A cross-linked sheet structured poly(3,4-ethylenedioxythiophene) grown on Ni foam: Morphology control and application for long-life cyclic asymmetric supercapacitor

In this work, a cross-linked sheet structured conducting polymer ploy(3,4-ethylenedioxythiophene) (PEDOT) decorated on Ni foam is synthesized via one-step electrodeposition using the sodium p-toluenesulfonate (STSA) as surfactant and applied for supercapacitor electrode. The surfactants play a vital role in controlling the morphologies of PEDOT leading to the electrochemical performance difference. The optimized PEDOT electrode exhibits the highest capacitance of 711.6 mF cm⁻² at 3.0 mA cm⁻² in the three-electrode system. An asymmetric device (PEDOT/STSA//AC) is constructed by PEDOT/STSA (the positive electrode), activated carbon (AC) (the negative electrode) as well as 1 M Na₂SO₄ (the electrolyte). The device has been worked in a high-voltage range of 0–1.5 V, which displays the satisfied energy density of 14.0 Wh·kg⁻¹ at 535.5 W kg⁻¹. Furthermore, the PEDOT/STSA//AC device presents excellent rate capability and long-time cyclic stability.     

Phase-separated polymer electrolyte based on poly(vinyl chloride)/poly(ethyl methacrylate) blend

The characteristics of polymer electrolytes based on a poly(vinyl chloride) (PVC)/poly(ethyl methacrylate) (PEMA) blend are reported. The PVC/PEMA based polymer electrolyte consists of an electrolyte-rich phase that acts as a conducting channel and a polymer-rich phase that provides mechanical strength. The dual phase was simply developed by a single-step coating process. The mechanical strength of the PVC/PEMA based polymer electrolyte was found to be much higher than that of a previously reported PVC/PMMA-based polymer electrolyte (poly(methyl methacrylate), PMMA) at the same PVC content, and even comparable with that of the PVC-based polymer electrolyte. The blended polymer electrolytes showed ionic conductivity of higher than 10⁻³ S cm⁻¹ and electrochemical stability up to at least 4.3 V. A prototype battery, which consists of a LiCoO₂ cathode, a MCMB anode, and PVC/PEMA-based polymer electrolyte, gives 92% of the initial capacity at 100 cycles upon repeated charge–discharge at the 1 C rate.     

Bi-doped La1.5Sr0.5Ni0.5Mn0.5O4+δ as an efficient air electrode material for SOEC

Bi-doped La_1.5-xBi_xSr_0.5Ni_0.5Mn_0.5O_4+δ (LBSNM-x, x = 0, 0.05, 0.1, 0.15) was investigated as a potential air electrode for solid oxide electrolysis cell (SOEC). The effect of Bi doping on the structure, electrical conductivity, chemical compatibility with GDC electrolyte, electrochemical performance and thermal expansion coefficients (TECs) were investigated. XRD characterization results show that the solid solution content of Bi is less than or equal to 0.1. XPS characterization results indicate that Bi doping increases the oxygen vacancy content of LBSNM-x air electrode and thus greatly benefits its oxygen evolution reaction. Among the Bi-doped samples, LBSNM-0.1 electrode has the best electrochemical performance with its lowest Rp (polarization resistance) of 0.28 Ω cm² at 800 °C based on LBSNM-0.1/GDC half-cell. LBSNM-0.1 single cell with 70%CO₂ + 30%CO fuel gas feed on the fuel electrode has achieved current density of 811 mA cm⁻² at 800 °C and 1.4 V, a 62.2% increase relative to that of LSNM single cell. In addition, LBSNM-0.1 single cell exhibits excellent stability at 800 °C and 1.3 V with 70%CO₂ + 30%CO feed gas on the fuel electrode. These results prove that Bi-doped LBSNM-0.1 is an efficient air electrode for SOEC.     

