Water electrolysis will be an essential element of the future energy system, with hydrogen serving as a climate-friendly energy storage medium. To make electrolyzers suitable for market penetration at scale, the cost of manufacturing megawatt electrolyzers must be minimized, with no detrimental effects to their performance and lifetime. Here we show a facile and cost-effective manufacturing method to produce one-piece Ti-based bipolar plates. Low-cost and commercially and readily available feedstock materials (blank sheets, expanded metals and nonwovens) are positively joined using an innovative welding process, diffusion bonding. This approach reduces the contact resistances that can occur with multi-part bipolar plates by around 75%, reducing the number of components and therefore significantly simplifying stack assembly. Ex-situ tests on the contact pressure distribution on the active cell surface reveal a homogeneous pattern with values of about 3.75 MPa ( +/- 1.25 MPa). In a first proof-of-concept, a five-cell short stack with a 100 cm2 active cell area, average cell voltages of 1.71 V at 2 A cm-2 could be achieved using our new stack concept.(c) 2023 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).

Three different steel adaptors for the measurement of tensile strength values of glass-ceramic sealants were experimentally tested and analyzed by finite element analysis. It was shown that both the joining geometry and the adaptor design have an influence on the measured strength. An optimized adaptor design is proposed which offers a more uniform distribution of axial stresses within the sealing plane of the sample. Modelling results are compared with measured strength data. It was possible to obtain a tenfold increase of the measured strength values due to the optimization of adaptor setup and a mean fracture stress of 66 MPa was obtained for the material combination of KeraGlass ST K02 with Crofer® 22 APU.

Lightweight SOFC stacks are currently being developed for stationary applications such as residential CHP units, for automotive applications such as APU and for portable devices. Within the EU funded project the so-called Jülich CS-design has been improved for lightweight SOFC stacks using glass-ceramic sealings that decouple the thermal stresses within the stack and at the same time allows optimal sealing and contacting. The design is highly suitable for industrial low-cost manufacturing and automated assembly. To determine the effect on the thermomechanical behaviour of the fuel cell stack, modelling and coupled thermomechanical analysis have been performed. Based on the analysis results in combination with the manufacturing experience, test results, and post-test analysis from previous stack design, substantial changes have been made to the CS-design in order to improve mechanical robustness of the stack. The manufacturing of single parts, particularly due to the improved design of sheet metal interconnects, as well as the assembling processes are suitable for low-cost mass manufacturing. The novel decal concept of glass-ceramic sealant screen printed on foil in order to produce green tapes is used for joining the stack layers offering an enormous potential for cost savings in industrial assembly process. The new design CSV(D2.0 in the MMLCR=SOFC project) furthermore has extended the process window of the laser welding joining process. First CSV–design stack tests showed a comparable electrochemical performance to the previous CSIV design. The good adhesion of the glass sealant applied on steel sheet by screen printed tape and good contacting behaviour between cells and interconnects were furthermore confirmed by post-test analysis.

Glass-ceramic composites are used as sealants for high temperature applications, e.g. in planar solid oxide fuel cell (SOFC) stacks. This study focuses on the implementation of more than one sheet of different composite materials within the individual joint between two adjacent plates, producing a multilayer or a, so called, laminate sealant. Each sheet should be tailored for a specific function and, in combination with the other layers, fulfil the overall requirements for the joining of SOFC stacks. In a first attempt to improve the bonding strength, different laminar combinations were screen-printed to yield a triple layer design. Varied filler materials were used, e.g. yttria-stabilised zirconia fibres and particles, and silver particles together with a glass matrix based on the system BaO-CaO-SiO2. The joining partners were steel plates of ferritic chromium-containing steel (Crofer22APU). The multilayer designs tested were based on two material combinations: one with ceramic and one with metal fillers. The three layers were set up by establishing two sheets of identical type on the outer sides, and one reinforcement layer in the centre plane. It was especially with a design with outer layers containing ceramic fillers in which an electrical insulation ability greater than 1 k Omega cm(2) and gas-tightness of 10(-9) mbar ls(-1) were achieved.

Glass–ceramic sealants are commonly used as joining materials for planar solid oxide fuel cells stacks. Several requirements need to be fulfilled by these materials: beside of electrical insulation and appropriate thermal expansion, a good adhesion on the ceramic and metallic components of a SOFC stack is necessary to form a gas-tight joint. Even though the joining process might have been successful, failures and leaks often occur during the stack operation due to fracture of the brittle material under thermal stresses or during thermal cycling of the components. This study focusses on composite materials consisting of a glass matrix based on the system of BaO–CaO–SiO2 and various filler materials, e.g. yttria-stabilized zirconia fibres or particles and silver particles. In order to evaluate a possible reinforcing influence of the filler material of the composite, tensile strength tests were carried out on circular butt joints. The highest strength values were found for the composite material with addition of silver particles, followed by the glass matrix itself without any filler addition and the lowest values were measured for the composite with YSZ particles. SEM investigations of cross-sections of the joints elucidated these results by the microstructure of the glass-ceramic sealants.