Meeting the growing demand for lithium-ion batteries in electric vehicles and portable devices requires efficient lithium extraction methods. Electrochemical approaches, particularly those that leverage energy-efficient direct lithium extraction, are emerging as promising solutions. This talk explores both continuous and intermittent concepts for lithium-ion recovery, emphasizing advancements in material selection, membrane integration, and electrode stability.

Intermittent lithium-ion extraction is explored using lithium iron phosphate (LFP), a widely available battery material with a high theoretical capacity and favorable lithium insertion potential. Despite these benefits, LFP faces performance stability challenges. Our work investigates the role of additional cations and dissolved oxygen on LFP stability, finding that calcium cations and dissolved oxygen contribute to capacity fading. In contrast, sodium and magnesium cations have minimal impact. Performance is enhanced through continuous nitrogen flushing of the electrolyte and carbon coating of the LFP electrode, resulting in a lithium extraction capacity of 21 mg per gram of electrode material. This approach achieves an energy consumption of 3.03 ± 0.5 Wh per mole of lithium, with a capacity retention of 82% over 10 cycles. This system is of particular use for the processing of hydrometallurgical media within the context of lithium-ion battery recycling.

To continuously extract lithium from seawater, mine water, or other aqueous media, one can use continuous operation of electrochemical systems that integrate lithium-ion-selective ceramic membranes (LISICON). We show the facile operation of a simple redox-flow electrolyte, enabling continuous lithium recovery at a high purity of 93.5% and a Li/Mg selectivity factor of approximately 500,000:1. This concept is not limited to redox-flow battery technology; instead, our work shows that a fuel cell (fueled with oxygen and hydrogen) can also co-produce electricity and separate lithium-ion during continuous operation.

A robust supply chain of main Li-ion battery (LIBs) components has become critical since the rapid growth in energy demand storage, the so-called Green transition promoting the market of electric vehicles, and the ubiquitous presence of batteries in portable applications has spread out LIBs manufacturing and components needs. The dependence of these materials on third countries, with China as the main battery grade supplier, has prompted the European Committee to develop a new EU regulatory framework for batteries, which encourages battery recycling as an alternative supply chain, targeting, for example the recovery by 2027 of at least 50% of the lithium contained in spent batteries and its reutilization for the manufacturing of new cathode materials by 2035 at 10%, value increased to 12% and 20%for Ni and Co respectively. [1] Current LIBS recycling is carried out at an industrial scale using pyrometallurgical and hydrometallurgical processes. However, these technologies have several inherent limitations; in most cases, these methods face difficulties in recovering lithium and focus on extracting nickel and cobalt; in addition, they suffer from an intensive consumption of energy or chemical reagents, lengthy operational procedures with low recovery rates, and the generation of hazardous wastewater or polluting gas emissions, thus involving severe environmental impacts [2, 3].

In this communication, we develop an electrochemical method - ion pumping technology- to selectively extract lithium from battery spent; based on the use of lithium-selective-electrodes, such as olivine LiFePO₄ (Figure 1), as well as, we have proven the viability of the same technology to recover Ni and Co from NMC spent, in this case based on the use of Prussian Blue Analogues, K_xNi[Fe(CN)₆]y - z H₂O. The materials selectivity and the influence of critical extraction parameters (current density, time…) were analyzed by constant current measurements and Inductively coupled plasma mass spectrometry. The results demonstrate this technology's potential for electrochemical recovery of lithium and multivalent cations in short operational times.

Pyrometallurgy is one of the most relevant processes to recycle Lithium-ion Batteries (LIB). It involves the melting of the waste batteries in a shaft furnace at around 1500ºC. Two main products are obtained: an alloy, rich in Ni, Co, Cu, Fe; and a slag, which mainly contains Li and Al [1]. Typically, this slag was not valorised, and its main application was as a filling material in the construction sector. In 2021, one of the main European companies in the field of battery recycling published a patent where they claim a hydrometallurgical process to recover lithium from this slag, by leaching with H₂SO₄ and then precipitating Al to leave Li in solution [2]. The present study arose as an attempt to investigate the possibility of lithium extraction from leaching solutions containing aluminium.

Our approach focuses on exploring electrochemical capture technologies, such as faradaic deionization, to minimize the chemical usage and provide a more cost-effective, energy-efficient and environmentally sustainable solution. For that purpose, various lithium metal oxides (LMO, LFP, LMFP, NMC) were tested as active materials for electrochemical lithium recovery. Lithium manganese oxide (LMO) emerges as a promising candidate leading to the synthesis of Truncated-Octahedral LMO (Tr-Oh-LMO) [3], theoretically more stable than commercial LMO, to enhance the robustness of the process. Electrodes were prepared in two configurations, carbon paper (CP) and buckypaper (BP), and tested across different electrolyte compositions and pH values.To assess the performance, a novel Electrode Endurance Diagram was proposed to visualize the influence of pH on electrode stability during cycling. This tool enables a quick and comparative evaluation of the performance of different materials across a range of pH levels. Additionally, various characterization techniques, such as XRD and SEM-EDS, are employed to investigate electrode degradation mechanisms as a function of pH and aluminum presence.

