Micro-nano Hierarchical Structure Research Articles

Anti-corrosive superhydrophobic coatings for reinforcement protection: recycling of concrete garbage

Purpose The purpose of this paper was to prepare a ternary hierarchical rough particle to accelerate the anti-corrosive design for coastal concrete infrastructures. Design/methodology/approach A kind of micro-nano hydrophobic ternary microparticles was fabricated from SiO2/halloysite nanotubes (HNTs) and recycled concrete powders (RCPs), which was then mixed with sodium silicate and silane to form an inorganic slurry. The slurry was further sprayed on the concrete surface to construct a superhydrophobic coating (SHC). Transmission electron microscopy and energy-dispersive X-ray spectroscopy mappings demonstrate that the nano-sized SiO2 has been grafted on the sub-micron HNTs and then further adhered to the surface of micro-sized RCP, forming a kind of superhydrophobic particles (SiO2/HNTs@RCP) featured of abundant micro-nano hierarchical structures. Findings The SHC surface presents excellent superhydrophobicity with the water contact angle >156°. Electrochemical tests indicate that the corrosion rate of mild steel rebar in coated concrete reduces three-order magnitudes relative to the uncoated one in 3.5% NaCl solution. Water uptake and chloride ion (Cl-) diffusion tests show that the SHC exhibits high H2O and Cl- ions barrier properties thanks to the pore-sealing and water-repellence properties of SiO2/HNTs@RCP particles. Furthermore, the SHC possesses considerable mechanical durability and outstanding self-cleaning ability. Originality/value SHC inhibits water uptake, Cl- diffusion and rebar corrosion of concrete, which will promote the sustainable application of concrete waste in anti-corrosive concrete projects.

Gel-confined fabrication of fully bio-based filtration membrane for green capture and rapid detection of airborne microbes

Air filtration has become a desirable route for collecting airborne microbes. However, the potential biotoxicity and sterilization of current air filtration membranes often lead to undesired inactivation of captured microbes, which greatly limits microbial non-traumatic transfer and recovery. Herein, we report a gel-confined phase separation strategy to rationally fabricate a fully bio-based filtration membrane (SGFM) using soluble soybean polysaccharide and gelatin. The versatile SGFM features fascinating honeycomb micro-nano architecture and hierarchical interconnected porous structures for microbial capture, and achieves a lower pressure drop, higher interception efficiency (99.3%), and superior microbial survivability than commercial gelatin filtration membranes. Particularly, the water-dissolvable SGFM can greatly simplify the elution and extraction process after bioaerosol sampling, thereby bringing about maximum sample transfer and vigorous recovery of collected microbes. Meanwhile, green capture coupled with ATP bioluminescence endows the SGFM with rapid and quantitative detection capability for airborne microbes. This work may pave the way for designing green protocols for the detection of bioaerosols.

Attaining superhydrophobic and superoleophilic bronze surface by picosecond laser texturing and post-heat treatment

As a bearing material, bronze has high strength and hardness but is poor in anti-adhesion property. In this study, we propose a method to prepare a superhydrophobic and superoleophilic bronze surface by combining laser surface texturing and post-heat treatment. A picosecond laser was employed to produce pore arrays with varying spacings and depths on the bronze surface, which exhibited micro-nano hierarchical structures. A further post-heat treatment of the laser-textured sample at 150 °C in the ambient led to the formation of a superhydrophobic surface with a maximum water contact angle of 158° and with superoleophilicity. It was found that pore spacings played a significant role in forming the surface hierarchical structures, which were covered with the laser-ablated micro-nano particles. The pore depth, however, showed little influence on the surface wettability. Analysis of the surface chemical compositions by X-ray photoelectron spectroscopy (XPS) indicates that the C element mainly exists in the form of the C–C(H) group, which reduces the surface energy and leads to superhydrophobicity. It was also verified that the wettability transition of the bronze surface before and after heating was independent of the oxide transition. Rubbing tests were conducted to evaluate the durability of the surface hierarchical structure. Anti-icing and self-cleaning functions were demonstrated showing the potential of the developed method for preparing a superhydrophobic and superoleophilic surface.

