Triple Phase Boundary Research Articles

Electrochemically-Assisted Synthesis of Platinum Nanoparticles Using Gas-Diffusion Electrocrystallization (GDEx) and Their Electrocatalytic Activity for Methanol Oxidation

In recent years, interest in using unsupported catalysts, especially Pt-based nanomaterials, has resurged in direct methanol fuel cells (DMFC). Unsupported catalysts eliminate the problems related to the corrosion of carbon catalyst supports, thus improving the long-term stability of DMFC. In addition, the design of catalyst synthesis protocols to tailor nanostructured materials with high surface area and catalytic activity improves catalyst performance.1 Consequently, we recently reported a method for the synthesis of platinum group metal (PGM, i.e., Pt, Pd, Rh) nanoparticles (NPs), using a process called Gas Diffusion Electrocrystallization (GDEx) (Fig. 1a).2 The simultaneous electrochemical reduction of CO2 and water occurs at the triple-phase boundary of uncatalyzed gas-diffusion electrodes, producing H2 and CO. Both gases, but especially H2, are reducing agents for water-soluble noble metal ions leading to the formation of small metal nanoclusters. CO can also act as a capping agent. Furthermore, the presence of CO2 stabilizes the pH, avoiding the formation of metal (hydr)oxides.In this work, we used the GDEx process to synthesize unsupported Pt NPs using polyvinyl pyrrolidone (PVP, 55000 Mw) as a stabilizer and evaluated their electrocatalytic activity for methanol oxidation. The synthesis was performed at -30 mA cm-2, using 3.0 mM Pt4+ (as H2PtCl4) as metal precursor and different concentrations of PVP (i.e., 0.0, 0.01, 0.1 and 1.0 g L-1). We chose low concentrations of stabilizer to facilitate its removal after synthesis, as clean surface catalysts are required for electrocatalytic applications. The size distribution of the Pt NPs, measured using Scanning Electron Microscopy (SEM), was 64 ± 22, 60 ± 22, 42 ± 18, and 38 ± 12 nm for PVP 0.0, PVP 0.01, PVP 0.1, and PVP 1.0, respectively. For comparison, the reduction of 3.0 mM Pt4+ using 1.0 g L-1 PVP with only H2 (either electrogenerated or bubbled) produced bigger and much more polydisperse particles (100 nm–1000 nm), highlighting the importance of the GDEx process and the presence of CO to synthesize small NPs using low concentrations of stabilizer. Furthermore, Transmission Electron Microscopy (TEM) images (Fig. 1b) revealed that the NPs are nanoclusters of single crystals of 2 nm–4 nm in diameter.The synthesized Pt NPs were cleaned using NaOH,3 and their electrocatalytic activity was evaluated in acidic media. The CV curves of Pt NPs in 0.5 M H2SO4 are shown in Fig. 1c. All catalysts showed hydrogen adsorption-desorption peaks from -0.2 to 0.1 VAg/AgCl. The calculated electrochemical surface area (ECSA), obtained by integrating the charge in the hydrogen adsorption-desorption region, was 7.6 ± 0.7, 14.1 ± 1.2, 33.6 ± 1.2, and 30.3 ± 1.0 m2 g-1 Pt for PVP 0.0, PVP 0.01, PVP 0.1 and PVP 1.0 respectively. The MeOH electro-oxidation experiments were performed in 0.5 M H2SO4 containing 1.0 M MeOH, and the CV curves are shown in Fig. 1d. The forward anodic peak (If) at about 0.7 VAg/AgCl corresponds to MeOH oxidation, while the backward anodic peak (Ib) at about 0.5 VAg/AgCl corresponds to the oxidation of the incompletely oxidized carbonaceous species formed in the forward sweep. The mass activity (MA), defined by the forward peak current density per unit of catalyst loading, was 71 ± 2, 136 ± 7, 463 ± 28, and 341 ± 25 mA mg-1 Pt for PVP 0.0, PVP 0.01, PVP 0.1, and PVP 1.0 g L-1, respectively. Hence, the MA scale with the ECSA . Besides, ECSA (and hence MA) increases when the PVP concentration during synthesis increases. However, this trend is not followed for a PVP concentration of 1.0 g L-1. Even though all catalysts were cleaned using the same protocol, residual PVP might still be left on the surface of Pt NPs synthesized using 1.0 g L-1 PVP, lowering their electrocatalytic activity.Overall, the GDEx process was a useful tool for synthesizing unsupported Pt NPs using low concentrations of stabilizer and with high electrocatalytic activity. This project has received funding from the European Union's Horizon 2020 Research and Innovation program under Grant Agreements n° 730224 (PLATIRUS) and n° 958302 (PEACOC) 1. E. Antolini, J. Perez, J. Mat. Sci, 2011, 46, 4435–4457.2. X. Dominguez-Benetton, O. Martinez-Mora, J. Fransaer, EP21165681, 2021.3. A. Zalineeva, S. Baranton, C. Coutanceau, G. Jerkiewicz, Langmuir, 2015, 31, 1605–1609. Figure 1

