Electrochemical performance of porous Ni-alloy electrodes for hydrogen evolution reaction from seawater electrolysis

The hydrogen evolution reaction in seawater is investigated using porous Ni–Cr–Fe, Ni–Fe–Mo, Ni–Fe–C and Ni–Ti electrodes, prepared by elemental powder reactive synthesis methods. The open porosity of the four kinds of electrode materials is 23.05%, 20.47%, 25.27%, and 29.05%, respectively. The electrochemical performance of the four kinds of electrodes has been researched by polarization measurement, cyclic voltammetry and electrochemical impedance spectroscopy. The preliminary results demonstrate that the porous Ni–Cr–Fe electrode has superior catalytic activity and relatively good long-term stability for hydrogen evolution reaction in seawater. The high efficiency and reasonable stability of the porous Ni–Cr–Fe electrode catalyst demonstrate its promising applications in the rising hydrogen revolution.

The hydrogen evolution reaction in seawater is investigated using porous Ni–Cr–Fe, Ni–Fe–Mo, Ni–Fe–C and Ni–Ti electrodes, prepared by elemental powder reactive synthesis methods.     

Robust fabrication of nanomaterial-based all-solid-state ion-selective electrodes

Currently, nanomaterial-based all-solid-state ion-selective electrodes (ASS-ISEs) have become attractive tools for ion sensing in environmental and biological applications. However, nanomaterial solid contact can easily fall off the electrode surface owing to poor adhesion. This poses serious limits to the wide use of these sensors. Herein, we report a general and facile method for the robust fabrication of nanomaterial-based ASS-ISEs. It is based on the silver-based conductive adhesive (CA) with excellent electronic conductivity and strong adhesion ability as the binder to construct nanomaterial-based solid contact. The solid-contact Ca²⁺-ISE based on single-walled carbon nanotubes (SWCNTs) is chosen as a model. The proposed electrode based on CA-SWCNTs shows a linear response in the concentration range of 10⁻⁶ to 10⁻³ M with a slope of 25.96 ± 0.36 mV per decade and a detection limit of 1.7 × 10⁻⁷ M. In addition, the CA-SWCNT-based Ca²⁺-ISE exhibits an improved potential stability and reduced water film compared to the coated-wire ISE. Above all, experiments also show that the CA-SWCNT-based electrode exhibits nearly the same electrochemical characteristics as the classical only SWCNT-based electrode in term of resistance, capacitance and potential stability. We believe that CA-nanomaterial-based solid contacts provide an appealing substitute for traditional solid contacts based on nanomaterials.

For the first time, a general and facile approach for the robust fabrication of nanomaterial-based solid contact ISEs is reported.     

Self-supporting carbon-rich SiOC ceramic electrodes for lithium-ion batteries and aqueous supercapacitors

Fabrication of precursor-derived ceramic fibers as electrodes for energy storage applications remains largely unexplored. Within this work, three little known polymer-derived ceramic (PDC)-based fibers are being studied systemically as potential high-capacity electrode materials for electrochemical energy devices. We report fabrication of precursor-derived SiOC fibermats via one-step spinning from various compositions of siloxane oligomers followed by stabilization and pyrolysis at 800 °C. Electron microscopy, Raman, FTIR, XPS, and NMR spectroscopies reveal transformation from polymer to ceramic stages of the various SiOC ceramic fibers. The ceramic samples are a few microns in diameter with a free carbon phase embedded in the amorphous Si–O–C structure. The free carbon phase improves the electronic conductivity and provides major sites for ion storage, whereas the Si–O–C structure contributes to high efficiency. The self-standing electrodes in lithium-ion battery half-cells deliver a charge capacity of 866 mA h g_electrode⁻¹ with a high initial coulombic efficiency of 72%. As supercapacitor electrode, SiOC fibers maintain 100% capacitance over 5000 cycles at a current density of 3 A g⁻¹.

Fabrication of precursor-derived ceramic fibers as electrodes for energy storage applications remains largely unexplored.     

