MOFs-derived hybrid nanosheet arrays of nitrogen-rich CoS2 and nitrogen-doped carbon for efficient hydrogen evolution in both alkaline and acidic media

Rational design of highly active, economical and stable electrocatalysts for hydrogen evolution reaction (HER) is still a great challenge for future applications. Herein, we use a 2D metal-organic framework array as the reactive template and precursor, to fabricate a hybrid nanosheet array of nitrogen-rich CoS₂@nitrogen-doped carbon on Ti foil substrate (N–CoS₂@NC/Ti) through a simple thermal treatment in the presence of thiourea. Owing to the prominent synergistic effect of the coupling between CoS₂ and NC, a high content of Co-N_x species as well as unique nanoarray architectures, the as-synthesized N–CoS₂@NC/Ti electrode exhibits remarkable activity and robust durability for HER under both acidic and alkaline conditions, which is obviously superior to the CoS₂@NC/Ti.     

Phosphorus-doped nickel selenides nanosheet arrays as highly efficient electrocatalysts for alkaline hydrogen evolution

Earth-abundant transition-metal dichalcogenides are considered as promising electrocatalysts to accelerate the hydrogen evolution reaction （HER）. Among them, the pyrite nickel diselenide (NiSe₂) has been received special attention due to its low cost and high conductivity, but it suffers a poor HER performance in alkaline media possibly attributed to its inadequate hydrogen adsorption free energies. Here, we report a novel P-doped NiSe₂ nanosheet arrays anchored on the carbon cloth with an obviously optimized HER performance. The catalyst only needs a low overpotential of 86 mV at a current density of 10 mA cm^?2 and a Tafel slop of 61.3 mV dec^?1,as well as maintains a long-term durability for 55 h in 1.0 M KOH, which is superior to the pristine NiSe₂ (135 mV@10 mA cm^?2) and most recently reported non-noble metal electrocatalysts. The XRD, EDS, TEM and XPS results validated the successful doping of P element into NiSe₂ nanosheet, while the density functional theory (DFT) calculation demonstrated the P doping can optimize the electronic structures and the hydrogen adsorption free energy of NiSe₂. This work thus opens up new ways for rationally designing high-efficient HER electrocatalysts and beyond.     

Ga doped Ni3S2 ultrathin nanosheet arrays supported on Ti3C2-MXene/Ni foam: An efficient and stable 3D electrocatalyst for oxygen evolution reaction

Exploring cost-efficient electrocatalysts for oxygen evolution reaction (OER) is still a huge challenge in the electrochemical energy conversion technology. In this work, Gallium (Ga)-doped Ni₃S₂ nanosheet arrays grown on Ti₃C₂-MXene/nickel foam (Ga–Ni₃S₂/Ti₃C₂/NF) have been synthesized by a successive hydrothermal and sulfidization process. The Ga doping modulates the electronic structure of Ni₃S₂, so tuning the adsorption energies of oxygen intermediate (1OOH). The Ga–Ni₃S₂/Ti₃C₂/NF delivers outstanding catalytic activities toward OER with an overpotential of 340 mV at 100 mA cm^?2, and exhibits superior electrochemical durability. The excellent OER performance of Ga–Ni₃S₂/Ti₃C₂/NF can be ascribed to the 3D sheet arrays morphology and optimized electronic structure. Density functional theory (DFT) calculations also demonstrate that electronic disturbance attributed to Ga doping effectively improves the activity of Ni sites, leading to stronger binding strength of 1OOH intermediate at Ni sites nearby Ga. This study provides insights into the fabrication of advanced electrocatalysts for application.     

