Hydrogen production from waste-derived synthesis gas over Ni(x)Fe(3-x)-CeO2 catalyst: optimization of Ni/Fe ratio

In this study, the effect of the Ni/Fe molar ratio on the Ni_(x)Fe_(3-x)-CeO₂ catalyst was investigated for the high-temperature water-gas shift reaction, which produces hydrogen from waste-derived synthesis gas. The catalysts were synthesized via a co-precipitation method, using different Ni/Fe molar ratios (0.5:2.5, 1.0:2.0, 1.5:1.5, 2.0:1.0, and 2.5:0.5). The physicochemical properties of these catalysts were analyzed by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), temperature-programmed reduction using hydrogen (H₂-TPR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and H₂-O₂ pulse analyses to determine their reaction performance. The Ni_1.0Fe_2.0-CeO₂ catalyst exhibited the highest activity (X_co = 88%, T = 500 °C) without any side reactions at a high gas hourly space velocity of 41,823 mL·g⁻¹ h⁻¹, compared to the other catalysts tested, owing to its high oxygen vacancies and oxygen storage capacity (OSC). In addition, when the Ni/Fe molar ratio was higher than 1, a side reaction (methanation) occurred. Therefore, it was concluded that the Ni_1.0Fe_2.0-CeO₂ catalyst is optimal for hydrogen production via the high-temperature water-gas shift reaction from waste-derived synthesis gas.     

Hollow hexagonal NiSe–Ni3Se2 anchored onto reduced graphene oxide as efficient electrocatalysts for hydrogen evolution in wide-pH range

Integrating transition metal complexes with carbon-based materials, especially graphene, is a useful strategy for synthesizing effective hydrogen evolution catalysts. Herein, we report a design of hollow hexagonal NiSe–Ni₃Se₂ nanosheets grown on reduced graphene oxide (NiSe–Ni₃Se₂/rGO) by a simple hydrothermal method as an effective catalyst for hydrogen evolution reaction (HER) in the full pH range. In 0.5 M H₂SO₄, the NiSe–Ni₃Se₂/rGO possesses 112 mV to achieve 10 mA cm^?2 and a small Tafel slope (61 mV dec^?1). In 1.0 M PBS and 1.0 M KOH, the overpotentials are 261 and 188 mV at 10 mA cm^?2, and Tafel slopes are 103 and 92 mV dec^?1, respectively. Meanwhile, it owns good cycle stability and durability over 20 h in the whole pH range (0-14). In all solutions, the HER performance of NiSe–Ni₃Se₂/rGO is better than that of NiSe–Ni₃Se₂. This is because the rGO substrate accelerates the electron transfer and improves the electrical conductivity, increasing HER activity of catalyst.     

Ternary NiCoFe nanosheets for oxygen evolution in anion exchange membrane water electrolysis

Tuning nickel-based catalyst activity and understanding electrolyte and ionomer interaction for oxygen evolution reaction (OER) is crucial to improve anion exchange membrane (AEM) water electrolyzers. Herein, an investigation of multimetallic Ni_0.6Co_0.2Fe_0.2 OER activity, coupled with in-situ Raman spectroscopy to track dynamic structure changes, was carried out and compared to other Ni catalysts. The effect of KOH concentration, KOH purity, ionomer type, and electrolyte with organic cations was evaluated. The Ni_0.6Co_0.2Fe_0.2 catalyst achieved 10 mA/cm² at 260 mV overpotential with stability over 50 h and 5000 cycles in 1 M KOH. In-situ Raman spectroscopy showed that Ni_0.6Co_0.2Fe_0.2 activity originates from promoting Ni(OH)₂/NiOOH transformation at low potentials compared to bi- and mono-metallic nickel-based catalysts. Fumion anion ionomer in the catalyst inks led to a lower OER activity than catalysts with inks containing Nafion ionomer. The OER activity of Ni_0.6Co_0.2Fe_0.2 is adversely influenced in the presence of fumion anion ionomer and benzyltrimethylammonium hydroxide (BTMAOH) with possible phenyl oxidation under applied high anodic potentials. The alkaline AEM water electrolyzer circulating 1 M KOH electrolyte, with a Pt/C cathode and a Ni_0.6Co_0.2Fe_0.2 anode, achieved 1.5 A/cm² at 2 V.     