Synthesis of coaxial carbon@NiMoO4 composite nanofibers for supercapacitor electrodes

This work reports the synthesis of coaxial carbon@NiMoO₄ nanofibers for supercapacitor electrode applications. Thin NiMoO₄ nanosheets are uniformly coated on the conductive electrospun carbon nanofibers by a microwave assisted hydrothermal method to form a hierarchical structure, which increases the porosity as well as the conductivity of the electrode. The thickness of the NiMoO₄ can be easily adjusted by varying the precursor concentrations. The high specific surface area (over 280 m² g⁻¹) and conductive carbon nanofiber backbone increase the utilization of the active pseudocapacitive NiMoO₄ phase, resulting a high specific capacitance of 1840 F g⁻¹.

This work reports the synthesis of coaxial carbon@NiMoO₄ nanofibers for supercapacitor electrode applications.     

Sulfonated graphene oxide/Nafion composite membranes for high temperature and low humidity proton exchange membrane fuel cells

Iron oxide (Fe₃O₄) nanoparticles anchored over sulfonated graphene oxide (SGO) and Nafion/Fe₃O₄–SGO composites were fabricated and applied as potential proton exchange membranes in proton exchange membrane fuel cells (PEMFCs) operated at high temperature and low humidity. Fe₃O₄ nanoparticles bridge SGO and Nafion through electrostatic interaction/hydrogen bonding and increased the intrinsic thermal and mechanical stabilities of Nafion/Fe₃O₄–SGO composite membranes. Nafion/Fe₃O₄–SGO composite membranes increased the compactness of ionic domains and enhanced the water absorption and proton conductivity while restricting hydrogen permeability across the membranes. The proton conductivity of Nafion/Fe₃O₄–SGO (3 wt%) composite membrane at 120 °C under 20% relative humidity (RH) was 11.62 mS cm⁻¹, which is 4.74 fold higher than that of a pristine recast Nafion membrane. PEMFC containing the Nafion/Fe₃O₄–SGO composite membrane delivered a peak power density of 258.82 mW cm⁻² at a load current density of 640.73 mA cm⁻² while operating at 120 °C under 25% RH and ambient pressure. In contrast, under identical operating conditions, a peak power density of only 144.89 mW cm⁻² was achieved with the pristine recast Nafion membrane at a load current density of 431.36 mA cm⁻². Thus, Nafion/Fe₃O₄–SGO composite membranes can be used to address various critical problems associated with commercial Nafion membranes in PEMFC applications.

Preparation process of Nafion/Fe₃O₄–SGO composite membranes.     

Waste sawdust-based composite as an interfacial evaporator for efficient solar steam generation

Interfacial evaporation is the technology of localizing heat energy at the air–water interface and is used for getting potable water from salty or seawater effectively. In this work, we introduce a novel interfacial evaporator by blending different weight ratios of waste sawdust (1 g, 2 g, 3 g and 4 g) with bisphenol-A epoxy resin (LY556) and triethyltetramine hardener (HY951). The fabricated epoxy hardener sawdust (EHS) composite material was subjected to various characterizations for the possibility of using it in solar steam generation. Consequently, EHS displayed high light absorption, amorphous structure, functional groups, and large number of pores. The main objective of the study was to investigate interfacial solar steam generation with and without interfacial evaporators (EHS-1g, EHS-2g, EHS-3g, and EHS-4g) under indoor conditions. The maximum mass loss of water, evaporation rate and evaporation efficiency were found to be 4.5 g, 1.398 kg m⁻² h⁻¹, and 92.99%, respectively, for the EHS-4g evaporator. The salinity of the distilled condensed water was measured and was below the WHO standards. The results are due to (i) the large number of cross-linked porous structures used to permeate water at the evaporative surface by capillary action, (ii) low thermal conductivity of the composite that offers an efficient broad and strong light absorption, and (iii) existence of a larger hydraulic diameter and small tortuosity of pores, which reduces the salt ion penetration distance and dispatch back to bulk water.

