NF Electrode Research Articles

Hierarchical Metal Sulfides Heterostructure as Superior Bifunctional Electrode for Overall Water Splitting.

The development of highly active bifunctional electrocatalysts for overall water splitting is of significant importance, but huge challenges remain. The key element depends on engineering the electronic structure and surface properties of material to achieve improved catalytic activity. Herein, a hierarchical nanowire array of metal sulfides heterostructure on nickel foam (FeCoNiSx /NF) was designed as a novel type of hybrid electrocatalyst for overall water splitting. The hybrid structure endowed plenty of catalytic active sites, strong electronic interactions, and high interfacial charge transferability, leading to superior bifunctional performance. As a result, the FeCoNiSx /NF catalyst delivered low overpotentials of 97 and 260 mV at the current density of 50 mA cm-2 for hydrogen and oxygen evolution reactions, respectively. Moreover, the FeCoNiSx /NF-based water electrolyzer exhibited a small potential of 1.57 V for a high current density of 50 mA cm-2 . These results indicate the promising application potential of FeCoNiSx /NF electrode for hydrogen generation. This work provides a new approach to develop robust hybrid materials as the highly active electrode for electrocatalytic water splitting.

In situ growth Fe and V co-doped Ni3S2 for efficient oxygen evolution reaction at large current densities

Industrial electrolysis of water is one of the effective strategies for green hydrogen production in the future. Nevertheless, the large-scale applications of water electrolysis are still intractable issues hindered by the high overpotentials and inferior reaction kinetics on the anode. Herein, a facile one-step hydrothermal method was applied to in situ growth the Fe and V co-doped Ni 3 S 2 electrocatalyst on nickel foam substrate (Fe, V–Ni 3 S 2 /NF). In 1 M KOH electrolyte, the as-prepared Fe, V–Ni 3 S 2 /NF electrode exhibited an improved water oxidation activity with ultralow overpotentials of 253 and 370 mV to realize large current densities of 100 and 1000 mA/cm 2 , respectively. More importantly, the Fe, V–Ni 3 S 2 /NF electrode existed an activation process during 100 h chronopotentiometry testing period. Detailed characterizations revealed that elements of V and S in the electrocatalyst were oxidized and dissolved into the electrolyte, making the electrocatalyst undergo surface reconstruction and resulting in a faster kinetic reaction rate, thus leading to enhanced oxygen evolution reaction activities. Collectively, the resultant Fe, V–Ni 3 S 2 /NF in this work provides new cogitation towards design and synthesis of low-cost electrocatalyst with large current densities for water oxidation. • Fe,V–Ni 3 S 2 /NF electrode was hydrothermal prepared and used as OER electrocatalyst. • Ni 3 S 2 is converted to NiOOH during the electrochemical oxidation process. • The electrode can attain 100 and 1000 mA/cm 2 with overpotentials of 253 and 370 mV. • The enhanced OER activity owned to the surface reconstruction by V, S etching.

Formation of carnation-like ZIF-9 nanostructure to achieve superior electrocatalytic oxygen evolution

Rational design and controllable synthesis of metal-organic frameworks nanosheets is critical for electrochemical catalysis. Herein, a carnation-like ZIF-9 nanostructure made of nanosheets is grown on nickel foam (ZIF-9/NF) by a simple one-step solvothermal method, the morphology evolution and the electrocatalytic oxygen evolution properties have been investigated by controlling the solvothermal time. The binder-free ZIF-9-d/NF (60 h, solvothermal time is 60 h) electrode delivers efficient electrocatalytic oxygen evolution reaction activity with low overpotentials of 312 and 337 mV at 50 and 100 mA cm−2, respectively. Furthermore, ZIF-9-d/NF (60 h) exhibits excellent stability without obvious attenuation for at least 30 h at 200 mA cm−2. The excellent performances can be attributed to the combination of the highly exposed active sites in the ZIF-9-d nanosheets, as well as the effective electron conduction and mass transfer. This work provides much possibilities for ZIF-9 nanosheets as binder-free electrode for electrocatalyst.

