Hydrophilic Patterns Research Articles

Defect-Density-Controlled Phase-Change Phenomena.

Juxtaposing hydrophilicity and hydrophobicity on the same surface, known as hybrid surface engineering, can enhance phase-change heat transfer. However, controlling hydrophilicity on hybrid surfaces in a scalable fashion is a challenge, limiting their application. Here, using widely available metal meshes with variable dimensions and by controlling the patterning pressure, we scalably fabricate hybrid surfaces having spot and gridlike patterns using stamping. Using fog harvesting in a controlled chamber, we show that optimized hybrid surfaces have a ∼37% higher fog harvesting rate when compared to homogeneous superhydrophobic surfaces. Furthermore, condensation frosting experiments reveal that, on grid-patterned hybrid surfaces, frost propagates at ∼160% higher velocity and provides ∼20% less frost coverage when compared to homogeneous superhydrophobic surfaces. During defrost, our hybrid surfaces retain more water when compared to superhydrophobic surfaces due to the presence of hydrophilic patterns and melt water pinning. We adapt our fabrication technique to roll-to-roll patterning, demonstrating wettability contrast on round metallic geometries via atmospheric water vapor condensation. This work provides guidelines for the rapid, substrate-independent, and scalable fabrication of hybrid wettability surfaces for a wide variety of applications.

A polarization converter array based on microcavity patterned hydrophobic layer induced twisted-radial liquid crystals

We report a facile method to prepare an array of liquid-crystal polarization converters (LCPCA) based on hydrophobic microcavity arrays. The reactive ion etching (RIE) technique was chosen to treat the homeotropic polyimide (PI⊥) layers through a metal mask with a through-hole array. Under the selective RIE treatment, a hydrophobic–hydrophilic pattern is obtained due to the increase in surface energy in the etched area from ∼34.6 to ∼73.2 mN/m. The etched area forms a microcavity with a diameter of 520 μm, depth of ∼23 nm, and center distance of 690 μm, which is consistent with the dimensions of the metal mask. Since the walls of the microcavity retain hydrophobicity, the liquid-crystal (LC) molecules show a radial arrangement in the microcavity. Combining a substrate covered by a parallel rubbed homogeneous polyimide (PI∥) layer with the substrate covered by a microcavity-patterned PI⊥ layer can form a “sandwich” structure. The LC molecules in the microcavities are arranged in a twisted-radial texture, which can convert linearly polarized light to radially or azimuthally polarized light depending on the polarization direction of the incident light. The proposed method has the merits of simple steps, controllable size, and easy to fabricate large-area arrays. Our LCPCA has potential applications in tight focus, material processing, biological tissue analysis, particle capture, and optical data storage.

Cactus-Inspired Photonic Crystal Chip for Attomolar Fluorescence Multi-analysis.

Automation and efficiency requirements of environmental monitoring are the pursuit of spontaneous sampling and ultrasensitivity for current sensory systems or detection apparatuses. In this work, inspired by cactus hierarchical structures, we develop a cactus-inspired photonic crystal chip to integrate spontaneous droplet sampling and fluorescence enhancement for sensitive multi-analyte detection. A conical hydrophilic pattern on hydrophobic surfaces can give rise to unidirectional Laplace pressure, which drives droplet transport to the assigned photonic crystal site. The nanostructure of photonic crystals has bigger capillarity to drive the droplet wetting uniformly into the photonic crystal matrix while performing prominent fluorescence enhancement by their photonic bandgap. A low to attomolar (2.24 × 10-19 M) fluorescence limit of detection (LOD) sensitivity can be achieved by the synergy of spontaneous droplet sampling and fluorescence enhancement. Focused on eutrophic water problems and algae pollution monitoring, a femtomolar (1.83 × 10-15 M) LOD and identification of various microcystins in urban environmental water can be achieved. The suitable integration of the unidirectional droplet transport by Laplace pressure and fluorescence enhancement by photonic crystals can achieve the spontaneous sampling and signal enhancement for ultratrace detections and sample survey of environmental monitoring and disease diagnosis.

