Two-step Electrodeposition Research Articles

Preparation of Co(OH)2@NiFe/NF bifunctional electrocatalyst by electrodeposition for efficient water splitting

The use of earth-abundant metals such as nickel, iron and cobalt is an effective strategy to develop active bifunctional electrocatalysts for water splitting. Herein, a novel binder-free nickel foam (NF) supported Co(OH)2 composite on NiFe electrocatalyst (denoted as Co(OH)2@NiFe/NF) is developed using simple two-step electrodeposition. The unique structure of Co(OH)2 nanoflowers grown on NiFe nanosheets is observed by SEM. The prepared catalyst has high activity for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The overpotential of HER is 87 mV and that of OER is only 191 mV with current density of 10 mA cm−2 in 1 M KOH. In addition, Co(OH)2@NiFe/NF is used as anode and cathode, which requires only 1.52 V to reach current density of 10 mA cm−2 and 60 h stability, superior to many other advanced electrocatalysts. This provides a new way to prepare low-cost, high-performance and stable electrochemical water electrolysis electrocatalyst.

Improvement of electrocatalytic properties of copper nanofoam modified by coral reef-like nickel-cobalt electrocatalyst for water splitting

Synthesis of a stable and efficient electrocatalyst for hydrogen evolution reaction (HER) using earth-abundant elements and inexpensive regents is essential to produce green H2 as an alternative to fossil fuels. In this study, a novel electrocatalyst has been developed using a Cu-foam substrate with a large surface area and electrochemically modified by Ni-Co bimetallic catalyst. A simple and effective two-step electrodeposition method has been applied using a solution of Ni and Co precursors to form NiCo@Cu-foam electrode. The SEM results indicated a porous structure for Cu-foam substrate with numerous active sites for the electrodeposition of Ni-Co electrocatalyst. The synergistic effect of Ni, Co, and Cu atoms with high conductivity and low overpotential has made NiCo@Cu-foam an excellent electrocatalyst. Remarkably, in 0.5 M H2SO4 acidic media, NiCo@Cu-foam electrode showed increased electrocatalytic activity to provide a current density of 100 mA.cm−2 compared to the corresponding values for Co@Cu-foam and Ni@Cu-foam electrodes at − 0.12, − 0.16, and − 0.19 V vs. RHE. Moreover, the fabricated catalyst showed a low Tafel slope of 67 mV.cm−1 and outstanding long-term stability for H2 evolution without considerable decrease at different overpotentials and current densities. The present study introduced an attractive candidate with improved performance for water splitting and clean energy production fabricated by inexpensive starting materials.

Evaluation of electrosynthesized reduced graphene oxide-Ni/Fe/Co-based (oxy)hydroxide catalysts towards the oxygen evolution reaction.

In this work, the specific role of the addition of graphene oxide (GO) to state-of-the-art nickel-iron (NiFe) and cobalt-nickel-iron (CoNiFe) mixed oxides/hydroxides towards the oxygen evolution reaction (OER) is investigated. Morphology, structure, and OER catalytic activity of the catalysts with and without GO were studied. The catalysts were fabricated via a two-step electrodeposition. The first step included the deposition of GO flakes, which, in the second step, were reduced during the simultaneous deposition of NiFe or CoNiFe. As a result, NiFe-GO and CoNiFe-GO were fabricated without any additives directly on the nickel foam substrate. A significant improvement of the OER activity was observed after combining NiFe with GO (OER overpotential η(10 mA·cm-2): 210 mV) compared to NiFe (η: 235 mV) and GO (η: 320 mV) alone. A different OER activity was observed for CoNiFe-GO. Here, the overall catalytic activity (η: 230 mV) increased compared to GO alone. However, it was reduced in comparison to CoNiFe (η: 224 mV). The latter was associated with the change in the morphology and structure of the catalysts. Further OER studies showed that each of the catalysts specifically influenced the process. The improvement in the OER by NiFe-GO results mainly from the structure of NiFe and the electroactive surface area of GO.

