Nickel Selenide Research Articles

Morphological modulation of cobalt selenide on carbon cloth by Ni doping for high-performance electrodes in supercapacitors

Transition metal selenides are desirable electrode materials in supercapacitors due to the good electron conductivity and high theoretical specific capacity. In this work, the relationship between the elemental composition and electrochemical performance of cobalt nickel selenide is studied. Cobalt nickel selenide samples with different morphologies are prepared on the carbon cloth by a solvothermal technique and selenation process using different Ni amounts. Ni doping is observed to modulate the morphology of CoSe 2 and enhance the electrochemical properties. The Co 0.8 Ni 0.2 Se 2 electrode shows a high specific capacitance of 1472 mF cm −2 at a current density of 1 mA cm −2 as well as good cycling stability. As a verification of the practicality, the asymmetrical supercapacitor assembled shows a capacity of 120 mF cm −2 after 8000 cycles at 1 mA cm −2 while delivering a superior power density 3.75 mW cm −2 with an energy density of 0.052 mWh cm −2 . These results demonstrate the high potential of Co 0.8 Ni 0.2 Se 2 as electrode materials in supercapacitors.

Optimization of nickel selenide for hydrogen and oxygen evolution reactions by response surface methodology

In this study, the electrocatalytic activity of Ni-Se electrode synthesized on nickel foam by pulse electrodeposition was optimized through the design of experiments (DOE) approach using the response surface methodology (RSM) for both hydrogen and oxygen evolution reactions. The frequency (f), duty cycle (dc), current density (i), and electrodeposition time (sum of tons) were chosen as the parameters of the pulse electrodeposition method. The analyses of variance (ANOVA) were performed on the responses of the designed experiments that included the required overpotential at the current density of 10 mA/cm2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) (η10,HER and η10,OER), active surface area (Rf) and intrinsic electrocatalytic activity (i/Rf). The results indicated that η10,HER, η10,OER, and Rf are mainly influenced by duty cycle and electrodeposition time, while i/Rf is affected by frequency and time. The optimized NiSe2 electrode synthesized under optimal conditions of pulse electrodeposition (low duty cycle and prolonged electrodeposition time) showed the most desirable values for η10,HER, η10,OER, and Rf, equal to 44 mV (vs. RHE), 235 mV (vs. RHE) and 14700, respectively. The nanostructured NiSe2 demonstrated the highest potential in the bifunctional application of OER and HER.

Copper-Incorporated heterostructures of amorphous NiSex/Crystalline NiSe2 as an efficient electrocatalyst for overall water splitting

• Novel Cu-implanted heterostructure of amorphous NiSe x /crystalline NiSe 2 is prepared. • Catalyst needs overpotential of 156.9 mV for HER and 339 mV for OER at 10 mA cm −2. • The catalyst-based electrolyzer requires a low cell voltage of 1.62 V at 10 mA cm −2. • The catalyst-based electrolyzer shows a long-term stability of 21.5 h in 1.0 M KOH. In this research, we designed a novel heterostructure of porous amorphous-crystalline nickel selenide incorporated with copper (Cu-(a-NiSe x /c-NiSe 2 )) and shelled over one-dimensional TiO 2 nanorods (NRs) to simultaneously accelerate both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) kinetics in alkaline environment. The Cu-(a-NiSe x /c-NiSe 2 )/TiO 2 NRs supported by carbon cloth displayed as an effective bifunctional catalyst, which required low overpotentials of 156.9 mV for HER and 339 mV for OER to achieve a current response of 10 mA cm −2 in 1.0 M KOH medium. An electrolyzer derived from the Cu-(a-NiSe x /c-NiSe 2 )/TiO 2 NRs material allowed an operation voltage of 1.62 V at 10 mA cm −2 along with good long-term stability after 21.5 h operation towards water splitting in alkaline medium. This achievement was resulted from the fine-tuned 3D porous architecture of the amorphous NiSe x -crystalline NiSe 2 heterostructures doped by copper, which led to significant modulation of electronic properties as well as large surface of exposed electroactive site/types, thereby effectively promoting the catalytic performance. This study suggested a rational approach of structure and shape engineering to design a potential catalyst for producing green hydrogen via water spitting.