Numerical study on TPB density and percolation properties of microstructure reconstruction of nickel/yttria stabilized zirconia cermet anode based on discrete element method

Microstructure is essential for electrochemistry and transport in Ni/YSZ cermet anodes. Targeting the complexity and irregularity of porous networks, the percolation theory is widely used to model electrode microstructures in representative element (RE) scale based on an ideal prototype of particle units. With the pros of simplicity and generality, however, the idealized particle model deviates somehow the true state of particle clusters. Modeling connections between a lot of particles, the discrete element method (DEM) provides a more realistic state, meanwhile brings high computation cost. This paper provides a combined approach which starts from a DEM-based model for compaction and evolution between particle arrays, then analyzes the statistical properties, e.g. density of triple phase boundary (TPB) and percolations of particles. With consideration of multiple-particle overlaps, the DEM-fitted relationship of percolation probability vs. coordination number presents a smaller percolation threshold and a slower growing rate before reaching a full percolation, compared with some published formulae based on the percolation theory. Simulations at different temperatures are employed to study the effects of sintering. This work has significance of understanding the evolution and optimization of the electrode microstructure, not limited to Ni/YSZ system, and is helpful for more accurate solid oxide fuel cell modeling.

High performance finite element simulations of infiltrated solid oxide fuel cell cathode microstructures

To better understand the effects of infiltration on local electrochemistry and transport in solid oxide fuel cell (SOFCs) electrodes, high-throughput, high-performance finite element simulations are presented within dozens of SOFC cathodes containing synthetically generated nanoscale infiltrates. The computational approach retains the complex microstructural morphologies of cathodes, including those of the three backbone phases (gas, ion, and electron conductors) and the infiltrates (an electron conductor), in meshed domains and computes distributions of local electrochemical quantities within the domains. Simulations were implemented on a supercomputer and converged for 48 distinct microstructural subvolumes, with varying backbone heterogeneities and infiltrate loadings. Analyzing both the ensemble (averaged over subvolumes) and the local (evaluated within subvolumes) performance metrics indicate that infiltration of an electron conductor significantly improves the electrochemical performance of each backbone in a linear fashion with the increase of triple phase boundary content, but the essential ionic transport pathways of the backbone are unchanged. These results shed light into the design and fabrication of optimal electrodes in fuel cells.

Characteristic dual-domain composite structure of reduced graphene oxide and its application to higher specific capacitance

In this article, characteristic dual-domain structures of rGO layers, to be applied to fascinating electrode materials for energy storage systems, such as supercapacitors, are reported. Conductive atomic force microscopy (C-AFM) technique reveals that the rGO surface consists of a dual-domain structure of graphene and GO components, which provide simultaneous electric-electrolyte pathways to the electrode, and that the amount, configuration, and connectivity of both domains are depend on the reduction level of rGO. The rGO sheet having a finely connected and well-balanced dual-domain composite structure provided higher specific capacitance compared to others. Using a concept of triple-phase boundary (TPB) where three phases, i.e., pseudo-type ceramic particle and the dual-domains coincide, hybrid composite sheets of Fe2O3@rGO and MnO2@rGO were also fabricated and examined for further enhancing specific capacitance. Besides, the reduction mechanism of the rGO layer by hydrazine to develop such dual-domain structures and the formation behavior of freestanding rGO sheets from rGO suspension were discussed in this study.

