Superior Hydrogen Evolution Reaction Activity Research Articles

Fe@Fe2P Core‐Shell Nanorods Encapsulated in Nitrogen Doped Carbon Nanotubes as Robust and Stable Electrocatalyst Toward Hydrogen Evolution

AbstractHere, we report an efficient hydrogen evolution reaction (HER) electrocatalyst (Fe@Fe2P/NCNT) fabricated from the phosphorization of partially oxidized iron nanorod encapsulated in nitrogen doped carbon nanotubes (Fe@Fe2O3/NCNT) synthesized from iron trichloride and melamine, which only requires ∼0 mV and 78.2 mV overpotentials to achieve cathodic current densities of 1 mA cm−2 and 10 mA cm−2 with Tafel slope of 52.2 mV dec−1 in acidic media, which exhibits higher HER electrocatalytic activity compared to Fe/NCNT requiring a overpotential of 118.5 mV to attain 10 mA cm−2 with Tafel slope of 92.3 mV dec−1. Due to the phosphorization process, additional active sites coming from Fe2P boost the electrocatalytic activity of Fe@Fe2P/NCNT resulting in decrement in overpotentials by 40.3 mV and 186 mV for 10 mA cm−2 and 50 mA cm−2 compared to Fe/NCNT electrocatalyst, respectively. Meanwhile, Fe@Fe2P/NCNT exhibits ignorable degradation in HER activity after 6000 potential cycles suggesting that the Fe@Fe2P/NCNT with superior HER activity and stability could potentially replace the benchmark Pt/C (overpotential@10 mA cm−2: 31 mV) as efficient HER electrocatalyst for water splitting.

Structure, stability, electronic, magnetic, and catalytic properties of monometallic Pd, Au, and bimetallic Pd-Au core-shell nanoparticles.

Bimetallic core-shell nanoparticles (CSNPs) often exhibit excellent and tunable properties, depending on their composition, sizes, morphology, atomic arrangement, thickness, and sequence of both core and shell. In this study, the geometrical structure, thermodynamic stability, chemical activity, electronic and magnetic properties, and catalytic activity in the hydrogen evolution reaction (HER) of 13- and 55-atom Pd, Au NPs, and Pd-Au CSNPs were systematically investigated using density functional theory calculations. The results showed that Au atoms prefer to segregate to the surface-shell, while Pd atoms were inclined to aggregate in the core region for bimetallic Pd-Au CSNPs; therefore, Pd@Au CSNPs with an Au surface-shell were thermodynamically more favorable than both the monometallic Pd/Au NPs and the Au@Pd CSNPs with a Pd surface-shell. The Pd surface-shell of the Au@Pd CSNPs displayed a positive charge, while the Au surface-shell of the Au@Pd CSNPs exhibited a negative charge due to the charge transfer in the Pd-Au CSNPs, resulting in that the d-band center of Au@Pd with the Pd surface-shell showed larger shift toward the Fermi level and higher chemical activity. The Pd@Au CSNPs with the Au surface-shell showed similar d-band curves and d-band centers with monometallic Au NPs. All 13-atom Pd, Au NPs, and Pd-Au CSNPs were magnetic, while the 55-atom NPs were non-magnetic with symmetry partial density of states' curves except for Pd55. Changing the location of Pd and Au atoms in the Pd-Au CSNPs influenced their total magnetic moments. In addition, an opposite trend was found: small 13-atom NPs with a Pd surface-shell showed superior HER activity to the ones with an Au surface-shell, while large 55-atom NPs with an Au surface-shell possessed higher HER activity than the ones with a Pd surface-shell.

