Active Sites For Hydrogen Evolution Reaction Research Articles

Theoretical calculations and controllable synthesis of MoSe2/CdS-CdSe with highly active sites for photocatalytic hydrogen evolution

It is still of great practical significance to exploring low-cost and earth-abundant alternative materials as cocatalyst for photocatalytic hydrogen evolution. The density functional theory (DFT) calculations indicated that both the basal plane and the edge of mixed phase MoSe2 provide the highly catalytic activity for hydrogen evolution reaction (HER). Based on this, the mixed phase MoSe2 was designed as an excellent cocatalyst because of superior ability to receive electrons and optimal active sites for HER. Herein, the ternary (1T/2H) MoSe2/CdS-CdSe structure was prepared by a simple hydrothermal method. The hydrazine monohydrate as reductant helps to control 1T phase content of MoSe2, and the maximum content of 1T phase MoSe2 reaches 66.5%. The results showed that the H2 evolution rate of the optimized MoSe2/CdS-CdSe reached a value of 24.34 mmol h−1 g−1 and a high quantum efficiency (QE) of 28.5% at 500 nm. A volcano-like correlation has been presented for the first time to illustrate the effect of structures of MoSe2 on photocatalytic activity for HER, which provides the direction of design of MoSe2 cocatalyst.

Active Sites in Single-Layer BiOX (X = Cl, Br, and I) Catalysts for the Hydrogen Evolution Reaction.

Although few-layer bismuth oxyhalides (BiOX, X = Cl, Br, and I) have been shown to be appropriate for photocatalytic hydrogen production, the hydrogen evolution reaction (HER) activity of BiOX is unrevealed. Herein, the origins of catalytic activity on single-layer BiOX are investigated by using the density functional theory. The grand potential calculations show that the Bi- and BiO-terminations of single-layer BiOX are stable in O-poor and O-rich environments, respectively. The Bi- and BiO-terminations of single-layer BiOX are found to have obviously active sites for HER, whereas the (001) basal planes are inert. The Gibbs free energies for the adsorption of hydrogen atoms on the Bi- and BiO-terminations are close to the optimal value of 0 eV, indicating that single-layer BiOX possess favorable HER performances. The enhanced HER activities on the Bi- and BiO-terminations are attributed to the localized edge states around the Fermi level, which are caused by the Bi 6p-orbital density of the fringe bismuth atoms and O 2p-orbital density of the fringe oxygen atoms, respectively. The results of this work suggest that single-layer BiOX are a family of promising catalysts for water splitting.

Tungsten phosphide (WP) nanoparticles with tunable crystallinity, W vacancies, and electronic structures for hydrogen production

Tungsten phosphide (WP) has attracted increasing attention in hydrogen evolution reaction (HER) due to its unique catalytic and electronic properties. However, its high preparation temperature often leads to particle excess growth and coarsening. Although tremendous efforts have been made to enlarge the surface areas and reduce particle size, the required high preparation temperature still limits its development. Herein, a facile self-exothermic reduction strategy under an extremely low temperature (300 °C) is proposed to prepare the ultra-fine WP nanoparticles with rich W vacancies. Remarkably, as revealed by XRD, TEM, ICP-OES and XPS analysis, the crystallinity, W vacancies and electron distribution of WP can be well controlled. The W vacancies can activate the neighboring P atoms and the bridge sites as active sites for HER, but also will change the electron distribution, which in turn deteriorates the conductivity of WP. By means of controllable W vacancies, the optimized low crystalline WP catalyst with a moderate number of W vacancies can be obtained, exhibiting a superior HER activity in acidic solution with a small Tafel slope (52 mV dec−1), which are smaller than most of WP-based catalysts and among the best records. Furthermore, this work will open a new horizon for both preparation and HER performance improvement of other transition metal phosphides.

