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The depletion of clean water resources and the consequent accumulation of contaminants in aquatic systems must be urgently addressed by means of innovative solutions. Electro-oxidation (EO) is considered a promising technology, prized for its versatility and eco-friendliness. However, the excessively high prices and the toxicity associated with some of the materials currently employed for EO impede its broader application. This study introduces cost-effective Ni-Mn binary oxide anodes prepared on Ni foam (NF) substrate. A scalable synthesis route that enables a 35-fold increase in the production of active material through a single optimization step has been devised. The synthesized binary oxide material underwent electrochemical characterization, and its effectiveness was assessed in an electrochemical flow-through cell, benchmarked against single Ni or Mn oxides and more conventional alternatives like boron-doped diamond (BDD) and dimensionally-stable anode (DSA). The novel binary oxide anode demonstrated exceptional performance, achieving complete removal of phenol at very low current density of 5 mA cm−2, along with an 80% of chemical oxygen demand (COD) decay within only 60 min. The NF/NiMnO 3 anode outperformed the BDD and DSA when using comparable projected surface areas, owing to its high porosity and ability to produce hydroxyl radicals, as confirmed from the degradation profiles in the presence of radical scavengers. Furthermore, GC/MS analysis served to elucidate the degradation pathways of phenol. [Display omitted] • A cost-effective Ni-Mn binary oxide anode was prepared on Ni foam for EO applications. • NiMnO 3 synthesis was scaled up by 35-fold, demonstrating the practical applicability for large-scale water treatment. • 3D-printed divided electrochemical cell was used to enhance the separation of anodic and cathodic reactions. • Optimized NiMnO 3 electrodes reached 100% phenol removal efficiency setting a new benchmark for organic pollutant removal. • Comprehensive process optimization led to maximize the efficiency of the EO system. [ABSTRACT FROM AUTHOR]

Hydrogen (H 2) is considered as a renewable energy source which has the potential to replace the fossil fuel-based economy. When it comes to achieve H 2 production in a sustainable manner, biological methods are preferred among all other technologies. Out of the biological processes, microbial electrolysis cell (MEC) and dark fermentation (DF) have attracted significant attention for H 2 production because the energy requirement is significantly reduced and a wide range of organic matter can be used as substrate. However, the underlying biochemical reactions and generated energy molecule(s)/products associated with DF or MEC, can benefit in achieving higher H 2 production when coupled together. The DF can provide better substrate with high conductivity to overcome charge transfer challenges associated with MEC, and thereby it can further help to improve energy recovery. Thus, this review provides insights into the technological, microbiological, and economic competitiveness of coupling DF-MEC while it also identifies limitations and potential solutions. [Display omitted] • Comprehensive evidences gathered for linking DF and MEC. • DF and MEC exhibit synergies leading to a higher H 2 yield. • Insights into technological and economical challenges. • Biological components in MEC are poorly studied. • Prospective for future research and economic competitiveness. [ABSTRACT FROM AUTHOR]

Due to the increasing worldwide water scarcity associated with the climate change there is the need to increase the injection of wastewater into the overall water cycle. As a consequence wastewater treatment is within the largest energy use sector in many developed countries. In recent years, capacitive deionization (CDI), which is based on the principle of electrosorption of ions on charged high surface area electrodes, the same as charging and discharging an electrochemical double-layer capacitor, has been reported to be a promising technology which is an alternative to other classical water treatment methods such as reverse osmosis (RO) and evaporation processes. We see that this technology is gaining increased scientific interest since 2006. However, not too many publications indicate the feasibility of the kWh/m3consumption in CDI systems for brackish water treatment (500–30,000 ppm). The common assumption proposes that the main problem may be the ions adsorption capability of the electrode material during discharging. However, in energy efficiency terms, desorption processes may be even more difficult since experience diffusional complications mainly when high currents are used. This presentation will provide an overview of current strategies for operating these systems aiming to improve energy recovery and lead this process to the point of making these systems an option for use in water treatment plants. [ABSTRACT FROM PUBLISHER]

