lkemhjel

• Emhjellen, Linn Katinka Susanne Shi & Haugsrud, Reidar (2025). Oxygen Exchange Across the Melting Point of V2O5–Advancing Beyond Solids? Advanced Functional Materials. ISSN 1616-301X. 35(31). doi: 10.1002/adfm.202501274. Full text in Research Archive Show summary

  Oxide melts have the potential to enhance the performance and reduce operating temperature in sustainable chemical and electrochemical technologies by improving the kinetics of the oxygen reduction reaction and oxide ion transport. This study provides the first in situ investigation of the effects of the solid-liquid phase transition on the rate of oxygen exchange for V2O5, both as single-phase material and as a component in a ZrV2O7-30mol%V2O5 composite. Upon melting of the V2O5 phase, the rate coefficients for both surface and bulk oxygen kinetics increase several orders of magnitude. The rate-determining step of the oxygen exchange reaction shifts from incorporation to dissociative adsorption. Oxygen kinetics of molten V2O5 matches, and in some cases surpasses state-of-the-art solid-state oxide-based materials. Although liquid oxide-based components may offer enhanced performance and efficiency, addressing challenges related to chemical and mechanical stability is required before application in next-generation electrochemical cells and oxygen transport membranes can be viable.

• Emhjellen, Linn Katinka Susanne Shi; Thoreton, Vincent; Xing, Wen & Haugsrud, Reidar (2025). Superior Oxygen Exchange Kinetics on Bi2O3-Based Mixed Conducting Composites. ACS Physical Chemistry Au. 5(2), p. 239–248. doi: 10.1021/acsphyschemau.4c00111. Full text in Research Archive Show summary

  The kinetics of oxygen exchange dictate the rate of redox reactions, which is crucial for electrochemical-based sustainable technologies. In this study, we use isotope exchange pulse responses to elucidate the oxygen exchange mechanism for (Bi0.8Tm0.2)2O3−δ (BTM)–(La0.8Sr0.2)0.99MnO3−δ (LSM) composites. With an optimized composition and microstructure, these composites can achieve polarization resistances below 0.01 Ω·cm2 at 700 °C. Analysis of the oxygen exchange rate, , by splitting it into elementary processes using the serial two-step scheme, demonstrates that both the dissociative adsorption and incorporation of oxygen are accelerated in BTM–LSM compared to the parent phases. Dissociative adsorption of molecular oxygen is rate-limiting below 900 °C in the range 0.002–0.05 atm O2 and below 850 °C in 0.21 atm O2. Cation interdiffusion or changes in the electronic structure at the interface between the two materials create an electrocatalytically active region spanning 1–40 nm around the BTM–LSM phase boundary. Oxygen exchange coefficients within this region were estimated to be 2–3 orders of magnitude higher compared to those of the entire composite surface. We propose two potential pathways for oxygen exchange in BTM–LSM, with calculated pO2 dependencies for each rate-determining step (rds). The pO2 dependency of reveals that molecular oxygen is involved in the rds.

• Emhjellen, Linn Katinka Susanne Shi; Liu, Xin; Polfus, Jonathan M. & Haugsrud, Reidar (2022). Native point defects and polaron transport in zirconium pyrovanadate. Solid State Ionics. ISSN 0167-2738. 386, p. 1–8. doi: 10.1016/j.ssi.2022.116033. Full text in Research Archive
• Emhjellen, Linn Katinka Susanne Shi; Xing, Wen; Li, Zuoan & Haugsrud, Reidar (2022). Oxygen permeability and surface kinetics of composite oxygen transport membranes based on stabilized δ-Bi2O3. Journal of Membrane Science. ISSN 0376-7388. 660, p. 1–6. doi: 10.1016/j.memsci.2022.120875. Full text in Research Archive Show summary

  Composite ceramic membranes based on the ionic conducting Tm-stabilized δ-Bi2O3 (BTM) and the electronic conducting (La0.8Sr0.2)0.99MnO3-δ (LSM) exhibit among the highest oxygen flux values reported for Bi2O3-based membranes. Here, we use pulse-response isotope exchange (PIE) and oxygen flux measurements to elaborate on limiting factors for the oxygen permeation in BTM - 40-70 vol% LSM composites. Once both phases percolate, between 30 and 50 vol% BTM, the flux is essentially independent of the BTM/LSM volume ratio. The oxygen permeability is under mixed diffusion- and surface control, gradually becoming more bulk-limited with increasing temperature. The oxygen exchange coefficients of BTM-LSM are significantly higher than its constituent phases, revealing that a cooperative surface exchange mechanism enhances the kinetics. Some of the Tm was substituted with Pr to introduce electronic conductivity in BTM. (Bi0.8Tm0.15Pr0.05)2O3-δ (BTP) exhibits higher surface exchange coefficients compared to BTM, but the oxygen flux remains one order of magnitude lower than that of percolating BTM-LSM composites.

