HER Catalysts Research Articles

N-Doped amorphous MoSx for the hydrogen evolution reaction.

Herein, the functions of a N dopant in crystalline MoS2 catalysts during the electrochemical hydrogen evolution reaction (HER) were reported via a combined experimental and first-principles approach. However, studies on the N doping of amorphous MoSx, which is a more active catalyst, have not been reported to date. In this study, via a simple method, we fabricated N-doped amorphous MoSx for the first time and studied the correlations between the N dopant and the HER performance. Via X-ray photoelectron spectroscopy and theoretical formation energy calculations, we have found that a N dopant in basal plane S2- plays a very important role in the improvement of the HER performance and remains stable during this dynamic transformation process. A N dopant in basal plane S2- can increase the number of active sites toward the HER and enhance the conductivity of the catalysts as well as a N dopant in c-MoS2. In addition to this, the first-principles calculations further suggested that a N dopant in basal plane S2- could improve the activity of unsaturated MoV active sites by bringing its hydrogen adsorption free energy closer to zero. As a result, N-doped amorphous MoSx possesses an overpotential of 143 mV at 10 mA cm-2 and a Tafel slope of 57 mV dec-1, much better than those of a-MoSx. These results provide useful insights for the future development of nonmetal-doped MoSx catalysts in the HER.

In situsynthesized low-PtCo@porous carbon catalyst for highly efficient hydrogen evolution

Synthesis of a highly efficient HER catalyst with low Pt that exceeds the efficiency of the commercial 20 wt% Pt/C.

Hierarchical nanoporous intermetallic compounds with self-grown transition-metal hydroxides as bifunctional catalysts for the alkaline hydrogen evolution reaction

Transition metal (TM)-doped intermetallic compounds that are composed of a surface Pt-TM alloy with a self-grown hydroxide serve as bifunctional alkaline HER catalysts.

Algorithm screening to accelerate discovery of 2D metal-free electrocatalysts for hydrogen evolution reaction

By using algorithm screening and DFT computations, we establish a method to accelerate the search for highly efficient HER metal-free catalysts, and a novel metal-free 2D material, a C3N monolayer, is proposed as an efficient HER catalyst.

Metal organic framework (MOF) derived iron phosphide as a highly stable and efficient catalyst for hydrogen evolution

A facile and universal strategy for preparing metal phosphides using MOFs was designed and a highly efficient HER catalyst was developed.

Chimney effect of the interface in metal oxide/metal composite catalysts on the hydrogen evolution reaction

Precise atomic-level control of composition and geometric structure at the interface between two catalyst components can effectively tune the catalytic properties. Herein, we found a “chimney effect” formed on the interface between the metal oxide and Nickel metal for the hydrogen evolution reaction, using density functional theory calculations and experimental methods. This special chemical environment around the interface leads the neighboring sites to be immune to the H2O* and OH* adsorption and to only selectively adsorb H* properly. Meanwhile, it is also beneficial for the smooth adsorption of the reactant (H*) on the interface and the easy desorption of the product (H2) from the catalyst surface (ΔGH* close to zero). This phenomenon appears similar to a chimney of hydrogen evolution around the metal oxide/metal interface. Such “chimney effect” is a result of the interfacial charge transfer between the metal and metal oxide, and should be the nature of the interface-induced synergistic effect in metal oxide/metal composite catalysts for HER. Experiments further confirm that the catalytic activity of metal oxide/metal composites for HER can be enhanced by increasing the amount of the chimney - the interfacial metal atoms.

Composition of Ag-WO3 core-shell nanostructures as efficient electrocatalysts for hydrogen evolution reaction

The development of non-noble metal catalysts is considered a noteworthy topic of hydrogen production from water cracking. Electrocatalytic activity of WO3 as a cheap and promising catalyst for HER is impacted by crystal phase structure, oxygen vacancy and surface state. The present paper designs Ag-WO3 catalysts with core-shell structure using Ag@C as a template with ultrasonic synthesis method to improve the structure properties and increase the active sites of hydrogen adsorption. Also, atomic Ag serves as the function of hydrogen absorption channel for the shell of tungsten oxide. As the results suggest, Ag-WO3(0.8) CSNSs at ratio of WCl6 : Ag@C with 0.8 shows the more effective Electrocatalytic activity towards the HER with low over potential of − 207 mV at a current density of 10 mA cm−2, small tafel slope (52.4 mV dec−1), larger active area Cdl (54.92 mF cm−2) and high exchange current density. This paper gives an effective measure for hydrogen production by using Ag-WO3 core-shell structure as alternative catalysts to platinum catalysts.