Constructing perovskite/alkaline-earth metal composite heterostructure by infiltration to revitalize CO2 electrolysis

Solid oxide electrolysis cell (SOEC) can efficiently convert CO2 to CO using renewable energy sources, which can alleviate the threatening impact of excessive CO2 emissions on the human life and environment. Moreover, it also realizes chemical storage of available electricity to ease the energy consumption crisis. Designing cathode materials with abundant active sites and high-efficiency electrochemical catalytic activity toward CO2 reduction is crucial for realizing practical applications of SOEC. Herein, construction of a composite heterostructure of alkaline-earth metal compounds and Sr2Fe1.5Mo0.5O6−δ (SFM) double perovskite oxides by alkaline-earth metal infiltration was proposed. This strategy enriched the reactive sites and led to the expansion of the triple-phase boundary, thereby effectively improving the electrochemical performance of SOEC. The experimental results show that the infiltration of alkaline-earth metal led to significant increase in the surface active sites, improvement in the adsorption and activation process of CO2, and promotion of the formation of activated carbonate intermediates. The current density on the CaCO3-infiltrated SFM cathode reached 1.723 A cm−2, while the current density on the SFM cathode could only reach 1.117 A cm−2 at 1.8 V and 800 °C. The alkaline-earth metal infiltration strategy not only improves the electrochemical performance, but also maintains excellent stability after 100 h of operation at high temperature and 12 redox cycles. All these results indicate that the construction of heterostructure through alkaline-earth metal infiltration provides an effectual strategy for improving the electrochemical performance of SOEC.

Highly dispersed nickel species on iron-based perovskite for CO2 electrolysis in solid oxide electrolysis cell

Feasible construction of cathode materials with highly dispersed active sites can extend the triple-phase boundaries, and therefore leading to enhanced electrode kinetics for CO 2 electrolysis in solid oxide electrolysis cell (SOEC). Herein, highly dispersed nickel species with low loading (1.0 wt%) were trapped within the La 0.8 Sr 0.2 FeO 3– δ -Ce 0.8 Sm 0.2 O 2– δ via a facial mechanical milling approach, which demonstrated excellent CO 2 electrolysis performance. The highly dispersed nickel species can significantly alter the electronic structures of the LSF-SDC without affecting its porous network and facilitate oxygen vacancy formation, thus greatly promote the CO 2 electrolysis performance. The highest current density of 1.53 A·cm −2 could be achieved when operated under 800 °C at 1.6 V, which is about 91% higher than the LSF-SDC counterpart. Highly dispersed nickel species with low loading on perovskite can alter its electronic structure and facilitate the oxygen vacancy formation, thus greatly promote the CO 2 electrolysis.

Nanoemulsion-Coated Ni-Fe Hydroxide Self-Supported Electrode as an Air-Breathing Cathode for High-Performance Zinc-Air Batteries.

To improve the energy conversion efficiency and durability of zinc-air batteries (ZABs) for large-scale implementations, here we propose an "air-breathing" strategy to significantly enlarge triple-interfaces with intensified mass transfer. By dip-coating the aerophilic perfluorochemical compounds (PFC) and amphiphilic ionomers into the self-supported electrodes, (1) the high solubility of O2 in the PFC nanoemulsions greatly increases triple-phase boundaries and facilitates the efficient supply/removal of O2 from the electrolyte; (2) the ionomers with hydrophobic and hydrophilic functionalities enable fast gas, water, and ion transport to the triple-phase boundaries; and (3) the self-supported electrode without binder ensures fast electron transfer while the firm integration prevents catalyst shedding. By applying this strategy, the ZABs show a high power density of 115 mW cm-2 and a narrow discharge/charge gap of 0.64 V at 10 mA cm-2 and a long-cycling durability (over 1000 h). This work provides a universal approach to promote gas-evolving reactions for electrochemical applications.

Hanging meniscus configuration for characterizing oxygen-reduction electrocatalysts in highly concentrated electrolytes

• Hanging meniscus configuration method was newly developed for porous catalysts. • This method evaluates oxygen reduction activity in highly concentrated electrolyte. • This method complements conventional rotating disk electrode (RDE) method. Oxygen reduction reaction (ORR) in metal-air batteries or fuel cells often require highly concentrated electrolyte for higher conductivity and electrochemical stability. However, conventional rotating disk electrode (RDE) method is ineffective to evaluate ORR activity in the real systems, because the scarce dissolved oxygen in highly concentrated electrolyte fails to provide significant ORR on RDE. Herein, we report a hanging meniscus configuration method for evaluating the electrocatalytic activity in highly concentrated electrolyte solutions, utilizing atmospheric oxygen through the triple-phase boundary. The newly developed method evaluated the ORR activity of silver and platinum catalysts in highly concentrated KOH electrolyte for zinc-air batteries, enabling the characterization in more realistic experimental condition.

