Principles and applications of high temperature ion conducting ceramic in power generation - fuel cells and oxygen membranes

High temperature membranes can be used in numerous applications including ceramic filters, selective sieves, removal of impurities, oxygen and hydrogen separation, electrochemical devices such as solid oxide fuel cells and solid oxide electrolysers. The fabrication process is oriented at achieving desired properties of the final product, including proper conductivity, size and density of pores, tortuosity, mechanical stability in high operating temperatures and others. Among the mentioned applications, solid oxide fuel cells and oxygen separation membranes represent materials with mixed ionic and electronic conductivity (MIEC) which will be further discussed in the lecture. Such material are often referred as membranes designed specifically for transport of ions and electrons

A review of developments in electrodes for regenerative polymer electrolyte fuel cells

The design of electrodes for unitised regenerative polymer electrolyte fuel cells (URFC) requires a delicate balancing of transport media. Gas transport, electrons and protons must be carefully optimised to provide efficient transport to and from the electrochemical reaction sites. This review is a survey of recent literature with the objective to identify common components and design and assembly methods for URFC electrodes, focusing primarily on the development of a better performing bifunctional electrocatalyst for the oxygen reduction and water oxidation. Advances in unitised regenerative fuel cells research have yielded better performing oxygen electrocatalysts capable of improving energy efficiency with longer endurance and less performance degradation over time. Fuel cells using these electrocatalyst have a possible future as a source of energy

Fundamentals of Gas Diffusion Electrodes and Electrolysers for Carbon Dioxide Utilisation: Challenges and Opportunities

Electrocatalysis plays a prominent role in the development of carbon dioxide utilisation technologies. Many new and improved CO2 conversion catalysts have been developed in recent years, progressively achieving better performance. However, within this flourishing field, a disconnect in catalyst performance evaluation has emerged as the Achilles heel of CO2 electrolysis. Too often, catalysts are assessed in electrochemical settings that are far removed from industrially relevant operational conditions, where CO2 mass transport limitations should be minimised. To overcome this issue, gas diffusion electrodes and gas-fed electrolysers need to be developed and applied, presenting new challenges and opportunities to the CO2 electrolysis community. In this review, we introduce the reader to the fundamentals of gas diffusion electrodes and gas-fed electrolysers, highlighting their advantages and disadvantages. We discuss in detail the design of gas diffusion electrodes and their operation within gas-fed electrolysers in both flow-through and flow-by configurations. Then, we correlate the structure and composition of gas diffusion electrodes to the operational performance of electrolysers, indicating options and prospects for improvement. Overall, this study will equip the reader with the fundamental understanding required to enhance and optimise CO2 catalysis beyond the laboratory scale

Importance of Catalysis for Achieving Net Zero

It is critical to develop a broad portfolio of affordable and efficient technologies that can manage and ultimately overcome the climate crisis. The burden of developing such technologies to reverse the adverse effects of emissions without compromising the living standards lie with the scientific and engineering community in both academia and industry. In this article, we discuss some of the technologies that are either reaching commercial maturity or are currently under investigation in the scientific community. We also discuss the magnitude and scale required to achieve Net Zero targets. The accompanying video is a detailed technical case study on electrolysers used to produce hydrogen from water using renewable energy to store vast amount of renewable energy

Techno-economic assessment of enhanced Biogas&Power-to-SNG processes with high-temperature electrolysis integration

Biogenic energy sources are essential elements of the decarbonization pathways, but are strongly constrained by the limited availability. In this context, Biogas&Power-to-X technologies are strongly supported as a promising solution to foster renewable power generation and drive sector coupling opportunities. This work investigates enhanced Synthetic Natural Gas (SNG) production processes for the repurposing of biogas plants. As an alternative to combined heat and power applications via internal combustion engines, the Italian legislation is supporting biogas-to-biomethane upgrading, focusing on the transport market. The proposed integrated plant scheme is a flexible solution based on Power-to-Hydrogen and methanation, able to exploit both electric and gas grid connections, enhancing biomethane production. Advanced process schemes are studied combining solid oxide electrolysers that exploit the methanation waste heat as input thermal energy and flexible PEM electrolysers that improve the part-load operation. The calculated efficiency at max load is about 55% for the Power-to-Methane block and nearly 75% for the overall integrated plant. Results show limited sensitivity of efficiency to input power variations, making the system suitable for the recovery of surplus renewable power generation

Solid oxide electrochemical reactors and processes for carbon dioxide and water splitting

