Electrode Scaffold Research Articles

Ionic Conductivity over Metal/Water Interfaces in Ionomer‐Free Fuel Cell Electrodes

AbstractIon conduction and oxygen reduction reaction (ORR) kinetics at metal/water interfaces are important in determining the performance of proton exchange membrane fuel cells (PEMFCs). However, the coupled ion transport and electrochemical reactions in ionomer‐free domains of catalyst layers are still unclear. In this work, we deconvolute the ion transport and oxygen reduction reaction (ORR) by studying metal/water interfaces of platinum (Pt) and gold (Au) ionomer‐free porous cathodes. In our experiments, a conventional membrane electrode assembly (MEA) was used for electrochemical characterization of ionomer‐free electrodes. Cyclic voltammetry (CV) and polarization curve measurements at different relative humidity (RH) conditions show that active surface area and ORR current density increases with RH. We also use microstructured electrode scaffold (MES) apparatus for measurement of the ionic conductivity in the cathode. The results show that the ionic conductivity increases with the RH and water coverage. The potential dependence of ionic conductivity for Au approximately follows the classical Guoy‐Chapman electrical double layer (EDL) behavior, while the ionic conductivity of the Pt electrode did not show a strong potential dependence, indicating that it could also be affected by other mechanisms, such as formation of surface oxide and diffusion of adsorbed hydrogen on its surface.

Electrochemical conversion of methane to ethylene in a solid oxide electrolyzer

Conversion of methane to ethylene with high yield remains a fundamental challenge due to the low ethylene selectivity, severe carbon deposition and instability of catalysts. Here we demonstrate a conceptually different process of in situ electrochemical oxidation of methane to ethylene in a solid oxide electrolyzer under ambient pressure at 850 °C. The porous electrode scaffold with an in situ-grown metal/oxide interface enhances coking resistance and catalyst stability at high temperatures. The highest C2 product selectivity of 81.2% together with the highest C2 product concentration of 16.7% in output gas (12.1% ethylene and 4.6% ethane) is achieved while the methane conversion reaches as high as 41% in the initial pass. This strategy provides an optimal performance with no obvious degradation being observed after 100 h of high temperature operation and 10 redox cycles, suggesting a reliable electrochemical process for conversion of methane into valuable chemicals.

Structure-Activity Relationships of Hierarchical Three-Dimensional Electrodes with Photosystem II for Semiartificial Photosynthesis.

Semiartificial photosynthesis integrates photosynthetic enzymes with artificial electronics, which is an emerging approach to reroute the natural photoelectrogenetic pathways for sustainable fuel and chemical synthesis. However, the reduced catalytic activity of enzymes in bioelectrodes limits the overall performance and further applications in fuel production. Here, we show new insights into factors that affect the photoelectrogenesis in a model system consisting of photosystem II and three-dimensional indium tin oxide and graphene electrodes. Confocal fluorescence microscopy and in situ surface-sensitive infrared spectroscopy are employed to probe the enzyme distribution and penetration within electrode scaffolds of different structures, which is further correlated with protein film-photoelectrochemistry to establish relationships between the electrode architecture and enzyme activity. We find that the hierarchical structure of electrodes mainly influences the protein loading but not the enzyme activity. Photoactivity is more limited by light intensity and electronic communication at the biointerface. This study provides guidelines for maximizing the performance of semiartificial photosynthesis and also presents a set of methodologies to probe the photoactive biofilms in three-dimensional electrodes.

Three-dimensional carbon material as stable host for dendrite-free lithium metal anodes

For its low redox potential (−3.04 V vs. SHE) and the high theoretical specific capacity (3860 mA h g−1), lithium metal is regarded as one of the most promising anode materials for next-generation batteries. However, the poor cycling performances and serious safety hazards caused by the inhomogeneous lithium deposition severely hinder the practical applications of Li metal batteries. Here, we introduce 3-D carbon materials which are subsequently in-situ transformed into LiC6 as electrode scaffold. Such lithiophilic 3-D structure with a high specific surface area enables dendrite-free deposition of Li metal, resulting in a high coulombic efficiency up to 97% after 300 cycles. We propose that besides 3-D structure, LiC6 intermediate may be responsible for the dendrite-free growth of Li, offering a potential new strategy to design high performance anodes for Li metal batteries.

