The influence of specific adsorption of the sulfo group in the perfluorosulfonic acid ionomer, Nafion, on the oxygen reduction reaction (ORR) of a carbon-supported Pt/C catalyst using a thin-film rotating disk electrode was investigated. The relationship between the catalyst activity and coating of the Pt/C catalyst with Nafion was quantitatively evaluated through electrochemical measurements, operando X-ray absorption spectroscopy (XAS), and CO stripping voltammetry. Activity of the Pt/C catalyst decreased with increasing ionomer-to-carbon weight ratios. To date, the effect of specific adsorption on a catalyst has been investigated using CO stripping voltammetry. However, quantitative evaluation of specific adsorption at the ORR potential (0.50−1.0 V) has not been performed yet. We quantitatively evaluated the specific adsorption during the ORR by measuring the 5d orbital vacancy of the Pt/C catalyst using operando XAS. The difference in the electronic structures of Pt in the high potential range, with and without the ionomer, was successfully established.

A solid solution of GaN and ZnO (GaN:ZnO) is promising as a photocatalyst for visible light-driven overall water splitting to produce H2. However, several obstacles still exist in the conventional preparation procedure of GaN:ZnO. For example, the atomic distributions of Zn and Ga are non-uniform in GaN:ZnO when a mixture of the metal oxides, i.e., Ga2O3 and ZnO, is used as a precursor. In addition, GaN:ZnO is generally prepared under harmful NH3 flow for long durations at high temperatures. Here, a facile synthesis of GaN:ZnO with homogeneous atomic composition via a simple and safe procedure is reported. A layered double hydroxide (LDH) containing Zn 2+ and Ga 3+ was used to increase the uniformity of the atomic distributions of Zn and Ga in GaN:ZnO. We employed urea as a nitriding agent instead of gaseous NH3 to increase the safety of the reaction. Through the optimization of reaction conditions such as heattreatment temperature and content of urea, single-phase GaN:ZnO was successfully obtained. In addition, the nitridation mechanism using urea was investigated in detail. NH3 released from the thermal decomposition of urea did not directly nitride the LDH precursor. X-ray absorption and infrared spectroscopies revealed that Zn(CN2)-like intermediate species were generated at the middle temperature range and Ga-N bonds formed at high temperature along with dissociation of CO and CO2.