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Global warming and air pollution have forced greater attention to new energy sources to replace fossil fuels. Among several eco-friendly energy sources, polymer electrolyte membrane fuel cells have been increasingly investigated since they have zero emissions, high energy density, and high energy efficiency. Carbon-supported Pt catalyst is generally used for the cathodic catalyst in polymer electrolyte membrane fuel cells. However, Pt/C catalysts corrode under start-up/shut-down conditions. Pt agglomeration, separation, and loss can occur due to the carbon corrosion, which results in a rapid performance loss. Metal oxide is a promising candidate as an alternative support since it shows high stability in the high potential. Of several metal oxides, titanium oxides and tin oxides have been widely investigated. Their performance is comparable to the Pt/C catalyst, and they have shown even higher durability than the Pt/C catalyst in accelerated stress tests simulating start-up/shut-down conditions. In this paper, we summarize the development of metal oxide supports for the Pt catalyst in the five most recent years. In recent studies, the characteristics of metal oxides have been varied using new synthesis methods, annealing temperature, precursors, and dopants, which results in enhanced ORR activity and durability. Advanced metal oxides have shown high durability and exhibited acceptable performance compared to the state-of-the-art Pt/C catalysts.

In recent years, the on-resistance, power loss and cell density of Si power devices have not exhibited significant improvements, and performance is approaching the material limits. GaN is considered an attractive material for future high-power applications because of the wide band-gap, large breakdown field, high electron mobility, high switching speed and low on-resistance. Here we report on the Ohmic contact resistance and reversebias characteristics of AlGaN/GaN Schottky barrier diodes with and without annealing. Annealing in oxygen at 500℃ resulted in an increase in the breakdown voltage from 641 to 1,172 V for devices with an anode-cathode separation of 20 μm. However, these annealing conditions also resulted in an increase in the contact resistance of 0.183 Ω-mm, which is attributed to oxidation of the metal contacts. Auger electron spectroscopy revealed diffusion of oxygen and Au into the AlGaN and GaN layers following annealing. The improved reverse-bias characteristics following annealing in oxygen are attributed to passivation of dangling bonds and plasma damage due to interactions between oxygen and GaN/AlGaN. Thermal annealing is therefore useful during the fabrication of high-voltage GaN devices, but the effects on the Ohmic contact resistance should be considered.