Absorption of gas in liquid media is an important step in applications ranging from environmental remediation to bioreactor design, yet it is often limited by slow interfacial mass transport. Here, we show how continually replenished aerophilic surfaces significantly enhance gas uptake across a gas-liquid interface. Similar to superhydrophobic surfaces, they feature hierarchical micro/nanotextures designed to retain a stable trapped gas layer underwater known as the plastron. We fabricate aerophilic surfaces with microcapsule features covered with nanoscopic pinning points and varying inter-feature spacings using laser ablation. Testing for CO2 uptake in a potassium hydroxide solution at near-neutral pH, we find that they attain 80% of the maximum saturation concentration within one hour, while conventional diffusion from an overhead CO2 atmosphere reaches only 20%. Using bromothymol blue colorimetry, we observe a 20-fold enhancement in the mass transfer rate from aerophilic surfaces compared to an equivalent planar gas-liquid interface with the same projected area. Counterintuitively, the enhanced mass transfer rate is not driven by an increase in interfacial area. Instead, it arises from a 24-fold increase in the liquid-side mass transfer coefficient, likely resulting from reduced resistance to mass transfer across the gas-liquid interface in the plastron. Environmental scanning electron microscopy confirms our plastron model of hemispherical gas caps pinned atop microtextures, with interfacial area calculations corroborating findings from colorimetry. These results highlight the potential of dynamically replenished aerophilic surfaces to overcome mass transport limitations in multiphase systems with gases and liquids, with potential applications in carbon capture and sustainable energy.

As hydrogen energy systems advance globally, management of hydrogen ingress remains a significant challenge. When hydrogen gas contacts a metal, it dissociates into hydrogen atoms, which subsequently enter and embrittle the metal. This detrimental process not only affects hydrogen pipelines but also metal components in aqueous corrosive environments, such as heat exchanger tubes in geothermal systems. Disrupting hydrogen ingress at the metal interface is therefore crucial to prevent subsequent embrittlement within the metal. Here, we show that cloaking liquid films as thin as 1 nm minimize hydrogen ingress into steel. These films, made from Krytox lubricant, are immiscible with water and preferentially wet steel in aqueous environments. Using a Devanathan-Stachurski electrochemical permeation cell, we show that in mildly acidic electrolytes, cloaking liquid films reduce hydrogen diffusivity in steel by 80% and the subsurface hydrogen concentration, a measure of hydrogen uptake in the steel, is decreased by 86%. X-ray photoelectron spectroscopy confirms the stability of the cloaking barrier film after 25 h of accelerated electrochemical permeation testing. In alkaline environments, similar reductions in hydrogen diffusivity (82%) and subsurface hydrogen concentration (90%) were observed, demonstrating the versatility of these films as barriers to hydrogen ingress. Additionally, we apply these thin cloaking films to enhance the barrier properties of defective zirconia coatings on steel. Although zirconia impedes hydrogen ingress, pinhole defects in the zirconia coating can provide pathways for hydrogen entry. We show that thin cloaking liquid films combined with a 75 nm zirconia coating reduce hydrogen diffusivity in steel by 84%, even when defects are present. Thicker composite coatings of zirconia and lubricant-impregnated microtextured surfaces could further enhance long-term protection against hydrogen ingress in practical applications.

Biomass combustion provides energy needs for millions of people worldwide. However, soot accumulation on the combustors’ walls significantly reduces heat transfer efficiency. Herein, we demonstrate how microtextured surfaces minimize soot accumulation by enhancing soot oxidation. We investigate soot layers from the combustion of paraffin wax as a model for wood-based soot, and find that randomly microtextured glass obtained by sandblasting shows a 71% reduction in the time taken to oxidize 90% of surface soot coverage when compared to smooth glass at 530 °C. We also study grooved microtextures fabricated via laser ablation and find that grooves with widths between 15 and 50 µm enhance soot oxidation, while the expedited advantage is lost when the groove width is 85 µm. X-ray photoelectron spectroscopy validates the superior extent of soot removal on microtextures down to a sub-nanometer length-scale. The high density of sharp features such as peaks and edges on microtextures, and the conformality of the soot layer to the microtextures contribute to increased soot oxidation. We also demonstrate enhanced soot oxidation on microtextured stainless steel, the principal material of construction in biomass combustors. Microtextured surfaces that facilitate soot oxidation upon contact could significantly improve performance and longevity in various combustion applications.

This study introduces a compact xerographic 3D printing system that utilizes precise layer-by-layer dry powder transfer techniques, facilitating the fabrication of 3D objects directly on metal substrates. By leveraging electrostatic force to coat dry fluoroethylene vinyl ether powder onto metallic surfaces, our innovative method significantly broadens the spectrum of printable materials. Through the optimization of electrostatic potentials and powder transfer efficiency, the system successfully demonstrates the ability to produce intricate 3D structures with heights ranging from millimeters to centimeters. This novel approach not only showcases the potential for creating flexible electronic materials with complex 3D geometries directly on the metal substrate but also opens new avenues for diverse material applications within the field of advanced xerographic 3D printing technology.

