages of water electrolysis on NiAg films were much lower than those on Ni and Ag films. It was ascribed to high catalytic activity and rapid bubble separation on 3D micro/nanoporous NiAg films.

Efficient and stable MoS2 catalyst integrated on Si photocathodes by photoreduction and post-annealing for water splitting

MoS2 has been studied as an efficient and cheap hydrogen evolution reaction (HER) catalyst; however, its effective integration with a photocathode remains a challenge. Here, crystalline MoS2 catalyst was deposited on top of a ∼2 nm Al2O3 protected n+p-Si photocathode using a simple photoreduction method following a post-annealing. The amount of MoS2 is optimized for HER of the photocathode, balanced between its catalytic effect and light absorption. High efficiency with 0.35 V onset potential vs. reversible hydrogen electrode and 34.5 mA/cm2 saturated photocurrent and high stability after 2 min ultrasonication or under 40 h continuous HER were observed. Such properties are much superior to the corresponding photocathodes coated by the traditional electrodeposited amorphous MoS2. Furthermore, the MoS2 layer is also an effective support for Pt nanoparticles with considerable reduction in the Pt amount while keeping the photoelectrochemical reactivity. This study indicates that the cheap-made MoS2 can be an efficient and stable HER catalyst for the Si photocathode.

MoS2 Nanosheet Assembling Superstructure with a Three-Dimensional Ion Accessible Site: A New Class of Bifunctional Materials for Batteries and Electrocatalysis

The layered molybdenum disulfide (MoS2) nanostructured materials are of great interest for electrochemical energy storage and conversion and electrocatalytic water splitting. However, they still exhibit very limited performance because of their limited active sites. To create more efficient MoS2 materials, herein, we develop a simple yet efficient approach to a unique column-like MoS2 superstructure composed of edge-terminated MoS2 nanosheets (CLET MoS2). These MoS2 nanosheets as building blocks with fully exposed active edges are oriented in a preferred manner, rendering CLET MoS2 that exhibits excellent electrochemical performance in both lithium ion storage and hydrogen evolution reaction (HER). Compared with that of commercial MoS2, these hierarchical MoS2 superstructures possess much higher specific capacity and superior cycling performance for lithium ion storage and excellent electrocatalytic activity and stability for HER with a very low Tafel slope of 39 mV decade–1, showing their great potential...

Amorphous flower-like molybdenum-sulfide-@-nitrogen-doped-carbon-nanofiber film for use in the hydrogen-evolution reaction

A novel amorphous flower-like molybdenum sulfides@nitrogen doped carbon nanofibers (MoSx@NCNFs) films are successfully synthesized by combining electrospinning, carbonization and a mild hydrothermal process. NCNFs, as a conductive substrate, can accelerate the electron transfer rate and depress the aggregation of MoSx nanoparticles. The resultant amorphous flower-like MoSx on NCNFs exposes abundant S2−/S22− active edge sites which is of great importance for hydrogen evolution reaction (HER) catalytic performance. Electrochemical measurements demonstrate the superior electrocatalytic activity of MoSx@NCNFs toward HER deriving from the synergistic effect between NCNFs and amorphous MoSx. The overpotential is only 137mV to reach the current density of 10mAcm−2 with a Tafel slope of 41mVdecade−1 at MoSx@NCNFs. Meanwhile, MoSx@NCNFs exhibits satisfactory long-time stability for HER. Noteworthy, the obtained composites show a free-standing structure which can be directly used as electrode materials. This work provides a feasible way to design promising noble-metal free electrocatalysts in the aspect of energy conversion.

A highly efficient and stable biphasic nanocrystalline Ni–Mo–N catalyst for hydrogen evolution in both acidic and alkaline electrolytes

The hydrogen evolution reaction (HER) is of critical importance for sustainable hydrogen production from water electrolysis. In this work, we report a highly efficient and stable noble metal free HER catalyst, which is composed of homogeneously distributed metallic Ni and NiMo4N5 nanocrystals. The biphasic nanocrystalline Ni–Mo–N catalyst shows very low overpotential (53mV in 0.5M H2SO4 and 43mV in 1M KOH, at current density 20mA/cm2) and good stability for HER in both acidic and alkaline electrolytes, which is a promising low cost alternative for platinum based HER catalysts.