Optimal catalyst layer structure of polymer electrolyte membrane fuel cell

In a membrane electrode assembly (MEA) of polymer electrolyte membrane fuel cells, the structure and morphology of catalyst layers are important to reduce electrochemical resistance and thus obtain high single cell performance. In this study, the catalyst layers fabricated by two catalyst coating methods, spraying method and screen printing method, were characterized by the microscopic images of catalyst layer surface, pore distributions, and electrochemical performances to study the effective MEA fabrication process. For this purpose, a micro-porous layer (MPL) was applied to two different coating methods intending to increase single cell performances by enhancing mass transport. Here, the morphology and structure of catalyst layers were controlled by different catalyst coating methods without varying the ionomer ratio. In particular, MEA fabricated by a screen printing method in a catalyst coated substrate showed uniformly dispersed pores for maximum mass transport. This catalyst layer on micro porous layer resulted in lower ohmic resistance of 0.087 Ω cm² and low mass transport resistance because of enhanced adhesion between catalyst layers and a membrane and improved mass transport of fuel and vapors. Consequently, higher electrochemical performance of current density of 1000 mA cm^-2 at 0.6 V and 1600 mAcm⁻² under 0.5 V came from these low electrochemical resistances comparing the catalyst layer fabricated by a spraying method on membranes because adhesion between catalyst layers and a membrane was much enhanced by screen printing method.     

Co,Fe-ions intercalated Ni(OH)2 network-like nanosheet arrays as highly efficient non-noble catalyst for electro-oxidation of urea

Developing a highly active, low-cost, and durable nanostructured catalytic material is of significant interest in fuel cell applications owing to its efficient energy conversion, ease of preparation and operation, and reduced emission of pollutants. In this work, various ratio (0.01, 0.03, and 0.05 mmol) of cobalt (Co), and iron (Fe) doped nickel hydroxide (Ni(OH)₂) nanosheet arrays were grown on Ni foam surface (Co–Ni(OH)₂ and Fe–Ni(OH)₂) via a simple one-step process. The Co–Ni(OH)₂ and Fe–Ni(OH)₂ nanosheet array on Ni foam electrodes were explored as potential candidate towards electro-oxidation of urea. Notably, 0.03 mmol Co doped Ni(OH)₂/Ni foam electrode displayed lowest-onset oxidation potential (0.21 V) and enhanced electro-oxidation of urea (59.7 mA) owing to its large amount of electrocatalytic active sites, densely assembled nanosheet array structures with porous surfaces, and electronic diffusion channels, which might promote interface electrochemical reaction. In addition, synergistic effect between Co metal with Ni(OH)₂ has also promotes enhanced electro-oxidation of urea in contrast to Fe–Ni(OH)₂ nanosheet array, Ni(OH)₂, and Ni foam electrodes. Chronoamperometric i-t curve of Co–Ni(OH)₂/Ni foam electrode obviously exhibited higher catalytic current, highly stable and durable properties in contrast to Fe–Ni(OH)₂ nanosheet arrays. As-fabricated Co–Ni(OH)₂/Ni foam can be explored as a new type of potential low-cost catalyst for electro-oxidation of urea, which reveals promising use in future fuel cell energy applications.     

Photocured PEO-based solid polymer electrolyte and its application to lithium–polymer batteries

A solid polymer electrolyte (SPE) based on polyethylene oxide (PEO) is prepared by photocuring of polyethylene glycol acrylates. The conductivity is greatly enhanced by adding low molecular weight poly(ethylene glycol) dimethylether (PEGDME). The maximum conducticity is 5.1×10⁻⁴ S cm⁻¹ at 30°C. These electrolytes display oxidation stability up to 4.5 V against a lithium reference electrode. Reversible electrochemical plating/stripping of lithium is observed on a stainless steel electrode. Li/SPE/LiMn₂O₄ as well as C(Li)/SPE/LiCoO₂ cells have been fabricated and tested to demonstrate the applicability of the resulting polymer electrolytes in lithium–polymer batteries.     