Borocarbonitrides, BxCyNz, 2D Nanocomposites with Novel Properties

Abstract Chemical doping of graphene is necessary to generate a band gap that is valuable for a range of applications. Chemical doping of graphene with elements like nitrogen and boron gives rise to useful properties. In this context, recent studies of borocarbonitrides, BxCyNz, comprising carbon, and the two elements on either side of it, are of significance. While uniformly homogeneous compositions of borocarbonitrides may be hard to generate, there have been efforts to synthesize them by solid state as well as gas phase routes. The products obtained show evidence for the presence of B-C and C-N bonds besides B-N and C-C bonds (but no N-N bonds), and possible occurrence of random BCN networks in addition to graphene and BN domains. Properties of borocarbonitrides depend on the composition, and the method of synthesis, enabling one to traverse from the insulating BN to the conducting graphene. In this account, we present important features of borocarbonitrides including synthesis, characterization, properties and potential applications. Surface oxygen functionalities and amine-groups of borocarbonitrides have been quantitatively determined by the fluorescence labeling of surface species (FLOSS) technique. Typical applications are in gas adsorption and energy devices such as supercapacitors and fuel cells as well as electrochemical sensors. Performance of borocarbonitrides as a HER catalysts is impressive, showing electrochemical activity close to that of Pt. It is possible to covalently link a BCN layer to other 2D nanosheets and the materials obtained by such cross-linking with layers of C3N4, MoS2 and MoSe2 show outstanding HER performance and other useful characteristics. Interestingly, heterostructures of BCN with nanosheets of MoS2 and other 2D materials can be formed reversibly by supramolecular means, which show good visible-light driven photochemical hydrogen evolution activity.

Ternary Os-Ag-Si electrocatalysts for hydrogen evolution are more efficient than Os-Au-Si

Hydrogen is considered as a promising energy source because of its high combustion heat and clean products. Among the various hydrogen evolution methods, electrocatalysis is the most convenient and effective way. However it is still problematic to find low-cost and high-efficiency electrocatalysts. In this work, Os-Ag-Si and Os-Au-Si ternary electrocatalysts were investigated. It is interesting that Os-Ag-Si exhibits higher hydrogen evolution performance than that of Os-Au-Si, even though Ag is a worse HER catalyst than Au. The optimal ternary catalyst Os-Ag-Si with mass ratio of 15:15:70 (Os:Ag:Si) was synthesized by a facile SiH bond reduction method, which shows superior hydrogen evolution reaction performance with a low Tafel slope of 40 mV·dec−1. In addition, the current density of Os-Ag-Si-15 catalyst surpasses that of 20% Pt/C when the overpotential is larger than 160 mV. The introduction of Ag in the Os-Ag-Si ternary catalyst could enhance the electrocatalytic activity, reduce the cost of catalysts, and even be better than Os-Au-Si.

Earth-Abundant Transition-Metal-Based Electrocatalysts for Water Electrolysis to Produce Renewable Hydrogen.

Fundamentals of water electrolysis, and recent research progress and trends in the development of earth-abundant first-row transition-metal (Mn, Fe, Co, Ni, Cu)-based oxygen evolution reaction (OER) and hydrogen evolution (HER) electrocatalysts working in acidic, alkaline, or neutral conditions are reviewed. The HER catalysts include mainly metal chalcogenides, metal phosphides, metal nitrides, and metal carbides. As for the OER catalysts, the basic principles of the OER catalysts in alkaline, acidic, and neutral media are introduced, followed by the review and discussion of the Ni, Co, Fe, Mn, and perovskite-type OER catalysts developed so far. The different design principles of the OER catalysts in photoelectrocatalysis and photocatalysis systems are also presented. Finally, the future research directions of electrocatalysts for water splitting, and coupling of photovoltaic (PV) panel with a water electrolyzer, so called PV-E, are given as perspectives.