Metallic FePSe3 nanoparticles anchored on N-doped carbon framework for All-pH hydrogen evolution reaction

The present nonprecious hydrogen evolution electrocatalysts deliver high activity either in acid or alkaline media, indicating the urgent demand for development of pH-universal catalysts. In this work, we report a high-performance electrcatalyst based on ternary iron phosphoselenide (FePSe3) nanoparticles anchored on N-doped carbon framework for hydrogen evolution reaction (HER) in acidic, neutral and basic media. The FePSe3 nanoparticles with metallic nature enable to fully utilize accessible edge sites, and the highly open yet interconnected three-dimensional framework creates large surface area, exposing abundant active sites and providing convenient charge/ionic diffusion pathway. DFT calculations reveal the synergistic electronic interaction between Se and P, leading to optimal electronic structures and hydrogen adsorption free energy on Fe, P and Se sites, thus facilitating HER kinetics. As a result, the obtained FePSe3/NC exhibits superior HER activities with low overpotentials of 70, 140.1 and 118.5 mV to afford 10 mA cm−2 current density in acidic, neutral and basic media, as well as robust stability in all-pH range. This work highlights the dual-anion effect to radically construct all-pH HER electrocatalysts.

(Keynote) One-Pot Synthesis of Manganese Oxides and Cobalt Phosphides Nanohybrids with Abundant Hetero-Interfaces in Amorphous Matrix for Efficient Hydrogen Evolution in Alkaline Solution

Transition metal phosphides (TMPs), albeit promising as hydrogen evolution reaction (HER) catalysts, suffer from the sluggish water dissociation step in alkaline solution, and metal oxides(hydroxides) have been employed to address this problem. However, limited active interface between metal oxides(hydroxides) and phosphides was achieved, leading to unsatisfactory catalytic efficiencies. Therefore, it is still a key challenge to develop a facile way to synthesize the hybrid catalyst of transition metal oxide/phosphide with numerous nanointerfaces. Herein, we report a highly efficient HER catalyst of manganese oxides and cobalt phosphides nanohybrids nanosheets array (denoted as Mn-O@Co-P) with numerous nano-heterointerfaces, facilely grown on carbon cloth (CC) by a simple one-pot process for the first time. The obtained Mn-O@Co-P/CC shows superior activity for HER in alkaline solution with a low overpotential of 96 mV at 10 mA cm-2, a small Tafel slope of 56 mV dec-1 and excellent long-term durability. This work offers a promising one-pot method to synthesize hybrid materials with abundant hetero-nanointerfaces, which is proved to be the powerful strategy for constructing efficient HER catalysts in alkaline solution.

Defect-rich MoSx/carbon nanofiber arrays on carbon cloth for highly efficient electrocatalytic hydrogen evolution

Engineering MoS2 catalysts with more active sites and higher conductivity is an effective way to improve its electrochemical activity. Herein, defect-rich amorphous MoSx/carbon nanofiber (CF) arrays on carbon cloth (CC) support (denoted as MoSx/CF/CC) was designed and fabricated, which served as an efficient free-standing electrocatalyst for hydrogen evolution reaction (HER) in acid media. This architecture was beneficial to expose more active catalytic sites and improve the electron/ion transport. In addition, abundant defects altered preferred growth direction of MoSx, resulting in the formation of irregular MoSx particles at the surface of CF arrays. The as-synthesized MoSx/CF/CC-2 exhibited excellent stability and superior HER activity, with a small onset overpotential (107 mV) and low Tafel slope (51 mV dec−1). Such excellent electrochemical performance was attributed to the enriched active sites and shortened charge diffusion distance. This work would pave a new way for rational design and fabrication of defect-rich MoSx-based composite electrode for renewable energy applications.