Bioinspired Under-Liquid Dual Superlyophobic Surface for On-Demand Oil/Water Separation.

Porous membranes with under-liquid dual superlyophobic properties, which are difficult to achieve because of a thermodynamic contradiction, have attracted considerable interest in the field of switchable oil/water separation. Herein, a bioinspired mesh membrane with alternating hydrophilic and hydrophobic chemical patterns on its surface that endows it with superamphiphilic and under-liquid dual superlyophobic properties is fabricated by a simple liquidus modification process. The as-prepared membrane possesses a combination of under-oil superhydrophobic and under-water superoleophobic characteristics in the absence of external stimuli. Moreover, it can effectively perform the on-demand separation of various oil/water systems, including immiscible oil/water mixtures and oil/water emulsions owing to its under-liquid dual superlyophobic properties.

Pushing the Limit of Beetle‐Inspired Condensation on Biphilic Quasi‐Liquid Surfaces

AbstractMassive studies concern the development of low‐carbon water and energy systems. Specifically, surfaces with special wettability to promote vapor‐to‐liquid condensation have been widely studied, but current solutions suffer from poor heat transfer performances due to inefficient droplet removal. In this study, the limit of condensation on a beetle‐inspired biphilic quasi‐liquid surface (QLS) in a steam environment is pushed, which provides a heat flux 100 times higher than that in atmospheric condensation. Unlike the beetle‐inspired surfaces that have sticky hydrophilic domains, the biphilic QLS consists of PEGylated and siloxane polymers as hydrophilic and hydrophobic quasi‐liquid patterns with the contact angle hysteresis of 3° and 1°, respectively. More importantly, each hydrophilic slippery pattern behaves like a slippery bridge that accelerates droplet coalescence and removal. As a result, the condensed droplets grow rapidly and shed off. It is demonstrated that the biphilic‐striped QLS shows a 60% higher water harvesting rate in atmospheric condensation and a 170% higher heat transfer coefficient in steam condensation than the conventional beetle‐inspired surface. This study provides a new paradigm to push the limit of condensation heat transfer at a high heat flux, which sheds light on the next‐generation surface design for water and energy sustainability.

Improve Wettability of Polycaprolactone (PCL) /Chitosan of Wound Dressings by Plasma Jet

Surface wettability plays a significant role in determining the function of the wound dressing. They should have hydrophobic surfaces for the adsorption of bacteria and a hydrophilic surface necessary to improve cell attachment for most anchorage-dependent cell types. Furthermore, the Hydrophobicity / Hydrophilicity of the surface can be used to direct cellular processes such as cell initial correlation, adhesion, and migration during wound healing, as a result such surface can change its surface wettability which increases the dressing's usefulness. In this research, nanomembres were prepared from polycaprolactone and chitosan solution (with different amounts of CS (0.05, 0.1, 0.2, and 0.4) % (w/w)) by the electrospinning method. These membranes were characterized by Fourier-transform infrared FTIR spectroscopy and their wettability, contact angle, porosity and swelling values were determined. These were improved by plasma treating the electrospun nanomebranes. Best results were obtained for the plasma treated electrospum nanomembranes at 4% chitosan. It resulted in a surface with a combination of hydrophobic and hydrophilic patterns, which has a lot of promise in the realm of tissue engineering for things like cell patterning and guiding.