Preparation of Co-S/NixSey/C@TiO2 composite electrode and the performance improvement strategies for the electrooxidation of H2O2

BackgroundThe cleanliness and ease of storage and transportation of H2O2 make it a promising fuel of fuel cell, but improving the catalytic activity of H2O2 electrooxidation is a prerequisite. MethodThe Co-S/NixSey/C@TiO2 electrode was prepared by “vapor deposition” and “two-step electrodeposition”, and the electrode was scaled up and fabricated into a rotating cylinder electrode to improve the catalytic performance of H2O2 electrooxidation. Significant findingsThe presence of Se-Se bonds and the synergistic effect of Co-S compound and NixSey gave the electrode a reduced oxidation potential for the electrooxidation of H2O2. The three-dimensional (3D) structure of the electrode facilitated the exposure of the catalyst active site, and the loading of Co-S compound improved the hydrophilicity of electrode. It's important to note that an original rotating cylinder electrode system was fabricated using an enlarged Co-S/NixSey/C@TiO2 electrode to weaken concentration polarization and reduce bubble adsorption on the electrode surface. Through the study, rotation of electrode and circulation of reaction solution exhibit positive effect for the electrooxidation reaction. Especially with a rotation speed of 37 r min−1 of electrode, the performance was improved by 85%. This study provides new strategies for improving the performance of H2O2 electrooxidation, which is of high research significance.

Fabrication of Fluorine-Free Superhydrophobic Surface on Aluminum Substrate for Corrosion Protection and Drag Reduction

A fluorine-free cerium palmitate superhydrophobic surface on an aluminum plate was fabricated via a two-step electrodeposition method. The mechanical durability, anti-corrosion performance, water repellency and drag reduction properties were tested. The results indicate that a superhydrophobic surface with a densely packed convex island shape with micro-pores and nano-scale strips was formed on the aluminum plate. Furthermore, the as-prepared surface exhibits excellent water-repelling ability with a water contact angle of 162.3° and a sliding angle of 1.5°. Owing to the protective effect of the convex island structure on the surface, the surface also shows superb mechanical durability, which is a shortcoming of ordinary electrodeposited surfaces. Moreover, compared with bare aluminum, the corrosion inhibition efficiency of the superhydrophobic surface is 99.55% and the surface drag decreases by 65.3% at a lower flow rate. Therefore, it is believed that the environmentally friendly fluorine-free superhydrophobic surface has promising potential applications in marine engineering.

Porous-Structured Three-Dimensional Iron Phosphides Nanosheets for Enhanced Oxygen Evolution Reaction

A rational designing nanostructured Earth-abundant and non-precious electrocatalysts for promoting an anodic oxygen evolution reaction (OER) is crucial for cutting-edge energy conversion and storage fields. Herein, we demonstrate a porous structured three-dimensional (3-D) FeP nanosheets on NiO modified Ni electrode (PS-3D-FeP@NiO|Ni) using of a facile and two-step electrodeposition strategy that exhibits enhanced OER under alkaline electrolyte. The as-developed porous-structured 3-D FeP nanosheets on NiO modified Ni electrode exhibits the best OER catalytic activity in relations of low onset potential (ղonset) of ~1.37 V (vs. RHE), small overpotential (η) of ~0.17 V to produce the current densities of 10 mA cm−2, lower Tafel slope value of ~40.0 mV/dec, higher turn-over frequency (TOF) of 0.435 s−1, and long-term stability when compared to other CoP@NiOǀNi, NiP@NiOǀNi, CuP@NiOǀNi, NiP|NF (nickel foam), and commercial IrO2|Ni electrodes established in this study. The anodic current density is calculated at the potential of ~1.80 V to be ~580, ~365, ~145, ~185, ~516, and 310 mA cm−2 for PS-3D-FeP@NiO|Ni, CoP@NiOǀNi, NiP@NiOǀNi, CuP@NiOǀNi, IrO2|Ni, and FeP|NF electrodes, respectively. The porous structured 3-D FeP nanosheets on NiO modified Ni electrode demonstrated a highest current density of ~580 mA cm−2 at ~1.80 V in comparison to other electrodes employed in the current investigation. The outperforming OER activity of PS-3D-FeP@NiO|Ni is majorly associated to its porous-structured 3-D sheet-like morphology, large amount of electrochemical active surface area, high electrical conductance characteristics and self-activated/supported active sites, facilitating the catalytic properties. The surface morphology, crystalline structure, chemical composition, and distribution of Fe, P and O elements have not been altered significantly after had a long-term OER test. These experimental results reveal that further optimization of porous structured 3D FeP nanomaterials is highly anticipated for practical water electrolysis systems.