Nickel cobalt phosphide with three-dimensional nanostructure as a highly efficient electrocatalyst for hydrogen evolution reaction in both acidic and alkaline electrolytes

Transition metal phosphides (TMPs) are promising candidates for noble metal free electrocatalysts in water splitting applications. In this work, we present the facile synthesis of nickel cobalt phosphide electrocatalyst with three-dimensional nanostructure (3D-NiCoP) on the nickel foam, via hydrothermal reaction and phosphorization. The as-prepared electrocatalyst exhibits an excellent activity for hydrogen evolution reaction (HER) in both acidic and alkaline electrolytes, with small overpotentials to drive 10 mA/cm2 (80 mV for 0.5 M H2SO4, 105 mV for 1 M KOH), small Tafel slopes (37 mV/dec for 0.5 M H2SO4, 79 mV/dec for 1 M KOH), and satisfying durability in long-term electrolysis. 3D-NiCoP also shows a superior HER activity compared to single metal phosphide, such as cobalt phosphide and nickel phosphide. The outstanding performance for HER suggests the great potential of 3D-NiCoP as a highly efficient electrocatalyst for water splitting technology.

Encapsulation of Ni3Fe Nanoparticles in N‐Doped Carbon Nanotube–Grafted Carbon Nanofibers as High‐Efficiency Hydrogen Evolution Electrocatalysts

AbstractThe exploration of cost‐effective yet high‐efficiency inexpensive electrocatalysts for the hydrogen evolution reaction (HER) is of critical significance for future renewable energy conversion technologies. A feasible electrospinning strategy to construct a novel 1D hierarchical nanoarchitecture comprising Ni3Fe nanoalloy‐encapsulated carbon nanotubes grown onto N‐doped carbon nanofibers (abbreviated as Ni3Fe@N‐C NT/NFs) is demonstrated here. Benefiting from the abundant firmly immobilized Ni3Fe nanoparticles for catalytic sites and hierarchical fibrous nanostructures for effective electron transport and mass diffusion, the resultant Ni3Fe@N‐C NT/NFs display an extraordinary HER activity with a low overpotential of 72 mV to reach a current density of 10 mA cm−2 in KOH medium and a remarkable stability for 40 000 s. Theoretical studies corroborate that the resultant Ni3Fe@N‐C NT/NFs exhibit a favorable Gibbs free energy of hydrogen adsorption (ΔGH* = −0.14 eV), further manifesting their superior HER activity. The present work will advance the development of highly efficient nonprecious electrocatalysts for energy conversion.

Phase‐Controlled Synthesis of 1T‐MoSe2/NiSe Heterostructure Nanowire Arrays via Electronic Injection for Synergistically Enhanced Hydrogen Evolution

AbstractThe crystal phase significantly affects the properties and functions of molybdenum dichalcogenides (MoX2). Phase‐engineered synthesis is challenging for constructing metallic‐phase 1T‐MoX2 for better electrocatalysis than their semiconducting counterparts. Here, 1T‐MoSe2 nanosheet arrays are successfully prepared on metallic NiSe nanowires to couple the synergistic effects of efficient hydrogen formation and water dissociation for hydrogen evolution reaction (HER). Systematic investigations reveal that the electronic injection from NiSe to MoSe2 induces the phase transition from 2H‐ to metallic 1T‐phase. Benefiting from the phase engineering for enhancing intrinsic activity, the heterostructure for synergistically boosting water dissociation—as well as hierarchical 3D catalyst configuration for abundant active sites, efficient electron transport and mass transfer—the obtained shell/core 1T‐MoSe2/NiSe exhibits superior HER activity and durability. Such a strategy paves a new way for fabricating various 1T‐MoX2‐based heterostructures for diverse applications.

Ultralow Overpotential of Hydrogen Evolution Reaction using Fe‐Doped Defective Graphene: A Density Functional Study

AbstractWe report great promises of single (transition metal) atom catalysts (SACs) anchored to single‐ and double‐ vacancy sites of the defective graphene structures for hydrogen evolution reaction (HER). Among 120 candidates with all 3d, 4d, and 5d‐block transition metals considered, the inexpensive Fe‐based SAC catalyst shows a theoretical overpotential of 5 mV, the lowest value reported to date theoretically or experimentally. With the help of various electronic structural analysis, we reveal that the key to the observed superior HER activity of Fe‐based SAC is the enhanced ionicity of bonding between hydrogen and the corresponding SAC and the lack of ensemble effect that causes the *H binding weaker to be nearly at the top of the HER activity volcano.

