Michael Lang

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.

High Temperature Water Electrolysis Using Metal Supported Solid Oxide Electrolyser Cells (SOEC)

Metal supported cells as developed at DLR for use as solid oxide fuel cells by applying plasma deposition technologies were investigated in operation of high temperature steam electrolysis. The cells consisted of a porous ferritic steel support, a diffusion barrier layer, a Ni/YSZ fuel electrode, a YSZ electrolyte and a LSCF oxygen electrode. During fuel cell and electrolysis operation the cells were electrochemically characterised by means of i-V characteristics and electrochemical impedance spectroscopy measurements including a long-term test over 2000 hours. The results of electrochemical performance and long-term durability tests of both single cells and single repeating units (cell including metallic interconnect) are reported. During electrolysis operation at an operating temperature of 850 °C a cell voltage of 1.28 V was achieved at a current density of -1.0 A cm-2; at 800 °C the cell voltage was 1.40 V at the same operating conditions. The impedance spectra revealed a significantly enhanced polarisation resistance during electrolysis operation compared to fuel cell operation which was mainly attributed to the hydrogen electrode. During a long-term test run of a single cell over 2000 hours a degradation rate of 3.2% per 1000 hours was observed for operation with steam content of 43% at 800 °C and a current density of -0.3 Acm-2. Testing of a single repeating unit proved that a good contacting of cell and metallic interconnect is of major importance to achieve good performance. A test run over nearly 1000 hours showed a remarkably low degradation rate.

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.