NiSe2@NixSy nanorod on nickel foam as efficient bifunctional electrocatalyst for overall water splitting

Electrocatalytic water splitting technology has become one of the most promising methods to solve the energy crisis, which can produce a large amount of high purity H₂ and O₂. It is necessary to develop efficient and stable water splitting catalyst for reducing the overpotential of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and accelerating their reaction kinetics. A series of NiSe₂@Ni_xS_y nanoarrays was firstly in situ grown on the nickel foam through the typical hydrothermal, selenylation and sulfuration pathways. The Na₂SeO₃ homogeneous solution is formed by hydrothermal and the selenization process is done at the temperature of 180^。C. Then the nickel foam (NF) is put into the Na₂SeO₃ solution to form NiSe₂ material at the temperature of 120^。C. After that, the NiSe₂ materials were sulfuretted with different amounts of sulfur to form NiSe₂@Ni_xS_y hybrid materials. The experimental results demonstrate that the NiSe₂@Ni_xS_y material as a 3D electrode can maximize the synergistic reaction between NiSe₂ and Ni_xS_y, thus exhibiting an efficient and comprehensive water splitting performance. The NiSe₂@Ni_xS_y-1 material presents a superior OER performance with requiring the overpotential of only 206 mV at 100 mA cm⁻². Moreover, the NiSe₂@Ni_xS_y-0.3 material presents a superior HER performance with requiring the overpotential of only 148 mV at 100 mA cm⁻². It is worth noting that when NiSe₂@Ni_xS_y-1 material and the NiSe₂@Ni_xS_y-0.3 material was used as cathode and anode, only 1.53 V cell voltage is needed to produce a current density of 10 mA cm⁻² throughout the water splitting process, which is one of the smallest values reported so far. Density functional theory calculations results show that the Ni₃S₂ has the best water adsorption energy, so it is an active species in the process of catalysis. However, NiSe₂ has more density distribution around the Fermi level, indicating that it exhibits better metallic properties, which makes the NiSe₂@Ni_xS_y-1 hybrid material exhibit better electronic conductivity.     

CoSe2@NiSe2 nanoarray as better and efficient electrocatalyst for overall water splitting

Electrocatalytic water splitting is identified as one of the most promising solutions to energy crisis. The CoSe₂@NiSe₂ materials were first prepared and in situ grown on nickel foam by typical hydrothermal and selenification process at 120 °C. The results show that the CoSe₂@NiSe₂ material used as the 3D substrates electrode can maximize the synergy between the CoSe₂ and NiSe₂, and also exhibits high efficiency of water splitting reaction. The lower overpotential of only 235 mV is presented to attain 20 mA cm⁻² compared to the benchmark of RuO₂ electrodes (270 mV @ 20 mA cm⁻²). Besides, the CoSe₂@NiSe₂ material also shows a remarkable improved hydrogen evolution reaction activity compared to NiSe₂ (192 mV@10 mA cm⁻²) and Co precursor catalysts (208 mV@10 mA cm⁻²) individually, which a low overpotential of only 162 mV is achieved at 10 mA cm⁻². The CoSe₂@NiSe₂ catalysts exhibit excellent water splitting performance (cell voltage of 1.50 V@ 10 mA cm⁻²) under alkaline conditions. It was proved that the high water splitting performance of the catalyst is attributed to high electrochemical activity area and synergistic effect. The work offers new ideas for the exploitation of synergistic catalysis of composite catalysts and adds new examples for the exploitation of efficient, better and relatively non-toxic electrocatalysts.     