Synergistic coupling of CoFe-layered double hydroxide nanosheet arrays with reduced graphene oxide modified Ni foam for highly efficient oxygen evolution reaction and hydrogen evolution reaction

Novel CoFe-LDH (layered double hydroxide) nanosheet arrays in situ grown on rGO (reduced graphene oxide) uniformly modified Ni foam were synthesized by a citric acid-assisted aqueous phase coprecipitation strategy. Systematic characterizations indicates that the series of Co_xFe₁-LDH/rGO/NF (x = 4, 3, 2) all show Co_xFe₁-LDH nanosheets (150–180 × 15 nm) grown vertically on the surface of rGO/NF. Especially, the Co₃Fe₁-LDH/rGO/NF exhibits the best performance with overpotentials of 250 and 110 mV at 10 mA cm^?2 in 1 M KOH for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. When it is used as cathode and anode simultaneously for overall water splitting, they require 1.65 and 1.84 V at 10 and 100 mA cm^?2, respectively. Excellent performance of Co₃Fe₁-LDH/rGO/NF is due to the nanosheet arrays structure with open channels, synergistic coupling between Co₃Fe₁-LDH and rGO enhancing electrical conductivity, and in-situ growth of Co₃Fe₁-LDH on rGO/NF enhancing stability.     

Self-supported three-dimensional WP2 (WP) nanosheet arrays for efficient electrocatalytic hydrogen evolution

The development of highly efficient, stable, eco-friendly and low-cost noble-metal-free electrocatalysts is still a great challenge to generate large scale hydrogen fuel from water. In this concern, self-supported WP₂ and WP nanosheet (NS) arrays were prepared through an in-situ solid-phase phosphidation of WO₃ nanosheet arrays on carbon cloth (CC), whereas, different phosphating temperatures of 650 °C, 800 °C for 2 h, has been utilized to attain different WP₂ NS/CC, WP NS/CC catalysts. Remarkably, the electrocatalysts of WP₂ and WP NS arrays exhibit an outstanding hydrogen evolution (HER) performance in acidic environment, with a low overpotential of 140 mV and 175 mV at 10 mA cm⁻², a Tafel slope of 85 mV dec⁻¹ and 103 mV dec⁻¹, respectively. Furthermore, Density Functional Theory (DFT) calculations reveal that the enhanced HER activity of WP₂ catalyst is attributed to the lowered hydrogen adsorption free energy on WP₂ surface, which is much lesser than that on the WP catalyst surface. As a result, WP₂ exhibit superior intrinsic catalytic activity than WP. This study offers a valuable way for the synthesis of highly efficient three-dimensional self-supporting catalytic electrodes, and beneficial for realizing the intrinsic electrocatalytic properties of tungsten phosphide for improved water splitting reactions.     

Ni foil supported FeNiP nanosheet coupled with NiS as highly efficient electrocatalysts for hydrogen evolution reaction

The investigation and development of bimetallic phosphosulphide electrocatalyst with low cost and abundant reserves is extremely significant for the improvement of the efficiency of hydrogen evolution reaction (HER), while it remains a challenge. Herein, we explored a feasible method to prepare three-dimensional (3D) self-supported FeNiP-S/NF-5 nanosheet arrays on Ni foil (NF) by hydrothermal method and in situ phosphorization and following sulfurization treatment. The as-obtained FeNiP-S/NF-5 only needs a potential of 183 mV vs. RHE to reach 20 mA cm⁻², which is smaller than that of FeNiP/NF (187 mV vs. RHE) and FeNiS/NF-5 (239 mV vs. RHE), presenting excellent electrocatalytic stability. Such outstanding performance of the FeNiP-S/NF-5 can be attributed to following several reasons: (i) bi-metallic phosphide and sulphide have the high intrinsic activity because of its synergistic effect; (ii) the 3D nanosheet arrays structure of FeNiP-S/NF-5 is conducive to expose plentiful active sites and facilitate the electrolyte penetration along with electron transportation; (iii) the sulfurization process followed phosphorization treatment could further optimize their electronic structure and inhibited the surface oxidation of catalyst in the catalytic process.     

NiFe layered double hydroxide nanosheet arrays for efficient oxygen evolution reaction in alkaline media

Exploring efficient oxygen evolution reaction (OER) catalysts synthesized from low-cost and earth-abundant elements are crucial to the progression of water splitting. In this paper, NiFe layered double hydroxide (LDH) nanosheets were grown on Ni foam (NF) through a straightforward hydrothermal method. The Fe doping effects were systematically investigated by controlling Ni/Fe ratios and Fe valence states, and the in-depth influence mechanisms were discussed. The results indicate that, through controlling structure morphology and enhancing Ni²⁺ oxidation, NiFe_III(1:1)-LDH displays the best and outstanding OER performance, with a low over potential of 382 mV at 50 mA cm^?2, a low Tafel slope of 31.1 mVdec^?1 and only 20 mV increase after 10 h continuous test at 50 mA cm^?2. To our knowledge, this is one of the best OER electrocatalysts in alkaline media to date. This work provides a facile and novel strategy for the fabrication of bimetallic LDH catalysts with desired structures and compositions.     