Interlaced rosette-like MoS2/Ni3S2/NiFe-LDH grown on nickel foam: A bifunctional electrocatalyst for hydrogen production by urea-assisted electrolysis

In targeting the most important energy and environmental issues in current society, the development of low-cost, bifunctional electrocatalysts for urea-assisted electrocatalytic hydrogen (H₂) production is an urgent and challenging task. In this work, interlaced rosette-like MoS₂/Ni₃S₂/NiFe-layered double hydroxide/nickel foam (LDH/NF) is successfully synthesized by a two-step hydrothermal reaction. Due to its unique interlaced heterostructure, MoS₂/Ni₃S₂/NiFe-LDH/NF exhibits excellent bifunctional catalytic activity towards the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER) in 1.0 M KOH with 0.5 M urea. In a concurrent two-electrode electrolyser (MoS₂/Ni₃S₂/NiFe-LDH/NF(+,-)), only voltage of 1.343 V is required to reach 50 mA cm⁻², which is 216 mV lower than for pure water splitting. Furthermore, after 16 h of urea electrolysis in 1.0 M KOH with 0.5 M urea, the current density remains at 98% of the original value. Thus, the catalyst is not only favorable for H₂ production, but also has great significance for the problem of urea-rich wastewater treatment.     

Self-supported iron-doped nickel sulfide as efficient catalyst for electrochemical urea and hydrazine oxidation reactions

The electrochemical oxidation of urea and hydrazine over self-supported Fe-doped Ni₃S₂/NF (Fe–Ni₃S₂/NF) nanostructured material is presented. Among the various reaction conditions Fe–Ni₃S₂/NF-2 prepared at 160 °C for 8 h using 0.03 mM Fe(NO₃)₃ shows the best results for the hydrazine and urea oxidation reactions. The potential values of 0.36, 1.39, and 1.59 V are required to achieve the current density of the 100 mA cm^?2 in 1 M hydrazine (Hz), 0.33 M urea, and 1 M KOH electrolyte, respectively. The onset potential in 1 M KOH, 0.33 M Urea +1 M KOH, and 1 M Hz + 1 M KOH values are 1.528, 1.306, and 0.176 respectively. The Fe–Ni₃S₂/NF-2 shows stable performance at 10 mA cm^?2 until 50 h and at 60 mA cm^?2 over the 25 h. A cell of PtC//Fe–Ni₃S₂/NF-2 requires the potential of 0.49, 1.46, and 1.59 V for the hydrogen production in 1 M Hz + 1 M KOH, 0.33 M Urea +1 M KOH, and 1 M KOH electrolyte, respectively, at a current density of 10 mA cm^?2, and almost 90% stable for the hydrogen production over the 80 h in all electrolytes. The improvement of the chemical kinetics of urea and hydrazine oxidation is due to the synergistic effect of the adsorption and fast electron transfer reaction on Fe–Ni₃S₂/NF-2. The doped Fe ion facilitates the fast electron transfer and the surface of Ni₃S₂ support to the urea and hydrazine molecule adsorption.     

Controlled synthesis of three-dimensional branched Mo–NiCoP@NiCoP/NiXCoYH2PO2 core/shell nanorod heterostructures for high-performance water and urea electrolysis

It is necessary to design reasonably efficient bifunctional electrocatalyst, but it is still a difficult problem for the water and urea electrolysis. Therefore, we firstly constructed a novel Mo–NiCoP@NiCoP/Ni_XCo_YH₂PO₂ (MNCP@NCP/Ni_XCo_YH₂PO₂) core/shell nanorod heterostructure by hydrothermal and two-step phosphating on nickel foam (NF). It is worth noting that Mo-doping could availably regulate the electronic structure of NiCoP(NCP), resulting in the increased exposure of the active center and the increased inherent activity of each site. Furthermore, a strategy of improving catalyst activity was proposed, that is, the NiCoP nanorod core and Mo–NiCoP/Ni_XCo_YH₂PO₂ nanorod shell was constructed by the two phosphating reactions to come into being mixed transition-metal phosphides (TMPs), thus improving the synergistic catalytic effect of the material. In addition, the water and urea electrolysis apparatus was installed from two MNCP@NCP/Ni_XCo_YH₂PO₂ electrodes to actuate a current density of 10 mA cm^?2, the necessary cell voltage was merely 1.348 V in 1.0 M KOH with 0.5 M urea for urea electrolysis, while the higher 1.522 V of cell voltage was required in 1.0 M KOH for water electrolysis, which is one of the best catalytic activities reported so far. Experimental results show that the oxyhydroxide is the real active site during urea electrolysis process. Density functional theory calculation shows that the doping of Mo and Co increase the water adsorption energy and conductivity of the oxyhydroxide material, so the water splitting performance of the catalyst is improved. Therefore, this work provided a new way to design bifunctional electrocatalysts by Mo-doping and two-step phosphating process.     