Dynamic-Stacking of Reduced Graphene Oxide for Active Hydrogen Evolution

Despite remarkable electronic and mechanical properties of graphene, improving catalytic activity of graphene, an atomically-flat, inert and stable carbon network, remains a challenging issue in both fundamental and application studies. In particular, the adsorption of most molecules and ions, including hydrogen (H2 or H+), on graphene is not favorable, underlining the challenge for efficient electrochemical catalytic reaction on graphene electrode. Various defects, edges, and functionalization have been suggested to resolve the issue aiming to have catalytic graphene, but cost-effective, clean and active catalysis with graphene has not been realized yet. Here, we introduce dynamic-stacking of reduced graphene oxide (rGO) via an electrochemical way; conventional hydrogen evolution reaction (HER) was used as a dynamic process, generating hydrogen bubbles during electrochemical deposition of rGO on metallic WTe2, which creates a unique porous rGO structure on the atomically-distorted WTe2 surface with optimized edges and surface acidic groups. The hydrogen bubble template method enables an ideal, stable carbon structure for active HER with a Tafel slope of 39 mV·dec-1 and a double layer capacitance of 12.41 mF·cm-2. As our new dynamic synthesis method improves the catalytic activity of one of the most inert materials, graphene, new strategies for designing novel catalysts could be conceived for promising energy applications. Figure 1. 1a) schematically description of the electrochemical synthesis of the rGO film on WTe2 by hydrogen bubble template method. Fig. 1b) shows the graphite and WTe2 shows poor HER activity (blue and black curve). Meanwhile, a striking HER activity is observed with our hybrid rGO-WTe2 (red curve) with a much smaller onset overpotential (vs reversible hydrogen electrode, RHE) and Tafel slope 39 mV·dec-1 (Fig. 1c). The unique HER performance of our rGO-WTe2 catalyst was investigated in terms of electrochemical surface area via double-layer capacitance (Cdl) measurements in Fig. 1d). The Cdl value was calculated by the slope of current density (at a voltage of 0.135 V vs. RHE) versus scan rate, and the value was 12.41 mF·cm-2, which is 5,000 times higher than that of state-of-the-art 3D graphene networks.[3] Fig. 1e) shows the optical microscopy image of rGO. The as-synthesized rGO on WTe2 substrate exhibits a highly porous structure in the SEM images in Fig. 1 (f-g). The characteristic dimension of the porous structure ranges from 100 nm - 2 μm in diameters with many edges exposed between rGO porous walls; the rGO flakes are stacked in a random way to have many edges as HER active sites. As HR-TEM images shown in Fig. 1 (h-i), the rGO flakes are mixed with crystal and amorphous graphene with an interlayer spacing of 0.43 nm. Keywords: hydrogen evolution reaction, hydrogen bubble template, reduced graphene oxide, tungsten ditelluride (WTe2)

The 2D nickel‑molybdenum bimetals sulfide synergistic modified hollow cubic CdS towards enhanced photocatalytic water splitting hydrogen production

The 2D(two-dimension) nickel‑molybdenum bimetals sulfide synergistic modified hollow cubic CdS is fabricated by the continuous chemical precipitation, vulcanized and hydrothermal methods, there, the hollow cubic CdS is vulcanized from the CdCO3 and then the 2D Ni-Mo-S lamellas grow on the surface of the CdS. Evaluated by the photocatalytic hydrogen production, the photocatalytic performance of the CdS/Ni-Mo-S exhibits an obvious enhancement of about ~80 folds than the single CdS. Studied by the electrochemical measurements, the main reasons for the HER(hydrogen evolution reaction) enhancement are ascribed to that the Pt-like behavior bimetals Ni-Mo-S can quickly accept and transfer-diffuse the photo-generated electrons to water, the 2D ultrathin lamellas can provide sufficient HER active sites and shorten the transferring time, and the hollow nanostructure can increase the solar utilization.