Radiative cooling layer boosting hydrophilic-hydrophobic patterned surface for efficient water harvesting

Water harvesting from fog is of considerable interest as a nominated solution to freshwater shortage in arid and underdeveloped regions. The unique hydrophilic and hydrophobic patterns on the dorsal surface of the Namib Desert Beetle have been shown to be an evolving and effective strategy for harvesting water from air. Illuminated by the Namib desert beetle, different elaborate patterns based on aluminum plates were established and their water harvesting efficiency was investigated from a comparative perspective. The results showed that the vein-like patterned surfaces had the highest (786.15 mg∙cm−2 h−1) water collection efficiency. However, the heat released during the condensation process affected the water collection rate. In order to reduce the re-evaporation rate of water droplets, a radiant cooling layer was designed on the other side of the water collection plate to release the condensation heat. The radiation cooling layer employed MgHPO4ꞏ0.78 H2O as the functional particle and P(VDF-HFP) as the adhesive. Benefitted from radiative cooling layer, the water collection efficiency could be increased by 198.51 mg∙cm−2 h−1. The water collection material with double-sided function structure has low preparation costs and green raw materials. This work provides an effective way to develop key materials with freshwater harvesting capabilities.

Construction of nanoreactors on TiO2 nanotube arrays as a POCT device for sensitive colorimetric detection

With increasing attention to personalized healthcare, miniaturized and easily implementable devices are desired for point-of-care testing (POCT). Herein, hydrophilic patterns were designed on freestanding TiO2 nanotube arrays (TiNTs) as nanoreactors for a naked-eye colorimetric assay. With a high aspect ratio, TiNTs can provide a long observation length combined with a limited volume. Moreover, by combining the photocatalytic property of TiO2 and spatiotemporal controllability of light, hydrophilic nanoreactors were fabricated with minimal volume, and thus the indicator and analyte are limited in a confined void by the hydrophobic surroundings, thus allowing a higher sensitivity for sensing. We believe the proposed sensing platform could provide a promising strategy in developing POCT devices for routine health monitoring.

Tunable wettability of jet electrodeposited micro-nano structures modified by laser radiation

In this paper, the wettability contrast surfaces were prepared via modifier-free composite processing. Nickel particles were added in electrolytes to fabricate micro-nano hierarchical structures by magnetic field induced jet electrodeposition. Laser surface modification was used to selectively draw patterns on the coating surface. After aging in the air for 25 days, the coatings prepared by magnetic field induced jet electrodeposition exhibited superhydrophobic, and the patterns achieved hydrophilicity or hydrophobicity by different laser fluences. Moreover, the morphologies and chemical composition of micro-nano hierarchical structures were changed by different laser fluences. Micro melted spots and hydrophilic nickel oxide appeared on the coating surface after laser surface modification. The wettability of the coating was altered by hydrophobic nickel hydroxide hydroxylated from NiO and organic substances from the air. However, the micro-nano structures were damaged by laser surface modification and cannot adsorb organic substances from the air. In addition, the superhydrophobic coatings and the hydrophilic patterns were corrosion-resistant. Ecorr and jcorr were −0.2607 V and 7.225 × 10−6 A/cm2, −0.5078 V and 9.354 × 10−6 A/cm2, respectively. Thus, the modifier-free processing, which combines magnetic field induced jet electrodeposition and laser surface modification, offers potential in the areas of green preparation for wettability contrast surfaces.

Design and optimization of hybrid superhydrophobic–hydrophilic pattern surfaces for improving fog harvesting efficiency

Inspired by the fog harvesting capacity of a wettability gradient pattern on the back of Stenocara beetles, we provide a facile and low-cost method for the fabrication of hybrid superhydrophobic–hydrophilic pattern surfaces, with smooth aluminum alloy substrate as the hydrophilic component and superhydrophobic sticky paper of varying hole sizes as the superhydrophobic component. The fog harvesting efficiency is evaluated by adjusting and combining the hole size of the hybrid superhydrophobic–hydrophilic pattern surfaces. The prepared single aperture hybrid superhydrophobic–hydrophilic pattern surface exhibits an enhanced fog harvesting efficiency compared with the uniform superhydrophobic and hydrophilic surfaces. Furthermore, the fog harvesting efficiency of the prepared combined aperture hybrid superhydrophobic–hydrophilic pattern surface is 88.3 % higher than that of the single set-up. The dynamic fog harvesting mechanism demonstrates that the optimal combined aperture hybrid surface maximizes the number of coalesced droplets within a certain period to collect additional water droplets, thus optimizing the fog harvesting efficiency. The fog harvesting efficiency reaches a maximum of 362.5 mg/cm2/h. The hybrid superhydrophobic–hydrophilic pattern surface prepared in this study has potential applications in atmospheric water collecting.