Electrodeposition of NiS/Ni2P nanoparticles embedded in amorphous Ni(OH)2 nanosheets as an efficient and durable dual-functional electrocatalyst for overall water splitting

To develop earth-abundant and cost-effective catalysts for overall water splitting is still a major challenge. Herein, a unique “raisins-on-bread” Ni–S–P electrocatalyst with NiS and Ni₂P nanoparticles embedded in amorphous Ni(OH)₂ nanosheets is fabricated on Ni foam by a facile and controllable electrodeposition approach. It only requires an overpotential of 120 mV for HER and 219 mV for OER to reach the current density of 10 mA cm⁻² in 1 M KOH solution. Employed as the anode and cathode, it demonstrates extraordinary electrocatalytic overall water splitting activity (cell voltage of only 1.58 V @ 10 mA cm⁻²) and ultra-stability (160 h @ 10 mA cm⁻² or 120 h @50 mA cm⁻²) in alkaline media. The synergetic electronic interactions, enhanced mass and charge transfers at the heterointerfaces facilitate HER and OER processes. Combined with a silicon PV cell, this Ni–S–P bifunctional catalyst also exhibits highly efficient solar-driven water splitting with a solar-to-hydrogen conversion efficiency of 12.5%.     

Novel route of NiCr-layered double hydroxide nanosheets synthesis on nickel foam as a bifunctional electrocatalyst for water splitting process

In this study, we present a novel direct synthetic route for producing NiCr-layered double hydroxide (LDH) nanosheets on a nickel foam surface using the Successive Ionic Layer Deposition (SILD) method. The morphology of the nanolayers was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Additionally, the electrocatalytic properties of the nanolayers were examined using electrochemical techniques. The NiCr-layered double hydroxide nanolayers produced through SILD using sodium hexahydroxochromate (III) anion precursor were found to be ultrathin “nanosheets” with a hydrotalcite-like structure and low crystallinity. The efficacy of electrodes based on these nanolayers as cathode and anode materials in electrocatalytic cells for hydrogen production through electrolytic water splitting in alkaline media were investigated. Our results showed that the electrode based on NiCr-LDH nanolayers exhibited good kinetics in both the cathode and anode areas.     

Ni/NiO@rGO as an efficient bifunctional electrocatalyst for enhanced overall water splitting reactions

Herein, we fabricated bifunctional, noble metal-free, highly efficient nickel/nickel oxide on reduced graphene oxide (Ni/NiO@rGO) by chemical synthesis approach for electrochemical water splitting reaction. Its structural and morphological characterization using thermogravimetric analysis (TGA), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), energy dispersive analysis of X-ray (EDAX) and X-ray diffraction (XRD) represents, Ni/NiO@rGO is having Ni/NiO NPs ∼10 nm (±2 nm) on graphene oxide with face-centered cubic (FCC) crystal structure. Moreover, the presence of Ni/NiO (2.26%), O (6.56%), N (0.74%) and C (90.44%) from EDAX analysis further confirms the formation of Ni/NiO@rGO and it also supported by FTIR studies. This nanocatalyst is examined further for electrocatalytic water splitting reactions (HER and OER). It demonstrated low overpotential 582 mV to achieve current density at 10 mA cm⁻² and smaller Tafel slope of 63 mV dec⁻¹ obtained in 0.5 M H₂SO₄ towards HER. Also, at the other end at onset potential of 1.6 V vs. RHE towards OER. It demonstrated low overpotential 480 mV to achieve current density at 10 mA cm⁻² and smaller Tafel slope of 41 mV dec⁻¹ in 0.5 M KOH towards OER observed. Hydrogen fuel is eco-friendly to the environment and noteworthy performance of earth-saving reactions.     

Hierarchical flower-like CoS2-MoS2 heterostructure spheres as efficient bifunctional electrocatalyst for overall water splitting

Electrochemical water splitting technique requires high-efficient bifunctional electrocatalysts to obtain large-scale hydrogen production for resolving the impending energy and environmental crisis. Herein, hierarchical flower-like CoS₂-MoS₂ heterostructure hybrid spheres grown on carbon cloth (CoS₂-MoS₂/CC) were prepared by sulfuring wheel-shaped polyoxometalate {Co₂₀Mo₁₆}. The as-prepared CoS₂-MoS₂/CC as bifunctional electrocatalyst manifests excellent alkaline oxygen evolution and hydrogen evolution activities with low overpotentials of 240 mV for OER and 60 mV for HER at 10 mA cm^?2, respectively. When assembled as two-electrode cell, CoS₂-MoS₂/CC delivers an extremely low cell-voltage of 1.52 V at 10 mA cm^?2 accompanied with remarkable long-term durability. Additionally, CoS₂-MoS₂/CC exhibits favorable overall-water-splitting performance in simulated seawater. The superior performance of CoS₂-MoS₂/CC should be ascribed to the optimized intrinsic electron structure via electron transfer from MoS₂ to CoS₂ along with the synergistic effect of well-exposed heterostructure interfaces and favorable diffusion channels. This work offers a practical strategy for exploring high-efficient bifunctional electrocatalysts for overall water splitting.     

