2D MXenes Embedded Perovskite Hydrogels for Efficient and Stable Solar Evaporation

Solar evaporation is a facile and promising technology to efficiently utilize renewable energy for freshwater production and seawater desalination. Here, the fabrication of self-regenerating hydrogel composed of 2D-MXenes nanosheets embedded in perovskite La 0.6Sr 0.4Co 0.2Fe 0.8O3- δ (LSCF)/polyvinyl alcohol hydrogels for efficient solar-driven evaporation and seawater desalination is reported. The mixed dimensional LSCF/Ti3C2 composite features a localized surface plasmonic resonance effect in the polymeric network of polyvinyl alcohol endows excellent evaporation rates (1.98 kg m-2 h-1) under 1 k Wm-2 or one sun solar irradiation ascribed by hydrophilicity and broadband solar absorption (96%). Furthermore, the long-term performance reveals smooth mass change (13.33 kg m-2) during 8 h under one sun. The composite hydrogel prompts the dilution of concentrated brines and redissolves it back to water (1.2 g NaCl/270 min) without impeding the evaporation rate without any salt-accumulation. The present research offers a substantial opportunity for solar-driven evaporation without any salt accumulation in real-life applications.

Overview of Approaches to Increase the Electrochemical Activity of Conventional Perovskite Air Electrodes

The progressive research trends in the development of low-cost, commercially competitive solid oxide fuel cells with reduced operating temperatures are closely linked to the search for new functional materials as well as technologies to improve the properties of established materials traditionally used in high-temperature devices. Significant efforts are being made to improve air electrodes, which significantly contribute to the degradation of cell performance due to low oxygen reduction reaction kinetics at reduced temperatures. The present review summarizes the basic information on the methods to improve the electrochemical performance of conventional air electrodes with perovskite structure, such as lanthanum strontium manganite (LSM) and lanthanum strontium cobaltite ferrite (LSCF), to make them suitable for application in second generation electrochemical cells operating at medium and low temperatures. In addition, the information presented in this review may serve as a background for further implementation of developed electrode modification technologies involving novel, recently investigated electrode materials.

Effect of Steam to Carbon Dioxide Ratio on the Performance of a Solid Oxide Cell for H2O/CO2 Co-Electrolysis

The mixture of H₂ and CO, the so-called syngas, is the value-added product of H₂O and CO₂ co-electrolysis and the feedstock for the production of value-added chemicals (mainly through Fischer-Tropsch). The H₂/CO ratio determines the process in which syngas will be utilized and the type of chemicals it will produce. In the present work, we investigate the effect of H₂O/CO₂ (steam/carbon dioxide, S/C) ratio of 0.5, 1 and 2 in the feed, on the electrochemical performance of an 8YSZ electrolyte-supported solid oxide cell and the H₂/CO ratio in the outlet, under co-electrolysis at 900 °C. The B-site iron doped lanthanum strontium chromite La₀.₇₅Sr₀.₂₅Cr₀.₉Fe₀.₁O_3-δ (LSCF) is used as fuel electrode material while as oxygen electrode the state-of-the art LSM perovskite is employed. LSCF is a mixed ionic-electronic conductor (MIEC) operating both under a reducing and oxidizing atmosphere. The cell is electrochemically characterized under co-electrolysis conditions both in the presence and absence of hydrogen in the feed of the steam and carbon dioxide mixtures. The results indicate that under the same concentration of hydrogen and different S/C ratios, the same electrochemical performance with a maximum current density of approximately 400 mA cm^-2 is observed. However, increasing p(H₂) in the feed results in higher OCV, smaller iV slope and R_p values. Furthermore, the maximum current density obtained from the cell does not seem to be affected by whether H₂ is present or absent from the fuel electrode feed but has a significant effect on the H₂/CO ratio in the analyzed outlet stream. Moreover, the H₂/CO ratio seems to be identical under polarization at different current density values. Remarkably, the performance of the LSCF perovskite fuel electrode is not compromised by the exposure to oxidizing conditions, showcasing that this class of electrocatalysts retains their reactivity in oxidizing, reducing, and humid environments.

Microextrusion Printing of Multilayer Hierarchically Organized Planar Nanostructures Based on NiO, (CeO2)0.8(Sm2O3)0.2 and La0.6Sr0.4Co0.2Fe0.8O3-δ

In this paper, NiO, La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and (CeO2)0.8(Sm2O3)0.2 (SDC) nanopowders with different microstructures were obtained using hydrothermal and glycol-citrate methods. The microstructural features of the powders were examined using scanning electron microscopy (SEM). The obtained oxide powders were used to form functional inks for the sequential microextrusion printing of NiO-SDC, SDC and LSCF-SDC coatings with resulting three-layer structures of (NiO-SDC)/SDC/(LSCF-SDC) composition. The crystal structures of these layers were studied using an X-ray diffraction analysis, and the microstructures were studied using atomic force microscopy. Scanning capacitance microscopy was employed to build maps of capacitance gradient distribution over the surface of the oxide layers, and Kelvin probe force microscopy was utilized to map surface potential distribution and to estimate the work function values of the studied oxide layers. Using SEM and an energy-dispersive X-ray microanalysis, the cross-sectional area of the formed three-layer structure was analyzed-the interfacial boundary and the chemical element distribution over the surface of the cross-section were investigated. Using impedance spectroscopy, the temperature dependence of the electrical conductivity was also determined for the printed three-layer nanostructure.

