Zn-air batteries (ZABs) as a potential energy conversion system suffers from low power density (typically≤200 mW cm^-2). Recently, 3D integrated air cathodes have demonstrated promising performance over traditional 2D plane ones, which is ascribed to enriched active sites and enhanced diffusion, but without experimental evidence. Herein, we applied a bubble pump consumption chronoamperometry (BPCC) method to quantitatively identify the gas diffusion coefficient (D) and effective catalytic sites density (ρ_EC) of the integrated air cathodes for ZABs. Furthermore, the D and ρ_EC values can instruct consequent optimization on the growth of Co embedded N-doped carbon nanotubes (CoNCNTs) on carbon fiber paper (CFP) and aerophilicity tuning, giving 4 times D and 1.3 times ρ_EC over the conventional 2D Pt/C-CFP counterparts. As a result, using the CoNCNTs with half-wave potential of merely 0.78 V vs. RHE (Pt/C: 0.89 V vs. RHE), the superaerophilic CoNCNTs-CFP cathode-based ZABs exhibited a superior peak power density of 245 mW cm^-2 over traditional 2D Pt/C-CFP counterparts, breaking the threshold of 200 mW cm^-2. This work reveals the intrinsic feature of the 3D integrated air cathodes by yielding exact D and ρ_EC values, and demonstrates the feasibility of BPCC method for the optimization of integrated electrodes, bypassing trial-and-error strategy.

Understanding bubbles evolution kinetics on electrodes with varied geometries is of fundamental importance for advanced electrodes design in gas evolution reaction. In this work, the evolution kinetics of electro-generated hydrogen bubbles are recorded in situ on three (i.e. smooth, nanoporous, and nanoarray) Pt electrodes to identify the geometry dependence. The bubble radius shows a time-dependent growth kinetic, which is tightly-connected to the electrode geometry. Among the three electrodes, the smooth one shows a typical time coefficient of 0.5, in consistence with reported values; the nanoporous one shows a time coefficient of 0.47, less than the classic one (0.5); while the nanoarray one exhibits fastest bubble growth kinetics with a time coefficient higher than 0.5 (0.54). Moreover, the nanoarray electrode has the smallest bubble detachment size and the largest growth coefficient (23.3) of all three electrodes. Based on the experimental results, a growth model combined direct bottom- injection with micro-convection is proposed to illustrate the surface geometry dependent coefficients, i.e., the relationship between geometry and bubble evolution kinetics. The direct injection of generated gas molecules from the bottom of bubbles at the three phase boundaries are believed the key to tailor the bubble wetting states and thus determine the bubble evolution kinetics.

Mass production of high-quality silver nanowires (Ag NWs) is of significant importance because of its potential applications in flexible transparent conductive devices. Halogen ions have been widely used for the synthesis of Ag NWs; however, owing to the lack of a deep insight into heterogeneous nucleation processes, usually a trace feeding amount (e.g. [Cl^–] < 0.25 mM) is used, which in turn lowers the concentration of precursor ([Ag⁺]). Here we systematically investigated the nucleation and growth behavior of Ag NWs and concluded that the number of heterogeneous nucleation sites was determined by the total surface area of AgCl seeds, which indicated a linear relationship between the concentrations of Ag⁺ and Cl^– during precipitation. Based on this mechanism, we successfully produced high-quality Ag NWs with Ag⁺ concentrations which were 20 times higher for a polyol system and 5 times higher for an aqueous system as compared to that in the previously reported strategies. Besides, by tailoring the heterogeneous nucleation sites by controlling the size of the AgCl seeds, the diameters of the final Ag NWs could be well controlled even at high Ag⁺ concentration. Based on the mechanistic understandings, this synthetic strategy could be extended to other AgX-seeds (X = Br^–, I^– and SO₄^2–) and the basic principles can be applied to help rational synthesis of other high-yield metal NWs with tunable sizes.

Carbon nanodots (CDs) formed by hydrothermal dehydration occur as mixtures of differently sized nanoparticles with different degrees of carbonization. Common ultracentrifugation has failed in sorting them, owing to their extremely high colloidal stability. Here, we introduce an ultracentrifugation method using a hydrophilicity gradient to sort such non-sedimental CDs. CDs, synthesized from citric acid and ethylenediamine, were pre-treated by acetone to form clusters. Such clusters "de-clustered" as they were forced to sediment through media comprising gradients of ethanol and water with varied volume ratios. Primary CDs with varied sizes and degrees of carbonization detached from the clusters to become well dispersed in the corresponding gradient layers. Their settling level was highly dependent on the varied hydrophilicity and solubility of the environmental media. Thus, the proposed hydrophilicity-triggered sorting strategy could be used for other nanoparticles with extremely high colloidalstability, which further widens the range of sortable nanoparticles. Furthermore, according to careful analysis of the changes in size, composition, quantum yield, and transient fluorescence of typical CDs in the post-separation fractions, it was concluded that the photoluminescence of the as-prepared hydrothermal carbonized CDs mainly arose from the particles' surface molecular state rather than their sizes.