Novel peapod-like Ni2P@N-doped carbon nanorods array on carbon fiber for efficient electrocatalytic urea oxidation and hydrogen evolution reaction

Designing and optimizing structure is an effective method to enhance electrocatalytic performance of transition metal-based catalysts. In this work, an innovative nanostructured electrode, consisted of peapod-like Ni₂P@N-doped carbon nanorods array coating on carbon fiber (CF@p-Ni₂P@NC), is devised and synthesized. The N-doped carbon layer is crucial for maintaining the peapod-like nanostructure, which allows for multi-channel electrolyte transport and gas product release. And the carbon layer coating Ni₂P nanoparticles also enhance electrical conductivity and stability, thus ensuring fast electron transport from/to active sites and the long-term stability of catalyst during urea oxidation reaction (UOR)/hydrogen evolution reaction (HER). Benefit from the reasonable structure, CF@p-Ni₂P@NC present perfect performance with getting 100 mA cm^?2 at potential/overpotential of 1.417/0.194 V for UOR/HER in 1.0 M KOH containing 0.5 M urea. In addition, the overall urea-electrolysis system using CF@p-Ni₂P@NC bifunctional electrode only requires 1.590 V to obtain 100 mA cm^?2.     

Nanorod-like NiFe metal-organic frameworks for oxygen evolution in alkaline seawater media

Searching for highly active and durable oxygen evolution reaction (OER) electrocatalysts is the key to break through the bottleneck of overall water splitting. Here, we prepare Ni_xFe-BDC (H₂BDC = terephthalic acid) nanorods with different Ni/Fe ratios by a facile solvothermal method for the OER. The optimal Ni₃Fe-BDC exhibits a low overpotential (η₁₀) of 265 mV and a Tafel slope of 90 mV·dec⁻¹ in 1 M KOH. Moreover, it shows a low η₁₀ of 280 mV and excellent stability in the mixture of 1 M NaCl and 1 M KOH, which has strong corrosion resistance to Cl⁻ anions. The role of Fe³⁺ not only increases the charge transfer rate of Ni₃Fe-BDC, but also affects the specific surface area of the catalyst with high electrochemical activity. Kinetic studies show that both Fe and Ni sites act as active centers, which catalyze synergistically to reduce the reaction kinetic energy barrier. Characterization results of the used Ni₃Fe-BDC reveal that the in situ formed rod-like Ni₃FeOOH is the active site for the OER.     

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.     

One-step preparation of Fe-doped Ni3S2/rGO@NF electrode and its superior OER performances

In order to improve the OER performance, Ni₃S₂-based catalysts were directly grown on Ni substrate by simultaneously doping of Fe and compositing with reduced graphene oxide (rGO). Synthesis and loading of Ni₃S₂/rGO were completed during a one-step hydrothermal process, in which Ni foam acted as support and Ni source of Ni₃S₂, as well as the subsequent current collector. It is found that either GO or Fe salt tuned Ni₃S₂ nanosheets into thinner and smaller interconnected nanosheets anchored on rGO, which enhanced the charge transfer resistance and improved the active sites. Hence, as-synthesized Fe-doped Ni₃S₂/rGO composite at 120 °C (Fe-2-Ni₃S₂/rGO@NF-120) exhibited an enhancement on OER performances: An overpotential of 247 mV at 20 mA cm⁻², and a small Tafel slope of 63 mV dec⁻¹, as well as an excellent stability of: 20 h maintaining at 20 mA cm⁻² or 50 mA cm⁻².     