Highly efficient hydrogen evolution over Co(OH)2 nanoparticles modified g-C3N4 co-sensitized by Eosin Y and Rose Bengal under Visible Light Irradiation

In this work, non-noble metal cobalt hydroxide nanoparticles [Co(OH)2 NPs] implanted uniformly on graphitic carbon nitride (g-C3N4) as a co-catalyst for hydrogen evolution reaction (HER) by in-situ chemical deposition method were reported. After co-sensitized by Eosin Y (EY) and Rose Bengal (RB) dyes, this photocatalyst exhibited a comparatively low onset potential (0.26V) for HER and high photocatalytic HER activity under visible light irradiation. The g-C3N4 not only provided a large area and nanoporous structure for the confined growth of Co(OH)2 NPs, but also greatly facilitated EY and RB (ER) molecules assembling on its surface, which promoted the charge transfer from dye to co-catalyst. The PL spectra and lifetime test showed the strong interaction between Co(OH)2 NPs and g-C3N4 could enhance the transferr rate of the photogenerated electron to reduce the carries recombination. About 431.9μmol of hydrogen generated over ER co-sensitized Co(OH)2/C3N4 in 3h. The apparent quantum efficiencies (AQE) of 29.6 and 27.3% were achieved at 520nm and 550nm over Co(OH)2/C3N4, respectively. In addition, this co-sensitized photocatalyst showed satisfied stability for HER, no remarkable decay of activity was observed in 900min reaction. These results imply that Co(OH)2 is a stable and efficient cheaper co-catalyst for photo-HER.

Nanostructured Amorphous Nickel Boride for High‐Efficiency Electrocatalytic Hydrogen Evolution over a Broad pH Range

AbstractA fruitful paradigm in the development of low‐cost and efficient water splitting systems for hydrogen generation is to search the highly active non‐noble catalysts towards hydrogen evolution reaction (HER). Here, the electrocatalytic HER activity of nanostructured amorphous nickel boride (Ni−B) alloy has been investigated. Amorphous Ni−B has exhibited excellent catalytic efficiency and long‐term stability for HER over a broad pH range, which is actually comparable to the performance of Pt. This high catalytic activity is due to the amorphous structure and the moderate electron structure of Ni−B. The Ni−B catalyst is easily obtained via electroless plating technique and we could get a supported Ni−B catalyst on desired substrates. Given the low cost, abundance, corrosion resistance, high efficiency and ease of fabrication, amorphous Ni−B is among the best alternatives to noble metal hydrogen evolution catalysts for water splitting.

P doped molybdenum dioxide on Mo foil with high electrocatalytic activity for the hydrogen evolution reaction

P doped MoO2 nanoparticle films on Mo foil used as electrodes for an efficient and stable electrocatalytic hydrogen evolution reaction (HER).

Two-dimensional TaC nanosheets on a reduced graphene oxide hybrid as an efficient and stable electrocatalyst for water splitting

A novel highly active and stable HER catalyst containing two-dimensional TaC nanosheets hybridized with reduced graphene oxide (2D TaC-RGO) was prepared as an efficient and stable hydrogen evolution reaction catalyst.

Palladium nanoparticles supported on graphene as an efficient electrocatalyst for hydrogen evolution reaction

A nanocomposite with Pd nanoparticles deposited on graphene is prepared through a facile and low cost approach. The Pd-graphene nanocomposite was easily synthesized using dip coating method on glassy carbon electrode (GCE). The resulting Pd-graphene nanocomposite was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). SEM indicates the formation of Pd nanoparticles with sizes in the range of 40–80 nm on graphene. Also, the behavior of as-prepared Pd-graphene nanocomposite as electrocatalyst for hydrogen evolution reaction (HER) was investigated by cyclic voltammetry in 0.5 M H2SO4. Pd-graphene nanocomposite shows an enhanced catalytic activity toward HER than Pd and graphene. These results demonstrate that graphene is an excellent support material for Pd nanoparticles. It was observed that the current density of Pd-graphene nanocomposite had a little decrease after continues 500 cycling, which shows the catalyst presents high stability in the recycling process. Furthermore, the chronoamperometric method confirmed that the fabricated catalyst has good stability for HER. The good catalytic activity suggests that the Pd-graphene nanocomposite can be a promising electrocatalyst in hydrogen production process.

