In Situ Fabrication of Ni–Mo Bimetal Sulfide Hybrid as an Efficient Electrocatalyst for Hydrogen Evolution over a Wide pH Range

Engineering antibonding orbital occupancy of NiMoO4-supported Ru nanoparticles for enhanced chlorine evolution reaction

Chlorine evolution reaction (CER) is crucial for industrial-scale production of high-purity Cl2. Despite the development of classical dimensionally stable anodes to enhance CER efficiency, the competitive oxygen evolution reaction (OER) remains a barrier to achieving high Cl2 selectivity. Herein, a binder-free electrode, Ru nanoparticles (NPs)-decorated NiMoO4 nanorod arrays (NRAs) supported on Ti foam (Ru-NiMoO4/Ti), was designed for active CER in saturated NaCl solution (pH = 2). The Ru-NiMoO4/Ti electrode exhibits a low overpotential of 20 mV at 10 mA cm-2 current density, a high Cl2 selectivity exceeding 90%, and robust durability for 90h operation. The marked difference in Tafel slopes between CER and OER indicates the high Cl2 selectivity and superior reaction kinetics of Ru-NiMoO4/Ti electrode. Further studies reveal a strong metal-support interaction (SMSI) between Ru and NiMoO4, facilitating electron transfer through the Ru-O bridge bond and increasing the Ru 3d-Cl 2p antibonding orbital occupancy, which eventually results in weakened Ru-Cl bonding, promoted Cl desorption, and enhanced Cl2 evolution. Our findings provide new insights into developing electrodes with enhanced CER performance through antibonding orbital occupancy engineering.

NiMOF-Derived MoSe2/NiSe Hollow Nanoflower Structures as Electrocatalysts for Hydrogen Evolution Reaction in Alkaline Medium

Metal-organic frameworks (MOFs) are crystalline porous materials for storage and energy conversion applications with three-dimensional pore structure, high porosity, and specific surface area, which are widely utilized in electrocatalysis. Herein, MoSe2/NiSe composites were synthesized by selenization reaction using NiMOF as the precursor. The composites were hollow nanoflower structures with a synergistic effect between MoSe2 and NiSe to promote rapid electron transfer, which exhibited good hydrogen evolution reaction performance in an alkaline medium. At a current density of 10 mA/cm2, the HER overpotential reaches 80 mV, the Tafel slope is 33.86 mV/dec, and the material has good stability, with polarization curves remaining essentially unchanged after 3000 cycles. These results indicate that the method has a promising application in the preparation of efficient and sustainable catalysts for hydrogen production in alkaline medium.

Manipulating heterointerface to boost formation and desorption of intermediates for highly efficient alkaline hydrogen evolution

Promoting water dissociation and H intermediate desorption play a pivotal role in achieving highly efficient hydrogen evolution reaction (HER) in alkaline media but remain a great challenge. Herein, we rationally develop a unique W-doped NiSx/Ni heterointerface as a favorable HER electrocatalyst which was directly grown on the Cu nanowire foam substrate (W-NiSx/Ni@Cu) by the electrodeposition strategy. Benefiting from the rational design of the interfaces, the electronic coupling of the W-NiSx/Ni@Cu can be efficiently modulated to lower the HER kinetic barrier. The obtained W-NiSx/Ni@Cu exhibits an enhanced HER activity with a low overpotential of 38 mV at 10 mA cm-2 and a small Tafel value of 27.5 mV dec-1, and high stability during HER catalysis. In addition, in-situ Raman spectra reveal that the Ni2+ active sites preferentially adsorb OH intermediate. The theoretical calculation confirms that the water dissociation is accelerated by the construction of W-NiSx/Ni heterointerface and H intermediate desorption can be also promoted by H spillover from S active sites in W-NiSx to Ni active sites in metal Ni. This work offers a valuable reference for rational designing heterointerface of electrocatalysts and provides an available method to accelerate the HER kinetics for the ampere-level current density under low overpotential.

Engineering heterostructured Mo2C/MoS2 catalyst with hydrophilicity/aerophobicity via carbothermal shock for efficient alkaline hydrogen evolution

The exploration of high-performance hydrogen evolution reaction (HER) catalysts is conducive to the development of clean hydrogen energy, yet still remains a challenge. Herein, we rapidly synthesize the Mo2C/MoS2 heterostructure on carbon paper (Mo2C/MoS2-CP) via carbothermal shock in only two seconds. The construction of the Mo2C/MoS2 heterostructure regulates the electronic structure of the Mo site and facilitates charge transfer during the HER process. Moreover, the catalyst exhibits enhanced hydrophilicity and aerophobicity, facilitating optimal electrolyte-catalyst interaction and efficient hydrogen bubble detachment for accelerated mass transfer. Consequently, Mo2C/MoS2-CP exhibits superior intrinsic alkaline HER activity, and excellent stability for 100 h. This finding provides a novel insight into the development of outstanding HER catalysts.

A self-supported porous NiMo electrocatalyst to boost the catalytic activity in the hydrogen evolution reaction

To develop hydrogen energy production and address the issues of global warming, inexpensive, effective, and long-lasting transition metal-based electrocatalysts for the synthesis of hydrogen are crucial. Herein, a porous electrocatalyst NiMo/Ni/NF was successfully constructed by a two-step electrodeposition process, and was used in the hydrogen evolution reaction (HER) of electrocatalytic water decomposition. NiMo nanoparticles were coated on porous Ni/NF grown on nickel foam (NF), leading to a resilient porous structure with enhanced conductivity for efficient charge transfer, as well as distinctive three-dimensional channels for quick electrolyte diffusion and gas release. Notably, the low overpotential (42 mV) and fast kinetics (Tafel slope of 44 mV dec-1) at a current density of 10 mA cm-2 in 1.0 M KOH solution demonstrate the excellent HER activity of the electrode, which was superior to that of recently reported non-noble metal-based catalysts. Additionally, NiMo/Ni/NF showed extraordinary catalytic durability in stability tests at a current density of 10 mA cm-2 for 70 h. The porous structure catalyst and the electrodeposition-electrocatalysis technique examined in this study offer new approaches for the advancement of the electrocatalysis field because of these benefits.

