Evaporation from nanopores plays an important role in various natural and industrial processes that require efficient heat and mass transfer. The ultimate performance of nanopore-evaporation-based processes is dictated by evaporation kinetics at the liquid–vapor interface, which has yet to be experimentally studied down to the single nanopore level. Here we report unambiguous measurements of kinetically limited intense evaporation from individual hydrophilic nanopores with both hydrophilic and hydrophobic top outer surfaces at 22 °C using nanochannel-connected nanopore devices. Our results show that the evaporation fluxes of nanopores with hydrophilic outer surfaces show a strong diameter dependence with an exponent of nearly −1.5, reaching up to 11-fold of the maximum theoretical predication provided by the classical Hertz–Knudsen relation at a pore diameter of 27 nm. Differently, the evaporation fluxes of nanopores with hydrophobic outer surfaces show a different diameter dependence with an exponent of −0.66, achieving 66% of the maximum theoretical predication at a pore diameter of 28 nm. We discover that the ultrafast diameter-dependent evaporation from nanopores with hydrophilic outer surfaces mainly stems from evaporating water thin films outside of the nanopores. In contrast, the diameter-dependent evaporation from nanopores with hydrophobic outer surfaces is governed by evaporation kinetics inside the nanopores, which indicates that the evaporation coefficient varies in different nanoscale confinements, possibly due to surface-charge-induced concentration changes of hydronium ions. This study enhances our understanding of evaporation at the nanoscale and demonstrates great potential of evaporation from nanopores.

Protonation can be used to tune diverse physical and chemical properties of functional oxides. Although protonation of nickelate perovskites has been reported, details on the crystal structure of the protonated phase and a quantitative understanding of the effect of protons on physical properties are still lacking. Therefore, in this work, we select NdNiO 3 (NNO) as a model system to understand the protonation process from pristine NNO to protonated H x NdNiO 3 (H-NNO). We used a reliable electrochemical method with well-defined reference electrode to trigger the protonation-induced phase transition. We found that the protonated H-NNO phase showed a colossal ∼13% lattice expansion caused by a large tilt of NiO 6 octahedra and displacement of Nd cations. Importantly, we further designed a novel device configuration to induce a gradient of proton concentration into a single NNO thin film to establish a quantitative correlation between the proton concentration and the lattice constant and transport property of H-NNO.

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Water splitting is one of the most promising methods for mass production of green hydrogen (H2), with the oxygen evolution reaction (OER) being the current main kinetic bottleneck. Cobalt (oxy-)­hydroxides are among the most active electrocatalysts for OER in alkaline electrolytes free from rare-earth metals. However, identifying the active phase of electrocatalysts under operational OER conditions is often difficult, which largely impedes the design of cobalt-based electrocatalysts with improved performance and durability. This lack of understanding is partially contributed by the difficulties in operando characterizations on the details of electrochemically driven phase transitions. In this work, we combine operando Raman spectroscopy and operando optical characterization to investigate the phase equilibrium and kinetics of the phase transition in CoO x H y driven by applied electrochemical driving force. We found an irreversible phase transition during the first electrochemical test, after which phase transition became fully reversible in each following cycle. We further established the relationship between kinetic parameters of the reversible phase transition and applied potential by using the time-resolved operando optical method. Our work provides a precise approach toward a better understanding of the electrochemically driven phase transition in OER electrocatalysts.