Carbon materials are promising to fulfill the worldwide need for advanced materials in many areas, particularly in electrochemical applications. However, achieving both high conductivity and surface functionalization in carbon electrodes remains a significant challenge. Herein, a scalable, sustainable, binder-free carbon disc electrode is developed in the desired size and shape. Subsequent femtosecond laser treatment introduces surface functionalization with pyrrolic and pyridinic nitrogen species (up to 12.6 at%, as determined by X-ray photoelectron spectroscopy) while preserving the bulk crystallinity and conductivity of the electrode. The laser-treated surfaces exhibit superhydrophilicity (water contact angle of 0 degrees) and oleophilicity (0 degrees for n-heptane, 25 degrees for n-heptadecane), enabling enhanced interaction with electrolytes and anchoring of metal species like iron ions. Electrochemical impedance spectroscopy confirms minimal resistance (<= 10 Omega) in 0.1M KOH, even after functionalization. The functionalized electrodes demonstrate improved stability in oxygen evolution reaction tests, with laser-treated samples showing 300-500 mV higher activity than untreated counterparts when Fe-impregnated. This work establishes a simple, industrial-scale method for creating multifunctional carbon electrodes with tailored surface properties, bridging the gap between material sustainability and electrochemical performance.

Gas bubble emergence is an important indicator of the performance in many processes, for example electrochemical reactions. Using a convolutional neural network (CNN) based on the Darknet/YOLO4-architecture; this software allows the detection and tracking of gas bubbles from high-speed camera videos, even on strongly textured backgrounds. Further, it evaluates growth rates, detachment size and merging of gas bubbles. This allows a good assessment of many important gas formation characteristics, thus helping performance evaluation and identify potential for improvement.

Abstract Structuring by femtosecond laser process is a promising technique for improving the performance of porous transport layers (PTL) in proton exchange membrane (PEM) electrolysis. As an increase in surface area and a raise of crevices always promotes corrosion, a method must be found to prevent a shortening of the component lifespan. In this paper a method of implanting additional elements from coatings into titanium, while simultaneously nitriding the surface by processing under nitrogen atmosphere is presented. Ruthenium and Iridium were chosen as materials because they are commonly used as catalyst and corrosion-inhibitor in PEM-cells. Especially ruthenium showed promising ability in decreasing corrosion rates while increasing surface conductivity at the same time. Specifically, in samples processed under nitrogen, the addition of ruthenium was able to decrease the impact of laser processing on corrosion rates by up to 46%.

This research investigates the impact of laser‐structuring of lead electrodes on the selectivity and production rate of hydrofuroin, a valuable jet fuel precursor derived from furfural (FF). Laser structuring of electrodes led to a slight enhancement in hydrofuroin selectivity, along with an improved production rate, suggesting promising advancements in electrosynthesis methodologies. The addition of acetic acid as an impurity did not significantly affect the selectivity or the production rate. This finding indicates that the catalytic activity of the electrode surface was not diminished by this impurity. Analysis via high‐performance liquid chromatography revealed the presence of two isomers of hydrofuroin, indicating a complex reaction pathway. Combined experimental and molecular dynamics simulations indicated inner sphere adsorption of FF and H+ ions and outer sphere dimerization reaction to form hydrofuroin. These findings offer insights into surface morphology, adsorption, and reaction pathways, guiding future optimization of catalytic systems for sustainable chemical synthesis.

Electrocatalytic hydrogenation (ECH) of biomass derived compounds is an emerging technology for the production of biofuels. Herein, the ECH of furfural was investigated systematically on femtosecond laser-structured copper electrodes, amending the work on commonly used bulk copper electrodes or electrodeposits. Laser-structuring was used to vary the amount of active sites and the crystallographic orientation on the copper electrodes (evidenced with scanning electron microscopy and X-ray diffraction), and to achieve nickel alloying with the structured copper surface. We showed that the production rate and the Faradaic efficiency for furfural ECH on both Cu (111) and Ni-alloyed Cu were substantially increased. This improvement was ascribed to more catalytic sites offered for hydrogen and interactions of furanic intermediates. Moreover, the Ni-alloyed Cu electrode enabled the stable production of 2-methylfuran even at large overpotentials. The mechanistic insights gained could open up new pathways to produce sustainable biofuel candidates with more stable electrodes.