Enhancing Ru-Cl interaction via orbital hybridization effect in Ru0.4Sn0.3Ti0.3 electrode for efficient chlorine evolution

Chlorine evolution reaction (CER) is a commercially valuable electrochemical reaction used at an industrial scale. However, oxygen evolution reaction (OER) during the electrolysis process inevitably leads to the decreased efficiency of CER. It is necessary to improve the selectivity of CER by minimizing or even eliminating the occurrence of OER. Herein, a ternary metal oxide (Ru0.4Sn0.3Ti0.3) electrode was fabricated and employed as an active and robust anode for CER. The Ru0.4Sn0.3Ti0.3 electrode exhibits an excellent CER performance in 6.0 M NaCl solution, with a low potential of 1.17 V (vs. saturated calomel electrode, SCE) at 200 mA cm-2 current density, a high Cl2 selectivity of over 90 %, and robust durability after consecutive operation for 160 h under 100 mA cm-2. The maximum O2-Cl2 potential difference between OER and CER further demonstrates the high Cl2 selectivity of Ru0.4Sn0.3Ti0.3 electrode. Theoretical studies show that the strong Ru 3d-Ti 3d orbitals hybridization effect makes the d-band center (εd) of Ru 3d and Ti 3d orbitals positively and negatively shifted, respectively, endowing Ru site with enhanced Cl adsorption ability (i.e. enhanced Ru-Cl interaction) and Ru0.4Sn0.3Ti0.3 electrode with superior CER activity. This work offers valuable insights into the development of advanced electrodes for CER in practical application.

Heterointerface manipulation in the architecture of Co-Mo2C@NC boosts water electrolysis

Heterostructures with tunable electronic properties have shown great potential in water electrolysis for the replacement of current benchmark precious metals. However, constructing heterostructures with sufficient interfaces to strengthen the synergistic effect of multiple species still remains a challenge due to phase separation. Herein, an efficient electrocatalyst composed of a nanosized cobalt/Mo2C heterostructure anchored on N-doped carbon (Co-Mo2C@NC) was achieved by in situ topotactic phase transformation. With the merits of high conductivity, hierarchical pores, and strong electronic interaction between Co and Mo2C, the Co-Mo2C@5NC-4 catalyst shows excellent activity with a low overpotential for the hydrogen evolution reaction (HER, 89 mV@10 mA cm-2 in alkaline medium; 143 mV@10 mA cm-2 in acidic medium) and oxygen evolution reaction (OER, 356 mV@10 mA cm-2 in alkaline medium), as well as high stability. Furthermore, this catalyst in an electrolyzer shows efficient activity for overall water splitting and long-term durability. Theoretical calculations reveal the optimized adsorption-desorption behaviour of hydrogen intermediates on the generated cobalt layered hydroxide (Co LDH)/Mo2C interfaces, resulting in boosting alkaline water electrolysis. This work proposes a new interface-engineering perspective for the construction of high-activity heterostructures for electrochemical conversion.

Nanocatalysis MoS2/rGO: An Efficient Electrocatalyst for the Hydrogen Evolution Reaction

In this study, a systematic investigation of MoS2 nanostructure growth on a SiO2 substrate was conducted using a two-stage process. Initially, a thin layer of Mo was grown through sputtering, followed by a sulfurization process employing the CVD technique. This two-stage process enables the control of diverse nanostructure formations of both MoS2 and MoO3 on SiO2 substrates, as well as the formation of bulk-like grain structures. Subsequently, the addition of reduced graphene oxide (rGO) was examined, resulting in MoS2/rGO(n), where graphene is uniformly deposited on the surface, exposing a higher number of active sites at the edges and consequently enhancing electroactivity in the HER. The influence of the synthesis time on the treated MoS2 and also MoS2/rGO(n) samples is evident in their excellent electrocatalytic performance with a low overpotential.

Superhydrophilic/superaerophobic amorphous Ni3S2/NiMoS electrocatalyst for enhanced hydrogen evolution

It is important to develop electrocatalysts that are cheap and have high activity for hydrogen evolution reaction (HER). In this work, Ni3S2/NiMoS with amorphous phase and unique candied-haws shaped nanoarray structure was successfully grown on nickel foam (Ni3S2/NiMoS/NF) as efficient HER catalyst. Combining Ni3S2 with NiMoS resulted in the extension of the heterointerfaces between the materials, which facilitated the HER process in alkaline medium. The amorphous Ni3S2/NiMoS with disordered atom arrangement provided abundant active sites. Also, the unique morphology of the catalytic electrode simultaneously enabled it exhibit superhydrophilicity and underwater superaerophobicity. It is beneficial for the sufficient diffusion of the electrolyte onto the catalyst surface and the fast departure of hydrogen bubbles from the surface. As a result, the activity of Ni3S2/NiMoS/NF was higher than that of Pt/C even at high current densities. It is very valuable for industrial applications that require high current density. The superior stability of Ni3S2/NiMoS/NF compared to Pt/C further demonstrated that this catalytic electrode has potential for industrial applications.