Hexagonal nickel selenide nanoflakes decorated carbon fabric: An efficient binder-free water loving electrode for electrochemical water splitting

In recent times, production of hydrogen by water splitting has introduced a new era to sustainable energy storage and fuel cell technology. To simplify the design of the water splitting devices and enhance its activity, a new thrust to develop low cost, stable, earth abundant electrocatalysts which can participate in both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is the need of the hour. Here, we report the two-step hydrothermally synthesized nickel diselenide hexagonal flakes deposited on carbon cloth (NiSe2/CC) which has acted as efficient electrocatalyst for both HER and OER in alkaline medium. Necessary characterizations are performed. The NiSe2 sheet comprises small hexagonal flakes in nanoscale with numerous active sites having hydrophilic nature insist us to choose it as an electrocatalyst resulting in enhanced charge transfer mechanism. The binder free NiSe2/CC exhibits superior catalytic activity employing overpotential of −111 mV and 210 mV in HER and OER to draw 10 mA/cm2 current density, respectively in 1M KOH solution. Sustainability of electrocatalyst is also investigated in extreme pH. Thus, the water splitting device which consists of NiSe2/CC electrodes as cathode and anode in 1M KOH electrolyte, requires only 1.47 V to achieve 10 mA/cm2 current density.

Optimization and characterization of pulse electrodeposited nickel selenide nanostructure as a bifunctional electrocatalyst by response surface methodology

The electrocatalytic activity of the pulse electrodeposited Ni–Se coating on nickel foam (NF) for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) was optimized by design of experiments. In this study as the first step of optimization, the condition of electrodeposition bath containing the ratio of Se/Ni, pH, and temperature was optimized. The response surface methodology (RSM) in central composite design (CCD) was used for experiments based on the parameters of the ratio of Se/Ni and pH. The prediction model after carrying out the analyses of variance (ANOVA) on the responses showed the best desirable values for the ratio of Se/Ni and pH were 0.7 and 3.6. The nanostructure Ni–Se electrode electrodeposited in the optimal condition requires 103 and 249 mV (vs. RHE) for delivering 10 mA/cm2 in HER and OER, respectively. To temperature survey, the optimized Ni–Se electrode was synthesized at 25, 40, and 60 °C. Results showed that the electrode electrodeposited at the ambient temperature with large electrochemically active surface area of 8960 and low Tafel slopes of 86 and 35 mV/dec has the superior electrocatalytic performance for HER and OER, respectively.

Development and characterization of regenerable chitosan-coated nickel selenide nano-photocatalytic system for decontamination of toxic azo dyes

In this investigation, chitosan-coated nickel selenide nano-photocatalyst (CS-NiSe) was successfully prepared through the chemical reduction method. FTIR spectroscopy confirmed the synthesis of CS-NiSe nano-photocatalyst. Further, XRD analysis exhibited a monoclinic crystalline phase of photocatalyst with a crystallite size of 32 nm based on Scherer's equation. The SEM micrographs showed that the photocatalyst has an average particle size of 60 nm. The bandgap of CS-NiSe was (2.85 eV) in the visible region of the spectrum. Due to this reason, the CS-NiSe was applied under solar light illumination for the photocatalytic activity of Erythrosine and Allura red dyes. The CS-NiSe presented the highest degradation efficiency of 99.53% for Erythrosine dye in optimized experimental conditions of 100 min at 30 °C, 30 ppm concentration, pH 5.0, and 0.14 g catalyst dose. For Allura red dye, a high degradation of 96.12% was attained in 120 min at pH 4.0, 100 ppm initial dye concentration, 35 °C temperature, and 0.1 g catalyst dose. The CS-NiSe showed excellent degradation efficiency and reduced to (95% for Erythrosine and 91% for Allura red dye) after five consecutive batches. Moreover, the statistical and neural network modelling analysis showed the significant influence of all studied variables on dyes degradation performance. The results demonstrated that CS-NiSe exhibited excellent photocatalytic performances for Erythrosine and Allura red dyes and could be a better photocatalyst for removing these dyes from industrial effluents.

