NiCo2O4 Nanoflowers Research Articles

Excellent electrochemical performance of N and Mn doped NiCo2O4 functional nanostructures: an effective approach for symmetric supercapacitor application

In supercapacitors (SCs), cobaltite spinel is considered as an excellent electrode material because it is abundant on earth, cost-effective, and theoretically capable of achieving high capacitance values. However, there are number of factors that prevent spinel cobaltite from achieving its maximum theoretical specific capacitance, including low electrical conductivity, insufficient active sites, and slow charge transport. For these reasons, it is necessary to simplify the structural and compositional design to overcome these limitations. An efficient solvothermal method followed by pyrolysis was successfully used to shape NiCo2O4 nanoflowers doped with N (Nitrogen) and Mn (Manganese). In addition to increasing the ion diffusion resistance and charge transfer resistance, N and Mn-doped NiCo2O4 provides an electrical conductivity system. The optimized N, Co, and Mn4 (NCoMn4) nanoflowers (4 wt% Mn-doped NiCo2O4) exhibits maximum specific capacitance of 269Fg−1 at 1Ag−1 current density with an exceptional retention of capacitance 92% after 5,000 uninterrupted cycles in the Na2SO4 media. The electrokinetic analysis of NCoMn4 further indicates that overall charge is stored predominantly through capacitance, as compared with other electrodes. It is also worth noting that the as-fabricated symmetric supercapacitor delivers the maximum energy density of 36.11 Whkg−1 at a power density of 1.04 kWkg−1 at 1 Ag−1 current density. This work opens a new path to develop hybrid electrodes for enhanced supercapacitor applications and will specify an efficient method for improving the charge transfer capability.

Sandwiched solar interfacial evaporation system: Integrating phase change material/hydrogel/NiCo2O4 nanoflower for superior desalination

Solar-driven interfacial evaporation is a kind of sustainable and eco-friendly method of water treatment to alleviate the global water crisis. Here we demonstrate a novel sandwiched solar interfacial evaporator integrating phase change material (PCM), sodium alginate hydrogel (SA), and NiCo2O4 nanoflower featuring superb evaporation and glorious thermal energy management to achieve efficient energy utilization and long-term evaporation stability. After being combined with filter paper, NiCo2O4 nanoflower composites are adopted as the light absorber on the top layer, which can achieve an absorption of about 96.5 % in the full spectral range. SA hydrogel has been used as an intermediate layer for rapid water supply to the evaporation interface and to prevent salt deposition. Under one sun irradiation (1 kW m−2), the evaporator exhibits a high evaporation rate (1.94 kg m-2h−1) and excellent endurance in the treatment of high salt-concentration water. In particular, benefiting from the rational combination of PCM, the water production reached up to 12.13 kg m−2, which is 2.23 kg m-2higher than that of the evaporator without PCM under natural solar irradiation for 9 h. This work presents a promising concept for maximally utilizing intermittent solar irradiation energy and prolonged salt-free deposition desalination.

Transition metal sulfide/oxide nanoflowers decorated on poly (aniline-2-sulfonic acid) modified polyacrylamide derived carbon cathode catalyst for bioenergy generation in microbial fuel cells

Microbial fuel cells (MFCs) are promising carbon-free energy devices with the potential to harvest power and treat wastewater simultaneously, which is crucial to meet the emerging energy challenges. Despite the high theoretical power output, the performance of MFCs is dependent on the cathodic oxygen reduction reaction (ORR) to generate electricity. Herein, a hybrid nanostructure of nickel-cobalt sulfide (NiCo2S4) nanosheets over NiCo2O4 nanoflowers on in-situ nitrogen and sulfur-doped carbon (NSC) is prepared by direct pyrolysis. Deposition of NiCo2S4 nanosheets improves the effective contact with the electrolyte and increases the catalytic sites for ORR. NiCo2S4/NiCo2O4@NSC shows an oxygen reduction peak at 0.150 V, limiting current of -0.093 mA, close to -0.107 mA for Pt/C and generates optimal power density of 831.74 mW m−2 comparable to Pt/C (857.92 mW m−2) and higher than NiCo2O4@NSC (665.86 mW m−2), NSC (650.28 mW m−2) and NC (485.98 mW m−2) air cathodes. This could be attributed to the high degree of graphitization, appropriate N and S content, a synergistic effect between the metal species and the heteroatoms, and better catalytic surface area utilization. The results suggest that M-N-S-based carbons could be potential cathodes for microbial fuel cells and similar energy devices.