Ultrafine Pt Nanoparticles Anchored on 2D Metal-Organic Frameworks as Multifunctional Electrocatalysts for Water Electrolysis and Zinc-Air Batteries

Multifunctional electrocatalysts are crucial to cost-effective electrochemical energy conversion and storage systems requiring mutual enhancement of disparate reactions. Embedding noble metal nanoparticles in 2D metal-organic frameworks (MOFs) are proposed as an effective strategy, however, the hybrids usually suffer from poor electrochemical performance and electrical conductivity in operating conditions. Herein, ultrafine Pt nanoparticles strongly anchored on thiophenedicarboxylate acid based 2D Fe-MOF nanobelt arrays (Pt@Fe-MOF) are fabricated, allowing sufficient exposure of active sites with superior trifunctional electrocatalytic activity for hydrogen evolution, oxygen evolution, and oxygen reduction reactions. The interfacial Fe─O─Pt bonds can induce the charge redistribution of metal centers, leading to the optimization of adsorption energy for reaction intermediates, while the dispersibility of ultrafine Pt nanoparticles contributes to the high mass activity. When Pt@Fe-MOF is used as bifunctional catalysts for water-splitting, a low voltage of 1.65 V is required at 100 mA cm-2 with long-term stability for 20 h at temperatures (65 °C) relevant for industrial applications, outperforming commercial benchmarks. Furthermore, liquid Zn-air batteries with Pt@Fe-MOF in cathodes deliver high open-circuit voltages (1.397 V) and decent cycling stability, which motivates the fabrication of flexible quasisolid-state rechargeable Zn-air batteries with remarkable performance.

MXene Hybrid Nanosheet of WS2/Ti3C2 for Electrocatalytic Hydrogen Evolution Reaction

Designing low-cost hybrid electrocatalysts for hydrogen production is of significant importance. Recently, MXene-based materials are being increasingly employed in energy storage devices owing to their layered structure and high electrical conductivity. In this study, we propose a facile hydrothermal strategy for producing WS2/Ti3C2 nanosheets that function as electrocatalysts in the hydrogen evolution reaction (HER). WS2 provides a high surface area and active sites for electrocatalytic activity, whereas MXene Ti3C2 facilitates charge transfer. As a result, the synthesized WS2/Ti3C2 offers an increased surface area and exhibits an enhanced electrocatalytic activity in acidic media. The WS2/Ti3C2 (10%) catalyst exhibited a low onset potential of -150 mV versus RHE for the HER and a low Tafel slope of ∼62 mV dec-1. Moreover, WS2/Ti3C2 (10%) exhibited a double-layer capacitance of 1.2 mF/cm-2, which is 3 and 6 times greater than those of bare WS2 and Ti3C2, respectively. This catalyst also maintained a steady catalytic activity for the HER for over 1000 cycles.

Engineering Double Sulfur-Vacancy in CoS1.097@MoS2 Core-Shell Heterojunctions for Hydrogen Evolution in a Wide pH Range

Heterostructured nanomaterials have arisen as electrocatalysts with great potential for hydrogen evolution reaction (HER), considering their superiority in integrating different active components but are plagued by their insufficient active site density in a wide pH range. In this report, double sulfur-vacancy-decorated CoS1.097@MoS2 core-shell heterojunctions are designed, which contain a primary structure of hollow CoS1.097 nanocubes and a secondary structure of ultrathin MoS2 nanosheets. Taking advantage of the core-shell type heterointerfaces and double sulfur-vacancy, the CoS1.097@MoS2 catalyst exhibits pH-universal HER performance, achieving the overpotentials at 10 mA cm-2 of 190, 139, and 220 mV in 0.5 M H2SO4, 1.0 M KOH, and 1.0 M PBS, respectively. Systematic theoretical results show that the double sulfur-vacancy can endow the CoS1.097@MoS2 core-shell heterojunctions with promoted electron/mass transfer and enhanced reactive kinetics, thus boosting HER performance. This work clearly demonstrates an indispensable role of double sulfur-vacancy in enhancing the electrocatalytic HER performance of core-shell type heterojunctions under a wide pH operating condition.

Optimizing Eg Orbital Occupancy of Transition Metal Sulfides by Building Internal Electric Fields to Adjust the Adsorption of Oxygenated Intermediates for Li-O2 Batteries

Li-O2 batteries are acknowledged as one of the most promising energy systems due to their high energy density approaching that of gasoline, but the poor battery efficiency and unstable cycling performance still hinder their practical application. In this work, hierarchical NiS2 -MoS2 heterostructured nanorods are designed and successfully synthesized, and it is found that heterostructure interfaces with internal electric fields between NiS2 and MoS2 optimized eg orbital occupancy, effectively adjusting the adsorption of oxygenated intermediates to accelerate reaction kinetics of oxygen evolution reaction and oxygen reduction reaction. Structure characterizations coupled with density functional theory calculations reveal that highly electronegative Mo atoms on NiS2 -MoS2 catalyst can capture more eg electrons from Ni atoms, and induce lower eg occupancy enabling moderate adsorption strength toward oxygenated intermediates. It is evident that hierarchical NiS2 -MoS2 nanostructure with fancy built-in electric fields significantly boosted formation and decomposition of Li2 O2 during cycling, which contributed to large specific capacities of 16528/16471 mAh g-1 with 99.65% coulombic efficiency and excellent cycling stability of 450 cycles at 1000 mA g-1 . This innovative heterostructure construction provides a reliable strategy to rationally design transition metal sulfides by optimizing eg orbital occupancy and modulating adsorption toward oxygenated intermediates for efficient rechargeable Li-O2 batteries.

Modulating the d-Band Center Enables Ultrafine Pt3 Fe Alloy Nanoparticles for pH-Universal Hydrogen Evolution Reaction

By providing dual active sites to synergistically accelerate H2 O dissociation and H+ reduction, ordered intermetallic alloys usually show extraordinary performance for pH-universal hydrogen evolution reaction (HER). Herein, activated N-doped mesoporous carbon spheres supported intermetallic Pt3 Fe alloys (Pt3 Fe/NMCS-A), as a highly-efficient electrocatalyst for pH-universal HER, are reported. The Pt3 Fe/NMCS-A exhibits low overpotentials (η10 ) of 13, 29, and 48 mV to deliver 10 mA cm-2 in 0.5 m H2 SO4 , 1.0 m KOH, and 1.0 m phosphate buffered solution (PBS), respectively, as well as robust stability to maintain the overall catalytic performances. Theoretical studies reveal that the strong Pt 5d-Fe 3d orbital electronic interactions negatively shift the d-band center (εd ) of Pt 5d orbital, resulting in reduced H* adsorption energy of Pt sites and enhanced acidic HER activity. With Pt and Fe acting as co-adsorption sites for H* and *OH intermediates, respectively, a low energy barrier is required for Pt3 Fe/NMCS-A to dissociate H2 O to afford H* intermediates, which greatly promotes the H* adsorption and H2 formation in alkaline and neutral conditions. The synthetic strategy is further extended to the synthesis of Pt3 Co and Pt3 Ni alloys with excellent HER activity in pH-universal electrolytes, demonstrating the great potential of these Pt-based alloys for practical applications.

