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CeO2-based surface modification is established as an effective strategy for improving the electrochemical performance of solid oxide electrolysis cells (SOECs), but the relevant mechanism has not been fully explored yet. Here, we employ focused ion beam-scanning electron microscopy to examine the microstructural evolution of bare nickel-based yttrium-stabilized zirconia (Ni/YSZ) electrode (reference cell) and Gd-doped CeO2 (CGO)-infiltrated Ni/YSZ electrode (optimized cell) before and after 100-h durability test. The initial current density of the optimized cell was 1.16 A cm−2 (at 1.3 V), which was 1.5 times larger than that of the reference cell. The voltage of the reference cell degraded dramatically due to a 1.16% reduction in the volume fraction of Ni, while the optimized cell showed a negligible degradation with a minor change in the volume fraction of Ni. It was confirmed that CGO nanoparticles formed a protective layer on the Ni surface during the electrolysis process, which prevented further evaporation of Ni. Overall, the infiltration of CGO into traditional Ni/YSZ electrode prevented decrease in the triple-phase boundary density and reduced the resistance by providing additional active sites for hydrogen evolution reaction. We believe that this work provides an efficient strategy for developing high-performance and long-term stable SOECs.

A novel molten salt method was employed to synthesize 10% Nb doped La0.6Sr0.4FeO3−δ (LSFN). The as-synthesized powders were pure and adopted a porous structure. Using LSFN as the oxygen electrode for a reversible solid oxide cell, the button cell exhibited a peak power density of 0.79 W cm−2 in H2 and an electrolysis current density of 0.89 A cm−2 at 1.3 V in 50% CO2/50% H2 at 800 °C. A large fraction of Fe2+ was found in LSFN, resulting in the improved performance. Our results indicate that the molten salt method is a promising approach for the synthesis of highly active perovskite electrode with a dopant of Nb.

© 2020 Elsevier B.V. Molten salts are a unique type of electrolyte enabling high-temperature electrochemical energy storage (EES) with unmatched reversible electrode kinetics and high ion-conductivities, and hence impressive storage capacity and power capability. However, their high tendency to evaporate and flow at high temperatures challenges the design and fabrication of the respective EES devices in terms of manufacturing cost and cycling durability. On the other hand, most of these EES devices require lithium-containing molten salts as the electrolyte to enhance performances, which not only increases the cost but also demands a share of the already limited lithium resources. Here we report a novel quasi-solid-state (QSS) electrolyte, consisting of the molten eutectic mixture of Na2CO3-K2CO3 and nanoparticles of yttrium stabilized zirconia (YSZ) in a mass ratio of 1:1. The QSS electrolyte has relatively lower volatility in comparison with the pristine molten Na2CO3-K2CO3 eutectic, and therefore significantly suppresses the evaporation of molten salts, thanks to a strong interaction at the interface between molten salt and YSZ nanoparticles at high temperatures. The QSS electrolyte was used to construct an iron-air battery that performed excellently in charge-discharge cycling with high columbic and energy efficiencies. We also propose and confirm a redox mechanism at the three-phase interlines in the negative electrode. These findings can help establish a simpler and more efficient approach to designing low-cost and high-performance molten salt metal-air batteries with high stability and safety.

Exploring high-performance electrocatalysts for the oxygen evolution reaction (OER) is pivotal for renewable energy storage and conversion. The surface self-reconstruction during the OER is considered as the key of highly active catalysts, whereas identifying the local electronic and geometric structure of the reconstruction-derived components is challenging. Herein, an in situ exsolution method towards the typical LaCo0.8Fe0.2O3−δ perovskite is developed to obtain a new type of lanthana-anchored CoFe catalyst. The optimized catalyst exhibits a low overpotential of 293 mV to reach the current density of 10 mA cm−2 in 0.1 M KOH. Most importantly, operando X-ray absorption spectroscopy (XAS) measurements demonstrate that the CoFe species in the catalyst are nearly transformed into unique (Co/Fe)O(OH) with a definite coordination-unsaturated structure under electrochemical conditions, which actually contributes to this superior performance. Moreover, the presence of the lanthana support promotes this transformation. Our work not only suggests a facile reconstructive strategy to dramatically enhance the OER activity of perovskite oxides in alkaline media, but also unravels the fine structure of true active sites through operando X-ray spectroscopic tracking.

Fabricating lanthanum strontium manganite (LSM) ceramics with certain shapes is important for the design and construction of high-temperature energy conversion and storage devices. Here, we describe a low-cost and environmentally friendly method for fabricating LSM ceramics via agar gel casting and high temperature sintering. This new approach uses temperature tuning to fabricate LSM gel bodies, not only by manufacturing in the secondary process but also by remolding and recycling during the gel casting process. The effect of the sintering temperature on the properties of LSM ceramics was investigated as well. As a result, the porosity and compressive strength of LSM ceramics sintered at 1000 &deg, C are ~60% and 5.6 MPa, respectively. When the sintering temperature increases to 1200 &deg, C, the porosity decreases to ~28%, whereas the compressive strength increases to 25 MPa, which is able to meet the requirement of cathode-supported SOFCs (solid oxide fuel cells).

Nanoscale perovskite oxides with enhanced electrocatalytic activities have been widely used as oxygen electrodes of reversible solid oxide cells (RSOC). Here, La0.6Sr0.4FeO3&minus, &delta, (LSF) nanoscale powder is synthesized via a novel molten salt method using chlorides as the reaction medium and fired at 850 &deg, C for 5 h after removing the additives. A direct assembly method is employed to fabricate the LSF electrode without a pre-sintering process at high temperature. The microstructure characterization ensures that the direct assembly process will not damage the porosity of LSF. When operating as a solid oxide fuel cell (SOFC), the LSF cell exhibits a peak power density of 1.36, 1.07 and 0.7 W/cm2 at 800, 750 and 700 &deg, C, respectively, while in solid oxide electrolysis cell (SOEC) mode, the electrolysis current density reaches 1.52, 0.98 and 0.53 A/cm2 under an electrolysis voltage of 1.3 V, respectively. Thus, it indicates that the molten salt routine is a promising method for the synthesis of highly active perovskite LSF powders for directly assembled oxygen electrodes of RSOC.

The energy and power density of conventional batteries are far lower than their theoretical expectations, primarily because of the slow reaction kinetics in the battery that is often working under ambient conditions. Here we describe a low-cost and high-temperature rechargeable iron-oxygen battery containing a bi-phase electrolyte of molten carbonate and solid oxide. This new design merges the merits of solid oxide fuel cell and molten metal-air battery, offering significantly improved battery reaction kinetics and hence the power capability without compromising the energy capacity. The as-fabricated battery prototype can be charged at high current density, and exhibit excellent stability and security in highly charged state without self-discharge. It typically exhibits 129.1 Wh kg-1 in specific energy and 2.8 kW kg-1 in specific power, and 388.1 Wh L-1 in energy density and 21.0 kW L -1 in power density based on the mass and volume of the molten salt, respectively.