Bifunctional Catalysts For Water Splitting Research Articles

Rational design of multi-component Fe(OH)3/Ni-NiO heterostructures bifunctional catalyst for electrochemical water splitting

Exploring economic-efficient bifunctional catalysts is critical for the production of green hydrogen through water splitting. Herein, we fabricate a novel hybrid catalyst with three-phase heterojunction (Fe(OH)3/Ni-NiO) via a simple electrodeposition and chemical precipitation method. Benefiting from the desirable amorphous-crystal interfaces, the electronic structure of Ni, NiO and Fe(OH)3 is regulated, which will optimize the adsorption of H intermediates (H*) and also reduce the kinetic barrier for the hydrogen evolution reaction (HER). The optimal Fe(OH)3–3/Ni-NiO/CC shows superior bifunctional activity with low overpotentials of 66 mV for HER and 220 mV for OER at 10 mA cm−2 in alkaline solution, respectively, as well as remarkable durability over a period of 40 h. Besides, Fe(OH)3–3/Ni-NiO/CC requires 1.52 and 1.72 V to deliver 10 and 100 mA cm−2 and shows no obvious increase in current within 40 h toward overall water splitting. Experimental and theoretical results show that the HER process is promoted by the synergistic effect of electronic redistribution between Ni, NiO and Fe(OH)3 due to the construction of three phase crystalline-amorphous heterogeneous interface. Meanwhile, Fe(OH)3 and NiO appeared reconstruction, transforming into FeOOH and NiOOH during OER process, respectively. This work offers a simple synthesis method for designing bifunctional catalysts for water splitting.

A Review of the Structure–Property Relationship of Nickel Phosphides in Hydrogen Production

Hydrogen, one of the most promising forms of new energy sources, due to its high energy density, low emissions, and potential to decarbonize various sectors, has attracted significant research attention. It is known that electrocatalytic hydrogen production is one of the most widely investigated research directions due to its high efficiency in the conversion of electricity to H2 gas. However, given the limited reserves and high cost of precious metals, the search for non-precious metal-based catalysts has been widely explored, for example, transition metal phosphides, oxides, and sulfides. Despite this interest, a detailed survey unveils that the surface and internal structures of the alternative catalysts, including their surface reconstruction, composition, and electronic structure, are poorly studied. As a result, a disconnection in the structure–property relationship severely hinders the rational design of efficient and reliable non-precious metal-based catalysts. In this review, by focusing on Ni5P4, a bifunctional catalyst for water splitting, we systematically summarize the material motifs pertaining to the different synthetic methods, surface characteristics, and hydrolysis properties. It is believed that a cascaded correlation may provide insights toward understanding the fundamental catalytic mechanism and design of robust alternative catalysts for hydrogen production.

Acanthosphere-like bimetallic sulfide Cu9S5/Mo2S3/NF as bifunctional catalyst for water splitting

Reducing the overpotential of water splitting is an important strategy for achieving low-cost and large-scale production of hydrogen (H2) and oxygen (O2). It is shown that bimetallic sulfide combines the advantages of a single component and an ideal structure for efficient electrocatalysis. Hence, an acanthosphere-like bimetallic sulfide electrocatalyst Cu9S5/Mo2S3/NF with high catalytic performance and superior durability was prepared by a simple one-pot method. In the oxygen evolution reaction (OER), the Cu9S5/Mo2S3/NF achieved a Tafel slope of 62.7 mV dec-1, and an overpotential of 224 mV at a current density of 10 mA cm−2. Concomitantly, it also possesses a small overpotential of 96 mV at 10 mA cm−2 and low Tafel slope of 81.6 mV dec-1 at the used of hydrogen evolution reaction (HER) catalyst. Moreover, the two-electrode system Cu9S5/Mo2S3/NF||Cu9S5/Mo2S3/NF single cell requires only 1.55 V to achieve a current density of 10 mA cm−2 in overall water splitting. This work highlights the advantages of bimetallic sulfide combines structural for overpotential of water splitting and provides an idea for modifying the catalytic performance of single metal sulfides and preparing high-performance bimetallic sulfide catalysts.

