The mechanical properties of polystyrene (PS) nanospheres of ca. 50-1000 nm in diameter were evaluated by using an atomic force microscope (AFM). The compressive elastic moduli of individual nanospheres were obtained by analyzing the AFM force-displacement curves on the basis of the Hertz and JKR contact theories. The results showed that the elastic moduli of PS nanospheres of different sizes were in the range of 2-8 GPa. The elastic modulus of PS nanospheres increased with the decrease of the sphere diameter, especially when the diameter was less than 200 nm. The measurement errors due to tip wear and the deformation at the bottom of the sphere were analyzed. Mechanisms for the size dependence on the elastic modulus of PS nanospheres were also discussed.

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Nitric oxide electroreduction reaction (NOER) is one of the most attractive routes for ammonia synthesis and pollutant treatment. However, the current research efforts toward the NOER mainly focus on metal surface catalysts, while low-cost and high-efficiency single-atom catalysts (SACs) are rarely explored. Herein, using first-principles computations, we systematically investigate the NOER performance of a series of transition-metal-atomdecorated graphitic carbon nitride monolayer (g-C 3 N 4 ) and identify single Cu-atomdecorated g-C 3 N 4 (Cu@g-C 3 N 4 ) as the most promising SAC candidate for the NOER. Our results indicate that Cu@g-C 3 N 4 harbors excellent catalytic activity for the NOER with a quite low limiting potential of 0.371 V and, interestingly, is promising to be synthesized due to extremely high stability. Most importantly, Cu@g-C 3 N 4 can efficiently suppress the competing hydrogen evolution reaction, in favor of achieving high Faradaic efficiency. Our work provides a promising SAC candidate for the NOER to resolve environmental pollution and sustainable ammonia production.

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