Construction of an Amethyst-like MoS2@Ni9S8/Co3S4 Rod Electrocatalyst for Overall Water Splitting

Transition metal sulphide electrocatalytic materials possess the bright overall water-splitting performance of practical electrocatalytic technologies. In this study, an amethyst-like MoS2@Ni9S8/Co3S4 rod electrocatalyst was constructed via a one-step hydrothermal method with in-situ-grown ZIF-67 nanoparticles on nickel foam (NF) as a precursor. The rational design and synthesis of MoS2@Ni9S8/Co3S4 endow the catalyst with neat nanorods morphology and high conductivity. The MoS2@Ni9S8/Co3S4/NF with the amethyst-like rod structure exposes abundant active sites and displays fast electron-transfer capability. The resultant MoS2@Ni9S8/Co3S4/NF exhibits outstanding hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalytic activities, with low overpotentials of 81.24 mV (HER) at 10 mA cm-2 and 159.67 mV (OER) at 50 mA cm-2 in 1.0 M KOH solution. The full-cell voltage of overall water splitting only achieves 1.45 V at 10 mA cm-2. The successful preparation of the amethyst-like MoS2@Ni9S8/Co3S4 rod electrocatalyst provides a reliable reference for obtaining efficient electrocatalysts for overall water splitting.

Scalable production of foam-like nickel-molybdenum coatings via plasma spraying as bifunctional electrocatalysts for water splitting

Foam-like NiMo coatings were produced from an inexpensive mixture of Ni, Al, and Mo powders via atmospheric plasma spraying. The coatings were deposited onto stainless-steel meshes forming a highly porous network mainly composed of nanostructured Ni and highly active Ni4Mo. High material loading (200 mg cm-2) with large surface area (1769 cm2 per cm2) was achieved without compromising the foam-like characteristics. The coatings exhibited excellent activity towards both hydrogen evolution (HER) and oxygen evolution (OER) reactions in alkaline media. The HER active coating required an overpotential of 42 mV to reach a current density of -50 mA cm-2 with minimum degradation after a 24 h chronoamperometry test at -10 mA cm-2. Theoretical simulations showed that several crystal surfaces of Ni4Mo exhibit near optimum hydrogen adsorption energies and improved water dissociation that benefit the HER activity. The OER active coating also consisting of nanostructured Ni and Ni4Mo required only 310 mV to achieve a current density of 50 mA cm-2. The OER activity was maintained even after 48 h of continuous operation. We envisage that the development of scalable production techniques for Ni4Mo alloys will greatly benefit its usage in commercial alkaline water electrolysers.

One-step synthesis of MoS2/NiS heterostructures with a stable 1T phase for an efficient hydrogen evolution reaction

Metallic phase (1T) MoS₂ has been regarded as an ideal catalytic material for the hydrogen evolution reaction (HER) due to its high active site density and favorable electrical conductivity. However, the preparation of 1T-phase MoS₂ samples requires tough reaction conditions and 1T-MoS₂ has poor stability under alkaline conditions. In this work, 1T-MoS₂/NiS heterostructure catalysts grown in situ on carbon cloth were prepared by a simple one-step hydrothermal method. The obtained MoS₂/NiS/CC combines the advantages of high active site density and a self-supporting structure, achieving stable 77% metal phase (1T) MoS₂. The combination of NiS and 1T-MoS₂ enhances the intrinsic activity of MoS₂ while the electrical conductivity is improved. These advantages enable the 1T-MoS₂/NiS/CC electrocatalyst to have a low overpotential of 89 mV (@10 mA cm^-2) and a small Tafel slope of 75 mV dec^-1 under alkaline conditions and provide a synthetic strategy of stable 1T-MoS₂-based electrocatalysts for the HER by a heterogeneous structure.

Lacunary polyoxometalate oriented construction of dispersed Ni3S2 confined in WO3 for electrocatalytic water splitting

Manufacturing low-cost, high-performance and earth-rich catalysts for hydrogen evolution (HER) and oxygen evolution reactions (OER) is critical to achieving sustainable green hydrogen production. Herein, we utilize lacunary Keggin-structure [PW₉O₃₄]^9- (PW₉) as a molecular pre-assembly platform to anchor Ni within a single PW₉ molecule by vacancy-directed and nucleophile-induced effects for the uniform dispersion of Ni at the atomic level. The chemical coordination of Ni with PW₉ can avoid the aggregation of Ni and favor the exposure of active sites. The Ni₃S₂ confined by WO₃ prepared from controlled sulfidation of Ni₆PW₉/Nickel Foam (Ni₆PW₉/NF) exhibited excellent catalytic activity in both 0.5 M H₂SO₄ and 1 M KOH solutions, which required only 86 mV and 107 mV overpotentials for HER at a current density of 10 mA∙cm^-2 and 370 mV for OER at 200 mA∙cm^-2. This is attributed to the good dispersion of Ni at the atomic level induced by trivacant PW₉ and the enhanced intrinsic activity by synergistic effect of Ni and W. Therefore, the construction of active phase from the atomic level is insightful to the rational design of dispersed and efficient electrolytic catalysts.