Medium-entropy alloy MoCoCu-P as an efficient bifunctional catalyst for water splitting

Medium/high-entropy alloy (MEA/HEA) catalysts have emerged as ideal candidates as multi-functional catalysts owing to their synergistic effects of multiple metal components on the boosted catalytic activity. However, the facile preparation and screening of suitable MEAs element to achieve high catalytic performance still remain challenging. In this work, we successfully synthesized a MoCoCu-P MEA electrocatalyst for water splitting electrocatalysis through a feasible electrodeposition method. The as-prepared MEA demonstrated an overpotential of 276.1 mV (j=10 mA/cm²) for OER with a Tafel slope of 38.3 mV/dec, coupled with an overpotential of 64.7 mV for HER (j=10 mA/cm²) with a Tafel slope of 87.7 mV/dec. Employed in an overall water electrolysis cell, MEA achieved a nearly 100% Faradaic efficiency and superior stability over than 50 hours at a high current density of 50 mA/cm2. X-ray photoelectron spectroscopy (XPS) analysis verify that high-valence Co and Mo are the most active sites for OER, while electron-rich Cu at the presence of P is responsible for the boosted HER in the MoCoCu-P MEA. This study not only provides a feasible electrodeposition strategy to obtain MEA catalysts with high activity and excellent stability, but also sheds fundamental lights on the identification of the active sites in MEA catalysis.

Unveiling the synergistic effect of amorphous CoW-phospho-borides for overall alkaline water electrolysis

Amorphous transition-metal-phospho-borides (TMPBs) are emerging as a new class of hybrid bifunctional catalysts for water-splitting. The present work reports the discovery of CoWPB as a new promising material that adds to the smaller family of TMPBs. The optimized compositions, namely Co4WPB5 and Co2WPB1 could achieve 10 mA/cm2 at just 72 mV and 262 mV of overpotentials for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, in 1 M KOH. Furthermore, the catalyst showed good performance in a 2-electrode assembly (1.59 V for 10 mA/cm2) with considerable stability (70 h stability, 10,000 operating cycles). Detailed morphological and electrochemical characterizations unveiled insights into the role of all elements in catalyst's improved performance. The presence of W was found to be crucial in improving the electronic conductivity and charge redistribution, making CoWPB suitable for both HER and OER. In computational simulation analysis, two configurations with different atomic environments, namely, CoWPBH and CoWPBO were found to have the lowest calculated overpotentials for HER and OER, respectively. It was found that the surface P-sites in CoWPBH were HER-active while the Co-sites in CoWPBO were OER-active sites. The study presents new knowledge about active sites in such multi-component catalysts that will foster more advancement in the area of water electrolysis.

A Hierarchical Polyoxometalate/Pd/Mos2 Hybrid: Developing an Efficient Novel Bifunctional Catalyst for Water Splitting

AbstractCatalytic water splitting is a promising approach to produce clean hydrogen fuel from renewable energy sources. However, developing hybrid heterostructures capable of efficiently breaking down water into its constituent elements, hydrogen, and oxygen, presents a considerable challenge. In this study, a novel hierarchical POM/Pd/MoS2 hybrid heterostructure, composed of sheets of MoS2 modified with Pd nanoparticles and combined with a cobalt‐based polyoxometalate (POM), serving as bifunctional catalyst for water splitting is reported. Through a synergistic synthetic approach, MoS2, acting as a reducing agent, triggers the nucleation and growth of Pd nanoparticles, which, in turn, serve as anchoring sites for the polymerization of the cobalt‐based POM into fibers. POM/Pd/MoS2 hybrid exhibits an enhanced oxygen evolution reaction (OER) activity, comparable to the benchmark catalysts Ir/C and IrO2/C in alkaline media, being its hydrogen evolution reaction (HER) activity similar to the activated Pd/MoS2 hybrid. The intriguing electrocatalytic capability of the resulting material for producing hydrogen and oxygen through electrochemical means arises from the enhanced charge storage capacity and conductivity of MoS2, the multi‐electron transfer facilitated by the POM, and the high electrocatalytic activity of the metals.

