Preparation and electrochemical properties of a novel porous Ti/Sn–Sb-RuOx/β-PbO2/MnO2 anode for zinc electrowinning

MnO₂ coatings prepared in a sulfate system (S-MnO₂) and MnO₂ prepared in a nitrate system (N-MnO₂) were successfully deposited on porous Ti/Sn–Sb-RuO_x/β-PbO₂ substrates by electrodeposition, and their electrochemical properties were studied in detail. The bath composition plays a very important role in the MnO₂ coating prepared by electrodeposition at a low current density. The results of scanning electron microscopy show that a Ti/Sn–Sb-RuO_x/β-PbO₂/MnO₂ electrode has a rough morphology and the unit cell is very good. At the same time, the surface cracks in the S-MnO₂ coating are larger than those in the N-MnO₂ coating. In addition, the N-MnO₂ coating is composed of a fluffy sheet-like substance. The surface morphology of the N-MnO₂ coating is denser than that of the S-MnO₂ coating. The S-MnO₂ coating consists of irregularly stacked granular particles. Further, the main crystal phase of MnO₂ is γ type, and the main valence state of MnO₂ is +4. The results show that the oxygen evolution potential of the N-MnO₂ electrode is 63 mV lower than that of the S-MnO₂ electrode, indicating that the N-MnO₂ electrode has better oxygen evolution activity and electrochemical stability, which can also be confirmed by EIS test results. Under the accelerated life test conditions, the N-MnO₂ electrode has a better service life of 77 h at a current density of 1 A cm⁻² in 150 g L⁻¹ H₂SO₄ and 2 g L⁻¹ Cl⁻ solution.

PbO₂ electrodes exhibit symmetry on the CV curve in MnSO₄ bath (oxidation peak occurs at 1.00–1.40 V) and asymmetry in Mn(NO₃)₂ plating solution (negative current value at 1.00–1.18 V). The current rapidly rises to a large peak current at 1.25 V.     

Electrochemical degradation of ciprofloxacin with a Sb-doped SnO2 electrode: performance,influencing factors and degradation pathways

Sb-doped SnO₂ electrodes were prepared with the practical sol–gel method and were used for the electrocatalytic degradation of ciprofloxacin (CIP) in aqueous solution. Results from the electrochemical characterization (including cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy) showed that the electrode with 16 coating times (SSO-16) had the highest oxygen evolution potential of 2.2 V (vs. SCE) and the highest electrochemically active area of 3.74 cm². The results of scanning electron microscopy and X-ray diffraction showed that the coating times could affect the surface morphology and crystal structure of the electrodes, and the SSO-16 electrode had a denser surface, higher crystallinity, and smaller grain size (28.6 nm). Moreover, the experimental parameters for CIP degradation with SSO-16 were optimized, and the removal ratio of CIP reached to almost 100% within 60 min. In addition, the possible degradation pathways of CIP were proposed. And the stability and reusability of the SSO-16 electrode were also studied. These results are valuable for the preparation of high electrocatalytic performance electrodes by a sol–gel coating method for electrochemical degradation of antibiotics.

Sb-doped SnO₂ electrodes with different coating times were prepared by an optimum sol–gel method and the application on the electrocatalytic degradation of ciprofloxacin in aqueous solution were investigated.     

The effects of deposition time and current density on the electrochemical performance of flexible and high-performance MnO2@PFG composite electrodes

A novel composite electrode has been fabricated by the direct deposition of MnO₂ onto graphene networks surrounding a paper fiber (PFG). The paper fiber between graphene sheets could be used as a flexible substrate for MnO₂ nanoparticles, and the microscopic morphologies and electrochemical performances of the MnO₂@PFG electrodes were tuned via regulating the deposition current densities and deposition times. 3D graphene on PFG served as a highly conductive backbone with a high surface area for the deposition of the MnO₂ nanoparticles, which provided high accessibility to electrolyte ions for shortening the diffusion paths. The MnO₂-10-600 s@PFG composite electrode achieved a maximum specific capacitance of 878.6 mF cm⁻² with an MnO₂ loading mass of 3.62 mg cm⁻² (specific capacitance of 187.7 F g⁻¹) at a current density of 0.5 mA cm⁻² in a 1 M NaSO₄ aqueous solution. Additionally, the MnO₂-10-600 s@PFG composite material with the most favorable composite ratio exhibited the highest energy density of 61.01 mW h cm⁻², maximum power density of 1249.78 mW cm⁻², excellent capacitance retention with no more than 7% capacitance loss after 10 000 cycles and good mechanical flexibility (about 91.06% of its original capacitance after 500 bending times). By combining the electric double layer capacitance of graphene networks with the pseudocapacitance of the MnO₂ nanostructures, the flexible electrode showed much enhanced electrochemical capacitance behaviors with robust tolerance to mechanical deformation; thus, it is promising for being woven into textiles for wearable electronics.

