In order to bring electrochemical CO2 reduction (eCO(2)R) to economical feasibility on an industrial scale, the conventional oxygen evolution reaction (OER) can be replaced with a value added reaction. In this work, we replace OER with chlorine evolution reaction (CER) in a paired synthesis with CO from CO2. Hereby, the reaction system is assessed at industrial relevant current densities with respect to electrolyte species & concentration and stability of up to 24 h. We report constant anodic FEs to Cl-2 of >97% for up to 400 mA/cm(2) with concurrent FEs to CO of 90% at 100 mA/cm(2) and 74% at 200 mA/cm(2) over 4.5 h, significantly exceeding previous studies for comparable systems. The FE for CER did not show any decline over 24 h of operation. KCl showed superior results over NaCl and CsCl in terms of cathodic FE and cell potential. CER is affected by educt limitation with FE dropping below 95% at an electrolyte concentration of 0.8 mol/L at 400 mA/cm(2). By successfully pairing eCO(2)R and CER with stable and high FEs at industrially relevant current densities, this work marks an important step towards an industrial application.

The treatment of emerging contaminants (ECs) with extremely low concentrations presents a significant challenge in advanced oxidation processes (AOPs) like electro-Fenton (EF). Combining EF with membrane distillation (MD) can concentrate the feed solution, thereby improving the reaction kinetics. Our innovation integrates MD with EF using a hydrophobic, electrically conductive membrane, offering a sustainable solution for continuous dewatering while simultaneously facilitating the EF reaction. The electroactive membrane, fabricated via a simple "spray and cure" method with Ag ink on polytetrafluoroethylene (PTFE) membrane, exhibited high electrical conductivity (60000 S/cm) and underwater oleophobicity. The hybrid EF-MD showed a 2.5-fold increase in methyl orange (MO) degradation and a 3.4-fold reduction in the total organic carbon (TOC) compared to EF alone at room temperature. Testing ibuprofen removal at 350 ppb, EF-MD achieved 81 % degradation within a 2-hour operation time in a temperature range of 20-60 degrees C. In comparison, EF alone required over 6 hat 60 degrees C to achieve a similar level of ibuprofen degradation. The fabricated Ag-PTFE membrane can be operated at low electric potential (-1 V), maintaining a steady state of 10 mA current, making it an energy-efficient technology for EC removal. Moreover, it shows exceptional antibiofouling characteristics as it completely deactivates E. coli by > 99 % at 1 V. The Ag-PTFE membrane can be fabricated at larger scales and can actively capture and degrade harmful micropollutants that are often resistant to conventional treatment methods. This results in cleaner, safer water for both consumption and environmental discharge.

Electrochemical processes offer defossilized alternatives to conventional routes. Key processes, such as hydrogen evolution and electrochemical CO2 reduction, are typically paired with the anodic oxygen evolution reaction (OER). However, the generated oxygen holds little value and the electrical costs associated with energy-intensive OER pose a significant economic barrier. The methanol oxidation reaction (MOR) to formate is a promising alternative to OER, requiring less energy and providing a value-added product. Extensive research focuses on MOR regarding high Faraday efficiencies, but conversion and product yields are mostly neglected. However, high conversion with sufficient yield is a prerequisite to transition from lab-scale catalysis towards feasible industrial applications. In this work, we investigated the selectivity of MOR to formate with progressing conversion at high current densities of up to 200mA/cm2 on hierarchically structured copper(II) oxide electrodes. We assessed the impact of the reaction conditions, including current density, temperature, flow rate, electrolyte composition, and membrane type. We found a positive influence of low current density and high temperature on the FE. Through tailored reaction conditions, we achieved a formate yield of 70% at 100mA/cm2 with an anodic potential of 1.33V vs. RHE. The anodic potential remained below typical OER potentials even at high conversion. For the first time, we demonstrated that MOR can achieve significant formate yields at high current density. Our results reveal the impact of conversion, reaction conditions and ion balance on selectivity and provide valuable insights for operating MOR at high yield in paired processes, e.g., with hydrogen evolution or CO2 reduction.