Gel-type polymer electrolytes with different types of ceramic fillers and lithium salts for lithium-ion polymer batteries

Gel-type polymer electrolytes are prepared using PVdF/PEGDA/PMMA, LiPF₆/LiCF₃SO₃ mixed lithium salts and ceramic fillers such as Al₂O₃, BaTiO₃ and TiO₂. The electrochemical properties of these electrolytes, such as electrochemical stability, ionic conductivity and compatibility with electrodes are investigated in addition to the physical properties. The charge–discharge performances of lithium-ion polymer batteries using these get-type polymer electrolytes are investigated. The gel-type polymer electrolytes containing a mixed lithium salt of LiPF₆/LiCF₃SO₃ (10/1, wt.%) exhibit more stable ionic conductivity and lower interfacial resistance than those containing only LiPF₆. In addition, an Al₂O₃ filler improves interfacial stability between the electrode and the polymer electrolyte. Stacking cells (MCMB 1028/LiCoO₂, 8 cm × 13 cm × 7 ea) composed of gel-type polymer electrolytes based on PVdF/PEGDA/PMMA, LiPF₆/LiCF₃SO₃ (10/1, wt.%) and Al₂O₃ filler maintain 95% of initial capacity after 100 cycles at a C/2 rate.     

A pH-differential dual-electrolyte microfluidic electrochemical cells for CO2 utilization

CO₂ can be converted to useful fuels by electrochemical processes. As an effective strategy to address greenhouse effect and energy storage shortage, electrochemical reduction of CO₂ still needs major improvements on its efficiency and reactivity. Microfluidics provides the possibility to enhance the electrochemical performance, but few studies have focused on the virtual interface. This work demonstrates a dual electrolyte microfluidic reactor (DEMR) that improves the thermodynamic property and raises the electrochemical performance based on a laminar flow membrane-less architecture. Freed from hindrances of a membrane structure and thermodynamic limitations, DEMR could bring in 6 times higher reactivity and draws electrode potentials closer to the equilibrium status (corresponded to less electrode overpotentials). The cathode potential was reduced from −2.1 V to −0.82 V and the anode potential dropped from 1.7 V to 1 V. During the conversion of CO₂, the peak Faradaic and energetic efficiencies were recorded as high as 95.6% at 143 mA/cm² and 48.5% at 62 mA/cm², respectively, and hence, facilitating future potential for larger-scale applications.     

Electro-oxidation of methanol based on electrospun PdO–Co3O4 nanofiber modified electrode

We presented a modified electrode based on electrospun PdO–Co₃O₄ nanofiber composite for electro-oxidation of methanol in alkaline media. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were adopted to characterize the structures and composition of the composite modified electrodes. The influential factors such as the component and amounts of nanofibers were also studied. After electrochemical pretreatment, the Nafion/PdO–Co₃O₄/GCE (the atomic ratio of Pd:Co = 2:1) exhibited the greatest electrocatalytic activity toward methanol electro-oxidation among the electrodes investigated. The present novel strategy is expected to reduce the cost of the catalyst of methanol electro-oxidation remarkably.     

Enhanced membrane electrode assembly performance by adding PTFE/Carbon black for high temperature polymer electrolyte membrane fuel cell

Phosphoric acid used as a proton-conductive medium in high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) poisons the Pt surface and prevents oxygen transport in the cathode catalyst layer. The hydrophobic binders in the catalyst not only maintain the catalyst layer structure but also control the phosphoric acid distribution. In this study, polytetrafluoroethylene (PTFE)/carbon black (Vulcan XC-72R) added to the catalyst layer generates an oxygen transport channel. The catalyst layers coated on the gas diffusion layer by the bar-coating method serve as the cathode. High PTFE content causes hydrophobicity in the catalyst layer. The membrane electrode assembly (MEA) with 6 wt% PTFE/Vulcan results in the highest peak power density (0.347 W cm⁻²) and voltage (0.653 V) at 0.2 A cm⁻². A critical reason for its high performance is having the lowest R_ct + R_mt values measured at 0.6 V and 0.4 V. These results could contribute to improving the MEA performance for HT-PEMFCs.     