A novel composite electrode has been fabricated by the direct deposition of MnO₂ onto graphene networks surrounding a paper fiber (PFG).     

Fabrication of novel electrochemical sensors based on modification with different polymorphs of MnO2 nanoparticles. Application to furosemide analysis in pharmaceutical and urine samples

A novel MnO₂ nanoparticles/chitosan-modified pencil graphite electrode (MnO₂ NPs/CS/PGE) was constructed using two different MnO₂ polymorphs (γ-MnO₂ and ε-MnO₂ nanoparticles). X-ray single phases of these two polymorphs were obtained by the comproportionation reaction between MnCl₂ and KMnO₄ (molar ratio of 5 : 1). The temperature of this reaction is the key factor governing the formation of the two polymorphs. Their structures were confirmed by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) and energy dispersive X-ray (EDX) analysis. Scanning electron microscopy (SEM) was employed to investigate the morphological shape of MnO₂ NPs and the surface of the bare and modified electrodes. Moreover, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used for surface analysis of the modified electrodes. Compared to bare PGE, MnO₂ NPs/CS/PGE shows higher effective surface area and excellent electrocatalytic activity towards the oxidation of the standard K₃[Fe(CN)₆]. The influence of different suspending solvents on the electrocatalytic activity of MnO₂ was studied in detail. It was found that tetrahydrofuran (THF) is the optimum suspending solvent regarding the peak current signal and electrode kinetics. The results reveal that the modified γ-MnO₂/CS/PGE is the most sensitive one compared to the other modified electrodes under investigation. The modified γ-MnO₂/CS/PGE was applied for selective and sensitive determination of FUR. Under the optimized experimental conditions, γ-MnO₂/CS/PGE provides a linear response over the concentration range of 0.05 to 4.20 μmol L⁻¹ FUR with a low limit of detection, which was found to be 4.44 nmol L⁻¹ (1.47 ng mL⁻¹) for the 1^st peak and 3.88 nmol L⁻¹ (1.28 ng mL⁻¹) for the 2^nd one. The fabricated sensor exhibits a good reproducibility and selectivity and was applied successfully for the determination of FUR in its dosage forms and in spiked urine samples with good accuracy and precision.

A novel MnO₂ nanoparticles/chitosan-modified pencil graphite electrode (MnO₂ NPs/CS/PGE) was constructed using two different MnO₂ polymorphs (γ-MnO₂ and ε-MnO₂ nanoparticles).     

Co(OH)F nanorods@KxMnO2 nanosheet core–shell structured arrays for pseudocapacitor application

In this work, Co(OH)F nanorods@K_xMnO₂ nanosheet core–shell nanostructure was assembled on Ni foam by a facile hydrothermal method and incorporated with an electrodeposition process. Benefiting from their core–shell nanostructure and heterogeneous nanocomposites, the arrays present high areal capacitance up to 1046 mF cm⁻² at 1 mA cm⁻² and display a remarkable specific capacitance retention of 118% after 3000 cycles. When the current density increases to 10 mA cm⁻², the capacitance is 821 mF cm⁻² displaying a good rate capability. The excellent electrochemical properties allow them to be used as a promising electrode material for pseudocapacitors and display wide application potential in the field of electrochemical capacitors.

In this work, Co(OH)F nanorods@K_xMnO₂ nanosheet core–shell nanostructure was assembled on Ni foam by a facile hydrothermal method and incorporated with an electrodeposition process.     