Sulfur-modified nickel selenide as an efficient electrocatalyst for the oxygen evolution reaction

The sluggish four-electron transfer of the oxygen evolution reaction (OER) limits the performance of water electrolyzers. Hence, OER electrocatalysts based on earth-abundant elements are urgently needed. Heteroatom doping has been an efficient approach to boost the intrinsic OER activity of the active sites by modifying the electronic structure. Here, a simple anion substitution strategy is reported that increases the OER activity of nickel selenides via a one-step hydrothermal treatment of a metal–organic framework precursor. The resulting S-substituted Ni3Se4 nanoparticles display distortion of their crystal lattice. As expected, the sulfur substitution modifies the electronic structure of Ni3Se4 and leads to outstanding electrocatalytic activity. All the S-substituted Ni3Se4 catalysts exhibit higher OER activities than the original Ni3Se4. The optimized catalyst achieves a current density of 10 mA cm−2 at an overpotential of 275 mV with a Tafel slope of 64 mV dec−1 in 1.0 M KOH. In addition to its electrochemical activity, the S-Ni3Se4-2 catalyst also exhibits good stability with only a 7.5% increase in overpotential at 50 mA cm−2 after 100 hours. This work demonstrates one strategy to modify the electronic structure of transition metal compounds by anion regulation.

Less is more: biological effects of NiSe2/rGO nanocomposites with low dose provide new insight for risk assessment

Nickel selenide nanomaterials (NiSe2 NMs) with different vacancies demonstrated high catalytic activity as electrocatalyst in oxygen evolution reaction. As the growing needs of the industrial applications in electrocatalyst, the increased occupational exposure and environmental releasing of NMs would be unavoidable. While, much efforts have been made to evaluate the ecological safety of such engineered NMs at unrealistically high concentrations, failed to provide the comprehensively guideline for exposure thresholds. To supplement the current knowledge gap, we testified the cytotoxicity of NiSe2/rGO nanocomposites with different surface defects under more realistic exposure mode. Compared with the short-term exposure and repetitive exposure, rat lung macrophages exhibited the augmented oxidative stress, dysfunction of mitochondria, damage of DNA and disorder of calcium homeostasis under the long-term NiSe2/rGO exposure. Noteworthily, no significant differences could be found between the NiSe2/rGO with different surface defects, indicated that the defect type of NMs were not the accurate predictor for real risk assessment. Collectively, the study provided the real potential toxic effects and exposure thresholds of NMs that might be highly possible industrial produced, and appealed the new insight for risk assessments of engineered NMs under the long-term exposure, which exhibited difference from the traditional evaluation of short-term and repetitive exposure.

Crystal structure refinements of stoichiometric Ni3Se2 and NiSe.

Single crystals of Ni3Se2 (trinickel diselenide) and NiSe (nickel selenide) with stoichiometric chemical compositions were grown in evacuated silica-glass tubes. The chemical compositions of the single crystals of Ni3Se2 and NiSe were determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS). The crystal structures of Ni3Se2 [rhombohedral, space group R32, a= 6.02813 (13), c= 7.24883 (16) Å, Z= 3] and NiSe [hexagonal, space group P63/mmc, a= 3.66147 (10), c= 5.35766 (16) Å, Z= 2] were analyzed by single-crystal X-ray diffraction and refined to yield R values of 0.020 and 0.018 for 117 and 85 unique reflections, respectively, with Fo > 4σ(Fo). R32 is a Sohncke type of space group where enantiomeric structures can exist; the single-domain structure obtained by the refinement was confirmed to be correct by a Flack parameter of -0.05 (2). The existence of Ni-Ni bonds was confirmed in both compounds, in addition to the Ni-Se bonds. The value of the atomic displacement parameter (mean-square displacement) of each atom in NiSe was larger than that in Ni3Se2. The larger amplitude of the atoms in NiSe corresponds to longer Ni-Se and Ni-Ni bond lengths in NiSe than in Ni3Se2. The Debye temperatures, θD, estimated from observed mean-square displacements for Ni and Se in Ni3Se2, were 322 and 298 K, respectively, while those for Ni and Se in NiSe were 246 and 241 K, respectively. The existence of large cavities in the structure and the weak bonding force are likely responsible for the brittle and soft nature of the NiSe crystal.