Unveiling the Synergistic Potential of Laser Chemical Solid‐Phase Deposition of Atomic Platinum‐Metal Layer on 2D Materials for Bifunctional Catalysts

AbstractThe formation of high‐density atomic metal layers on 2D materials enhances catalytic device development by providing a large surface area, precise control over active sites, and enhanced reactivity. Here, pulsed laser‐induced chemical solid‐phase deposition (LCSD) is introduced for achieving high‐density atomic metal layers. By leveraging high‐density plasma generated via pulsed nanosecond laser irradiation of thin salt layers on 2D materials, atomic‐scale metals are deposited onto abundant nucleation sites, creating dense atomic‐metal layers. This study engineers layered double hydroxide (LDH) materials layered with atomic platinum‐based alloys, exhibiting exceptional catalytic activity for overall water splitting. LDH's excellent oxygen evolution performance combined with remarkable advances in hydrogen evolution catalysis are achieved. Introducing a second element improves Pt layer dispersion and uniformity, resulting in extraordinary Pt distribution density and minimal overpotential. The LDH and Pt‐metal combination creates powerful synergistic effects, significantly enhancing catalytic performance and enabling superior bifunctional catalysts for water splitting. LCSD effectively fabricates stable nanocomposites designed for electrocatalytic applications, leveraging unique structures of atom‐scale metal‐supported composite 2D materials, enhancing overall electrocatalytic performance. This breakthrough impacts energy conversion and environmental protection, broadening electrocatalysis and revolutionizing atom‐scale metal‐supported composite 2D materials. Its practical applications span various areas, contributing to sustainable energy solutions and environmental preservation.

Synergistically Driven CoCr-LDH@VNiS2 as a Bifunctional Electrocatalyst for Overall Water Splitting and Flexible Supercapacitors.

Utilizing alternative energy sources to fossil fuels has remained a significant issue for humanity. In this context, efficient earth-abundant bifunctional catalysts for water splitting and energy storage technologies like hybrid supercapacitors have become essential for achieving a sustainable future. Herein, CoCr-LDH@VNiS2 was synthesized by hydrothermal synthesis. The CoCr-LDH@VNiS2 catalyst entails 1.62 V cell voltage to reach the current density of 10 mA cm-2 for overall water splitting. The CoCr-LDH@VNiS2 electrode illustrates a high electrochemical specific capacitance (Csp) of 1380.9 F g-1 at a current density of 0.2 A g-1 and an outstanding stability with 94.76% retention. Moreover, the flexible asymmetric supercapacitor (ASC) achieved an energy density of 96.03 W h kg-1@0.2 A g-1 at a power density of 539.98 W kg-1 with remarkable cyclic stability. The findings provide a new approach toward the rational design and synthesis of bifunctional catalysts for water splitting and energy storage.

Tuning coordination microenvironment of V2CTx MXene for anchoring single-atom toward efficient multifunctional electrocatalysis