Ultrafine MnO2 nanowires grown on RGO-coated carbon cloth as a binder-free and flexible supercapacitor electrode with high performance

Reduced graphene oxide coated carbon cloth has been used as a substrate for the growth of ultrafine MnO₂ nanowires (CC/RGO/MnO₂), forming binder-free and flexible supercapacitor electrode materials. The experimental results indicate that a maximum area-specific capacitance of 506.8 mF cm⁻² was gained from the CC/RGO/MnO₂ electrode at the current density of 0.128 mA cm⁻². Furthermore, the electrode exhibits excellent cycling stability (98.6% specific capacitance was still retained after 10 000 galvanostatic charge–discharge (GCD) tests when the current density was 1.28 mA cm⁻²). What''s more, the area-specific capacitance of the CC/RGO/MnO₂ electrode was hardly changed, when the electrode was operated under bending mechanical conditions. In addition, the charge storage performance and mechanism of the MnO₂ nanostructures was discussed.

Reduced graphene oxide coated carbon cloth has been used as a substrate for the growth of ultrafine MnO₂ nanowires (CC/RGO/MnO₂), forming binder-free and flexible supercapacitor electrode materials.     

Efficient coupling of MnO2/TiN on carbon cloth positive electrode and Fe2O3/TiN on carbon cloth negative electrode for flexible ultra-fast hybrid supercapacitors

Recent research and development of energy storage devices has focused on new electrode materials because of the critical effects on the electrochemical properties of supercapacitors. In particular, MnO₂ and Fe₂O₃ have drawn extensive attention because of their low cost, high theoretical specific capacity, environmental friendliness, and natural abundance. In this study, MnO₂ ultrathin nanosheet arrays and Fe₂O₃ nanoparticles are fabricated on TiN nanowires to produce binder-free core–shell positive and negative electrodes for a flexible and ultra-fast hybrid supercapacitor. The MnO₂/TiN/CC electrode shows larger pseudocapacitance contributions than MnO₂/CC. For example, at a scanning rate of 2 mV s⁻¹, the pseudocapacitance contribution of MnO₂/TiN/CC is 87.81% which is nearly 25% bigger than that of MnO₂/CC (71.26%). The supercapacitor can withstand a high scanning rate of 5000 mV s⁻¹ in the 2 V window and exhibits a maximum energy density of 71.19 W h kg⁻¹ at a power density of 499.79 W kg⁻¹. Even at 5999.99 W kg⁻¹, it still shows an energy density of 31.3 W h kg⁻¹ and after 10 000 cycles, the device retains 81.16% of the initial specific capacitance. The activation mechanism is explored and explained.

MnO₂ ultrathin nanosheet arrays and Fe₂O₃ nanoparticles are fabricated on carbon based TiN nanowires to produce binder-free and core–shell positive and negative electrodes for a flexible and ultra-fast hybrid supercapacitor.     

Nanostructured RuO2–Co3O4@RuCo-EO with low Ru loading as a high-efficiency electrochemical oxygen evolution catalyst

Electrochemical water splitting technology is considered to be the most reliable method for converting renewable energy such as wind and solar energy into hydrogen. Here, a nanostructured RuO₂/Co₃O₄–RuCo-EO electrode is designed via magnetron sputtering combined with electrochemical oxidation for the oxygen evolution reaction (OER) in an alkaline medium. The optimized RuO₂/Co₃O₄–RuCo-EO electrode with a Ru loading of 0.064 mg cm⁻² exhibits excellent electrocatalytic performance with a low overpotential of 220 mV at the current density of 10 mA cm⁻² and a low Tafel slope of 59.9 mV dec⁻¹ for the OER. Compared with RuO₂ prepared by thermal decomposition, its overpotential is reduced by 82 mV. Meanwhile, compared with RuO₂ prepared by magnetron sputtering, the overpotential is also reduced by 74 mV. Furthermore, compared with the RuO₂/Ru with core–shell structure (η = 244 mV), the overpotential is still decreased by 24 mV. Therefore, the RuO₂/Co₃O₄–RuCo-EO electrode has excellent OER activity. There are two reasons for the improvement of the OER activity. On the one hand, the core–shell structure is conducive to electron transport, and on the other hand, the addition of Co adjusts the electronic structure of Ru.

