[Paper Review] Bias-triggered conductivity relaxation (BCR): a unique tool to simultaneously investigate thermodynamics, kinetics and electrostatic effects of oxygen reactions in MIEC thin films

Alexander Stangl, Alexander Schmid+3 more|arXiv (Cornell University)|Jan 22, 2026

Advancements in Solid Oxide Fuel Cells0 citations

TL;DR

Introduces bias-triggered conductivity relaxation (BCR) as a novel method to simultaneously probe thermodynamics, kinetics, and electrostatics of oxygen reactions in mixed ionic-electronic conducting (MIEC) thin films, demonstrated on (La,Sr)FeO3−δ electrodes.

ABSTRACT

Mixed ionic electronic transfer (MIET) reactions, such as the oxygen reduction reaction (ORR) at oxide surfaces, are of paramount importance to manifold technologically highly relevant processes and fundamental understanding must be developed to improve performance and tailor highly efficient electrodes and catalysts. Understanding such complex multi-step reactions, requires the study of kinetic processes, underlying thermodynamic properties, i.e. ionic and electronic defect concentrations and electrostatic surface effects. However conventional techniques struggle to uncover the complete picture within the same sample/measurement. Here, we overcome this limitation by introducing bias-triggered conductivity relaxation (BCR) as a novel tool to investigate MIET reactions on oxides. It is based on alternating out-of-plane coulometric titration/polarization and in-plane electrical conductivity relaxation measurements, providing simultaneous electronic, ionic and extraordinarily rich surface kinetics information. This innovative combination of electrical and chemical driving forces synergizes information depth, with enhanced time resolution, versatility and speed, yet it lifts the weaknesses of the individual approaches, while remaining cost-effective and surprisingly simple. Furthermore, BCR allows to disentangle overpotential induced electrostatic modifications of the surface kinetics in a unique manner. We showcase the advantages of BCR in this work by studying the ORR in model (La,Sr)FeO$_{3-δ}$ thin film electrodes and reporting on their thermodynamic and kinetic properties.

Motivation & Objective

• Motivate the need to understand MIET reactions (e.g., ORR) in oxide surfaces for better electrodes and catalysts.
• Propose a method that jointly reveals thermodynamic defect concentrations, kinetic processes, and electrostatic surface effects within the same sample.
• Showcase the method's ability to disentangle electrostatic overpotential effects on surface kinetics.

Proposed method

• Introduce bias-triggered conductivity relaxation (BCR) combining coulometric titration/polarization with in-plane conductivity relaxation.
• Use alternating out-of-plane driving forces and in-plane conductivity measurements to extract electronic and ionic responses.
• Leverage the synergy of electrical and chemical driving forces to enhance time resolution and depth of information.
• Demonstrate the approach on model (La,Sr)FeO3-δ thin films to obtain thermodynamic and kinetic properties.
• Highlight the ability to disentangle overpotential-induced electrostatic modifications of surface kinetics.

Experimental results

Research questions

• RQ1 How can MIET reactions on oxide surfaces be probed in a way that extracts thermodynamic, kinetic, and electrostatic information simultaneously?
• RQ2 Can bias-triggered conductivity relaxation reveal the interplay between ionic/electronic defect concentrations and surface electrostatics during ORR on MIEC thin films?
• RQ3 What are the thermodynamic and kinetic properties of ORR in (La,Sr)FeO3-δ thin film electrodes as revealed by BCR?

Key findings

• BCR provides simultaneous electronic, ionic, and rich surface kinetic information from a single sample under combined electrical and chemical driving forces.
• The method enables disentangling overpotential-induced electrostatic modifications of surface kinetics in a unique manner.
• Application to (La,Sr)FeO3-δ thin films yields insights into their ORR thermodynamics and kinetics (specific values not provided in abstract).
• BCR offers enhanced time resolution, versatility, and cost-effectiveness compared to conventional techniques.