Constructing holey graphene monoliths via supramolecular assembly: Enriching nitrogen heteroatoms up to the theoretical limit for hydrogen evolution reaction

Carbocatalysts with low cost and high stability are highly desirable to substitute expensive Pt-based materials for electrocatalysis. High conductivity, highly porous structure and high concentration of dopants are essential for efficient metal-free carbon-based electrocatalysts. Herein, a facile method was utilized to fabricate nitrogen-rich holey graphene monoliths (Nr-HGM) from cheap molecules and ammonium sulfate with the nitrogen content close to the upper limit of nitrogen-doped carbons. Our sample showed relatively high electrochemical catalytic activity and stability for hydrogen evolution reaction (HER) in both acid and base electrolytes, surpassing state-of-the-art metal-free HER catalysts in the literature.

Fabricated of bimetallic Pd/Pt nanostructure deposited on copper nanofoam substrate by galvanic replacement as an effective electrocatalyst for hydrogen evolution reaction

The effective Pd/Pt bimetallic nanofoam catalyst (Pd/Pt NFC) was fabricated on Cu nanofoam substrate. The substrate was electrochemically prepared by copper reduction and covered with Pd/Pt NFC by galvanic replacement reaction in aqueous solutions of Pd (II) and Pt (IV). The catalyst was characterized by SEM, EDX, ICP-OES and EIS techniques. It was tested for the hydrogen evolution reaction (HER) in the acidic media by linear sweep voltammetry (LSV). Among of various compositions, Pd65Pt35 catalyst showed better performance in comparison with pure Pt NFC for HER. The mass activity of noble metals on the Pt NFC and Pd65Pt35 NFC, at the same potential of −300 mV vs. NHE, were about 3.21 mA μg−1Pt and 4.98 mA μg−1Pt+Pd, respectively. Consequently, proposed catalyst increased HER activity about 1.5 times and decreases Pt loading on the surface and cost of catalyst. The obtained results show that the Volmer-Heyrovsky mechanism controls the HER. The fabricated catalyst showed a good stability for HER by chronoamperometric method.

Immobilization of Pt Nanoparticles in Carbon Nanofibers: Bifunctional Catalyst for Hydrogen Evolution and Electrochemical Sensor

A facile strategy for the preparation of novel Pt nanoparticles/carbon nanofibers (PtNPs/CNFs) nanostructure by combining the electrospinning and carbonization process is demonstrated. PtNPs were obtained in polyacrylonitrile nanofibers (PANFs) through an in situ reduction as well as electrospinning, and then the PtNPs/PANFs nanostructure was converted to PtNPs/CNFs following a carbonization process. The formation and structure of the synthesized PtNPs/CNFs nanostructure were systematically characterized, suggesting that PtNPs with diameter of ca. 8.8nm were evenly dispersed in CNFs and nearly no aggregation was observed. The results indicate that the nanostructure possesses high catalytic activity for both hydrogen evolution reaction (HER) and electrochemical sensor, as well as long-term stability for HER, serving as a bifunctional catalyst. The present investigations provide a general route for the fabrication of novel electrocatalyst, which may also be extended to synthesize other metal nanoparticles/CNFs nanostructures.

In situ cobalt-cobalt oxide/N-doped carbon hybrids as superior bifunctional electrocatalysts for hydrogen and oxygen evolution.

Remarkable hydrogen evolution reaction (HER) or superior oxygen evolution reaction (OER) catalyst has been applied in water splitting, however, utilizing a bifunctional catalyst for simultaneously generating H2 and O2 is still a challenging issue, which is crucial for improving the overall efficiency of water electrolysis. Herein, inspired by the superiority of carbon conductivity, the propitious H atom binding energy of metallic cobalt, and better OER activity of cobalt oxide, we synthesized cobalt-cobalt oxide/N-doped carbon hybrids (CoOx@CN) composed of Co(0), CoO, Co3O4 applied to HER and OER by simple one-pot thermal treatment method. CoOx@CN exhibited a small onset potential of 85 mV, low charge-transfer resistance (41 Ω), and considerable stability for HER. Electrocatalytic experiments further indicated the better performance of CoOx@CN for HER can be attributed to the high conductivity of carbon, the synergistic effect of metallic cobalt and cobalt oxide, the stability of carbon-encapsulated Co nanoparticles, and the introduction of electron-rich nitrogen. In addition, when used as catalysts of OER, the CoOx@CN hybrids required 0.26 V overpotential for a current density of 10 mA cm(-2), which is comparable even superior to many other non-noble metal catalysts. More importantly, an alkaline electrolyzer that approached ∼20 mA cm(-2) at a voltage of 1.55 V was fabricated by applying CoOx@CN as cathode and anode electrocatalyst, which opened new possibilities for exploring overall water splitting catalysts.