Starch-based porous carbon microsphere composited NiCo2O4 nanoflower as bifunctional electrocatalyst for zinc-air battery

It is significant to explore and design outstanding bifunctional oxygen electrocatalysts to promote the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in zinc–air batteries. Herein, a novel porous carbon microspheres (CMS2) modified by NiCo2O4 nanoflower (CMS2–NiCo2O4) have been prepared as an ORR and OER catalyst. The hierarchical porous structure of CMS provides high conductivity and abundant active sites for ORR, whereas the synergistic effect of NiCo2O4 nanosheets and a small amount of FeZn oxides act as the positive phase for OER. The efficient oxygen catalytic activity is gained by creating a coupling interface between NiCo2O4 and CMS. The optimized CMS2–NiCo2O4 shows a half–wave potential of 0.82 V toward ORR and an overpotential of 392 mV toward OER. Particularly, CMS2–NiCo2O4 also exhibits an excellent peak power density (175.5 mW cm−2) as a catalyst for zinc–air batteries, which is superior to the commercial Pt/C + RuO2 catalyst (120.5 mW cm−2), and it also demonstrates a remarkable stability even after the charge–discharge cycles of 167 h. The prepared CMS2–NiCo2O4 is promising for the application of the bimetallic oxide catalyst for zinc–air battery.

Gas-liquid diffusion directed rational synthesis of Fe-doped NiCo2O4 nanoflower for efficient oxygen evolution reaction

Distinct from the traditional synthesis of NiCo2O4 nanoflowers from hydrothermal approach. Herein a facile gas-liquid diffusion method was exploited to prepare NiCo2O4 and Fe-doped NiCo2O4 nanoflower under ambient condition for oxygen evolution reaction (OER). The remarkable nanoflowers was generated by diffusing ammonia to the homogeneous solution of cobalt and nickel sulfate salt with slight amount of Fe sulfate salt to form a heterogeneous precipitation, followed by pyrolysis to afford the final product of NiCo2O4 or Fe-doped NiCo2O4. The remarkable feature of NiCo2O4 displays a spherical nanoflower morphology composed of lamellar structure with excellent dispersibility and greatly prompt the electron transfer and enable a high activity. By varying the ratio of Ni to Fe to 9:1, a superior OER performance with overpotential of 256 mV and Tafel slope of 69 mV·dec−1 at 10 mA·cm−2 was obtained. We attribute the superior performance to the excellent gas and ion transport channels due to the unique nanoflower structure as well as the well optimized electronic structure derived from Fe doping. Besides, we tentatively propose a detailed formation process for the formation of this nanoflower structure based on co-precipitation reaction. In conclusion, this approach offers a facile and efficient way for the preparation of high-performance ternary mixed metal oxides nanostructure which enable its large-scale production of OER catalyst.

Morphology-dependent solvothermal synthesis of spinel NiCo2O4 nanostructures for enhanced energy storage device application

Spinel NiCo2O4 is a remarkable electrode material for enhanced energy storage devices due to its unique tunable structure and shape. Herein, we have demonstrated a facile solvothermal approach to synthesize various nanostructures such as nanoparticles, nanoflowers self-assembled with nanoflakes, nanorods, and nanosheets of spinel NiCo2O4. The influence of solvents (such as water, ethanol, water-ethanol, and ethylene glycol etc.), urea, the molar concentration of reactant precursors Ni(NO3)2·6H2O and Co(NO3)2·6H2O, and calcination temperatures are varied for designing the various nanostructures of NiCo2O4. Further all electrode materials are tested for supercapacitor application. Among all as-synthesized nickel cobaltites, NiCo2O4 nanoflowers (NC-2) is found to be the best electrode materials for supercapacitor application with a high specific capacitance (415 F/g at 2 mV/s scan rate and 144.3 F/g at 1 A/g current density) under 1 M Na2SO4 electrolyte using three-electrode system. The higher specific capacitance of NiCo2O4 nanoflowers is attributed to its larger surface area, the higher number of active sites, and lower charge transfer resistance. Moreover, the NiCo2O4 nanoflowers electrodes were further fabricated for a two-electrode symmetric supercapacitor device and showed a specific capacitance of 80.2 F/g at 1 A/g current density and exhibit higher energy density of 17.4 Wh/kg with a power density of 329.7 W/kg. The fabricated symmetric device of NiCo2O4 nanoflowers displays outstanding durability upto 10,000 continuous charge-discharge cycles at 5 A/g.