Delicate and Fast Photochemical Surface Modification of 2D Photoresponsive Organosilicon Metal-Organic Frameworks.

Photoresponsive arylsilanes have been fascinating molecules for decades because of their unique photophysical characteristics and surface chemistry. Here we report the synthesis and fabrication of a crystalline two-dimensional trisilyl metal-organic framework (TSiMOF) orderly installed with the classical photoresponsive hexamethyltrisilane groups on the surface. Irradiated by UV light under air in minutes the fluorescence of the TSiMOF is turned on simultaneously with an intriguing surface transformation from superhydrophobic to hydrophilic. Thus, multifarious luminescent and hydrophilic patterns including logos, characters and Quick Response codes, etc. with good resolution are readily generated on the facilely fabricated TSiMOF film. The mechanism of this transformation is revealed by control experiments that the superficial trimethylsilyl groups suffering photochemical oxidation have been converted to hydroxyl groups.

Delicate and Fast Photochemical Surface Modification of 2D Photoresponsive Organosilicon Metal–Organic Frameworks

AbstractPhotoresponsive arylsilanes have been fascinating molecules for decades because of their unique photophysical characteristics and surface chemistry. Here we report the synthesis and fabrication of a crystalline two‐dimensional trisilyl metal–organic framework (TSiMOF) orderly installed with the classical photoresponsive hexamethyltrisilane groups on the surface. Irradiated by UV light under air in minutes the fluorescence of the TSiMOF is turned on simultaneously with an intriguing surface transformation from superhydrophobic to hydrophilic. Thus, multifarious luminescent and hydrophilic patterns including logos, characters and Quick Response codes, etc. with good resolution are readily generated on the facilely fabricated TSiMOF film. The mechanism of this transformation is revealed by control experiments that the superficial trimethylsilyl groups suffering photochemical oxidation have been converted to hydroxyl groups.

Gas Diffusion Layer with a Regular Hydrophilic Structure Boosts the Power Density of Proton Exchange Membrane Fuel Cells via the Construction of Water Highways.

The gas diffusion layer (GDL) is an essential carrier for the mass transmission of proton exchange membrane fuel cells (PEMFCs), which decides the peak power density of PEMFCs. Herein, a gas diffusion layer with a regularly arranged hydrophilic and hydrophobic pattern structure was prepared by a template method combined with the ultrasonic spray process. The peak power density was enhanced by 30% (from 520 to 678 mW/cm2) compared to an unpatterned structure, and the breakthrough pressure of the GDL was reduced from 13.61 to 2.96 kPa. In addition, the finite element analysis (FEA) results indicate that the polarization curve of calculation was highly consistent with the experimental results. Importantly, the capillary pressure of the hydrophilic area was about 0.3 kPa, much lower than that of the hydrophobic area (2 kPa), demonstrating that the hydrophilic and hydrophobic synergistic structure reduced the water transmission resistance in separating water and oxygen and builds a high-speed channel for water transmission.

Scaling laws for the droplet rebound with lateral motion after impacting on heterogeneous surfaces

After droplet impacting onto solid surfaces, various outcomes such as deposition, rebound and splashing are possible, which greatly depend on the surface wettability. In this paper, the spontaneous rebound with lateral motion of a water droplet impacting on a hydrophobic substrate decorated with the hydrophilic pattern is studied numerically and theoretically. The effects of multiple parameters on the droplet lateral motion are investigated, including the initial droplet diameter and impact velocity, the arrangement of hydrophilic patterns, and the surface energy gradient. The numerical results show that the dimensionless lateral velocity obeys some simple scaling laws. Moreover, the theoretical analysis of droplet impact is performed, and the same relationship between the lateral motion and the impact conditions is derived. The reliability of the proposed relationship is validated by some testing cases and previous experimental data. The results obtained here may strengthen our understanding of droplet manipulation and achieve the controllable rebound of impacting droplets.