Frequency Analysis of Water Electrolysis Current Fluctuations in a PEM Flow Cell: Insights into Bubble Nucleation and Detachment

A cross-shaped transparent electrolysis flow cell was designed to simultaneously perform polarization experiments to about 2 A cm−2 while monitoring the current response due to bubble formation and detachment. The flow cell was designed in order to accommodate a large electrolyte flow and have flow conditions similar to a PEM electrolyzer. Ir foil experiments using rapid electrochemical cycling techniques were performed first as a quality control measure for cell functionality. Literature quality cyclic voltammograms were obtained, with the anodically formed iridium oxide film growth plateauing after 1000 cycles. The performance of four different Ti current collector meshes were evaluated using a commercial IrO2 CCM using 3.5 M H2SO4 at 21 ± 0.5°C. The best performing current collector mesh had the largest triple-phase boundary (TPB) length of 56 mm and a porosity of 52%. Using Fourier Transform analysis, the bubble ratios for different current collector and frequency regimes were obtained. The lowest frequency bubble analysis (< 1 Hz) showed the best correlation with the performance of the different meshes.

A cathode-supported solid oxide fuel cell prepared by the phase-inversion tape casting and impregnating method

Cathode-supported Solid Oxide Fuel Cells (SOFCs) have unique advantages of stability and operating life, but the commercialization process is limited by manufacturing cost and poor electrochemical performance. In this paper, a cathode-supported SOFC with 3YSZ-LSM95| porous 8YSZ| dense 8YSZ| porous 8YSZ sandwich structure was successfully fabricated by phase-inversion tape casting and co-sintering method. The cathode support demonstrated finger shaped macropore with high porosity. The long-term stability of symmetric cells with and without impregnated LSC nanoparticals was evaluated and no obvious degregadion were observed. The peak power densities of single cell reached 464, 209, 271 and 144 mW cm−2 at 850, 800, 750 and 700 °C respectively when Ni nano-particles as the anode catalyst and LSC nano-particles as the cathode catalyst, showing a significant improvement in electrochemical performance compared with non-LSC cell. Additionally, the distribution of relaxation times (DRT) method was empoyed to analysis the polarization process at high-resolution, for better understanding the mechanism of electrochemical reaction of cells. The results indicated the impregnated LSC particles can increase the triple phase-boundaries (TPBs) for fast oxygen reduction reaction and improve the electrochemical performance. However, the optimization of anode and cathode are needed in the future work.

MoS2 nanosheet integrated electrodes with engineered 1T-2H phases and defects for efficient hydrogen production in practical PEM electrolysis

Low electrical conductivity and poor accessibility of MoS2 reaction sites raise great challenges in maximizing the triple-phase-boundary (TPB) sites of MoS2-based electrodes and minimizing ohmic losses for efficient hydrogen evolution reaction (HER) in practical proton exchange membrane (PEM) water electrolysis. Herein, we report a scalable hydrothermal approach to fabricate ionomer-free integrated electrodes with engineered 1 T-2 H heterophase and defect-rich MoS2 nanosheets (MoS2NSs) in-situ grown onto the carbon fiber paper (CFP). With an ultralow loading of 0.14 mg/cm2, a small voltage of 2.25 V was obtained at 2000 mA/cm2 in a practical cell with Nafion115 membrane, which outperforms all previously reported high-loading non-precious catalyst-based electrodes. Impressively, it shows 44 times higher mass activity than a high-loading and ionomer-mixed MoS2 assemblies electrode. This work builds a bridge from catalyst optimization to electrode fabrication and provides a promising direction for improving intrinsic catalytic activity, electrode conductivity and stability for practical PEM water electrolysis.