Mo,Fe-codoped metal phosphide nanosheets derived from Prussian blue analogues for efficient overall water splitting

Designing non-precious electrocatalysts with multiple active centers and durability toward overall water splitting is of great significance for storing renewable energy. This study reports a low-cost Mo, Fe codoped NiCoPx electrocatalysts derived from Co-Fe Prussian blue analogue and following phosphorization process. Benefitted from the optimized electronic configuration, hierarchical structure and abundant active sites, the Mo,Fe-NiCoPx/NF electrode has shown competitive oxygen evolution reaction (ƞ10 = 197 mV) and hydrogen evolution reaction performance (ƞ10 = 99 mV) when the current density is 10 mA cm−2 in 1 M KOH solution. Moreover, the integrated water splitting device assembled by Mo,Fe-NiCoPx/NF as both anode and cathode only needs a voltage of 1.545 V to reach 10 mA cm−2. Density functional theory results further confirm that the Mo, Fe codoped heterostructure can synergistically optimize the d-band center and Gibbs free energy during electrocatalytic processes, thus accelerating the kinetics of electrochemical water splitting. This work demonstrates the importance of rational combination of metal doping and interface engineering for advanced catalytic materials.

Nitrogen doped carbon encapsulated hierarchical NiMoN as highly active and durable HER electrode for repeated ON/OFF water electrolysis

Water electrolysis powered by tidal, wind and solar energies is an ideal green hydrogen production path. However, intermittent power supply and unpredictable power cut by renewable energy resources inevitably compel the electrode materials to suffer from the fluctuant working conditions or repeated start/stop operation, which always leads the deterioration of electrocatalyst. Herein, a novel hydrogen evolution reaction (HER) electrode with hierarchical NiMoN microrod arrays encapsulated by nitrogen doped ultra-thin carbon layer and in-situ grown on nickel foam (labelled NF) was reported. The prepared NiMoN@NC/NF electrode exhibits extremely low overpotentials less than 10 mV at 10 mA cm−2 for HER in both KOH and H2SO4 electrolytes. Importantly, it exhibits not only high stability during the 100 h repeated ON/OFF test, but also high oxidation resistance and corrosion resistance in acid electrolyte. The water electrolysis cell, using 100 cm2 NiMoN@NC/NF cathode and NiFe based anode, supplies a high current density of 100 mA cm−2 with a low cell voltage of 1.53 V at 88 °C. The appropriate nitrogen doping, carbon encapsulation, and the well-designed hierarchical structure of the NiMoN@NC/NF endow its optimized Gibbs free energy of H*, excellent activity and outstanding adaptability to harsh conditions, demonstrating its great prospect in the repeated ON/OFF electrolysis associated with changeful renewable electricity.

Facile synthesis of self support Fe doped Ni3S2 nanosheet arrays for high performance alkaline oxygen evolution

• Fe doped Ni 3 S 2 /NF were prepared via a facile hydrothermal method. • The OER performance of Ni 3 S 2 /NF was significantly enhanced after Fe doping. • A small PDS for doped Ni 3 S 2 /NF of 0.31 eV can be obtained at the Fe site. Transition metal sulfides are one of the most efficient earth-abundant oxygen evolution reaction (OER) electrocatalysts. In the present study, Fe doped Ni 3 S 2 nanosheets have been directly grown on nickel foam via a facile hydrothermal process. The OER electrocatalytic activity of Fe-Ni 3 S 2 /NF can be enhanced by adjusting the addition amount of Fe. It requires an overpotential of 246 mV to afford a current density of 20 mA cm −2 and a Tafel slope of 66 mV dec −1 , significantly lower than that of Ni 3 S 2 /NF electrode. This catalyst is highly stable, showing a slight overpotential rise of 15.1 mV over continuous testing for 20 h. In addition, combine EIS measurement and density functional theory calculations, revealing that Fe doped Ni 3 S 2 /Ni electrodes have both high conductivity and excellent intrinsic activity, leading to a promising OER electrocatalytic activity.