Improved Durability of High-Performance Intermediate-Temperature Solid Oxide Fuel Cells with a Ba-Doped La0.6Sr0.4Co0.2Fe0.8O3-δ Cathode

As a device for direct conversion of chemical energy into electrical energy, the solid oxide fuel cell (SOFC) contributes positively to the sustainable development strategy. However, the commercialization of fuel cells is still impeded by severe cathode degradation caused by its limited stability at operating temperatures and being prone to Cr-poisoning from Cr-containing alloy interconnectors commonly used in these cells. This paper reports the development of a high-durability Ba-doped LSCF(La0.6Sr0.4Co0.2Fe0.8O3-δ) cathode material under realistic fuel cell operating conditions in the presence of the Cr alloy. In particular, when tested in a symmetrical cell constructed of Ba-doped LSCF, the polarization resistance of the cell remains very low at 0.06 Ω cm2 after being tested at 800 °C for 120 h exposed to Cr in 3% humidified air. In contrast, for the undoped LSCF under the same testing conditions, the polarization resistance of the cell increases ∼10 times from 0.22 Ω cm2 of the pristine cell to 2.18 Ω cm2 after Cr-exposure testing. Furthermore, when tested in an anode-supported complete cell as a cathode under typical SOFC operation conditions at 750 °C, the cell with the Ba-doped LSCF cathode displays significantly low degradation rates of 0.00056% h-1 (without Cr) and 0.00310% h-1 (with Cr); both are much lower than that of the cell using the undoped LSCF cathode (0.00124% h-1 without Cr and 0.01082% h-1 with Cr). This enhanced durability and Cr-tolerance exhibited by the Ba-doped LSCF cathode stem from its higher crystal structure stability and improved chemical resistance compared to undoped LSCF.

Oxygen Transport Membranes for Efficient Glass Melting

Glass manufacturing is an energy-intensive process in which oxy-fuel combustion can offer advantages over the traditional air-blown approach. Examples include the reduction of NO_x and particulate emissions, improved furnace operations and enhanced heat transfer. This paper presents a one-dimensional mathematical model solving mass, momentum and energy balances for a planar oxygen transport membrane module. The main modelling parameters describing the surface oxygen kinetics and the microstructure morphology of the support are calibrated on experimental data obtained for a 30 μm thick dense La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) membrane layer, supported on a 0.7 mm porous LSCF structure. The model is then used to design and evaluate the performance of an oxygen transport membrane module integrated in a glass melting furnace. Three different oxy-fuel glass furnaces based on oxygen transport membrane and vacuum swing adsorption systems are compared to a reference air-blown unit. The analysis shows that the most efficient membrane-based oxyfuel furnace cuts the energy demand by ~22% as compared to the benchmark air-blown case. A preliminary economic assessment shows that membranes can reduce the overall glass production costs compared to oxyfuel plants based on vacuum swing adsorption technology.

Enhanced catalytic activity toward O₂ reduction on Pt-modified La₁-xSrxCo₁-yFeyO₃-δ cathode: a combination study of first-principles calculation and experiment

Using the first-principles calculation and the electronic conductivity relaxation (ECR) experimental technique, we investigated the adsorption and dissociation behaviors of O2 on Pt-modified La0.625Sr0.375Co0.25Fe0.75O3-δ (LSCF) surface. Toward the O2 reduction, the calculation results show that the perfect LSCF (100) surface is catalytically less active than both the defective (100) surface and the perfect (110) surface. O2 molecule can weakly adsorb on the perfect LSCF (100) surface with a small adsorption energy of about -0.30 eV, but the dissociation energy barrier of the O2 molecule is about 1.33-1.43 eV. Doping of Pt cluster on the LSCF (100) surface can remarkably enhance its catalytic activity. The adsorption energies of O2 molecules become -1.16 and -1.89 eV for the interfacial Feint site and the Ptbri bridge site of Pt4-cluster, respectively. Meanwhile, the dissociation energy barriers are reduced to 0.37 and 0.53 eV, respectively. The migration energy barrier of the dissociated oxygen from the interfacial Pt to the LSCF surface is 0.66 eV, and it is 2.58 eV from the top site of the Pt cluster to the interfacial Pt site, suggesting that it is extremely difficult for oxygen to migrate over the Pt cluster. The Bader charge analysis results further indicate that the charges transferring from Pt cluster to LSCF surface promote the adsorption and dissociation of O2 molecules. Experimentally, a dramatic decrease of the surface oxygen exchange relaxation time was observed on Pt-modified LSCF cathode, with a chemical surface exchange coefficient increased from 6.05 × 10(-5) cm/s of the bare LSCF cathode to 4.04 × 10(-4) cm/s of the Pt-modified LSCF cathode, agreeing very well with our theoretical predictions.