Vanadium Redox Flow Batteries (VRFB) are considered prime candidates for stationary energy storage due to their unique capability to decouple power and energy. With the aim of making electrochemical water desalination more energy efficient when scaling up the technology, potential benefits from repurposing a commercial VRFB stack as a Capacitive Deionization (CDI) module were studied. Accordingly, a 5-cell CDI Stack equipped with 1250 cm2 electrodes was assembled by revamping a 5kWh-VRFB. Electrosorption experiments showed a great versatility with a maximum salt adsorption capacity of 14.2 mg g−1 and an average salt adsorption rate of 0.321 mg g−1 min−1. Furthermore, a long-term test performed over 100 cycles validated the robustness of the system by achieving salt concentration reductions of 10–12 mM at a constant production rate of 4 L h−1 m−2. Moreover, adapting a VRFB stack specifically designed for energy optimization allowed a substantial reduction of energy consumption of 75% (from 0.84 kW h m−3 to 0.21 kW h m−3) by effectively recovering the energy employed in the desalination step. These results demonstrated the successful transition from VRFB to CDI showcasing the relevance of the Water-Energy Nexus and opening the path for exploring a second life of exhausted VRFB stacks. [Display omitted] • A transition from a VRFB system to a CDI pilot plant was accomplished. • Improved electrical and fluid dynamics of VRFB benefit CDI performance. • High values of SAC (14.2 mg g−1) and ASAR (0.321 mg g−1 min−1) were achieved. • Batch experiments attained Δ c 10–12 mM at 4 L h−1 m−2 and 0.21 kW h m. • Robustness of the CDI stack was demonstrated in a 100-cycles experiment. [ABSTRACT FROM AUTHOR]

Recently, the scientific interest in developing rechargeable aluminium-ion (Al-ion) batteries has increased, triggered by its theoretical capacity, low cost and low reactivity of aluminium metal. One of the main challenges is the development of cathode materials that reversibly intercalate AlCl 4 − in its structure. The most promising candidates are carbonaceous materials of very different nature. However, no systematic analysis has been performed so far to investigate the intrinsic parameters that determine their electrochemical performance. Here, different commercial available carbons such as pyrolytic graphite (PG), expanded graphite (EG), synthetic graphitic flakes (SGF) and two different carbon papers (H23C3 and H23I1) are systematically evaluated as cathodes in Al-ion batteries. The influence of their graphitic degree, particle size, porosity and mass loading on the battery performance is elucidated. Electrochemical tests combined with ex situ XRD demonstrated that only highly graphitic materials can intercalate AlCl 4 − obtaining a good battery performance. Synthetic graphite flakes (SGF) showed the best specific capacity (85 mAh g−1), rate capability and cycle life (>1600 cycles) due to the fast diffusion of the AlCl 4 − through its structure. Finally, high mass loading cathodes (SGF-HML) showed extraordinary areal capacity (5.6 mAh cm−2), almost doubling the high energy cathodes for Li-ion batteries (3 mAh cm−2). Image 1 [ABSTRACT FROM AUTHOR]