High-performance flexible supercapacitors with hierarchical structured cathode (NiCo2O4/Au/MnO2) and anode (NiCo2S4/PPy)

NiCo2O4 nanoflowers with high specific surface area were prepared on nickel foam (NF) by hydrothermal method and used as frameworks for developing cathode and anode of flexible asymmetric supercapacitor. With the unique nanoflower-like NiCo2O4 arrays as skeleton, the NiCo2O4/Au/MnO2 cathode was prepared by gold-spraying and electrochemical deposition and the NiCo2S4/PPy anode was prepared by second-hydrothermal and electro-polymerization. The hierarchical structured electrodes offer sufficient redox sites and adequate channels for accelerating ion and electron transport between electrodes and electrolyte. Moreover, the NiCo2S4/PPy was first reported as the anode, and its cycling stability (capacitance retention of 86.04 % after 5000 cycles) and specific capacitance (1612.5F/g at 1 A/g). The assembled flexible all-solid-state asymmetric supercapacitor (NiCo2O4/Au/MnO2 // NiCo2S4/PPy) displays a high energy density of 206.37 Wh kg−1 at a power density of 398.57 W kg−1 and an outstanding cyclability (capacitance retention of 83.41 % after 5000 cycles).

Design of NiCo2O4 nanoflowers decorated sulfurbridged covalent triazine frameworks nanocomposites for electrochemical simultaneous detection of acetaminophen and 4-aminophenol

Owing to the high toxicity of acetaminophen (ACOP) and 4-aminophenol (4-AP) when they are overused, the simultaneous determination of ACOP and 4-AP is crucial. In this present paper, an electrochemical sensor based on the nanocomposite of sulfurbridged covalent triazine frameworks (S-CTFs) and in situ formed nickel cobaltite (NiCo2O4) nanoflowers on S-CTFs, denoted as S-CTFs@NiCo2O4, was fabricated for the first time for sensitive detection of ACOP and 4-AP. S-CTFs@NiCo2O4 modified electrode exhibited the outstanding synergetic effects of S-CTFs (prominent enrichment ability and large surface area) and NiCo2O4 (excellent electrocatalytic activity). The developed electrode had the advantages of high reproducibility, repeatability, anti-interference and stability, and it exhibited a wide linear concentration range (2 ∼ 360 μM) and a low limit of detection (0.18 μM and 0.35 μM) for ACOP and 4-AP, respectively. In addition, the designed electrochemical sensor was evaluated towards the detecting ACOP and 4-AP in real samples with satisfactory recovery, illustrating that electrode has a broad prospect in the clinical application.

Reduced graphene oxide/hierarchal spinel nickel cobaltite nanoflowers composites for supercapacitor electrodes with ultrahigh capacitive and excellent rate performance

Researchers are extensively investigating transition metal oxides due to their unique porous architectural structure and remarkable electrochemical properties, which are suitable to boost the energy storage capabilities. In present work, facile chemical route was used to synthesize hierarchal spinel nickel cobaltite nanoflowers anchored reduced graphene oxide (NiCo2O4-rGO) as high performance electrode material. NiCo2O4 anchored rGO demonstrated specific capacitance of 2695 Fg-1 at 1 Ag-1, which is greater than pristine NiCo2O4 nanoflowers specific capacitance. NiCo2O4-rGO showed excellent stability and retention capability of 96% after 2500 cycles at 5 Ag-1. Furthermore, NiCo2O4–rGO exhibited maximum energy density of 93.57 WhKg−1 at power density of 250 WKg-1. We have achieved specific capacitance and retention capability which is higher than previously reported results. This enhancement is mainly attributed to the spinel structure of NiCo2O4 and its robust structural affinity with rGO. Moreover, rGO possesses extended surface area provided ample of active sites and exceptional synergetic effect which helped to enhance the induction and consequently transportation of e−/h+. More importantly due to its special morphological effects, in future NiCo2O4 anchored rGO nanoflowers may open new avenue in research but also used as an efficient electrode material for the construction of high performance supercapacitors.