Fe-doped (Ni,Mn)Co2O4 nanorod arrays on Ni foam as highly efficient electrocatalyst for oxygen evolution reaction in alkaline and neutral conditions with superb long-term stability

It is drawing increased interest to exploit highly active and durable electrocatalysts based on earth-abundant elements for oxygen evolution reaction (OER). In this work, we successfully synthesized Fe-doped (Ni,Mn)Co2O4 nanorod arrays on nickel foam (labeled as FNMCO/NF) via a anion-exchange route with subsequent annealing process. Experiments showed that the initial concentration of [Fe(CN)6]3- anions could affect the electrocatalytic activity of the as-synthesized FNMCO/NF integral electrode. The FNMCO-6/NF prepared from 6 mM of K3[Fe(CN)6] solution presented the strongest OER electrocatalytic activity. Only overpotential of 242 mV or 449 mV was required to reach the current density of 10 mA cm−2 in 1 M KOH solution or 0.1 M phosphate buffer solution (PBS). Also, after continuously catalyzing for 155 h at 100 mA cm−2 in 1 M KOH solution or 150 h at 20 mA cm−2 in 0.1 M PBS, the overpotential of the as-obtained FNMCO-6/NF electrode rarely varied, implying its superb durability.

Electrochemical grown Ni,Zn-MOF and its derived hydroxide as battery-type electrodes for supercapacitors

Todays, metal-organic frameworks (MOFs) and their derived structures are extensively investigated as the novel electrode materials for supercapacitors applications due to their stable porous architectures and exceptionally large specific surface areas. In this study, bimetallic Ni,Zn-MOF is first synthesized onto Ni foam via a novel indirect cathodic electrodeposition method for the first time. The fabricated Ni,Zn-MOFs onto Ni foam was converted to corresponding bi-metal hydroxide@C/Ni foam through direct chemical treating with 6 M KOH solution. The obtained Ni,Zn-MOFs/NF and Ni2-xZnx (OH)2 @C/NF electrodes were characterized through XRD, FT-IR, FE-SEM, AFM and EDS analyses. The results confirmed deposition of well-defined crystalline porous sheet-like structures of Ni3-xZnx(BTC)2 onto Ni foam, where its derived hydroxide@C electrode also exhibited similar morphology. In three-electrode system, the prepared Ni,Zn-MOF/Ni foam exhibited the superior storage capacities of 356.1 mAh g–1 and 255.5 mAh g–1 and capacity retentions of 94.2% and 84.5% after 6000 cycles at 5 and 15 A g–1, respectively. On the other hand, Ni,Zn-MOF derived hydroxide-C/Ni foam presented the superior capacities of 545 mAh g–1 and 406 mAh g–1 as well as proper cycling stabilities of 91.8% and 78.3% after 6000 cycling at the applied loads of 5 and 15 A g–1, respectively. The fabricated Ni,Zn-hydroxide-C/NF//N-PG/NF ASC device can deliver an of 34.5 W h kg−1 at a power density of 624 W kg−1. Based on these findings, both of these fabricated battery-type electrodes are introduced as the promising candidates for use in energy storage devices.

Three-dimensional crystalline-Ni5P4@amorphous-NiOx core–shell nanosheets as bifunctional electrode for urea electro-oxidation and hydrogen evolution