This paper presents a novel scalable electrode fabrication process suitable for large alkaline water electrolysers. Laser structuring technology is applied, and a large-scale development of active Ni-based cathodes is demonstrated. The most active electrode shows an overpotential of 104 mV at a current density of 300 mA cm-2 for the hydrogen evolution reaction at the end of the accelerated durability test protocol. Large 400 x 600 mm2 electrodes have been fabricated for the first time, and the electrodes thus fabricated are compared with state-of-theart electrodes in an industrial alkaline electrolyzer. Within the test period, the laser-structured Ni electrodes significantly outperformed the comparison electrodes. This impressively high activity is attributed to the existence of Ni oxide adjacent to the metallic Ni reaction sites.

A simple femtosecond laser alloying process is applied under two different process gases nitrogen and air to create novel molybdenum-nickel alloyed and surface enhanced catalysts. A three-day electrochemical test protocol is applied in an alkaline half-cell at 298 K and 353 K to examine the catalytic activity and initial degradation mechanisms in the hydrogen evolution reaction. It is found, that the surface enhancement and the stability of the electrode significantly depends on the process gas. Molybdenum is degraded at the beginning of the test protocol, but it is shown that higher concentrations are not necessarily required for an increase performance. The highest catalytic activity on an electrode alloyed with molybdenum under nitrogen emerges in a steady state operation at 353 K. An overpotential of 135 mV at-100 mA cm-2 is measured. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

An entirely femtosecond laser (fs-laser) based process for the production of stable, enlarged and alloyed nickel surfaces is presented. The process allows the use of metal foils and aqueous salt solutions as alloying element sources. We alloy iron from an aqueous element source as well as molybdenum and cobalt from commercially available foils on nickel mesh surfaces without further coating process. It is shown that the content of alloyed iron on the nickel mesh surface structured with the fs-laser depends on the concentration of the aqueous iron(II) sulfate solution used. The alloy content of cobalt and molybdenum is controlled by adjustable laser parameters. Cross-sections prepared by a focused ion beam and subsequent energy dispersive X-ray spectroscopy shows that molybdenum and nickel form alloyed nanoscale particles on the structured nickel surface. The combination of an aqueous iron(II) sulfate solution and a molybdenum metal foil leads to a ternary nickel-molybdenum-iron surface alloy. The presented fs-laser alloying process can be applied to further metal combinations and offers the potential to create new materials and properties.

A femtosecond laser process is presented increasing the surface area of copper electrocatalysts for an electrochemical CO2 reduction reaction (CO2RR). The laser treatment allows us to tune the surface morphology and the chemical composition of the copper electrocatalysts. This tunability is used to correlate the role of the surface area and catalyst dopants with the selectivity of the CO2RR. The liquid products of the CO2RR are monitored through ex situ nuclear magnetic resonance spectroscopy. The products' distribution shows that the electrode surface area plays a key role in the electrochemical conversion of CO2 into multicarbon liquid products. We show that sulfur dopants boost the production of formate. Remarkably, by co-doping sulfur and fluoride, we show that the chalcogenide dopant counteracts the known boosting effect of fluoride to convert CO2 into multicarbon products. Oxygen doping in the range of 2-19 atom % does not significantly affect the distribution of liquid products from CO2 electroreduction. In a broad perspective, this work highlights the potential of the femtosecond laser process to fine-tune surfaces to produce photo- and electrocatalyst materials.

ABSTRACT The thermohydraulic effect of microstructuring of the heat transfer surfaces of plate heat exchanger was studied experimentally. The aim of this enhancement strategy is to raise the heat transfer coefficient for the evaporation and condensation of the refrigerant in a vapor compression cycle up to the same level as typical single-phase heat transfer coefficients, when water is used as a secondary fluid. This would result in a better overall heat transfer performance. Titanium herringbone corrugated plates with no microstructure, micro-bump structures created by press rolling and femtosecond-laser-produced microstructures were studied. At first studies of the microstructured plates were performed in a visualization setup using 380 × 380 mm corrugated plate segments. Heat transfer and pressure drop were measured for liquid single-phase flow and evaporation with low vapor quality (x < 0.1). For the single-phase situation, the heat transfer coefficient of the microstructured plates dropped up to 5%, depending on the mass flux, while the pressure drop is not affected. For the evaporation situation, the heat transfer coefficient increased by about 25%, while the pressure drop stayed unchanged within the measurement uncertainty range. A second set of experiments was performed in an industrial-sized vapor compression cycle using R134a with a 100 kW plate evaporator and a 150 kW plate condenser. The microstructured plates gave a very moderate increase of less than 10% in heat transfer within the condenser, but a strong increase of about 40% in the evaporator as compared to the smooth plates.