Electrostatic spray catalytic particle coating on carbon electrode for enhancing electrochemical reaction

The uniform coating of catalytic materials on the electrode surface is essential for improving the performance of electrochemical reactions. In this study, the electrostatic spray coating technique is used to deposit Molybdenum disulfide (MoS₂) particles on carbon electrodes and examine the electrochemical hydrogen evolution reaction (HER) performance in a 0.1 M H₂SO₄ electrolyte. The experimental results reveal that the electrostatic spray coating method achieves a more uniform coating MoS₂ catalyst particles on the carbon fiber substrate. It provides good adhesion for electrocatalyst binding on the carbon paper electrodes. During HER analysis, a 25% higher current density is obtained from the electrostatic spray-coated electrodes compared to the manual spray-coated electrode at a potential of 0.95 V. Electrochemical impedance spectroscopy, and electrochemical surface area measurements indicate the superior electrochemical characteristics of the electrostatic spray-coated electrode. The faradaic efficiency of the electrostatic spray-coated electrode is close to 100% at a high applied potential of −1.6 V with a 0.0059 L volume of hydrogen generation. Moreover, chronoamperometric measurements demonstrate the excellent durability of the electrostatic spray-coated carbon electrodes. This study suggests that the facile electrostatic spray method is efficient for coating electrodes with high uniformity and good adhesion for various electrochemical applications.     

Gelled composite electrolyte comprising thermoplastic polyurethane and poly(ethylene oxide) for lithium batteries

Composite polymer electrolyte films consisting of poly(ethylene glycol) based thermoplastic polyurethane blended with poly(ethylene oxide) (denoted as TPU(PEG)/PEO) incorporating LiClO₄–PC have been prepared and their electrochemical properties were studied. The thermal analysis of the composite films were performed to demonstrate the miscibility of the polymer blend by using differential scanning calorimeter (DSC). TPU(PEG)/PEO based polymer electrolyte shows ionic conductivity of the order 6.4×10⁻⁴ S/cm at room temperature, irrespective of time evolution. Cyclic voltammogram shows that this composite electrolyte has good electrochemical stability in the working voltage ranging from 2 to 4.5 V. Cycling performances of Li/polymer electrolyte/LiCoO₂ cells are also followed. From AC impedance results, the recharging ability of the cells is proved to be dominated by the passive layer formation at Li electrode–polymer electrolyte interface.     

Enhancing photoelectrochemical activity of nanocrystalline WO3 electrodes by surface tuning with Fe(Ⅲ)

Tungsten oxide (WO₃) photoelectrodes with the surface tuned by Fe(Ⅲ) for photoelectrochemical water splitting were successfully synthesized. Nanostructured WO₃ films were prepared using doctor blade method, then a facile and economical deposition-annealing process was employed to fabricate Fe(Ⅲ) modified WO₃ films. The resulting composite's structural and optical properties were analyzed by SEM, EDX, XRD, UV–Vis spectrometry and XPS. The photoelectrochemical properties were evaluated by photocurrent density under 500 W Xe lamp with an intensity of 100 mW/cm². The Fe(Ⅲ) modified WO₃ electrode exhibited a larger photocurrent than the pure WO₃ electrode. Significantly, the optimized Fe(Ⅲ) modified WO₃ film achieved the maximum photocurrent density of 1.18 mA/cm² at 0.8 V vs. Ag/AgCl in the 0.2 M Na₂SO₄. The enhanced photocurrent was attributed to the extension of the light response and the electron hole separation at the interface Fe(Ⅲ)/WO₃ which was confirmed by Mott–Schottky and electrochemical impedance spectroscopy.     

A highly efficient A-site deficient perovskite interlaced within two dimensional MXene nanosheets as an active electrocatalyst for hydrogen production