After the temporary shock of the Covid-19 pandemic, the rapid recovery and resumed growth of the tourism sectors accelerates unsustainable tourism, resulting in local (over-)crowding, environmental damage, increased emissions, and diminished tourism acceptance. Addressing these challenges requires an active visitor management system at points of interest (POI), which requires local and timely POI-specific occupancy predictions to predict and mitigate crowding. Therefore, we present a new approach to measure visitor movement at an open-spaced, and freely accessible POI and evaluate the prediction performance of multiple occupancy and visitor count machine learning prediction models. We analyze multiple case combinations regarding spatial granularity, time granularity, and prediction time horizons. With an analysis of the SHAP values we determine the influence of the most important features on the prediction and extract transferable knowledge for similar regions lacking visitor movement data. The results underline that POI-specific prediction is achievable with a moderate relation for occupancy prediction and a strong relation for visitor count prediction. Across all cases, XGBoost and Random Forest outperform other models, with prediction accuracy increasing as the prediction time horizon shortens. For effective active visitor management, combining multiple models with different spatial aggregations and prediction time horizons provides the best information basis to identify appropriate steering measures. This innovative application of digital technologies facilitates information exchange between destination management organizations and tourists, promoting sustainable destination development and enhancing tourism experience.

This work describes the fabrication of a novel electroconductive membrane made of Ti3C2Tx (MXene) nanosheet coating through a one-step pressure-assisted technique. Ti3C2-MXene is firmly attached over a polyamide-imide (PAI) microfilter by employing a binder composed of carboxymethyl cellulose (CMC)/glutaraldehyde (GA). Through coating a proper amount of multilayer Ti3C2-MXene, the electrical conductivity of 174 +/- 0.16 S m(-1) is achieved. The rejection rates of reactive red 120 (RR120), reactive black (RB), and methyl orange (MO) by the pristine PAI membrane are 45.2%, 40.81%, and 33.65%, respectively. However, rejection rates significantly improve with the Ti3C2 MXene coating to over 99.71%, 97.95%, and 68.91% for RR120, RB, and MO. Applying a 4 V cathodic potential resulted in a flux recovery ratio (FRR) of 99.83% and a flux decline rate (FDR) of less than 1% during humic acid (HA) filtration. Without applying voltage, the MXene-coated membrane shows an FRR and FDR of 92.51% and 45.56%, respectively. Surface energy analysis reveals strong repulsive interactions between foulants and the membrane surface. Moreover, the surface free energy indicates that foulants such as sodium alginate (SA) and bovine serum albumin (BSA) exhibit stronger adhesion to the membrane than HA, consistent with the fouling experiment results.

Enabling the electrification of the chemical industry is crucial for the sector's transition toward zero emissions and a sustainable future. Approximately 2% of the globally used energy is dedicated to fertilizer production, including urea. The electrochemical synthesis of urea from a nitrogen source and CO2 based on renewable energy can contribute to reaching the ambitious goal of sustainable production with close to zero emissions. However, the current state of technology remains at a low readiness level and a small scale. The majority of studies in the field employ electrode surface areas in the order of 1 cm(2) and achieve moderate current efficiencies of <50%. They are mostly operated in batch mode in H-cells, which are prone to mass transport limitations, leading to a restriction of the achievable current density. In this perspective, we analyze the main challenges regarding highly efficient and scalable reactors for continuous production. We identify knowledge gaps and potential pitfalls. Finally, we propose guidelines to rapidly bridge the gap between fundamental research and industrial application.

Electrochemical hydrogen compression is a promising alternative to conventional mechanical compression due to low maintenance costs and high one-stage compression ratios. The typically employed planar systems, however, are intrinsically difficult to operate in high differential pressure environments. Tubular systems are inherently advantageous for high differential pressure systems but require innovative membrane electrode assembly development. This study unveils the first tubular EHC featuring a membrane electrode assembly supported by a stainless steel 3D-printed porous anode. The membrane electrode assembly for gas-phase electrochemistry is produced by spray coating the porous anode with Pt/C as the catalyst and joining the anode with a tubular catalyst-coated membrane. Electrochemical characterization demonstrates the functionality of the tubular EHC at current densities up to 60 mAcm−2 with a cell potential of 200 mV under non-pressurized conditions. Moreover, a pressure difference of 2 bar is achieved at 60 mAcm−2 within the first 60 min in continuous mode. By demonstrating the proof-of-principle for the first tubular EHC, this work paves the way for new research avenues in electrochemical process engineering, offering a broad spectrum of applications, from enhancing EHC technologies to advancing electrochemical CO2 reduction.