Electrolyte-supported solid oxide cells are often used for steam electrolysis. Advantages are high mechanical stability and a low degradation rate. The aim of this proof of concept study was to use a femtosecond laser to process the electrolyte of an electrolyte-supported solid oxide cell and evaluate the effect of this laser treatment on the electrochemical performance. The femtosecond laser treatment induces a macroscopic and a superimposed microscopic structure. It can be proven that the electrolyte remains gas tight and the electrochemical performance increases independently of the laser parameters. The initial area-specific resistance degradation during a constant current measurement of 200 h was reduced from 7.9% for a non-treated reference cell to 3.2% for one of the laser-treated cells. Based on electrochemical impedance measurements, it was found that the high frequency resistance of the laser-treated cells was reduced by up to 20% with respect to the reference cell. The impedance spectra were evaluated by calculating the distribution of relaxation times, and in advance, a novel approach was used to approximate the gas concentration resistance, which was related to the test setup and not to the cell. It was found that the low frequency polarization resistance was increased for the laser-treated cells. In total, the area-specific resistance of the laser-treated cells was reduced by up to 14%.

In the present work, the ultra-short pulse laser ablation method is applied to create novel surface alloys on NiFe electrodes for the oxygen evolution reaction (OER) in alkaline water electrolysis. The nickel-to-iron ratio in the alloy can be controlled with the ultra-short pulse laser ablation method by varying the thickness of electrochemically deposited iron layers onto the nickel mesh substrate. Besides the application of the additional catalyst, the laser treatment enhances the surface area and a defined micro- and submicrometer structure is created in a single step. The laser structured nickel-iron electrodes show a significantly lower overpotential of 249 mV than an electrochemically deposited Ni-NiFe alloy with 292 mV at 10 mA cm(-2), 298 K and 32.5 wt% KOH for the OER, although some loss of iron over time could not be prevented. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Annealing dependent absorption and quantum efficiency spectra are determined on femtosecond-laser, sulfur hyperdoped silicon solar cells in a spectral range from 300 to 2500 nm. Although the samples, which are rapidly quenched after annealing at T = 1250 degrees C, do not feature the highest sub-bandgap absorption, the highest sub-bandgap quantum efficiency is measured on the same level as on non-annealed samples, featuring the highest sub-bandgap absorption. Findings on annealing dependent absorption are carried over, in order to explain the measured quantum efficiency spectra. In the sub-bandgap spectral range conversion is more efficient, when deep sulfur centers are obtained from annealing at higher temperatures at preferably rapid quenching. For those annealing regimes the above-bandgap quantum efficiency is decreased, which is ascribed to less shallow sulfur donors. Lower temperatures or slow cooling rates results in shallow donors, featuring a more efficient conversion in the above-bandgap spectral range. This is on the expense of deep sulfur centers and the corresponding subbandgap conversion ability. Therewith it is concluded, that the main absorption occurs only in the laser-induced sulfur emitter layer. Furthermore, to some extent a prediction is proposed on sulfur hyperdoped silicon prepared by ion implantation and subsequent pulsed laser melting, featuring rapid cooling from the melt.

In this contribution, we report on the impact of direct dielectric barrier discharge argon plasma at atmospheric pressure on femtosecond laser engraving of aluminium. It is shown that the assisting plasma strongly affects the surface geometry and formation of spikes of both laser-engraved single lines and patterns of adjacent lines with an appropriate overlap. Further, it was observed that the overall ablation depth is significantly increased in case of large-scale patterning whereas no notable differences in ablation depth are found for single lines. Several possible mechanisms and underlying effects of this behaviour are suggested. The increase in ablation depth is supposed to be due to a plasma-induced removal of debris particles from the cutting point via charging and oxidation as supported by EDX analysis of the re-solidified debris. Furthermore, the impact of a higher degree of surface wrinkling as well as direct interactions of plasma species with the aluminium surface on the ablation process are discussed.