MoS2/NiS heterostructure grown on Nickel Foam as highly efficient bifunctional electrocatalyst for overall water splitting

It is great important to develop and explore a non-precious bifunctional electrocatalyst with high efficiency and good stability for Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) in alkaline electrolyte. Herein, a three-dimensional (3D) needle-like MoS₂/NiS heterostructure supported on Nickel Foam (NF) (MoS₂/NiS/NF) is synthesized by a simple hydrothermal method for the first time, which can act as a good bifunctional electrocatalyst for overall water splitting. As expected, the optimal MoS₂/NiS/NF exhibits excellent catalytic performance with a low overpotential of 87 and 216 mV at 10 mA cm⁻² for HER and OER in 1 M KOH electrolyte, respectively, accompanied by good cycle stability. Furthermore, the MoS₂/NiS/NF as bifunctional electrocatalyst in an electrolyzer shows high efficiency with a cell voltage of 1.5 V at 10 mA cm⁻², as well as superior durability. The present work may open a new direction to design and develop a non-precious bifunctional electrocatalyst with excellent catalytic activity for water splitting in the future.     

CoP-anchored high N-doped carbon@graphene sheet as bifunctional electrocatalyst for efficient overall water splitting

Electrocatalytic water splitting, as an ideal technology in renewable energy applications, suffers from high electrical energy consumption due to the slow kinetics of HER and OER reactions. Therefore, it is urgent to design efficient bifunctional catalysts to improve the reaction kinetics. Herein, a self-supported electrode, anchoring CoP nanoparticles on N-doped carbon/graphene (NC-G) and chemically growing on Ni foam as a whole electrode (denoted as NC-G-CoP/NF) displays promising electrocatalytic performance in 1.0 M KOH electrolyte, with a low overpotentials of 68 mV at 10 mA cm^?2 for HER and 255 mV at 50 mA cm^?2 for OER. This bifunctional electrocatalyst only needs 1.435 V to generate 10 mA cm^?2 for overall water splitting. The outstanding electrocatalytic performance is ascribed to the following factors: i) inherent nature of transition metal phosphides, ii) abundant and high dispersion N active sites in NC-G, iii) strong interaction between the NC-G and CoP nanoparticles, and iv) rapid electron transfer between the catalytic centers and Nickle foam. This provides a new perspective to design efficient electrocatalysts for electrocatalytic water splitting.     

Hydrogen production via highly efficient electrocatalyst based on 3D NixCo1-x(OH)2/NiFe-AM induce overall water splitting

The main factors limiting water splitting producing hydrogen production are overpotential, activity and persistence of electrocatalysts. Herein, a novel Ni_xCo_1-x(OH)₂ coupled with NiFe amorphous compound array growing on nickel foam substrate (expressed as Ni_xCo_1-x(OH)₂/NiFe-AM) was developed by facile hydrothermal and electrodeposition methods. Significantly, Ni_xCo_1-x(OH)₂/NiFe-AM with this unique structural exhibits superior activity and stability in the two half reactions of water electrolysis. In addition, when tested in an alkaline electrolyte with a current density of 10 mA cm⁻², the overpotentials of HER and OER was 157 mV and 196 mV (60 mA cm⁻²), respectively. The stability can up to 60 h. These test results show through constructing hierarchical nano-thron architecture enhanced electrocatalytic activity to produce hydrogen and oxygen.     

