Probing Operating Electrochemical Interfaces by Photons and Neutrons

Abstract

The operation of all electrochemical energy-related systems, such as supercapacitors, batteries, fuel cells, etc. depends largely on the processes occurring at electrochemical interfaces at which charge separation and chemical reactions occur. Evolution of structure and composition at the interface between electrodes and electrolytes affects all the device′s functional parameters including power and long-term performance stability. The analytical techniques capable of exploring the interfaces are still very limited, and more often only ex situ studies are performed. This sometimes leads to a loss of important pieces of the puzzle, hindering the development of novel technologies, as in many cases intermediates and electrochemical reaction products cannot be “quenched” for post-process analyses. Techniques capable of operando probing of electrochemical interfaces by photons and neutrons have become an extensively growing field of research. This review aims at highlighting approaches and developing ideas on the adaptation of photoelectron, X-ray absorption, vibrational spectroscopy, nuclear magnetic resonance, and X-ray and neutron reflectometry in electrochemical studies

Operando Neutron Depth Profiling to Determine the Spatial Distribution of Li in Li-ion Batteries

“…Increasing the sample to detector distance, leads to higher resolution but fewer counts. However the relatively low beam intensity as compared to photon techniques is considered to be a common drawback of neutron techniques (Harks et al, 2015;Itkis et al, 2015). As a result, high resolution set-ups employ multiple detectors to improve counting statistics (Parikh et al, 1990;Mulligan et al, 2012).…”

“…Being a light element, lithium is difficult to detect with X-rays, for which reason most photon techniques typically use the change in oxidation state of the heavier ions to observe lithium intercalation (Nonaka et al, 2006;Katayama et al, 2014) or changes in interatomic spacing upon lithium insertion or extraction (Ganapathy et al, 2014;Zhang et al, 2014). Neutrons probe atom cores and therefore favor detection of the lighter elements compared to X-rays (Itkis et al, 2015). Also the penetrative nature of neutrons and selectivity of the technique allows for probing small lithium concentrations in realistic battery pouch and coin cell set-ups without the introduction of noise (Whitney et al, 2009;Zhang et al, 2015;Vasileiadis et al, 2018).…”

Neutron Reflectometry for Studying Corrosion and Corrosion Inhibition

“…There are some interesting reviews of certain aspects of this area [26,117] that provide an outline of the key role of NR as an in situ probe for electrochemical systems. Recent important examples are those related to energy, such as supercapacitors, batteries and fuel cells, where the key physics occurs at an interface.…”

“…Recent important examples are those related to energy, such as supercapacitors, batteries and fuel cells, where the key physics occurs at an interface. Other experimental methods used to probe these important systems can be rather limited, particularly when conducted ex situ, and often lead to a loss of information and/or artefacts [117]. NR contrast variation is extremely helpful for electrochemical studies, particularly for systems containing light elements; for example, lithium ion battery anode and cathode materials [84,117], which cannot be easily detected by XRR.…”

“…Other experimental methods used to probe these important systems can be rather limited, particularly when conducted ex situ, and often lead to a loss of information and/or artefacts [117]. NR contrast variation is extremely helpful for electrochemical studies, particularly for systems containing light elements; for example, lithium ion battery anode and cathode materials [84,117], which cannot be easily detected by XRR. NR offers other advantages over other approaches used to study electrochemistry, which are often limited in their ability to study interfacial structures in situ due to the large volume of liquid relative to the fraction of molecules at the surface, leading to any signal arising from interfacial structure being swamped by that from the bulk.…”