Efficient bifunctional hydrogen and oxygen evolution reaction electrocatalyst based on the NU-1000/CuCo2S4 heterojunction

One of the current necessities to produce clean energy is the logical design of inexpensive noble-metal free electrocatalysts with developed structure and composition for electrochemical water splitting. In this study, we introduce a new core-shell-structured bifunctional electrocatalyst of NU-1000/CuCo₂S₄ for oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and overall water splitting for the first time. Own to unique structure with rich porosity, high electrical conductivity, high stability and larger density of active sites, this nanocomposite can produce water electrolysis in a 1 M KOH solution. The electrochemical measurements show overpotentials of 335 mV for OER and 93 mV for HER at a current density of 10 mAcm⁻². Also, the NU-1000/CuCo₂S₄ nanocomposite exhibits Tafel slope values of 110 mV dec⁻¹ and 103 mV dec⁻¹ for HER and OER, respectively. Besides, NU-1000/CuCo₂S₄ presents a significant long-term stability in a 72 h run. Additionally, NU-1000/CuCo₂S₄ requires 1.55 V to deliver 10 mA cm⁻² current density in overall water splitting. According to these results, we hope to use this electrocatalyst in producing oxygen and hydrogen from water.     

Co/Mo2C composites for efficient hydrogen and oxygen evolution reaction

Non-precious transition metal electrocatalysts with high catalytic performance and low cost enable the scalable and sustainable production of hydrogen energy through water splitting. In this work, based on the polymerization of CoMoO₄ nanorods and pyrrole monomer, a heterointerface of carbon-wrapped and Co/Mo₂C composites are obtained by thermal pyrolysis method. Co/Mo₂C composites show considerable performance for both hydrogen and oxygen evolution in alkaline media. In alkaline media, Co/Mo₂C composites show a small overpotential, low Tafel slope, and excellent stability for water splitting. Co/Mo₂C exhibits a small overpotential of 157 mV for hydrogen evolution reaction and 366 mV for oxygen evolution reaction at current density of 10 mA cm⁻², as well as a low Tafel slope of 109.2 mV dec⁻¹ and 59.1 mV dec⁻¹ for hydrogen evolution reaction and oxygen evolution reaction, respectively. Co/Mo₂C composites also exhibit an excellent stability, retaining 94% and 93% of initial current value for hydrogen evolution reaction and oxygen evolution reaction after 45,000 s, respectively. Overall water splitting via two-electrode water indicates Co/Mo₂C can hold 91% of its initial current after 40,000 s in 1 M KOH.     

Self-standing Co decorated Cu2O/CuS-based porous electrocatalyst for effective hydrogen evolution reaction in basic media

The self-standing Co decorated Cu₂O/CuS-based porous electrocatalyst was prepared with the help of simple electrodeposition and hydrothermal method. The structural characterizations of fabricated samples were performed with X-Ray diffraction spectroscopy and X-Ray photoelectron spectroscopy, while the morphology of catalysts was studied with the help of Field-Emission Spectroscopy and Transmission Electron Spectroscopy. The electrochemical performance of the hydrogen evolution reaction was checked in a basic electrolyte. The gradual increment in the electrochemical performance of Cu₂O was observed when it underwent sulfurization without and with Co precursor respectively. The best electrochemical performance for hydrogen evolution reaction with an overpotential of 150.29 mV to achieve a geometric current density of 10 mA/cm² was observed for the Cu₂O sample sulfurized with Co precursor. The results of different characterizations suggested that the improved electrochemical performance could be attributed to the increased intrinsic activity and surface porosity of the electrocatalyst after sulfurization.     