Fe-Incorporated Ni/MoO2 Hollow Heterostructure Nanorod Arrays for High-Efficiency Overall Water Splitting in Alkaline and Seawater Media

Developing high-efficiency and cost-effective bifunctional catalysts for water electrolysis is fascinating but still remains challenging. Thus, diverse strategies have been utilized to boost the activity toward oxygen/hydrogen evolution reactions (OER/HER) for water splitting. Among them, composition and structure engineering as an effective strategy has received extensive attention. Here, by means of a self-sacrificing template strategy and simultaneous regulation of the composition and structure, Fe-incorporated Ni/MoO₂ heterostructural (NiFe/Fe-MoO₂ ) hollow nanorod arrays are designed and constructed. Benefiting from abundant catalytic active sites, high intrinsic activity, and fast reaction kinetics, NiFe/Fe-MoO₂ exhibits superior OER (η₂₀  = 213 and 219 mV) and Pt-like HER activity (η₁₀  = 34 and 38 mV), respectively, in 1 m KOH and alkaline seawater media. This results in attractive prospects in alkaline water and seawater electrolysis with only voltages of 1.48 and 1.51 V, and 1.69 and 1.73 V to achieve current densities of 10 and 100 mA cm^-2 , respectively, superior to the Pt/C and RuO₂ pair as a benchmark. Undoubtedly, this work provides a beneficial approach to the design and construction of noble-metal-free bifunctional catalysts toward efficient hydrogen production from alkaline water and seawater electrolysis.

Three-Dimensional Au(NiMo)/Ti Catalysts for Efficient Hydrogen Evolution Reaction

In this study, NiMo catalysts that have different metal loadings in the range of ca. 28-106 µg cm^-2 were electrodeposited on the Ti substrate followed by their decoration with a very low amount of Au-crystallites in the range of ca. 1-5 µg cm^-2 using the galvanic displacement method. The catalytic performance for hydrogen evolution reaction (HER) was evaluated on the NiMo/Ti and Au(NiMo)/Ti catalysts in an alkaline medium. It was found that among the investigated NiMo/Ti and Au(NiMo)/Ti catalysts, the Au(NiMo)/Ti-3 catalyst with the Au loading of 5.2 µg cm^-2 gives the lowest overpotential of 252 mV for the HER to reach a current density of 10 mA·cm^-2. The current densities for HER increase ca. 1.1-2.7 and ca. 1.1-2.2 times on the NiMo/Ti and Au(NiMo)/Ti catalysts, respectively, at -0.424 V, with an increase in temperature from 25 °C to 75 °C.

Attractive Electron Delocalization Behavior of FeCoMoPB Amorphous Nanoplates for Highly Efficient Alkaline Water Oxidation

The rational design of high-performance and cost-effective electrocatalysts to overcome the kinetically sluggish water oxidation reaction is a grand challenge in water electrolysis. Transitional metals with incompletely filled d orbitals are expected to have intrinsic electronic interaction to promote the reaction kinetics, however, the construction of multiple active sites is still a bottleneck problem. Here, inspired by an amorphous alloy design strategy with chemical tunability, a noble-metal-free FeCoMoPB amorphous nanoplate for superior alkaline water oxidation is developed. The achieved overpotentials at current densities of 10, 100, and 500 mA cm^-2 are 239, 281, and 331 mV, respectively, while retaining a reliable stability of 48 h, outperforming most currently available electrocatalysts. Experimental and theoretical results reveal that the chemical complexity of the amorphous nanoplate leads to the formation of multiple active sites that is able to greatly lower the free energy of the rate-determining step during the water oxidation reaction. Moreover, the Mo element would result in an electron delocalization behavior to promote electron redistribution at its surrounding regions for readily donating and taking electrons. This amorphous alloy design strategy is expected to stimulate the development of more efficient electrocatalysts that is applicable in energy devices, such as metal-air batteries, fuel cells, and water electrolysis.

Nanoscale hetero-interfaces for electrocatalytic and photocatalytic water splitting

As green and sustainable methods to produce hydrogen energy, photocatalytic and electrochemical water splitting have been widely studied. In order to find efficient photocatalysts and electrocatalysts, materials with various composition, size, and surface/interface are investigated. In recent years, constructing suitable nanoscale hetero-interfaces can not only overcome the disadvantages of the single-phase material, but also possibly provide new functionalities. In this review, we systematically introduce the fundamental understanding and experimental progress in nanoscale hetero-interface engineering to design and fabricate photocatalytic and electrocatalytic materials for water splitting. The basic principles of photo-/electro-catalytic water splitting and the fundamentals of nanoscale hetero-interfaces are briefly introduced. The intrinsic behaviors of nanoscale hetero-interfaces on electrocatalysts and photocatalysts are summarized, which are the electronic structure modulation, space charge separation, charge/electron/mass transfer, support effect, defect effect, and synergistic effect. By highlighting the main characteristics of hetero-interfaces, the main roles of hetero-interfaces for electrocatalytic and photocatalytic water splitting are discussed, including excellent electronic structure, efficient charge separation, lower reaction energy barriers, faster charge/electron/mass transfer, more active sites, higher conductivity, and higher stability on hetero-interfaces. Following above analysis, the developments of electrocatalysts and photocatalysts with hetero-structures are systematically reviewed.

Flowery ln2MnSe4 Novel Electrocatalyst Developed via Anion Exchange Strategy for Efficient Water Splitting

Oxygen and hydrogen generated by water electrolysis may be utilized as a clean chemical fuel with high gravimetric energy density and energy conversion efficiency. The hydrogen fuel will be the alternative to traditional fossil fuels in the future, which are near to exhaustion and cause pollution. In the present study, flowery-shaped In₂MnSe₄ nanoelectrocatalyst is fabricated by anion exchange reaction directly grown on nickel foam (NF) in 1.0 M KOH medium for oxygen evolution reaction (OER). The physiochemical and electrical characterization techniques are used to investigate the chemical structure, morphology, and electrical properties of the In₂MnSe₄ material. The electrochemical result indicates that synthesized material exhibits a smaller value of Tafel slope (86 mV/dec), lower overpotential (259 mV), and high stability for 37 h with small deterioration in the current density for a long time. Hence, the fabricated material responds with an extraordinary performance for the OER process and for many other applications in the future.