The recovery of trace amounts of scandium from process tailings represents a challenging yet critical task for the growing demand for sustainable and renewable technologies. As an important step toward addressing the environmental and technical concerns related to current scandium separation approaches, we developed novel extractant-impregnated surfaces (EIS) that held a thin layer of extractant within a micropillar texturized substrate. Compared with traditional solvent extraction, the EIS requires significantly less volume of extractant and no agitation. About 95 % of scandium is separated from the complex feedstock prepared from industrial waste bauxite residue, and the selectivity of scandium is more than 200 times higher than that of aluminum. Adsorption isotherm and kinetic studies are performed, and the experimental data are in good agreement with the Langmuir isotherm model and indicate pseudo-second-order kinetics. Cryo time-of-flight secondary ion mass spectrometry depth profiling is conducted on post-extraction EIS to unveil the scandium ions transport behaviour. Moreover, it is confirmed the EIS scheme and its underlying principles can be applied to sandblasted polytetrafluoroethylene substrates, which proves the potential of using EIS design at larger scales.

Electrocatalytic reduction of CO2 (CO2RR) is an attractive method of converting CO2 to solar fuels. Much research in this field has been focused on developing novel catalysts to enhance the activity and product distribution (selectivity). Copper has been studied widely as it can produce both one carbon (C1) products such as methane and formate, and products with two or more carbons (C2+) such as ethylene, ethanol, and n-propanol1. Copper is not immune from the competing hydrogen evolution reaction: the poor solubility of CO2 in water (~34 mM at ambient conditions) limits the CO2RR current density, and hydrogen generation is favored if the aqueous CO2 concentration becomes locally undersaturated close to the catalyst during CO2RR2. This limitation is even more pronounced for nanotextured copper, because the increased active surface area leads to faster depletion of local CO2 thereby promoting hydrogen evolution over CO2RR. Hence, overcoming these CO2 availability limitations can enable higher CO2RR activity while reducing co-evolution of hydrogen. In this work, we develop a gasphilic CO2 trap that increases gas-liquid mass transfer and maintains supersaturated CO2 concentration around the catalyst during CO2RR. Gasphilic surfaces need a special combination of surface chemistry and texture to capture bubbles and form a sheet of gas underwater which is called a plastron3. By creating pyramidal textures, CO2 bubbles are efficiently captured within the textures and form a CO2 plastron. When this plastron is placed proximal to both smooth and nanostructured copper catalysts during CO2RR, the current density is enhanced and maintained throughout the reaction, when compared to two commonly used methods of CO2 delivery: headspace and bubbling in the bulk electrolyte. The plastron allows for quick replenishment of CO2 during the CO2RR reaction in the vicinity of the catalyst. As a result, the H2 Faradaic efficiency is reduced from 33% to 13% on smooth copper, and from 62% to 33% on nanostructured copper. This is accompanied by an increased production of C2+ products including ethylene, ethanol and propanol, as well as acetone and acetate at Faradaic efficiencies exceeding 1%. We highlight the importance of this catalyst-proximal plastron approach by comparing against recent aqueous-phase CO2RR studies, and discuss how this approach can inform optimal design of continuous CO2RR systems such as gas-diffusion electrodes. [1] Nitopi, S., Bertheussen, E., Scott, S. B., Liu, X., Engstfeld, A. K., Horch, S., Seger, B., Stephens, I. E. L., Chan, K., Hahn, C., Nørskov, J. K., Jaramillo, T. F. & Chorkendorff, I. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Chem. Rev. 119, 7610–7672 (2019). [2] Lobaccaro, P., R. Singh, M., Lee Clark, E., Kwon, Y., T. Bell, A. & W. Ager, J. Effects of temperature and gas–liquid mass transfer on the operation of small electrochemical cells for the quantitative evaluation of CO2 reduction electrocatalysts. Physical Chemistry Chemical Physics 18, 26777–26785 (2016). [3] Panchanathan, D., Rajappan, A., Varanasi, K. K. & McKinley, G. H. Plastron Regeneration on Submerged Superhydrophobic Surfaces Using In Situ Gas Generation by Chemical Reaction. ACS Appl. Mater. Interfaces 10, 33684–33692 (2018).

Electrochemical reduction of carbon dioxide (CO2RR) is an attractive approach toward converting CO2 to solar fuels. Novel catalyst chemistries and morphologies may provide high selectivity to both one-carbon (C1) and two-carbon (C2) products over hydrogen; however, the limited aqueous solubility of CO2 restricts the CO2RR current density. Here, we demonstrate how gasphilic bubble-trap surfaces enhance mass transfer and enrich and maintain CO2 concentration during CO2RR by forming a catalyst-proximal plastron layer, consequently increasing the CO2RR activity on both smooth and nanostructured copper as compared to the conventional headspace or bubbling modes of CO2 delivery. The H2 Faradaic efficiency is suppressed from 33% to 13% on smooth copper and from 62% to 33% on nanostructured copper, accompanied by enhanced formation of C2+ products, including ethylene, propanol, and ethanol, and >1% acetone and acetate. We highlight the importance of the catalyst-proximal plastron approach by comparing against recent aqueous-phase CO2RR studies.