Nanoscale CuTe electrocatalyst immobilized at conductor surface for remarkable hydrogen evolution reaction

Hydrogen generation from electrocatalytic water splitting is of supreme significance for resolving energy crisis and environmental concerns. However, developing earth-abundant, efficient, and durable electrocatalyst for high-performance hydrogen evolution and complete water splitting catalysis is a rare instance. We present here the first demonstration of unique copper tellurides nano-structures (CuTe-NS) based electrocatalyst executing HER with high activity and remarkable stability. CuTe-NS based electrocatalysts grown over conductive NiF via drop-casting approach and employed for HER, while achieving a current decade and a current density of 100 mA/cm² just at 0.25 V vs. RHE and 0.27 V vs. RHE, which is comparable to the benchmark Pt/C based HER catalyst. The catalyst demonstrates well-balanced kinetic behavior, low Tafel slope of 36 mV/dec, low charge transfer resistance of 1.71 Ω, high roughness factor, and remarkable stability for more than 60 h of electrolysis. Furthermore, post-catalysis characterizations demonstrate no change in catalyst integrity, morphological, and structural attributes even after many hours of electrolysis which show sustainable behavior of catalyst for long term HER activity. Because of electrochemical and structural stabilities after long term electrolysis experiments, accessible method of preparations, and cost-effectiveness, the catalysis is highly encouraging for real-life applications.     

Carbon supported nickel phosphide as efficient electrocatalyst for hydrogen and oxygen evolution reactions

Hydrogen production through water splitting is an efficient and green technology for fulfilling future energy demands. Carbon nanotubes (CNT) supported Ni₂P has been synthesized through a simpler hydrothermal method. Ni₂P/CNT has been employed as efficient electrocatalysts for hydrogen and oxygen evolution reactions in acidic and alkaline media respectively. The electrocatalyst has exhibited low overpotential of 137 and 360 mV for hydrogen and oxygen evolution reactions respectively at 10 mA cm^?2. Lower Tafel slopes, improved electrochemical active surface area, enhanced stability have also been observed. Advantages of carbon support in terms of activity and stability have been described by comparing with unsupported electrocatalyst.     

Electrochemical characterization of RuO2-Ta2O5/polyaniline composites as potential redox electrodes for supercapacitors and hydrogen evolution reaction

RuO₂-Ta₂O₅ electrode covered with polyaniline (PANI) was prepared by sintering and electrodeposition. X-ray photoelectron spectroscopy confirmed the presence of RuO₂-Ta₂O₅ and PANI and the strong interaction between RuO₂-Ta₂O₅ and PANI in the RuO₂-Ta₂O₅/PANI composite. The crystalline structure of RuO₂-Ta₂O₅/PANI was verified by XRD. SEM analysis revealed that the RuO₂-Ta₂O₅/PANI electrode had a nano-fibrous morphology with a crystal plane and some pores. The supercapacitive performance of RuO₂-Ta₂O₅/PANI was evaluated by cyclic voltammetry and charge-discharge chronopotentiometry. RuO₂-Ta₂O₅/PANI had a high specific capacitance (428 F/g), specific energy (26.7 Wh/kg at a discharge current density of 0.5 mA/cm²), and power density (2.4 kW/kg at a discharge current density of 4.0 mA/cm²). The attractive capacitive properties of RuO₂-Ta₂O₅/PANI may be attributed to the porous morphology of RuO₂-Ta₂O₅ covered with PANI. In addition, the as-prepared RuO₂-Ta₂O₅ and RuO₂-Ta₂O₅/PANI electrodes had Tafel slopes of −55.8 and −69.2 mV/dec, respectively, which make them potential H₂ evolution electrocatalysts.     

Free-standing carbon nanotubes as non-metal electrocatalyst for oxygen evolution reaction in water splitting

Oxygen evolution reaction (OER) has significant impact on the overall electrochemical water splitting. We introduce, for the first time, a facile approach towards the fabrication of versatile electrode composed of free-standing multiwalled carbon nanotubes (MWCNTs) as electrocatalyst for the water splitting reaction. Directly extracted MWCNTs as sheets from vertically grown arrays transferred over the glass substrate, are used without any post treatment as a working electrode for OER. Onset potential of 1.60 V was achieved for MWCNTs which is significantly reduced as compared to platinum based metal electrode (1.72 V) with excellent current density. No surface modification, metal-free nature, flexibility and low cost with excellent catalytic activity proved this material as a promising candidate for the replacement of metal based electrodes in electrochemical water splitting.     