Solvothermal synthesis of Pd10–Ni45–Co45/rGO composites as novel electrocatalysts for enhancement of the performance of DBFC

In this research, three Pd decorated Ni and Co catalyst nanoparticle were synthesized on reduced graphene oxide (rGO) supports are synthesized through a facile solvothermal procedure. Borohydride oxidation reaction (BOR) activity and performance of prepared electrocatalysts respect to NaBH₄ oxidation is evaluated by various electrochemical techniques in the three-electrode and the fuel cell configuration. Among the prepared catalysts, Pd₁₀–Ni₄₅–Co₄₅/rGO exhibits the highest BOR activity. The cyclic voltammograms showed that the measured current at 0.5 V for the electrode of Pd₁₀–Ni₄₅–Co₄₅/rGO is as much as 108 mA cm⁻² higher than Pd₁₀–Ni₉₀/rGO and 185 mA cm⁻² higher than Pd₁₀Co₉₀/rGO. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra were employed to study the morphology and crystal structure of the prepared catalyst. The results of DBFC test show that the Pd₁₀–Ni₄₅–Co₄₅/rGO nanoparticles as anodic catalyst, enhanced power density to 50.4 mW cm⁻² which is 10.5% and 45.2% higher than power density of DBFCs with Pd₁₀–Ni₉₀/rGO (45.6 mW cm⁻²) and Pd₁₀Co₉₀/rGO (34.7 mW cm⁻²) anode catalysts, respectively. These results indicate that the competency of operating procedure for assembling nickel alloys electrodes can improve the activity of the prepared catalysts for BOR considerably.     

In situ growth of NiCoFe-layered double hydroxide through etching Ni foam matrix for highly enhanced oxygen evolution reaction

It is of great significance to develop the nonprecious metal oxide electrocatalysts toward oxygen evolution reaction (OER) for water splitting. Herein we report an in-situ growth of the ternary NiCoFe-layered double hydroxide nanosheets on surface etching nickel foam (NiCoFe LDHs/NF) without adding any nickel precursor. In this method, etching Ni matrix by Fe³⁺ not only provides the slowly released nickel ions, but also intensifies the Fe–Ni interaction between the directly grown active species and Ni foam. Therefore the composition, electronic structure, and morphology of the electrocatalysts can be easily regulated only by adjusting Co²⁺:Fe³⁺ ratio in the precursor solution. The obtained NiCo₁Fe₁ LDH/NF, which is formed in 1:1 Co²⁺:Fe³⁺ solution, has highest content of Ni³⁺ and Co³⁺ active sites and the largest electrochemical active area. It exhibits an outstanding OER performance with a small overpotential of 231 mV at 10 mA cm^?2 and excellent durability at 50 mA cm^?2 in 1.0 M KOH solution.     

NiFe2O4–Ni3S2 nanorod array/Ni foam composite catalyst indirectly controlled by Fe3+ immersion for an efficient oxygen evolution reaction

A NiFe alloy was designed on nickel foam (NF) as a precursor using cathodic electrodeposition. NiFe₂O₄–Ni₃S₂ nanorods (NRs) composite catalysts were prepared by Fe³⁺ impregnation and further hydrothermal sulfuration methods. NiFe₂O₄–Ni₃S₂ nanosheets (NSs) were also prepared by direct hydrothermal sulfuration of the NiFe alloy for comparison. Compared to the dense NS structure of the NiFe₂O₄–Ni₃S₂ NSs/NF, the NiFe₂O₄–Ni₃S₂ NRs/NF showed better oxygen evolution performance due to its unique weed-like NR array structure composed of additional oxygen evolution reaction (OER) active sites, with a strong electron interaction for Ni and Fe and the active sulfide synergistic effect with oxides. Therefore, Driving a current density of 10 mA cm^?2 only requires an overpotential of 189 mV and the catalyst could provide 100 mA cm^?2 continuously and be constant for more than 80 h in 1.0 M KOH. This experiment indicated that Fe³⁺ immersion had an indirect regulating effect on the morphological growth of the catalyst, which provided a novel concept for designing better OER catalysts.     