Noble metals enhanced catalytic activity of anatase TiO2 for hydrogen evolution reaction

Although anatase TiO2 is a promising candidate for hydrogen evolution reaction in acidic media, the application of TiO2 is hindered by the poor electrical transport and reactivity of active sites. Here, we report on the hydrogen occupied mechanism, noble metal-doped effect and influence of noble metal on the hydrogen evolution activity of TiO2 by using the first-principles approach. We find that hydrogen prefers to occupy the tetrahedral interstice site because of the strongly localized hybridization between hydrogen and TiO2. Importantly, those noble metals can improve the electronic transport between the valence band and the conduction band near the Fermi level. Ag-doping and Au-doing are more thermodynamically stable than that of Pt-doping, Pd-doping and Ru-doping. In comparison with other noble metals, we find that Ag-doping is beneficial to enhance the hydrogen evolution reaction activity of TiO2 because hydrogenated Ag-doping weakens the electronic transfer between Ti-3d state and O-2p state near the Fermi level. Finally, our work indicates that Ag-doping is a promising TiO2 HER catalyst.

Proton Reduction Catalysis at a Modified Gallium Phosphide Photocathode Surface

Gallium phosphide (GaP) is a semiconductor with conduction and valence bands that straddle the potential of the proton reduction half-reaction and a bandgap of 2.26 eV, allowing for absorption of a significant portion of the solar spectrum and generation of a large photovoltage. These properties give GaP great potential as a photocathode material for the solar-driven water splitting reaction. However, a hurdle that needs to be overcome for the implementation of this material in photoelectrochemical cells is the large overpotential for the proton reduction half-reaction. This study investigates the pairing of cobalt bis(dichlorobenzenedithiolate) ((TBA)[Co(Cl2bdt)2]) – a molecular HER catalyst – with GaP photocathodes. (TBA)[Co(Cl2bdt)2] demonstrates good catalytic activity for proton reduction in acidic media and has previously been shown to strongly physisorb to graphitic surfaces through π-interactions. Herein is presented investigations into the physisorption of (TBA)[Co(Cl2bdt)2] to single crystal GaP wafers through a transparent, conductive graphitic thin film. Reduced graphene oxide (RGO) thin films are prepared on GaP through a novel method that is exceedingly gentle towards the underlying semiconducting material. Because of their graphitic character, these RGO films can participate in the π-interactions necessary for catalyst adsorption. X-ray photoelectron spectroscopy and electrochemistry are used to detect the presence of the catalyst on the RGO films. Photoelectrochemical experiments have been performed investigating the effects of an RGO thin film on homogeneous light-driven electrocatalysis at GaP photocathodes. Further experiments will delve into heterogeneous catalysis in which the catalyst is physisorbed to the GaP/RGO photocathode. Additionally, finite-element models of catalyzed photoelectrochemical reactions at a GaP-electrolyte interface will be discussed.

Protected Metallic MoS2 Nanosheets Outlast Pristine Metallic MoS2 Nanosheets for Hydrogen Evolution Reaction