The rational design of low-cost and high-performance multifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution/reduction reaction (OER/ORR) is essential for efficient overall water splitting and rechargeable metal-air battery. Herein, through density functional theory calculations, we creatively regulate the coordination microenvironment of V2CTx MXene (M−v−V2CT2, T = O, Cl, F and S) as substrates of single-atom catalysts (SACs), and then systematically explore their HER, OER, and ORR electrocatalytic performance. Our results disclose that Rh-v-V2CO2 is a promising bifunctional catalyst for water splitting (overpotentials of 0.19 and 0.37 V for HER and OER). Besides, Pt-v-V2CCl2 and Pt-v-V2CS2 possess desirable bifunctional OER/ORR activity with overpotentials of 0.49/0.55 V and 0.58/0.40 V, respectively. More interestingly, Pt-v-V2CO2 is a promising trifunctional catalyst under vacuum, implicit and explicit solvation conditions, which transcends commercially used Pt and IrO2 catalysts for HER/ORR and OER. The electronic structure analysis further demonstrates that surface functionalization can optimize the local microenvironment of the SACs and thus tune the interaction strength of intermediate adsorbates. This work provides a feasible strategy for developing advanced multifunctional electrocatalysts and enriches the application of MXene in energy conversion and storage.

Non‐noble metal Fe2O3@NiO as efficient bifunctional catalysts for water splitting

AbstractThe development of non‐noble metal catalysts is crucial for hydrogen production. In this study, electrochemically reconfigurable Fe2O3@NiO‐x composite catalysts were synthesized within tens of seconds using a simple microwave deposition method. Interestingly, Fe2O3@NiO‐5 exhibited a high‐speed and deep surface reconstruction capability, greatly enhancing the hydrogen evolution reaction (HER) activity. DFT calculations also confirmed that the reconstruction process optimized the adsorption energy of H2O and H intermediate to promote HER kinetics. The optimized Fe2O3@NiO‐5 electrode only afforded an overpotential of 295 mV at 10 mA cm−2 and it steadily functioned for 25 h for HER in 1 M KOH. In addition, benefiting from the combination of Fe2O3 and NiO layer during the synthesis process, Fe2O3 and NiO converted into FeOOH and NiOOH, respectively, resulted in the excellent oxygen evolution reaction (OER) activity of Fe2O3@NiO‐5. The as‐prepared Fe2O3@NiO‐5 only required an overpotential of 186 mV at 10 mA cm−2 and exhibited excellent stability for up to 144 h. As a bifunctional catalyst, the Fe2O3@NiO‐5 electrode can deliver a current density of 20 mA cm−2 at a low voltage of 1.78 V with high durability for water splitting. This work can provide a new perspective for constructing advanced non‐noble metal electrode.

Exploring Optimal Water Splitting Bifunctional Alloy Catalyst by Pareto Active Learning.

Design of bifunctional multimetallic alloy catalysts, which are one of the most promising candidates for water splitting, is a significant issue for the efficient production of renewable energy. Owing to large dimensions of the components and composition of multimetallic alloys, as well as the trade-off behavior in terms of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) overpotentials for bifunctional catalysts, it is difficult to search for high-performance bifunctional catalysts with multimetallic alloys using conventional trial-and-error experiments. Here, an optimal bifunctional catalyst for water splitting is obtained by combining Pareto active learning and experiments, where 110 experimental data points out of 77946 possible points lead to effective model development. The as-obtained bifunctional catalysts for HER and OER exhibit high performance, which is revealed by model development using Pareto active learning; among the catalysts, an optimal catalyst (Pt0.15 Pd0.30 Ru0.30 Cu0.25 ) exhibits a water splitting behavior of 1.56 V at a current density of 10 mA cm-2 . This study opens avenues for the efficient exploration of multimetallic alloys, which can be applied in multifunctional catalysts as well as in other applications.

