Rudolf Henne

Development and characterization of vacuum plasma sprayed thin film solid oxide fuel cells

The vacuum plasma spraying (VPS) process allows the production of thin solid oxide fuel cells (SOFCs) with low internal resistances. This enables the reduction of the cell operating temperature without a significant decrease in power density. Consequently, the long-term stability of the cells can be improved and low-cost materials can be used.Different material combinations and spray parameter variations were applied to develop thin-film SOFCs, which were plasma sprayed in a consecutive deposition process onto different porous metallic substrates. The use of Laval nozzles, which were developed at the German Aerospace Center (DLR), and the use of conical F4V standard nozzles enable the fabrication of thin gas tight yttria- and scandia-stabilized ZrO2 (YSZ and ScSZ) electrolyte layers and of porous electrode layers with high material deposition rates. The optimization of the VPS parameters has been supported by laser doppler anemometry (LDA) investigations.The development of the plasma-sprayed cells with a total thickness of approximately 100 µm requires an overall electrical and electrochemical characterization process of the single layers and of the completely plasma-sprayed cell assembly. The plasma-sprayed cell layers reveal high electrical conductivities. The plasma-sprayed cells show very good electrochemical performance and low internal resistances. Power densities of 300 to 400 mW/cm2 at low operating temperatures of 750 to 800 °C were achieved. These cells can be assembled to high performance SOFC stacks with active cell areas up to 400 cm2, which can be operated at reduced temperatures and good long-term stability.

Development of vacuum plasma sprayed thin-film SOFC for reduced operating temperature

The reduction of the operating temperature of planar solid oxide fuel cells (SOFCs) to an intermediate temperature regime of 650–800°C is an important objective in current development activities worldwide, in order to reduce production costs and improve long-term stability. In addition, existing conventional SOFC production processes must be further developed towards automated production lines, and new manufacturing processes with the potential for mass production must be established to meet the strict cost targets for the successful introduction of SOFCs in the strongly competitive energy market. DLR the German aerospace research centre has developed a novel planar thin-film SOFC concept which is based on advanced plasma spray processes. These manufacturing techniques allow the subsequent deposition of the entire membrane-electrode assembly (MEA) onto a porous metallic substrate within a very short process time, and has the potential to be developed into an automated continuous production process. By applying the plasma spray technology single cells were fabricated and characterised as having high performance in the temperature range 750–900°C and good long-term behaviour. Further development work will concentrate on the assembly of stacks with several large-scale cells with dimensions of 10 × 10 and 20 × 20 cm 2 , in order to obtain stack performance and durability results.

The 2016 Thermal Spray Roadmap

Considerable progress has been made over the last decades in thermal spray technologies, practices and applications. However, like other technologies, they have to continuously evolve to meet new problems and market requirements. This article aims to identify the current challenges limiting the evolution of these technologies and to propose research directions and priorities to meet these challenges. It was prepared on the basis of a collection of short articles written by experts in thermal spray who were asked to present a snapshot of the current state of their specific field, give their views on current challenges faced by the field and provide some guidance as to the R&D required to meet these challenges. The article is divided in three sections that deal with the emerging thermal spray processes, coating properties and function, and biomedical, electronic, aerospace and energy generation applications.

Thermal Plasma Chemical Vapor Deposition of Si-Based Ceramic Coatings from Liquid Precursors

In this paper a process based on the use of rf inductively coupled plasma is applied for the synthesis and deposition of Si-base ceramic materials (i.e., SiC, Si3N4, SiO2). The starting materials are low-cost liquid disilanes. The atomization process is first investigated and the structure of the resulting coatings is characterized by means of X-ray diffraction, scanning electron microscopy as well as with transmission electron microscopy. Results of the influence of some processing parameters (i.e., chamber pressure, spray distance, substrate cooling, plasma gas nature and composition, precursor composition and atomization parameters) on the phase and microstructure of the coating is reported. Control of the microstructure (or nanostructure) as well as the phase content, namely the α/β ratio of the phases for SiC and Si3N4, can be achieved with such a synthesis and deposition technique.

High-velocity DC-VPS for diffusion and protecting barrier layers in solid oxide fuel cells (SOFCs)

High-temperature fuel cells of the solid oxide fuel cell (SOFC) type as direct converter of chemical into electrical energy show a high potential for reducing considerably the specific energy consumption in different application fields. Of particular interest are advanced lightweight planar cells for electricity supply units in cars and other mobile systems. Such cells, in one new design, consist mainly of metallic parts, for example, of ferrite steels. These cells shall operate in the temperature range of 700 to 800 °C where oxidation and diffusion processes can be of detrimental effect on cell performance for long-term operation. Problems arise in particular by diffusion of chromium species from the interconnect or the cell containment into the electrolyte/cathode interface forming insulating phases and by the mutual diffusion of substrate and anode material, for example, iron and chromium from the ferrite into the anode and nickel from the anode into the ferrite, which in both cases reduces performance and system lifetime. Additional intermediate layers of perovskite-type material, (e.g., doped LaCrO3) applied with high-velocity direct-current vacuum plasma spraying (DC-VPS) can reduce such effects considerably if they are stable and of high electronic conductivity.

Thermal plasma processing of nanostructured Si-based ceramic materials

A novel thermal plasma process, based on Thermal Plasma Chemical Vapor Deposition (TPCVD) for producing nanostructured ceramics from liquid precursors is described. The process combines the rapid thermal decomposition of low-cost liquid precursors injected into an Inductively Coupled Plasma (ICP) with a fast gas phase condensation due to the high cooling rate and short residence time existing in such a plasma. Examples of synthesis of Si-based nanostructured ceramic materials (SiC, Si3N4) as powders or coatings are given. Deposition rates of up to 10 μm/min can be achieved by the present technique.

Manufacturing of Solid Oxide Fuel Cells ‐ A Challenge for DC and RF Plasma Deposition Processes ‐ 1, 2

ABSTRACT: It is expected that fuel cells and particularly solid oxide fuel cells (SOFC) as direct converters of chemical energy into electrical energy will gain an important position in future stationary electric power generation. SOFCs of present development state operate in a temperature range of around 900 °C. Their efficiency is considerably higher and their operation less burdened by wastes and environmental problems compared to presently applied systems. Therefore, there exists great interest to make such SOFC units available in a technical scale. A main precondition for a wide spread application of SOFCs is particularly a considerable reduction of the production costs. Besides the improvement of presently used methods mainly basing on sintering techniques, also new technologies have been under consideration and development. In this connection DC and RF plasma deposition processes became attractive for producing components or even entire cells. But further process improvements are needed to meet the special quality and economic demands of the SOFCs.

Graded Thermoelectric Materials by Plasma Spray Forming

Plasma spraying is a consolidation process for powders with the additional capability of a composition control of the spray formed structures. The paper reports on the first steps to adapt this method to the production of functionally graded thermoelectric materials with a locally maximized figure of merit. Iron disilicide (FeSi 2 ) was used to test the performance of the technique on thermoelectric material. It was found that plasma spray forming is applicable to produce dense materials with thermoelectric properties comparable to hot pressed ones. Problems were however found with the thermal stability of the microstructure. Final goal is the employment of plasma spraying to form compositionally graded materials of the Mg 2 (Si,Ge,Sn) system. Here we report on the preparation and thermoelectric transport properties of Si-rich quasibinary Mg 2 (Si,Ge) and Mg 2 (Si,Sn) mixed crystals by mechanical alloying.