Catalytically enhanced thin and uniform TaS2 nanosheets for hydrogen evolution reaction

Though the transition-metal dichalcogenides (TMDs) were proven to have a better performance on the hydrogen evolution reaction (HER), the bulk production of active TMD materials remains a challenging work. This report overcomes those barriers by showing a simple procedure to synthesize TaS2 nanosheets through modifying the arc discharge process. The usage of chloride as the transporting agent reduces the growth period of the formed TaS2 with active edge sites. TaS2 is found to have a uniform thickness (4 nm) with high crystallinity and adopt a 2H polytype (double-layered hexagonal) structure. The as-synthesized TaS2 has superior activity for HER with the potential of 280 mV.

Efficient hydrogen evolution performance of phase-pure NiS electrocatalysts grown on fluorine-doped tin oxide-coated glass by facile chemical bath deposition

The production of hydrogen, the future fuel, on stable, efficient, and robust electrocatalysts represents an attractive approach for the conversion and storage of carbon-free energy resources. In this study, earth-abundant nickel sulfide (NiS) electrocatalyst were grown on fluorine-doped tin oxide (FTO) substrate by a simple and cost-effective chemical bath deposition for hydrogen evolution reaction (HER). Energy dispersive X-ray analysis and X-ray photoelectron spectra indicated the presence of highly pure NiS. The HER performance of the catalyst was examined in alkaline solution (1.0 M NaOH; pH = 13.5). Notably, NiS film prepared at 100 °C demonstrated superior HER activity with an overpotential of 290 mV to afford a current density of 10 mA/cm2 and a Tafel slope of 143.4 mV/dec which are among the promising results obtained for sulfide-based HER electrocatalysts. The catalyst exhibited 100% faradaic efficiency and electrochemical stability which indicate its potential as noble-metal-free HER electrocatalyst.

Two-Dimensional MoS2 Confined Co(OH)2 Electrocatalysts for Hydrogen Evolution in Alkaline Electrolytes.

The development of abundant and cheap electrocatalysts for the hydrogen evolution reaction (HER) has attracted increasing attention over recent years. However, to achieve low-cost HER electrocatalysis, especially in alkaline media, is still a big challenge due to the sluggish water dissociation kinetics as well as the poor long-term stability of catalysts. In this paper we report the design and synthesis of a two-dimensional (2D) MoS2 confined Co(OH)2 nanoparticle electrocatalyst, which accelerates water dissociation and exhibits good durability in alkaline solutions, leading to significant improvement in HER performance. A two-step method was used to synthesize the electrocatalyst, starting with the lithium intercalation of exfoliated MoS2 nanosheets followed by Co2+ exchange in alkaline media to form MoS2 intercalated with Co(OH)2 nanoparticles (denoted Co-Ex-MoS2), which was fully characterized by spectroscopic studies. Electrochemical tests indicated that the electrocatalyst exhibits superior HER activity and excellent stability, with an onset overpotential and Tafel slope as low as 15 mV and 53 mV dec-1, respectively, which are among the best values reported so far for the Pt-free HER in alkaline media. Furthermore, density functional theory calculations show that the cojoint roles of Co(OH)2 nanoparticles and MoS2 nanosheets result in the excellent activity of the Co-Ex-MoS2 electrocatalyst, and the good stability is attributed to the confinement of the Co(OH)2 nanoparticles. This work provides an imporant strategy for designing HER electrocatalysts in alkaline solutions, and can, in principle, be expanded to other materials besides the Co(OH)2 and MoS2 used here.