The optimized RuO₂/Co₃O₄–RuCo-EO electrode with Ru loading of 0.064 mg cm⁻² exhibits the excellent oxygen evolution activity with an overpotential of 220 mV at the current density of 10 mA cm⁻² and a Tafel slope of 59.9 mV dec⁻¹.     

Preparation of a SnO2–Sb electrode on a novel TiO2 network structure with long service lifetime for degradation of dye wastewater

Developing effective electrodes with long service lifetime for electrochemical degradation of dyes is of paramount importance for their practical industrial applications. We constructed a novel SnO₂–Sb electrode (Ti/TiO₂-NW/SnO₂–Sb electrode) based on a uniform TiO₂ network structure decorated Ti plate (Ti/TiO₂-NW) for a long-term electrocatalytic performance. The SnO₂–Sb coating layer on this electrode was grown on the Ti/TiO₂-NW by pulse electrodeposition. The introduction of the three-dimensional TiO₂-NW enhances the bonding strength between the Ti substrate and the SnO₂–Sb surface coating. An accelerated life test shows that the service life of Ti/TiO₂-NW/SnO₂–Sb electrode is 11.15 times longer than that of the traditional Ti/SnO₂–Sb electrode. The physicochemical properties of the electrodes were characterized through SEM, EDS, XRD and HRTEM. In addition, through LSV, EIS, CV and voltammetric charge analysis, it is found that compared with the traditional electrode, the Ti/TiO₂-NW/SnO₂–Sb electrode possesses a higher oxygen evolution potential, a lower charge transfer resistance and a larger electrochemical active surface area. Besides, this novel electrode also exhibits an outstanding electrocatalytic oxidation ability for degradation of acid red 73 in simulated sewage. After a 5 hours'' test, the removal efficiency of acid red 73 and the COD reached 98.6% and 71.8%, respectively, which were superior to those of Ti/SnO₂–Sb electrode (89.1% and 58.8%). This study highlights the excellent stability of the Ti/TiO₂-NW/SnO₂–Sb electrode and provides an energy-efficient strategy for dye degradation.

A novel TiO₂ network structure modified SnO₂–Sb electrode has been prepared by electrodeposition with long service lifetime and low energy consumption.     

High mass loading flower-like MnO2 on NiCo2O4 deposited graphene/nickel foam as high-performance electrodes for asymmetric supercapacitors

The implementation of high mass loading MnO₂ on electrochemical electrodes of supercapacitors is currently challenging due to the poor electrical conductivity and elongated electron/ion transport distance. In this paper, a NiCo₂O₄/MnO₂ heterostructure was built on the surface of three-dimensional graphene/nickel foam (GNF) by a hydrothermal method. The petal structured NiCo₂O₄ loaded on graphene played a wonderful role as a supporting framework, which provided more space for the growth of high mass loading MnO₂ microflowers, thereby increasing the utilization rate of the active material MnO₂. The GNF@NiCo₂O₄/MnO₂ composite was used as a positive electrode and achieved a high areal capacitance of 1630.5 mF cm⁻² at 2 mA cm⁻² in the neutral Na₂SO₄ solution. The asymmetric supercapacitor assembled with the GNF@NiCo₂O₄/MnO₂ positive electrode and activated carbon negative electrode possessed a wide voltage window (2.1 V) and splendid energy density (45.9 Wh kg⁻¹), which was attributed to the satisfactory electroactive area, low resistance, quick mass diffusion and ion transport caused by high mass loading MnO₂.

A NiCo₂O₄/MnO₂ heterostructure with high mass loading MnO₂ microflowers was built on the surface of 3D graphene/nickel foam for the preparation of an asymmetric supercapacitor with splended energy density (45.9 Wh kg⁻¹).     