Porous flower-like nickel nitride as highly efficient bifunctional electrocatalysts for less energy-intensive hydrogen evolution and urea oxidation

Finding a suitable replacement for the high potential of anodic water electrolysis (oxygen evolution reaction (OER)) is significant for hydrogen energy storage and conversion. In this work, a simple and scalable method synthesizes a structurally unique Ni₃N nanoarray on Ni foam, Ni₃N-350/NF, that provides efficient electrocatalysis for the urea oxidation reaction (UOR) that transports 10 mA cm⁻² at a low potential of 1.34 V. In addition, Ni₃N-350/NF exhibits electro-defense electrocatalytic performance for hydrogen evolution reaction, which provides a low overpotential of 128 mV at 10 mA cm⁻². As proof of concept, all-water-urea electrolysis measurement is carried out in 1 M KOH with 0.5 M Urea with Ni₃N-350/NF as cathode and anode respectively. Ni₃N-350/NF||Ni₃N-350/NF electrode can provide 100 mA cm⁻² at a voltage of only 1.51 V, 160 mV less than that of water electrolysis, which proves its commercial viability in energy-saving hydrogen production.     

Fabrication of robust CoP/Ni2P/CC composite for efficient hydrogen evolution reaction and the reduction of graphene oxide

Developing the novel catalysts with an excellent performance of hydrogen generation is essential to facilitate the application of hydrogen evolution reaction (HER). Herein, a heterostructured cobalt phosphide/nickel phosphide/carbon cloth (CoP/Ni₂P/CC) composite was fabricated via an interfacial engineering strategy to achieve the modification of CoP nanoleaf on Ni₂P nanosheet skeleton supported by carbon cloth. By virtue of the unique heterostructure, abundant exposing active sites and the synergistic coupling effect of CoP and Ni₂P nanoparticles, the elaborated CoP/Ni₂P/CC composite exhibits a robust catalytic property. Among fabricated composites, the optimal CoP/Ni₂P/CC-4 catalyst behaves an excellent HER performance at a wide pH range (overpotentials of 67, 71 and 95 mV to afford 10 mA cm^?2 in 0.5 M H₂SO₄, 1 M KOH and 1 M PBS, respectively). The HER current density of this composite shows a negligible degradation after continuous test for 24 h. Charmingly, the HER process of this catalyst was innovatively applied to reduce graphene oxide, and thus exploiting the fabrication route of reduced graphene oxide (rGO). We are sure that this work will provide a firm guideline for the exploitation of pH-universal HER catalysts and the exploration of HER application.     

Defects-rich nickel nanoparticles grown on nickel foam as integrated electrodes for electrocatalytic oxidation of urea

Designing highly efficient, low cost and long-term stable electro-catalysts is the key step for the commercial applications of fuel cells. Electro-oxidation of urea, a hydrogen-rich fuel, is the anodic reaction of direct urea fuel cells. Herein, defects-rich nickel nanoparticles grown on nickel foam as integrated electrodes have been designed and easily fabricated by incomplete reduction of Ni(OH)₂. The Ni²⁺ defects coupled with oxygen vacancies are proposed to be mainly present in the form of amorphous NiO_x, which is the island phase in the metallic nickel nanoparticles and confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy. The synergistic effect between metallic metal with high conductivity and numerous defects with good affinity to O contributes to the high catalytic activity towards oxidation of urea with an onset potential of 0.35 V vs Hg/HgO in 2 M KOH +0.33 M urea. Additionally, the defects-rich nickel nanoparticles present good long-term stability.     

Porous NiFe alloys synthesized via freeze casting as bifunctional electrocatalysts for oxygen and hydrogen evolution reaction

Binder-free NiFe-based electrocatalyst with aligned pore channels has been prepared by freeze casting and served as a bifunctional catalytic electrode for oxygen and hydrogen evolution reaction (OER and HER). The synergistic effects between Ni and Fe result in the high electrocatalytic performance of porous NiFe electrodes. In 1.0 M KOH, porous Ni₇Fe₃ attains 100 mA cm⁻² at an overpotential of 388 mV with a Tafel slope of 35.8 mV dec⁻¹ for OER, and porous Ni₉Fe₁ exhibits a low overpotential of 347 mV at 100 mA cm⁻² with a Tafel slope of 121.0 mV dec⁻¹ for HER. The Ni₉Fe₁//Ni₉Fe₁ requires a low cell voltage of 1.69 V to deliver 10 mA cm⁻² current density for overall water splitting. The excellent durability at a high current density of porous NiFe electrodes has been confirmed during OER, HER and overall water splitting. The fine electrocatalytic performances of the porous NiFe-based electrodes owing to the three-dimensionally well-connected scaffolds, aligned pore channels, and bimetallic synergy, offering excellent charge/ion transfer efficiency and sizeable active surface area. Freeze casting can be applied to design and synthesize various three-dimensionally porous non-precious metal-based electrocatalysts with controllable multiphase for energy conversion and storage.     