Interfacial evaporation is the technology of localizing heat energy at the air–water interface and is used for getting potable water from salty or seawater effectively.     

Alternative electrodes for HTMs and noble-metal-free perovskite solar cells: 2D MXenes electrodes

The high cost of hole transporting materials (HTMs) and noble metal electrodes limits the application of perovskite solar cells (PSCs). Carbon materials have been commonly utilized for HTMs and noble-metal-free PSCs. In this paper, a more conductive 2D MXene material (Ti₃C₂), showing a similar energy level to carbon materials, has been used as a back electrode in HTMs and noble-metal-free PSCs for the first time. Seamless interfacial contact between the perovskite layer and Ti₃C₂ material was obtained using a simple hot-pressing method. After the adjustment of key parameters, the PSCs based on the Ti₃C₂ electrode show more stability and higher power conversion efficiencies (PCE) (13.83%, 27% higher than that (10.87%) of the PSCs based on carbon electrodes) due to the higher conductivity and seamless interfacial contact of the MXene electrode. Our work proposes a promising future application for MXene and also a good electrode candidate for HTM and the noble-metal-free PSCs.

The 2D Mxene material was successfully used as the counter electrode of the perovskite solar cell and achieved power conversion efficiencies of 13.84%.     

Hybrid composite of Nafion with surface-modified electrospun polybenzoxazine (PBz) fibers via ozonation as fillers for proton conducting membranes of fuel cells

Nafion was investigated for its compatibility in the preparation of hybrid composites with electrospun Polybenzoxazine (PBz) surface-modified fibers by evaluating the effects on the surface and structure of the composite. A PBz fiber mat was first crosslinked by thermal treatment after electrospinning to enhance the mechanical integrity of the fibers prior to modification. Further surface modification via free radical ozonation was carried out by potentiating oxygen-based functional groups of hydroxyl radicals (–OH) onto fibers'' exposed surfaces. The sequential modifications by crosslinking and ozone treatment were evaluated by analyzing surface properties using XPS, ATR-FTIR and water contact angle which determined the enhanced properties of the fibers that were beneficial to the target functionality. Electron spectroscopy confirmed that fibers'' surfaces were changed with the new surface chemistry without altering the chemical structure of PBz. The presence of higher oxygen-based functional groups on fibers'' surfaces based on the resulting atomic compositions was correlated with the change in surface wettability by becoming hydrophilic with contact angle ranging from 21.27° to 59.83° compared to hydrophobic pristine PBz fibers. This is due to electrophilic aromatic substitution with hydroxyl groups present on the surfaces of the fibers endowed by ozonation. The resulting surface-modified fiber mat was used for the preparation of composites by varying two process parameters, the amount of Nafion dispersion and its homogenization and curing time, which was evaluated for compatibility and interaction as fillers to form hybrid composites. The analyses of SEM images revealed the effects of shorter homogenization and curing time on composites with rougher and wrinkled surfaces shown on the final hybrid composite''s structure while decreasing the amount of Nafion at the same homogenization time but longer curing time showed its influence on improvement of compatibility and surface morphology.

Nafion compatibility in the preparation of hybrid composites with electrospun Polybenzoxazine (PBz) surface-modified fibers via ozonation by evaluating the effects on the surface and structure of the composite.     

Porous carbon–carbon composite electrodes for vanadium redox flow batteries synthesized by twin polymerization

Highly porous carbon–carbon composite electrodes have been synthesized by surface twin polymerization on a macroporous polyacrylonitrile (PAN)-based substrate. For this purpose the compound 2,2′-spirobi[benzo-4H-1,3,2-dioxasiline] (Spiro), being a molecular precursor for phenolic resin and silica, was polymerized onto PAN-based felts with subsequent thermal transformation of the hybrid material-coated felt into silica-containing carbon. The following etching step led to high surface carbon–carbon composite materials, where each carbon component served a different function in the battery electrode: the carbon fiber substrate possesses a high electron conductivity, while the amorphous carbon coating provides the catalytic function. For characterization of the composite materials with respect to structure, porosity and pore size distribution scanning electron microscopy (SEM) as well as nitrogen sorption measurements (BET) were performed. The electrochemical performance of the carbon felts (CF) for application in all-vanadium redox flow batteries was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Compared to the pristine PAN-based felt the composite electrodes show significantly enhanced surface areas (up to 35 times higher), which increases the amount of vanadium ions that could be adsorbed onto the surface and thus contributes to an increased performance.