High performance asymmetric supercapacitors based on Ti3C2Tx MXene and electrodeposited spinel NiCo2S4 nanostructures

Spinel metal sulfides have been investigated for a wide range of applications mostly in electrochemical energy storage owing to their better electronic conductivity and high reversible redox activity. Herein, we report a facile fabrication approach for the binder-free supercapacitor electrodes based on spinel NiCo₂S₄ (NCS) on various substrates such as Cu-foil (CF), Ni-foam (NF), and vertical graphene nanosheets grown on carbon tape (VG) via a single step-controlled electrodeposition technique. The obtained electrodeposited NiCo₂S₄ grown on Cu-foil (denoted as CF-NCS) in symmetric assembly shows a high specific capacitance of 167.28 F g⁻¹ compared to NCS grown on Ni-foam and VG substrates, whereas, symmetric NiCo₂S₄ grown on a VG substrate device exhibits better cycling performance (81% for 3000 cycles) compared to CF-NCS and NF-NCS. Furthermore, an asymmetric supercapacitor was assembled in combination with MXene (Ti₃C₂T_x) as a negative electrode (denoted as TCX). As a result, the CF-NCS//TCX device exhibits a high areal capacitance of 48.6 mF cm⁻² at 2 mA cm⁻² of current density. We also report good specific capacitance of 54.57 F g⁻¹ at 2 A g⁻¹; in addition, the CF-NCS//TCX assembly delivers maximum areal and gravimetric energy density of 14.86 mWh cm⁻² and 14.86 Wh kg⁻¹ respectively. In contrast, the VG-NCS//TCX device showed improved cycling stability with 85% of capacitance retention over 5000 cycles owing to its highly porous structure and multiple conductive networks in the VG substrate and provides structural stability to NCS with fast ion diffusion. This experiment favors 2D MXene as a capacitive electrode that provides a replacement for carbon-based electrodes in asymmetric assembly with superior electrochemical performance. Hence, the hierarchical NCS structure grown on the various substrates in combination with MXene serve as a promising material for energy storage application.

Spinel metal sulfides have been investigated for a wide range of applications mostly in electrochemical energy storage owing to their better electronic conductivity and high reversible redox activity.     

Novel mesoporous Co3O4–Sb2O3–SnO2 active material in high-performance capacitive deionization

Capacitive deionization (CDI), as an emerging eco-friendly electrochemical brackish water deionization technology, has widely benefited from carbon/metal oxide composite electrodes. However, this technique still requires further development of the electrode materials to tackle the ion removal capacity/rate issues. In the present work, we introduce a novel active carbon (AC)/Co₃O₄–Sb₂O₃–SnO₂ active material for hybrid electrode capacitive deionization (HECDI) systems. The structure and morphology of the developed electrodes were determined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Brunauer–Emmett–Teller (BET)/Barrett–Joyner–Halenda (BJH) techniques, as well as Fourier-transform infrared (FT-IR) spectroscopy. The electrochemical properties were also investigated by cyclic voltammetry (CV) and impedance spectroscopy (EIS). The CDI active materials AC/Co₃O₄ and AC/Co₃O₄–Sb₂O₃–SnO₂ showed a high specific capacity of 96 and 124 F g⁻¹ at the scan rate of 10 mV s⁻¹, respectively. In addition, the newly-developed electrode AC/Co₃O₄–Sb₂O₃–SnO₂ showed high capacity retention of 97.2% after 2000 cycles at 100 mV s⁻¹. Moreover, the electrode displayed excellent CDI performance with an ion removal capacity of 52 mg g⁻¹ at the applied voltage of 1.6 V and in a solution of potable water with initial electrical conductivity of 950 μs cm⁻¹. The electrode displayed a high ion removal rate of 7.1 mg g⁻¹ min⁻¹ with an excellent desalination–regeneration capability while retaining about 99.5% of its ion removal capacity even after 100 CDI cycles.

Capacitive deionization (CDI), as an emerging eco-friendly electrochemical brackish water deionization technology, has widely benefited from carbon/metal oxide composite electrodes.     

Robust catalytically-activated LSM-BCZY-based composite steam electrodes for proton ceramic electrolysis cells

