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La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) is the state-of-the-art air electrode material for solid oxide electrochemical cells using oxide-ion electrolytes, yet its application in proton ceramic electrochemical cells (PCCs) remains limited, mainly attributed to its instability under operating conditions of high temperature and high humidity. To address this issue, coating a PrCoO3−δ (PCO) catalyst onto the LSCF scaffold has been evaluated in this study. The introduction of the PCO coating not only enhances the LSCF electrode's electrochemical performance but also significantly improves its steam tolerance by preventing direct contact between steam and LSCF. A PCC single cell with the PCO-coated LSCF air electrode exhibited a peak power density of 1.14 W cm−2 in fuel cell mode and a current density of 2.04 A cm−2 at an applied voltage of 1.3 V in electrolysis cell mode at 650 °C. Furthermore, single cells demonstrated excellent durability under operating conditions of high temperature and high humidity, maintaining stable operation for over 1100 h at a current density of −0.5 A cm−2 in humid air at 600 °C. This research highlights the potential of surface modification on LSCF as a promising air electrode for PCCs to achieve efficient and stable operations. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) is one of the principal greenhouse gases accountable for global warming and extreme climate changes. Electrochemically converting CO2 into carbon monoxide (CO) is a promising approach for CO2 utilization in achieving industrial decarbonization. High-temperature CO2 electrolysis via solid oxide electrolysis cells (SOECs) has great potential, including high-energy efficiency, fast electrode kinetics, and competitive cost; however, this technology still has challenges associated with developing highly active, robust CO2 electrodes for SOECs. We report novel Ruddlesden–Popper structured Pr1.2Sr0.8Mn0.4Fe0.6O4−δ (RP-PSMF) with in situ exsolved Fe nanoparticles as the CO2 electrode in SOECs for direct CO2 conversion to CO. The mechanism of CO2 electrolysis is studied by using the distribution of relaxation times method from electrochemical impedance spectroscopy. La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM)-electrolyte supported SOECs with the RP-PSMF cathode have achieved exceptionally high current densities of 2.90, 1.61, 0.91, and 0.48 A·cm−2 at an applied voltage of 1.5 V at 800, 750, 700, and 650 °C, respectively. Moreover, SOECs with the RP-PSMF cathode have exhibited a stable electrolysis performance for 100 h under a current cycling operation. These results suggest that RP-PSMF with exsolved Fe nanoparticles is a highly promising cathode for high-temperature direct CO2 electrolysis cells. [ABSTRACT FROM AUTHOR]

Direct CO2 electrolysis using solid oxide electrolysis cells (CO2-SOECs) holds promise to efficiently convert carbon dioxide to carbon monoxide and oxygen. Cathodes with desirable catalytic activity and chemical stability play a critical role in the development of direct CO2-SOECs. Although Sr2Fe1.5Mo0.5O6−δ (SFM) has exhibited promise for direct CO2-SOECs due to its redox stability, it suffers from insufficient activity for the CO2 reduction reaction (CO2RR). Here we report interface engineering of nanosized Pr6O11 on the SFM cathode obtained through infiltration to promote the CO2RR performance for direct CO2-SOECs. The effect of Pr6O11 loading on the performance of the CO2RR is systematically investigated. At 800 °C, the current density of the Pr6O11 infiltrated SFM cathode with an optimum Pr6O11 loading of 14.8 wt% reaches 1.61 A cm−2 at 1.5 V, more than double that of the SFM cathode (0.76 A cm−2) under the same operating conditions. X-ray photoelectron spectroscopy (XPS) characterization and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis indicate that the adsorption ability of CO2 on the SFM cathode has been significantly improved by the formation of Pr6O11. Temperature-programmed desorption (TPD) of CO2 measurements further manifest that a 14.8 wt% Pr6O11-SFM cathode has better CO desorption capacity. In addition, polarization resistance of the SFM cathode has significantly decreased with the addition of Pr6O11. Three-electrode measurement was used to analyze the improved electrode kinetics. These results demonstrate that the formation of Pr6O11 in the SFM cathode through infiltration is a promising approach for increasing CO2RR activity for CO2-SOECs. [ABSTRACT FROM AUTHOR]