Porous interwoven CoSe2/C microsphere: a highly efficient and stable nonprecious electrocatalyst for hydrogen evolution reaction

For the first time, a porous CoSe2/C microsphere interwoven by ultrathin CoSe2 and carbon nanosheets is synthesized by a simple solvothermal method. Compared with bare CoSe2, the CoSe2/C hybrid exhibits much better performance for hydrogen evolution reaction (HER): The hybrid demonstrates a Tafel mechanism rather than the Heyrovsky mechanism of CoSe2; it has a low onset potential (− 189 mV vs RHE) and an ultra-low Tafel slope (34 mV dec−1); current density increases by more than 2.5 times at equipotential; the hybrid also exhibits remarkable long-term stability even after 1000 cycles. At root, the superior HER performance of CoSe2/C stems from its unique porous microsphere intertwined by ultrathin CoSe2 nanosheets and conductive carbon nanosheets, which not only facilitate the electron transfer and ion diffusion, but also produce abundant electrocatalytic active sites for HER. This facile and scalable synthetic method can be extended to synthesize nonprecious transition-metal-based catalysts with unique nanoarchitecture and outstanding HER performance.

Insight into the superior activity of bridging sulfur-rich amorphous molybdenum sulfide for electrochemical hydrogen evolution reaction

Hydrogen evolution reaction (HER) activity of the molybdenum sulfide-based electrocatalysts originates from diverse types of active sulfur (S) sites, different S configurations, the ratio of molybdenum to S, and the crystallinity. The bridging S22− has been considered as the major active site for HER. However, to realize more efficient electrocatalysts, newer architectures based on molybdenum sulfide are required to allow more active S sites beyond the endemic structural limits. Hence, the facile aging approach is used to maximize the bridging S22− in amorphous molybdenum sulfide by adding (NH4)2Sx, leading to the highest proportion of bridging S22− (up to 67%). Additionally, the effect of S configuration on HER activity in molybdenum sulfide is systematically studied by controlling of the amount of bridging S22−. The bridging S-rich electrocatalysts exhibits an excellent HER activity with low onset potential of −96 mV and Tafel slope of 46 mV dec−1, and stability for 1000 cycles.

Compositional regulation and modification of the host CdS for efficient photocatalytic hydrogen production: Case study on MoS2 decorated Co0.2Cd0.8S nanorods

Compositional regulation and modification of CdS are effective strategies to enhance its photocatalytic activity and stability. Herein, a series of MoS2 modified Co0.2Cd0.8S nanorods (CCS) was synthesized by a hydrothermal method and used for photocatalytic hydrogen evolution reaction (HER) under visible light irradiation. The results indicated that the HER activity and stability of CdS could be substantially improved by the introduction of Co2+ into CdS lattice, which can accelerate the separation of photoinduced charge carriers and avoid the formation of high oxidation power holes (h+) due to the upward shift of the valence band edge. The HER performance of CCS could be further enhanced by the decoration of MoS2 nanosheets. CCS loaded with 5% MoS2 (wt%) showed the highest activity (2835.6 μmol·g−1·h−1), which is about 8.9 and 1.6 times higher than that of CdS and CCS. The type II heterojunction formed between CCS and the intimately contacted MoS2 accounts for the improvement as MoS2 can serve as trapping centers for photoinduced electrons (e−) and active sites for HER. This work demonstrated that the activity and the stability of CdS for photocatalytic HER could be boosted by a consolidation of CoS with the host CdS to form a solid solution and a further decoration with low-cost MoS2 cocatalyst.