A facial method for constructing superhydrophobic surface by one-step surface etching combined with melt blowing process

It is a challenge to prepare fluorine-free superhydrophobic surfaces by simple methods. In this work, a simple and effective method for constructing a superhydrophobic surface was developed by combining in situ nanofibrillating melt blowing processs and one-step surface etching. Firstly, the randomly stacked meltblown microfibers as microstructure transformed the wetting performance of the surface from hydrophilic to hydrophobic. Then, by tuning the etching time, the outmost nanofibrils within the microfibers were exposed to form nanostructure thereby achieving superhydrophobic performance with a contact angle of 153°. The superhydrophobicity of the as-prepared nonwoven was maintained after various harsh treatments, such as strong acid, strong alkaline, sandpaper abrasion, and ultrasonic washing, showing stable water repellency ability. In addition, the superhydrophobic nonwoven showed promising application in self-cleaning and oil–water separation. Thus, this work not only prepares a superhydrophobic surface but also proposes a new idea for designing a micro-nano hierarchical structure on the surface.

Multifunctional superhydrophobic coatings with self-cleaning and anti-fouling properties for corrosion protection of metals

Superhydrophobic coatings have self-cleaning, antifouling, and anti-corrosion properties due to their unique surface properties, but their disadvantages such as poor durability, poor mechanical properties, and complicated preparation methods severely limit their practical applications. Here, superhydrophobic coatings with high abrasion resistance and long-lasting corrosion resistance were prepared by a simple spraying method using stearic acid-modified titanium dioxide nanoparticles (TiO2), polyphenylene sulfide (PPS) as the base material, and doped polyvinylidene difluoride (PVDF). The SA-TiO2 can provide low surface energy and rough structure, and the PPS itself has high mechanical strength and corrosion resistance properties. The PVDF doping can generate cross-linking inside the coating to improve the densification and mechanical strength of the coating, while the formation of irregular micrometer-sized protrusions can play a role in protecting the nano-surface. he synergistic effect of the various components results in an excellent mechanical stability of the coating, which remains superhydrophobic after a 400 cm sanding test. In addition, the coating has excellent corrosion resistance, and the electrochemical impedance spectroscopy (EIS) results show that the impedance modulus of the coating is as high as 21.99 kΩ·cm2. The coating has a hierarchical micro-nano structure, and shows excellent mechanical and corrosion resistance, which is of great potential for practical applications.

Superior droplet bouncing, anti-icing/anti-frosting and self-cleaning performance of an outstanding superhydrophobic PTFE coating

The prevention of ice/frosting formation is crucial in cold region for various applications. Superhydrophobic coatings are known for their excellent anti-icing/anti-frosting properties. In this study, a durable superhydrophobic PTFE coating on a stainless steel surface was fabricated with a high water contact angle of 171.4° and a low rolling angle of 1.1°. The freezing of water droplets on the coating exhibits a significantly prolonged duration of 809 s at −10 °C, representing a 25-fold increase compared to the uncoated stainless steel surface. The ice adhesion strength is reduced by 83.7%, making ice easier to remove. Anti-frosting tests show that a thinner and lower-density layer of frost formed on the PTFE coating due to its micro-nano hierarchical structure. Furthermore, the superhydrophobic PTFE coating demonstrates excellent mechanical stability, droplet bouncing dynamics and self-cleaning properties. It is anticipated that this durable superhydrophobic PTFE coating will be a candidate for anti-icing/anti-frosting and self-cleaning applications

Lotus leaf inspired hierarchical micro-nano structure on NdYbZr2O7 ceramic pellet with enhanced volcanic ash repellence

Lotus leaf inspired hierarchical micro-nano structure on NdYbZr2O7 ceramic pellet with enhanced volcanic ash repellence

Aluminum Micropillar Surfaces with Hierarchical Micro- and Nanoscale Features for Enhancement of Boiling Heat Transfer Coefficient and Critical Heat Flux.

The rapid progress of electronic devices has necessitated efficient heat dissipation within boiling cooling systems, underscoring the need for improvements in boiling heat transfer coefficient (HTC) and critical heat flux (CHF). While different approaches for micropillar fabrication on copper or silicon substrates have been developed and have shown significant boiling performance improvements, such enhancement approaches on aluminum surfaces are not broadly investigated, despite their industrial applicability. This study introduces a scalable approach to engineering hierarchical micro-nano structures on aluminum surfaces, aiming to simultaneously increase HTC and CHF. One set of samples was produced using a combination of nanosecond laser texturing and chemical etching in hydrochloric acid, while another set underwent an additional laser texturing step. Three distinct micropillar patterns were tested under saturated pool boiling conditions using water at atmospheric pressure. Our findings reveal that microcavities created atop pillars successfully facilitate nucleation and micropillars representing nucleation site areas on a microscale, leading to an enhanced HTC up to 242 kW m-2 K-1. At the same time, the combination of the surrounding hydrophilic porous area enables increased wicking and pillar patterning, defining the vapor-liquid pathways on a macroscale, which leads to an increase in CHF of up to 2609 kW m-2.