Efficient Mo–Co(OH)2/Co3O4/Ni foam electrocatalyst for overall water splitting

Bifunctional catalysts for water splitting based on 3d transition metals are well-documented. Herein, a Co3O4 layer was introduced between tremella-like Mo–Co(OH)2 and nickel foam through electrodeposition(1st)-pyrolysis-electrodeposition(2nd) strategy as the conductive secondary substate. The secondary electrodeposition particularly led to introduce the Mo species into the surface layer of Co(OH)2. The as-prepared Mo–Co(OH)2/Co3O4/NF-x(x represents the deposition time) was further applied as the catalyst for HER, OER and the overall water-splitting reactions. Notably, the Mo–Co(OH)2/Co3O4/NF-800 catalyst exhibited outstanding activity to achieve a current density of 10 ​mA ​cm-2, with overpotentials of 116 ​mV and 234 ​mV for HER and OER in 1 ​M KOH, respectively. Moreover, a cell voltage of 1.62V was only required to achieve the current density of 10 ​mA ​cm-2, when the catalyst was assembled as the anode and cathode simultaneously. Several characterizations were performed, including HRTEM, XRD, SEM and XPS analysis, to explore the structure-activity relationship of the Mo–Co(OH)2/Co3O4/NF catalyst. Notably, the existence of the Co3O4 nanosheet middle layer enhanced the electro-chemical active surface area of the whole Mo–Co(OH)2/Co3O4/NF catalyst, which boosted the conductivity of the catalyst. Moreover, the XPS analysis revealed that the doped Mo6+ can attract the electrons from Co2+, increasing the active sites that are favorable for the OER and HER. The unique synthetic strategy adapted in this work will open up a new approach for the construction of heteroatom-doped multilayered heterostructure to achieve effective catalytic activity for overall water-splitting.

Constructing collaborative interface between Mo2N and NiS as efficient bifunctional electrocatalysts for overall water splitting

Solar-driven electrocatalytic water splitting is a promising technology to produce renewable hydrogen fuel. To accomplish this perspective, it is urgent to exploit high-efficiency and robust bifunctional electrocatalysts. Herein, a hybrid Mo2N/NiS heterojunction with synergistic effect is developed as bifunctional electrocatalyst for high-efficiency water splitting in alkaline media. Through high-temperature calcination and in-situ hydrothermal growth process, NiS nanocrystals are successfully anchored on porous Mo2N to produce a well-defined heterointerface by forming MoS bonds. The optimized Mo2N/NiS hybrids exhibit a much-enhanced electrocatalytic activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) than that of individual Mo2N and NiS in 1.0 M KOH. Moreover, benefitting from the robust chemical stability of Mo2N substrate, Mo2N/NiS hybrids presents an excellent long-term durability. The density functional theory calculations reveal that the improved HER and OER activities are primarily enabled by the synergistic effect of interface between Mo2N and NiS, NiS accelerates the water dissociation while Mo2N optimize the intermediates adsorption. When the as-prepared Mo2N/NiS heterojunction is used as bifunctional catalysts in a photovoltaic water splitting system, it exhibits a favorable solar-to-hydrogen energy conversion efficiency of 8.4 %, which is superior to some of reported noble-metal based catalysts. This work provides a facile and efficient strategy to design and fabricate the bifunctional catalysts for water splitting.

Regeneration of textile sludge into Cu8S5 decorated N, S self-doped interconnected porous carbon as an advanced bifunctional electrocatalyst for overall water splitting

The utilization of hazardous textile sludge as a precursor for energy production has broad practical application prospects for both sustainable economic and environmental development. Herein, a novel Cu8S5 decorated N, S self-doped interconnected porous carbon (Cu8S5/NSC) with abundant mass transfer channel is successfully designed through a direct pyrolysis strategy of textile sludge waste. Benefiting from the synergistic catalysis between Cu8S5 nanoparticles and the abundant mass transfer channel of the N, S self-doped porous carbon, the Cu8S5/NSC-900 catalyst exhibits excellent electrocatalytic activity and stability with small overpotentials of 313 and 137 mV at 10 mA cm−2 for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. Significantly, the resultant water splitting system achieves a current density of 10 mA cm−2 at 1.64 V, outperforming the benchmark Pt/C||RuO2. Therefore, this study offers an environment-compatible route for synthesizing attractive bifunctional catalysts for water splitting directly from textile sludge waste.