Monodispersed and well-dispersed RhxP nanoparticles decorated on phosphorus-doped nitride carbon for efficient alkaline and acidic hydrogen evolution

Abstract Metal phosphides (MPs) synthesized by solid-state reaction have shown considerable potential in hydrogen evolution reaction (HER) from water splitting compared with that of Pt. However, large-sized MP nanoparticles (NPs) with irregular morphologies are inevitably achieved via the solid-state reaction with high-temperature calcination, which lead to the reduced availability of the active sites. Here, a simple and straightforward strategy was developed to synthesize monodispersed, uniformly distributed, and small RhxP NPs decorated on phosphorus-doped nitride carbon (PNC) via the pyrolysis of rhodium(Ш) chloride, triphenylphosphine, and melamine (RhxP/PNC-m). The RhxP/PNC-m that served as a HER electrocatalyst displayed excellent performance with the overpotentials of 24 and 27 mV at 10 mA cm−2 in basic and acidic solutions, respectively. This catalyst also showed good long-term stability in both media. The high-performance of RhxP/PNC-m should be attributed to the small, monodispersed, and highly distributed RhxP NPs on PNC support, which can supply abundant catalytically active sites for HER. The developed strategy for the synthesis of small RhxP NPs may offer new opportunities toward the electrochemical applications of other metal phosphides.

Bimetallic Ni‒Co phosphide nanosheets self-supported on nickel foam as high-performance electrocatalyst for hydrogen evolution reaction

In this work, bimetallic nickel-cobalt phosphide (Ni-Co-P/NF) self-supported on nickel foam (NF) is synthesized for hydrogen evolution reaction (HER). A two-step method of electrodeposition with subsequently low-temperature phosphatizing is adopted. The physicochemical characterizations of the as-prepared Ni-Co-P/NF show that the surface is covered by metallic phosphide compounds (NiCoP, NiP and Co2P) with unique morphology, consisted of nanosheets randomly dispersed on villiform 3D integrated framework. The electrochemical characterizations demonstrate that Ni-Co-P/NF exhibits the highest performance for HER, in 1.0 M KOH aqueous solution, compared to other as-prepared electrocatalysts. Specifically, it requires very low overpotential values of 85, 210 and 350 mV for delivering large current densities of −10, −500 and −1,500 mA cm−2, respectively, revealing a low Tafel slope of 46 mV dec−1. Besides, Ni-Co-P/NF also displays long-term durability lasting 24 h without obvious deactivation. This work highlights that the NiCoP, NiP and Co2P active phases play a crucial role for the good HER activity. In addition, the unique morphology with self-supported structure provides large electrochemical surface area, allowing the exposure of higher amount of active sites for HER. These self-supported electrocatalysts, without binder, could also improve the electrode's HER activity and stability. This work, therefore, provides a controllable and feasible strategy to synthesize bimetallic phosphides of unique morphology with high HER activity.

In situ formation of ultrathin C3N4 layers on metallic WO2 nanorods for efficient hydrogen evolution

The number and conductivity of active sites of electrocatalysts have become the main factors for excellent performances for hydrogen evolution reaction (HER). In this work, in situ formation of ultrathin C3N4 layers coating on the surface of metallic WO2 nanorods (WO2@C3N4) as electrocatalysts for HER has been realized by a facile dopamine (PDA) coating on WO3 nanorods precursor and following calcination process. Firstly, the uniform polydopamine (PDA) layer has been coated on the surface of WO3 nanorods (WO3@PDA) through a hydrogen thermal process. The ultrathin C3N4 layers with large graphitization degree after calcination of WO3@PDA can improve the conductivity and stability of catalysts during HER. The formation of one dimensional WO2 nanorods may expose more active sites for HER. Benefited from the synergistic effect between WO2 and C3N4 layers as well as the protection cap of ultrathin C3N4 layers, the obtained core-shell structured WO2@C3N4 nanorods exhibit excellent HER performances and high durability in acidic solution, which only require an overpotential of 98 mV to generate a current density of 10 mA cm−2. Therefore, this work provides a new strategy for constructing transition metal oxides electrocatalyst with high activity and stability by introducing ultrathin C3N4 layer coupled with 1D nanostructure.

