伊藤 省吾

Proton-exchange-membrane hydrogen fuel cells (PEMFCs) are an important energy device for achieving a sustainable hydrogen society. Carbon-based catalysts used in PEMFCs’ cathode can degrade significantly during operation-voltage shifts due to the carbon deterioration. The longer lifetime of the system is necessary for the further wide commercialization of PEMFCs. Therefore, carbon-free catalysts are required for PEMFCs. In this study, highly crystallized conducting Sb-doped SnO2 (Sb-SnO2) nanoparticles (smaller than 7 nm in size) were synthesized using an ozone-assisted hydrothermal synthesis. Pt nanoparticles were loaded on Sb-SnO2 supporting particles by polyol method to be “Pt/Sb-SnO2 catalyst”. The Pt/Sb-SnO2 catalyst showed a high oxygen reduction reaction (ORR) mass activity (178.3 A g−1-Pt @ 0.9 V), compared to Pt/C (149.3 A g−1-Pt @ 0.9 V). In addition, the retention ratio from the initial value of electrochemical surface area (ECSA) during 100,000-voltage cycles tests between 1.0 V and 1.5 V, Pt/SnO2 and Pt/Sb-SnO2 catalyst exhibited higher stability (90% and 80%), respectively, than that of Pt/C catalyst (47%). Therefore, the SnO2 and Sb-SnO2 nanoparticles synthesized using this new ozone-assisted hydrothermal method are promising as carbon-free catalyst supports for PEMFCs.

Fully printable carbon-based multiporous-layered-electrode perovskite solar cells (MPLE-PSCs) are easy to fabricate and have excellent durability. In this study, the porosity of the mesoporous TiO2 layer as the electron transport layer in MPLE-PSCs was controlled by varying the particle diameter of TiO2 nanoparticles from 14 nm to 98 nm. Furthermore, the results of absorbed photon-to-current conversion efficiency, visible light reflectance spectroscopy, pore-size distribution, X-ray diffraction, field emission scanning electron microscopy, and photovoltaic parameters of MPLE-PSCs are discussed. Although the porous TiO2 layer with smaller nanoparticles showed higher photoabsorption, it was found that the more voids of perovskite crystals created in the TiO2 porous layer, the smaller the particle size (<18 nm). The porous TiO2 layers with particles over 26 nm are well filled with perovskite crystals, resulting in a higher photovoltaic capacity with TiO2 particles over 26 nm. As a result, the short-circuit current density (JSC) showed a maximum value using 43 nm TiO2 particles, with an average power conversion efficiency (PCE) of 10.56 ± 1.42%. Moreover, the PCE showed a maximum value of 12.20% by using 26 nm TiO2 nanoparticles.

Abstract The impact of NiOx layers on the performance of inverted perovskite solar cells (PSCs) has been investigated using multiple analysis methods (thermal gravimetric, differential thermal analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and Soft X-ray photoelectron spectroscopy) of NiOx layers, which were made by spray pyrolysis deposition at different temperatures. The analyses of this study indicate that the efficiency of inverted PSC increases with the Scherrer crystallite size of NiOx. We also observed that the band state of the NiOx layer was changed by Na+ ions migrated from the glass substrate, which also had an impact on the efficiency. The results clearly showed that under high fabrication temperature, migration of matter from the substrate to the hole transport layer affects the electronic structure. Therefore, how these materials are engineered will be important to increase the efficiency of inverted PSCs.

To fabricate fully printed carbon-based multiporous-layered-electrode perovskite solar cells (MPLE-PSCs), a polymer binder thickener had to be added to the carbon paste for the conductive carbon electrode. The polymer binder thickener is a key material to control the dispersion of carbon particles, viscosity for screen printing, and thickness and porosity of carbon electrodes. In this work, the role and effect of polymer binder thickeners for high-temperature carbon porous electrodes on MPLE-PSCs have been investigated in detail. Several carbon pastes with/without polymer binder thickeners (4 types of ethyl cellulose and 2 types of hydroxypropyl cellulose, which have different viscosities) were compared. What we understand in this paper are (1) Aggregation and dispersion of carbon particles are controlled by the polymer binder thickener (ethyl cellulose and/or hydroxypropyl cellulose); (2) For the porous carbon electrodes, the polymer binder thickeners are carbonized during the sintering procedure at 400 °C and can be kept on the surface of carbon particles as the additional carbon surface skin, which improves the conductivity; (3) The polymer binder thickeners can help the formation of a fine mesoporous structure in the annealed carbon electrodes. Combinations of results between viscosity, thermal, and specific surface area analyses revealed the close relationship between device performance and printability, dispersibility, and porosity brought by the polymer binder thickeners. As a result, the addition of a 20 wt % polymer binder thickener improved the average power conversion efficiency (PCE) from 9.52 ± 2.04 to 10.86 ± 0.85%, achieving a champion PCE of 12.06%.