Trimetallic oxyhydroxides as active sites for large-current-density alkaline oxygen evolution and overall water splitting

• FeCoNi(S) exhibited a low overpotential of 252 and 293 mV to deliver current densities of 100 and 500 mA cm -2 in alkaline media, respectively. • When FeCoNi(S) was used as a bifunctional catalyst for overall water splitting, only a low cell voltage of 1.84 V was needed to acquire 500 mA cm -2 with stability over 2000 h. • As the active sites, the Ni(Fe,Co) trimetallic oxyhydroxides evolved from FeCoNi(S) during reconstruction displayed the lowest overpotential for OER with the trend of Ni(Fe,Co)OOH > Ni(Co)OOH > NiOOH, which was also applicable to oxides, selenides, etc. Earth-abundant electrocatalysts for large-current-density water splitting under alkaline condition are desirable. Oxygen evolution reaction, which is a bottleneck of the overall water splitting, faces the problems of complicated reconstruction and deficiency in rational design of active sites. Herein, we report a series of transition metal chalcogenides for alkaline OER. Among them, FeCoNi(S) displayed a low overpotential of 293 mV to deliver a current density of 500 mA cm −2 , which is in the top level of non-precious metal based OER electrocatalysts. A combination of (ex) in situ characterizations and DFT calculation shows that Ni(Fe,Co) trimetallic oxyhydroxides were the active sites for highly-efficient OER. Furthermore, for FeCoNi(S), when used as a bifunctional catalyst for water splitting, it only required a cell voltage of 1.84 V to deliver ∼500 mA cm −2 with extraordinary long-term stability over 2000 h. This work provides the comprehension of high-efficiency, robust catalysts for OER and overall water splitting at large current densities in alkaline media.

One-step in-situ sprouting high-performance NiCoSxSey bifunctional catalysts for water electrolysis at low cell voltages and high current densities

Engineering high-performance non-precious metal-based bifunctional catalysts for water splitting are still facing some issues especially at industry-relevant current densities. Here, this challenge is addressed by the new approach to grow extra-stable nickel cobalt sulfur-selenide (NiCoSxSey) nanosheet catalysts on nickel–cobalt foam (NCF), and the obtained NiCoSxSey affords the low overpotentials of 345 mV for hydrogen evolution reaction (HER) and 427 mV for oxygen evolution reaction (OER) at 1000 mA cm−2 (j1000). Meanwhile, the NiCoSxSey/NCF also shows the excellent long-term stability for both HER and OER processes driven with j100 for 100 h and j500 for 24 h. In addition, the cell voltage assembled with NiCoSxSey/NCF is only 1.84 V at j500 in 1 M KOH, and the I-t characteristic shows a low decay (<3 %) after 50 h operation at j100. The ab-initio simulations reveal that the CoS2-CoSe2, Ni3S2-Ni3Se2 and CoS2-Ni3Se2 interfaces are the active sites for HER.

Interfacial hetero‐phase construction in nickel/molybdenum selenide hybrids to promote the water splitting performance

In this work, a novel hetero-phase interface structure (NiMoSe/NF-2), consisting of crystalline (NiSe) and amorphous (MoSex), was constructed by annealing Ni0.85Se/MoSex hybrid (NiMoSe/NF-1), synthesized through hydrothermal and selenylation steps. For hydrogen evolution and oxygen evolution reaction, the NiMoSe/NF-2 exhibited an overpotential of 91 mV (10 mA cm−2) and 307 mV (100 mA cm−2) with the Tafel slope of 48.1 mV dec−1 and 30.9 mV dec−1, respectively, superior to NiMoSe/NF-1. Meanwhile, much higher stability with 10 and 14 h tests was also respectively achieved for HER and OER. Using the NiMoSe/NF-2 as anode and cathode, the electrolyzer showed a long-time stability up to 14 h with the current density of 100 mA cm−2 at the potential of 1.91 V for overall water splitting. The density functional theory calculation validates that the crystalline/amorphous hetero-phase structure remarkably reduces the Gibbs free energy difference for both HER/OER and the increased occupation densities of electronic states near Fermi level accelerated charge transfer rate during electrocatalytic process. The hydrogen and oxygen intermediates desorption are facilitated by the downshift of Ni d-band center. The proposed crystalline/amorphous hetero-phase structure is prospective for designing bifunctional catalysts for water splitting.