3D CVD Graphene Oxide on Ni Foam towards Hydrogen Evolution Reaction in Acid Electrolytes at Different Concentrations

Thin layers of graphene and graphene oxide coated on nickel foam substrate was synthesized by a chemical vapor deposition method and used as a hydrogen evolution reaction (HER) catalyst in acidic condition. The graphene oxide carbocatalyst with oxygen functional groups, large amounts of active sites, and hydrophilic property exhibits superior HER activity as compared to the pristine nickel foam and graphene. The graphene oxide coated on nickel substrate exhibits an overpotential of -83.2 mV vs. RHE at a current density of 10 mA cm- 2 and an excellent electrochemical stability up to 7 hours in 1.0 M H2SO4. In addition, the effect of electrolyte concentrations was also studied in 0.1, 0.5, 1.0, and 2.0 M H2SO4. At high concentration, the HER activity is higher because large amounts of protons can increase the ionic conductivity in the electrolyte and can participate in the reaction generating more hydrogen when compared to the lower concentration. We believe that the graphene oxide-coated Ni electrode, which can be operated in an acidic environment, can be practically used as an alternative electrocatalyst towards HER.

Nanostructured nickel ferrite embedded in reduced graphene oxide for electrocatalytic hydrogen evolution reaction

A non-noble metal electrocatalyst, nickel ferrite (NFO) having average particle size of 10.5 nm embedded onto the reduced graphene oxide (RGO) sheet, has been developed towards hydrogen evolution reaction (HER) in acidic medium. The phase purity and chemical coupling of NFO with RGO are established through X-ray diffraction, Raman and X-ray photoelectron spectroscopy studies. The NFO/RGO catalyst exhibits superior HER activity than bare NFO and other reported catalysts such as sulfides, carbides, phosphides, bimetals of molybdenum and iron-cobalt. A low onset overpotential of 5 mV (vs. RHE) with high cathodic current density, low Tafel slope of 58 mV dec−1, low charge transfer resistance of 10.2 Ω, 99% Faradaic efficiency and turnover frequency of 0.48 s−1 is obtained by virtue of mixed valent states of Fe, high specific surface area (109 m2 g−1), excellent coupling between NFO and the RGO sheet creating oxygen vacancy.

Facile air oxidative induced dealloying of hierarchical branched PtCu nanodendrites with enhanced activity for hydrogen evolution

In this work, we utilized a facile air oxidative dealloying approach to synthesize PtCu hierarchical branched nanodendrites (HBNDs). The systematical investigation on the morphology, composition, and structure of PtCu HBNDs by various techniques demonstrates they are three-dimensional open porous nanostructures. The PtCu HBNDs show composition-dependent catalysis in hydrogen evolution reaction (HER). The Pt1Cu1.03-D with average size about 40 nm composed of integrated ultrathin branches, presents the highest HER activity with only 20 mV overpotential to achieve 10 mA/cm2, 19.34 A/mgPt and 9.64 mA/cm2 in mass and specific activity at −0.2 V, and excellent durability. The superior HER activity is attributed to the unique porous dendritic structure and electronic synergistic interactions between Pt and Cu as indicated by X-ray photoelectron spectroscopy and density functional theory calculation. This work opens up a new facile route to design large accessible surface and high-performance electrocatalysts with low utilization of Pt for electrochemical energy conversion.

Trace Amount of Platinum Supported on Carbonized Biomorphic Wood for Efficient Electrochemical Hydrogen Evolution in Alkaline Condition

AbstractCarbonized biomorphic wood (Bio‐C), which features unique properties such as highly ordered microtexture, well‐developed porous structure, and low charge transfer resistance, was prepared as a promising scaffold with trace amount of platinum (Pt) supported to efficiently electrocatalyze hydrogen evolution reaction (HER). Pt/Bio‐C nanocomposites demonstrated superior HER activity with a current density reaching as high as ∼58 mA cm−2 at −0.2 V vs. reversible hydrogen electrode (RHE) in strongly alkaline condition.