A Combined Numerical and Experimental Study of Evaporative Cooling for Polymer Electrolyte Fuel Cells

State-of-the-art liquid cooling of polymer electrolyte fuel cells (PEFC) requires a complex multi-layer design of bipolar plates [1] which is responsible for about 75 % of stack volume and approximately 80 % of its mass [2]. Additionally, an external humidifier is often required to ensure a proper humidification and thus ionic conductivity of the proton exchange membrane [3] at elevated temperatures.Evaporative cooling shows the potential to reduce the stack volume, mass, complexity and cost by up to 30 % by simplifying the design of bipolar plates. Additionally, it allows a better internal humidification which enables higher operating temperatures without external humidification [4]. In our concept, liquid water is fed to each cell through dedicated water channels in the anode flow-field. Subsequently, the water is distributed in a specially designed gas diffusion layer with a mixed hydrophilic and hydrophobic pattern (Figure 1) [5]. Once in contact with the gas flow, the water in the hydrophilic lines evaporates, cools the cell and is eventually released as vapor with the exhaust gases.In our previous work [6] we have elaborated the potentials and limits of this concept on the stack and system level. In this study, we focus on the experimental and numerical investigation of water evaporation from GDLs with patterned wettability [7] in a technical cell environment. Ex-situ evaporation experiments have been carried out with a patterned Toray 060 GDL (7 x 3 cm2, 14 hydrophilic lines, pattern: 500 µm hydrophilic, 940 µm hydrophobic) and nitrogen as a carrier gas. The operating temperature (22 to 90 °C) as well as the gas velocity (0.2 to 7 m/s) has been varied whereas the pressure is kept constant (ambient at cell outlet).In order to further foster the understanding of the underlying evaporation phenomena, a simplistic 2-D water vapor transport model has been developed in this study. Fickian diffusion is taken into account in the GDL and gas channel, while convection is only considered in the channel. Water evaporation is modeled according to the Hertz-Knudsen-Schrage equation [8]. The projected contact area between hydrophilic lines and gas channel is an input parameter to the model and has been determined by ex-situ X-Ray tomographic imaging (XTM).Figure 3 shows that the evaporation rate and thus the related cooling power increases significantly with temperature. This fact is attributed to the higher water saturation pressure as well as to the increased diffusivity at higher temperature. Further, it can be seen that the evaporation rate increases with gas speed. We attribute the strong increases at low gas speed to the fact that the evaporation is only limited by the saturation of the gas channels in this regime. At higher gas speeds, however, the increase in evaporation rate is less pronounced. We hypothesize that the water vapor transport through the GDL is limiting the evaporation rate. Evaporation kinetics have not been a limiting factor in the investigated parameter space, since the interface between hydrophilic and hydrophobic lines is fully saturated in the conducted simulations.Furthermore, the modelling results show that the evaporation rate and thus cooling power is not homogenous along the channel (Figure 2). Based on these results, an optimized pattern structure is proposed to achieve a more uniform cooling and evaporation distribution.Finally, a cooling power density of more than 1 W/cm2 can be achieved which is sufficient for cooling state-of-the-art fuel cell systems.

Low-Cost Laser Micromachining Super Hydrophilic-Super Hydrophobic Microgrooves for Robotic Capillary Micromanipulation of Microfibers.