Needle-like CoP/rGO growth on nickel foam as an efficient electrocatalyst for hydrogen evolution reaction

In this work, CoP/NF is synthesized at different temperature (250 °C, 300 °C, 350 °C) (denoted as CoP/NF-T, T = 250, 300, 350). Then, CoP/NF-300 with the best performance towards hydrogen evolution reaction (HER), is used to synthesize compounds with different ratio of reduced graphene oxide (rGO) (CoP/rGO/NF-X, X (quality ratio of rGO/CoP) = 1,3,5). In terms of morphology, under the synergistic effect of rGO, uniform and dense CoP provides the possibility to increase the electrochemical area. While CoP/rGO/NF-3 shows the minimum overpotential of 136 mV to drive 50 mA/cm, and the smallest Tafel slope 135 mV/dec among as-synthesized materials. Furthermore, CoP/rGO/NF-3 has good stability during at least 25 h. These result can be construed as the large electrochemical active area, high conductivity and long-time stability.     

Tunably fabricated nanotremella-like Bi2S3/MoS2: An excellent and highly stable electrocatalyst for alkaline hydrogen evolution reaction

Reasonable design of efficient and stable catalysts with low cost and abundant natural reserves is vital for electrocatalytic water splitting. Herein, novel nanotremella-like Bi₂S₃/MoS₂ composites with different mass ratios between Bi₂S₃ and MoS₂ have been successfully prepared through a hydrothermal approach and further applied to hydrogen evolution reaction (HER) in 1.0 M KOH electrolyte for the first time. When the mass ratio of Bi₂S₃ and MoS₂ is 5:5, as-prepared nanotremella-like Bi₂S₃/MoS₂ (marked as BMS-5) manifests favorable HER catalytic activity with overpotential of 124 mV at current density of 10 mA cm⁻² and relatively low Tafel slope of 123 mV dec⁻¹. Moreover, it exhibits an extraordinary durability for uninterrupted hydrogen generation. The enhanced HER performances are ascribed to the synergistic effects between Bi₂S₃ and MoS₂, giving rise to large electrocatalytic active area and fast HER kinetics. The results pave a new path to design and construct excellent Bi₂S₃/MoS₂ nanomaterials for electrocatalytic hydrogen generation.     

Synthesis and electrocatalytic activity of Ni0.85Se/MoS2 for hydrogen evolution reaction

Recently, the replacement of expensive platinum-based catalytic materials with non-precious metal materials to electrolyze water for hydrogen separation has attracted much attention. In this work, Ni_0.85Se, MoS₂ and their composite Ni_0.85Se/MoS₂ with different mole ratios are prepared successfully, as electrocatalysts to catalyze the hydrogen evolution reaction (HER) in water splitting. The result shows that MoS₂/Ni_0.85Se with a molar ratio of Mo/Ni = 30 (denoted as M30) has the best catalytic performance towards HER, with the lowest overpotential of 118 mV at 10 mA cm⁻², smallest Tafel slope of 49 mV·dec⁻¹ among all the synthesized materials. Long-term electrochemical testing shows that M30 has good stability for HER over at least 30 h. These results maybe due to the large electrochemical active surface area and high conductivity. This work shows that transition metal selenides and sulfides can form effective electrocatalyst for HER.     

CuFe electrocatalyst for hydrogen evolution reaction in alkaline electrolysis

The development of high performance, stable catalyst with non-precious metals for electrochemical hydrogen evolution reaction for alkaline electrolysis is in demand. Here-in, we report the synthesis of CuFe layered double hydroxide (LDH) electrocatalyst on nickel foam via facile hydrothermal method. In alkaline electrolysis with 1 M NaOH electrolyte, CuFe LDH as cathode requires an overpotential of 159 mV to generate current density of 10 mA cm⁻². Which is ca. 51 mV and 7 mV lower than NiFe LDH and NiRu LDH. CuFe LDH exhibits significant electrocatalytic activity for HER. The higher catalytic activity of CuFe LDH compared to NiFe LDH may be achieved with higher proton adsorption by Cu compared to Ni. Also, the efficient charge transfer with interconnected LDH layers, favourable three dimensional structure facilitating easy electrolyte transfer to the active sites and hydrogen gas diffusion. This work may help in developing low cost and efficient hydroxide catalyst.     

