Production of a monolithic fuel cell stack with high power density.

The transportation sector is undergoing a technology shift from internal combustion engines to electric motors powered by secondary Li-based batteries. However, the limited range and long charging times of Li-ion batteries still hinder widespread adoption. This aspect is particularly true in the case of heavy freight and long-range transportation, where solid oxide fuel cells (SOFCs) offer an attractive alternative as they can provide high-efficiency and flexible fuel choices. However, the SOFC technology is mainly used for stationary applications owing to the high operating temperature, low volumetric power density and specific power, and poor robustness towards thermal cycling and mechanical vibrations of conventional ceramic-based cells. Here, we present a metal-based monolithic fuel cell design to overcome these issues. Cost-effective and scalable manufacturing processes are employed for fabrication, and only a single heat treatment is required, as opposed to multiple thermal treatments in conventional SOFC production. The design is optimised through three-dimensional multiphysics modelling, nanoparticle infiltration, and corrosion-mitigating treatments. The monolithic fuel cell stack shows a power density of 5.6 kW/L, thus, demonstrating the potential of SOFC technology for transport applications.

Passivation and activation of La0.6Sr0.4FeO3 thin film electrodes.

The oxygen exchange activity of thin dense La0.6Sr0.4FeO3 electrodes prepared by pulsed laser deposition was investigated by electrochemical impedance spectroscopy and electrical conductivity relaxation below 600 °C. The value of the surface exchange coefficient (kchem) measured at 491 °C decreased from an initial 4.4 × 10-6 cm s-1 to 1.7 × 10-7 cm s-1 after aging for 7 days. The rapid decrease in the oxygen exchange rate was accompanied by the increase in the surface concentration of 'non-lattice strontium' detected by X-ray photoelectron spectroscopy. Subsequent electrochemical tests over 40 days showed that the electrode performance could be recovered by rinsing the passivated electrode in deionized water. Repeated treatments eventually also led to improved stability of electrochemical performance.

A 4 × 4 cm2 Nanoengineered Solid Oxide Electrolysis Cell for Efficient and Durable Hydrogen Production.

Despite various advantages of high-temperature solid oxide electrolysis cells (SOECs) over their low-temperature competitors, the insufficient long-term durability has prevented the commercialization of SOECs. Here, we address this challenge by employing two nanoengineered electrodes. The O2 electrode consists of a La0.6Sr0.4CoO3-δ (LSC) and Gd,Pr-co-doped CeO2 (CGPO) nanocomposite coating deposited on a Gd-doped CeO2 (CGO) scaffold, and the H2 electrode comprises a Ni/yttria stabilized zirconia (YSZ) electrode modified with a nanogranular CGO coating. The resulting cell with an active area of 4 × 4 cm2 exhibits a current density exceeding 1.2 A cm-2 at 1.3 V and 750 °C for steam electrolysis while also offering excellent long-term durability at 1 A cm-2 with a high steam-to-hydrogen conversion of ∼56%. We further unravel the degradation mechanism of the most commonly used Ni/YSZ electrode under these conditions and describe the mitigation of the discussed mechanism on our nanoengineered electrode. Our findings demonstrate the potential of designing robust SOECs by nanoengineering electrodes through infiltration and have significant implications for the practical integration of SOEC technology in the future sustainable energy system.

High-Performance Microchanneled Asymmetric Gd(0.1)Ce(0.9)O(1.95-δ)-La(0.6)Sr(0.4)FeO(3-δ)-Based Membranes for Oxygen Separation.

A microchanneled asymmetric dual phase composite membrane of 70 vol % Gd(0.1)Ce(0.9)O(1.95-δ)-30 vol % La(0.6)Sr(0.4)FeO(3-δ) (CGO-LSF) was fabricated by a "one step" phase-inversion tape casting. The sample consists of a thin dense membrane (100 µm) and a porous substrate including "finger-like" microchannels. The oxygen permeation flux through the membrane with and without catalytic surface layers was investigated under a variety of oxygen partial pressure gradients. At 900 °C, the oxygen permeation flux of the bare membrane was 1.6 (STP) ml cm(-2) min(-1) for the air/He-case and 10.10 (STP) ml cm(-2) min(-1) for the air/CO-case. Oxygen flux measurements as well as electrical conductivity relaxation show that the oxygen flux through the bare membrane without catalyst is limited by the oxygen surface exchange. The surface exchange can be enhanced by introduction of catalyst on the membrane surface. An increase of the oxygen flux of ∼1.49 (STP) mL cm(-2) min(-1) at 900 °C was observed when catalyst is added for the air/He-case. Mass transfer polarization through the finger-like support was confirmed to be negligible, which benefits the overall performance. A stable flux of 7.00 (STP) ml cm(-2) min(-1) was observed between air/CO/CO2 over 200 h at 850 °C. Partial surface decomposition was observed on the permeate side exposed to CO, in line with predictions from thermodynamic calculations. In a mixture of CO, CO2, H2, and H2O at similar oxygen activity the material will according to the calculation not decompose. The microchanneled asymmetric CGO-LSF membranes show high oxygen permeability and chemical stability under a range of technologically relevant oxygen potential gradients.

TOF-SIMS characterization of impurity enrichment and redistribution in solid oxide electrolysis cells during operation.

TOF-SIMS analyses of state-of-the-art high temperature solid oxide electrolysis cells before and after testing under different operating conditions were performed. The investigated cells consist of an yttria stabilized zirconia (YSZ) electrolyte, a La1-xSrxMnO3-δ composite anode and a Ni-YSZ cermet cathode. The surfaces and cross-sections of the cells were analyzed, and several elemental impurities like Si, Ca and Na were identified and spatially mapped and their enrichment and migration during operation is reported. With advancing operation time, the concentration of these elements, especially Na and Ca, increases. For Si, a concentration gradient is found from the gas inlet to the gas outlet. Additionally, a loss of Ni percolation in the active cathode is observed in the same area where the Si enrichment is found. Based on the obtained TOF-SIMS results, the influence of the operating conditions on degradation is discussed.

Experimental determination of the Onsager coefficients of transport for Ce(0.8)Pr(0.2)O(2-delta).

For a mixed oxide-ion and electron conducting oxide, with oxygen vacancies (V(O)) and electrons (e') or holes (h ) as charge carriers, a flux of (V(O)) (J(i)) can in principle be driven, not only directly by its own electrochemical potential gradient (inverted Delta eta(i)), but also indirectly by that of electrons (inverted Delta eta(e)), and vice versa for the flux of electrons (J(e)). It is common practice to assume that electrons and mobile ions migrate independently, despite the lack of experimental evidence in support of this. Here, all the Onsager coefficients, including the cross coefficients, have been measured for Ce(0.8)Pr(0.2)O(2-delta) within the a(O(2)) range 10(-21)-1 at 800 degrees C, using local ionic and electronic probes in a four-probe configuration. The cross coefficients of transport were found to be negligible in comparison to the direct coefficients in the a(O(2)) range 10(-21)-10(-4), but of the same order of magnitude as the direct coefficients for high a(O(2)) values (10(-2)-1). This is in contrast to the commonly used assumption that the two types of carriers migrate independently, i.e. that L(ie) = 0.