Backbone electrodes based on an electronic conductor and a protonic conductor show advantages for proton ceramic electrolyzer cells (PCECs). This work, aims to shed further light on the nature of the rate determining steps in the anode operation and improve the reaction rate in high steam pressure electrolysis mode by (i) adjusting their catalytic activity through electrode infiltration with catalytic electronic-conducting nanoparticles; and (ii) electrochemical activation of surface species by applying a net current through the electrode. A composite formed by La_0.8Sr_0.2MnO_3−δ (LSM) and BaCe_0.2Zr_0.7Y_0.1O_3−δ (BCZY27) was deposited on proton-conducting BCZY27 electrolytes and studied in symmetrical cells to investigate the anode microstructure and electrochemical performance. Electrochemical impedance spectroscopy (EIS) measurements were performed in the 800–500 °C range under 3 bar of pressure of wet air (75% of steam). LSM/BCZY27 50/50 vol% showed the best performance with an electrode polarization resistance (R_p) of 6.04 Ω cm² at 700 °C and high steam pressure (0.75 bar of air and 2.25 bar of steam) whereas LSM/BCZY27 60/40 vol% presented a R_p of 18.9 Ω cm². The backbone electrodes were infiltrated using aqueous solutions of metal precursors to boost the electrocatalytic activity towards water splitting and oxygen evolution. The infiltrated cells were fired at 850 °C for 2 h to obtain the desired crystalline nanoparticles (Pr₆O₁₁, CeO₂, ZrO₂ and Pr₆O₁₁–CeO₂) and electrochemically tested under high steam pressures and bias currents to investigate the influence of catalytic activation on surface exchange kinetics. Among the tested catalysts, the lowest electrode polarization resistances (<0.2 Ω cm²) were reached for the Pr₆O₁₁, CeO₂ and Pr₆O₁₁–CeO₂ catalysts at 700 °C by applying current densities ranging from 1.57 to 14.15 mA cm⁻², and the Pr₆O₁₁–CeO₂-activated LSM/BCZY27 electrode exhibited the best performance. Finally, the effect of pO₂ and pH₂O was investigated aiming to characterize the rate limiting processes in the electrodes.

The infiltration of different catalytically-activated nanoparticles into LSM/BCZY27 backbone enabled to reduce the electrode polarization resistance towards water splitting and oxygen evolution under operation at high steam pressures (up to 5 bar).     

Nano-porous Al/Au skeleton to support MnO2 with enhanced performance and electrodeposition adhesion for flexible supercapacitors

A nano-porous Al/Au skeleton is constructed to effectively improve the utilization rate of the active MnO₂ and the overall adhesion between the current collector and MnO₂ in an electrodeposition system. The Al/Au current collector is prepared by first forming a nano-porous structure on the surface of Al foil through etching modification, and subsequently coating an ultra-thin Au layer onto the Al foil. The active MnO₂ is electrodeposited on the Al/Au current collector to fabricate a novel Al/Au/MnO₂ electrode. The nano-porous skeleton supports MnO₂ to grow autonomously inside-out. The ultra-thin Au layer acts as a transition layer to improve the overall conductivity of the current collector (0.35 Ω m⁻¹) and to improve the adhesion with MnO₂ as well. Owing to the highly porous structure, the electrochemical properties of the electrode are greatly improved, as evidenced by a remarkable specific capacitance of 222.13 mF cm⁻² at 0.2 mA cm⁻² and excellent rate capability of 63% capacitance retention at 6.0 mA cm⁻². Furthermore, the assembled solid-state symmetric supercapacitor exhibits a high energy density of 0.68 mW h cm⁻³, excellent cyclic stability (86.3% capacitance retention after 2000 cycles), and prominent flexibility.

A nano-porous Al/Au skeleton is constructed to effectively improve the utilization rate of the active MnO₂ and the overall adhesion between the current collector and MnO₂ in an electrodeposition system.     

Asymmetric faradaic assembly of Bi2O3 and MnO2 for a high-performance hybrid electrochemical energy storage device

In the current study, we have explored the coupling of Bi₂O₃ negative electrode and MnO₂ positive electrode materials as an asymmetric faradaic assembly for a high-performance hybrid electrochemical energy storage device (HEESD). Aiming at a low-cost device, both the electrodes have been synthesized by a simple, scalable, and cost-effective chemical synthesis method. After their requisite structure-morphological confirmation and correlation, these electrodes were separately examined for their electrochemical performance in a three-electrode configuration. The results obtained confirm that Bi₂O₃ and MnO₂ exhibit 910 C g⁻¹ and 424 C g⁻¹ specific capacity, respectively, at 2 A g⁻¹ current density. Notably, the performance of both electrodes has been analyzed using Dunn''s method to highlight the distinct nature of their faradaic properties. Afterwards, the asymmetric faradaic assembly of both electrodes, when assembled as a HEESD (MnO₂//Bi₂O₃), delivered 411 C g⁻¹ specific capacity at 1 A g⁻¹ current density due to the inclusive contribution from the capacitive as well as the non-capacitive faradaic quotient. Consequently, the assembly offers an excellent energy density of 79 W h kg⁻¹ at a power density of 702 W kg⁻¹, with a magnificent retention of energy density up to 21.1 W h kg⁻¹ at 14 339 W kg⁻¹ power density. Moreover, it demonstrates long-term cycling stability at 10 A g⁻¹, retaining 85.2% of its initial energy density after 5000 cycles, which is significant in comparison with the previously reported literature. Additionally, to check the performance of the device in real time, two HEESDs were connected in series to power a light-emitting diode. The results obtained provide significant insight into hybrid coupling, where two different faradaic electrodes can be combined in a synergistic combination for a high-performance HEESD.