Functionalizing nanosheets of metallic molybdenum disulfide (MoS2) provides a synthetic chemical route for controlling the electronic properties and stability within the traditionally thermally unstable metallic state. Metallic MoS2 nanosheets have been studied for HER due to their higher reactivity for HER, earth abundance, low-cost, and non-toxicity, which makes metallic MoS2 a candidate to replace platinum for HER. The functionalized nanosheets are more stable to the thermally initiated phase transformation from the metallic 1T phase to the semiconducting 2H phase. Furthermore, we show for an exemplary functionalized sample (Et2NPh-MoS2) that functionalization leads to better stability and long-term performance under HER conditions. These results provide a framework for understanding and controlling the balance between catalytic activity and stability for these unique 2D materials. Chemically-exfoliated, metallic (1T) MoS2 nanosheets are functionalized with organic phenyl rings containing electron donating or withdrawing groups. We find that MoS2 functionalized with the most electron donating functional group (p-(CH3CH2)2NPh-MoS2) is the most efficient catalyst for HER in this series, with initial activity similar to the pristine metallic phase of MoS­­­­­­ 2. The p-(CH3CH2)2NPh-MoS2 is more stable than unfunctionalized metallic MoS2 and outperforms unfunctionalized metallic MoS2 for continuous H2 evolution within 10 min under the same conditions. With regards to the entire studied series, the overpotential and Tafel slope for catalytic HER are both directly correlated with the electron donating strength of the pendant group on the phenyl ring. The results are consistent with a mechanism involving ground-state electron donation or withdrawal to/from the MoS2 nanosheets, which modifies the electron transfer kinetics and catalytic activity of the MoS2 sheet. We show that the functional groups preserve the metallic feature of the MoS2 films, inhibiting conversion to the thermodynamically stable semiconducting state (2H) when annealed at 150 °C for 24 h in a nitrogen atmosphere. We propose that this protection is critical to maintaining the catalytically active state of 1T MoS2 nanosheets. Our results demonstrate a strong correlation between the electron donating strength of substituents and the surface energetics, electron transfer resistance, and the HER catalytic activity of functionalized MoS2 nanosheets.

(Invited) Current Understandings of the Slow Kinetics of the Hydrogen Evolution Reaction in Alkaline Media

Efficient generation of H2 as a clean energy source from water constitutes one of the cornerstones of the so-called hydrogen economy. We are currently limited to precious metal such as Pt as effective HER catalysts in acid owing to the stability issue, but also in alkaline owing to the slow kinetics of HER in high pH environment. The origin of the slow HER rate in alkaline, and how to overcome this fundamental limitation have been under extensive debatable. By far there are three schools of thoughts led by Markovic, Gasteiger, and Koper, and their respective collaborators, although they all agree that the HER kinetics in alkaline is limited by the Volmer step M + H2O + eˉ ↔ M-Hads + OHˉ. Markovic et al.1 stated that and the reactive hydroxyl species (OHads ) accomondated by the surface oxophilic sites is responsible for the acceleration of this step. We recently provided the first experimental evidence of OHads accommodated by the Ru in both Pt-Ru and Ru systems within the HER/HOR potential region, and its promoting role on the HER/HOR kinetics in alkaline media.2 Gasteiger et al. 3 and Yushan () argued that H-binding energy (M-H) is the sole descriptor for the HER rate in a broad range of pH environments, although the origin of the difference in H-binding energy is not clear. Most recently, Koper’s group4 proposed a model that states a possible pH dependence of surface water (H2O) orientation and highlights the role of the reorganization of interfacial water for the HER kinetics to accommodate charge transfer through the electric double layer. In this talk, all the three mechanisms will be discussed in the context of new experimental and computational results achieved by us and others to update our understanding of the HER kinetics in alkaline pH. Acknowledgements: The authors gratefully acknowledge the financial support of the Department of Energy (DOE) via Energy Efficiency and Renewable Energy (EERE), under the auspices of an incubator effort lead by Proton On-Site and a new grant (grant #.. ) under the HydroGen initiative. Authors also acknowledge the support from arpa.e under their open initiative via a grant lead by Pajarito Powders, Albuquerque (grant # ). The support from (DOE) office of science under contract no DE-SC0012704 for building and maintaining the National Synchrotron Light Source-II (NSLS-II) at Brookhaven National Laboratory (BNL), Upton, NY and Thermo Fisher for instrumental support is gratefully acknowledged. References (1) Subbaraman, R.; Tripkovic, D.; Chang, K.-C.; Strmcnik, D.; Paulikas, A. P.; Hirunsit, P.; Chan, M.; Greeley, J.; Stamenkovic, V.; Markovic, N. M. Nat. Mater. 2012, 11, 550. (2) Li, J.; Ghoshal, S.; Bates, M. K.; Miller, T. E.; Davies, V.; Stavitski, E.; Attenkofer, K.; Mukerjee, S.; Ma, Z.-F.; Jia, Q. Angew. Chem. Int. Ed., n/a. (3) Durst, J.; Siebel, A.; Simon, C.; Hasche, F.; Herranz, J.; Gasteiger, H. A. Energy Environ. Sci. 2014, 7, 2255. (4) Ledezma-Yanez, I.; Wallace, W. D. Z.; Sebastián-Pascual, P.; Climent, V.; Feliu, J. M.; Koper, M. T. M. Nat. Energy 2017, 2, 17031.