Ir‐Au Bimetallic Nanoparticle Modified Silicon Nanowires with Ultralow Content of Ir for Hydrogen Evolution Reaction

AbstractReducing the size and increasing the dispersity of the noble metals are effective ways to decrease the dosage and simultaneously increase their electrocatalytic activities for hydrogen evolution reaction (HER). The Ir−Au bimetallic nanoparticle modified silicon nanowires (Ir−Au−Si) with ultralow content of Ir are prepared and served to catalyze HER in the acid condition. The small Ir−Au nanoparticles are in‐situ grown and uniformly dispersed on the surface of silicon nanowires. Ir−Au−Si exhibits a significantly increased activity in HER catalysis compared with Ir−Si and Pt−Au−Si. Ir provides the active sites for HER, Au increases the electron transfer rate, and the silicon nanowires improve the speed of the hydrogen gas evolution. The optimal Ir−Au−Si‐2 shows a low Tafel slope of 24 mV dec−1 and high mass activity, which are better than those of Ir−Si and Pt−Au−Si catalysts.

Structure and phase regulation in MoxC (α-MoC1-x/β-Mo2C) to enhance hydrogen evolution

Non-precious metal-based efficient electrocatalysts with superior activity and stability for the hydrogen evolution reaction (HER) are useful in solving energy and environmental crises. Herein, monodisperse inverse opal-like MoxC (α-MoC1-x/β-Mo2C) nanospheres were synthesized via a facile strategy to adjust the intrinsic activity and maximize the exposed active sites. In particular, the MoxC-0.4 with the optimal composition of α-MoC1-x/β-Mo2C (0.56/0.44) demonstrated a superior HER performance in 0.5 M H2SO4 with a small Tafel slope of 48 mV dec−1 and remarkable stability. Such prominent performance not only benefits from the inverse opal-like structure that provides more active sites for HER, but also should be ascribed to the strong synergistic effect between α-MoC1-x and β-Mo2C. Based on theoretical calculations, it is further verified that the synergistic effect of MoxC-0.4 is originated from the optimization of interaction with the H* induced by the heterostructure. Furthermore, this work will broaden our vision for highly efficient hydrogen production by bridging the microscopic structure with macroscopic catalytic performance.

Benchmarking the Activity, Stability, and Inherent Electrochemistry of Amorphous Molybdenum Sulfide for Hydrogen Production

AbstractAnodically electrodeposited amorphous molybdenum sulfide (AE‐MoSx) has attracted significant attention as a non‐noble metal electrocatalyst for its high activity toward the hydrogen evolution reaction (HER). The [Mo3S13]2− polymer‐based structure confers a high density of exposed sulfur moieties, widely regarded as the HER active sites. However, their intrinsic complexity conceals full understanding of their exact role in HER catalysis, hampering their full potential for water splitting applications. In this report, a unifying approach is adopted accounting for modifications in the inherent electrochemistry (EC), HER mechanism, and surface species to maximize the AE‐MoSx electroactivity over a broad pH region (0–10). Dramatic enhancements in HER performance by selective electrochemical cycling within reductive (overpotential shift, ηHER ≈ −350 mV) and electro‐oxidative windows (ηHER ≈ −290 mV) are accompanied by highly stable performance in mildly acidic electrolytes. Joint analysis of X‐ray photoelectron spectroscopy, Raman, and EC experiments corroborate the key role of bridging and terminal S ligands as active site generators at low pH, and reveal molybdenum oxysulfides (Mo5+OxSy) to be the most active HER moiety in AE‐MoSx in mildly acidic‐to‐neutral environments. These findings will be extremely beneficial for future tailoring of MoSx materials and their implementation in commercial electrolyzer technologies.