Potentiostatically deposited bimetallic cobalt–nickel selenide nanostructures on nickel foam for highly efficient overall water splitting

The fabrication of efficient electrocatalysts for water splitting is vital for production of clean fuels. Herein, cobalt–nickel selenide (CoNi2Se4) nanostructures were fabricated on a Ni foam substrate using a facile potentiostatic method at different deposition solution pH levels. Nanoparticle-, fluffy-, and flake-like CoNi2Se4 nanostructures were deposited by changing the aqueous solution pH to 2.0, 2.5, and 3.0, respectively. The desired flake-like CoNi2Se4 electrode fabricated at pH 3.0 presented the best electrocatalytic performance of all CoNi2Se4 nanostructures in this study and required overpotentials as low as 244 and 184 mV to deliver a current density of 10 mA cm−2 for the OER and HER in 1.0 M KOH, respectively. Furthermore, the electrodes presented long-term stability over 20 h at current densities of 10 and −10 mA cm−2. Besides, this bifunctional flake-like CoNi2Se4 electrocatalyst delivered outstanding overall water splitting performance and required an external potential of 1.63 V to deliver a current density of 10 mA cm−2.

Ta2NiSe5 nanosheets as a novel broadband saturable absorber for solid-state pulse laser generation

Two-dimensional (2D) ternary chalcogenides have attracted great attentions because of their novel chemical and physical properties arising from the synergistic effect and stoichiometric variation with the additional third element compared with their binary counterparts. Here, high-quality 2D tantalum nickel selenide (Ta2NiSe5) nanosheets are successfully fabricated by a liquid-phase exfoliation (LPE) method. The ultrafast excited carrier relaxation time and nonlinear optical absorption response are investigated and reveal that the prepared 2D Ta2NiSe5 nanosheets have excellent broadband saturable absorption properties, which are further illustrated by three passively Q-switched (PQS) all-solid-state lasers operating at 1.0, 2.0 and 2.8 µm with the Ta2NiSe5 nanosheet-based saturable absorber (SA). Furthermore, mode-locked laser operation with the pulse width as short as 356 fs is also realized at 1.0 µm. This work not only demonstrates the excellent nonlinear optical proprieties and optical modulation performance of Ta2NiSe5, but also paves the way for exploring the photonic and optoelectronic proprieties of ternary chalcogenide materials.

Nickel selenide from single-molecule electrodeposition for efficient electrocatalytic overall water splitting

The prepared electrode (NiSe-TMEDA/CC) from single-molecule electrodeposition is functional for both the OER and HER and shows a superior performance for overall water splitting with a low cell voltage in alkaline medium.

Metal-organic-framework derived hollow manganese nickel selenide spheres confined with nanosheets on nickel foam for hybrid supercapacitors.

Metal-organic framework (MOF) derived nanoarchitectures have special features, such as high surface area (SA), abundant active sites, exclusive porous networks, and remarkable supercapacitive performance when compared to traditional nanoarchitectures. Herein, we propose a viable strategy for the synthesis of hollow manganese nickel selenide spheres comprising nanosheets supported on the nickel foam (denoted as MNSe@NF) from the MOF. The MNSe nanostructures can demonstrate enriched active sites, and shorten the ion-electron diffusion pathways. When the MNSe@NF electrode is used as a cathode electrode for a hybrid supercapacitor, the electrode reflected impressive supercapacitive properties with a high capacity of 325.6 mA h g-1 (1172.16 C g-1) at 2 A g-1, an exceptional rate performance of 86.6% at 60 A g-1, and remarkable longevity (3.2% capacity decline after 15 000 cycles). Also, the assembled MNSe@NF∥AC@NF hybrid supercapacitors employing activated carbon on the nickel foam (AC@NF, anode electrode) and MNSe@NF (cathode electrode) revealed an impressive energy density of 66.1 W h kg-1 at 858.45 W kg-1 and an excellent durability of 94.1% after 15 000 cycles.