The increasing contributions of renewable energy sources into the electricity grid necessitates large-scale energy storage to balance supply and demand due to their inherent intermittency. Storing electrical energy in chemical bonds by electrolysis of CO2 and / or H2O is one option. The aims of this project were to develop and characterise (micro)-tubular solid oxide electrolysers for the reduction of CO2 and/or steam at temperatures of 700–800 °C. Micro-tubular hollow fibre reactors were fabricated by phase inversion. Ni(O) – yttria stabilised zirconia (YSZ) cermet electrodes (electrolysis cathode) and YSZ electrolyte (15-50 μm) were simultaneously co-extruded and sintered, followed by the application of a lanthanum strontium doped manganite (LSM) – YSZ|LSM electrode (electrolysis anode) onto the outer surface, which was subsequently sintered. At 800 °C, current densities of up to -1.0 A cm-2 were achieved at ca. 1.8 V for CO2 electrolysis with a silver wire and silver conductive paste cathodic lumen current collector. Replacing the silver wire with nickel and removing any paste additives resulted in a 50 % increase in current density. Electrode polarization for steam and co-electrolysis (H2O/CO2 co-feed) was 62-382 % lower compared to CO2 electrolysis, with the extent depending on the current collector design; the silver paste had a greater detrimental effect on the electrode performance of the SOE operating with CO2. Evidence supporting dual-step co-electrolysis with electro-generation of hydrogen preceding the heterogeneous chemical reaction of H2 with CO2 included electrochemical performance, adsorption modelling, diffusion considerations, and response to silver paste. However, isotopic studies to differentiate between (electro)chemical processes using labelled C18O2 and H216O were inconclusive due to oxygen-18 exchange occurring between C18O2 and H216O, within the alumina feed tube, despite the absence of a Ni-YSZ cathode acting as a catalyst. To further characterize the intrinsic CO2 reduction mechanism, the surface exchange kinetics of C18O2 on YSZ and oxide diffusion coefficients, without electrochemical polarization, were determined using secondary ion mass spectrometry. These results facilitated the analyses of SOE experiments using oxygen-18 tracers that compared the effect of applied current on oxide ion transport rates within the hollow fibre reactors. Techno-economical evaluation of intra-day energy storage using the micro-tubular reactors cyclically in electrolyser and fuel cell operational mode resulted in an electricity storage cost of £0.016 per kWh, considering capital and operating costs (assuming £0.1 per kWh electricity costs), which is lower than current pumped hydroelectric storage (£0.05 per kWh).Open Acces

Oxygen deficient layered double perovskite as an active cathode for CO2 electrolysis using a solid oxide conductor

A-site ordered PrBaMn2O5+?? was investigated as a potential cathode for CO2 electrolysis using a La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolyte. The A-site ordered layered double perovskite, PrBaMn2O5+??, was found to enhance electrocatalytic activity for CO2 reduction on the cathode side since it supports mixed valent transition metal cations such as Mn, which could provide high electrical conductivity and maintain a large oxygen vacancy content, contributing to fast oxygen ion diffusion. It was found that during the oxidation of the reduced PrBaMn2O5+?? (O5 phase) to PrBaMn2O6-?? (O6 phase), a reversible oxygen switchover in the lattice takes place. In addition, here the successful CO2 electrolysis was measured in LSGM electrolyte with this novel oxide electrode. It was found that this PrBaMn2O5+??, layered perovskite cathode exhibits a performance with a current density of 0.85 A cm-2 at 1.5 V and 850 ??C and the electrochemical properties were also evaluated by impedance spectroscopy.open0

An investigation into the feasibility of integrating intermediate-temperature solid oxide electrolysers with power plants

The detrimental effect of increasing global emissions of CO2 on the environment has prompted action to be taken to improve the environmental impact of hydrocarbon-based processes and fuel use. Therefore, producing hydrogen as an alternative fuel for vehicles fitted with fuel cells through solid oxide electrolyser cells (SOECs) has been considered. Coal fired power plants are major energy providers and are operational all day. Introducing SOECs into the plant to utilise hot steam and electricity during times of low energy demand may provide a step to large scale hydrogen production. Through modelling and experimentation of power plants and SOECs, this project aims to evaluate the feasibility of an integrated system based on the thermodynamic, techno-economic and SOEC performance analyses. Results show that SOECs, which operate between 600 and 1000 °C, take advantage of the heat of the steam, which increases electrolyser efficiency. Steam from before the intermediate pressure turbine at 560 °C and 46 atm was located from a simulation of a coal fired power plant. The intermediate-temperature steam of the plant was applicable to less used Gd-doped CeO2 (CGO) than yttria stabilised zirconia (YSZ) electrolyte that performs best at 900 °C, as shown experimentally. Modelling showed SOEC efficiency was improved by 25.2 % through an integrated system rather than traditional methods of heating water to steam, due to reduced energy requirements. Furthermore, the thermoneutral point of 4,644 A m -2 (1.31 V) formed a guide for the design and operation of SOECs. Analysis on the integrated system showed that 250 MW (7500 kg hr-1) and 290 MW (8700 kg hr-1) H2 can be produced with SOECs sized at 43,300 and 50,100 m -2, respectively, for scenarios of 7% steam extraction and a purely H2 production plant, at a cost of 3.76 $ kg H2-1. Although an integrated system shows promise for large scale hydrogen production, further development for suitable electrolytes and hydrogen storage and infrastructure is required