To directly use a CO2–CH4 gas mixture for power and CO co-production by proton-conducting solid oxide fuel cells (H-SOFCs), a layer of in situ reduced La0.6Sr0.2Cr0.85Ni0.15O3−δ (LSCrN@Ni) is fabricated on a Ni–BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) anode-supported H-SOFC (H-DASC) for on-cell CO2 dry reforming of CH4 (DRC). For demonstrating the effectiveness of LSCrN@Ni, a cell without adding the LSCrN@Ni catalyst (H-CASC) is also studied comparatively. Fueled with H2, both H-CASC and H-DASC show similar stable performance with a maximum power density ranging from 0.360 to 0.816 W cm−2 at temperatures between 550 and 700 °C. When CO2–CH4 is used as the fuel, the performance and stability of H-CASC decreases considerably with a maximum power density of 0.287 W cm−2 at 700 °C and a sharp drop in cell voltage from the initial 0.49 to 0.10 V within 20 h at 0.6 A cm−2. In contrast, H-DASC demonstrates a maximum power density of 0.605 W cm−2 and a stable cell voltage above 0.65 V for 65 h. This is attributed to highly efficient on-cell DRC by LSCrN@Ni. [ABSTRACT FROM AUTHOR]

The significant role of perovskite defect chemistry through A-site doping of strontium titanate with lanthanum for CO2 electrolysis properties is demonstrated. Here we present a dual strategy of A-site deficiency and promoting adsorption/activation by making use of redox active dopants such as Mn/Cr linked to oxygen vacancies to facilitate CO2 reduction at perovskite titanate cathode surfaces. Solid oxide electrolysers based on oxygen-excess La0.2Sr0.8Ti0.9Mn(Cr)0.1O3+δ, A-site deficient (La0.2Sr0.8)0.9Ti0.9Mn(Cr)0.1O3−δ and undoped La0.2Sr0.8Ti1.0O3+δ cathodes are evaluated. In situ infrared spectroscopy reveals that the adsorbed and activated CO2 adopts an intermediate chemical state between a carbon dioxide molecule and a carbonate ion. The double strategy leads to optimal performance being observed after 100 h of high-temperature operation and 3 redox cycles, suggesting a promising cathode material for CO2 electrolysis. [ABSTRACT FROM AUTHOR]

Electron doping in perovskites is an effective approach to design and tailor the structure and property of materials. In A2BB′O6−δ-type double perovskites, B-site cation order can be tunable by A-site modification, potentially leading to significant effect on the oxygen nonstoichiometry of the compounds. La3+-doped Sr2FeMoO6−δ (Sr2−xLaxFeMoO6−δ, SLFM with 0 ≤x≤ 1) double perovskites have been designed and characterized systematically in this study as anode materials for solid oxide fuel cells. Rietveld refinement of powder X-ray diffraction reveals a crystalline symmetry transition of SLFM from tetragonal to orthorhombic with the increase of La content, driven by the extra electron onto the antibonding orbitals of eg and t2g of Fe/Mo cations. An increase in Fe/Mo anti-site defect accompanies this phase transition. Solid oxide fuel cells incorporating the Sr1.8La0.2FeMoO6−δ (SLFM2) anode demonstrate impressive power outputs and stable performance under direct CH4 operation because of its altered electronic structure, desired oxygen vacancy concentration and enhanced reducibility. Density functional theory plus U correction calculations provide an insight into how La doping affects the Fe/Mo anti-site defects and consequently the oxygen transport dynamics. [ABSTRACT FROM AUTHOR]

Solid oxide electrolysis cells (SOECs) can directly convert CO2 to CO and O2 that are important building blocks for chemical production and other applications. However, the use of SOECs for direct CO2 electrolysis has been hampered mainly due to the absence of a stable, highly catalytically active and cost effective cathode (fuel electrode) material. Here we report a ceramic SOEC cathode material of perovskite-structured Sr1.9Fe1.5Mo0.4Ni0.1O6−δ for direct CO2 electrolysis. By annealing at 800 °C in H2, homogeneously dispersed nano-sized NiFe alloy nanoparticles are exsolved from the Sr1.9Fe1.5Mo0.4Ni0.1O6−δ perovskite lattice. The exsolved NiFe nanoparticles significantly enhance the chemical adsorption and surface reaction kinetics of CO2 with the cathode. SOECs with the novel cathode have demonstrated a peak current density of 2.16 A cm−2 under an applied voltage of 1.5 V at 800 °C and have demonstrated stable direct CO2 electrolysis performance during 500 h of operation under current density above 1 A cm−2 at 800 °C. [ABSTRACT FROM AUTHOR]

