Hexis (Switzerland)

Gallium nitride (GaN) is a promising material for nonlinear optics. It offers a second-order nonlinearity up to 20 pm/V and a third-order nonlinearity that is one order of magnitude higher than in silicon nitride at 1550 nm [1], [2]. Owing to its large bandgap of 3.4 eV GaN has a wide transparency range and is free of two-photon and three-photon absorption in the technologically important erbium-gain window. Recent advances have explored integrated GaN waveguide as a new platform for integrated photonics, demonstrating second-harmonic generation, four-wave mixing, soliton generation [2]–[4], supercontinuum generation and chip-based f-2f interferometry [5].

Recent research carried out at the University of St Andrews and HEXIS has focussed on a novel A-site deficient perovskite: La0.20Sr0.25Ca0.45TiO3 (LSCTA-) as a potential replacement material for the Ni-based cermet. LSCTA- is a mixed ionic and electronic conductor, which exhibits a high effective electrical conductivity for this class of limited conductivity perovskite, allowing a single-phase anode ‘backbone’ to be employed and removing the challenges associated with utilisation of a structural Ni phase. Co-impregnating this ‘backbone’ with a variety of transition/platinum group metals, as well as Ce0.80Gd0.20O1.90 (CG20), produces intricately nanostructured anode materials with high electrocatalytic activity for fuel oxidation. Here we provide an overview of the first ‘all-oxide’ SOFC stack test at HEXIS, as well as an in depth exploration of the ‘powder-to-power’ development of these co-impregnated LSCTA- anodes including: ceramic processing, catalyst selection, short-term testing, characterisation by AC impedance spectroscopy and durability testing of promising candidate catalyst systems.

3D microstructure-performance relationships in Ni-YSZ anodes for electrolyte-supported cells are investigated in terms of the correlation between the triple phase boundary (TPB) length and polarization resistance (Rpol). Three different Ni-YSZ anodes of varying microstructure are subjected to eight reduction-oxidation (redox) cycles at 950 °C. In general the TPB lengths correlate with anode performance. However, the quantitative results also show that there is no simplistic relationship between TPB and Rpol. The degradation mechanism strongly depends on the initial microstructure. Finer microstructures exhibit lower degradation rates of TPB and Rpol. In fine microstructures, TPB loss is found to be due to Ni coarsening, while in coarse microstructures reduction of active TPB results mainly from loss of YSZ percolation. The latter is attributed to weak bottlenecks associated with lower sintering activity of the coarse YSZ. The coarse anode suffers from complete loss of YSZ connectivity and associated drop of TPBactive by 93%. Surprisingly, this severe microstructure degradation did not lead to electrochemical failure. Mechanistic scenarios are discussed for different anode microstructures. These scenarios are based on a model for coupled charge transfer and transport, which allows using TPB and effective properties as input. The mechanistic scenarios describe the microstructure influence on current distributions, which explains the observed complex relationship between TPB lengths and anode performances. The observed loss of YSZ percolation in the coarse anode is not detrimental because the electrochemical activity is concentrated in a narrow active layer. The anode performance can be predicted reliably if the volume-averaged properties (TPBactive, effective ionic conductivity) are corrected for the so-called short-range effect, which is particularly important in cases with a narrow active layer.

La0.20Sr0.25Ca0.45TiO3 (LSCTA-) shows promise as a novel Solid Oxide Fuel Cell anode backbone material (to replace Ni-based cermets). Thick film ceramic processing techniques have been used as the primary method in controlling the characteristics of the fuel electrode (layer thickness, porosity, grain connectivity and the ultimate interaction with catalyst particles) in order to produce a microstructural architecture which has the potential to deliver higher electronic (and ionic) conductivity, improved current distribution and more durable performance in fuel cell testing. Results of preliminary studies into the ceramic processing of LSCTA- are presented here.

Galileo 1000 N is an SOFC-based micro-CHP system for single family homes. This contribution reports on the newest achievements in the lab on efficiency, durability and cyclability of SOFC stacks and complete micro-CHP systems. It also shows results of the field tests. Achievements are total efficiencies of 95% (LHV) and electrical efficiencies of around 35% (AC net, LHV). The longest system test had been running for more than 40 000 h. More recent tests have achieved power degradations below 1% per 1000 h and cycling tests have shown a tolerance against at least 20 on-off cycles. The contribution also reports on the next steps to market introduction of the Galileo 1000 N.

Abstract Perovskite‐type materials have been synthesised and investigated with regards to their physical properties including specific surface area (BET), phase purity, sinter behaviour, coefficient of thermal expansion (CTE) and electrical conductivity. We investigated the effect of Sr variation on La1–xSrxFeO3–δthe influence of A‐site stoichiometry on (La0.8Sr0.2)yFeO3–δand the impact of substitution of iron by nickel or copper up to 20 mol%. The over‐stoichiometric compositions indicate secondary phases independent of the calcination temperature. Stoichiometric and understoichiometric compositions become single phase perovskites after calcination at 1,200 °C. The substitution of Fe by Ni or Cu on the B‐site, (La0.2Sr0.8)0.95Ni/CuxFe1–xO3, is viable, but limited to 20 mol%. Cu substitution and under‐stoichiometry lower the melting point and thus consequently influence the sintering temperature.The diverse LSF composition as well as Ni/Cu substitutions affects the CTE. The CTE matches quite well with YSZ, by a 15% A‐site deficiency, as well as with Ni substitution on the B‐site. Compatibility tests at 1,000 °C prove that Ni increases the reactivity of LSF with YSZ. In case of the CGO, no indication of reactions or interdiffusion could be observed. The substitution of iron by 20 mol% nickel or copper significantly enhances the electrical conductivity of the basic composition (La0.8Sr0.2)0.95FeO3–δ.