Synthesis of Air‐stable 1T Phase of Molybdenum Disulfide for Efficient Electrocatalytic Hydrogen Evolution

AbstractPhase engineering of MoS2 from the thermodynamically stable 2H phase to the metastable 1T phase has been demonstrated as an effective way to enhance the electrocatalytic activity for hydrogen evolution reaction (HER). However, the development of highly stable and efficient 1T‐MoS2‐based electrocatalysts toward HER still remains a great challenge. Herein, a facile hydrothermal strategy was introduced for the preparation of stable 1T‐MoS2 via a reduced graphene oxide (RGO)‐assisted process. The optimal catalyst of MoS2/RGO can keep highly stable in air over 90 days without significant activity fading due to Mo−O interactions, which effectively prevent the transformation of 1T phase back to 2H. The catalyst affords superior HER catalytic activity with a low overpotential of 213 mV versus reversible hydrogen electrode (RHE) at a current density of −10 mA cm−2, a small Tafel slope of 43 mV dec−1, a high exchange current density of 0.83 mA cm−2, and excellent durability, which outperforms its corresponding 2H counterpart. The enhanced electrocatalytic activity of the optimal MoS2/RGO sample is associated with the RGO, which can not only facilitate charge transfer along MoS2 nanosheets but also stabilize the 1T‐MoS2 with a high exposure of active sites for HER. This work paves a new pathway for designing highly efficient MoS2‐based electrocatalysts through phase engineering.

One-Dimensional Porous Hybrid Structure of Mo2C-CoP Encapsulated in N-Doped Carbon Derived from MOF: An Efficient Electrocatalyst for Hydrogen Evolution Reaction over the Entire pH Range.

The development of outstanding noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) has attracted broad interest. Herein, a novel one-dimensional (1D) HER hybrid catalyst consisted of cobalt phosphide (CoP) and molybdenum carbide (Mo2C) nanoparticles wrapped by nitrogen-doped graphitic carbon (called CoP/Mo2C-NC) was successfully fabricated by a facile continuous-flow method and a simple two-step annealing process. During these processes, the successful synthesis of the MoO3 nanorods coated with cobalt zeolitic imidazolate frameworks (Co-ZIF-67) (Co-ZIF-67@MoO3) through the continuous-flow method plays a key role. The as-synthesized CoP/Mo2C-NC hybrid electrocatalyst exhibits a significantly enhanced HER electrocatalytic activity over the entire pH range relative to that of the control materials CoP, Mo2C-NC, and physically mixed CoP and Mo2C-NC. The outstanding HER catalytic performance is mainly due to the fact that the electron cloud transfers from Co to Mo in CoP/Mo2C-NC through the Co-P-Mo bond, resulting in the formation of a high valence state for Co (Co3+) species and lower valence states for Mo (i.e., Mo2+, Mo3+) species, providing the abundant HER active sites. Moreover, the Gibbs free energy (Δ GH*) of CoP/Mo2C-NC obtained by the density function theory calculations indicates a good balance between the Volmer and Heyrovsky/Tafel steps in HER kinetics. Such a cobalt zeolitic imidazolate framework-mediated strategy depicted in this work offers an interesting perspective for developing highly efficient noble-metal-free electrocatalysts for hydrogen production.

Structurally Ordered Intermetallic Cobalt Stannide Nanocrystals for High-Performance Electrocatalytic Overall Water-Splitting.

The synthesis of structurally ordered non-noble intermetallic cobalt stannide (CoSn2 ) nanocrystals and their utilization for high-performance electrocatalytic overall water-splitting is presented. The structurally and electronically beneficial properties of the tetragonal CoSn2 exhibit a considerably low overpotential for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) on fluorine-doped tin oxide (FTO) and Ni foam (NF). Loss of Sn from the crystal lattices and oxidation of Co under strongly alkaline conditions furnishes highly disordered amorphous active CoOx (H), the catalytically active structure for OER. The Co0 atoms in the CoSn2 act as active sites for HER and the presence of Sn provides efficient electrical conductivity. This intermetallic phase is a novel type of cost-effective and competitive bifunctional electrocatalysts and predestinated for overall water-splitting devices: A two-electrode electrolyzer with CoSn2 on NF delivers a cell voltage of merely 1.55 V at 10 mA cm-2 maintaining long-term stability.