Electrochemical Reduction of Aqueous CO2 to Synthesis Gas Using β Palladium Hydride

Electrochemical reduction of CO2 (CO2RR) to value-added liquid fuels or chemical feedstocks using off-peak electricity or intermittent renewable energy sources is a green approach for energy storage and carbon recycling. However, the difficult activation of CO2 to form the CO2 ∙− intermediate and the competitive hydrogen evolution (HER) in aqueous electrolytes make the Faradaic efficiency and selectivity for the CO2RR remain very low. From another perspective, CO2 reduction to CO, with co-production of H2 from water, is very appealing as the mixture of CO and H2 with controlled ratio can be used as syngas for methanol synthesis and Fischer-Tropsch reactions. In this approach, catalyst search is therefore no longer limited to metals with low HER activity such as Au and Ag. Materials with fair HER activity can be potentially considered for the CO2RR. Interestingly, Pd, a good HER catalyst, has been found to continuously produce CO in the CO2RR, which is however counterintuitive to that Pd is prone to CO poisoning.[1] In this work, we have re-examined Pd for the CO2RR using in situ XAS and in situ XRD, and have found that Pd transforms into β-PdH under the CO2RR condition. DFT calculations suggest that CO adsorption energy on the PdH surface is greatly reduced compared to that on the Pd surface, which is most likely the cause for high selectivity of CO2RR to CO when using Pd as the electrocatalyst.[2] [1] Y. Hori, Modern Aspects of Electrochemistry, Springer, New York, 2008, vol. 42, ch. 3, pp. 89–189. [2] Wenchao Sheng, Shyam Kattel, Siyu Yao, Binhang Yan, Zhixiu Liang, Christopher J. Hawxhurst, Qiyuan Wu and Jingguang G. Chen, Energy & Environmental Science, 10, 1180-1185 (2017)

In situ promoting water dissociation kinetic of Co based electrocatalyst for unprecedentedly enhanced hydrogen evolution reaction in alkaline media

Carbon-encapsulated 3d-transition metal (TM) hybrid structure (denoted as M@C) have been considered as a promising candidate for HER. In recent years, the Co@C composites have exhibited effective HER catalytic performance in acidic media. However, the catalytic performance of Co@C in alkaline media is still unsatisfactory because of the sluggish water dissociation in Volmer step. In this work, by using carbon encapsulated metal Co nanoparticles hybrid structure (CoNP@C) as precatalyst, we firstly demonstrate that the HER activity of Co-based precatalysts could be unprecedentedly promoted through a simple in situ electrochemical activation process. Compared with initial CoNPs@C precatalyst, the activated catalyst realizes about 3.5-fold improved activity and the overpotential greatly decreases from 191 mV to 58 mV at 10 mA cm−2. Specially, the remarkable reduced Tafel slope (from 113 mV dec−1 to 51 mV dec−1) indicates that the sluggish kinetics of the water dissociation step (Volmer step) is effectively speeded up by in situ electrochemical activation. Such a highly enhanced catalytic performance is mainly due to the in situ introduction of cobalt hydroxides NPs as water dissociation promoter and the synergetic effects among core Co NPs, middle layered carbon structure and outer cobalt hydroxides NPs. Our study offers a generic strategy for development of high-performance 3d-transition metal hybrid based HER catalysts in alkaline media.

Platinum nanoparticles deposited nitrogen-doped carbon nanofiber derived from bacterial cellulose for hydrogen evolution reaction