Self‐Assembled 3D Hierarchical Porous Hybrid as Platinum‐Like Bifunctional Nonprecious Metal Catalyst toward Oxygen Reduction Reaction and Hydrogen Evolution Reaction

AbstractA class of novel CoNC active nanoparticles anchored on 3D hierarchical porous graphene‐like carbon nanosheets compositions (CoNC@3D HPG) with high porosity, high specific surface area, interconnected pores, and a hierarchical pore structure are synthesized, which are perfect as electrochemical electrode scaffolds, giving rise to efficient and rapid pathways for ion and electron transport, which certainly facilitate the mass transport. This hybrid catalyst possesses outstanding oxygen reduction reaction (ORR) activity through a four‐electron transfer process. Most importantly, the ORR activity of this material is superior to Pt/C catalyst, better stability and fuel (methanol and CO) tolerance than Pt/C catalyst. Besides, the CoNC@3D HPG also exhibits outstanding electrocatalytic performance as an efficient hydrogen evolution reaction catalyst with zero onset overpotential, low overpotential at large current density, small Tafel slope, high exchange current density, and excellent durability. It is worth noting that this outstanding bifunctional catalyst is prepared by a novel resin‐based self‐assembly growth methodology at large‐scale.

Polypyrrole‐Assisted Co3O4 Anchored Carbon Fiber as a Binder‐Free Electrode for Seawater Batteries

AbstractAn efficient, durable and cost‐effective air electrode is essential to achieve a practicable metal‐air battery. The conventional preparation of electrode uses polymer binders to ensure good physical contacts between catalysts and the electrode scaffold. However, the use of polymer binders introduces inevitable loss of the electrochemically active surface area and restricts access of the reactants, owing to the electrically insulating properties and hydrophobic properties of polymer binders. In this work, a binder‐free air electrode is structured by using Co oxide anchored on carbon fiber tissues with the assistance of polypyrrole‐doped carbon (PPy/C) through a simple infiltration technique. The fabricated binder‐free electrode exhibits excellent bifunctional stability for seawater batteries, presenting a comparable performance to the binder‐included Pt/C+IrO2 electrode.

A three-dimensional hybrid pacemaker electrode seamlessly integrates into engineered, functional human cardiac tissue in vitro

Pacemaker systems are an essential tool for the treatment of cardiovascular diseases. However, the immune system’s natural response to a foreign body results in the encapsulation of a pacemaker electrode and an impaired energy efficiency by increasing the excitation threshold. The integration of the electrode into the tissue is affected by implant properties such as size, mechanical flexibility, shape, and dimensionality. Three-dimensional, tissue-like electrode scaffolds render an alternative to currently used planar metal electrodes. Based on a modified electrospinning process and a high temperature treatment, a conductive, porous fiber scaffold was fabricated. The electrical and immunological properties of this 3D electrode were compared to 2D TiN electrodes. An increased surface of the fiber electrode compared to the planar 2D electrode, showed an enhanced electrical performance. Moreover, the migration of cells into the 3D construct was observed and a lower inflammatory response was induced. After early and late in vivo host response evaluation subcutaneously, the 3D fiber scaffold showed no adverse foreign body response. By embedding the 3D fiber scaffold in human cardiomyocytes, a tissue-electrode hybrid was generated that facilitates a high regenerative capacity and a low risk of fibrosis. This hybrid was implanted onto a spontaneously beating, tissue-engineered human cardiac patch to investigate if a seamless electronic-tissue interface is generated. The fusion of this hybrid electrode with a cardiac patch resulted in a mechanical stable and electrical excitable unit. Thereby, the feasibility of a seamless tissue-electrode interface was proven.

