High Temperature Electrolysis

The growing emissions of CO₂ and other greenhouse gases has led to a global environmental warning. In order to restraint climate change, the use of sustainable and renewable alternatives to fossil derived products is needed nowadays more than ever. Renewable energies are partially covering those needs in recent decades.

As explained in previous sections, SOECs generally operate at high temperature. A high operating temperature increases the efficiency of SOECs, but it also accelerates the degradation rate.

Sealants for high-temperature fuel cells and electrolyzers must exhibit special properties due to the high operating temperatures, the reactive atmospheres, and the electric voltage between the sealed interconnects. Various technological approaches and material classes are being pursued for this application. At the same time, there are also successful stack concepts that completely abandon the use of sealants. With regard to the materials in consideration, metallic brazing alloys and such based on mica compression seals play a marginal role and are only used in individual cases. Glass-ceramic seals are predominantly used and are therefore the focus of this section. A general insight into the topic of glass-ceramic sealants and their properties as well as strategies for their development will be provided. The content will help you better understand the behavior of complex glass-ceramic sealants. Important sections also embrace discussions on their degradation behavior under typical SOC conditions as well as their mechanical properties.

The practical operation of solid oxide electrolysis cell (SOEC) involves complex physicochemical coupling processes between “multi-physics fields” at “multiple scales”. Mathematical simulation and modeling can explain the inherent connections and influencing mechanisms of multi-physics fields at different scales, which are crucial for the study of SOEC’s basic electrochemical characteristics and the development of engineering applications. In this chapter, we mainly summarize different simulation techniques for SOEC from the perspective of spatial scale categories. Models related to single cells and stacks are mainly based on the continuum hypothesis, and the macroscopic characteristics such as the distribution of multi-physics fields, input/output power, and cell efficiency inside single cells/stacks are obtained through traditional computational fluid dynamics using finite volume method or finite element method. This article first introduces the relevant conservation equations and modeling methods of macroscopic models based on the continuum hypothesis. Then, numerical simulation methods for heterogeneous electrode structures at the electrode scale are introduced, including the lattice Boltzmann method, kinetic Monte Carlo method, and phase field method. Finally, we also introduce the application of machine learning methods in SOEC simulation and provide prospects for future research.

Proton-conducting cell technology has been of ever-growing interest since the first studies reported by Iwahara et al. in the early 1980.

Steam electrolysis using SOEC operates in the range of 700–1000 °C. The advantage of using high temperature electrolysis is the improvement of electrochemical reaction rates and reduction of electrical energy demand. However, high operating temperature also accelerates oxidation of electrode under high steam environment

Solid oxide electrolysis cells are ceramic multilayer devices based on crystalline oxides with ionic and mixed ionic-electronic properties. Due to their ceramic nature, strong shape limitations have to be considered since conventional manufacturing methods for multilayer ceramics are based on tape casting, screen printing, extrusion, or dip coating, which ultimately result in planar or tubular geometries.

In order to design a high performing and durable SOE stack or system, all the relevant length-scales should be addressed using different approaches and tools, and all the components of the Balance-of-Plant need to be properly dimensioned and integrated.  This chapter adresses the requirements of building an SOE stack and system with an optimised performance and durability.

This book has tried to expose the status of high-temperature electrolysis. We have covered fundamental aspects, summarized the different materials employed in the devices, showed their performances and covered degradation issues and cell, stack and system scale. Important aspects regarding modelling or alternative novel designs have been also discussed.