Structurally Ordered Intermetallic Cobalt Stannide Nanocrystals for High‐Performance Electrocatalytic Overall Water‐Splitting

AbstractThe synthesis of structurally ordered non‐noble intermetallic cobalt stannide (CoSn2) nanocrystals and their utilization for high‐performance electrocatalytic overall water‐splitting is presented. The structurally and electronically beneficial properties of the tetragonal CoSn2 exhibit a considerably low overpotential for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) on fluorine‐doped tin oxide (FTO) and Ni foam (NF). Loss of Sn from the crystal lattices and oxidation of Co under strongly alkaline conditions furnishes highly disordered amorphous active CoOx(H), the catalytically active structure for OER. The Co0 atoms in the CoSn2 act as active sites for HER and the presence of Sn provides efficient electrical conductivity. This intermetallic phase is a novel type of cost‐effective and competitive bifunctional electrocatalysts and predestinated for overall water‐splitting devices: A two‐electrode electrolyzer with CoSn2 on NF delivers a cell voltage of merely 1.55 V at 10 mA cm−2 maintaining long‐term stability.

Fe5C2 nanoparticles as low-cost HER electrocatalyst: the importance of Co substitution

Constructing and understanding the doping effect of secondary metal in transition metal carbide (TMC) catalysts is pivotal for the design of low-cost hydrogen evolution reaction (HER) electrocatalysts. In this work, we developed a wet-chemistry strategy for synthesizing Co-modified Fe5C2 nanoparticles ((Fe1−xCox)5C2 NPs) as highly active HER electrocatalysts in basic solution. The structure of (Fe1−xCox)5C2 NPs was characterized by X-ray diffraction (XRD), extended X-ray absorption fine structure spectra (EXAFS) and scanning/transmission electron microscopy (S/TEM), indicating that the isomorphous substitution of cobalt in the lattice of Fe5C2. (Fe0.75Co0.25)5C2 exhibited the best HER activity (174 mV for j = −10 mA/cm2). Computational calculation results indicate that Co provides the most active site for HER. X-ray adsorption spectra (XAS) studies further suggested that the electron transfer in Fe–C bonds are enhanced by the substitution of Co, which modulates the hydrogen adsorption on the adjacent electronic-enriched carbon, and therefore promotes HER activity. Our results affirm the design of low-cost bimetallic TMCs based HER catalysts.

Spherical Ruthenium Disulfide-Sulfur-Doped Graphene Composite as an Efficient Hydrogen Evolution Electrocatalyst.

The exploition of cost-efficient and high-performance catalysts to boost hydrogen generation in overall water splitting is crucial to economically obtain green hydrogen energy. Herein, we propose a novel electrocatalyst consisting of spherical RuS2 on S-doped reduced graphene oxide (s-RuS2/S-rGO) with high catalytic behavior toward hydrogen evolution reaction (HER) in all pH conditions, especially in alkaline electrolytes. RuS2/S-rGO delivers small overpotentials of 25 and 56 mV at current densities of 10 and 50 mA cm-2, respectively, and a low Tafel slope of 29 mV dec-1 with good stability for 100 h in basic solutions. This performance is comparable to and even exceeds that of documented representative electrocatalysts, including the benchmark Pt/C; since the price of Ru is about 1/25th that of Pt, this novel electrocatalyst offers a low-cost alternative to Pt-based HER electrocatalysts. Ruthenium-centered sites of RuS2 in this hybrid catalyst are responsible for the HER active sites, and S doping in RuS2 also exerts an important function for the HER activity; density functional theory calculations disclose that the water dissociation ability and adsorption free energy of hydrogen intermediate adsorption (Δ GH*) for RuS2 are very close to those of Pt. A homemade electrolyzer with an s-RuS2/S-rGO (cathode)//RuO2/C (anode) couple presents a relatively low voltage of 1.54 V at a current density of 20 mA cm-2, while maintaining negligible deactivation over a 24 h operation.