Achieving Self-Supported Hierarchical Cu(OH)2/Nickel-Cobalt Sulfide Electrode for Electrochemical Energy Storage.

Herein, nickel-cobalt sulfide (NCS) nanoflakes covering the surface of Cu(OH)2 nanorods were achieved by a facile two-step electrodeposition strategy. The effect of CH4N2S concentration on formation mechanism and electrochemical behavior is investigated and optimized. Thanks to the synergistic effect of the selected composite components, the Cu(OH)2/NCS composite electrode can deliver a high areal specific capacitance (Cs) of 7.80 F cm-2 at 2 mA cm-2 and sustain 5.74 F cm-2 at 40 mA cm-2. In addition, coulombic efficiency was up to 84.30% and cyclic stability remained 82.93% within 5000 cycles at 40 mA cm-2. This innovative work provides an effective strategy for the design and construction of hierarchical composite electrodes for the development of energy storage devices.

A Novel Two-Step Electrochemical Deposition Method for Sn-Pd Electrocatalyst Synthesis for a Potential Application in Direct Ethanol Fuel Cells

Sn-Pd electrocatalysts with a constant atomic ratio of 60 at.% Sn-40 at.% Pd suitable for potential application in direct ethanol fuel cells were synthesized using a novel two-step electrodeposition method. First, Sn was electrodeposited in various forms of dendrites, from spear-like and needle-like to individual fern-like dendrites to a network of intertwined fern-like dendrites, by varying the cathodic potential and then performing electrodeposition of Pd at a constant current density in the second step. A morphological and elemental analysis of Sn and Sn-Pd electrocatalysts was performed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) techniques, while the size of Sn dendrites was analyzed using the particle size distribution (PSD) method. Cyclic voltammetry (CV) and chronoamperometry were applied in order to study the catalytic behavior of Sn-Pd electrocatalysts in the ethanol oxidation reaction (EOR), while CO stripping was used to estimate the antipoisoning capability of the electrocatalysts. The Sn surface morphology of the sub-layer was highly correlated with the electrocatalytic activity of the examined Sn-Pd electrocatalysts. The high activity it presented towards the EOR showed the suitability of the Sn-Pd electrocatalyst constructed from individual fern-like Sn dendrites as a sub-layer. Compared to Pd alone, this Sn-Pd catalyst showed more than 3 times higher activity and improved EOR kinetics. This enhancement in the catalytic activity of the Sn-Pd electrocatalysts is attributed to both the morphological characteristics of Sn as a sub-layer and the bifunctional effect.

Construction of a type-II BiVO4/BiOI heterojunction for efficient photoelectrocatalytic degradation of β-naphthol and coal gasification wastewater under visible-light irradiation.