Co,Fe-ions intercalated Ni(OH)2 network-like nanosheet arrays as highly efficient non-noble catalyst for electro-oxidation of urea

Developing a highly active, low-cost, and durable nanostructured catalytic material is of significant interest in fuel cell applications owing to its efficient energy conversion, ease of preparation and operation, and reduced emission of pollutants. In this work, various ratio (0.01, 0.03, and 0.05 mmol) of cobalt (Co), and iron (Fe) doped nickel hydroxide (Ni(OH)₂) nanosheet arrays were grown on Ni foam surface (Co–Ni(OH)₂ and Fe–Ni(OH)₂) via a simple one-step process. The Co–Ni(OH)₂ and Fe–Ni(OH)₂ nanosheet array on Ni foam electrodes were explored as potential candidate towards electro-oxidation of urea. Notably, 0.03 mmol Co doped Ni(OH)₂/Ni foam electrode displayed lowest-onset oxidation potential (0.21 V) and enhanced electro-oxidation of urea (59.7 mA) owing to its large amount of electrocatalytic active sites, densely assembled nanosheet array structures with porous surfaces, and electronic diffusion channels, which might promote interface electrochemical reaction. In addition, synergistic effect between Co metal with Ni(OH)₂ has also promotes enhanced electro-oxidation of urea in contrast to Fe–Ni(OH)₂ nanosheet array, Ni(OH)₂, and Ni foam electrodes. Chronoamperometric i-t curve of Co–Ni(OH)₂/Ni foam electrode obviously exhibited higher catalytic current, highly stable and durable properties in contrast to Fe–Ni(OH)₂ nanosheet arrays. As-fabricated Co–Ni(OH)₂/Ni foam can be explored as a new type of potential low-cost catalyst for electro-oxidation of urea, which reveals promising use in future fuel cell energy applications.     

Self-standing,hybrid three-dimensional-porous MoS2/Ni3S2 foam electrocatalyst for hydrogen evolution reaction in alkaline medium

Self-standing and hybrid MoS₂/Ni₃S₂ foam is fabricated as electrocatalyst for hydrogen evolution reaction (HER) in alkaline medium. The Ni₃S₂ foam with a unique surface morphology results from the sulfurization of Ni foam showing a truncated-hexagonal stacked sheets morphology. A simple dip coating of MoS₂ on the sulfurized Ni foam results in the formation of self-standing and hybrid electrocatalyst. The electrocatalytic HER performance was evaluated using the standard three-electrode setup in the de-aerated 1 M KOH solution. The electrocatalyst shows an overpotential of 190 mV at ?10 mA/cm² with a Tafel slope of 65.6 mV/dec. An increased surface roughness originated from the unique morphology enhances the HER performance of the electrocatalyst. A density functional approach shows that, the hybrid MoS₂/Ni₃S₂ heterostructure synergistically favors the hydrogen adsorption-desorption steps. The hybrid electrocatalyst shows an excellent stability under the HER condition for 12 h without any performance degradation.     

Synthesis of Co2FeAl alloys as highly efficient electrocatalysts for alkaline hydrogen evolution reaction