Engineering of microstructures of protonic ceramics by a novel rapid laser reactive sintering for ceramic energy conversion devices

The solid state reactive sintering (SSRS) characteristic with the assistance of sintering aids (e.g., NiO) has been proven to be an effective method for achieving high-quality proton conducting oxide electrolytes at relatively low sintering temperatures (e.g., <1400 °C). In this work, instead of performing a long-term (e.g., >10 h) SSRS in a conventional high-temperature furnace, a novel rapid laser heating process was used to perform SSRS, which was named as rapid laser reactive sintering (RLRS). This RLRS method was confirmed to be able to sinter protonic ceramics with well-engineered microstructures within a short time (e.g., <10 s). Using the proton conducting oxides of BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb) and BaZr0.8Y0.2O3-δ (BZY20) as case study, the crack-free protonic ceramic parts of straight strips (~10 mm in length, ~1 mm in width, and 30–200 μm in thickness), spiral strips (~200 mm in length, ~1 mm in width, and 30–200 μm in thickness), and squared films (~4.5 mm in both length and width and 30–200 μm in thickness) were successfully fabricated by RLRS method. The sintered parts usually showed fully dense large-grained and highly porous regions, which can potentially serve as electrolytes and electrode scaffolds for single cells or half-cells. The X-ray diffraction results indicated that the pure perovskite structures were obtained for both BCZYYb and BZY20 by RLRS from inexpensive carbonates and single metal oxides. The preliminary electrochemical impedance measurement for the dense strips after removal of porous regions by picosecond laser machining showed a reasonable in-plane protonic conductivities. This new RLRS method demonstrated the feasibility and promise of the rapid additive manufacturing of hierarchical ceramic energy conversion devices.

Nanostructured SOFC Electrode Scaffolds Prepared via High Temperature in situ Carbon Templating of Hybrid Materials

High surface area, nanostructured solid oxide fuel cell (SOFC) electrode scaffold materials were prepared at traditional sintering temperatures by heating hybrid inorganic-organic gels in an inert atmosphere. The prepared materials were yttria-stabilized zirconia (YSZ, 8 mol% Y2O3), gadolinium doped ceria (GDC, Gd0.2Ce0.8O3-δ) and strontium titanate (STO, SrTiO3). YSZ, GDC, and STO were prepared via the citric acid gel (Pechini) method; in addition, YSZ and GDC were prepared via the propylene oxide gel method. Gels were sintered between 1050oC and 1350oC in argon, leaving behind a hard carbon template which created and preserved the scaffold nanostructure. This carbon template was completely removed upon heating in air to 700oC. Surface areas up to 83, 95, and 99 m2/g were achieved for YSZ, GDC, and STO, respectively. The tunability of this method was assessed by varying the carbon template concentration. For the propylene oxide gels, this was accomplished by controlling the amount of glucose added to the gel formulation while the amount of citric acid was controlled for the citric acid gels. In all cases, the surface areas increased with increasing carbon template concentration. In some cases, amorphous or impure phases were obtained upon sintering as determined by x-ray diffraction. However, the desired phases formed upon heating to 700°C in air (Fig. 1). This in situ carbon templating approach creates high surface area, nanostructured SOFC scaffolds at traditional sintering temperatures without unusual processing steps or complex deposition techniques. As expected, preliminary data suggests that SOFC electrodes comprised of these materials have improved performance (Fig. 2). Figure 1

Composite LSF-YSZ and LSCrF-YSZ Electrode Scaffolds for Infiltrated SOFC Cathodes

Conductive scaffolds were investigated for use in fabrication of SOFC cathodes in order to reduce the number of perovskite infiltration steps required to achieve sufficient conductivity. Initial work involved composites of Sr-doped LaFeO3 (LSF) and YSZ. Although no new phases form when LSF-YSZ composites are calcined to 1623 K, shifts in the lattice parameters indicate Zr can enter the perovskite phase. Measurements on dense, LSF-YSZ composites show that the level of Zr doping depends on the Sr:La ratio. Because conductivity of undoped LSF increases with Sr content but both the ionic and electronic conductivities of Zr-doped LSF decrease with the level of Zr in the perovskite phase, there is an optimum initial Sr content corresponding to La0.9Sr0.1FeO3 (LSF91). Although scaffolds made with 100% LSF had a higher conductivity than scaffolds made with 50:50 LSF-YSZ mixtures, the 50:50 mixture provided better interfacial structure with the electrolyte and sufficient conductivity, providing the better cathode performance upon infiltration of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF). To minimize Zr doping, we also examined scaffold composites made from La0.8Sr0.2CrxFe1-zO3-δ (LSCrF) and YSZ. For intermediate Cr contents, it was possible to prevent Zr doping and maintain reasonable performance of cathodes made from LSCrF-YSZ composites.