Outstanding Electrochemical Supercapacitor Performances of NiCo2O4 Nanoflowers

Cost-efficient and dynamic electrode materials are required for high-performance renewable energy storage devices. A cost-effective and simple hydrothermal method was employed to prepare NiCo2O4(NCO) nanoflowers (NFs) as an electrode material for high-energy storage electrochemical supercapacitors. The as-prepared nanoflowers were characterized by XRD, BET, SEM, and TEM. NCO-NFs were first coated on nickel foam and then used as a binder-free electrode in a supercapacitor device. The fabricated asymmetric supercapacitor device showed excellent electrochemical properties. The highly conductive NCO-NFs material not only shows a high specific capacitance of 410F g−1 at a scan rate of 5 mV s−1 but also exhibits good cycling stability of 91% capacitive retention after 5000 cycles. The device also delivers a high energy density of 30 Wh kg−1 at a power density of 165 W kg−1. Our method provides a simple and promising strategy for high-performance supercapacitor electrode application.

Silver nanoparticles as a conductive bridge for high‐performance flexible all‐solid‐state asymmetric supercapacitor

With the rapid development of portable electronic devices, it is strongly urgent to explore the flexible and sustainable supercapacitor with lightweight, large power/energy density, good cycle stability, outstanding coulombic efficiency, and excellent operational safety. Herein, a novel and flexible all-solid-state asymmetric supercapacitor is assembled from silver (Ag) or/and cobalt acid nickel (NiCo2O4) nanoparticles coated with hollow carbon micro-skeleton (HCMS-Ag and [email protected]2O4-Ag). The [email protected]2O4-Ag electrode is subsequently prepared by a facile hard template combined with hydrothermal method. The morphology analysis shows that plenty of NiCo2O4 nanoflowers composed of a tremendous number of nanoneedles are uniformly grown on the three-dimensional hollow carbon micro-skeleton. This unique and novel structure endows the prepared electrode with a high specific capacitance of 527.4 F g−1 at a current density of 0.5 A g−1 and outstanding rate capability of 75%. The assembled pliable asymmetric supercapacitor possesses a maximum energy density of 42.67 Wh kg−1, long cycle life (97.4% capacitance retention), and excellent flexibility. Therefore, this work opens new horizon to develop the next-generation carbon composites for flexible all-solid-state asymmetric supercapacitor with high levels of electrochemical properties.

Three-dimensional NiCo2O4 nanosheets and nanoflowers electrodeposited with palladium nanoparticles on nickel foam for the hydrogen evolution reaction

By combining NiCo2O4 with good hydrogen evolution reaction (HER) properties and palladium (Pd) nanoparticles with excellent conductivity, a highly efficient and stable catalyst is prepared for HER. The NiCo2O4 nanosheets and NiCo2O4 nanoflowers are produced on the nickel foam (NF) with a large specific surface area by a one-step hydrothermal method and the NiCo2O4 nanoflowers are uniformly distributed in the NiCo2O4 nanosheets to form a three-dimensional (3D) electrode. Compared to conventional NiCo2O4, the 3D NiCo2O4 electrode provides more active sites (Ni and Co) for oxygen adsorption thus reducing the energy required to break H–O bonds to promote HER. When NiCo2O4/NF is combined with Pd nanoparticles (Pd/NiCo2O4/NF), the HER performance is improved greatly because of the synergistic effects rendered by the 3D structure of NiCo2O4 and Pd nanoparticles. The overpotential of Pd/NiCo2O4/NF is 69 mV at a current density is 10 mA/cm2 and it is stable for 10 h in alkaline environments. The materials design and properties provide useful information for future development of commercial hydrogen production.

Facile synthesis of lightweight 3D hierarchical NiCo2O4 nanoflowers/reduced graphene oxide composite foams with excellent electromagnetic wave absorption performance

Considering the high filling ratios, high densities, and narrow absorbing bandwidths of the current electromagnetic wave (EMW) absorbers, in this work, we successfully synthesized a 3D hierarchical NiCo2O4 nanoflowers/reduced graphene oxide (NiCo2O4/RGO) composite foam by a simple method under gentle condition. The NiCo2O4 nanoflowers and unique 3D foam structure are beneficial to the refraction and scattering of EMW, which endows the prepared 3D foam with highly efficient EMW absorption performance. When the ratio between NiCo2O4 and RGO in the foam is 1:1, 5% mass fraction of NiCo2O4/RGO foam in paraffin wax can reach a minimum reflection loss (RLmin) value of -52.2 dB with a thin thickness merely 2.6 mm. Simultaneously, the effective absorption bandwidth (EAB, RL exceeding -10 dB) is 7.04 GHz that covers the whole Ku band (10.96-18 GHz). Moreover, the effects of the thickness of the absorber and the loading ratios of the foam in paraffin wax matrix on the EMW absorption properties are also carefully investigated. The results indicate that the optimum EMW absorption performance of NiCo2O4/RGO can be tuned in different bands. The EMW absorption mechanism is ascribed to the proper impedance matching and larger dielectric and magnetic loss produced by the synergy of NiCo2O4 and RGO. Therefore, the NiCo2O4/RGO hybrid foam is ideal candidate to be used as high-efficient EMW absorbers with low filling ratio, light weight, and broad frequency bandwidths.