We report a unique composite of La_0.4Sr_0.4Ti_0.9Ni_0.1O_3-δ (LSTN) nanoparticles interlaced with two dimensional Ti₃C₂T_x (MXene) nanosheets, providing high conductivity. LSTN heterostructure synthesized by the sol-gel method produces a large oxygen vacancy and creates a variable valence state while, MXene synthesized from Hydrofluoric acid (HF) treatment resulted in a highly hydrophilic and conductive surface, thereby enhancing the charge transferability. For OER, the LSTN/MXene 66.67% electrode exhibits a benchmark of 10 mA cm^?2 at a potential of 1.56 (V vs RHE) in 1 M KOH. It has exhibited the lowest Tafel slope of 44 mV dec^?1 and highest mass activity (60 mA g^?1 @ 1.59 V) due to quicker ions diffusion and increased available exposed area. Moreover, the efficient LSTN/MXene 66.67% electrode showed good long-term durability during a 24 h stability test at a current density of 100 mA cm^?2. The strong interfacial interaction and high charge transfer among LSTN nanoparticles and 2D MXene nanosheets not only provide good structural strength to the composite but also improves the redox activity of LSTN/MXene 66.67% catalyst towards OER. This work provides improved conductive properties of perovskite by developing a composite of perovskite and MXene, that has significantly enhanced electrochemical properties of the catalyst by undergoing fast kinetics.     

Honeycomb micro/nano-architecture of stable β-NiMoO4 electrode/catalyst for sustainable energy storage and conversion devices

Multi-functionality is a highly desirable feature in designing new electrode material for both energy storage and conversion devices. Here, we report a well-integrated and stable β-NiMoO₄ that was fabricated on three dimensional (3D) nickel foam (NF) by a simple hydrothermal approach. The obtained β-NiMoO₄ with interesting honeycomb like interconnected nanosheet microstructure leads to excellent electrochemical activity. As an electrode for Supercapatteries, β-NiMoO₄–NF showed a high specific capacity of 178.2 mA h g⁻¹ (916.4 F g⁻¹) at 5 mA cm⁻² current density. Most importantly, the fabricated symmetric device exhibits a maximum specific energy of 35.8 W h kg⁻¹ with the power output of 981.56 W kg^-1 and excellent cyclic stability. In methanol electro-oxidation, the β-NiMoO₄ –NF catalyst deliver the high current density of 41.8 mA cm⁻² and much lower onset potential of 0.29 V with admirable long term stability. Apart from the above electrochemical activity, the β-NiMoO₄ –NF honeycomb microstructure demonstrates a promising non-noble electrocatalyst for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and showed a considerable overpotential of 351 mV (OER) and 238 mV (HER). The attractive multifunctional electrochemical activity of β-NiMoO₄–NF could be originates from their unique honeycomb micro/nano structure which can acts as an “ion reservoir” and thus leads to superior energy storage and conversion processes.     

Tantalum nitride coated AISI 316L as bipolar plate for polymer electrolyte membrane fuel cell

Tantalum nitride (TaN) thin films are deposited on AISI 316L stainless steel by inductively coupled, plasma-assisted, reactive magnetron sputtering at various N₂ flow rates. TaN film behavior is investigated in simulated polymer electrolyte membrane fuel cell (PEMFC) conditions by using electrochemical measurement techniques for application as bipolar plates. The results of a potentio-dynamic polarization test under PEMFC cathodic and anodic conditions indicate that the corrosion current density of the TaN_x films is of the order of 10⁻⁷ A cm⁻² (at 0.6 V) and 10⁻⁸ A cm⁻² (at −0.1 V), respectively; these results are considerably better than the individual results for metallic Ta films and AISI 316L stainless steel. The TaN_x films exhibit superior stability in a potentio-static polarization test performed under PEMFC cathodic and anodic conditions. The interfacial contact resistance of the films is measured in the range of 50-150 N cm⁻², and the lowest value is 11 mΩ cm² at a compaction pressure of 150 N cm⁻².     

Cycling and at-rest stabilities of a complementary electrochromic device containing poly(3,4-ethylenedioxythiophene) and Prussian blue

PEDOT-based electrochromic devices (ECDs) have been investigated intensively in recent years. In order to obtain an ECD having long cycle life, the counter electrode and electrolyte used should be compatible in the electrochemical environment. Prussian blue (PB) is proven to be electrochemically stable when cycling in non-aqueous solutions. Thus a new organic-inorganic complementary ECD was assembled in combination with a PMMA-based gel polymer electrolyte. This ECD exhibited deep blue-violet when applying −2.1 V and became light blue when applying 0.6 V. Under these conditions, the transmittance of the ECD at 590 nm changed from 13.8% (−2.1 V) to 60.5% (+0.6 V) with a coloration efficiency of 338 cm²/C. The cell retained 55% of its maximum transmittance window (ΔT_max) after 50,640 repeated cycles. Moreover, the at-rest stability test revealed a transmittance window (ΔT) decay of 9.6% over a period of 107 days. Therefore, the proposed PEDOT-PB ECD may have potential for practical applications.     