Capillary self-alignment technique can achieve highly accurate and fast alignment of micro components. Capillary self-alignment technique relies on the confinement of liquid droplets at receptor sites where hydrophobic–hydrophilic patterns are widely used. This paper reports a low-cost microsecond pulse laser micromachining method for fabrication of super hydrophilic–super hydrophobic grooves as receptor sites for capillary self-alignment of microfibers. We investigated the influence of major manufacturing parameters on groove sizes and wetting properties. The effects of the width (20 µm–100 µm) and depth (8 µm–36 µm) of the groove on the volume of water droplet contained inside the groove were also investigated. We show that by altering scanning speed, using a de-focused laser beam, we can modify the wetting properties of the microgrooves from 10° to 120° in terms of the contact angle. We demonstrated that different types of microfibers including natural and artificial microfibers can self-align to the size matching super hydrophilic–super hydrophobic microgrooves. The results show that super hydrophilic–super hydrophobic microgrooves have great potential in microfiber micromanipulation applications such as natural microfiber categorization, fiber-based microsensor construction, and fiber-enforced material development.

Enhanced condensation on a biphilic-zigzag surface due to self-arrangement of crystals on a micro-structured surface

Applying micro-nano hierarchical structures or hydrophilic patterns on superhydrophobic surfaces has showed the potential to increase the condensation efficiency by promoting the coalescence-induced jumping. In this study, the crystal self-arrangement is demonstrated using a capillary flow to combine the advantages of the hierarchical structures and the biphilic wettability for the further enhancement of the condensation efficiency. Such flow transports the crystals to the inner tips of the V-shapes during the evaporation of an ethanol-water film on the zigzag structured surface. These crystals induce the condensations inside the V-shapes that guide the condensed droplets to the gap between the zigzag structures, which promotes the coalescence between the condensed droplets. Consequently, the developed surface increases the jumping frequency by up to 1385%, and the cumulative volume of the jumping droplets and the heat transfer coefficient on the developed surface are approximately 2.2 and 2.7 times higher than that of the state-of-the-art superhydrophobic surface. Our findings pave the way for enhancing the efficiency of the jumping-mode condensation for diverse applications by providing a scalable method, which maximizes the profits that the hierarchical structures and the biphilic wettability give.

Persistent reduction of boiling incipience of ethanol on biphilic porous textured surfaces

Boiling of highly wetting fluids is of great interest to thermal management of high-powered electronic devices, enhancement of which conventionally relies on functional modifications of surface shape and structure so as to promote bubble generation and growth. In this paper we attempt to combine the approach of porous texturing with a novel technique of surface wettability engineering to enhance saturated pool boiling of ethanol. Thin layers of microporous and nanoporous surface topographies were chemically deposited on an aluminum substrate by anodization in phosphoric acid and sulfuric acid, respectively. Boiling on the textured surfaces recorded over-twofold increases in terms of the heat transfer coefficient compared with that on a plain smooth surface, which can be attributed to a proliferation of active nucleation sites. The boiling incipience point on both porous surfaces, however, exhibited an interesting dependence on the initial wetting state of the surface. With the application of amphiphobic coatings of fluoropolymer modified with halloysite nanotubes, we managed to engender a biphilic (i.e., spatially alternating hydrophobicity and hydrophilicity) pattern on the porous-textured surfaces. The repeat control experiments on the hybrid surfaces showed an equally efficient mode of nucleate boiling, whose inception, by contrast, seemed to occur at consistently low superheats. The remarkable reduction (by more than 80%) of the minimum superheat at the boiling onset hints at an alternative nanobubble-related mechanism for heterogeneous bubble nucleation, which is notably less affected by incondensable gas, to the classic vapor-trapping-cavity model.

Molecular droplets vs bubbles: Effect of curvature on surface tension and Tolman length

Droplets and bubbles are thought to be two sides of the same coin; this work determines how true this is at the molecular scale. Stable cylindrical nanodroplets and nanobubbles are obtained in Molecular Dynamics (MD) simulations with three-phase contact lines pinned by alternate hydrophobic and hydrophilic patterns. The surface tension and Tolman length for both types of curved interfaces are obtained with the Kirkwood–Buff method, based on the difference between normal and tangential pressure components. Both bubble and droplet cases are compared to the flat interface case for reference. Results show that the surface tension decreases linearly while the Tolman length increases linearly with the gas/liquid density ratio. By running a careful parameter study of the flat interface over a range of densities, the effect of the density ratio can be corrected isolating the effects of curvature on the surface tension and Tolman length. It is found that such effects start to be seen when the equimolar curvature radius goes down to 20 reduced Lennard–Jones (LJ) units. They have the same magnitude but act with opposite signs for nanodroplet and nanobubble interfaces. Considering effects of the density ratio and curvature, a fitted Tolman equation was obtained, which predicts the surface tension of a curved interface. Results obtained by the fitted Tolman equation agree well with those obtained by the MD simulations except at very small curvature radius (<10 reduced LJ units) due to the accumulation of the curvature dependence of the Tolman length.