• Theoretical capacitive ion-exchange mechanism is validated in a CDI pilot plant. • Mechanism for modifying mono and divalent cation concentrations was explained. • Solution with lower conductivity and SAR values were consistently produced. • R Mg/Na > 5–6 and water production rate of 0.5–0.8 L m−2 h−1 were achieved. • Robustness of the mechanism was confirmed in long-term cycling. Soil salinization poses a significant challenge to agricultural activities. To address this, the agricultural industry seeks an irrigation water solution that reduces both ionic conductivity and sodium adsorption rate (SAR), thereby diminishing the risks of soil sodification and fostering sustainable crop production. Capacitive deionization (CDI) is an attractive electrochemical technology to advance this search. Recently, a one-dimensional transient CDI model unveiled a capacitive ion-exchange mechanism presenting the potential to adjust the treated water composition by modifying monovalent and divalent cation concentrations, thereby influencing the SAR index. This behavior would be achieved by using electrodes rich in surface functional groups able to efficiently capture divalent cations during conditioning and releasing them during charging while capturing monovalent ions. Beyond the theoretical modelling, the current experimental research demonstrates, for the first time, the effectiveness of the capacitive ion-exchange mechanism in a CDI pilot plant using real water samples spiked with solutions containing specific mono and divalent ions. Electrosorption experiments and computational modeling, specifically Density-Functional Theory (DFT), were used along with the analysis of the surface functional groups present in the electrodes to describe the capacitive ion-exchange phenomenon and validate the steps involved on it, highlighting the conditioning as a critical step. Various operational and flow modes confirm the versatility of CDI technology, achieving separation factors (R Mg/Na) of 5–6 in batch, raising production from 0.5 to 0.8 L m−2 h−1 (batch) to 8.0–8.1 L m−2 h−1 when using single pass although reducing R Mg/Na to 2. The reliability of the CDI technology in reducing SAR was also successfully tested with different influent compositions, including magnesium and calcium. Finally, the robustness of the capacitive ion-exchange mechanism was validated by a second CDI laboratory 9-cell stack cycled over 350 cycles. Our results confirm the reported theoretical model and expands the conclusions through the experiments in a pilot plant showing direct implications for employing CDI in agricultural applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Capacitive Deionization (CDI) is a non-energy intensive water treatment technology. To harness the enormous potential of CDI requires improving performance, while offering industrially feasible solutions. Following this idea, the replacement of costly metallic components has been proposed as a mean of limiting corrosion problems. This work explores the use of nanostructured hybrid networks to enable free-form and metal-free CDI devices. The strategy consists of producing interpenetrated networks of highly conductive flexible carbon nanotube (CNT) fibre fabrics and nanostructured metal oxides, γAl 2 O 3 and TiO 2 , through ultrasound-assisted nanoparticle infiltration and sintering. In the resulting hybrids, a uniform distribution of porous metal oxide is firmly attached to the nanocarbon network while the flexibility, high conductivity and low-dimensional properties of the CNTs are preserved. These electrodes present a high porosity (105–118 m2 g−1), notably low electrical (<0,1 kΩ cm2) and low charge transfer resistance (4 Ω), thus enabling the infiltration of aqueous electrolytes and serving as current collector. In this work we built a large asymmetrical cylindrical CDI device solely made of these electrodes and conventional plastics. The cell provides, high average salt adsorption rates of 1.16 mg·g−1 AM ·min−1 (0.23 mg·g−1 CDIunit ·min−1), low energy consumption (0.18 W h·g salt −1) and stable electrochemical performance above 50 cycles for brackish water desalination. [Display omitted] [ABSTRACT FROM AUTHOR]

In the quest for searching for new redox-flow battery chemistries, cycling stability must be carefully evaluated since it is one of the most important parameters of new active species. However, it is challenging to elucidate the intrinsic stability during operation of a redox flow battery. The symmetrical flow battery cell is a powerful tool that helps to unambiguously determine the cycling stability. Herein, trustworthiness of this technique is critically re-evaluated. Potassium ferrocyanide in alkaline media is used as a case study since i) it is the best performing species for the catholyte of alkaline flow batteries in terms of reversibility, solubility, costs and environmental compatibility and ii) the cycling stability of this species is still under strong debate. Potassium ferrocyanide is found to be stable at pH 14 upon electrochemical cycling when the oxygen evolution reaction is prevented, which should encourage researchers to resume the use of this species. The results also reveal that care should be taken when interpreting results from this powerful technique to avoid misleading conclusions. Image 1 • In alkaline media the OER may occurs during ferrocyanide oxidation. • The occurrence of side reaction causes the capacity fading in alkaline media. • Ferrocyanide does not decompose upon electrochemical cycling in alkaline media. • Free CN ions do not appear to be released. • Charge unbalancing is identified as a significant cause for capacity fade. [ABSTRACT FROM AUTHOR]