A hybrid electrochemical energy storage device assembled with faradaic Bi₂O₃ and MnO₂ electrodes exhibits superior electrochemical performance with a high energy density of 79 W h kg⁻¹ at a power density of 702 W kg⁻¹.     

Hybrid ZnO–graphene electrode with palladium nanoparticles on Ni foam and application to self-powered nonenzymatic glucose sensing

A self-powered nonenzymatic glucose sensor electrode boasts the advantages of both a glucose sensor and fuel cell. Herein, an electrode composed of ZnO–graphene hybrid materials on nickel foam (NF) is prepared by electrodeposition of Pd NPs. The electrode is characterized systematically and the dependence of electrocatalytic oxidation of glucose on the concentrations of KOH and glucose, temperature, and potential limit in the anodic direction is investigated. The Pd/NF-ZnO–G electrode shows high catalytic activity, sensitivity, stability, and selectivity in glucose detection, as exemplified by an electrocatalytic glucose oxidation current of 222.2 mA cm⁻² under alkaline conditions, high linearity in the glucose concentration range from 5 μM to 6 mM (R² = 0.98), and high sensitivity of 129.44 μA mM⁻¹⁻¹ cm⁻². The Pd/NF-ZnO–G electrode which exhibits superior electrocatalytic activity under alkaline conditions has large potential in nonenzymatic glucose sensing and direct glucose fuel cells and is suitable for miniaturized self-powered nonenzymatic glucose sensing.

A self-powered nonenzymatic glucose sensor electrode boasts the advantages of both a glucose sensor and fuel cell.     

MnO2/ZnCo2O4 with binder-free arrays on nickel foam loaded with graphene as a high performance electrode for advanced asymmetric supercapacitors

ZnCo₂O₄ nanosheets were successfully arrayed on a Ni foam surface with graphene using a hydrothermal method followed by annealing treatment; then MnO₂ nanoparticles were electrodeposited on the ZnCo₂O₄ nanosheets to obtain a synthesized composite binder-free electrode named MnO₂/ZnCo₂O₄/graphene/Ni foam (denoted as MnO₂/ZnCo₂O₄/G/NF). After testing the binder-free composite electrode of MnO₂/ZnCo₂O₄/G/NF via cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy testing, we found that it exhibited ultrahigh electrochemical properties, with a high specific areal capacitance of 3405.21 F g⁻¹ under a current density of 2 A g⁻¹, and wonderful cycling stability, with 91.2% retention after 5000 cycles. Moreover, an asymmetric supercapacitor (ASC) based on MnO₂/ZnCo₂O₄/G/NF//G/NF was successfully designed. When tested, the as-designed ASC can achieve a maximum energy density of 46.85 W h kg⁻¹ at a power density of 166.67 W kg⁻¹. Finally, the ASC we assembled can power a commercial red LED lamp successfully for more than 5 min, which proves its practicability. All these impressive performances indicate that the MnO₂/ZnCo₂O₄/graphene composite material is an outstanding electrode material for electrochemical capacitors.

Schematic illustration of formation process of MnO₂/ZnCo₂O₄/G/NF composite electrode.     