The development of cost-effective non-precious metal electrocatalysts is a major challenge for water splitting applications, but it is important for the realization of renewable energy systems. Alloying has proved an effective way to design metal-based electrocatalysts, and by controlling the annealing temperature, the surface morphology and crystallinity of the alloy can be tuned to control the hydrogen evolution reaction (HER) performance. In this work, with a simple coprecipitation method, we have prepared Co₂FeAl alloys at different annealing temperatures (550 °C–670 °C), which exhibit excellent crystallinity and electrocatalytic performance for HER in alkaline solution. Among all conditions, the Co₂FeAl alloys prepared at 620 °C shows the better crystallinity and the higher purity, and it could achieve a low overpotential of 149 mV at 10 mA cm^?2 in alkaline solution. The overpotential demonstrates persistent stability with only 3 mV change after over 1000 cycles. Both density functional theory (DFT) calculations and experimental results revealed that alloying optimizes the electronic structure near the Fermi surface of the system, improving the electron transport efficiency and enhancing the catalytic activity. These Co₂FeAl alloys are appealing candidates for high-performance alkaline HER electrocatalytic electrodes in water electrolysis due to their outstanding electrocatalytic properties.     

Enhanced alkaline/seawater hydrogen evolution reaction performance of NiSe2 by ruthenium and tungsten bimetal doping

The exploration of high-efficiency and stable electrocatalysts for alkaline and seawater hydrogen evolution reaction (HER) is the key to realize energy conversion, but there is still a significant challenge owing to the slow HER kinetics in alkaline and seawater systems. In this study, we prepared nickel foamed-supported Ru, W co-doped NiSe₂ (Ru, W–NiSe₂/NF) by a brief two-step hydrothermal strategy and the prepared Ru, W–NiSe₂/NF displays exceptional HER property, requiring only a low overpotential of 100 and 353 mV to reach 10 mA cm⁻² in 1 M KOH and natural seawater, respectively, far superior to Ru–NiSe₂/NF, W–NiSe₂/NF and NiSe₂/NF. Electrochemical surface area (ECSA) and operando electrochemical impedance spectroscopy (EIS) verify the abundant active sites and superior electron transfer rate of Ru, W–NiSe₂, which optimized the HER kinetics in alkaline solution and natural seawater. The ECSA normalization and TOF results indicated that Ru, W co-doping increased the intrinsic activity of NiSe₂. This study revealed the impact of bimetallic doping on the intrinsic activity of NiSe₂, and provided a practical strategy for designing and developing the HER electrocatalysts with excellent performance.     

NiCo2O4 nanowire arrays rich in oxygen deficiencies for hydrogen evolution reaction

The rational design of highly efficient electrocatalysts to generate hydrogen by catalyzing hydrogen evolution reaction still remains a challenge. Herein, we report a simple strategy to significantly enhance the catalytic activities of NiCo₂O₄ nanowire arrays by simply tuning the amount of oxygen vacancies. Remarkably, the oxygen-deficient NiCo₂O₄ catalysts obtained in Ar environment show significantly improved catalytic activities toward hydrogen evolution reaction with the requirement of 104 mV overpotential to afford 10 mA cm⁻², 122 mV less than that for air-sintered NiCo₂O₄ (226 mV). Moreover, such catalysts also exhibit superior long-term durability for 24 h at 100 mA cm⁻². The present study further promotes the application of NiCo₂O₄ in other energy storage and conversion system.     

Nanocoral-like NiSe2 modified with CeO2: A highly active and durable electrocatalyst for hydrogen evolution in alkaline solution

The excessive exhaustion of conventional fossil fuels and increasingly severe environmental issues prompt us to grope for high-performance and cost-effective catalysts for hydrogen evolution reaction (HER) by electrocatalytic water splitting. In this work, nanocoral-like NiSe₂ catalysts modified with CeO₂ have been successfully prepared through one-pot hydrothermal route and utilized to electrocatalytic HER in alkaline solution. It turns out that nanocoral-like NiSe₂ (labeled as CNS-2) catalyst delivers current densities of 10 and 50 mA cm⁻² at overpotentials of only 130 and 242 mV, respectively. Additionally, CNS-2 takes on a small Tafel slope of 115 mV dec⁻¹ and low charge transfer resistance, revealing a quicker Faradaic process and more favorable HER kinetics. Furthermore, it displays considerable long-term stability during the constant hydrogen producing. The strategy of fabricating NiSe₂ modified with CeO₂ unfolds a novel angle of view for exploiting highly efficient and durable catalysts for electrocatalytic HER.     