Porous Pd/NiFeOx Nanosheets Enhance the pH‐Universal Overall Water Splitting

AbstractModulating the morphology and chemical composition is an efficient strategy to enhance the catalytic activity for water splitting, since it is still a great challenge to develop a bifunctional catalyst for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) over a wide pH range. Herein, Pd/NiFeOx nanosheets are synthesized with tightly arranged petal nanosheets and uniform mesoporous structure on nickel foam (NF). The porous 2D structure yields a larger surface area and exposes more active sites, facilitating water splitting at all pH values. The overpotential of Pd/NiFeOx nanosheets for OER is only 180, 169, and 310 mV in 1 m KOH, 0.5 m H2SO4, and 1 m phosphate‐buffered saline (PBS) conditions at 10 mA cm−2 current density, as well as excellent HER activity with ultralow overpotential in a wide pH range. When using porous Pd/NiFeOx nanosheets as bifunctional catalysts for water splitting, it just required a cell voltage of 1.57 V to reach a current density of 20 mA cm−2 with nearly 100% faradic efficiency in alkaline conditions, which is much lower than that of benchmark Pt/CǁRuO2 (1.76 V) couples, along with the improving stability benefiting from the good corrosion resistance of the inner NiFeOx nanosheets.

Co-doped Pyrrhotite Fe7S8 nanosheets as bifunctional electrocatalysts for water splitting

The development of low-price and highly efficient catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has always been challenging with regard to water splitting. Pyrrhotite Fe7S8 has become a research hotspot due to its abundant reserves, high electrical conductivity and excellent catalytic activity. In general, introducing metal heteroatoms into transition metal sulfides (TMSs) can effectively enhance the activity and stability of TMSs. Herein, Co-doped pyrrhotite Fe7S8 nanosheets were obtained by a straightforward two-step method consisting of hydrothermal treatment followed by subsequent heat treatment. Results from XPS analysis and contact angle measurements showed that doping optimized the chemical environment around iron atoms and enhanced the adsorption of water molecules on the surface of Fe7S8, thereby greatly improving the electrocatalytic efficiency of water electrolysis. Compared with other counterparts, Co0·95Fe6·05S8 exhibited superior OER activity with an overpotential of 311 mV at a current density of 10 mA cm−2, and higher performance towards HER with an overpotential of 284 mV at 10 mA cm−2 in alkaline solution. In sum, Co0·95Fe6·05S8 is promising as a bifunctional catalyst for water splitting under alkaline conditions.

Two-dimensional metallic MoS2-amorphous CoNi(OH)2 nanocomposite for enhanced electrochemical water splitting in alkaline solutions

We report the preparation of nanocomposite consisting of metallic MoS2 and electrodeposited amorphous CoNi(OH)2 nanosheets on carbon paper for efficient electrochemical water splitting in the alkaline solutions. The synergistic effect between metallic MoS2 and amorphous CoNi(OH)2 nanosheets enables the excellent catalytic activity of nanocompsite towards hydrogen evolution reaction (HER) in 0.1 M KOH with a low overpotential of 178 mV at a current density of 10 mA/cm2 and Tafel slope of 60.9 mV/decade. The current density of MoS2-CoNi(OH)2 nanocomposite for HER at the overpotential of more than 0.190 V is even higher than that of the commercial Pt/C catalyst. Moreover, the MoS2-CoNi(OH)2 nanocomposite is also active towards electrochemical oxygen evolution and can act as a bifunctional catalyst for water splitting in 0.1 M KOH. Our work povides a simple and effective way to engineer phases and prepare two-dimensional nanocomposites for effecient water splitting in alkaline aqueous solutions.