Tubular GDEs have been mainly characterized in H-cell environments without consideration of changing flow conditions and scale-up possibilities. In this study, a continuous flow reactor for tubular GDEs is presented, which allows for different electrode configurations and manipulation of flow conditions to control mass transfer. 3D printed copper GDEs are employed for CO2 electroreduction while membrane electrode assemblies (MEAs) from stainless steel electrodes are used on the anode side. We demonstrate the impact of the gas supply in either flow-through or flow-by mode on catalyst performance. Flow-through mode yields a variety of typical products, such as CO, HCOOH, CH4 and C2H4. Flow-by mode results in mainly CH4, which we link to a higher surface coverage of reaction intermediates with diffusion as the governing transport mechanism in flow-by operation. Additionally, a hybrid porosity GDE is introduced that combines different functional domains in one electrode for improved CO2 mass transfer. Microcomputed tomography confirms the successful realization of these domains in close proximity to each other. With the presented approach, we aim to highlight the importance of the reaction environment for an effective scale-up of tubular concepts in CO2 electroreduction and many other electrochemical applications.

Ferrate (Fe(VI)) is of great interest in energy storage solutions, organic synthesis, and wastewater treatment due to its decent oxidation potential and non-toxic end-product formation, making it a green oxidizer. The electrochemical generation of ferrate in NaOH at current densities of j >= 100 mA cm-2 is presented using low-cost sacrificial iron anodes, mild steel, and spheroidal graphite cast iron (ductile iron). Under optimized reaction parameters with 40 wt.% (14 m) NaOH and a ZrO2-based diaphragm, spheroidal graphite cast iron shows no signs of passivation in 5 h experiments even at j = 150 mA cm-2. The results are used in a novel electrolysis cell with a combined geometric anode surface area of 230 cm2, incorporated in a mini-plant suitable for continuous synthesis. This setup produces a peak ferrate concentration of 10.1 g L-1 (84 mm) after 5 h in 1.6 L anolyte volume, resulting in a total ferrate mass of 16.2 g. Optimal electrolysis temperatures are between 35 and 50 degrees C. The highest current efficiency is 63.0%, and the lowest specific energy consumption is 9.2 kWh kg-1 ferrate. The presented work is an essential step toward the continuous electrochemical synthesis of ferrate using sacrificial anodes under basic conditions.

Electrochemical reduction of CO 2 poses a vast potential to contribute to a defossilized industry. Despite tremendous developments within the field, mass transport limitations, carbonate salt formation, and electrode degradation mechanisms still hamper the process performance. One promising approach to tweak CO 2 electrolysis beyond today's limitations is pulsed electrolysis with potential cycling between an operating and a regeneration mode. Here, we rigorously model the boundary layer at a silver electrode in pulsed operation to get profound insights into the dynamic reorganization of the electrode microenvironment. In our simulation, pulsed electrolysis leads to a significant improvement of up to six times higher CO current density and 20 times higher cathodic energy efficiency when pulsing between −1.85 and −1.05 V vs SHE compared to constant potential operation. We found that elevated reactant availability in pulsed electrolysis originates from alternating replenishment of CO 2 by diffusion and not from pH-induced carbonate and bicarbonate conversion. Moreover, pulsed electrolysis substantially promotes carbonate removal from the electrode by up to 83 % compared to constant potential operation, thus reducing the risk of salt formation. Therefore, this model lays the groundwork for an accurate simulation of the dynamic boundary layer modulation, which can provide insights into manifold electrochemical conversions.