In Situ Growth of NiSe2-MoSe2 Heterostructures on Graphene Nanosheets as High-Performance Electrocatalyst for Hydrogen Evolution Reaction

Developing highly efficient and stable electrocatalysts for hydrogen evolution reaction (HER) is regarded as a crucial way to reduce energy loss in water splitting. Herein, NiSe2/MoSe2 heterostructures grown on graphene nanosheets (NiSe2-MoSe2 HTs/G) have been in situ synthesized by a simple hydrothermal reaction. As an electrocatalyst for HER, NiSe2-MoSe2 HTs/G delivers superior performance with a low Tafel slope of 65 mV dec−1, a small overpotential of 144 mV at 10 mA cm−2, and long-term stability up to 24 h. The superior performance for HER can be mainly ascribed to the synergistic effects of NiSe2-MoSe2 heterostructures, which can facilitate the rapid electron transfer from the electrode to the exposed MoSe2 edges to take part in the HER reaction, thus boosting the HER kinetics. Moreover, the graphene matrix with high conductivity can not only improve the overall conductivity of the composite but also greatly increase the exposed active sites, therefore further promoting the HER performance. This study provides a simple route for fabricating bimetallic selenides-based heterostructures on graphene as an efficient and stable electrocatalyst for HER.

Defect engineering tuning electron structure of biphasic tungsten-based chalcogenide heterostructure improves its catalytic activity for hydrogen evolution and triiodide reduction

The design and exploration of high-efficiency and low-cost electrode catalysts are of great significance to the development of novel energy conversion technologies. In this work, metal and nonmetal heteroatoms co-doped biphasic tungsten-based chalcogenide heterostructured catalyst (Co-WS₂/P-WO_2.9) with rich defects is successfully synthesized by a vulcanization technique. The electrocatalytic performance of WS₂/WO₃ in the hydrogen evolution reaction (HER) and triiodide reduction reaction is significantly enhanced by modifying and optimizing its electronic structure through a defect engineering strategy. As an electrocatalyst for HER, the optimized Co-WS₂/P-WO_2.9 exhibits a low overpotential at 10 mA cm^-2 of 146 and 120 mV with small Tafel slopes of 86 and 74 mV dec^-1 in alkaline and acidic electrolyte, respectively. In addition, a Co-WS₂/P-WO_2.9 assembled solar cell yields a short circuit current density of 15.85 mA cm^-2, an open-circuit voltage of 0.74 V, a fill factor of 0.66, and a competitive power conversion efficiency (7.83%), which is comparable or higher than conventional Pt-based solar cell (16.02 mA cm^-2, 0.70 V, 0.63, 7.14%). The formation of a heterostructure in Co-WS₂/P-WO_2.9 leads to the presence of a built-in electric field in the interfacial region between Co-WS₂ and P-WO_2.9, which leads to an increased open-circuit voltage from 0.70 V for Pt to 0.74 V for Co-WS₂/P-WO_2.9. This work can provide a technical support for developing high-performance heterostructured catalysts, which open up a way for improving catalytic performance of heterostructured catalysts in the field of electrocatalysis.

Engineering transition metal catalysts for large-current-density water splitting

Electrochemical water splitting plays a crucial role in transferring electricity to hydrogen fuel and appropriate electrocatalysts are crucial to satisfy the strict industrial demand. However, the successfully developed non-noble metal catalysts have a small tested range and the current density is usually less than 100 mA cm^-2, which is still far away from the practical application standards. Aiming to provide guidance for the fabrication of more advanced electrocatalysts with a large current density, we herein systematically summarize the recent progress achieved in the field of cost-efficient and large-current-density electrocatalyst design. Beginning by illustrating the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) mechanisms, we elaborate on the concurrent issues of non-noble metal catalysts that are required to be addressed. In view of large-current-density operating conditions, some distinctive features with regard to good electrical conductivity, high intrinsic activity, rich active sites, and porous architecture are also summarized. Next, some representative large-current-density electrocatalysts are classified. Finally, we discuss the challenges associated with large-current-density water electrolysis and future pathways in the hope of guiding the future development of more efficient non-noble-metal catalysts to boost large-scale hydrogen production with less electricity consumption.

CoS2 Nanoparticles Anchored on MoS2 Nanorods As a Superior Bifunctional Electrocatalyst Boosting Li2 O2 Heteroepitaxial Growth for Rechargeable Li-O2 Batteries

Developing an excellent bifunctional catalyst is essential for the commercial application of Li-O₂ batteries. Heterostructures exhibit great application potential in the field of energy catalysis because of the accelerated charge transfer and increased active sites on their surfaces. In this work, CoS₂ nanoparticles decorated on MoS₂ nanorods are constructed and act as a superior cathode catalyst for Li-O₂ batteries. Coupling MoS₂ and CoS₂ can not only synergistically enhance their electrical conductivity and electrochemical activity, but also promote the heteroepitaxial growth of discharge products on the heterojunction interfaces, thus delivering high discharge capacity, stable cycle performance, and good rate capability.