A comparison study of MnO2 and Mn2O3 as zinc-ion battery cathodes: an experimental and computational investigation

The high specific capacity, low cost and environmental friendliness make manganese dioxide materials promising cathode materials for zinc-ion batteries (ZIBs). In order to understand the difference between the electrochemical behavior of manganese dioxide materials with different valence states, i.e., Mn(iii) and Mn(iv), we investigated and compared the electrochemical properties of pure MnO₂ and Mn₂O₃ as ZIB cathodes via a combined experimental and computational approach. The MnO₂ electrode showed a higher discharging capacity (270.4 mA h g⁻¹ at 0.1 A g⁻¹) and a superior rate performance (125.7 mA h g⁻¹ at 3 A g⁻¹) than the Mn₂O₃ electrode (188.2 mA h g⁻¹ at 0.1 A g⁻¹ and 87 mA h g⁻¹ at 3 A g⁻¹, respectively). The superior performance of the MnO₂ electrode was ascribed to its higher specific surface area, higher electronic conductivity and lower diffusion barrier of Zn²⁺ compared to the Mn₂O₃ electrode. This study provides a detailed picture of the diversity of manganese dioxide electrodes as ZIB cathodes.

MnO₂ and Mn₂O₃ cathodes for zinc ion batteries were experimentally and computationally explored.     

Novel construction of carbon nanofiber/CuCrO2 composite for selective determination of 4-nitrophenol in environmental samples and for supercapacitor application

A simple hydrothermal process has been used to prepare a carbon nanofiber/copper chromium dioxide (CNF/CuCrO₂) composite for the selective detection of 4-nitrophenol (4-NP) and supercapacitor applications. The electrochemical sensor was developed with a glassy carbon electrode (GCE) modified with the CNF/CuCrO₂ composite by the drop-casting method. The structural formation of the prepared materials was confirmed by infrared spectroscopy, electrochemical impedance spectroscopy, Raman spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. To investigate the electrochemical efficiency of the electrode, various electroanalytical techniques, namely, differential pulse voltammetry (DPV), cyclic voltammetry (CV) and galvanostatic charge–discharge tests, were employed. The GCE/CNF/CuCrO₂ modified electrode exhibited excellent electrocatalytic behavior for the detection of 4-NP under optimized conditions with a low detection limit (0.022 μM), long linear response range of 0.1–150 μM, and high sensitivity (20.02 μA μM⁻¹ cm⁻²). The modified electrode was used for the detection of 4-NP in real samples with satisfactory results. In addition, the GCE/CNF/CuCrO₂ electrode has advantages such as stability, reproducibility, repeatability, reliability, low cost, and practical application. The CNF/CuCrO₂ composite coated Ni-foam electrodes also exhibited excellent supercapacitor efficiency, with a high specific capacitance of up to 159 F g⁻¹ at a current density of 5 A g⁻¹ and outstanding cycling stability. Hence, the CNF/CuCrO₂ composite is a suitable material for 4-NP sensors and energy storage applications.

A simple hydrothermal process has been used to prepare a carbon nanofiber/copper chromium dioxide (CNF/CuCrO₂) composite for the selective detection of 4-nitrophenol (4-NP) and supercapacitor applications.     

Rational design of asymmetric supercapacitors via a hierarchical core–shell nanocomposite cathode and biochar anode

Hierarchical MnO₂ nanosheets attached on hollow NiO microspheres have been designed by a facile hydrothermal process. The core–shell structure is achieved by decorating an MnO₂ nanosheet shell on a hollow NiO sphere core. The highly hollow and porous structure exhibits a high surface area, shortened ion diffusion length, outstanding electrochemical properties (558 F g⁻¹ at a current density of 5 mA cm⁻²), and excellent cycling stability (83% retention after 5000 cycles). To further evaluate the NiO/MnO₂ core–shell composite electrode for real applications, three asymmetric supercapacitors (NiO/MnO₂//pomelo peel (PPC), NiO/MnO₂//buckwheat hull (BHC), and NiO/MnO₂//activated carbon (AC)) are assembled. The results demonstrated that NiO/MnO₂//BHC delivered a substantial energy density (20.37 W h kg⁻¹ at a power density of 133.3 W kg⁻¹) and high cycling stability (88% retention after 5000 cycles) within a broad operating potential window of 1.6 V.

Hierarchical MnO₂ nanosheets standing on hollow NiO microspheres have been designed by a facile hydrothermal process. Furthermore, asymmetric supercapacitors via core/shell NiO/MnO₂ cathode and biochar anode were assembled.