• Energy Research

AbstractThis paper presents a multi‐scale model of a solid oxide fuel cell (SOFC) stack consisting of five anode‐supported cells. A two‐dimensional isothermal elementary kinetic model is used to calculate the performance of single cells. Several of these models are thermally coupled to form the stack model. Simulations can be carried out at steady‐state as well as dynamic operation. The model is validated over a wide range of operating conditions including variation of temperature, gas composition (both on anode and cathode side), and pressure. Validation is carried out using polarization curves and impedance spectra. The model is then used to explain the pressure‐induced performance increase measured at constant fuel utilization of 40%. Results show that activation and concentration overpotentials are reduced with increasing pressure.

In this contribution the influence of pressure on an SOFC is studied with steam-reformed methane as a fuel. Experiments were performed with a reformate containing 58.4% H2, 20% H2O, 12.2% CO, 5.5% CO2 and 3.9% CH4 and another mixture containing 18% H2, 34% H2O, 2% CO, 27% CO2 and 19% CH4 as well as a hydrogen/nitrogen mixture. The influence of pressure on OCV, power density at constant voltage and constant current as well as on gas composition was examined for the different fuels. Power density increases of up to 70% were found.

Higher penetration of renewable energy sources in the energy mix and increasing pressure to decarbonize society introduces new challenges. Energy storage and grid stabilization systems are necessary to address the intermittent nature of renewable energy sources (wind, solar etc.) [1]–[4]. Renewable energy storage in form of hydrogen offers an attractive option for energy storage [5], [6]. With advent of hydrogen economy and growing number of fuel cell vehicles, local production and supply of hydrogen infrastructure for refueling stations is essential [7]–[9]. An r-SOC electrochemical reactor system is capable addressing these multiple challenges of energy storage and coupling the energy storage sector with hydrogen economy sector. Electricity storage is achieved by operating such a system in electrolysis mode (reduction of H2O). Electrical energy is converted to chemical energy in form of hydrogen. The produced hydrogen can be supplied into gas grids or stored locally which can be supplied to hydrogen refueling stations. During high demand for electricity, the system can be switched to fuel cell mode during which the stored hydrogen is efficiently converted to electricity. r-SOC systems offer an interesting feasible solution for the following challenges: 1) Efficient electricity storage, 2) Grid stabilization required for intermittent renewable energy, 3) Sector coupling of energy storage sector with hydrogen economy supply chain and 4) A decentralized solution for the above challenges via e.g. hydrogen refueling stations. An r-SOC system as described above poses certain technical challenges as requirements of a stand-alone SOEC (solid oxide electrolysis cell) system and a stand-alone SOFC (solid oxide fuel cell) system are different from each other. The simplest design approach for an r-SOC system calls for thermoneutral or exothermic electrolysis operation, although this will yield low round trip efficiencies in the range of 35 % [10]. Coupling highly efficient endothermic electrolysis and exothermic fuel cell mode allows for significantly higher round trip efficiencies up to 60 %. Therefore thermal integration, storage and management between the two modes of operation are crucial. In this study, a process system study of an r-SOC electrochemical reactor system is performed. Process system analysis is performed based on experimental investigation of a commercially available r-SOC reactor carried out under pressurized conditions. Opportunities of integrating thermal energy storage are investigated. Detailed process system architectures are discussed and effects of key system operating parameters are analyzed. Achievable system roundtrip efficiencies for the different scenarios using currently available r-SOC reactor technology are quantified. Reference [1] P. J. Hall and E. J. Bain, “Energy-storage technologies and electricity generation,” Energy Policy, vol. 36, no. 12, pp. 4352–4355, Dec. 2008. [2] H. Ibrahim, A. Ilinca, and J. Perron, “Energy storage systems—Characteristics and comparisons,” Renew. Sustain. Energy Rev., vol. 12, no. 5, pp. 1221–1250, Jun. 2008. [3] A. Evans, V. Strezov, and T. J. Evans, “Assessment of sustainability indicators for renewable energy technologies,” Renew. Sustain. Energy Rev., vol. 13, no. 5, pp. 1082–1088, Jun. 2009. [4] R. M. Dell and D. A. J. Rand, “Energy storage - A key technology for global energy sustainability,” J. Power Sources, vol. 100, pp. 2–17, 2001. [5] A. Sternberg and A. Bardow, “Power-to-What? - Environmental assessment of energy storage systems,” Energy Environ. Sci., vol. 8, no. 2, pp. 389–400, 2015. [6] H. Chen, T. N. Cong, W. Yang, C. Tan, Y. Li, and Y. Ding, “Progress in electrical energy storage system: A critical review,” Prog. Nat. Sci., vol. 19, no. 3, pp. 291–312, Mar. 2009. [7] J. a Turner, “Sustainable hydrogen production.,” Science, vol. 305, no. 5686, pp. 972–974, 2004. [8] M. Ball and M. Wietschel, “The future of hydrogen - opportunities and challenges,” Int. J. Hydrogen Energy, vol. 34, no. 2, pp. 615–627, 2009. [9] G. Mulder, J. Hetland, and G. Lenaers, “Towards a sustainable hydrogen economy: Hydrogen pathways and infrastructure,” Int. J. Hydrogen Energy, vol. 32, no. 10–11, pp. 1324–1331, 2007. [10] J. Mermelstein and O. Posdziech, “Development and Demonstration of a Novel Reversible SOFC System for Utility and Micro Grid Energy Storage,” 2016, vol. 306, no. July, pp. 59–70.