Synthesis, characterization and electrochemical evaluation of composite electrodes – synthesized via twin polymerization – for utilization in vanadium redox flow batteries.     

Fabrication of composite material of RuCo2O4 and graphene on nickel foam for supercapacitor electrodes

Supercapacitors are energy storage devices with the advantage of rapid charging and discharging, which need a higher specific capacitance and superior cycling stability. Hence, a composite material consisting of RuCo₂O₄ and reduced graphene oxide with a nanowire network structure was synthesized on nickel foam using a one-step hydrothermal method and annealing process. The nanowire network structure consists of nanowires with gaps that provide more active sites for electrochemical reactions and shorten the diffusion path of electrolyte ions. The prepared electrodes exhibit outstanding electrochemical performance with 2283 F g⁻¹ at 1 A g⁻¹. When the current density is 10 A g⁻¹, the specific capacitance of the electrodes is 1850 F g⁻¹, which maintains 81% of the initial specific capacitance. In addition, the prepared electrodes have a long-term cycling life with capacitance retention of 92.60% after 3000 cycles under the current density of 10 A g⁻¹. The composite material is a promising electrode material for high-performance supercapacitors.

The RuCo₂O₄/rGO@NF composite electrode has been prepared by a one-step hydrothermal method and annealing process, with high specific capacitance and excellent cycle stability.     

Enhanced electrochemical properties of cerium metal–organic framework based composite electrodes for high-performance supercapacitor application

Cerium metal–organic framework based composites (Ce-MOF/GO and Ce-MOF/CNT) were synthesized by a wet chemical route and characterized with different techniques to characterize their crystal nature, morphology, functional groups, and porosity. The obtained Ce-MOF in the composites exhibit a nanorod structure with a size of ∼150 nm. The electrochemical performance of the composites was investigated in 3 M KOH and 3 M KOH + 0.2 M K₃Fe(CN)₆ electrolytes. Enhanced electrochemical behavior was obtained for the Ce-MOF/GO composite in both electrolytes and exhibited a maximum specific capacitance of 2221.2 F g⁻¹ with an energy density of 111.05 W h kg⁻¹ at a current density of 1 A g⁻¹. The large mesoporous structure and the presence of oxygen functional groups in Ce-MOF/GO could facilitate ion transport in the electrode/electrolyte interface, and the results suggested that the Ce-MOF/GO composite could be used as a high-performance supercapacitor electrode material.

The presence of oxygen functional groups in GO enhances the charge storage behavior of Ce-MOF/GO composites for use as supercapacitor electrode materials.     

Self-supporting S@GO–FWCNTs composite films as positive electrodes for high-performance lithium–sulfur batteries

Although lithium–sulfur (Li–S) batteries are a promising secondary power source, it still faces many technical challenges, such as rapid capacity decay and low sulfur utilization. The loading of sulfur and the weight percentage of sulfur in the cathode usually have a significant influence on the energy density. Herein, we report an easy synthesis of a self-supporting sulfur@graphene oxide-few-wall carbon nanotube (S@GO–FWCNT) composite cathode film, wherein an aluminum foil current collector is replaced by FWCNTs and sulfur particles are uniformly wrapped by graphene oxide along with FWCNTs. The 10 wt% FWCNT matrix through ultrasonication not only provided self-supporting properties without the aid of metallic foil, but also increased the electrical conductivity. The resulting S@GO–FWCNT composite electrode showed high rate performance and cycle stability up to ∼385.7 mA h g_electrode⁻¹ after 500 cycles and close to ∼0.04% specific capacity degradation per cycle, which was better than a S@GO composite electrode (353.1 mA h g_electrode⁻¹). This S@GO–FWCNT composite self-supporting film is a promising cathode material for high energy density rechargeable Li–S batteries.