Heterogeneous electro-Fenton (HEF) coupled with anodic oxidation offers a plug-and-treat and chemical-free process over a wide range of pH values for removing recalcitrant micropollutants (MPs). This work introduces a self-standing and Fe-containing tubular carbon as a gas diffusion electrode (GDE) for HEF. Unlike planar Fe-containing carbon electrodes, as-synthesized carbons contain no fluorinated polymer as a subgroup of perfluoroalkyl and polyfluoroalkyl substances (PFAS), omitting the risk of secondary pollution due to undesired PFAS release during electrolysis. The implementation of GDE enables the increase of current densities up to 25mAcm−2, approaching relevant conditions for real-life applications. The altering pore structure on the gas channel side illustrates the possibility of minimizing GDE flooding without using hydrophobic and fluorinated polymers. GDEs without catalyst shows a specific H2O2 production rate of 3.6mgcm−2h−1 with a current efficiency of 56% at an applied current density of 8.5mAcm−2. Additionally, the Fe-containing GDE removes sulfamethoxazole (SMX) and carbamazepine (CBZ), revealing a declined degradation rate in a mixture, especially for a more recalcitrant pollutant such as CBZ. This work reveals the potential of as-synthesized self-standing tubular GDEs as PFAS-free electrodes for a decentralized and modular water treatment unit.

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Paired electrolysis combines value-added oxidation and reduction reactions and thus increases electron and process efficiency. This work develops a process to oxidize hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) on the anode and reduce acetoin to 2-butanone on the cathode in a 25 cm2 flow cell. First, we analyze the influence of an ion exchange membrane on the process and assess ion migration. We develop a stable process with a bipolar membrane. We then increase the current density and the reactant concentration. At 150 mA cm-2, we reach a combined yield of above 140% and a product concentration of 1.45 mol2-butanone L-1 and 0.9 molFDCA L-1. The space-time yields are 0.25 mu molFDCA s-1 cm-2 and 0.34 mu mol2-butanone s-1 cm-2. We then substitute the potassium-based electrolyte with a more cost-effective sodium-based electrolyte. We counteract the detrimental increase in cell voltage by adding Na2SO4 as a supporting electrolyte without impairing the reaction metrics. With this work, we provide a structured approach for developing paired electrolysis processes, showcased with the biobased products FDCA and 2-butanone toward the efficient electrochemical valorization of biomass.

We describe a cascade for sustainable 2-butanone from biotechnologically derived acetoin by adapting the process to the needs of both bio- and electrocatalysis.

The conventional anodic oxygen evolution (OER) in electrochemical CO2 reduction (CO2R) needs to be replaced as it accounts for a major share in energy consumption while being a product of little to no value. In this work, we replace OER by glycerol oxidation reaction (GOR) to synthesize products such as formate, lactate and glycolate. Hereby, for the first time, GOR was successfully paired with cathodic CO2R to formate in a flow reactor at a significant current density of 50 mA/cm2 producing value added anode products with a simultaneously reduced cell voltage. Using a porous platinum anode, GOR reduced the anode potential as well as cell potential by ∼1 V compared to OER. We report an anodic Faraday efficiency (FE) of 30% to ∼53% for liquid products, of which lactate dominates. The structure of the electrode has a significant impact on the dominant product as mainly formate is synthesized on a planar electrode, where the cummulated FE for all liquid products is up to 76%. The concurrent FE to formate at cathode and anode reached a values of up to 74% and 30% respectively and 66% and 76%, respectively, considering all value-added products. By successfully pairing GOR with CO2R in a flow cell reactor, this work marks an important step towards energy-efficient and economically viable processes.

Carbon is an established electrode material in electrochemical reactors, e.g., for the generation of hydrogen peroxide (H 2 O 2 ). Common structures are graphite felts or carbon fibers. These materials usually lack adequate electrochemical activity, hence more selectively active moieties need to be introduced. Furthermore, the commonly porous materials require immobilization concepts which normally include polymeric binders that partly block the porous surface and may entail secondary pollution. This work introduces carbon nanofibers (CNFs), synthesized on nickel foams via catalytic carbon decomposition, as a novel, binder‐free electrode with two‐level porosity. The fibers are in the range of few nanometers and comprise embedded nickel nanoparticles (30–250 nm). The CNFs are deposited as a thin layer on a nickel foam, not affecting its intrinsically open‐porous nature. The as‐synthesized CNF/Ni foams show H 2 O 2 production rates as high as 1.1 mg h −1 cm −2 at pH 3 and a cathodic potential of 0.11 V versus reversible hydrogen electrode (RHE) through multiple reaction pathways catalyzed by CNF and embedded nickel nanoparticles. In an electro‐Fenton process, the removal of carbamazepine (CBZ), a frequently detected micropollutant in water bodies is assessed, demonstrating an almost complete depletion after 10 min (c CBZ,0 = 4 mg L −1 ). These results unveil the potential of the integrated production of CNF/Ni foam electrodes with scale‐up perspectives for oxygen reduction reactions.