The electrochemical urea oxidation (UOR) involves the generation of gases bubbles, which often cause the blockage of the electrode surface leading to decline activity. Herein, we report the growth of Ni5P4 nanosheets on nickel foam as bifunctional electrode (CA-Ni5P4@NiOx/NF) for urea electrolysis. The results indicated that a thin layer of amorphous NiOx formed on the surface of Ni5P4 nanosheets to yield a unique crystalline@amorphous core–shell structure, which can be maintained during long time urea electrolysis. The outstanding UOR performance of CA-Ni5P4@NiOx/NF was attributed to the unique structure, which not only combine the good conductivity and abundant active sites, but also rendered the CA-Ni5P4@NiOx/NF superhydrophilic and aerophobic that significantly facilities the release of gases bubbles formed during UOR to avoid the blockage of the active sites. As a result, the CA-Ni5P4@NiOx/NF electrode exhibited excellent performance for UOR, which only needs 1.45 V (vs. RHE) to deliver a current of 100 mA/cm2. When used as anode for direct urea fuel cell (DUFC), it could reach a maximal power density as high as 3.4 mW/cm2with an OCV of 0.76 V. The CA-Ni5P4@NiOx/NF also exhibited excellent activity for hydrogen evolution reaction (HER), with -0.089 V (vs. RHE) to deliver a current of 10 mA/cm2. The electrolyzer constructed with CA-Ni5P4@NiOx as both anode and cathode could run for more than 10 h at a high current load about 100 mA/cm2 without appreciable potential change, indicating the superb stability of the CA-Ni5P4@NiOx electrode. Our work provides new insights for understanding as well as the development of advanced electrode for DUFC and urea electrolysis.

Fabrication of a composite material of Gd2O3, Co3O4 and graphene on nickel foam for high-stability supercapacitors

The Gd2O3/Co3O4/rGO/NF electrode was prepared using a one-step hydrothermal method and annealing process, with high specific capacitance and excellent cycle stability.

Oxygen vacancy-engineered ultrathin NiCo2O4 nanosheet arrays derived from MOFs as an advanced electrode for supercapacitors.

To overcome the poor electronic conductivity and slow ion transport of NiCo2O4, ultrathin nanosheet arrays with oxygen vacancies are constructed by a facile NaBH4 reduction method using a bimetallic MOF as the precursor. Benefiting from the advantages of highly exposed surface area and short paths for charge transport of ultrathin 2D nanosheets, as well as the improved electronic conductivity arising from oxygen vacancies, the optimal 0.1-Ov-NiCo2O4/NF electrode shows excellent electrochemical performance, largely outperforming pristine NiCo2O4/NF.

Ir-Doped Co(OH)2 nanosheets as an efficient electrocatalyst for the oxygen evolution reaction.

In recent years, Co-based metal-organic frameworks (Co-MOFs) have received significant research interest because of their large specific surface area, high porosity, tunable structure and topological flexibility. However, their comparatively weak electrical conductivity and inferior stability drastically restrict the application of Co-MOFs in the synthesis of electrocatalysts. In this study, ZIF-67 was grown on nickel foam by a room temperature soaking method, and then Ir-Co(OH)2@ZIF-67/NF was assembled by a hydrothermal method. The prepared Ir-Co(OH)2@ZIF-67/NF nanosheets exhibit remarkable conductivity, larger electrochemical active surface area and wider electron transport channels. Only ultralow overpotentials of 198 mV, 263 mV, and 300 mV were needed for Ir-Co(OH)2@ZIF-67/NF to reach the current densities of 10 mA cm-2, 50 mA cm-2, 100 mA cm-2, meanwhile, no obvious degradation of the current density at 10 mA cm-2 was observed for about 16 h. This work may provide a promising strategy for developing high-performance MOF-derived materials as electrocatalysts for the OER under alkaline conditions.

The controlled synthesis of nitrogen and iron co-doped Ni3S2@NiP2 heterostructures for the oxygen evolution reaction and urea oxidation reaction.

At present, global resources are nearly exhausted and environmental pollution is becoming more and more serious, so it is urgent to develop efficient catalysts for hydrogen production. Herein, nitrogen and iron co-doped Ni3S2 and NiP2 heterostructures with high efficiency oxygen evolution reaction (OER) and urea oxidation reaction (UOR) performances were firstly successfully prepared on nickel foam by hydrothermal and high-temperature calcination methods. Benefiting from the hierarchical structure, the exposure of more active sites and the doping effect of N and Fe, the N-Fe-Ni3S2@NiP2/NF material showed excellent electrocatalytic activity for the OER and UOR. The N-Fe-Ni3S2@NiP2/NF material displays excellent catalytic OER performance; the overpotential is only 251 mV to drive 100 mA cm-2 current density, while for the UOR, the potential is only 1.353 V to drive 100 mA cm-2 current density, which is one of the best catalytic activities reported so far. It is worth noting that scanning electron microscopy showed that the surface of N-Fe-Ni3S2@NiP2/NF is rough and has some mesopores, which may have resulted in an increase of active sites during the electrocatalytic process. The N-Fe-Ni3S2@NiP2/NF electrode couple also has relatively long-term durability in alkaline solutions, maintaining a stable current density for 15 h at 1.35 V. The density functional theory (DFT) calculation shows that the in situ generated Fe doped nanooxides exhibit strong water adsorption energy, which may be one of the reasons for the good catalytic activity. Our work is conducive to the rational design of electrocatalysts for efficient hydrogen production from water splitting and wastewater treatment.