Highly durable Sr-doped LaMnO3-based cathode modified with Pr6O11 nano-catalyst for protonic ceramic fuel cells based on Y-doped BaZrO3 electrolyte

Sr-doped LaMnO3 (LSM) is one of the state-of-the-art cathodes with outstanding chemical stability but suffers from poor electrochemical activity. It is promising that LSM can be used as good cathode for protonic ceramic fuel cells (PCFCs), provided that its catalytic activity can be improved. Herein, we have developed a high-performance and durable LSM-based cathode used for PCFCs with stable Y-doped BaZrO3 electrolyte. In this work, commercial LSM cathode is mixed with high-performance BaZr0.85Y0.15O3-δ particles. Pr6O11 nano-catalysts are homogeneously dispersed into the composite cathode, resulting in a significant decrease in the cathode polarization resistance from 0.51 to 0.12 Ω·cm2 at 600 °C. The power output improves by ~96% at 600 °C. Distribution of relaxation time analysis indicates that the processes of oxygen adsorption/dissociation and oxygen species diffuse to triple phase boundary sites are significantly promoted by Pr6O11. Furthermore, the 100 h stability tests show that the modified cathode is extremely stable.

Generalized Poisson-Nernst-Planck-Based Physical Model of the O2∣LSM∣YSZ Electrode

The paper presents a generalized Poisson-Nernst-Planck model of an yttria-stabilized zirconia electrolyte developed from first principles of nonequilibrium thermodynamics which allows for spatial resolution of the space charge layer. It takes into account limitations in oxide ion concentrations due to the limited availability of oxygen vacancies. The electrolyte model is coupled with a reaction kinetic model describing the triple phase boundary with electron conducting lanthanum strontium manganite and gaseous phase oxygen. By comparing the outcome of numerical simulations based on different formulations of the kinetic Eqs. with the results of EIS and CV measurements we attempt to discern the existence of separate surface lattice sites for oxygen adatoms and surface oxides from the assumption of shared ones. Moreover, we show that the mass-action kinetics model is sensitive to oxygen partial pressure unlike exponential kinetics models. The resulting model is fitted to a dataset of EIS and CVs spanning multiple temperatures and pressures, using various relative weights of EIS and CV data in the fitness function. The model successfully describes the physics of the interface around the OCV.

Gas Diffusion Layers: Experimental and Modeling Approach for Morphological and Transport Properties

ConspectusElectrochemical technologies are key to decarbonizing the energy sector. Electrification of the energy sector is underway with battery technologies dominating the light-duty electric vehicles market. It is more challenging to decarbonize historically difficult to decarbonize sectors, such as heavy-duty transportation, planes, ships, and the chemical manufacturing industry (ammonia, cement, steel). Green hydrogen produced via electrolysis will be used as a fuel and a feedstock in some of these processes. At the heart of the hydrogen economy are polymer electrolyte fuel cells (PEFCs), devices that convert hydrogen into electricity. Gas diffusion layers (GDLs) have an integral role in PEFCs, as they are porous carbon layers that transport reactants and products and also remove heat and conduct electricity. To improve the PEFCs’ performance and reduce degradation of materials, an understanding of coupled morphological properties and transport phenomena in the GDLs is needed. In this Account, we emphasize the integration of experimental and modeling approaches to achieve complete understanding of materials and transport properties of the GDLs. Our approach builds in complexity from simpler ex situ experiments to in situ and last to 3-D integrated modeling predictions. GDL morphology is complex, as its fabrication includes several stochastic steps (immersion of GDL in various baths to achieve the desired surface wettability) and only 3-D techniques, such as X-ray computed tomography can capture morphology correctly. Porosity, pore-size distribution, tortuosity, and formation factor are the most important morphological properties of the GDLs. For PEFC applications, water is generated in the catalyst layers and is transported through the GDLs. Therefore, GDL wettability directly impacts water permeability through the GDLs. Using in situ water injection experiments, we directly observe which pores water fill at what liquid pressure. This result provides information about the GDL’s affinity to intake water. GDLs are typically of mixed wettabilities, and internal wettability until recently has been unknown. Having images of water inside the GDL enabled us to track the triple-phase boundary at the fiber–water–air interface to obtain local contact angles in the locations where water was present. The percentage of contact angles that were hydrophilic correlated well to the percentage of surface oxides on the GDL surface using X-ray photoelectron spectroscopy (XPS). We envision many other groups using the method of XPS to determine internal surface wettability of the GDLs, as it is relatively fast. Heat transport and evaporation/condensation of water in the GDL is studied using in situ X-ray CT experiments. These provide direct insight into pore-scale water transport under thermal gradients. Three-dimensional geometries of GDLs are exported for transport simulations using the lattice Boltzmann method (LBM). Similarly, we advocate for building the LBM simulations, from water injection studies first to validate the model only to operando PEFC models later. LBM coupling with a continuum model enables a computational saving, allowing us to map local temperature, reactant, and product distributions in the GDLs.