The nitrogen-doped carbon nanofiber derived from low and high proportion polyaniline doped bacterial cellulose (BC) was obtained via polymerization followed by pyrolysis. The resulting products were named LN-BC and HN-BC accordingly. Platinum nanoparticles modified LN-BC and HN-BC was then prepared (Pt@LN-BC and Pt@HN-BC) via electrochemical deposition. The morphologies of LN-BC and HN-BC indicated that the BC lost its nanowire structure after polyaniline modification and pyrolysis under nitrogen atmosphere. Platinum nanoparticles with diameters ranging from 3 to 5 nm can be well dispersed in the HN-BC support. The HER performance of Pt@LN-BC and Pt@HN-BC was fully investigated. Electrochemical results showed that the Pt-based catalysts had better HER activity than the Pt free catalysts in acid, indicating the HER activity was mainly from Pt. Besides, Pt@HN-BC had better HER activity than Pt@LN-BC in acid, suggesting N-doping rate was an important factor in enhancing HER activity. And the 10Pt@HN-BC (deposition for 10 s) with 4.38 wt% Pt loading was the best HER catalyst among the Pt@HN-BC. The onset potential (@ −1 mA cm−2) and overpotential (@ −10 mA cm−2) of the 10Pt@HN-BC in 0.5 M H2SO4 is −18 and −47 mV, respectively. The corresponding Tafel slope was −35 mV dec−1, which is quite comparable to that of Pt/C (10 wt%). The electrochemical double layer capacitance (Cdl) and turnover frequency (TOF) were estimated and presented in the work. Long-term stability test confirmed that the 10Pt@HN-BC had excellent stability, which was important for practical application.

The study on the active origin of electrocatalytic water splitting using Ni-MoS2 as example

Two-dimensional layered sulfide (MoS2, VS2, WS2) has aroused intense scholarly interest, and its fascinating chemical properties and physical structure provide the possibility of further triggering the catalytic activity of the Ni. In this paper, we chose Ni and MoS2, which are both commonly used in electrocatalytic water splitting, to prepare the hybrid and then used it as a template to study the origin activity. With the method of experimental and theoretical reciprocal verification, it was discovered that the strong binding energy of Ni to MoS2 enables Ni to grow flat along the MoS2 surface to facilitate the Ni particles refinement and dispersion. Besides, the weakening of NiH bond demonstrated the subsequent recombination and release process of H in Ni-MoS2 catalyst is relatively easy. We hope this study may be extended to other two-dimensional transitional metal dichalcogenides based interface engineering to filtrate logical HER catalysts in alkaline media, and stimulate the rational design of the Ni-based materials as well as other transition metal catalysts.

Carbon coated nickel - Nickel oxide composites as a highly efficient catalyst for hydrogen evolution reaction in acid medium

Carbon coated nickel - nickel oxide composites (Ni/NiO@C/GR-t-w) was synthesized from the direct carbonization of the composites composed of Ni-MOF-74 and graphene oxide (GO). Due to the synergetic effects of Ni, NiO and graphene, Ni/NiO@C/GR-t-w all exhibited the electrocatalytic performance to HER in acidic medium. When the GO content was 8% and the carbonization temperature was 900 °C, the composites (Ni/NiO@C/GR-900-8) showed the best electrocatalytic properties with an lower overpotential of 108 mV (vs. RHE) at 10 mA cm−2, a smaller Tafel slope of 44 mV dec−1 and a good stability in a 0.5 M H2SO4 solution. The excellent electrocatalytic performance enabled Ni/NiO@C/GR composites to be a favorable HER catalyst to replace the expensive Pt-based materials in the applications of the hydrogen production.

Hydrogen Evolution Reaction on Hybrid Catalysts of Vertical MoS2 Nanosheets and Hydrogenated Graphene

Two-dimensional (2D) molybdenum sulfide (MoS2) is an attractive noble-metal-free electrocatalyst for hydrogen evolution (HER) in acids. Tremendous effort has been made to engineer MoS2 catalysts with either more active sites or higher conductivity to enhance their HER activity. However, little attention has been paid to synergistically structural and electronic modulations of MoS2. Herein, 2D hydrogenated graphene (HG) is introduced into MoS2 ultrathin nanosheets for the construction of a highly efficient and stable catalyst for HER. Owing to synergistic modulations of both structural and electronic benefits to MoS2 nanosheets via HG support, such a catalyst has improved conductivity, more accessible catalytic active sites, and moderate hydrogen adsorption energy. On the optimized MoS2/HG hybrid catalyst, HER occurs with an overpotential of 124 mV at 10 mA cm–2, a Tafel slope of 41 mV dec–1, and a stable durability for 24 h continuous operation at 30 mA cm–2 without observable fading. The high performance...