Interface engineering of Ni0.85Se/Ni3S2 nanostructure for highly enhanced hydrogen evolution in alkaline solution

Interface engineering is considered as an effective strategy to improve the hydrogen evolution reaction (HER) performance of electrocatalysts. Herein, the Ni_0.85Se/Ni₃S₂ heterostructure grown on nickel foam (NF) is synthesized via successive wet-chemical processes. The obtained Ni_0.85Se/Ni₃S₂ heterostructure is firstly investigated as an HER electrocatalyst in alkaline media and exhibits more excellent electrochemical properties over Ni₃S₂. And it delivers a low overpotential of 145 mV at a current density of ?10 mA cm^?2, and superior stability. Based on the analysis of high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectra (XPS), the enhanced HER activity is due to the modulation of surface electronic structure, ascribing from the construction of heterointerface between Ni_0.85Se and Ni₃S₂. Meanwhile, the Ni_0.85Se/Ni₃S₂ heterostructure prepared in this work is also verified to be employed as a promising alternative to noble metal catalysts in HER.     

Synergistic regulation of hydrogen adsorption/desorption via dual interfaces of Cu/Ni/Ni(OH)2 toward efficient hydrogen evolution reaction

Nickel-based catalysts have attracted tremendous attention as alternatives to precious metal-based catalysts for electrocatalytic hydrogen evolution reaction (HER) in virtue of their conspicuous advantages such as abundant reserves and high electrochemical activity. Nevertheless, a great challenge for Ni-based electrocatalyst is that nickel sites possess too strong adsorption for key intermediates H1, which severely suppresses the hydrogen-production activities. Herein, we report a hierarchical architecture Cu/Ni/Ni(OH)₂ consisting of dual interfaces as a high-efficient electrocatalyst for HER. The Cu nanowire backbone could provide geometric spaces for loading plenty of Ni sites and the formed Ni/Cu interface could effectively weakened the adsorption intensity of H1 intermediates on the catalyst surface. Moreover, the H1 adsorption could be further controlled to appropriate states by in-situ formed Ni(OH)₂/Ni interface, which simultaneously promotes water adsorption and activation, thus both Heyrovsky and Volmer steps in HER could be obviously accelerated. Experimental and theoretical results confirm that this interface structure can promote water dissociation and optimize H1 adsorption. Consequently, the Cu/Ni/Ni(OH)₂ electrocatalyst exhibits a low overpotential of 20 mV at 10 mA cm^?2 and an ultralow Tafel slope of 30 mV dec^?1 in 1.0 M KOH, surpassing those of reported transition-metal-based electrocatalysts and even the prevailing commercial Pt/C.     

Pd/Hemin-rGO as a bifunctional electrocatalyst for enhanced ethanol oxidation reaction in alkaline media and hydrogen evolution reaction in acidic media

H₂ generation needs a cost-effective, robust, stable, long-durable, and super-active electrocatalyst. This study reveals a rapid and facile method for fabricating Pd NPs on Hemin-rGO as novel support. The obtained electrocatalyst was characterized by UV–Vis, XPS, FESEM, EDS, HRTEM, and AFM. The electrochemical measurements reveal the superb effect of Hemin-rGO for enhancing the catalytic activity of Pd as bifunctional electrocatalysts for hybrid water electrolysis (hydrogen evolution reaction (HER) and ethanol electrooxidation reaction (EOR)). Pd/Hemin-rGO displays a low peak potential (−210 V) with remarkable current density (1.95 A mg⁻¹ Pd) in 0.1 M EtOH and 0.1 M NaOH. The ratio of j_f/j_b of Pd/Hemin-rGO compared with Pd electrocatalyst reveals this novel support's ani-poisoning effect. Besides, it shows the Tafel slope of 26 mV dec⁻¹ and overpotentials of 47 and 131 mV were obtained at 10 and 100 mA cm⁻² in acidic media toward HER. Exploring and designing new electrocatalysts may be enhanced by this research, which can use Hemin as a novel support for noble metals such as Pt, Pd, Rh, Au, and Ru for diverse energy-related applications.     