A simple method for the preparation of a nickel selenide and cobalt selenide mixed catalyst to enhance bifunctional oxygen activity for Zn-air batteries.

Developing a low-cost, simple, and efficient method to prepare excellent bifunctional electrocatalysts toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical in rechargeable zinc–air batteries. Non-stoichiometric M0.85Se (M = Ni or Co) nanoparticles are synthesized and modified on nitrogen-doped hollow carbon sphere (NHCS). The NHCS loaded Ni0.85Se (Ni0.85Se-NHCS) with rich Ni3+ presents higher OER activity, whereas the NHCS-loaded Co0.85Se (Co0.85Se-NHCS) with abundant Co2+ displays better ORR activity, respectively. When Co0.85Se-NHCS is mixed with Ni0.85Se-NHCS in a mass ratio of 1 : 1, the resulting mixture (Ni0.85Se/Co0.85Se-NHCS-2) shows better ORR and OER dual catalytic functions than a single selenide. Moreover, zinc–air batteries equipped with Ni0.85Se/Co0.85Se-NHCS-2 as the oxygen electrode catalyst exhibit excellent charge and discharge performance as well as improved stability over precious metals. This work has developed a simple and effective method to prepare excellent bifunctional electrocatalysts for ORR and OER, which is beneficial for the practical large-scale application of zinc–air batteries.

Tuning the morphologic and electronic structures of self-assembled NiSe/Ni3Se2 heterostructures with vanadium doping toward efficient electrocatalytic hydrogen production

Tailoring the nonprecious nickel selenide heterogeneous electrocatalysts with controllable morphology and electronic structures is of prime importance to enhance the catalytic efficiency for hydrogen production evolution (HER). Here, we report the solvothermal in-situ synthesis of vanadium-incorporated NiSe/Ni3Se2 heterogeneous structures (VNS) on porous nickel foam, which function as an efficient electrode toward HER, together with superior catalytic activity and durability. Impressively, the self-assembled VNS electrode delivers the current densities of 100, 500 and 1000 mA cm−2 at quite low overpotentials of 175, 275 and 348 mV with 85% iR-compensation toward HER in 1.0 M KOH solution. Mott-Schottky analysis indicates that the vanadium doping alters the flat band potential of VNS, and in turn affects the electrons migration behavior at electrode and electrolyte interface. Benefiting from its dramatically increased catalytic active sites exposure, enhanced charge transport capability, and optimized electronic structure, the hierarchical VNS heterostructures exhibit an impressive HER electrocatalytic performance in alkaline media. More broadly, this research provides a promising strategy for design and exploitation of more advanced electrocatalysts for large-scale hydrogen production on selenides using heteroatom vanadium incorporation.

Controlled synthesis of NiSe-Ni0.85Se nanocomposites for high-performance hybrid supercapacitors

Abstract Constructing nanostructured multiphase composite is an effective way for optimizing the performance of electrode materials. Here we report our findings in design and fabrication of a high-performance electrode material composed of two-phase nickel selenide (NiSe-Ni0.85Se) nanoparticles, which exhibits a high specific capacity of 669 C g−1 at 1 A g−1 and 460 C g−1 at 20 A g−1, indicating its good rate capability (~69%). Moreover, a hybrid supercapacitor composed of NiSe-Ni0.85Se positive electrode and reduced graphene oxide (rGO) negative electrode delivers a specific capacitance of 101 F g−1, high energy of 41 Wh kg−1 and good cycling stability with ~80% capacity retention after 5000 cycles at 10 A g−1. These findings provide an important insight into rational design of nanostructured multiphase nickel selenide materials for energy storage systems.