Development of NiMH-based Fuel Cell/Battery (FCB) system: Characterization of Ni(OH)2/MnO2 positive electrode for FCB

The performance of the positive electrode composed of a mixture of nickel hydroxide (Ni(OH)₂) and a small amount of manganese dioxide (MnO₂) was investigated for the positive electrode of Fuel Cell/Battery (FCB) system. It was found that the positive electrode can function not only as an active material of secondary batteries when it is charged but also as a catalyst of fuel cells when oxygen is supplied, which was confirmed by the following characterization: electrochemical characterization was performed with cyclic voltammetry (CV) and galvanostatic discharge curve in oxygen and oxygen-free atmosphere. CV of Ni(OH)₂/MnO₂ positive electrode exhibited the redox reaction of Ni(OH)₂ as well as oxygen reduction reaction. It was observed that the discharge curves of positive electrode had two working potentials in half cell test when the electrode was charged and oxygen was supplied: one from the reactions of nickel oxyhydroxide (NiOOH); the other from the fuel cell reactions of manganese dioxide (MnO₂). It was also observed that the discharge curves had two working voltages in full cell test when the cell was fully charged and oxygen was supplied: one at 1.2 V from the battery reactions of NiOOH; the other at 0.8 V from the fuel cell reactions of MnO₂. In particular, the discharge capacity of overcharged cell was improved approximately 2 times compared with a battery of the same electrode quantity due to the additional function of this system as a fuel cell by using oxygen generated by water electrolysis. XRD analysis showed that there was no crystal structure change before and after (over)charge–discharge cycles. In summary, these experimental results showed that the novel bi-functional FCB system could provide an improved overall energy density per weight compared with conventional secondary batteries.     

Electrospun nickel oxide/polymer fibrous electrodes for electrochemical capacitors and effect of heat treatment process on their performance

Electrospinning is a versatile method for preparation of submicron-size fibers under ambient temperature. We demonstrate a new approach based on this method for preparing an electrode which consists of the fibers coated with nickel oxide (NiO) and acetylene black (AB) on their surfaces. The NiO/polymer fibrous electrodes show the electrochemical responses based on the electrochemical reaction of Ni(OH)₂ which is produced from NiO in alkaline aqueous solution. The capacitance of the test half cell with the as-prepared NiO/polymer fibrous electrode in 1 mol l⁻¹ KOH aqueous solution is 5.8 F g⁻¹ (per gram of NiO). Heat treatment (at 150 °C for 1 h in the air) of the NiO/polymer fibrous electrode increases the capacitance of the NiO/polymer fibrous electrode. The capacitance of the cell with the heat treated (HT) NiO/polymer fibrous electrode is 163 F g⁻¹ (per gram of NiO). SEM observation of the heat treated electrode suggests that partial melt of the fibers on the current collector forms the conducting passes and networks between the NiO particles and the collector and increases the specific capacity of the fibrous electrode.     

Electrochemical supercapacitor behavior of Ni3(Fe(CN)6)2(H2O) nanoparticles

Nanosized Ni₃(Fe(CN)₆)₂(H₂O) was prepared by a simple co-precipitation method. The electrochemical properties of the sample as the electrode material for supercapacitor were studied by cyclic voltammetry (CV), constant charge/discharge tests and electrochemical impedance spectroscopy (EIS). A specific capacitance of 574.7 F g⁻¹ was obtained at the current density of 0.2 A g⁻¹ in the potential range from 0.3 V to 0.6 V in 1 M KNO₃ electrolyte. Approximately 87.46% of specific discharge capacitance was remained at the current density of 1.4 A g⁻¹ after 1000 cycles.