Fabrication of 3D NiO-YSZ structures for enhanced performance of solid oxide fuel cells and electrolysers

Increasing densities of (electrode–electrolyte-pore) triple phase boundaries (TPBs) / reaction sites enhance performances of solid oxide electrochemical reactors (SOERs) in both fuel cell (SOFC) and electrolyser (SOE) modes. Inkjet 3D printing is capable of construction of ceramic microstructures on support layers, enabling fabrication of SOERs with enhanced active area to geometric area ratios, thereby up-scaling effective areas / TBP lengths per unit volume.A Ni(O)-YSZ functional layer was designed and 3D inkjet printed with a surface of circular pillars, a facile geometry for printing that increased the interfacial to geometric area ratio. Deposition of further functional layers and sintering resulted in fully fabricated reactors with structures: H2O-H2 | Ni(O)-YSZ support | Ni(O)-YSZ pillars | YSZ | YSZ-LSM | O2, Air. The corresponding planar structured cell also was fabricated with the same components, for comparison of its electrochemical performance with that of the pillar-structured cell. The latter exhibited performance enhancement over its planar counterpart by factors of ca. 1.5 in fuel cell mode, ca. 3 in steam electrolysis mode, and ca. 4–5 in CO2 electrolysis mode, thereby demonstrating the potential of geometric structuring of electrode | electrolyte interfaces by 3D printing for developing higher performance SOERs.

Improved Toluene Response of Mixed-Potential Type YSZ-Based Gas Sensors Using CeO2-Added Au Electrodes

YSZ-based potentiometric sensors employing thin CeO2-added Au sensing electrodes (SEs) were fabricated by using a spin-coating method, and effects of the CeO2 addition on their toluene sensing properties were examined. The sensor response (ΔE) to 50 ppm toluene of the sensors using 8 wt% CeO2-added Au SEs tended to decrease with an increase in the number of spin-coating cycles (x: 5, 10, 15; i.e., the thickness of SEs). However, ΔE of the sensors using 24 wt% CeO2-added Au SEs showed an opposite behavior to what was observed for 8 wt% CeO2-added Au SEs. The sensor using the thickest SE (x: 15) showed the largest ΔE (e.g., ca. 212 mV for 50 ppm toluene) at 450 °C among all the sensors examined and responded even to 0.5 ppm toluene. ΔE exponentially increased with an increase in logarithmic toluene concentration in the range higher than 10 ppm. These obtained results indicate that electrochemical toluene oxidation proceeds at triple-phase boundaries in SE with gas (Au/CeO2/gas) in addition to conventional TPBs (SE/YSZ/gas) in addition to the conventional interface at SE/YSZ/gas, because CeO2 is a mixed ionic and electronic conductor. The electrochemical reactions at TPBs of the sensor were also discussed on the basis of the I–E characteristics and the electrochemical impedance properties.

An ingenious design of nanoporous nafion film for enhancing the local oxygen transport in cathode catalyst layers of PEMFCs

An intractable issue accompanied with continuously reducing the Pt loading in cathodes of polymer electrolyte membrane fuel cells (PEMFCs) deals with a sudden increase in the oxygen transport resistance in cathode catalyst layers (CCLs), especially the local oxygen transport resistance that results from oxygen permeating through Nafion ultrathin film covering on Pt surface. Herein, we successfully regulate a nanoscale distribution of Nafion film via using polyvinyl alcohol (PVA) as a sacrificial pore-forming agent, which can well multiply triple-phase boundaries and provides more oxygen reduction reaction sites. The pore-forming mechanism is clarified via molecular dynamics (MD) simulation, while the oxygen transport resistance and fuel cell performance are electrochemically measured in situ. The results shows that the as-created nanopores on/in the Nafion film could greatly diminish the local oxygen transport resistance from 0.37 s cm−1 to 0.08 s cm−1, corresponding to a 78% decrease, thus improving fuel cell performance. It is believed that the nanoscale controlling of Nafion ionomer morphology in CCLs is innovative and instructive in PEMFC electrode design and could shed light on numerous types of electrochemical equipment.