Rational design of free-standing 3D Cu-doped NiS@Ni2P/NF nanosheet arrays for hydrogen evolution reaction

Using low cost and high efficiency non-precious bimetallic phosphosulphide as electrocatalyst for hydrogen evolution reaction (HER) is not only convenient but also environment-friendly for industrial production. Therefore, we propose a simple and efficient method to prepare a series of Cu-doped bimetallic phosphosulphide nanosheet arrays on nickel foam (CuNiS@Ni₂P/NF). The CuNiS@Ni₂P/NF exhibits the superior HER performance with appropriate doping amount of Cu. It just needs a potential of 144 mV to obtain the current density of 10 mA cm⁻² in 1.0 M KOH, which is smaller than that of CuNiS@Ni₂P/NF-0.25 (206 mV) and CuNiS@Ni₂P/NF-0.125 (219 mV). The excellent HER performance of CuNiS@Ni₂P/NF nanosheet arrays can be ascribed to: (i) the moderate Cu-doped effectively optimized the electronic structure and morphology of the electrocatalyst; (ii) typical nanosheet arrays structures exposing more active sites; (iii) the high immanent activity excited by the multi-component synergy.     

High-performance alkaline hydrogen evolution of NiMoP2 nanowire boosted by bimetallic synergic effect

Hydrogen evolution reaction (HER) in alkaline conditions usually requires a higher overpotential compared with acidic conditions due to the extra energy barrier originating from the additional water dissociation step. In this work, the theoretical calculation has confirmed that this challenge can be solved by the bimetallic synergic effect on binary transition metal catalysts. We report a simple method to synthesize NiMoP₂ nanowires with (100) plane which can precisely expose Ni and Mo atom. The synthesized NiMoP₂ nanowires exhibit a small overpotential of 87 mV to reach 10 mA cm⁻² with a low Tafel slope of 66 mV dec⁻¹ and long-term stability in alkaline solutions.     

Self-supported Ni2P nanotubes coated with FeP nanoparticles electrocatalyst (FeP@Ni2P/NF) for oxygen evolution reaction

Bimetallic phosphides have been widely investigated as electrocatalysts for oxygen evolution reaction (OER) due to their efficient activity and environmental friendliness. While the reasonable design and controllable synthesis of bimetallic phosphide with typical nanostructure is still a great challenge. Hence, we put forward a novel and straightforward way for constructing FeP nanoparticles coated Ni₂P ultrathin nanotube arrays on the surface of Ni foil (FeP@Ni₂P/NF), which is synthesized through two steps of electrodeposition and subsequent in-situ phosphorization process. The obtained FeP@Ni₂P/NF shows excellent electrochemical activity for OER, and it only needs potential of 1.52 V vs. RHE to reach the current density of 50 mA cm⁻² in an alkaline media. The excellent electrocatalytic activity of FeP@Ni₂P/NF mainly benefits from: (i) the synergistic effect between FeP and Ni₂P promoting electron transfer; (ii) the formation of the unique 3D ultrathin nanotube arrays increasing the quantity of active sites and avoiding the agglomeration of catalysts during testing. In addition, the influence of reaction condition on the electrochemical activity for OER has also been investigated through altering the phosphorization temperature of precursor.     

Crafty design of chemical bonding to construct MoO2/CdS nanorod photocatalysts for boosting hydrogen evolution

An efficient MoO₂/CdS photocatalyst has been successfully constructed by a relatively facile way to construct a specific combination mode through chemical bond, which results in strong interaction between MoO₂ nanoparticles and CdS nanorods. X-ray photoelectron spectroscopy further confirms the formation of Mo–S bonding, which acts as a connection bridge and develops an intimate contact between CdS-NRs and MoO₂ nanoparticles. Benefitting from the synergic effect of the enhancement on the light absorption, carriers’ efficient separation and lower the overpotential of hydrogen evolution, the obtained MoO₂/CdS composite has shown an excellent enhancement in photocatalytic H₂ generation and the optimal H₂ evolution rate reaches as high as 30 times than that of pure CdS nanorods. We have experimentally shed light on the mechanism of this excellent enhancement performance in detail. Moreover, our work can broaden the construction and the application of developing other efficient photocatalytic material containing transition metal oxide.