Chemical bath synthesis of NiCo2O4 nanoflowers with nanorods like thin film for flexible supercapacitor application-effect of urea concentration on structural conversion

In a simple chemical bath deposition, the flexible NiCo2O4 thin films with different nanostructures such as nanoflakes, nanoflowers with the surface composed of nanorods have been synthesized on stainless steel by changing the urea concentration of precursor. This study showed that the concentration of urea has a crucial role in the structural conversion of nanostructures. Here, the NiCo2O4 nanoflowers with nanorods like thin film demonstrated superior supercapacitive performance exhibiting a maximum specific capacitance of 702 F g−1 ascribed to the higher electronic conductivity of NiCo2O4 and lower ionic diffusion resistance due to nanoflowers with nanorods like mixed morphology. In further, the higher concentration of urea during synthesis leads to disorientation and overgrowth of the NiCo2O4 nanoflowers which deteriorated its supercapacitive performance. The two flexible solid state symmetric supercapacitor devices have been successfully fabricated using polyvinyl alcohol–KOH and polyvinyl alcohol-LiClO4 gel electrolytes. In comparison, the device with polyvinyl alcohol-LiClO4 gel exhibited superior performance exhibiting a maximum specific capacitance of 132 F g−1 with an energy density of 18.52 Wh kg−1 and a power density of 3.13 kW kg−1.

Influence of Urea on the Synthesis of NiCo2O4 Nanostructure: Morphological and Electrochemical Studies

The widespread use of miniature electronic devices calls for energy-dense storage strategies. The supercapacitor-based energy storage devices with high areal capacitance are desired energy storage alternative. It is still a challenge to fabricate supercapacitor-based energy devices with consistent performance. The porous metal oxides with large areal capacitance are desired materials for electrode, but there exists a limited understanding of the influence of synthesis parameters on microstructural properties, which largely govern their electrochemical performance. In the present work, hierarchal spinel nickel cobaltite (NiCo₂O₄) nanostructures were synthesized in the presence of the varying amount of hydrolyzing agent via a simple hydrothermal method coupled with a simple post-annealing process. This work focuses on understanding the influence of hydrolyzing agent in controlling the microstructure and hence ensuing electrochemical properties of the NiCo₂O₄ based electrode. Based on the urea hydrolyzing content, the as synthesized NiCo₂O₄ nanostructure varied from the rod, plate to nanoflower. The mesoporous nanostructures, with urea content 1.49 gm, exhibit a sizeable BJH surface area (79.2 m² g-1) and high mesopore volume (0.140 cm³ g-1). Remarkably, the NiCo₂O₄ nanoflower shows high specific capacitance of 3143.451 F/g at 2 mV/s scan rate, 1264.5 F/g at 1 A/g current density, energy density of 56 Wh/kg and power density of 8,400 W/kg in 3 M KOH electrolyte. The capacitance loss after 5000 cycles is 48% at the current density of 10 A/g, indicating their excellent cycling stability. The impressive electrocatalytic activity is largely ascribed to the high intrinsic electronic conductivity, superior mesoporous nanostructures and rich surface Ni active species of the NiCo₂O₄ materials, which can largely boost the interfacial electroactive sites and charge transfer rates indicating promising applications as electrodes in future supercapacitors.

Electrochemical Properties of Nanoflower-Like NiCo2O4 Electrode Material

A nanoflower-like NiCo2O4 was successfully synthesized on Ni foam by a facile hydrothermal process with sodium dodecyl sulfate (SDS) by annealing in air atmosphere. The special architecture consists of uniform ultra-thin layers with a lateral size of several hundred nanometers intercrossed with each other, which promote the surface Faraday reaction and relive the volume expansion. The as-fabricated NiCo2O4 nanoflower delivers a specific capacitance of 752 F g–1 at 1 A g–1, and 78.6% retainable capacitance after 5000 cycles.