Nanostructured SOFC Electrode Scaffolds Prepared via High Temperature in situ Carbon Templating of Hybrid Materials

High surface area solid oxide fuel cell (SOFC) electrode scaffold materials were prepared at traditional sintering temperatures by sintering hybrid inorganic-organic gels in argon. The prepared materials were yttria-stabilized zirconia (YSZ, 8 mol% Y2O3), gadolinia doped ceria (GDC, Ce0.8Gd0.2O3-δ) and strontium titanate (STO, SrTiO3). Gels were prepared via the citric acid (Pechini) method and the propylene oxide method. The gels were sintered between 1050oC and 1350oC in argon, creating an amorphous carbon template in situ, which preserved a ceramic scaffold nanostructure. The carbon template was removed upon heating in air to 700oC. Specific surface areas up to 83, 95, and 99 m2/g were achieved for YSZ, GDC, and STO, respectively. The carbon template concentration and resulting surface areas are tunable by modifying the gel formulations. Symmetric cathode cells were prepared with traditional and nanostructured YSZ. As expected, the gel-derived, nanostructured YSZ improved electrode performance.

Composite LSF-YSZ and LSCrF-YSZ Electrode Scaffolds for Infiltrated SOFC Cathodes

Fabrication of SOFC cathodes by infiltration of LSCF into composite scaffolds were investigated. Two composite materials, LSF-YSZ and LSCrF-YSZ, were tested as potential SOFC cathode scaffolds for cells operating at 973K. Zr migration in LSF-YSZ scaffold was determined to be harmful, but changing the Sr dopant level in LSF was found to tune the Zr migration. LSCrF-YSZ scaffold was able to eliminate Zr migration, but the poor sinterability of the LSCrF hindered sintering of the electrolyte. Although problems still exist, both scaffolds showed improved performance at low LSCF loading due to the reduced ohmic loss.

Nanofiber-structured Pr0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ-Gd0.2Ce0.8O1.9 symmetrical composite electrode for solid oxide fuel cells

Abstract In this research, nanofiber-structured Pr0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (PSCFN) electrode scaffolds were impregnated with Gd0.2Ce0.8O1.9 (GDC) nanoparticles to prepare PSCFN-GDC nanofiber-structured composite electrodes, which could function well as a novel electrode material for symmetrical solid oxide fuel cells (SSOFCs). The polarization resistances of PSCFN-GDC (1:0.56) composite electrodes as cathode and anode were 0.044 and 0.309 Ω cm2 at 800 °C, respectively, indicating that the composite electrodes demonstrated excellent electrochemical performances for both oxygen reductions and fuel oxidation reactions. La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte-supported single cells with the PSCFN-GDC symmetrical composite electrodes showed excellent long-term stability in wet H2 (97% H2-3% H2O) and wet CH4 (97% CH4-3% H2O) for 100 h with constant current density at 800 °C. A conversion electrode method was applied by interchanging the atmosphere of cathode and anode to solve the problem of PSCFN-GDC symmetrical single cell's carbon deposition in wet CH4. After working three cycles for 384 h, carbon deposition was not found in the symmetrical electrode scaffold. Taken together, the results described above demonstrated that the PSCFN-GDC composite material acted as a promising symmetrical electrode for SSOFCs, and the conversion electrode method would make for a good application to process carbon deposition generated by hydrocarbon fuels.

Performance optimization of LSCF/Gd:CeO2 composite cathodes via single-step inkjet printing infiltration