Herein, a novel type-II BiVO4/BiOI (BVOI) heterojunction electrode material was successfully fabricated by using a facile two-step electrodeposition approach. The experimental results revealed that BiOI nanosheets were deposited onto the surface of BiVO4 particles successfully, with the special morphology providing more active sites, which was beneficial to the improvement of PEC performance. According to the electrochemical performance tests, it could be observed that the construction of a heterojunction effectively promoted the separation of photoinduced electron-hole pairs and increased the transfer rate of surface charges. Under visible-light irradiation, the BVOI-300 photoanode possessed the highest PEC β-naphthol degradation rate at pH = 7, which approximately reached 82%, whose corresponding kinetic constant was 1.4 and 1.5 times higher than those of pure BiVO4 and BiOI. After five cycles, the degradation rate still remained at 64.61%. The band structure of the BVOI electrode was deduced, and the PEC mechanism of the BVOI electrode was investigated through the radical trapping quenching experiments and ESR test, which indicated that the ˙OH, h+ and ˙O2- radicals were crucial active species in the PEC β-naphthol degradation process. For the BVOI-300 working electrode, the TOC content of coal gasification wastewater (CGW) decreased from 94.44 to 54.4 mg L-1, and the removal rate reached 42.4%. GC-MS was used to identify the organic components of coal gasification wastewater, which was expected to provide reference for remedying actual gasification wastewater containing refractory organic pollutants and offer a new development direction for the treatment of actual coal chemical wastewater.

Polymethylene blue nanospheres supported honeycomb-like NiCo-LDH for high-performance supercapacitors

Assembly of battery-type supercapacitor hybrid device (BSHD) using capacitive electrode and battery-type electrode is considered as a reliable way. In this work, honeycomb-like nickel cobalt layered double hydroxide/polymethylene blue/carbon cloth (NiCo-LDH/PMB/CC) composite electrode materials with hierarchical structure have been synthesized via two-step electrodeposition. While providing a handful of specific capacitance for the composite, PMB nanospheres offer rich active sites for growth of NiCo-LDH. In addition, the morphology and electrochemical performance of NiCo-LDH/PMB/CC are dominated by mole ratios of Ni/Co. At the mole ratio of Ni/Co = 3/1, NiCo-LDH/PMB/CC-31 displays excellent specific capacity of 1075 C g−1 at 1 A g−1 and maintains 70.6% at ultra-high current density of 40 A g−1. The assembled BSHD, constructed with NiCo-LDH/PMB/CC-31 as cathode and activated carbon as anode, displays outstanding specific energy of 40.7 Wh kg−1 at specific power of 808.4 W kg−1 and prominent capacity retention (89.7% after 2000 cycles). Notably, the assembled BSHD still achieves specific energy of 25.0 Wh kg−1 at 12.0 kW kg−1, which demonstrates decent specific energy of it at high specific power.

Enhancement of photocatalytic activity in ZnO NWs array due to Fe2O3 NPs electrodeposited on the nanowires surface: The role of ZnO-Fe2O3 interface

In this work, the electrodeposition technique was explored to obtain: (i) ZnO film, (ii) ZnO microrods (ZnO MRs), and (iii) ZnO nanowires array (ZnO NWA) on a slide of indium tin oxide coated glass as substrate. The ZnO NWs were decorated with Fe 2 O 3 nanoparticles (Fe 2 O 3 NPs). Thus, a two-step electrodeposition method was performed. In the first step, ZnCl 2 aqueous solution was employed to rise the ZnO NWs; The molar concentration, temperature, and time were explored to understand the influence of parameters on structural properties and morphology. In the second step, the Fe 2 O 3 NPs were incorporated on the surface of nanowires by electrodeposition of FeCl 3 (200 μM) aqueous solution for 1 min. This was confirmed by electron microscopy. In addition, the X-ray photoelectron spectroscopy (XPS) probed that the attachment of Fe 2 O 3 NPs on ZnO NWs induced a significant increment in the density of oxygen defects. The photocatalytic activity of samples was measured by photodegradation of methylene blue (MB). Findings proved that the ZnO-Fe 2 O 3 heterostructure enhanced the photocatalytic activity due to the charge transfer mechanism at the interface. The Fe 2 O 3 NPs prevent the degradation of ZnO NWs across photocatalytic cycles of the MB solution, showing a reduction in the global degradation efficiency of 1.93% after 3 cycles.