Hydrogen production by alkaline water electrolysis has attracted great attention due to the feasibility of large scale H-2 production and the use of non-precious electrode materials. In particular, efficient electrodes towards the hydrogen evolution reaction (HER) consist of porous or skeletal Ni-based catalysts. In this contribution, a unique surface processing technique using a femtosecond (fs) laser pulse process was utilized to enlarge the surface area of Ni aiming to enhance significantly the HER-activity. Fs laser structured Ni surfaces were processed using different laser process parameters (e.g. fluence, spot size and scan line overlap). Surface morphology was studied by scanning electron microscopy. Under the chosen process conditions arrays of conical surface structures were obtained, which are significantly covered by redeposited particles using a fluence far above the ablation threshold. Electrochemical investigations (CV, EIS, steady-state polarization curves) conducted in 29.9 wt.-% KOH at 333 K (industrial conditions) point out that the fs laser structured electrodes reveal a high and adjustable surface area with a roughness factor between 6 and 73. The roughness of the fs laser structured surfaces has a significant impact on the HER leading to a reduced overpotential (eta(300) = 280 mV, reduction by approximately 45 % compared to smooth Ni). In fact, the results clearly show the feasibility of the fs laser pulse technique for processing highly structured electrodes without affecting the intrinsic HER-activity significantly. (C) 2017 Elsevier Ltd. All rights reserved.

This article presents an overview of the fabrication methods of black silicon, their resulting morphologies, and a quantitative comparison of their optoelectronic properties. To perform this quantitative comparison, different groups working on black silicon solar cells have cooperated for this study. The optical absorption and the minority carrier lifetime are used as benchmark parameters. The differences in the fabrication processes plasma etching, chemical etching, or laser processing are discussed and compared with numerical models. Guidelines to optimize the relevant physical parameters, such as the correlation length, optimal height of the nanostructures, and the surface defect densities for optoelectronic applications are given.

The characteristics of laser doped sulfur emitters are strongly dependent on annealing processes. We show how annealing increases the efficiency of silicon solar cells with such an emitter. Sheet resistance analysis reveals that up to an annealing temperature of 400 °C the emitter sheet resistivity increases. A lower sulfur donor concentration is concluded, which likely occurs by means of sulfur diffusion and capturing of sulfur donors at intrinsic silicon defects. Above that temperature, the emitter sheet resistance decreases, which we find to originate from healing of laser induced structural defects involving traps within the depletion zone of the silicon pn-junction.

With Fourier-transform photocurrent spectroscopy and spectral response measurements, we show that silicon doped with sulfur by femtosecond laser irradiation generates excess carriers, when illuminated with infrared light above 1100 nm. Three distinct sub-bandgap photocurrent features are observed. Their onset energies are in good agreement with the known sulfur levels S+, S0, and S20. The excess carriers are separated by a pn-junction to form a significant photocurrent. Therefore, this material likely demonstrates the impurity band photovoltaic effect.

We combine aluminum back surface field (Al-BSF) solar cell precursors with an additional rear side infrared active floating emitter in a tandem cell configuration. This emitter is implemented area selectively by fs-laser hyperdoping in a sulfurous atmosphere. Its design as a floating emitter conceals losses induced by the laser process as long as n-doping occurs. All processes are adapted and supplemented by just a single new process step.

In this letter, we demonstrate that silicon can be doped with electrically active sulfur donors beyond the solubility limit of 3 × 1016 cm−3. We investigate the sulfur doping profile at the surface of femtosecond-laser processed silicon with secondary ion mass spectroscopy (SIMS) and capacitance-voltage measurements. SIMS confirms previous observations that the fs-laser process can lead to a sulfur hyperdoping of 5×1019 cm−3 at the surface. Nevertheless, the electrical measurements show that less than 1% of the sulfur is electrically active as a donor.