Application of Femtosecond Laser Processing Method in the Sustainable Conservation of Stone Cultural Relics: An Example of Green Schist in Wudang Mountain, China

The ancient building complex in Wudang Mountain, China, is known as the “Museum of Ancient Chinese Architectural Accomplishments”. However, the valuable stone components are preserved in open or semi-open environments and environmental factors such as rain seriously threaten its sustainable conservation. In this context, a femtosecond laser processing method has been demonstrated to be able to prepare hierarchical micro-nano structures on the stone surface to regulate its wettability, achieving the purpose of sustainable conservation. In this paper, the processing mechanism and performance of the femtosecond laser on green schist, a local stone material in the Wudang Mountain, are systematically investigated. It is found that green schist, as a typical non-homogeneous material, exhibits significant differences in its absorption of femtosecond laser with different compositions. Among them, quartz, chlorite, and muscovite are the three main compositions, and they are mainly characterized by cold ablation, thermal melting, and expansion under the irradiation of the femtosecond laser (238 fs, 100 kHz, 40 μJ, 33 μm, 500–40,000 pulses), respectively, and it is difficult to achieve a uniform and stable surface structure. Based on this, we prepared grooves with a spacing of 100–400 μm by scanning the femtosecond laser. Through the characterization of surface morphology, elemental composition, and three-dimensional structure, the processing mechanism of the hierarchical micro-nano structures of green schist under the irradiation of the femtosecond laser is comprehensively revealed. Finally, the wettability modulation result of water contact angle up to 147° is achieved by processing the grooves with an optimal spacing of 400 μm. The results of this research are of guiding significance for the sustainable conservation of ancient buildings and cultural relics.

Superhydrophobic Co-MOF-based sponge for efficient oil-water separation utilizing photothermal effect

Effectively addressing crude oil spills remains a global challenge due to its high viscosity and limited flow characteristics. In this study, we successfully prepared a modified sponge (PCP@MS) by embedding the photothermal material of Co-HHTP and coating the melamine sponge (MS) with low-surface-energy polydimethylsiloxane (PDMS). The PCP@MS exhibited outstanding hydrophobicity with WCA of 160.2° and high oil absorption capacity of 59–107 g/g. The PCP@MS showed high separation efficiency of 99.2% for various oil-water mixtures, along with notable self-cleaning properties and mechanical stability. The internal micro-nano hierarchical structure on the sponge surface significantly enhanced light absorption, synergizing with the photo-thermal conversion properties of Co-HHTP, enabled PCP@MS to achieve a surface temperature of 109.2 °C under 1.0 solar light within 300 s. With the aid of solar radiation, PCP@MS is able to heat up quickly and successfully lowering the viscosity of the surrounding crude oil, resulting in an oil recovery rate of 8.76 g/min. Density functional theory (DFT) calculation results revealed that Co-HHTP featured a zero-gap band structure, rendering advantageous electronic properties for full-wavelength light absorption. This in situ solar-heated absorbent design is poised to advance the practical application of viscous oil spill cleanup and recovery.

The synthesis of CdS hierarchical micro-nanostructures with different pore structure and their influence on the photocatalytic ethanol transformation

The synthesis of CdS hierarchical micro-nanostructures with different pore structure and their influence on the photocatalytic ethanol transformation

Experimental and theoretical study of hierarchical NiCo-TiO2 nanocomposite superhydrophobic surface for improving corrosion resistance