Suppression of secondary electron emission of oxygen free copper by two-step electrodeposition of rGO/Cu composite coating

We prepared a reduced-graphene-oxide/Cu (rGO/Cu) composite coating to suppress the total secondary electron yield by two-step electrodeposition. We found that driven by the applied electric field, copper ions can enter the interior of graphene oxide (GO) film and nucleate, while the surface is still GO. The rGO/Cu composite coating was obtained by heat treatment with a combination of hydrogen and argon. After heat treatment, XPS analysis shows that the oxygen content of rGO on the surface of the composite coating is reduced from 31.29 at.% to 11.00 at.%, and the carbon content is 85.25 at.%. Raman analysis shows that rGO is still mainly sp2 hybrid structure. The deposited copper particles sintered in the composite coating and formed Cu-O-C chemical bond. The maximum secondary electron yield (δmax) is 1.10, which is close to the δmax of rGO coating (1.09). Compared with the rGO coating, the presence of copper in the rGO/Cu composite coating slightly increases the TEY, but significantly improves the bonding strength between the coating and the substrate at high temperatures.

Growth of Ni-Co-S Nanoflakes on Ni Bowl-Like Micro/Nano Array as a Non-Enzymatic Electrode for Detection of Glucose

A new synthetic procedure to Metal/metal sulfide hierarchical pore array composites was described. That is, a layer of Ni-Co-S nanoflakes was in situ constructed on the Ni ordered bowl-like micro/nanoarrays through a two-step electrodeposition method with the assistance of a colloidal sphere template. Such as-grown hierarchical composites could increase the specific surface areas and provide more active sites for electrocatalytic reactions. It exhibited a high catalytic activity to glucose, with a high sensitivity of 1210.1 μM‧mM-1cm-2 and a wide linear range from 0.5 μM to 2.0 mM. This work provides another candidate material for the development of planar non-enzymatic glucose sensors.

Biomimetic slippery liquid-infused porous surface on the basis of hierarchical ZIF-67@Cu dendrite: Preparation and corrosion inhibition

In the harsh environment, the corrosion of Cu leads to the failure of pipelines, condenser, printed circuit board and so forth. Thus, protecting Cu from corrosion is critically important from both science and engineering backgrounds. In this report, the hierarchical structure compositing dendritic Cu and ZIF-67 is prepared onto Cu by a two-step electrodeposition protocol. After thiol modification and oil infusion, bio-inspired superhydrophobic surface (SHS) and slippery liquid-infused porous surface (SLIPS) is respectively achieved, and sophisticated techniques are used for characterizing chemical composition, morphology, topology and wettability. Scanning Kelvin probe is employed to know the surface potential distribution before and after the biomimetic transformation. Using different electrochemical approaches, the corrosion inhibition effect is elucidated. In 3.5 wt% NaCl corrosive medium, |Z|0.01Hz of SLIPS is as high as 1.35 × 108 Ω·cm2 at the initial immersion stage. The value is remarkably enhanced compared with SHS (6.76 × 104 Ω·cm2) and bare Cu (8.74 × 103 Ω·cm2). After soaking for 168 h, |Z|0.01Hz value of SHS and SLIPS is 3.84 × 104 Ω·cm2 and 4.93 × 106 Ω·cm2, illustrating that SLIPS has high resistance to protect Cu from corrosion.

Two-step electrodeposition synthesis of NiCo2S4/MoSx composite on nickel foam as electrodes for supercapacitors

This work reports a simple, eco-benign, pollution-free two-step electrodeposition technology to prepare NiCo2S4/MoSx composites on nickel foam (NF). It was then employed as electrodes for all-solid symmetric supercapacitors. The NiCo2S4/ MoSx/NF composite can provide a superior specific capacity of 1494.52 F/g at 1 A/g, and also deliver good stability of ∼93.03% after 1000 cycles. The NiCo2S4/MoSx/NF was assembled as the positive and negative electrodes of an all-solid symmetric supercapacitor (NiCo2S4/MoSx/NF // NiCo2S4/MoSx/NF). This assembly exhibits an energy density of 32.54 Wh/kg with the power density 285.72 W/kg, and superior cycle life retention rate of 84.46% and Coulombic efficiency of 100% after 1000 charge-discharge cycles, respectively. The excellent electrochemical property of the NiCo2S4/MoSx/NF composite is ascribed to the synergistic effect between the MoSx and NiCo2S4, suggesting it has excellent prospects as an electrode for supercapacitors.

