Fabrication and structural characterization of interdigitated thin film La1 − x Sr x CoO 3 (LSCO) electrodes

For the prospective use as micro-Solid Oxide Fuel Cell (μ-SOFC) cathodes and for the investigation of reaction kinetics, La1 − xSrxCoO3 (LSCO) mixed ionic electronic conducting thin films were deposited by DC and RF sputtering onto a number of different substrate materials and characterized. Standard photolithographic and wet chemical etching methods were utilized to microstructure the LSCO films and XRD, SEM, AFM, WDS, and RBS were used to characterize their structure, topography, and chemistry. Sputtering resulted in very homogeneous and smooth thin crystalline films with Sr deficiency and submicron sized grains. Hydrochloric acid was found to readily etch LSCO with the etching quality strongly dependent on substrate material. LSCO films were most easily etched when deposited directly on silicon substrates, etched at intermediate rates when deposited on Gd:CeO2 films, and most resistant to etching after deposition onto single crystal yttria stabilized zirconia (YSZ) substrates. Imperfect etching was attributed to interface formation and the presence of impuritie

Micro-solid oxide fuel cells: status, challenges, and chances

Abstract: Micro-solid oxide fuel cells (micro-SOFC) are predicted to be of high energy density and are potential power sources for portable electronic devices. A micro-SOFC system consists of a fuel cell comprising a positive electrode-electrolyte-negative electrode (i.e. PEN) element, a gas-processing unit, and a thermal system where processing is based on micro-electro-mechanical-systems fabrication techniques. A possible system approach is presented. The critical properties of the thin film materials used in the PEN membrane are discussed, and the unsolved subtasks related to micro-SOFC membrane development are pointed out. Such a micro-SOFC system approach seems feasible and offers a promising alternative to state-of-the-art batteries in portable electronics. Graphical abstract: Graphical Abstract tex

Micro-solid oxide fuel cells running on reformed hydrocarbon fuels

Micro‐solid oxide fuel cell (micro‐SOFC) systems are predicted to have a high energy density and specific energy and are potential power sources for portable electronic devices. A micro‐SOFC system is under development in the frame of the ONEBAT project [1‐3]. In this presentation, we report on the fabrication and characterization of a sub‐system assembly consisting of a startup heater and a micro‐reformer bonded to a Si chip with electrochemically‐active micro‐SOFC membranes. A functional carrier including fluidic channels for gas feed and integrated heaters was bonded to a microreformer with an overall size of 12.7 mm x 12.7 mm x 1.9 mm [4‐7]. As a catalyst, a foam‐like material made of ceria‐zirconia nanoparticles doped with rhodium was used to fill the 58.5 mm3 reformer cavity. This micro‐reformer allows for high methane and butane conversion of > 90 % with a hydrogen selectivity of > 80 % at 550 °C in the reformer [7, 8]. A silicon chip with 30 free‐standing micro‐SOFC membranes (390 μm x 390 μm) with a thickness of less than 500 nm was bonded to the carrier‐reformer assembly described above. The micro‐SOFC membrane consisted of an yttria‐ stabilized zirconia thin film electrolyte. Both Pt‐based and ceramic‐based electrode materials were tested regarding the thermal stability and carbon poisoning at temperatures below 600 °C. The functional‐carrier mirco‐reformer micro‐SOFC assembly was electrochemically tested with hydrocarbon fuel between 300 °C and 600 °C. The fuel cell performance and the microstructural evolution of the anode are discussed as well

Micro-solid oxide fuel cells as power supply for small portable electronic equipment

Micro-solid oxide fuel cell (SOFC) systems are anticipated for powering small, portable electronic devices, such as laptop, personal digital assistant (PDA), medical and industrial accessories. It is predicted that micro-SOFC systems have a 2-4 higher energy density than Li-ion batteries [1]. However, literature mainly focuses on the fabrication and characterization of thin films and membranes for micro-SOFC systems [2-12]; the entire system approach is not yet studied in detail. We will therefore discuss in this paper the entire approach from the fabrication of thin films and membranes up to the complete system, including fuel processing, thermal management and integration

Fabrication and structural characterization of interdigitated thin film La(1-x)SrcCoO(3)(LSCO) electrodes

ISSN:1385-3449ISSN:1573-866

Oxygen evolution reaction (OER) mechanism under alkaline and acidic conditions

Density functional theory (DFT) simulations of the oxygen evolution reaction (OER) are considered essential for understanding the limitations of water splitting. Most DFT calculations of the OER use an acidic reaction mechanism and the standard hydrogen electrode (SHE) as reference electrode. However, experimental studies are usually carried out under alkaline conditions using the reversible hydrogen electrode (RHE) as reference electrode. The difference between the conditions in experiment and calculations is then usually taken into account by applying a pH-dependent correction factor to the latter. As, however, the OER reaction mechanisms under acidic and under alkaline conditions are quite different, it is not clear a priori whether a simple correction factor can account for this difference. We derive in this paper step by step the theory to simulate the OER based on the alkaline reaction mechanism and explain the OER process with this mechanism and the RHE as reference electrode. We compare the mechanisms for alkaline and acidic OER catalysis and highlight the roles of the RHE and the SHE. Our detailed analysis validates current OER simulations in the literature and explains the differences in OER calculations with acidic and alkaline mechanisms

Anti-Ferromagnetic RuO2: A Stable and Robust OER Catalyst over a Large Range of Surface Terminations

Rutile RuO2 is a prime catalyst for the oxygen evolution reaction (OER) in water splitting. Whereas RuO2 is typically considered to be non-magnetic (NM), it has recently been established as being anti-ferromagnetic (AFM) at room temperature. The presence of magnetic moments on the Ru atoms signals an electronic configuration that is markedly different from what is commonly assumed, the effect of which on the OER is unknown. We use density functional theory (DFT) calculations within the DFT+U approach to model the OER process on NM and AFM RuO2(110) surfaces. In addition, we model the thermodynamic stability of possible O versus OH terminations of the RuO2(110) surface and their effect on the free energies of the OER steps. We find that the AFM RuO2(110) surface gives a consistently low overpotential in the range 0.4-0.5 V, irrespective of the O versus OH coverage, with the exception of a 100% OH-covered surface, which is, however, unlikely to be present under typical OER conditions. In contrast, the NM RuO2(110) surface gives a significantly higher overpotential of ∼0.7 V for mixed O/OH terminations. We conclude that the magnetic moment of RuO2 supplies an important contribution to obtaining a low overpotential and to its insensitivity to the exact O versus OH coverage of the (110) surface

Monolayer nitrides doped with transition metals as efficient catalysts for water oxidation: the singular role of nickel

Exploration of precious-metal-free catalysts for water splitting is of great importance in developing renewable energy conversion and storage technologies. In this paper, on the basis of density functional theory calculations, we reveal the link between the oxygen evolution reaction (OER) activities and the electronic properties of pure and first-row transition-metal (TM)-doped AlN and GaN two-dimensional monolayers. We find that Ni-doped layers are singularly appealing because they lead to a low overpotential (0.4 V). Early TM dopants are not suited for the OER because they bind the intermediate species OH or O too strongly, which leads to very large overpotentials, or no OER activity at all. The late TM dopants Cu and Zn show less or no OER activity as they bind the intermediate species too weakly. Although in many cases the overpotential can be traced back to an OOH intermediate species being adsorbed too weakly compared to an OH species, the Ni dopant breaks this rule by stabilizing the OOH adsorbant. The stabilization can be correlated with a switch from a high-spin to a low-spin state of the dopant atom. This ability to change spin states offers an exciting ingredient for the design of OER catalysts