The effect of solid oxide fuel cell cathode microstructure modification on its electrochemical activity is investigated. Inkjet printing infiltration was used to develop a nano-decoration pattern on the composite cathode scaffolds. Two types of composite La0.6Sr0.4Co0.2Fe0.8O3−δ:Ce0.9Gd0.1O1.9 cathodes with different volume ratios (60:40 and 40:60 vol%) were fabricated using inkjet printing of suspension inks. The electrodes were altered by single-step inkjet printing infiltration of ethanol-based Ce0.9Gd0.1O1.9 ink. After heat treatments in air at 550 °C the cathodes’ surfaces were shown to be nano-decorated with Ce0.9Gd0.1O1.9 particles (~20–120 nm in size) dispersed uniformly onto the electrode scaffold. The nano-engineered microstructure enhanced the active triple phase boundary of the electrode and promoted the surface exchange reaction of oxygen. Electrochemical impedance tests conducted on symmetrical cells showed a reduction in the polarization resistance of between 1.3 and 2.9 times. The effect was found to be more pronounced in the 60:40 vol% composite cathodes. Ageing of infiltrated electrodes up to 60 h in air revealed enhanced stability of gadolinium doped ceria nanoparticles decorated electrodes ascribed to the suppression of SrO surface segregation. This work demonstrated that single-step inkjet printing infiltration can produce reproducible performance enhancements and thus offers a cost-effective route for commercial solid oxide fuel cell infiltration processing.Graphical abstract

Vapor-Phase Polymerized Poly(3,4-Ethylenedioxythiophene) on a Nickel Nanowire Array Film: Aqueous Symmetrical Pseudocapacitors with Superior Performance.

Three-dimensional (3D) nanometal scaffolds have gained considerable attention recently because of their promising application in high-performance supercapacitors compared with plain metal foils. Here, a highly oriented nickel (Ni) nanowire array (NNA) film was prepared via a simple magnetic-field-driven aqueous solution deposition process and then used as the electrode scaffold for the vapor-phase polymerization of 3,4-ethylenedioxythiophene (EDOT). Benefiting from the unique 3D open porous structure of the NNA that provided a highly conductive and oriented backbone for facile electron transfer and fast ion diffusion, the as-obtained poly(3,4-ethylenedioxythiophene) (PEDOT) exhibited an ultra-long cycle life (95.7% retention of specific capacitance after 20 000 charge/discharge cycles at 5 A/g) and superior capacitive performance. Furthermore, two electrodes were fabricated into an aqueous symmetric supercapacitor, which delivered a high energy density (30.38 Wh/kg at 529.49 W/kg) and superior long-term cycle ability (13.8% loss of capacity after 20 000 cycles). Based on these results, the vapor-phase polymerization of EDOT on metal nanowire array current collectors has great potential for use in supercapacitors with enhanced performance.

Graphene synthesized on porous silicon for active electrode material of supercapacitors

We present graphene synthesized by chemical vapour deposition under atmospheric pressure on both porous nanostructures and flat wafers as electrode scaffolds for supercapacitors. A 3nm thin gold layer was deposited on samples of both porous and flat silicon for exploring the catalytic influence during graphene synthesis. Micro-four-point probe resistivity measurements revealed that the resistivity of porous silicon samples was nearly 53 times smaller than of the flat silicon ones when all the samples were covered by a thin gold layer after the graphene growth. From cyclic voltammetry, the average specific capacitance of porous silicon coated with gold was estimated to 267 μF/cm2 while that without catalyst layer was 145μF/cm2. We demonstrated that porous silicon based on nanorods can play an important role in graphene synthesis and enable silicon as promising electrodes for supercapacitors.

On-Chip Supercapacitor Electrode Based On Polypyrrole Deposited Into Nanoporous Au Scaffold

On-chip supercapacitors hold the potential promise for serving as the energy storage units in integrated circuit system, due to their much higher energy density in comparison with conventional dielectric capacitors, high power density and long-term cycling stability. In this study, nanoporous Au (NP-Au) film on-chip was employed as the electrode scaffold to help increase the electrolyte-accessible area for active material. Pseudo-capacitive polypyrrole (PPY) with high theoretical capacitance was deposited into the NP-Au scaffold, to construct the tailored NP-Au/PPY hybrid on-chip electrode with improved areal capacitance. Half cell test in three- electrode system revealed the improved capacitor performance of nanoporous Au supported PPY electrode, compared to the densely packed PPY nanowire film electrode on planer Au substrate (Au/PPY). The areal capacitance of 37 mF/cm2∼10 mV/s, 32 mF/cm2∼50 mV/s, 28 mF/cm2∼100 mV/s, 16 mF/cm2∼500 mV/s, were offered by NP-Au/PPY. Also, the cycling performance was enhanced via using NP-Au scaffold. The developed NP-Au/PPY on-chip electrode demonstrated herein paves a feasible pathway to employ dealloying derived porous metal as the scaffold for improving both the energy density and cycling performance for supercapacitor electrodes.