A porous MOF-derived NiMn2O4 material and its superior energy storage performance for high-performance supercapacitors

A binder-free C@NiMn2O4 electroactive material was prepared through the calcination of a pristine Ni,Mn-MOF at 600 °C for 4 h. The fabricated C@NiMn2O4/NF electrode exhibits an area specific capacitance of 5.39 F cm−2 at 2 mA cm−2.

Construction of Fe-Co-Ni-Sx/NF nanomaterial as bifunctional electrocatalysts for water splitting

Development of efficient and earth-abundant electrocatalyst for water splitting is necessary and significance. Herein, a Fe-Co-Ni-Sx/NF electrode was synthesized through hydrothermal reaction and calcination method. The Fe-Co-Ni-Sx/NF evenly distribute on the NF substrate under the action of ethylenediamine tetraacetic acid (EDTA). Fe-Co-Ni-Sx/NF electrode has excellent catalytic activity. The overpotential is 209 mV for HER, and 280 mV for OER at current density of 10 mA cm−2. The test result of two-electrode system shows that the cell potential of 1.70 V is required to reach the current density of 10 mA cm−2. The preparation strategy of Fe-Co-Ni-Sx/NF can improve the catalytic activity of transition metal sulfides, which has profound significance to further improve the catalytic activity of the catalyst.

Mesoporous FeMoV Oxide Nanosheets Supported on Nickel Foam as Highly Efficient Electrocatalysts for the Oxygen Evolution Reaction

The development of non-noble metal-based electrocatalysts with high efficiency for the oxygen evolution reaction (OER) is of great importance for the practical application of electrocatalytic water splitting. Herein, we have synthesized tri-metal-based FeMoV oxide nanosheets on three-dimensional nickel foam (FeMoV/NF) for the OER by a simple hydrothermal method. Thanks to the decreased charge-transfer resistance and modified electronic structure, the optimized Fe0.5Mo0.1V0.4/NF electrode exhibits excellent OER performance with a low overpotential of 296 mV to deliver a current density of 100 mA cm–2 and a small Tafel slope of 48.9 mV dec–1 in a 1 M KOH solution; both values are much lower than those of commercial RuO2 supported on nickel foam (392 mV and 129 mV dec–1, respectively). This work may provide a promising strategy for the design of highly efficient and low-cost electrocatalysts for the OER.

Ru-Incorporated Nickel Diselenide Nanosheet Arrays with Accelerated Adsorption Kinetics toward Overall Water Splitting.

Developing high-efficiency electrocatalysts toward overall water splitting is an increasingly important area for sustainable energy evolution. Theoretical calculation results demonstrate that the incorporation of Ru optimizes the Gibbs free energy of adsorption of H2 O molecules and intermediates for the hydrogen/oxygen evolution reactions (HER/OER) on metal selenide sites, thus boosting electrocatalytic overall water splitting. Accordingly, ruthenium modified nickel diselenide nanosheet arrays are designed and construct on nickel foam (Ru-NiSe2 /NF). The obtained Ru-NiSe2 /NF electrode with a stable 3D structure shows greatly improved OER and HER activity in alkaline solution. Particularly, toward OER, it only requires 210mV to obtain a current density of 10 mA cm-2 , and the formation of the intermediate nickel oxyhydroxide as active center during the OER process is captured by in situ Raman. Moreover, the overall water splitting can be driven by a voltage of merely 1.537V to obtain 10mA cm-2 . This work provides an available strategy for selenides to enhance electrochemical properties and inspires more studies to explore highly efficient electrocatalysts toward full water splitting.