The superhydrophobicity of surfaces is a critical characteristic to prevent the corrosion problem, as a significant challenge under corrosive environments. In the present study, the nickel-cobalt (NC) alloy micro-nano hierarchical structure, along with the insertion of TiO2 nanoparticles (NCT) prepared by the economical and facile electrodeposition and myristic acid (MA) fatty acid physically adsorbed on the surface of NCT to reduce surface energy. The stability improvement of the prepared micro-nano scale composite due to the presence of TiO2 nanoparticles preserves the superhydrophobic feature created by the hierarchical structure and the fatty acid placed on the surface. The surface morphology and roughness, and the crystal structure of electrochemical deposited films were investigated using FE-SEM, AFM and XRD techniques, respectively. Also, mechanical and chemical stability, wetting behavior, and anti-corrosion properties were evaluated. The contact angle of 153° for the optimized Christmas tree-like nanocomposite (MA/NCT-2) implies the superhydrophobic property of the prepared coating. The excellent stability of MA/NCT-2 under corrosive different conditions, along with its supreme corrosion resistance confirm the potential of MA/NCT-2 for corrosion protection. Moreover, molecular dynamic (MD) simulations were performed in this first trial to determine wettability, intrinsic propagation mechanism, and structural evolution of water nanodroplets on copper (Cu) substrate and various coatings. The pristine substrate and NCT coating electrodeposited on the surface of Cu (NCT@Cu) were used to model the composite surfaces coated with MA. The last part concerned the study of the contact of this protective material with those surfaces and its possible improved performance as a superhydrophobic coating.

Ternary Zn3V3O8 superstructure and synergistic modification of separator promote high performance and stable zinc ion battery

Aqueous zinc-ion batteries have attracted much attention from researchers owing to their safety and eminent energy density. However, the exploration of an appropriate cathode with high reversible capacity is still a huge challenge. In this manuscript, the ternary Zn3V3O8 superstructure with an energy density of 317 Wh kg−1 was successfully prepared with a micro-nano ternary hierarchical structure and the incorporation doping of nitrogen and carbon (ZVO@CN). Thanks to the multilevel morphology and high conductivity of carbon and nitrogen, the novel ZVO@CN cathode delivers the eminent reversible capacity of 192 mAh/g at 5 A/g after 2200 cycles for aqueous zinc ion battery. Importantly, the ex-situ XRD and XPS were adopted to explore the energy storage kinetics. Consequently, the pristine material is been transformed to Zn3(OH)2V2O7·2H2O in the initial charging at 1.3 V, and this phase transition is nonreversible. After the second cycle, the intercalation/extraction of Zn2+ in Zn3(OH)2V2O7·2H2O supplies the reversible capacity. Besides, to solve the rapid capacity delay caused by dendrite growth at low current density on the Zn anodes, the C3N4 coating Zn is prepared to modify the separator (Zn@C3N4@GF). It has effectively relieved the negative effect of Zn dendrite with highly improved stability. When the ZVO@CN and Zn@C3N4@GF were used as cathode and separator, the batteries exhibited a dominant discharge capacity of 235 mAh/g at 0.1 A/g after 380 cycles, only reducing the 50 mAh/g compared to the initial capacity. This means it only decreases the discharge capacity of 0.13 mA g−1 per cycle.

Durable self-cleaning anti-reflective and antifog micro-nanostructures fabricated by laser ablation of vanadium-coated glass surfaces

In this study, low-cost laser marker ablation of vanadium-coated glass was adopted to prepare self-cleaning, anti-reflective, and anti-fog micro-nano structures on its surface. The surface had a hierarchical micro-nano structure composed of a quasi-periodic microstructure and ∼100 nm-sized worm-like clusters interspersed with dispersed nanoparticles. The solar spectrum (AM 1.5) weighted average transmission of treated glass was enhanced by 3.87% over control glass in the wavelength range of 400–1100 nm. Importantly, the water contact angle of the laser-treated samples achieved and maintained 0° for a duration of 25 days, and the laser-treated samples achieved and maintained excellent anti-fog performance for 150 days. The antifog performance degraded substantially afterward, though was still noticeable compared to the reference even after 428 days of storage in the laboratory. Furthermore, co-achievement of exceptional self-cleaning anti-fog performance and broadband transmission enhancement through laser treatment of glass has rarely been previously reported.

