Nanomechanical resonators have an unprecedented mass sensitivity sufficient to detect single molecules, viruses or nanoparticles. The challenge with nanomechanical mass sensors is the direction of nano-sized samples onto the resonator. In this work we present an efficient inertial sampling technique and gravimetric detection of airborne nanoparticles with a nanomechanical resonant filter-fiber. By increasing the nanoparticle momentum the dominant collection mechanism changes from diffusion to more efficient inertial impaction. In doing so we reach a single filter-fiber collection efficiency of 65 ± 31% for 28 nm silica nanoparticles. Finally, we show the detection of single 100 nm silver nanoparticles. The presented method is suitable for environmental or security applications where low-cost and portable monitors are demanded. It also constitutes a unique technique for the fundamental study of single filter-fiber behavior. We present the direct measurement of diffusive nanoparticle collection on a single filter-fiber qualitatively confirming Langmuir's model from 1942.

toward the oxygen evolution reaction (OER) was measured in 1M KOH at room temperature. All materials showed comparable OER activity with Tafel slopes in the range 56-98 mV/dec. The overvoltage at 10 mA • cm −2 , measured on a well-defined geometric surface area, was in the range 0.38-0.45 V. The best performing materials among the ones investigated were LaNiO 3 (multiphase) and La 2 Ni 0.9 Fe 0.1 O 4 . The chemical stability of the stoichiometric materials was also assessed in 31wt% and 45 wt% KOH respectively at 100 • C and 220 • C. All materials were partially decomposed after 1 week of exposure at 220 • C. After 1 week of exposure at 100 • C LaNiO 3 had formed secondary phases whereas LaNi 0.6 Fe 0.4 O 3 and La 2 Ni 0.9 Fe 0.1 O 4 showed only traces of secondary phase. The main secondary phases were in all cases La(OH) 3 , NiO, Ni(OH) 2 and Fe 2 O 3 . These observations indicate that the investigated oxygen electrode materials are not suitable for operation in alkaline electrolysis cells above 100 • C.

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