Multi-active site CoNi-MOFs as non-noble bifunctional electrocatalysts for highly efficient overall water splitting

The high-efficiency non-precious metal catalysts for oxygen evolution (OER) and hydrogen evolution (HER) are of great significance to the development of renewable energy technologies. Herein, a multiple active sites CoNi-MOFs-DBD electrocatalyst modified by low temperature plasma (DBD) was successfully synthesized by converting metal hydroxyfluoride on nickel foam into a well-arranged MOFs array using vapor deposition. The as-prepared CoNi-MOFs-DBD electrode showed better HER and OER catalytic activity, super hydrophilicity, and excellent stability. In an alkaline medium, the overpotential of HER is 203 mV at 10 mA cm^?2 and that of OER is 168 mV at 40 mA cm^?2. When CoNi-MOFs-DBD was used as a bifunctional electrocatalyst for overall water splitting in a two-electrode system, a current density of 10 mA cm^?2 can be achieved at a low voltage of 1.42 V, which shows great potential in electrocatalytic water splitting.     

Electrodeposited nickel–iron–carbon–molybdenum film as efficient bifunctional electrocatalyst for overall water splitting in alkaline solution

Designing and synthesizing of efficient and inexpensive bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is one of the current research topics. In this study, NiFeCMo film in nickel mesh substrate is prepared by one-step direct-current electrodeposition method. The obtained NiFeCMo film shows the excellent electrocatalytic activity, which only requires overpotentials of 254 mV for HER and 256 mV for OER to drive current density of 10 mA cm⁻², with corresponding Tafel slopes of 163.9 and 60.3 mV·dec⁻¹ in 30% KOH medium, respectively. Moreover, NiFeCMo film only needs a low cell voltage of 1.61 V to drive current density of 10 mA cm⁻² in an alkaline electrolyzer. Such remarkably HER and OER properties of NiFeCMo alloy is attributed to the increased effective electrochemically active surface area and the synergy effect among Ni, Fe, C and Mo.     

Highly active Ni/Co-metal organic framework bifunctional electrocatalyst for water splitting reaction

Rational design of electrocatalycally active materials with excellent performance for renewable energy conversion is of great interest. We have developed a nanosheet array of Ni/Co metal-organic framework (MOF) grown on CoO modified Ni foam (CoO/NF) substrate via the solvothermal process. The high surface area and low resistance of Ni/Co-MOF@CoO/NF (NC@CoO/NF) catalyst contribute to efficient water splitting. We have prepared a series of NC-n/CoO/NF (n = 1–4) catalysts to optimize the molar ratio of the Co atom in Ni MOF-74. Among them, NC-2@CoO/NF shows an excellent electrochemical performance in alkaline medium, i.e., low overpotential of 290 and 139 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. For a two-electrode system with NC-2@CoO/NF, a low cell voltage of 1.54 V at 10 mA cm^?2 has been obtained for overall water splitting which is much smaller than that with commercial Ir/C– Pt/C pair. This excellent performance can be attributed to the synergistic effects of Ni/Co-MOF and CoO/NF. In addition, the as-prepared NC-2@CoO/NF exhibits excellent long-term stability. The computational simulation also supports experimental results.     

Electronic regulation and core-shell hybrids engineering of palm-leaf-like NiFe/Co(PO3)2 bifunctional electrocatalyst for efficient overall water splitting

Constructing efficient and stable bifunctional electrocatalysts for overall water splitting remains a challenge because of the sluggish reaction kinetics. Herein, the core-shell hybrids composed of Co(PO₃)₂ nanorod core and NiFe alloy shell in situ grown on nickel foam (NiFe/Co(PO₃)₂@NF) are synthesized. Owing to the hierarchical palm-leaf-like structures and strong adhesion between NiFe alloys, Co(PO₃)₂ and substrates, the catalyst provides a large surface area and rapid charge transfer, which facilitates active sites exposure and conductivity enhancement. The interfacial effect in the NiFe/Co(PO₃)₂ core-shell structure modulates the electronic structure of the active sites around the boundary, thereby boosting the intrinsic activity. Benefiting from the stable structure, the durability of the catalyst is not impaired by the inevitable surface reconfiguration. The NiFe/Co(PO₃)₂@NF electrode presents a low cell voltage of 1.63 V to achieve 10 mA cm^?2 and manifests durability for up to 36 h at different current densities.     