One-step synthesis of functional slippery lubricated coating with substrate independence, anti-fouling property, fog collection, corrosion resistance, and icephobicity

Ranging from industrial facilities to residential infrastructure, functional surfaces encompassing functionalities such as anti-fouling, fog collection, anti-corrosion, and anti-icing play a critical role in the daily lives of humans, but creating these surfaces is elusive. Bionic dewetting and liquid-infused surfaces have inspired the exploitation of functional surfaces. However, practical applications of these existing surfaces remain challenging because of their inherent shortcomings. In this study, we propose a novel functional slippery lubricated coating (FSLC) based on a simple blend of polysilazane (PSZ), silicone oil, and nano silica. This simple, nonfluorine based, and low-cost protocol promotes not only hierarchical micro-nano structure but also favorable surface chemistry, which facilitates robust silicone oil adhesion and excellent slippery properties (sliding angle: ∼1.6°) on various solid materials without extra processing or redundant treatments. The highly integrated competence of FSLC, characterized by robustness, durability, strong adhesion to substrates, and the ability for large-area preparation, render them ideal for practical production and application. The proposed FSLC holds outstanding application potentials for anti-fouling, self-cleaning, fog collection, anti-corrosion, and anti-icing functionalities.

Self-cleaning anti-fog micro-nanostructures by laser marker patterning nickel-coated glass

To minimise potential damage and crack on glass induced by direct laser patterning, this study employed a cost-effective laser marker for the rapid ablation of nickel (Ni)-coated glass substrates to fabricate super-hydrophilic micro-nanostructures. Most of laser energy was consumed by ablating Ni film with minimal deposited on glass, leading to shallow micron structure to support the nanostructure. The investigation systematically explored the influence of Ni thickness and laser scan hatch distance on the resultant properties of the treated glass by scanning electron microscope (SEM), atomic force microscope (AFM), confocal microscope, X-ray photoelectron spectroscopy (XPS), gonoimeter, spectrophotometer and real-time assessments of anti-fogging and self-cleaning performance. The treated glass surface exhibited a hierarchical micro-nanostructure featuring a quasi-periodical hillock-hollow micron structure and widely distributed nanoparticles. This unique surface structure yielded an exceptionally low contact angle of 0°, exhibiting remarkable self-cleaning and antifogging capabilities that persisted for over 9 months without apparent degradation. Such durable exceptional self-cleaning and anti-fog performance was rarely been reported in the literature and was attributed to the stable micro-nanostructure and robust chemical bondings present on the surface, showcasing significant potential for widespread commercial applications.

I-GLAD: a new strategy for fabricating antibacterial surfaces

The paper uses inverted glancing angle deposition (I-GLAD) for creating antibacterial surfaces. Antibacterial surfaces are found in nature, such as on insect wings, eyes, and plant leaves. Since the bactericidal mechanism is purely physical for these surfaces, the antimicrobial resistance of bacteria to traditional chemical antibiotics can be overcome. The technical problem is how to mimic, synthesize, and scale up the naturally occurring antibacterial surfaces for practical applications, given the fact that most of those surfaces are composed of three-dimensional hierarchical micro-nano structures. This paper proposes to use I-GLAD as a novel bottom-up nanofabrication technique to scale up bio-inspired nano-structured antibacterial surfaces. Our innovative I-GLAD nanofabrication technique includes traditional GLAD deposition processes alongside the crucial inverting process. Following fabrication, we explore the antibacterial efficacy of I-GLAD surfaces using two types of bacteria: Escherichia coli (E. coli), a gram-negative bacterium, and Staphylococcus aureus (S. aureus), a gram-positive bacterium. Scanning electron microscopy (SEM) shows the small tips and flexible D/P (feature size over period) ratio of I-GLAD nanoneedles, which is required to achieve the desired bactericidal mechanism. Antibacterial properties of the I-GLAD samples are validated by achieving flat growth curves of E. coli and S. aureus, and direct observation under SEM. The paper bridges the knowledge gaps of seeding techniques for GLAD, and the control/optimization of the I-GLAD process to tune the morphologies of the nano-protrusions. I-GLAD surfaces are effective against both gram-negative and gram-positive bacteria, and they have tremendous potentials in hospital settings and daily surfaces.

Synergy of Pd2+/S2--Doped TiO2 Supported on 2-Methylimidazolium-Functionalized Polypyrrole/Graphene Oxide for Enhanced Nitrogen Electrooxidation.