Palladium-coated polyaniline nanofiber electrode as an efficient electrocatalyst for hydrogen evolution reaction

In this study, polyaniline (PANI) with abundant protonated regions was used for the first time as a palladium (Pd) support for enhanced performance in hydrogen evolution reaction (HER). For this purpose, the hierarchical Pd@PANI nanofiber electrode was easily synthesized by electrochemical polymerization of aniline on Au followed by potential-controlled electrochemical deposition of Pd nanoclusters on the PANI. The reported catalyst was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. Linear sweep voltammetry analysis was performed to evaluate the HER performance. Ion transfer behavior was investigated using electrochemical impedance spectroscopy analysis. The electrochemical tests show that the Pd@PANI/Au electrode has a low overpotential of ～60 mV at 10 mA cm^?2 and a small Tafel slope of 35 mV dec^?1 for HER in acidic media, with high catalytic activity and stability. These features will make the Pd@PANI/Au a promising candidate as a high-performance electrocatalyst for HER applications.     

Hierarchical molybdenum carbide/N-doped carbon as efficient electrocatalyst for hydrogen evolution reaction in alkaline solution

Development of highly-active and noble-metal-free electrocatalysts for hydrogen evolution reaction (HER) is of critical challenge for water splitting, and optimizing the structure and the composition of the relative materials is very necessary to obtain the high-quality catalysts. Herein, a novel molybdenum carbide/N-doped carbon (Mo₂C/NC) hybrid is fabricated by using the hierarchical polyaniline tube network as a carbon source and a reactive template, and the as-fabricated Mo₂C/NC hybrid possesses a uniform hierarchical tube structure. The coupling of the ultrafine Mo₂C nanoparticles and the N-doped carbon substrate provides the abundant active sites and accelerates the charge transfer process. The final Mo₂C/NC catalyst gives the excellent catalytic activity for HER in alkaline condition, which shows a lower overpotential of 142 mV at 10 mA cm^?2 and a small Tafel slope of 61 mV decade^?1 in 1 M KOH.     

In-situ construction of electrodeposited polyaniline/nickel-iron oxyhydroxide stabilized on nickel foam for efficient oxygen evolution reaction at high current densities

We report an in-situ construction method for the NiFe-based oxyhydroxide OER electrocatalyst supported on the nickel foam (NF) substrate with the polyaniline (PANI) interlayer by sequential electrochemical deposition steps (NF/PANI/NiFe–OH). The ultra-thin nanosheet for the nickel-iron (oxy)hydroxides tightly grown on the porous PANI exhibits the enhanced electrochemical characteristics associated with the promotion roles of the PANI layer, which increases the number of active sites, facilitates the charge transfer, and accelerates water transport across the interfaces of the electrode. The as-prepared NF/PANI/NiFe–OH has reliable lower overpotentials of 260, 340, and 490 mV without iR-correction at 50, 100, and 200 mA cm^?2 of high current densities, respectively. The smaller Tafel slope, larger ECSA, and TOF values of the electrode reveal its high intrinsic activity. Moreover, the electrode shows good stability and durability without the damage of morphology, change of surface chemical state, and substantial loss of active components at high current density.     

Facile one-pot synthesis of binder-free nano/micro structured dendritic cobalt activated nickel sulfide: a highly efficient electrocatalyst for oxygen evolution reaction