Evaporative Cooling for Polymer Electrolyte Fuel Cells – a Model Based System Level Analysis

Polymer electrolyte fuel cells (PEFC) are a promising alternative to conventional propulsion systems since they reach peak system efficiencies above 60 % [1] and power densities of more than 640 W/L [2]. State-of-the-art PEFC system power densities are almost in accordance with U.S. Department of Energy 2020 targets (650 W/L), however, to reach the ultimate target of 850 W/L, a substantial decrease in system volume is required [3].In a conventional PEFC, the cooling system contributes significantly to stack and system volume. The state-of-the-art cooling solution aims at transferring the waste heat to a liquid coolant that flows through separate cooling channels in the bipolar plates. Therefore, a complex multi-layer design of bipolar plates is required [4] which contributes to about 75 % of stack volume and approximately 80 % of its mass [5]. The coolant is subsequently chilled in an external heat exchanger which requires a high surface area due to the small temperature gradient and thus shows a high volume demand.In order to facilitate the heat transfer, high stack operating temperatures are necessary. However, to ensure a proper humidification and thus ionic conductivity of the proton exchange membrane [6] at elevated temperatures, an external humidifier is often required which contributes substantially to the system volume.As an auspicious alternative, evaporative cooling can contribute to reach the ultimate power density target, since it shows the potential to reduce the stack volume, mass, complexity and cost up to 30 % by simplifying the design of bipolar plates [7]. Additionally, it allows a better internal humidification which enables higher operating temperatures without an external humidifier.In our concept, liquid water is fed to each cell through dedicated water channels in the anode flow-field. Subsequently, the water is distributed in a specially designed gas diffusion layer with a mixed hydrophilic and hydrophobic pattern (Figure 1) [8]. Once in contact with the gas flow, the water in the hydrophilic lines evaporates, cools the cell by taking up the heat of evaporation and is eventually released as vapor with the exhaust gases.Our previous work [9] has proven, that sufficient cooling power can be provided by evaporative cooling. Main findings showed, that the evaporation rate and thus the cooling power increases with temperature as well as cathode stoichiometry and decreases with system pressure (Figure 2). On the other hand, operating conditions show a significant impact on stack performance and power consumption of balance of plant (BoP).Therefore, a zero-dimensional fuel cell system model has been developed in the present work to analyze interactions between BoP and the fuel cell stack in an evaporatively cooled system. From the analysis of the power demand of the air compressor and the stack power, optimal operating conditions are elaborated in order to maximize the net system power. Simulation results show that the temperature has only limited impact at low current densities, whereas the peak system power decreases with temperature. Acomparison between conventional and evaporative cooling shows no significant performance difference at 70 °C but a slight decrease in peak power for evaporative cooling at 90 °C. However, since the heat rejection of conventional cooling systems is typically limited to about 1.45 kW/K [3], evaporative cooling shows the additional benefit of an increased peak power (Figure 3).In addition, a system efficiency map for evaporative cooling has been calculated (Figure 4) which shows that the highest efficiencies can be reached at low pressure (1 to 1.5 bar), medium to high temperature (70 °C to 90 °C) and low cathode stoichiometry (2 to 3), similar to a conventionally cooled system.Further, the water balance of an evaporatively cooled fuel cell system has been investigated and main findings show, that a sufficient amount of water can be retained from the exhaust gas at condenser outlet temperatures below 60 °C to supply sufficient water to the stack.