Corrosion is a detrimental process that can impact the performance and lifetime of many infrastructural systems. In this research, lubricant-impregnated surfaces (LIS) for corrosion protection are systematically developed and studied. Using microtextures with controlled geometry and spacing, this study shows that the corrosion resistance on LIS is greatly enhanced compared to bare iron as determined by a reduction in the corrosion current density by three orders of magnitude. Furthermore, it shows that the spreading characteristics of the lubricant are important toward ensuring effective corrosion protection. Krytox, a lubricant that covers both inside the textures as well as the top of the textures, provides two orders of magnitude greater corrosion protection as compared to silicone oil that does not cover texture tops. The practical applicability of LIS are highlighted to demonstrate corrosion protection on carbon steel in brine.

Spiral motifs are pervasive in nature, art, and technology due to their functional property of providing compact length. Nature is particularly adept at spiral patterning, and yet, the spirals observed in seashells, hurricanes, rams' horns, flower petals, etc. all evolve via disparate physical mechanisms. Here, we present a mechanism for the self-guided formation of spirals from evaporating saline drops via a coupling of crystallization and contact line dynamics. These patterns are in contrast to commonly observed patterns from evaporation of colloidal drops, which are discrete (rings, concentric rings) or continuous (clumps, uniform deposits) depending on the particle shape, contact line dynamics, and evaporation rate. Unlike the typical process of drop evaporation where the contact line moves radially inward, here, a thin film pinned by a ring of crystals ruptures radially outward. This motion is accompanied by a nonuniform pinning of the contact line due to crystallization, which generates a continuous propagation of pinning and depinning events to form a spiral. By comparing the relevant timescales of evaporation and diffusion, we show that a single dimensionless number can predict the occurrence of these patterns. These insights on self-guided crystallization of spirals could be used to create compact length templates.

combination of hard, soft and nanoscale organic components results in robust superhydrophobic surfaces that can withstand mechanical abrasion and chemical oxidation, and exhibit excellent substrate adhesion.

Hydrophobic surfaces that are robust can have widespread applications in drop-wise condensation, anti-corrosion, and anti-icing. Recently, it was shown that the class of ceramics comprising the lanthanide series rare-earth oxides (REOs) is intrinsically hydrophobic. The unique electronic structure of the rare-earth metal atom inhibits hydrogen bonding with interfacial water molecules resulting in a hydrophobic hydration structure where the surface oxygen atoms are the only hydrogen bonding sites. Hence, the presence of excess surface oxygen can lead to increased hydrogen bonding and thereby reduce hydrophobicity of REOs. Herein, we demonstrate how surface stoichiometry and surface relaxations can impact wetting properties of REOs. Using X-ray Photoelectron Spectroscopy and wetting measurements, we show that freshly sputtered ceria is hydrophilic due to excess surface oxygen (shown to have an O/Ce ratio of ∼3 and a water contact angle of ∼15°), which when relaxed in a clean, ultra-high vacuum environment isolated from airborne contaminants reaches close to stoichiometric O/Ce ratio (∼2.2) and becomes hydrophobic (contact angle of ∼104°). Further, we show that airborne hydrocarbon contaminants do not exclusively impact the wetting properties of REOs, and that relaxed REOs are intrinsically hydrophobic. This study provides insight into the role of surface relaxation on the wettability of REOs.

In this study, the catalytic activity and hydrogen selectivity of Ni/α-Al2O3, Ni/hydrotalcite, Raney nickel, Ru/C and Ru/γ-Al2O3 catalysts for hydrothermal hydrogen production from lignocellulosic biomass have been evaluated. The feedstocks included glucose, cellulose, fructose, xylan, pulp, lignin and bark. The experiments were carried out at 380°C in a batch reactor with 2wt% feed concentration. It was found that the gasification of glucose, fructose, cellulose, xylan and pulp resulted in comparable gas yields (±10% at 60min), whereas lignin was substantially harder to gasify. Interestingly, gasification yield of bark which has a high lignin content was comparable to those of carbohydrates after 60min reaction time. For a given feedstock, catalyst type affected both the gasification yield and the product distribution. Ni/α-Al2O3 and Ni/hydrotalcite catalysts were not only highly active for the gasification of carbohydrates, but also had better hydrogen selectivity when compared to Raney nickel, Ru/C and Ru/γ-Al2O3. In particular, gasification of bark in the presence of these catalysts resulted in negligible amounts of alkanes.