Reasonable design and preparation of non-noble metal electrocatalysts with predominant catalytic activity and long-term stability for oxygen evolution reaction (OER) are essential for electrocatalytic water splitting. Ni foam (NF) is highlighted for its 3D porous structure, impressive conductivity and large specific surface area. Herein, nano/micro structured dendritic cobalt activated nickel sulfide grown on 3D porous NF (Co–Ni₃S₂/NF) has been successfully synthesized by one-step hydrothermal method. Due to the ingenious incorporation of Co, Co–Ni₃S₂/NF electrode shows auspicious electrocatalytic performance for OER compared with Ni₃S₂/NF electrode. As a result, Co–Ni₃S₂/NF needs overpotential of only 274 and 459 mV at current density of 10 and 50 mA cm⁻², respectively, while Ni₃S₂/NF requires overpotential of 344 and 511 mV. At potential of 2.0 V (vs. RHE), Co–Ni₃S₂/NF displays current density of 191 mA cm⁻², while Ni₃S₂/NF just attains current density of only 135 mA cm⁻². Moreover, Co–Ni₃S₂/NF demonstrates excellent stability for uninterrupted OER in alkaline electrolyte. The strategy of designing and preparing cobalt activated nickel sulfide grown on NF renders a magnificent prospect for the development of metal-sulfide-based oxygen evolution catalysts with excellent electrocatalytic performances.     

ZIF67@MoO3 NSs@NF composite electrocatalysts reinforced by chemical bonds and oxygen vacancy for efficient oxygen evolution reaction and overall water-splitting

A kind of composite electrocatalysts with the structure of MoO₃ nanosheets coated by ZIF67 nanocrystals and grown on the nickel foam substrate (ZIF67@MoO₃ NSs@NF) is prepared and mainly used as the electrode for oxygen evolution reaction (OER) and overall water splitting. The excellent electrocatalytic activity of ZIF67@MoO₃ NSs@NF are demonstrated. It can use the overpotential (?) of 178 mV and 386 mV respectively to drive 10 mA cm^?2 and 50 mA cm^?2. It is also observed that the ZIF67@MoO₃ NSs@NF electrode has the highest initial current density (45.7 mA cm^?2) at 1.618 V and can maintain more than 90% of the initial current density after 20,000 s. The ZIF67@MoO₃ NSs@NF electrode also shows the small HER overpotential of 135 mV at 10 mA cm^?2. Furthermore, the voltage of ZIF67@MoO₃ NSs@NF as a bifunctional overall water splitting catalysts is 1.58 V at 10 mA cm^?2, which is superior to another noble metal electric catalyst combination RuO₂/NF(+)//Pt–C/NF(?). And the ZIF67@MoO₃ NSs@NF(+)//ZIF67@MoO₃ NSs@NF(?) combination can maintain more than 90% of the initial current density after 65,000 s at 1.58 V. The main reason is the composite interface of MoO₃ NSs and ZIF67 phases with Co–O bonds, C–O–Mo bonds and oxygen vacancies defects facilitates the increase of the active sites and efficient electron transfer rate.     

Recent advances in CoSe2 electrocatalysts for hydrogen evolution reaction

Hydrogen as a sustainable alternative fuel is recognized as a primary choice for future energy supply due to its high gravimetric energy density and zero carbon emission upon combustion. Electrochemical water splitting is a promising strategy for effective and sustainable hydrogen production. Nowadays, research is focused on developing non-precious, stable, and highly efficient electrocatalysts for hydrogen evolution reaction (HER). Among them, CoSe₂ has attracted tremendous attention as HER electrocatalyst due to its unique electronic configuration that ensures fast charge transport, excellent catalytic activity, and good chemical stability. So far, a lot of reviews on electrocatalytic water splitting based on transition metal dichalcogenides and cobalt-based materials are reported. However, the review on CoSe₂ electrocatalyst for hydrogen evolution reaction is limited up-to-date. Hence in the present review, a comprehensive literature survey on CoSe₂ electrocatalyst for hydrogen evolution reaction is done and reported. In this review, the crystal structures of CoSe₂, their phase transformation strategy, their hydrogen evolution reaction mechanism in acidic and alkaline electrolytes are highlighted. The various synthesis procedures adopted to produce CoSe₂ based materials, the relation between its structure and composition with their electrocatalytic activities are discussed. Moreover, the effective ways to enhance the electrocatalytic performance of CoSe₂ based materials such as its morphological modification, constructing heterostructures, and heteroatom doping are reviewed.     