The electrosynthesis of nitrate catalyzed by electrochemical nitrogen oxidation reaction (NOR) is considered as an alternative and sustainable approach to the conventional industrial manufacture, but optimizing the electrocatalytic NOR performance and fabricating the efficient NOR electrocatalysts at the design level still encounter great challenges. Herein, unique Pd2+- and S2--doped TiO2 (Pb/S-TiO2) nanoparticles are successfully in situ grown on the surface of 2-methylimidazolium-functionalized polypyrrole/graphene oxide (2-MeIm/PPy/GO), which present the typical hierarchical micro-nanostructures, resulting in the excellent electrocatalytic NOR performance with the highest NO3 - yield of 72.69 µg h-1 mg-1 act. and the maximum Faraday efficiency of 8.92% at 2.04V (vs reversible hydrogen electrode) due to the synergistic effect of each component. Due to the doping effect, the appropriate oxygen evolution reaction (OER) activity is achieved by Ti-site, where OER principally occurs, providing *O during the non-electrochemical step of NOR, while the electrocatalytic NOR process as the electrochemical conversion of inert N2 to active *NO intermediates mainly occurs at the Pd-site. Especially, the sulfate radicals in situ formed on Pb/S-TiO2@2-MeIm/PPy/GO further promote nitrogen adsorption and decrease the reaction energy barrier, resulting in the acceleration of NOR. It provides theoretical and practical experience for the design and preparation of NOR electrocatalysts.

Coupling effects of dielectric loss in N-doped carbon double-shelled hollow particles for high-performance microwave absorption

Microwave absorbing materials with lightweight and high-performance are of great significance for electronic technique, ecological environment and defense applications. The hollow structure of carbon microspheres is beneficial to achievement of high-performance microwave absorption due to high interfacial polarization. However, the key characteristic is still unclear to control interfacial polarization. Herein, double-shelled N-doped carbon hollow particles derived from polypyrrole by self-sacrifice template were synthesized. The polymerization process was controlled by the interface between solid and pyrrole acid liquid in Fe3O4 disperse system, subsequently, micro-nano structure of carbon was tuned. The N-doped carbon double-shelled hollow particles (DSHS) show a strong dielectric loss due to coupling effect of resistance loss and interfacial polarization owing to the double-shelled hollow structure. Thus, DSHS shows a high-performance microwave absorption with minimum reflection loss (RLmin) of −75.10 dB at a thickness of 2.48 mm and effective absorption bandwidth (RL ≤ -10 dB) of 6.08 GHz and 4.05 GHz covering the whole Ku band and almost the whole X with a thickness of 2.21 mm and 3.00 mm, respectively. This work provides a simple approach for synthesizing N-doped carbon particles with distinct micro-nano hierarchical structure, double-shelled hollow microspheres assembled by nanoparticles have potential application as a high-performance MAM.

Boosting carrier separation and transport in CuGaO2 photocathodes by coupled effects of surface polarization and facet-junction

This study investigates the synergistic enhancement of carrier separation and transport in CuGaO2 photocathodes, achieved through the coupled effects of surface polarization and facet-junction engineering. Delafossite CuGaO2 microspheres, which exhibit a flower-like micro-nano hierarchical structure, are synthesized facilely through a one-pot hydrothermal process. These microspheres self-assemble from CuGaO2 nanosheets, driven by electrostatic forces among crystal facets. Morphology and size are systematically modulated by pH values, solvent composition, and reaction temperature. The CuGaO2 nanosheets, serving as fundamental building blocks, manifest notable surface polarization effects that facilitate the efficient transport of photo-generated carriers. The facet-junction formed between intersecting CuGaO2 nanosheets facilitates the collection of photo-generated electrons and holes on both sides of the interface, leading to spatial separation. Consequently, the CuGaO2 microspheres synergistically combine nanoscale surface polarization and microscale facet-junction effects, promoting the effective separation and rapid transport of electron-hole pairs generated under visible-light irradiation. The resulting simple bare photocathode, constructed using CuGaO2 microspheres, demonstrates a photocurrent density of 32 μA/cm2 at zero-bias, with a peak incident photon-to-current efficiency of 12.72 % at a 450 nm wavelength. Further optimization of the CuGaO2 photocathode yields a better photocurrent density of 138 μA/cm2 at 0.33 VRHE. These results underscore the significance of integrating nanoscale surface polarization effects with microscale facet-junction effects to achieve efficient separation and rapid transport of photo-generated carriers in photoelectrochemical cells.