Tungsten promoted nickel phosphide nanosheets supported on carbon cloth: An efficient and stable bifunctional electrocatalyst for overall water splitting

It is of great significance to develop a highly active, durable and inexpensive bifunctional electrocatalyst for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we report a tungsten-doped nickel phosphide nanosheets based on carbon cloth (W–Ni₂P NS/CC) as an efficient bifunctional catalyst through simple hydrothermal and phosphorization for overall water splitting in 1 M KOH. The W–Ni₂P NS/CC exhibits excellent electrochemical performance with low overpotentials for HER (η₁₀ = 71 mV, η₅₀ = 160 mV) and OER (η₂₀ = 307 mV, η₅₀ = 382 mV) in 1 M KOH, as well as superior long-term stability. Moreover, W–Ni₂P NS/CC as a bifunctional catalyst reveals remarkable activity with a low voltage of 1.55 V to reach a current density of 20 mA cm⁻². This work provides a viable bifunctional catalyst for the overall water splitting.     

Effect of annealing temperature on the bifunctional electrocatalytic properties of strontium nickelate (SrNiO3) nanoparticles for efficient overall water splitting

The global trend in energy demand has paved way for clean hydrogen (H₂) energy production at large scale. To address this issue, perovskite (ABX₃) nanomaterials are widely researched to replace the noble metal electrocatalysts for electrochemical water splitting. In this work, the effect of annealing temperature on the structural and electrochemical properties of combustion derived strontium nickelate (SrNiO₃) nanoparticles are studied. Benefitting from the unique features of perovskites, SrNiO₃ nanoparticles displays excellent OER and HER activity in 1.0 M KOH with an overpotential of 259 mV and 451 mV to achieve 10 mAcm^?2 respectively. SrNiO₃ nanoparticles show superior HER activity when annealed at higher temperature and subtle change in OER activity. The stability of SrNiO₃ nanoparticles were noteworthy as it shows no degradation even after 12 h. The overall water splitting of highly active SrNiO₃ nanoparticles was carried out in a two-electrode system and the setup posted a cell voltage of 1.88 V at 10 mAcm^?2 after continuous water splitting for 24 h. Thus, SrNiO₃ nanoparticles may possibly serve as a potential bifunctional electrocatalyst for H₂ production.     

Bimetallic metal-organic framework derived electrocatalyst for efficient overall water splitting

The development of bifunctional catalysts that can be applied to both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is widely regarded as a key factor in the production of sustainable hydrogen fuel by electrochemical water splitting. In this work, we present a high-performance electrocatalyst based on nickel-cobalt metal-organic frameworks for overall water splitting. The as-obtained catalyst shows low overpotential to reaches the current density of 10 mA cm⁻² with 249 mV for OER and 143 mV for HER in alkaline media, respectively. More importantly, when the electrolyzer was assembled with the as-prepared catalyst as anode and cathode simultaneously, it demonstrates excellent activity just applies a potential of 1.68 V to achieve 10 mA cm⁻² current density for overall water splitting.     

Bimetallic-metal organic framework-derived Ni3S2/MoS2 hollow spheres as bifunctional electrocatalyst for highly efficient and stable overall water splitting

Herein, strongly coupled Ni₃S₂/MoS₂ hollow spheres derived from NiMo-based bimetal-organic frameworks are successfully synthesized for overall water splitting via a one-pot solvothermal method followed by sulfurization. A well-defined hollow spherical structure with a heterointerface between Ni₃S₂ and MoS₂ is constructed using solvothermal and sulfurization processes. Owing to their bimetallic heterostructure, porous hollow carbon structure with large surface area, and numerous exposed active sites, the Ni₃S₂/MoS₂ hollow spheres are found to be efficient electrocatalysts for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The heterostructured Ni₃S₂/MoS₂ hollow spheres show small overpotentials of 303 and 166 mV to reach a current density of 10 mA cm^?2 for the OER and HER in 1.0 M KOH, respectively. Furthermore, an overall water-splitting electrolyzer consisting of the Ni₃S₂/MoS₂ hollow spheres as both the anode and cathode requires a very low cell voltage of 1.62 V to drive a current density of 10 mA cm^?2 with outstanding long-term stability for 100 h. Our findings offer a new pathway for the design and synthesis of electrochemically advanced bifunctional catalysts for various energy storage and conversion applications.     