Sequential electrodeposition fabrication of graphene/polyaniline/MnO2 ternary supercapacitor electrodes with high rate capability and cyclic stability

The incorporation of various capacitive materials to fabricate multi-component electrodes has emerged as a feasible methodology toward high-performance supercapacitors. In this paper, a facile two-step electrodeposition method is proposed to construct polyaniline (PANI)/MnO2 hybrid nanostructure on reduced graphene oxide (RGO) matrix for the ternary supercapacitor electrodes. By the sequential potentiostatic methods, PANI is first electropolymerized on RGO hydrogel films before MnO2 granules are electrodeposited on the RGO/PANI conductive substrates to obtain the free-standing composite films. The resulting RGO/PANI/MnO2 ternary composite electrodes present significantly promoted capacitive properties compared with the binary RGO/PANI electrodes. Particularly, the optimized electrode and corresponding all-solid-state device could achieve the high specific capacitances of 942.6 and 205.0 F g–1 at 1 A g–1 with superb capacitance retention of 86.4% and 80.3% at 30 A g–1, respectively. The device delivers a maximum energy density of 41.0 Wh kg–1 and demonstrates outstanding capacitance holdings of 96.1% after 10,000 cycles at 30 A g−1, 87.8% after 5000 cycles at 10 A g−1, and 82.5% after 3000 cycles at 5 A g−1, respectively. The prominent electrochemical performances of the ternary composite can be ascribed to the fact that graphene supplies the conductive matrix to immobilize the active pseudocapacitive constituents, while PANI and MnO2 can compensate each other to surmount the disadvantages of inferior conductivity or stability.

Interface regulation of Pt quantum dots doped nickel phosphide and cobalt hydroxide to promote electrocatalytic overall water splitting

The transition metal phosphates are earth-abundant minerals that have been shown to perform well in electrocatalytic water splitting, whereas these catalysts still tend to have excessively high overpotentials and slow kinetics in HER and OER processes. In the present work, hybrid catalysts consisting of Pt quantum dots doped NiP (NiP-Pt) nano-embroidery spheres and Co(OH)2 nanosheets were successfully prepared by two-step electrodeposition method. The excellent catalytic performance of the catalyst relies principally on the synergistic interaction between NiP and Pt quantum dots. Additionally, the NiP-Pt exhibits strong electronic interactions at the interface with Co(OH)2. Consequently, the catalyst has a strong catalytic performance in terms of HER and OER catalytic performance. In terms of HER, an overpotential of only 40 mV is required when the current density reaches 10 mA cm−2, corresponding to a Tafel slope of 49.85 mV·dec−1. At the same time, the catalyst also performs well at OER, with a current density of 10 mA cm−2 at an overpotential of 186 mV and a Tafel slope of 53.049 mV·dec−1 much less than most electrocatalysts. This study involving electrodeposition and doping of quantum dots provides a new idea for the efficient synthesis of fundamental HER and OER bifunctional catalysts.

Facile preparation of antimony sulfide and 3,4,9,10-perylenetetracarboxylic diimide composite nanomaterials modified fluorine-doped tin oxide glass for efficient detection of hydrazine

• A facile method for the preparation of a novel heterojunction of PTCDI and Sb 2 S 3 . • A novel chemical sensor used for quantitative detection of hydrazine. • Low detection limit (13.95 nM) and a wide linear range (1 μM–1000 μM). A novel heterojunctions of 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) nanosheets coupled with antimony sulfide (Sb 2 S 3 ) nanorods were synthesized by two-step electrodeposition. The addition of the inorganic nanomaterial Sb 2 S 3 significantly improved the stability of the PTCDI organic nanomaterial, which already had excellent sensing properties for hydrazine. At the same time, the two materials formed a heterojunction to improve the efficiency of electron transfer when the composite electrode was used to detect hydrazine. The sensor’s response current generated by the electrochemical reaction displayed that the PTCDI/Sb 2 S 3 composite nanomaterials hold high electrocatalytic performance. The results exhibited that the obtained sensor had outstanding analytical performance according to the detection limit (13.95 ± 0.16 nmol·L −1 ), sensitivity (0.1678 μA·μmol −1 ·L·cm −2 , 0.1103 μA·μmol −1 ·L·cm −2 ).