Efficient electrocatalytic oxygen evolution by Fe3C nanosheets perpendicularly grown on 3D Ni foams

The development of efficient and earth-abundant catalyst for the oxygen evolution reaction (OER) is an important challenge for the renewable energy research community. Here, we report a facile method to design a nanosheet-like structure of Fe₃C, perpendicularly grown on Ni foam (NF) as a catalyst for OER by hydrothermal reaction and annealing treatment at a low temperature. The synthesized Fe₃C has good conductivity, small charge transfer resistance (R_ct), high active site density, and excellent stability, which make it highly efficient OER catalyst. Fe₃C/NF has a low overpotential of 262 mV at a current density of 10 mA cm⁻² and a small Tafel slope of 49 mV dec⁻¹. Remarkably, Fe₃C/NF also has good electrochemical stability, which helps maintain its activity in 1.0 M KOH solution for at least 100 h. Therefore, the simple method to prepare perpendicularly grown Fe₃C on a NF substrate can enhance the OER properties, which make Fe₃C/NF a promising material for replacing noble metal-based catalysts for OER applications.     

In-situ construction of Mn–Fe mixed oxides nanoparticles on reduced graphene oxide with superior lithium storage property

In this paper, porous Mn₃O₄–Fe₃O₄ nanoparticles with highly uniform composition are in-situ anchored on reduced graphene oxide (rGO) nanosheets by a simple cyanometallic framework template method. Thanks to the synergistic effects between the porous Mn₃O₄–Fe₃O₄ nanoparticles and the well-conductive rGO nanosheets, the Mn₃O₄–Fe₃O₄/rGO composites present superior electrochemical lithium storage performances with a great reversible capacity of 1013 mAh g^?1 after 100 cycles at 0.1 A g^?1, satisfactory rate capability of 510 mAh g^?1 at 3.0 A g^?1, and eminent long-term cycle stability of 804 mAh g^?1 after 500 cycles at 0.5 A g^?1. It is demonstrated that the rGO can not only act as a conducting matrix, but also buffer the volume expansion and avoid the aggregation of the Mn₃O₄–Fe₃O₄ nanoparticles during charging-discharging. The work provides a simple strategy for designing and fabricating advanced multi-component metal oxide-based anodes for high-performance lithium-ion battery.     

Autogenous growth of highly active bifunctional Ni–Fe2B nanosheet arrays toward efficient overall water splitting

Developing an effective and low-cost bifunctional electrocatalyst for both OER and HER to achieve overall water splitting is remaining a challenge to meet the needs of sustainable development. Herein, an electroless plating method was employed to autogenous growth of ultrathin Ni–Fe₂B nanosheet arrays on nickel foam (NF), in which the whole liquid phase reduction reaction took no more than 20 min and did not require any other treatments such as calcination. In 1.0 M KOH electrolyte, the resulted Ni–Fe₂B ultrathin nanosheet displayed a low overpotential of 250 mV for OER and 115 mV for HER to deliver a current density of 10 mA cm^?2, and both OER and HER activities remained stable after 26 h stability testing. Further, the couple electrodes composed of Ni–Fe₂B could afford a current density of 10 mA cm^?2 towards overall water splitting at a cell voltage of 1.64 V in 1.0 M KOH and along with excellent stability for 26 h. The outstanding electrocatalytic activities can be attributed to the synergistic effect of electron-coupling across Ni and Fe atoms and active sites exposed by large surface area. The effective combination of low cost and high electrocatalytic activity brings about a promising prospect for Ni–Fe₂B nanosheet arrays in the field of overall water splitting.