Controllable Synthesis of a Loofah-Like Cobalt-Nickel Selenide Network as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction

The rational design and construction of noble metal-free electrocatalysts featuring high efficiency and low cost are important for the hydrogen evolution reaction (HER). A significant development in the synthesis of a loofah-like Co_0.6Ni_0.4Se₂ architecture (expressed as Co_0.6Ni_0.4Se₂-LN) electrocatalyst on carbon cloth through a three-step method is reported. Both the ionic liquid 1-dodecyl-3-methylimidazolium acetate (IL, [C₁₂MIm]Ac) and the molar ratio of Co to Ni play a pivotal role in the synthesis of Co_0.6Ni_0.4Se₂-LN with 3D hierarchical architecture. Co_0.6Ni_0.4Se₂-LN exposes abundant active sites and provides hierarchical and stable transfer channels for both electrolyte ions and electrons, which results in outstanding HER performance. Impressively, Co_0.6Ni_0.4Se₂-LN shows a low overpotential of 163 mV at 10 mA cm^-2, a small Tafel slope of 40 mV dec^-1, and superior stability to continuously catalyze the generation of H₂ for 40 h. This study offers a new perspective to the synthesis of high-efficiency inexpensive electrocatalysts for HER and also presents a good example for investigating the potential application of ILs in the synthesis of functional materials.

Synergistic mechanism of Ni(OH)2/NiMoS heterostructure electrocatalyst with crystalline/amorphous interfaces for efficient hydrogen evolution over all pH ranges

Designing and fabricating efficient electrocatalysts is a practical step toward the commercial application of the efficient hydrogen evolution reaction (HER) over all pH ranges. Herein, novel Ti@Ni(OH)₂-NiMoS heterostructure with interface between crystalline Ni(OH)₂ and amorphous NiMoS was rationally designed and fabricated on Ti mesh (denoted as Ti@Ni(OH)₂-NiMoS). Acid etching and calcination experiments helped in accurate elucidation of the synergistic mechanism as well as the vital role on crystalline Ni(OH)₂ and amorphous NiMoS. In acidic solutions, the HER performance of Ti@Ni(OH)₂-NiMoS was mainly attributed to the amorphous NiMoS. In neutral, alkaline, and natural seawater solutions, the HER performance was mainly determined by the synergistic interface behaviors between the Ni(OH)₂ and NiMoS. The crystalline Ni(OH)₂ accelerated water dissociation kinetics, while the amorphous NiMoS provided abundant active sites and allowed for fast electron transfer rates. To deliver current densities of 10 mA·cm^-2 in acidic, neutral, alkaline, and natural seawater solutions, the Ti@Ni(OH)₂-NiMoS required overpotentials of 138, 198, 180 and 371 mV, respectively. This paper provides general guidelines for designing efficient electrocatalyst with crystalline/amorphous interfaces for efficient hydrogen evolution over all-pH ranges.

Co doped MoS2 nanosheet: a stable and pH-universal electrocatalyst for efficient hydrogen evolution reaction

Generally, the hydrogen generation of non-noble metal based electrocatalysts is limited by the high overpotential and acid-base environment of electrolyte. Therefore, it is essential to develop hydrogen evolution reaction (HER)...

Carbon nitride based Schottky junction with a Ni–Mo synergistic interaction for highly efficient photocatalytic hydrogen production

A CN/3NiMoP2 Schottky junction with a Ni–Mo synergistic interaction demonstrates a comparable photocatalytic HER performance to CN/3 wt% Pt and satisfactory stability.

MWCNT-modified MXene as cost-effective efficient bifunctional catalyst for overall water splitting

Utilization of cost-effective, bifunctional, and efficient electrocatalysts for complete water splitting is desirable for sustainable clean hydrogen energy.

Microwave-Assisted Auto-Combustion Synthesis of Binary/Ternary Co x Ni1-x Ferrite for Electrochemical Hydrogen and Oxygen Evolution

Enormous efforts have been dedicated to engineering low-cost and efficient electrocatalysts for both hydrogen evolution and oxygen evolution reactions (HER and OER, respectively). For this, the current contribution reports the successful synthesis of binary/ternary metal ferrites (Co x Ni1-x Ferrite; x = 0.0, 0.1, 0.3, 0.5, 0.7, and 1.0) by a simple one-step microwave technique and subsequently discusses its chemical and electrochemical properties. The X-ray diffraction analysis substantiated the phase purity of the as-obtained catalysts with various compositions. Additionally, the morphology of the nanoparticles was identified via transmission electron microscopy. Further, the vibrating sample magnetometer justified the ferromagnetic character of the as-prepared products. The electrochemical measurements revealed that the as-prepared materials required the overpotentials of 422-600 and 419-467 mV for HER and OER, respectively, to afford current densities of 10 mA cm-2. In the general sense, Ni cation substitution with Co influenced favorably toward both HER and OER. Among all synthesized electrocatalysts, Co0.9Ni0.1Ferrite displayed the highest performance in terms of OER in 1 M KOH solution, which is related to the synergistic effect of multiple parameters including the optimal substitution amount of Co, the highest Brunauer-Emmett-Teller surface area, the smallest particle size among all samples (26.71 nm), and the lowest charge transfer resistance. The successful synthesis of ternary ferrites carried out for the first time via a microwave-assisted auto-combustion route opens up a new path for their applications in renewable energy technologies.

One-Step Synthesis of Bifunctional Nickel Phosphide Nanowires as Electrocatalysts for Hydrogen and Oxygen Evolution Reactions

The Ni₂P nanowires were simply synthesized via a rapid one-step hydrothermal approach, in which deionized water, red phosphorus, nickel acetate, and hexadecyl trimethyl ammonium bromide were used as the solvent, phosphor and nickel sources, and active agent, respectively. The as-synthesized Ni₂P nanowire clusters were composed of uniform nanowires with length of about 10 μm and diameter of about 40 nm. The Ni₂P nanowires exhibited enhanced electrocatalytic activity for both hydrogen evolution reaction and oxygen evolution reaction This work provides good guidance for the rational design of nickel phosphides with unique nanostructures for highly efficient overall water splitting.

