• Energy Research

In contrast to fossil fuel or nuclear energy based electrical power intermittent renewable energy such as solar and wind need to balance the mismatch of energy supply and demand to allow stable and secure grid operation requiring energy storage technologies. A promising device is the solid oxide electrochemical cell (SOC) which can be operated reversibly, i.e. an SOC can act as an electrolyser to store electricity in the form of hydrogen and it can act as a fuel cell to produce electricity, water and heat. With this technology a single stack can be integrated into one system to address different markets such as hydrogen production, power-to-gas, energy storage and distributed power generation. When electrolyzing both steam and CO2 in co-electrolysis operating mode, synthesis gas can be produced to be converted by further downstream catalytic processes into fuels such as methane, gasoline or diesel. Due to the high operating temperature of 750-900 °C and the possibility to re-use waste heat from industrial processes very high electrical efficiency can be achieved. However, maintaining the performance during long-term operation represents still a major challenge. Solid oxide cells and stacks are characterized and tested at DLR regarding electrochemical performance and degradation for both reversible and co-electrolysis operation. In cooperation with a car manufacturer (AUDI AG, Germany) and a stack supplier (Sunfire GmbH, Germany) DLR works on the investigation of SOC stacks during near-system operating conditions in electrolysis as well as reversible operating mode. The electrochemical performance is monitored during long-term tests to be compared with identical stacks implemented in an industrial reversible SOC (RSOC) system in order to determine and better understand degradation processes occurring in different operating modes. The concept of the power-to-gas facility with 300 kW power and first results of stack tests are presented. DLR also works on the evaluation of solid oxide cells for co-electrolysis of CO2 and H2O aiming at the production of synthetic fuels. Cell behaviour and durability are assessed under various operating conditions. Results will be reported and discussed and remaining challenges for maturing the technology are addressed.

In contrast to fossil fuel or nuclear energy based electrical power intermittent renewable energy such as solar and wind need to balance the mismatch of energy supply and demand to allow stable and secure grid operation requiring energy storage technologies. A promising device is the solid oxide electrochemical cell (SOC) which can be operated reversibly, i.e. an SOC can act as an electrolyser to store electricity in the form of hydrogen and it can act as a fuel cell to produce electricity, water and heat. With this technology a single stack can be integrated into one system to address different markets such as hydrogen production, power-to-gas, energy storage and distributed power generation. When electrolyzing both steam and CO2 in co-electrolysis operating mode, synthesis gas can be produced to be converted by further downstream catalytic processes into fuels such as methane, gasoline or diesel. Due to the high operating temperature of 750-900 °C and the possibility to re-use waste heat from industrial processes very high electrical efficiency can be achieved. However, maintaining the performance during long-term operation represents still a major challenge. Solid oxide cells and stacks are characterized and tested at DLR regarding electrochemical performance and degradation for both reversible and co-electrolysis operation. In cooperation with a car manufacturer (AUDI AG, Germany) and a stack supplier (Sunfire GmbH, Germany) DLR works on the investigation of SOC stacks during near-system operating conditions in electrolysis as well as reversible operating mode. The electrochemical performance is monitored during long-term tests to be compared with identical stacks implemented in an industrial reversible SOC (RSOC) system in order to determine and better understand degradation processes occurring in different operating modes. The concept of the power-to-gas facility with 300 kW power and first results of stack tests are presented. DLR also works on the evaluation of solid oxide cells for co-electrolysis of CO2 and H2O aiming at the production of synthetic fuels. Cell behaviour and durability are assessed under various operating conditions. Results will be reported and discussed and remaining challenges for maturing the technology are addressed.

The traditional approach to enhance the performance of Solid Oxide Cells (SOC)relies on the functional materials with improved properties, such as enhanced electro-catalytic activity and optimized microstructure. Perovskite based Mixed Ionic and Electronic Conductors (MIEC) change the paradigm of the active sites in SOC electrodes by offering double phase boundaries (DBs) in addition to triple phase boundaries (TPBs). For instance, compounds from the (LaxSr1-x)1-yCo1-zFezO3-δ (LSCF) improved functionality of the air electrode, via a higher ionic conductivity, while compounds from the LaxSr1-xTiO3-δ (LST) due to dimensional stability in both reducing and oxidizing conditions significantly enhance tolerance of the fuel electrode towards redox cycles. Ce1-xGdxO2-α (CGO) itself present a significant MIEC behavior above 600 °C, typical of SOC operation. Hereby, we present the results of studies related to the development of flexible and durable (LaxSr1-x)1-yTiO3-δ (LST) – Ce1-xGdxO2-α (CGO) based fuel electrodes and (LaxSr1-x)1-yCo1-zFezO3-δ (LSCF) – Ce1-xGdxO2-α (CGO) based air electrode. Model electrodes with various phase proportion were produced and electrochemically characterized in relevant atmosphere and at various temperature. The identification of electrochemical processes on the active sites, the understanding of the electrochemical behavior and the identification of the rate limiting processes as a function of the operating temperature will be presented. The results obtained with DBs based electrodes implemented in a metal supported SOC and operated both in fuel cell and electrolysis mode will be presented and critically discussed in terms of performance, durability and tolerance towards poisons. The discussion will be further extended to the use of such materials in other traditional planar cell architectures.

Presentation of the EU project EVOLVE: material development and first cell prototype testing

The aim of the present study is the measurement and understanding of sulfur poisoning phe-nomena in Ni/gadolinium-doped ceria (CGO) based solid oxide fuel cells (SOFC) operating on reformate fuels. The sulfur poisoning behavior of commercial, high-performance electro-lyte-supported cells (ESC) with Ni/Ce0.9Gd0.1O2‒(CGO10) anodes operated with different fuels was thoroughly investigated by means of current-voltage characteristics and electro-chemical impedance spectroscopy, and compared with Ni/Yttria-stabilized zirconia (YSZ) anodes. Various methane- and carbon monoxide-containing fuels were used in order to eluci-date the underlying reaction mechanism. The analysis of the cell resistance increase in H2/H2O/CO/CO2 fuel gas mixtures revealed that the poisoning behavior is mainly governed by an inhibited hydrogen oxidation reaction at low current densities. At higher current densities, the resistance increase becomes increasingly large, indicating a particularly severe poisoning effect on the carbon monox...

In this paper we present the combine modeling and experimental study of electrochemical hydrogen oxidation at an alternative perovskite based mixed-conducting SOFC anode. Two types of button cells without and with addition of nickel (Ni) were fabricated based on La0.1Sr0.9TiO3-α(LST)-CGO composite anodes and dense YSZ electrolytes. Electrochemical experiments were performed using symmetrical cell configuration in H2/H2O fuel mixture systematically varying applied potentials and operating temperatures. The previously developed model, which includes thermal chemistry at each surface, charge-transfer processes and reactive porous media transport, was employed. It was found that in the case of conventional LST based anodes heterogeneous and charge transfer chemistry at LST surface has capacitive behavior and alters the impedance spectra. However, if nickel is added the influence of LST surface chemistry is diminished leading to an improvement of cell performance.

Abstract Protonic ceramic cells (PCCs) offer variety of potential applications for electrochemical energy conversion, however a lot of challenges remain in the development of PCCs for industrial scale manufacturing processes. As it was successfully demonstrated for the solid oxide cells, metal supported architecture is a good alternative for PCCs with many attractive advantages in terms of stabilities in operation and reduction of raw critical materials. In this review, proposed architectures, component materials and processing options are summarized. The challenges and prospects are discussed.