Cellulose nanocrystals (CNC) derived Mo2C@sulfur-doped carbon aerogels for hydrogen evolution

Hydrogen evolution reaction (HER), is considered as an ideal alternative approachs to settle the energy crisis. Therefore, we need to explore efficient and stable non-Pt-based electrocatalysts for hydrogen production from water electrolysis. In this work, S-doped ultrafine molybdenum carbide anchored on cellulose nanocrystals (CNC) derived carbon composite aerogels (Mo2C@S-CA) were synthesized for HER by a simple one-step carbonization method, utilizing inorganic-organic hybrid ammonium molybdate/CNC (AMM/CNC) as precursor. The obtained Mo2C@S-CA aerogels can not only provide plenty of active sites, but also accelerate the hydrogen release from the reaction surface of the electrocatalysts. The as-synthesized catalysts exhibit superior HER activity with a small overpotential value of 176 mV vs. RHE at 10 mA cm−2 and excellent long-term stability after 10,000 cycles in 0.5 M H2SO4. These superb properties make the catalyst be a promising electrocatalyst for the HER. This work highlights the importance of biomass-derived multifunctional value-added composite aerogels in enhancing the electrolysis of water.

Ultrafine and Ligand-Free Precious Metal (Ru, Ag, Au, Rh and Pd) Nanoclusters Supported on Phosphorus-Doped Carbon.

We report the use of phosphorus-doped carbon (P-C) as support to grow ultrasmall (1-3 nm) and ligand-free precious metal nanocrystals (PMNCs) via chemical reduction. We show that the valence states of surface phosphorus species are critical in tuning the affinity between the carbon support and metal precursors, which rationally controls the loading size and uniformity of resultant PMNCs. Five kinds of PMNCs, including Ru, Ag, Au, Rh, and Pd, were grown in situ to demonstrate the key role of surface phosphorus sites on the P-C support. As a proof-of-concept application, Ru nanocatalysts with an average diameter of 1.0±0.2 nm supported on P-C were examined for the electrocatalytic hydrogen evolution reaction (HER). Ultrasmall and ligand-free Ru nanocatalysts exhibited superior HER activity and stability compared to its counterparts with surface agents or larger sizes. An overpotential of 27.6 mV (vs. reversible hydrogen electrode) for Ru nanocatalysts was achieved at a current density of 10 mA cm-2 . This novel method opens a new avenue to immobilize ligand-free and well-dispersed PMNCs on carbon; and, more importantly, it provides a new library of supported PMNCs with high catalytic activity.

Molybdenum Carbide Nanoparticles Coated into the Graphene Wrapping N-Doped Porous Carbon Microspheres for Highly Efficient Electrocatalytic Hydrogen Evolution Both in Acidic and Alkaline Media.

Molybdenum carbide (Mo2C) is recognized as an alternative electrocatalyst to noble metal for the hydrogen evolution reaction (HER). Herein, a facile, low cost, and scalable method is provided for the fabrication of Mo2C‐based eletrocatalyst (Mo2C/G‐NCS) by a spray‐drying, and followed by annealing. As‐prepared Mo2C/G‐NCS electrocatalyst displays that ultrafine Mo2C nanopartilces are uniformly embedded into graphene wrapping N‐doped porous carbon microspheres derived from chitosan. Such designed structure offer several favorable features for hydrogen evolution application: 1) the ultrasmall size of Mo2C affords a large exposed active sites; 2) graphene‐wrapping ensures great electrical conductivity; 3) porous structure increases the electrolyte–electrode contact points and lowers the charge transfer resistance; 4) N‐dopant interacts with H+ better than C atoms and favorably modifies the electronic structures of adjacent Mo and C atoms. As a result, the Mo2C/G‐NCS demonstrates superior HER activity with a very low overpotential of 70 or 66 mV to achieve current density of 10 mA cm−2, small Tafel slope of 39 or 37 mV dec−1, respectively, in acidic and alkaline media, and high stability, indicating that it is a great potential candidate as HER electrocatalyst.

Cobaloxime anchored MoS2 nanosheets as electrocatalysts for the hydrogen evolution reaction

Cobaloxime anchored MoS2 nanosheets.