Electrocatalysts for hydrogen evolution reaction

In addition to the historical importance of water electrolysis, hydrogen evolution reaction (HER) is the heart of various energy storage and conversation systems in the future of renewable energy. The HER electrocatalysis can be well conducted by Pt with a low overpotential close to zero and a Tafel slope around 30 mV dec^?1; however, the practical developments to satisfy the growing demands require cheaper electrocatalysts. Noble metals are still the promising candidates, though further improvement is needed to enhance the HER efficiency in performance. Three categories of non-noble metal electrocatalysts are under heavy investigations: (i) alloys, (ii) transition metal compounds, and (iii) carbonaceous nanomaterials. The most practical option, based on the electrocatalytic activity and electrochemical stability, seems to be the transition metal compounds MX (where M is Mo, W, Ni, Co, etc. and X is S, Se, P, C, N, etc.). Among these compounds, some like MoS₂ and WC can display metallic properties and a Pt-like electrocatalytic activity, but they still need serious modifications for the practical performance. In general, similar strategies have been employed to improve the HER performance of all of these materials such as doping (both cation and anion), controlling the crystallinity and amorphism, and increasing the active sites by changing the morphology. Another important issue is the chemical and physical structure of the carbon-based catalyst support, as carbon is normally a vital component even for the Pt electrocatalysts.     

Flower-like Co3O4 microstrips embedded in Co foam as a binder-free electrocatalyst for oxygen evolution reaction

Designing appropriate oxygen evolution reaction (OER) electrocatalysts to meet the requirements of high efficiency, long-term durability, and low cost remains the challenge for scientific community. Cobalt oxide (Co₃O₄) has been proven as a promising candidate for OER with attractive activity and stability in alkaline media. In this study, flower-like Co₃O₄ microstrips have been successfully prepared and directly embedded in Co foam (denoted as Co₃O₄@Co foam) by a green and facile two-step strategy including hydrothermal treatment and subsequent annealing process under relatively low temperatures. It demonstrates that the OER performance of the Co₃O₄@Co foam electrode can rival to the commercial RuO₂ on glassy carbon electrode. The Co₃O₄@Co foam electrode displays high OER activity with a low overpotential of 273 mV at a current density of 10 mA cm⁻², and a low Tafel slope of 61.8 mV dec⁻¹. The flower-like Co₃O₄ microstrips greatly increase the active surface area to expose more active sites, and the directly growth of Co₃O₄ microstrips on Co foam with intimate contact improves the electron transport and ensures the stability of the Co₃O₄@Co foam electrode.     

Electrospun fibrous active bimetallic electrocatalyst for hydrogen evolution

Fabricating earth-abundant bifunctional water splitting electrocatalysts with high efficiencies to replace noble metal-based Pt and IrO₂ catalysts is in great demand for the development of clean energy conversion technologies. Molybdenum disulfide (MoS₂) nanostructures have attracted much attention as promising material for hydrogen evolution reaction (HER). The production of hydrogen gas by help of potential efficient earth abundant metal oxides, and stable electrolysis seems a promising for hydrogen evolution reaction pathway in 1 M potassium hydroxide electrolyte media is a hot research topic in the field for clean energy conversion, renewable energies and storage. Here we propose asystem composed NiO nanostructures and MoS₂ deposited on (MoS₂@NiO). Here, by hydrothermal method NiO prepared and MoS₂@NiO by an electrospinning technique complex, can be used as catalyst to produce a large amount of hydrogen gas bubbles. The NiO nanostructures composite having highest synergistic behavior fully and covered by the MoS₂. For the MoS₂@NiO nano composite catalyst, experiment applied in 1 M KOH for the production of hydrogen evolution reaction which exhibits distinct properties from the bulk material. Overpotential values recorded low 406 mV and current density 10 mA cm⁻² measured. Co-catalysts characterized by using different techniques for deep study as scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Owing to their unique structure, as-prepared nanocomposite exhibited enhanced catalytic performance for HER due to high electroactive surface area and swift electron transfer kinetics. Based on the HER polarization curves at low potential electrochemical to examine the effects of intercalants HER catalytic efficiency. Our findings establish low Tafel slope (44 mV/decade) and the catalyst stable for at least 13 h. This simple exploitation of MoS₂@NiO composite catalysts depending on the intended application of their electrochemistry.