We report a synthesis of a self-supporting composite cathode film, wherein aluminum foil current collector is replaced by FWCNTs and sulfur particles are uniformly wrapped by graphene oxide along with FWCNTs.     

A tri-phase percolative ceramic composite with high initial permeability and composition-independent giant permittivity

The drastic change of properties near the percolation threshold usually limits the practical applications of percolative composite materials. In this work, a tri-phase system, i.e. a BaTiO₃ (BTO)/Ni_0.5Zn_0.5Fe₂O₄ (NZFO)/BaFe₁₂O₁₉ (BFO) ceramic composite, is proposed and investigated in detail. The BFO phase was in situ formed during a hybrid process of sol–gel and self-combustion methods. The content of the BFO phase could be tuned conveniently by controlling the preparation conditions. The as-prepared BTO/NZFO/BFO tri-phase composite exhibited unprecedented stable dielectric properties that were distinct from those of conventional percolative composites above the percolation threshold due to the existence of a third phase. When the volume fraction of the NZFO phase exceeds 55%, the electrical conductivity and effective permittivity of the composite remain at a stable value of about 10⁻⁵ S cm⁻¹ and 10 000, respectively, which is almost independent of the composition. Such behavior is the result of the synergistic control effect of the percolation effect and specific phase composition in the system. It is evident that the stability of the dielectric properties of the composite is chiefly contributed by the introduction of the BFO phase. Meanwhile, the composite exhibited a relatively high permeability of ∼17 with 90% NZFO loading, and its saturated magnetization is larger than 73 emu g⁻¹, approximately 95% of the pure NZFO phase. The finding of our BTO/NZFO/BFO tri-phase ceramic composite with stable giant permittivity and extremely high permeability paves a new way to solve the difficulty of property instability above the percolation threshold in the utilization of percolative materials.

A tri-phase BTO/BFO/NZFO ceramic featuring the microwave-absorbing-material BFO formed in situ possessed giant permittivity and permeability, and stabilizing properties around the percolation threshold.     

Possible scenario of forming a catalyst layer for proton exchange membrane fuel cells

Ionomer in the catalyst layer provides an ion transport channel which is essential for many electrochemical devices. As the ionomer and electrochemical catalyst are packed together in the catalyst layer, it is difficult to have a clear image of the ionomer distribution in the catalyst layer and how the ionomer is in contact with Pt or carbon. A highly dispersed catalyst was deposited on the TEM SiN grid directly using the same (ultrasonic spray) or a similar way as the catalyst was deposited on the membrane. By analyzing the distribution of various elements (C, F, S, Pt etc.), we found that the ionomer may coexist in the catalyst layer in three ways: ionomer covered Pt particles due to the relatively strong interaction between Pt and the ionomer; ionomer covered C particles; packed free ionomer in between the aggregated catalyst particles. The results show that the ionomer is prone to covering the surface of Pt particles as further evidenced by the accelerated degradation test (ADT).

Ionomer in the catalyst layer provides an ion transport channel which is essential for many electrochemical devices.     

Preparation and performance study of a PVDF–LATP ceramic composite polymer electrolyte membrane for solid-state batteries

Recently, safety issues in conventional organic liquid electrolytes and the interface resistance between the electrode and electrolyte have been the most challenging barriers for the expansion of lithium batteries to a wide range of applications. Here, an ion-conductive PVDF-based composite polymer electrolyte (CPE) consisting of lithium aluminum germanium phosphate (Li_1.3Al_0.3Ti_1.7(PO₄)₃) and polyvinylidene fluoride (PVDF) is prepared on a Li metal anode via a facile casting method. The ionic conductivity and electrochemical stability were enhanced by incorporating an appropriate amount of LATP into the PVDF-based composite polymer electrolyte, and the optimum content of LATP in the hybrid solid electrolyte was approximately 90 wt%. The corresponding solid-state battery based on an SEI-protected Li anode, the PVDF–LATP electrolyte, and a LiMn₂O₄ (LMO) cathode exhibited excellent rate capability and long-term cycling performance, with an initial discharge capacity of 107.4 mA h g⁻¹ and a retention of 91.4% after 200 cycles.

