The relationship between the oxidation potential determined by electrochemical measurements and the ionization energies measured by gas-phase ultraviolet photoelectron spectroscopy (UPS) has long been a focus of research of various groups. The focus of this study is to reveal such a correlation for redox molecules, which are chemically attached to metal electrodes. X-ray photoelectron spectroscopy, UPS, and cyclic voltammetry were performed for three types of ferrocene-terminated self-assembled monolayers possessing different electron-donating abilities. The results of these experiments indicate a linear relation with a slope of ∼0.7 between the UPS-derived energy of the highest occupied molecular orbital (HOMO) and the electrochemical oxidation potential. This indicates that the HOMO energy can be used to determine the oxidation potential of chemically modified electrodes.

Ferrocene-terminated self-assembled monolayers (SAMs) have been studied in the last quarter-century to determine the relationship between their electrochemical properties and microscopic structures as a prototypical chemically modified electrode. Although electronic structures are directly related to the electrochemical properties, knowledge of such a relation concerning ferrocene-terminated SAMs is extremely limited. In this study, we deposited a small amount of ionic liquid onto three types of ferrocene-terminated SAMs possessing different ionization energies and performed X-ray and ultraviolet photoelectron spectroscopies to elucidate the changes in the electronic structure resulting from the adsorption of the ionic liquid.For a low-ionization-energy system, spontaneous oxidation of the ferrocene moieties occurred while their electrochemical activities were retained; for other systems, only minor changes were observed. This result indicates that the interaction between the ionic liquid and ferroceneterminated SAMs facilitates electron transfer when the energy difference between the highestoccupied molecular orbital of the ferrocene moieties and the Fermi level of the electrode becomes small.

A simple, mild, reproducible, and controllable nanodeposition method for ionic liquids (ILs) by ejection of IL solution through a high-speed electromagnetic valve (pulse valve) to a substrate under vacuum is proposed (pulse-valve method). Sequential deposition of an IL [1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIM-TFSI)] on Au(111) substrates from its methanol solution was examined by adopting the pulse-valve method and the deposited IL films were analyzed by X-ray photoelectron spectroscopy (XPS) and tapping-mode atomic force microscopy (AFM). The amount of IL deposited per a pulse was successfully reduced to less than an equivalent thickness of 0.2 nm. The deposited IL was homogeneously distributed over a substrate area of 1 × 1 cm2 substrate area and the deposited amount was reproducible for independent depositions.

Alternating catalyst layer structure (ACLS) is a promising low-platinum technology for the PEFC application. This report discusses modification of ACLS in recent years, focusing on the enhancement of oxygen reduction reaction activity (ORR) and load cycle durability. For modified-ACLS electrodes (M-electrodes), single cell measurement showed about 6 times ORR specific activity compared with commercial Pt3Co/C. Excellent durability of M-electrodes was confirmed even with a Pt loading of 0.025 mgPt/cm2, revealing the possibility of their application as ultra-low-platinum PEFC anodes.

An iridium electrocatalyst powder with a platinum-coated porous titanium layer is conventionally used as the anode in polymer electrolyte membrane (PEM) electrolyzers. However, these noble metals are scarce and expensive. To reduce their use, we developed an alternating catalyst layer structure (ACLS) consisting of multiple sputter-deposited iridium sheets and air-gap layers without a platinum coating layer. The ACLS electrocatalyst exhibited lower overvoltage at low iridium loading compared with a powder catalyst, and there was almost no voltage rise during 7,000 h of operation. The ACLS is effective for reducing the amount of noble metals used in PEM electrolyzers.