Efficient and direct conversion of CO2 to hydrocarbons through electrolysis is a promising approach for energy storage and CO2 utilization. In this study, high temperature co-electrolysis of H2O–CO2 and low temperature methanation processes are synergistically integrated in a micro-tubular reactor. The temperature gradient along the micro-tubular reactor provides favorable conditions for both the electrolysis and methanation reactions. Moreover, the micro-tubular reactor can provide high volumetric factor for both the electrolysis and methanation processes. When the cathode of the micro-tubular reactor is fed with a stream of 10.7% CO2, 69.3% H2 and 20.0% H2O, an electrolysis current of −0.32 A improves CH4 yield from 12.3% to 21.1% and CO2 conversion rate from 64.9% to 87.7%, compared with the operation at open circuit voltage. Furthermore, the effects of the inlet gas composition in the cathode on the CO2 conversion rate and the CH4 yield are systematically investigated. Higher ratio of H : C in the inlet results in higher CO2 conversion rate. Among all the cases studied, the highest CH4 yield of 23.1% has been achieved when the inlet gas in the cathode is consisted of 21.3% CO2, 58.7% H2 and 20.0% H2O with an electrolysis current of −0.32 A. [ABSTRACT FROM AUTHOR]

A solid oxide electrolysis cell with novel asymmetric-porous structured electrodes has been fabricated by the combination of freeze-drying tape-casting and impregnation methods. The electrodes possess unique channel-like pores with nano- or sub-micron-sized catalysts homogeneously coated on the inner face of the porous scaffold. The straight channel-like pores in the electrodes facilitate mass transport while the nano- or sub-micron-sized catalysts promote the electrode electrochemical reactions. The cell demonstrates low electrode polarization resistance values of 0.27, 0.19 and 0.14 Ω cm2 at OCV in 50 vol% H2O–25 vol% H2–25 vol% CO2 at 800, 850 and 950 °C, respectively. The cell DC voltage–current density dependence is generally linear at all temperatures, and high current densities of 0.8, 1.1 and 1.66 A cm−2 for 50 vol% H2O–25 vol% H2–25 vol% CO2 co-electrolysis have been obtained with 1.30 V applied voltage at 800, 850 and 900 °C, respectively. Compared to that of the cell fabricated by conventional or phase-inversion methods, the mass transportation limitation phenomenon in the porous electrodes is mitigated and cell performance is greatly improved. [ABSTRACT FROM AUTHOR]

Crystallographic structural changes were investigated for Sr2Fe1.5Mo0.5O6−δ, an electrode material for symmetric solid oxide fuel cells. The samples of this material were heated and cooled in wet hydrogen and wet oxygen atmospheres, to simulate the reducing and oxidizing conditions experienced under actual fuel cell operating conditions, and their structures and oxygen contents were determined using in situ powder neutron diffraction. The existence of a reversible tetragonal to cubic phase transition was established to occur between room temperature and 400 °C, both on heating and cooling in either oxygen or hydrogen. The oxygen content reaches a low value of 5.50(2) at 850 °C in wet hydrogen. Excellent correlations are observed between the oxygen content of the structure and the conductivities reported in the literature. [ABSTRACT FROM AUTHOR]

Donor and acceptor co-doped SrTiO3 materials have shown interesting features in their conductivity and reducibility. In this work, 10 mol% Na+ or K+ as acceptor dopants have been introduced into the A-site of donor-doped strontium titanate, SrTi0.8Nb0.2O3, and the doping impact on their properties has been studied. By doping with Na or K, the sinterability of SrTi0.8Nb0.2O3 in reducing atmospheres has been improved. Na0.1Sr0.9Ti0.8Nb0.2O3 and K0.1Sr0.9Ti0.8Nb0.2O3 show metallic conduction behavior after being sintered at 1400 °C in 5% H2/N2. Electrical conductivity reaches 1180 S cm−1 at 400 °C and 272 S cm−1 at 800 °C for K0.1Sr0.9Ti0.8Nb0.2O3, which is higher than that of Sr0.99Ti0.8Nb0.2O3 prepared under similar conditions, indicating the improved reducibility of acceptor doped SrTi0.8Nb0.2O3. Such improvement may be attributed to the improved oxide ionic conductivity and cation mobility at high temperatures. Reduced polarization resistance is also observed using Na0.1Sr0.9Ti0.8Nb0.2O3 and K0.1Sr0.9Ti0.8Nb0.2O3 as anodes on YSZ electrolytes, suggesting improved catalytic activity by Na/K-doping. [ABSTRACT FROM AUTHOR]