While Electrical Double-Layer Capacitors (EDLC's) have been proven to achieve round-trip efficiencies of over 95%, electrical efficiencies of Capacitive Deionization (CDI) systems are still far from those values. Since this issue seems to be crucial for CDI to commercially compete with other water treatment processes including Reverse Osmosis (RO) it is essential that these efficiencies be improved. In this work, the electrical response of a commercial EDLC's and a CDI system are compared. Results of asymmetric constant current experiments reveal that the main electrical inefficiency occurs during the discharge stage (i.e. in CDI this refers as salt desorption or electrode's regeneration). Here, we propose an operational mode of CDI focused on improving performance of regeneration by simply conducting this stage in a more concentrated solution (3.5M NaC) brine water. The experimental findings suggest that this operational strategy led to 1) an increase from ≈40% to 75% in the round-trip efficiency of CDI, approaching (although admittedly not reaching) those of EDLC's; 2) a drop in ohmic resistance in the discharge cycle of 92% (from 19.77 Ω to 1.45 Ω) consequently increasing the amount of energy that could be potentially recovered from 0.24 J to 0.50 J, and thus, reducing significantly the energy consumption of the process; 3) a wider range of deionization/regeneration current density ratios (0.1–1.25) in which high efficiency values (65–75%) are still maintained. In general, we find that this operational mode might have practical relevance as it implies that CDI systems may be operated with a higher degree of flexibility allowing them to be coupled more readily with renewable energy technologies. Furthermore, the use of a highly concentrated electrolyte (i.e. not deionized water) during regeneration offers an innovative solution for brine concentration. Image 1 • The electrical performance of a CDI flow-cell and an EDLC were compared. • Low round-trip efficiency of CDI cell was mainly associated to discharge step. • New operational mode based on electrolyte replacement was successfully tested. • Round-trip efficiency of CDI can be boosted up to 75%. • Wider range of charge/discharge current density ratios can be used. [ABSTRACT FROM AUTHOR]

Recently, new electrode materials and electrolytes for hybrid supercapacitors with enhanced performance have been extensively studied. However, the energy storage mechanism of these hybrid devices has not been assessed in detail. In this sense, Electrochemical Impedance Spectroscopy is one of the most powerful techniques to better understand the physicochemical phenomena involved in this new kind of supercapacitors. In this work, Impedance Spectroscopy was used for the first time to analyse the energy storage mechanism in supercapacitors with non-aqueous electrolytes with organic redox molecules dissolved, as a function of the frequency and bias voltage. In addition, a simple electrical model has been developed to describe the behavior of the supercapacitor with a very good correlation with the experimental results. This investigation provides useful information delving into the behavior of the devices which is fundamental for their future practical applications. [ABSTRACT FROM AUTHOR]

Abstract: The use of TiO2 electrodes may solve the two main drawbacks of photocatalytic processes: i) the necessity of recovering the catalyst and ii) the low quantum yield in the use of the radiation. This work focuses on the correlation between the photoelectrochemical properties of TiO2 electrodes and their activity for the photoelectrocatalytic oxidation of methanol. Particulate TiO2 electrodes prepared by deposition of P25-TiO2 nanoparticles on titanium (TiO2/Ti) or conductive glass support (TiO2/ITO) seem to be effective for charge carrier transference on TiO2 surface favouring the formation of OH radicals and consequently, the oxidation of molecules. In contrast, thermal TiO2 electrodes prepared by annealing of titanium (Ti) present better properties for charge carrier separation as a consequence of the application of a potential bias. Despite reducing charge carrier recombination by applying an electric potential bias, the activity of thermal electrodes remains lower than that of P25-particulate electrodes. TiO2 structure of P25-particulate electrodes does not completely allow developing a potential gradient. However, their adequate TiO2 layer characteristics for charge carrier transfer lead to a reduction in charge carrier recombination making up for the lack of charge carrier separation when applying an electric potential bias. TiO2/Ti showed the highest values of activity. Therefore, the combination of the suitable TiO2 surface properties for charge carrier transfer with an adequate conductive support seems to increase the properties of the electrode for allowing charge carrier separation. The scaling-up calculations for a TiO2/ITO electrode do lead to good estimations of the activity and photocurrent of larger electrodes since this photoanode made from ITO as conductive support does not seem to be significantly affected by the applied potential bias. [Copyright &y& Elsevier]