Reduced graphene oxide/Ni foam supported ZIF-67 derived CuCo2S4@CoS2 core-shell heterostructure for boosted electrochemical energy storage

Designing novel multiple composite material with core-shell structure has been demonstrated as an effective method to improve the electrochemical properties of energy storage due to the synergistic effects and structural advantages between the ingredients. Herein, a novel rGO@CuCo2S4@CoS2/NF composite material with core-shell structure was synthesized by ZIF-67 derivatives and the solvothermal method. The composite material overcomes the shortcomings of MOF as an electrode material and provides a large contact area for the active materials and the electrolyte solution. The rGO@CuCo2S4@CoS2/NF electrode exhibits an excellent specific capacity is 1101.2 C g − 1 (2447.1 F g − 1) at a current density of 1 A g − 1 and outstanding cycling performance after 10,000 cycles (79.2% of the initial value). Meanwhile, a typical asymmetric supercapacitor (ASC) device based on rGO@CuCo2S4@CoS2/NF as the cathode and AC as the anode (rGO@CuCo2S4@CoS2/NF//AC) achieves a maximum energy density of 52.46 Wh kg−1 with the power density of 750.02 W kg−1. Moreover, the device maintains the cycle stability of 88.2% after 10,000 cycles, demonstrating that rGO@CuCo2S4@CoS2/NF could be a potential electroactive material in advanced energy storage systems.

Self-assembled MoS2/C nanoflowers with expanded interlayer spacing as a high-performance anode for sodium ion batteries

Two-dimensional (2D) MoS2 nanomaterials have been extensively studied due to their special structure and high theoretical capacity, but it is still a huge challenge to improve its cycle stability and achieve superior fast charge and discharge performance. Herein, a facile one-step hydrothermal method is proposed to synthetize an ordered and self-assembled MoS2 nanoflower (MoS2/C NF) with expanded interlayer spacing via embedding a carbon layer into the interlayer. The carbon layer in the MoS2 interlayer can speed the transfer of electrons, while the nanoflower structure promotes the ions transport and improves the structural stability during the charging/discharging process. Therefore, MoS2/C NF electrode exhibits exceptional rate performance (318.2 and 302.3 mA·h·g−1 at 5.0 and 10.0 A·g−1, respectively) and extraordinary cycle durability (98.8% retention after 300 cycles at a current density of 1.0 A·g−1). This work provides a simple and feasible method for constructing high-performance anode composites for sodium ion batteries with excellent cycle durability and fast charge/discharge ability.

3D V–Ni3S2@CoFe-LDH core-shell electrocatalysts for efficient water oxidation

Studying cheap and efficient electrocatalysts is of great significance to promote the sluggish kinetics of oxygen evolution reaction (OER). Here, we adopted a simple two-step method to successfully prepare the 3D V–Ni3S2@CoFe-LDH core-shell electrocatalyst. The V–Ni3S2@CoFe-LDH/NF shows excellent OER performance with low overpotential (190 mV at 10 mA/cm2 and 240 mV at 50 mA/cm2), small Tafel slope (26.8 mV/dec) and good long-term durability. Excitingly, to reach the same current density, V–Ni3S2@CoFe-LDH/NF electrode even needs much smaller overpotential than RuO2. Furthermore, the outstanding OER activity of V–Ni3S2@CoFe-LDH/NF is ascribed to the following reasons: (1) V–Ni3S2 nanorod cores improve the conductivity and ensure the fast charge transfer; (2) CoFe-LDH nanosheets interconnected with each other provide more exposed active sites; (3) the unique 3D core-shell structures are favorable for electrolyte diffusion and gas releasing. Our work indicates that building 3D core-shell heterostructure will be a useful way to design good electrocatalysts.