Preparation of TiO2 nanosheet-carbon nanotube composite as immobilization platform for both primary and secondary antibodies in electrochemical immunoassay

TiO2 nanosheets (TNSs) were synthesized and deposited on multi-wall carbon nanotubes (MWCNTs) to form a nano-composite through a hydrothermal method, followed by the characterization with various spectroscopic and microscopic techniques. The TNS-MWCNT composite was then applied as not only an electrode scaffold to immobilize primary antibody, but also as a carrier to load secondary antibody and horseradish peroxidase (HRP). In both cases, bis(sulfosuccinimidyl) suberate sodium salt acted as an amino cross-linker to covalently bind the biomolecules on TNS-MWCNT composite through their surface primary amino groups. After the sandwich-type immunoreaction, HPR was quantitatively captured on the electrode surface via the binding between secondary antibody and antigen, and electrochemical response of the immunosensor was then amplified by a H2O2 mediated HRP catalytic reaction. Using α-Fetoprotein as a model analyte, a linear range between 0.005 and 320 ng mL−1 with a detection limit of 2.0 pg mL−1 was achieved by differential pulse voltammetry. The improved immunosensor performance could be attributed to the biocompatibility and high specific surface area of TNS, and excellent electrical conductivity of MWCNTs, which accelerated the electron transfer at the electrode surface.

Electrical conductivity and porosity in stainless steel 316L scaffolds for electrochemical devices fabricated using selective laser sintering

Battery electrode microstructures must be porous, to provide a large active surface area to facilitate fast charge transfer kinetics. In this work, we describe how a novel porous electrode scaffold, made from stainless steel 316L powder can be fabricated using selective laser sintering by proper selection of process parameters. Porosity, electrical conductivity and optical microscopy measurements were used to investigate the properties of fabricated samples. Our results show that a laser energy density between 1.50–2.00J/mm2 leads to a partial laser sintering mechanism where the powder particles are partially fused together, resulting in the fabrication of electrode scaffolds with 10% or higher porosity. The sample fabricated using 2.00J/mm2 energy density (60W–1200mm/s) exhibited a good electrical conductivity of 1.80×106S/m with 15.61% of porosity. Moreover, we have observed the porosity changes across height for the sample fabricated at 60W and 600mm/s, 5.70% from base and increasing to 7.12% and 9.89% for each 2.5mm height towards the top surface offering graded properties ideal for electrochemical devices, due to the changing thermal boundary conditions. These highly porous electrode scaffolds can be used as an electrode in electrochemical devices, potentially improving energy density and life cycle.

Electrochemical immunosensor constructed using TiO2 nanotubes as immobilization scaffold and tracing tag

A ternary TiO2 nanotube (TNT) composite and a signal antibody and horseradish peroxidase (HRP) functionalized TNT were designed as an electrode scaffold for immobilization of high quantity of capture antibody and a tracing tag for immunosensing, respectively. The polyaniline (PANI) was coated on TNTs by chemical oxidative polymerization, and gold nanoparticles were deposited on TNT-PANI with a routine chemical reduction. Various techniques including scanning electron microscopy, energy dispersive X-ray, transmission electron microscope, X-ray diffraction, Fourier transform infrared spectra, X-ray photoelectron spectra, impedance and electrochemical techniques were used to characterize the nano-materials. Using bis(sulfosuccinimidyl) suberate as amino cross-linker, the TNT composite could be further functionalized with protein G′ for oriented immobilization of capture antibody on electrode surface. Upon sandwich-type immunoreaction, the signal antibody on the tracing tag was quantitatively captured on the surface to generate sensitive electrochemical response with a H2O2 mediated HRP catalytic reaction. With α-fetoprotein as an analyte model, the immunosensor showed a linear range of 0.01–350ngmL−1 with a detection limit of 1.5pgmL−1. The accelerated electron transfer by the ternary composite, oriented immobilization of capture antibody and high loading of HRP on the TNT tracing tag greatly amplified the electrochemical signal, and led to the superior performance of the immunoassay.