Recent Advances in Alkaline Exchange Membrane Water Electrolysis and Electrode Manufacturing

Water electrolysis to obtain hydrogen in combination with intermittent renewable energy resources is an emerging sustainable alternative to fossil fuels. Among the available electrolyzer technologies, anion exchange membrane water electrolysis (AEMWE) has been paid much attention because of its advantageous behavior compared to other more traditional approaches such as solid oxide electrolyzer cells, and alkaline or proton exchange membrane water electrolyzers. Recently, very promising results have been obtained in the AEMWE technology. This review paper is focused on recent advances in membrane electrode assembly components, paying particular attention to the preparation methods for catalyst coated on gas diffusion layers, which has not been previously reported in the literature for this type of electrolyzers. The most successful methodologies utilized for the preparation of catalysts, including co-precipitation, electrodeposition, sol-gel, hydrothermal, chemical vapor deposition, atomic layer deposition, ion beam sputtering, and magnetron sputtering deposition techniques, have been detailed. Besides a description of these procedures, in this review, we also present a critical appraisal of the efficiency of the water electrolysis carried out with cells fitted with electrodes prepared with these procedures. Based on this analysis, a critical comparison of cell performance is carried out, and future prospects and expected developments of the AEMWE are discussed.

Hierarchical molybdenum-doped NiCoP@carbon microspheres: a highly-efficient electrocatalyst for the hydrogen evolution reaction

Herein, we present hierarchical Mo-doped NiCoP@carbon microspheres that exhibit a noticeable enhancement in catalytic activity and fast kinetics for hydrogen evolution. An overpotential of 74.6 mV at 10 mA cm^-2 and 54.9 mV dec^-1 can be achieved. These results demonstrated the excellent electrochemical properties arising from the intrinsic characteristics of elemental doping and morphology control. We believe that this work opens a new avenue to fabricating TMD-based catalysts via the engineering of transition metal compounds.

Dual-cation-doped MoS2nanosheets accelerating tandem alkaline hydrogen evolution reaction

Molybdenum disulfide (MoS₂) nanosheets are promising candidates as earth-abundant and low-cost catalyst for hydrogen evolution reaction (HER). Nevertheless, compared with the benchmark Pt/C catalyst, the application of MoS₂nanosheets is limited to its relatively low catalytic activity, especially in alkaline environments. Here, we developed a dual-cation doping strategy to improve the alkaline HER performance of MoS₂nanosheets. The designed Ni, Co co-doped MoS₂nanosheets can promote the tandem HER steps simultaneously, thus leading to a much enhanced catalytic activity in alkaline solution. Density functional theory calculations revealed the individual roles of Ni and Co dopants in the catalytic process. The doped Ni is uncovered to be the active site for the initial water-cleaving step, while the Co dopant is conducive to the H desorbing by regulating the electronic structure of neighboring edge-S in MoS₂. The synergistic effect resulted by the dual-cation doping thus facilitates the tandem HER steps, providing an effective route to raise the catalytic performance of MoS₂materials in alkaline solution.

Plasmon-enhanced hydrogen evolution reaction on a Ag-branched-nanowire/Pt nanoparticle/AgCl nanocomposite

A plasmon-enhanced photocatalytic system was designed with Ag-Pt-AgCl nanocomposites. Branched nanowires of Ag (AgBNWs) were first synthesized on indium-doped tin oxide-coated glass by electrodeposition. Then, the AgBNWs were dipped into an aqueous solution of Na2[PtCl6] at different concentrations from 1 to 5 mM to deposit Pt nanoparticles (PtNPs) on the AgBNWs via galvanic displacement. During the PtNP deposition, eluted Ag+ ions reacted with Cl- ions to precipitate AgCl on the AgBNWs. The obtained AgBNW/PtNP/AgCl nanocomposites exhibited plasmonic absorption at approximately 465 nm. The nanocomposites were then examined as photoelectrodes for hydrogen evolution. The hybridization of the PtNPs on the AgBNWs significantly decreased the overpotential for water splitting in the dark, and the large number of PtNPs resulted in a higher efficiency compared to a conventional catalyst. Under blue-light irradiation (479 nm, 100 mW cm-2), the overpotential decreased by -110 mV, and the current density increased by 27.8 mA cm-2. Under red-light irradiation (631 nm, 100 mW cm-2), the shift in onset potential was small, which could be attributed to the mismatching of the plasmonic absorption band with the excitation wavelength. The nanocomposite without AgCl (AgBNW/PtNP) was less effective at lowering the overpotential but more effective at improving the onset potential than AgBNW/PtNP/AgCl. These electrochemical behaviors were explained by the synergistic effect of the plasmon-induced photocurrent and charge transfer between Ag, Pt, and AgCl. The nanocomposite retained its photocatalytic activity after 400 cycles; therefore, the AgBNW/PtNP/AgCl nanocomposite could be useful for hydrogen evolution devices.

Hierarchical Architectures Based on Ru Nanoparticles/Oxygen-Rich-Carbon Nanotubes for Efficient Hydrogen Evolution

Highly active and durable electrocatalysts are essential for producing hydrogen fuel through the hydrogen evolution reaction (HER). Here, a uniform deposition of Ru nanoparticles strongly interacting with oxygen-rich carbon nanotube architectures (Ru-OCNT) through ozonation and hydrothermal approaches has been designed. The hierarchical structure of Ru-OCNT is made by self-assembly of oxygen functionalities of OCNT. Ru nanoparticles interact strongly with OCNT at the Ru/OCNT interface to give excellent catalytic activity and stability of the Ru-OCNT, as further confirmed by density functional theory. Owing to the hierarchical structure and adjusted surface chemistry, Ru-OCNT has an overpotential of 34 mV at 10 mA cm^-2 with a Tafel slope of 27.8 mV dec^-1 in 1 M KOH, and an overpotential of 55 mV with Tafel slope of 33 mV dec^-1 in 0.5 M H₂ SO₄ . The smaller Tafel slope of Ru-OCNT than Ru-CNT and commercial Pt/C in both alkaline and acidic electrolytes indicates high catalytic activity and fast charge transfer kinetics. The as-proposed chemistry provides the rational design of hierarchically structured CNT/nanoparticle electrocatalysts for HER to produce hydrogen fuel.