Recently, safety issues in conventional organic liquid electrolytes and the interface resistance between the electrode and electrolyte have been the most challenging barriers for the expansion of lithium batteries to a wide range of applications.     

Microstructure and properties of SiC ceramic brazed with Zr–Cu composite filler metal

The microstructure and properties of SiC ceramic brazed with Zr–Cu composite filler metal were investigated. Combined with the brazing experiment, the microstructure of the interface reaction layer and the brazed SiC ceramic joint was analyzed, and the shear strength was used to evaluate the mechanical properties of the joint. The results show that both Zr–Cu + SiC_p and Zr–Cu + Mo composite filler metals can braze SiC ceramic, and the products of the interface reaction layer are mainly ZrC and Zr₂Si. The addition of SiC_p and Mo to Zr–Cu-based composite filler metal improves the nuclear properties of the composite filler metal and its joint, reduces the coefficient of thermal expansion of the composite filler metal and SiC ceramic joint, and improves the mechanical properties of the joint. The shear properties of the joint increase with the increase of the content of SiCp and Mo in the Zr–Cu composite filler metals. The shear strength of the joint reaches the maximum (82 MPa) when the content of SiC particles is 10 vol% of the Zr–Cu + SiCp composite filler metal, and the average value of the shear strength reaches the maximum of 74 MPa when the content of Mo is 6 vol% of the Zr–Cu + Mo composite filler metal.

The microstructure and properties of SiC ceramic brazed with Zr–Cu composite filler metal were investigated.     

Anhydrous proton conductivity of electrospun phosphoric acid-doped PVP-PVDF nanofibers and composite membranes containing MOF fillers

A high-temperature proton exchange membrane was fabricated based on polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone (PVP) blend polymer nanofibers. Using electrospinning method, abundant small ionic clusters can be formed and agglomerated on membrane surface, which would facilitate the proton conductivity. To further enhance the conductivity, phosphoric acid (PA) retention as well as mechanical strength, sulfamic acid (SA)-doped metal–organic framework MIL-101 was incorporated into PVP-PVDF blend nanofiber membranes. As a result, the anhydrous proton conductivity of the composite SA/MIL101@PVP-PVDF membrane reached 0.237 S cm⁻¹ at 160 °C at a moderate acid doping level (ADL) of 12.7. The construction of long-range conducting network by electrospinning method combined with hot-pressing and the synergistic effect between PVP-PVDF, SA/MIL-101 and PA all contribute to the proton conducting behaviors of this composite membrane.

A composite SA/MIL101@PVP-PVDF membrane was fabricated via electrospinning and reached a conductivity of 0.237 S cm⁻¹ at 160 °C with a moderate acid doping level (12.7).     

Ion-selective membrane electrodes for clinical use

We review ion-selective solvent polymeric membrane electrodes for clinical use. The particular requirements that the clinical application set on the membrane are discussed in terms of selectivity, stability, lifetime, and response time. The performance of currently available electrodes is reviewed, with consideration of actual problems that arise in clinical practice.     

Novel dry electrodes for ECG monitoring

The development, fabrication and characterization of two novel dry bioelectrodes--conductive and capacitive ones--for biopotential monitoring are presented. The new electrodes have the potential to improve the applicability of dry electrodes in ambulant recording of ECG by reducing motion artifacts as well as the contact impedance to the skin. Furthermore, a passive filter network is integrated into the new electrodes to suppress slow offset fluctuation of the ECG signal caused e.g. by motions like breathing or changes in the electrode-skin interface properties. Compared to standard gel electrodes these new electrodes exhibit equivalent and superior contact impedances and biosignals. The integrated filter network effectively suppresses fluctuating offset potentials.