A high-performance oxygen electrode for solid oxide cells: Compositional optimisation of barium cobaltite-based composites

Solid oxide electrochemical cells are promising devices for energy conversion and chemical synthesis. In this respect, one of the main challenges to improving cell performance is the decrease in the polarisation resistance (Rp) of the oxygen electrodes. Here, the electrochemical properties of composite electrodes of Ba2Co9O14/Ce0.8Gd0.2O2-δ (BCO/CGO) are investigated by electrochemical impedance spectroscopy at 600–800 °C. The composite with 50 vol% CGO exhibits the lowest polarisation resistance, 0.3 Ω cm² at 600 °C in O2. The comparatively superior performance results from an increased triple-phase boundary (TPB) length due to the increased percolation of both phases. This successful result presents a high-performing oxygen electrode for solid oxide electrochemical systems.

Co-doped cerium oxide Fe0.25-xMnxCe0.75O2-δ as a composite cathode material for IT-SOFC

In this study, Fe-Mn co-doped ceria Fe0.25Mn0.00Ce0.75O2-δ (FMDC1), Fe0.23Mn0.02Ce0.75O2-δ (FMDC2), Fe0.21Mn0.04Ce0.75O2-δ (FMDC3), and Fe0.19Mn0.06Ce0.75O2-δ (FMDC4) powders are synthesized by sol gel method and evaluated as cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFC). The combination of Fe and Mn significantly enhanced the ceria catalytic activity and oxygen kinetics for redox-based reactions. The effects of the co-doping mechanism on the phase composition, optical behavior, and electrochemical performance are mainly investigated. The prepared samples are characterized by XRD, SEM, FTIR, UV–vis, and conductivity tests. X-ray diffraction analysis revealed well-developed crystallinity with a single phase cubic structure of synthesized cathode material. SEM depicted the highly porous facet for Fe0.19Mn0.06Ce0.75O2-δ (FMDC4) resulted in the large triple-phase boundaries for the reduction of ambient air. The inclusion of Mn3+and Fe3+ ions into CeO2 network created additional oxygen vacancies (Ov) and simultaneously reduced the optical band gap energy from 2.81 eV for FMDC1 (x = 0.00) to 2.54 eV for FMDC4 (x = 0.06). Among the four samples, FMDC4 possessed the highest electrical conductivity (∼0.89 Scm−1) at 650 °C and corresponding low activation energy of ∼0.301 eV, which lead to good catalytic activity with an enhanced electrochemical performance of the SOFC system. The open-circuit voltage (OCV) attained the value of ∼0.98 V, maximum power density of ∼335 mW cm−2 is obtained at 550 °C, which is comparable to previously reported electrodes. The results suggested that the combination of Fe and Mn into ceria can be used as an effective catalytic promoter for oxygen reduction reactions (ORR), and the composition of FMDC4 resulted in the peak conductivity, short term stability and highest power density as compared to other synthesized samples.

Microscale-decoupled charge-discharge reaction sites for an air electrode with abundant triple-phase boundary and enhanced cycle stability of Zn-Air batteries

Decreasing the charge-discharge voltage gap and increasing the cycling stability is pivotal but challenging for the practical application of rechargeable Zn-air battery (ZAB). Until now, many efforts have been paid in the electrocatalyst development for the air electrode, but few works have been done on the electrode structure design which is quite import for the battery performance. Herein, we design a decoupled air electrode by integrating a hydrophilic mesh active for oxygen evolution reaction (OER) with a hydrophobic layer active for oxygen reduction reaction (ORR). The decoupled air electrode could separate the OER and ORR sites at microscale, which could alleviate the oxidative corrosion of the ORR layer along cycling. Meanwhile, it also shows adjustable contact angle by fancily changing the texture of the mesh, which enables the optimal hydrophilicity towards abundant triple phase boundary for superior discharge performance. The ZAB based on the decoupled air electrode exhibits a small initial voltage gap of 0.75 V at 10 mA cm−2, and it was stably cycled for 240 h. This work provides a feasible strategy to simultaneously accelerate the electrochemical reaction and improve the electrode stability, and it could be inspiring for other multiphase reaction involved devices.