Since many fundamental processes at surface or interface are involved in energy conversion and transport in energy conversion devices and energy utilization systems, the knowledge and techniques in surface science are expected to highly contribute to the advancement of the energy technologies. This special issue introduces researches on the energy conversion and transport at interfaces, which are conduced based on surface science and its related techniques, expecting for further utilization and dissemination of surface science research in solving the energy-related issues.

All-solid-state Li batteries attract considerable attention as a next-generation energy storage device due to their higher energy density and safety than conventional Li-ion batteries with a liquid electrolyte. To further improve battery performance, it is crucial to reduce the large resistance at the interfaces in the batteries. Here, we discuss the fundamental understanding of interface resistances from surface science and semiconductor physics. We reveal that the atomic arrangement of electrode-electrolyte interfaces plays a key role in reducing interface resistance. In addition, we evaluate the interface resistance between electrodes and current collectors. We stress that fundamental understandings based on surface and interfacial physics are critical for developing all-solid-state Li batteries.

Tribology is an interdisciplinary field that covers friction, wear, and lubrication, and has been developed to improve the properties of sliding surfaces of machines. In this paper, recent progress in tribology research is introduced with focusing on the development of analytical methods of solid-liquid interface. The role of tribology will be further expanded for the construction of energy-saving society in the future.

Electrochemical lithiation/delithiation processes of a Si thin film sputter-deposited on a solid electrolyte sheet was investigated by x-ray photoelectron spectroscopy coupled with electrochemical analysis. After the first lithiation, a broad Li 1s peak composed of lithium silicides, lithium silicates, lithium oxide, and lithium carbonate appears. In addition, Si 2p peaks corresponding to bulk Si and native oxide significantly shift to lower binding energy due to the formation of lithium silicides and lithium silicates. After the successive delithiation, the Si 2p peak corresponding to lithium silicides shifts to higher binding energy because of the decrease of lithium content in lithium silicides, while the other species such as lithium silicates, lithium oxide, and lithium carbonate remained as irreversible species.

Chemical-state imaging of materials using X-ray microscopes has been developed and applied to various materials such as composites, batteries, ceramics and so on. In this article, after features of X-ray microscopy are discussed, analytical approaches for chemical-state imaging are reviewed by showing typical application to materials : scanning transmission X-ray microscope (STXM), transmission X-ray microscope (TXM), and X-ray absorption spectroscopy imaging (XAS-imaging). X-ray microscopes can provide indispensable information for investigating “trigger sites” that are specific structures or locations in materials where key reactions progress. For this end, analytical approaches using information science and/or applied mathematics will be required to deal with big data obtained by X-ray microscopes.

Spin caloritronics is an emerging research field based on the combination of spintronics and thermoelectrics, in which the interplay between spin, heat, and charge currents plays an essential role. In this article, we show that interfaces in magnetic hybrid structures strongly affect the transport and interconversion of these currents, providing a useful way to improve thermo-spin and magneto-thermoelectric conversion efficiencies.

One of the biggest issues in the hydrogen economy is “hydrogen embrittlement” of metal induced by hydrogen entering and diffusing into the material. Hydrogen diffusion in metallic materials is difficult to grasp owing to the non-uniform compositions and structures of metal. Here a time-resolved “operando hydrogen microscope” was used to interpret local diffusion behaviour of hydrogen in the microstructure of a stainless steel with austenite and martensite structures. The martensite/austenite ratios differed in each local region of the sample. The path of hydrogen permeation was inferred from the time evolution of hydrogen permeation in several regions. We proposed a model of hydrogen diffusion in a dual-structure material and verified the validity of the model by simulations.