The electrochemical chlor-alkali electrolysis remains an energy-intensive production process even though many improvements have been developed over the last decades. Oxygen depolarized cathodes (ODC) reduce energy consumption by approximately 25% while oxygen is consumed instead of hydrogen being evolved. The switchable ODC (sODC) facilitates the oxygen-consuming and the conventional hydrogen-evolving modes with the same electrode. In this study, we investigate sODCs for demand-side electrolysis by switching between modes. Experimental investigations covered current densities ranging from 50 mA cm−2 to 525 mA cm−2, and we evaluated the long-term effect of switching between the two modes on the system's stability. In addition, cell potential, Faraday efficiency and contact angle measurements were compared for pristine and used sODCs after up to 1600 switching cycles. The lab cell was implemented in 3D-CFD simulations to investigate a nitrogen flushing process between the two modes to prevent the formation of explosive mixtures in the electrolyzer. sODCs showed a stable and continuously high Faraday efficiency. However, an increase in cell potential over 1000 switching cycles of up to 7.8% was observed, which was attributed to electrolyte flooding. Still, the sODC is well comparable to the conventional ODC with a marginal difference in cell potential (0.07 V), which demonstrates its high potential for industrial application. 3D-CFD simulations were compared to experimental flushing time measurements. We implemented the resulting flushing times for a safe operation in the subsequent switching cycles. The verified CFD simulations can help to further optimize the flushing procedure for an economically feasible switching process in industry-sized cells. Switchable electrodes enable flexibility to react to fluctuating boundary conditions such as the electricity price and can be implemented in many processes beyond the chlor-alkali electrolysis.

Production of biobased platform chemicals and polymersvia electrochemicalroutes enables the direct utilization of electrical energy from renewablesources. To date, the integration of electrochemical conversions inprocess chains remains largely unexplored, and the reactions are oftenstudied using synthetic solutions. This work demonstrates the biphasicelectro-oxidation of hydroxymethylfurfural (HMF) to 2,5-furandicarboxylicacid (FDCA) and couples the electrochemical oxidation with the biphasicdehydration of fructose to HMF. The integrated approach eradicatesthe intermediate HMF purification as the HMF-rich organic productphase is fed directly into the electrochemical flow-cell reactor.Here, HMF is extracted into the aqueous phase and oxidized to FDCAon a Ni-(OH)-2/NiOOH catalyst in a 0.1 M KOH solution at pH 13. TheFDCA then remains in the aqueous phase, enabling direct recirculationof the HMF-containing organic phase. We demonstrate a FDCA yield ofclose to 80% with a feed from HMF synthesis. Further, we analyze theinfluence of the phase ratio (organic to aqueous) and current densityfor biphasic electrochemical oxidation. By adjusting the gap width,we were able to decrease the average cell voltage from 7 V down to3 V at a current density of 30 mA cm(-1). This work presents a promising integrated process for the synthesisof green platform chemicals and provides insight into biphasic solutionsin electrochemical conversions. This work exploresthe biphasic electrochemical oxidationof HMF to FDCA and demonstrates the direct electrochemical conversionof the raw organic product phase of HMF synthesis to FDCA.

Understanding and controlling the gas–liquid–solid interface at gas diffusion electrodes (GDE) is a long-standing challenge in electrochemical engineering. Especially, flooding of gas diffusion electrodes is detrimental to high Faraday efficiencies and a long-term stable process. A detailed understanding and quantification of permeation through GDEs will contribute to enhanced control as a remedy for performance loss. Here, we present macroscopic experiments for the reduction of CO2 in a bipolar membrane reactor configuration and focus on the effect of high current densities on the wetting, flooding, and weeping of the GDE. We monitor and quantify anolyte, catholyte, and GDE permeate to understand ion movements in the cell. We report high current densities of up to 300 mA/cm2 and reach up to 80% Faraday efficiency for CO. However, these realistic process conditions entail an increase in the weeping rate and ion concentration up to the saturation of bicarbonate. For the first time, we observe that the permeating electrolyte gives a fingerprint of the composition inside the GDE, being significantly different compared to the bulk concentration in the feed channel, i.e., catholyte.