Thin-film iron-oxide nanobeads as bifunctional electrocatalyst for high activity overall water splitting

Developing only Fe derived bifunctional overall water splitting electrocatalyst both for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) while performing at low onset overpotential and with high catalytic stability is a rare instance. We present here the first demonstration of unique iron-oxide nanobeads (FeO_x-NBs) based electrocatalyst executing both OER and HER with high activity. Thin-film electrocatalytic FeO_x-NBs assembly is surface grown via simple spray coating (SC). The unique SC/FeO_x-NBs propels OER initiating water oxidation just at 1.49 V_RHE (η = 260 mV) that is the lowest observable onset potential for OER on simple Fe-oxide based catalytic films reported so far. Catalyst also reveals decently high HER activity and competent overall water splitting performance in the FeO_x-NBs two-electrode system as well. Catalyst also presents stable kinetics, with promising high electrochemically active surface area (ECSA) of 1765 cm², notable Tafel slopes of just 54 mV dec^1? (OER) and 85 mV dec^1? (HER), high exchange current density of 1.10 mA cm^2? (OER), 0.58 mA cm^2? (HER) and TOF of 74.29s^1?@1.58V_RHE, 262s^1?@1.62V_RHE (OER) and 82.5s^1?@-0.45V_RHE, 681s^1?@-0.56V_RHE (HER).     

NiS2@V2O5/VS2 ternary heterojunction for a high-performance electrocatalyst in overall water splitting

Water splitting is regarded as an effective way to produce hydrogen energy to solve the energy crisis all over the world. However, the electrocatalysts suffer from expensive prices, high voltage, and sluggish kinetics. The heterojunction is composed of two semiconductors and can accelerate electron transfer by relying on interface engineering. Herein, we first prepare NiS₂@V₂O₅/VS₂ ternary heterojunction electrocatalyst, showing the low OER overpotential of 333 mV and HER overpotential of 216 mV at 10 mA cm^?2, as well as good stability. Meanwhile, the NiS₂@V₂O₅/VS₂ heterojunction is assembled to the two-electrode system for overall water splitting, exhibiting a very low voltage value of 1.49 V, which is much superior to that of the benchmark RuO₂//Pt/C system. The energy band calculation reveals the mechanism that the NiS₂ and VS₂ lower the Fermi level of V₂O₅, thus promoting the electrons transfer in the electrocatalytic reactions. Our work opens up a novel route for heterojunction application in the electrocatalytic field.     

Facile synthesis of three-dimensional spherical Ni(OH)2/NiCo2O4 heterojunctions as efficient bifunctional electrocatalysts for water splitting

Synthesis of highly efficient, non-noble and bi-functional electrocatalysts is exceedingly challenging and necessary for water splitting devices. In this work, three-dimensional spherical Ni(OH)₂/NiCo₂O₄ heterojunctions are prepared by a one-step hydrothermal method and the hybrids are explored as efficient electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline electrolyte via tuning different Ni/Co atomic ratios of heterojunctions. The optimized Ni(OH)₂/NiCo₂O₄ (S (1:1)) exhibits high electrocatalytic activity with an ultralow over-potential of 189 mV at 10 mA cm⁻² for the HER. With regard to the OER, the over-potential of the as-synthesized S (1:1) heterojunction is only 224 mV at the current density of 10 mA cm⁻². The improved catalytic performance of the Ni(OH)₂/NiCo₂O₄ heterojunctions is attributed to the chemical synergic combining of Ni(OH)₂ and NiCo₂O₄, large specific surface area for exposing more accessible active sites, and heterointerface for activating the intermediates that facilitates electron/electrolyte transport. The prepared catalyst exhibits good durability and stability in HER and OER catalyzing conditions. This study provides a feasible approach for the building of highly efficient bifunctional water splitting electrocatalysts and stimulates the development of renewable energy conversion and storage devices.