Two-step electrodeposition synthesis of iron cobalt selenide and nickel cobalt phosphate heterostructure for hybrid supercapacitors

Exploring novel heterostructure with multiscale nanoarchitectures and modulated electronic structure is crucial to improve the electrochemical properties of electrode materials for supercapacitors (SCs). In this study, a two-step electrodeposition approach which involves suitable efficient procedures, is leading to in-situ preparation of iron cobalt selenide (Fe0.4Co0.6Se2) @ nickel cobalt phosphate (NiCo(HPO4)2·3H2O, denoted as NiCo-P) hybrid nanostructure on carbon cloth (CC) substrate. Particularly, depositing two-dimensional (2D) NiCo-P nanosheets on the surface of Fe0.4Co0.6Se2 nanobelts results in formation of well-organized Fe0.4Co0.6Se2@NiCo-P nanocomposite with large surface area, hierarchical porous nanoarchitecture as well as numerous electroactive sites, leading to enhanced electroactivity and accelerated mass/electron transfer. Benefiting from its unique nanoarchitecture and synergistic effect of two components, the obtained free-standing Fe0.4Co0.6Se2@NiCo-P electrode demonstrates gravimetric capacity (Cm)/volumetric capacity (Cd) of 202.3 mAh/g/319.6 mAh cm−3 at 1 A g−1 and good cyclic stability (83.9% capacity retention over 5000 cycles), which are superior to those of pure Fe0.4Co0.6Se2 and NiCo-P electrodes. Impressively, it was established that an aqueous hybrid supercapacitor (HSC) based on Fe0.4Co0.6Se2@NiCo-P and rape pollen derived hierarchical porous carbon (RPHPC) achieves gravimetric energy density (Em)/volumetric energy density (Ed) of 64.4 Wh kg−1/10.7 mWh cm−3 and a long cycle life with 90.3% capacity retention over 10,000 cycles. This report offers a perspective to design selenide/phosphate heterostructure on conducting substrate for electrochemical energy storage applications.

Ni film decorated on Au-Ag alloy line to enhance graphene/cobalt hydroxide electrodes for micro-supercapacitors

A nanocomposite of graphene, cobalt hydroxide and nickel can conveniently be synthesized on gold-silver alloy lines. Using a two-step electrodeposition method, the scaly morphology is pre-deposited on a Ni film, followed by the interconnecting corrugated graphene/cobalt hydroxide composite nanomaterial. Due to the pre-deposited Ni film, the area capacity of the graphene/cobalt hydroxide/Ni electrode is 1.6-times of the graphene/cobalt hydroxide electrode. The kinetic analysis of the graphene/cobalt hydroxide/Ni electrode displays diffusion and non-diffusion contributions of 38% and 62% at 10 mV s−1, respectively. X-ray photoelectron spectroscopy exhibits the oxidation of Co2+ to Co3+ dedicated to the OH- ion insertion. Furthermore, graphene/cobalt hydroxide/Ni//activated carbon flexible micro-supercapacitor (MSC) was assembled by gel KOH-PVA electrolyte, graphene/cobalt hydroxide/Ni (positive electrode), and activated carbon (negative electrode), which manifests maximum volumetric energy of 18.6 mWh cm−3. Moreover, MSC retains over 94% capacitance after 10,000 cycles. After 1,000 continuous bending/unbending cycles at a 180° bending angle with the frequency of 100 mHz, the capacitance retention of MSC is still maintained at 97% of the initial value. The results show outstanding flexibility and mechanical stability of MSC based on graphene/cobalt hydroxide/Ni electrode and confirm that further chemical and physical optimization may lead to the development of quasi-solid-state hybrid MSCs.