Oxygen Generation Using Catalytic Nano/Micromotors.

Gaseous oxygen plays a vital role in driving the metabolism of living organisms and has multiple agricultural, medical, and technological applications. Different methods have been discovered to produce oxygen, including plants, oxygen concentrators and catalytic reactions. However, many such approaches are relatively expensive, involve challenges, complexities in post-production processes or generate undesired reaction products. Catalytic oxygen generation using hydrogen peroxide is one of the simplest and cleanest methods to produce oxygen in the required quantities. Chemically powered micro/nanomotors, capable of self-propulsion in liquid media, offer convenient and economic platforms for on-the-fly generation of gaseous oxygen on demand. Micromotors have opened up opportunities for controlled oxygen generation and transport under complex conditions, critical medical diagnostics and therapy. Mobile oxygen micro-carriers help better understand the energy transduction efficiencies of micro/nanoscopic active matter by careful selection of catalytic materials, fuel compositions and concentrations, catalyst surface curvatures and catalytic particle size, which opens avenues for controllable oxygen release on the level of a single catalytic microreactor. This review discusses various micro/nanomotor systems capable of functioning as mobile oxygen generators while highlighting their features, efficiencies and application potentials in different fields.

Parameters Optimization of Catalytic Tubular Nanomembrane-Based Oxygen Microbubble Generator.

A controllable generation of oxygen gas during the decomposition of hydrogen peroxide by the microreactors made of tubular catalytic nanomembranes has recently attracted considerable attention. Catalytic microtubes play simultaneous roles of the oxygen bubble producing microreactors and oxygen bubble-driven micropumps. An autonomous pumping of peroxide fuel takes place through the microtubes by the recoiling microbubbles. Due to optimal reaction-diffusion processes, gas supersaturation, leading to favorable bubble nucleation conditions, strain-engineered catalytic microtubes with longer length produce oxygen microbubbles at concentrations of hydrogen peroxide in approximately ×1000 lower in comparison to shorter tubes. Dynamic regimes of tubular nanomembrane-based oxygen microbubble generators reveal that this depends on microtubes' aspect ratio, hydrogen peroxide fuel concentration and fuel compositions. Different dynamic regimes exist, which produce specific bubble frequencies, bubble size and various amounts of oxygen. In this study, the rolled-up Ti/Cr/Pd microtubes integrated on silicon substrate are used to study oxygen evolution in different concentrations of hydrogen peroxide and surfactants. Addition of Sodium dodecyl sulfate (SDS) surfactants leads to a decrease of bubble diameter and an increase of frequencies of bubble recoil. Moreover, an increase of temperature (from 10 to 35 °C) leads to higher frequencies of oxygen bubbles and larger total volumes of produced oxygen.

Catalytic/magnetic assemblies of rolled-up tubular nanomembrane-based micromotors.

Nano/-micromotors self-assembling into static and dynamic clusters are of considerable promise to study smart, interactive, responsive, and adaptive nano/-micromaterials that can mimic spatio-temporal patterns, swarming, and collective behaviors widely observed in nature. Previously, the dynamic self-assembly of bubble-propelled catalytic micromotors initiated by capillary forces has been reported. This manuscript shows novel self-assembly modes of magnetic/catalytic Ti/FeNi/Pt tubular micromotors. When chemical fuel (hydrogen peroxide) is added it is decomposed on contact with Pt catalyst into oxygen and water. Here, the non-bubbling motion and autonomous assembly of catalytic/magnetic nanomembranes, i.e. without nucleation/generation of oxygen bubbles, are shown. Moreover, magnetic Ti/FeNi/Pt micromotors are spun using an external magnetic field and they form dynamic clusters balanced by attractive magnetic and repulsive hydrodynamic interactions. Micromotors form dynamic clusters, undergo precession and rapidly propagate through the solution.

Oxygen Microbubble Generator Enabled by Tunable Catalytic Microtubes.

Rolled-up catalytic Ti/Cr/Pt microtubes, consisting of inorganic nanomembranes integrated on-chip, are used to generate oxygen microbubbles in solutions of hydrogen peroxide. Oxygen bubble parameters (frequency, radius and volumetric flow rate) are optimized at different concentrations of hydrogen peroxide and common dish soap. Increasing the aspect ratio of the microtube (e.g., tube length/diameter) leads to the formation of smaller bubbles, but at higher frequencies. Longer tubes produce less total oxygen volume in comparison to shorter tubes. We attribute this observation to the specific dynamic behaviours of bubbles in tubes.

TiO2 Nanomembranes Fabricated by Atomic Layer Deposition for Supercapacitor Electrode with Enhanced Capacitance.

TiO2 is a promising environment friendly, low cost, and high electrochemical performance material. However, impediments like high internal ion resistance and low electrical conductivity restrict its applications as electrode for supercapacitor. In the present work, atomic layer deposition was used to fabricate TiO2 nanomembranes (NMs) with accurately controlled thicknesses. The TiO2 NMs were then used as electrodes for high-performance pseudocapacitors. Experimental results demonstrated that the TiO2 NM with 100 ALD cycles had the highest capacitance of 2332 F/g at 1 A/g with energy density of 81 Wh/kg. The enhanced performance was ascribed to the large surface area and the interconnectivity in the case of ultra-thin and flexible NMs. Increased ALD cycles led to stiffer NMs and decreased capacitance. Moreover, one series of two supercapacitors can light up one light-emitting diode with a working voltage of ~ 1.5 V, sufficiently describing its application values.