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.

Nickel Selenide Quantum Dot Applications in Electrocatalysis and Sensors

AbstractQuantum dots (QDs) are semiconducting materials with diameters ranging from 2–10 nm. Amongst these QDs, nickel selenide quantum dot (NiSeQD) materials have gained much interest from researchers over the past few years due to their outstanding properties. These include excellent catalytic activity, good electrical conductivity for charge transfer, and excellent thermodynamic stability. NiSeQD material is relatively cheap, less toxic, and can be synthesised easily. Due to the fascinating and remarkable properties of NiSeQD, the material has been applied in various electrochemical fields, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and solar cells. This review focuses on the application of NiSeQD and its composites in the various analytical fields in the search for alternative renewable sources of energy. Interestingly, NiSeQD material can be modified with different materials to improve its sensitivity, reactivity, and limit of detection. The effects of modification with other materials such as iron (Fe), cobalt (Co), and graphene (GN) are mentioned. Additionally, the application of NiSeQD in glucose sensing is discussed briefly. In these aforementioned applications, NiSeQD has shown excellent electrocatalytic capability with satisfactory detection limits and good conductivity. Thus, further exploration of it to other fields is essential. This review highlights the importance of NiSeQD in water purification, and no report has been documented in the literature on its application in water purification. Some gaps are still open for the use of NiSeQD material as an electroactive platform for sensing devices in water treatment.

Selenium-enriched amorphous NiSe1+x nanoclusters as a highly efficient cocatalyst for photocatalytic H2 evolution

Exploiting and fabricating of novel non-noble metal cocatalysts with abundant active sites is highly required to boost the photocatalytic performance. Herein, selenium-enriched amorphous NiSe1+x nanoclusters (a-NiSe1+x) as a novel cocatalyst were rationally integrated with the TiO2 to greatly boost its hydrogen-generation rate via a simple photoinduced deposition route. It was interesting to find that in comparison with the crystalline nickel selenide (c-NiSe), the a-NiSe1+x evidently displayed more unsaturated active Se atoms because of its highly irregular arrangement structure and small particle size (0.5–2 nm). Photocatalytic results revealed that the a-NiSe1+x nanoclusters could significantly improve the hydrogen-production activity of TiO2 (4095.3 μmol h−1 g−1, AQE = 19.6%), which is higher than that of pristine TiO2 and c-NiSe/TiO2. The outstanding performance of a-NiSe1+x/TiO2 can be attributed to the synergism of facilitated photoelectron transfer from TiO2 to a-NiSe1+x cocatalyst and excellent H2-production active site of Se atoms, which was well revealed by density functional theory (DFT) calculations and in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) measurement. Based on the above results, an enriched Se-mediated mechanism is raised for the boosted H2-generation rate of a-NiSe1+x/TiO2. Moreover, the present a-NiSe1+x can also be used as the general cocatalyst for typical g-C3N4 and CdS photocatalysts. Considering the gentle preparation, low-cost and admirable activity, the a-NiSe1+x cocatalyst would have tremendousprospects for the fabrication of advanced photocatalytic materials.

In-situ doping of Co in nickel selenide nanoflower for robust electrocatalysis towards oxygen evolution

The state-of-the-art catalytic materials for oxygen evolution reaction (OER) are Ru and Ir precious metals. Despite of high activity in OER, large-scale production and application of these materials are restricted by low abundance and high price. Exploring inexpensive and efficient electrocatalytic materials for OER is a hot spot of research. Herein, Co-doped nickel selenide (Co–NiSe) nanoflowers are solvothermally in-situ grown on nickel foam (NF), which acts as a robust catalytic electrode for OER. In 1.0 M KOH electrolyte, the required overpotential is 380 mV to reach a current density of 100 mA cm−2. The Tafel slope is 111.0 mV dec−1. A long-term catalytic stability for OER is obtained. Cobalt doping not only produces more catalytically active sites for OER, but also promotes charge transport through electronic interaction with NiSe.