• Emhjellen, Linn Katinka Susanne Shi; Strandbakke, Ragnar & Haugsrud, Reidar (2021). Electrical transport in a molten-solid V2O5–ZrV2O7 composite. Journal of Materials Chemistry A. ISSN 2050-7488. 9(34), p. 18537–18545. doi: 10.1039/D1TA03750A. Full text in Research Archive Show summary

  Molten-solid composite oxides are candidates as oxygen transport membranes (OTMs) at intermediate temperatures (500–700 °C). Effects of the constituent phases and interphases on surface reactions and transport processes in these composites are elusive. Here we contribute fundamental insight to such materials systems, applying electrochemical impedance spectroscopy (EIS) and electromotive force (emf) measurements to investigate the electrical conductivity characteristics of a 30 mol% V2O5–ZrV2O7 composite with a eutectic melting point at ∼670 °C. When V2O5 melts and increases the V2O5 volume percolation, the electrical conductivity increases by a factor of 10 and the activation energy increases from 0.21 to ∼0.7 eV. The oxygen red-ox reaction at the surface changes from being rate limited by charge transfer processes to mass transfer processes as a consequence of fast oxygen exchange in molten V2O5 as compared to the all-solid composite. These effects coincide with the ionic transport number rising from essentially zero to ∼0.4, reflecting a significant increase in the relative oxide ion conductivity. Oxygen permeation across a 30 mol% V2O5–ZrV2O7 membrane was estimated to be in the same order as for several dual-phase membranes, but one magnitude lower than for single-phase mixed conducting membranes at intermediate temperatures.

View all works in NVA

• Xing, Wen; Emhjellen, Linn Katinka Susanne Shi; Haugsrud, Reidar & Li, Zuoan (2022). Ceramic composite oxygen transport membranes based on stabilised Bi2O3. Full text in Research Archive
• Emhjellen, Linn Katinka; Xing, Wen; Li, Zuoan & Haugsrud, Reidar (2019). Electrochemical Transport in Molten/Solid Composite V2O5-ZrV2O7. Full text in Research Archive
• Emhjellen, Linn Katinka; Bjørheim, Tor Svendsen; Fontaine, Marie-Laure; Li, Zuoan & Norby, Truls Eivind (2018). Novel Molten/solid Oxygen Transport Membranes for CO2 Capture. Full text in Research Archive
• Emhjellen, Linn Katinka Susanne Shi; Haugsrud, Reidar & Bjørheim, Tor Svendsen (2025). Oxygen transport and surface kinetics in molten and solid composites. Universitetet i Oslo. Full text in Research Archive Show summary

  Oxygen-permeable ceramics are essential for gas separation and electrochemical technologies, including applications in the steel and chemical industries, as well as in low-carbon or clean energy systems such as oxyfuel combustion and solid oxide fuel cells. However, slow oxygen reduction and evolution at the surfaces often hinder the development of these materials, highlighting the need for a deeper understanding of reaction pathways and rate-limiting steps in the oxygen exchange mechanism. This work demonstrates the notable oxygen flux and surface kinetics of Tm-doped Bi2O3- (BTM) and (La0.8Sr0.2)0.99MnO3-δ (LSM) composites - on par with state-of-the art oxygen permeable membranes - and offers fundamental insights into the surface processes in mixed-conducting dual-phase materials. Furthermore, oxide melts - with their lower activation barriers for oxygen transport and kinetics - are promising candidates for operation at intermediate temperatures. The literature on oxygen transport in melts is limited, and on surface kinetics, virtually non-existent. We present the first in-situ investigation of oxygen transport and surface exchange across the solid-liquid transition in V2O5, both as a single-phase material and as part of a ZrV2O7-30mol%V2O5 composite. Reaction rates increase by several orders of magnitude during the melting of V2O5.

• Emhjellen, Linn Katinka; Haugsrud, Reidar; Bjørheim, Tor Svendsen & Strandbakke, Ragnar (2017). Defects and Transport in SrFe1-xMoxO3-δ. Universitetet i Oslo. Full text in Research Archive

View all works in NVA