Synthesis of nanostructured clean surface molybdenum carbides on graphene sheets as efficient and stable hydrogen evolution reaction catalysts.

Small size molybdenum carbides (2.5 nm for MoC and 5.0 nm for Mo2C) with clean surface on graphene were prepared for efficient and stable hydrogen evolution reaction catalysts.

Cobalt diselenide nanobelts grafted on carbon fiber felt: an efficient and robust 3D cathode for hydrogen production.

Design and fabrication of low-cost, highly efficient and robust three-dimensional (3D) hierarchical structure materials for electrochemical reduction of water to make molecular hydrogen is of paramount importance for real water splitting applications. Herein, a 3D hydrogen evolution cathode constructed by in situ growing of cobalt diselenide nanobelts on the surface of commercial carbon fiber felt shows exceptionally high catalytic activity with 141 mV overpotential to afford a current density of 10 mA cm-2, and a high exchange current density of 5.9 × 10-2 mA cm-2. Remarkably, it also exhibits excellent catalytic stability, and could be used for more than 30 000 potential cycles with no decrease in the current density in 0.5 M H2SO4. This easily prepared 3D material with excellent electrocatalytic performance is promising as a realistic hydrogen evolution electrode.

Multiple Phases of Molybdenum Carbide as Electrocatalysts for the Hydrogen Evolution Reaction

AbstractMolybdenum carbide has been proposed as a possible alternative to platinum for catalyzing the hydrogen evolution reaction (HER). Previous studies were limited to only one phase, β‐Mo2C with an Fe2N structure. Here, four phases of Mo‐C were synthesized and investigated for their electrocatalytic activity and stability for HER in acidic solution. All four phases were synthesized from a unique amine–metal oxide composite material including γ‐MoC with a WC type structure which was stabilized for the first time as a phase pure nanomaterial. X‐ray photoelectron spectroscopy (XPS) and valence band studies were also used for the first time on γ‐MoC. γ‐MoC exhibits the second highest HER activity among all four phases of molybdenum carbide, and is exceedingly stable in acidic solution.

Multiple phases of molybdenum carbide as electrocatalysts for the hydrogen evolution reaction.

Molybdenum carbide has been proposed as a possible alternative to platinum for catalyzing the hydrogen evolution reaction (HER). Previous studies were limited to only one phase, β-Mo2C with an Fe2N structure. Here, four phases of Mo-C were synthesized and investigated for their electrocatalytic activity and stability for HER in acidic solution. All four phases were synthesized from a unique amine-metal oxide composite material including γ-MoC with a WC type structure which was stabilized for the first time as a phase pure nanomaterial. X-ray photoelectron spectroscopy (XPS) and valence band studies were also used for the first time on γ-MoC. γ-MoC exhibits the second highest HER activity among all four phases of molybdenum carbide, and is exceedingly stable in acidic solution.

HER Catalytic Activity of Electrodeposited Ni‐P Nanowires under the Influence of Magnetic Field

Nickel alloy electrodes both in plane and nanowire morphologies were fabricated by electrodeposition in sulfamate bath. With the increasing concentration of phosphorous acid in the electrolyte, the P content in the deposition increased accordingly. In the meantime, the grain refined and even became amorphous in microstructure as the P content was raised. For the nanowire electrode, vibrating sample magnetometer (VSM) measurement showed that its coercivity was anisotropic and decreased with P‐content. In addition, the easy axis for magnetization of the electrode was parallel to the axial direction of nanowire. The electrocatalytic activity measurement of the electrode in 0.5 M H2SO4 electrolyte showed that the nanowire electrode had higher activity than the plane one, and the alloying of P in Ni electrode raised its hydrogen evolution reaction (HER) performance. The enhanced performance of nanowire electrode was attributed to the smaller and more uniform hydrogen bubbles generated in HER reaction. Finally, the applied magnetic field (3.2 T) improved significantly the HER activity of Ni but not Ni‐P electrode. By using nanowire morphology and applying magnetic field, the current density at −0.75 V HER stability test of the Ni electrode increased fourfold more than its plane counterpart.