The behavior of a polybenzimidazole-based high-temperature polymer electrolyte membrane fuel cell using dimethyl ether (DME) as fuel was investigated under stationary and dynamic load conditions. The power density was enhanced significantly with an increase of both operating temperature and anodic water stoichiometry. Likewise, the power density decreased with increasing DME stoichiometry. The characterization of the dynamic operation showed a strong qualitative similarity to low-temperature direct methanol fuel cells. The development of the cell voltage after a spontaneous change of cell current density could be assigned to the electrochemical oxidation of an intermediate species.

The replacement of Pt-based catalysts by Fe-N-Cs in cathodes of high temperature polymer electrolyte membrane fuel cells (HT-PEMFC) can significantly reduce material costs.[1] In a previous study, we revealed the feasibility of Fe-N-C-based gas diffusion electrodes (GDEs) for oxygen reduction reaction under HT-PEMFC conditions (conc. H3PO4, 160 °C) and showed the demand for improving the catalyst layer (CL) morphology.[1] We discovered that Fe-N-C catalysts are feasible to maintain the cell performance within a wide range of PTFE contents from 20 to 50 wt% in the CL.[2] Non-ionic surfactants can enhance the wetting of the CL with electrolyte in HT-PEMFC, as Mack et al. revealed by a reduced break-in time of Triton™ complemented Pt/C electrodes.[3] Furthermore, Lee et al. reported improved dispersion of PTFE binder within the catalyst ink due to employed non-ionic surfactant and increased the HT-PEMFC performance of the Pt-based electrode.[4] Our actual study firstly reveals that the non-ionic surfactants Triton™ X-100 and as alternative the less-hazardous Tergitol™ 15-S-9 similarly affect the Fe-N-C ink sedimentation. Therefore, Fe-N-C-based (PMF-0011904, Pajarito Powder) GDEs are fabricated through ultrasonic spray coating with Tergitol™ contents of 0, 1, 20 and 50 wt% in the CL and a constant PTFE amount of 50 wt%. The H2O contact angle decreases with increasing Tergitol™ content in the Fe-N-C CL, revealing an increased wettability. Furthermore, contact angles with conc. H3PO4 are determined at room temperature (RT) and 160 °C. With this approach the wetting behaviors of the CL at HT-PEMFC conditions are imitated. The contact angle of H3PO4 of the 0 wt% Tergitol™ GDE unveils a decrease of 39 % from RT to 160 °C, for the 1 wt% Tergitol™ GDE by only 4 % and by 15 % for the 20 wt% Tergitol™ GDE. No significant change is observed for the 50 wt% Tergitol™ GDE. Tergitol™ provides a sufficiently wetted surface at RT, whereas without Tergitol™ the Fe-N-C CL must be moistened at higher temperatures. Furthermore, the GDE performance is accessed by hot pressing a polybenzimidazole-based membrane onto the CL and subsequent electrochemically characterization in a half-cell setup under HT-PEMFC condition at 160 °C in conc. H3PO4 electrolyte. Figure 1 reveals the effect of Tergitol™ on the GDE performance. A surfactant content above 1 wt% leads to electrode flooding by the electrolyte and thus a performance decay, as the surfactant increased the CL wetting. The results are complemented by detection of the iron content of the GDEs by inductively coupled plasma mass spectrometry (ICP-MS) and scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy (SEM/EDS) to compare CL morphologies and compositions along all GDEs. References: [1] J. Müller-Hülstede, T. Zierdt, H. Schmies, D. Schonvogel, Q. Meyer, C. Zhao, P. Wagner, and M. Wark, J. Power Sources, 537 231529 (2022). [2] T. Zierdt, J. Müller‐Hülstede, H. Schmies, D. Schonvogel, P. Wagner, and K. A. Friedrich, ChemElectroChem, 11 e202300583 (2024). [3] F. Mack, T. Morawietz, R. Hiesgen, D. Kramer, V. Gogel, and R. Zeis, Int J Hydrogen Energy, 41 (18), 7475-7483 (2016). [4] W. J. Lee, J. S. Lee, H. Y. Park, H. S. Park, S. Y. Lee, K. H. Song, and H. J. Kim, Int J Hydrogen Energy, 45 (57), 32825-32833 (2020). Figure 1

Abstract Quality control (QC) is an essential part of fuel cell technology industrialization, providing means to reduce cost of components, enhancing the reliability of the final product, and offering specification guidance for new entrants in the supply chain. The membrane electrode assembly (MEA), including membrane, catalyst layer (CL), and gas diffusion layer (GDL), as well as bipolar plate (BP), are key components of a proton exchange membrane (PEM) fuel cell, and the attributes of each component strongly correlate with the cell performance and longevity. To ensure the quality of the fuel cell, it is of great importance to characterize the properties with respect to the standardization of component/sub-component specifications. In collaboration with the fuel cell industry, this work aims at establishing compendiums of attributes, or so-called books of attributes, of key fuel cell components for the QC of PEM fuel cells through reviewing, identifying, categorizing, and prioritizing the main attributes/properties that determine their functionalities. The books of attributes for the major PEM fuel cell components include catalyst coated membrane (CCM) as a sub-assembly, GDL, and BP. To address the full spectrum of fuel cell components, gaskets and sub-gaskets are also included.

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...