Highly Active and Easily Fabricated NiCo2O4 Nanoflowers for Enhanced Methanol Oxidation

AbstractMetal oxides with tailored nanomorphology represent a powerful tool to improve the electrocatalytic activity. Herein NiCo2O4 nanoflowers were synthesized via facile microwave method. NiCo2O4 nanoflowers were characterized by scanning and transmission electron microscopy, X‐ray diffraction (XRD), Raman spectroscopy, N2 gas adsorption/desorption, and X‐ray photoelectron spectroscopy (XPS). Through comparing NiCo2O4 nanoparticle vs nanoflowers morphology, NiCo2O4 nanoflowers have a superior mass and specific electroactivity towards oxygen evolution reaction (OER) by achieving a current density of 10 mA/cm2 at an overpotential of only 280 mV in 1M KOH electrolyte. Moreover, NiCo2O4 nanoflowers display superior performance for methanol electrooxidation in fuel cells by achieving 200 A/g and recovers 92.3 % of the original activity through the addition of new (1M KOH + 0.5M methanol) electrolyte after 500 cycles.

Morphology-controlled synthesis of NiCo2O4 nanoflowers on stainless steel substrates as high-performance supercapacitors

NiCo2O4 nanostructures were synthesized via a chemical bath deposition method on stainless steel substrate by employing nickel chloride, cobalt chloride and urea as the starting reactants, at 343 K to 373 K for 5 h without the assistance of any additives. The influence of deposition temperature on the morphology (particle size and shape) of NiCo2O4 nanoflowers was examined. Also the shape‐dependent electrochemical properties of the nanoflowers electrodes were investigated. The mature nanoflowers structure and its improved electron conductivity is beneficial for supercapacitor application, the NiCo2O4 nanoflower thin films deposited at 363 K temperature onto stainless steel substrate exhibits 610 F/g at 1 mA/cm2, good rate capability with superior cycling performance up to 5000th cycles. Our findings demonstrate the importance of shape-controlled synthesis of NiCo2O4 nanoflowers on stainless steel substrate in development of high-performance energy-storage systems.

Bifunctional and highly sensitive electrochemical non-enzymatic glucose and hydrogen peroxide biosensor based on NiCo2O4 nanoflowers decorated 3D nitrogen doped holey graphene hydrogel

In this work, a simple strategy for fabricating a 3D nitrogen doped holey graphene hydrogel decorated with NiCo2O4 nanoflowers (NHGH/NiCo2O4) via a one-pot hydrothermal method with subsequent calcination is reported for the first time. The novel NHGH/NiCo2O4 nanocomposites featured high electrical conductivity, large and accessible surface areas, abundant active sites, and excellent electrocatalytic performance. Considering the excellent catalytic activity of NiCo2O4, a sensitive and bifunctional electrochemical non-enzymatic biosensor was established for the determination of glucose and hydrogen peroxide (H2O2). The obtained biosensor exhibited wide linear ranges (glucose: 0.005–10.95 mM; H2O2: 1–510 μM) and a low detection limits (glucose: 0.39 μM; H2O2: 0.136 μM) in alkaline solution (S/N = 3). Excellent electrocatalytic activity of this sensor was ascribed to the synergistic effects of the hybrid structure between the NiCo2O4 nanoflowers and NHGH. Furthermore, the sensitive biosensor also exhibited high selectivity and could be applied to determine glucose in real blood samples. Taken together, the results reveal that the proposed hybrid nanocomposite could be a promising electrochemical biosensor.

Mesoporous NiCo2O4 nanoflower constructed from nanosheets as electroactive materials for dye-sensitized solar cells

Binary metal compounds with a spinel structure could improve the electron transport, activating adsorption and active sites for electrocatalytic reaction. Furthermore, the electrocatalytic activity of electroactive materials also depends on their morphology and nanostructure. Herein, this work reported the fabrication of NiCo2O4 mesoporous nanoflowers and mesoporous nanospheres and their application as promising counter electrode (CE) electrocatalysts in dye-sensitized solar cells (DSSCs). The as-prepared NiCo2O4 mesoporous nanoflower contains abundant open space between nanosheets, generating the 3D porous nanostructure. When investigated as CE materials, NiCo2O4 nanoflowers exhibited high charge-transfer ability and intrinsic catalytic activity. The DSSC with NiCo2O4 nanoflowers displayed a much higher power conversion efficiency (PCE) of 7.32% than that based on the NiCo2O4 nanosphere CE (PCE = 5.58%), even comparable with that of commercial Pt CE (7.54%).