Overall, this work provides valuable insights into the influence of pH and aluminum on the stability of lithium oxide electrodes, emphasizing the need to optimize process conditions and explore alternative active materials to enhance the feasibility of electrochemical lithium extraction from aluminum-rich solutions.

Li-ion battery recycling is currently a topic of significant scientific interest, with numerous studies and research projects exploring new techniques and optimizing existing ones. This is further encouraged to cope with the need for an independent supply of the main battery materials (e.g. Li, Co, Ni), most of them classified as Critical Raw Materials (CRM) by international organisations such as the EU [1]. Battery recycling therefore aims at facing the rapid growth in energy demand and the so-called Green transition promoting the market of electric vehicles. Not to mention that battery recycling tackles environmental problems related to their disposal. Current recycling methods employed are primarily based on hydrometallurgical and pyrometallurgical processes. However, these technologies have several inherent limitations, including an intensive consumption of energy or chemical reagents, lengthy operational procedures with low recovery rates, and the generation of hazardous wastewater or polluting gas emissions, thus involving severe environmental impacts [2]. Consequently, the development of novel alternative and sustainable recycling techniques is imperative, with electrochemical recycling representing a promising avenue for advancement [3].
In this work, an electrochemical technique has been the subject of study using materials like Prussian Blue Analogues (KxNi[Fe(CN)6]y - z H2O), capable of reversible intercalation of divalent cations (Co and Ni). Following the acquisition of encouraging results from 965 ppm  of recovered CRM under static conditions in a microcell, the method was fully automated simulating a scenario closer to the final application utilising a semicontinuous  flow-through reactor and resulting in the recovery of 1600 ppm CRM and 121 Wh/g of energy consumption. This is accomplished through the integration of electrochemical techniques to study the electrochemical properties of the PBA and to develop the operational modes of the setup. Furthermore, an examination of the material's structural, morphological, compositional, and characteristics is conducted.
Accordingly, this study represents a novel automated electrochemical method for the recovery of nickel and cobalt from battery recycling wastewater
 

In recent years, there has been a notable increase in lithium production, mainly due to the development and widespread adoption of Li-ion batteries (LiBs) in electronic devices; additionally, further increments are expected since vehicle electrification is based on LiBs because of its high energy density, safety and relatively low cost [1]. Lithium could be produced from hard-rock ores and continental brines. The dependence of this metal on third countries has prompted the European Committee to develop a new EU regulatory framework for batteries, which requires ensuring the recovery by 2027of at least 50% of the lithium contained in spent batteries and its reutilization for the manufacturing of new cathode material by 2030 [2]. Current LIBs recycling is carried out at an industrial scale using pyrometallurgical and hydrometallurgical processes. However, in most cases, these methods face difficulties in recovering lithium and focus on extracting nickel and cobalt [3].

In this communication, we develop an electrochemical method - ion pumping technology- to selectively extract lithium from battery spent, based on the use of lithium-selective-electrodes, such as olivine LiFePO₄ (Figure 1A), which can intercalate lithium while neglecting the insertion of other co-cations present in the solution, e.g., case of Ni, Co, and Mn for NMC based spent. The value of material selectivity towards lithium and the influence of critical extraction parameters (current density, time…) were analyzed by constant current measurements (Figure 1B) and inductively coupled plasma mass spectrometry. The results demonstrate this technology's potential for electrochemical recovery of lithium, reaching purities higher than 98% in short times - 120 minutes.

Materials science has proven to be valuable in tuning the selectivity in the electrochemical separation of ions. In this contribution, we specifically focus on the exploration of polymers to address the selectivity of membranes and electrodes that are employed in electrochemical deionization (EDC) and electrodialysis (ED).

Several approaches with different types of polymers will be discussed. First, the build-up of a multilayer of charged polymers (poly(allylamine hydrochloride), PAH and poly(styrene sulfonate), PSS) onto commercial available cation-exchange membranes proved to be a facile and versatile approach in switching from Mg²⁺-selectivity to Na⁺-selectivity when applied in ECD [1]. Next, in the presence of a series of mineral acids (HCl, HNO₃, H₂SO₄, and H₃PO₄) a conductive polymer (polyaniline, PAni) was electrodeposited onto carbon electrodes. When employed under ECD conditions, the PAni/H₂SO₄ system exhibits promising behavior for tuning ion selectivity [2]. Among the tested ECD electrodes, this system achieved a notable 20% reduction in chloride adsorption while maintaining consistent sulfate adsorption. Lastly, hydrophobic polymers (poly(vinylidene fluoride), PVDF, poly(vinyl chloride), PVC, polyacrylonitrile, PAN) were blended with an ionomer to obtain anion-exchange membranes.[3,4] In electrodialysis, the nitrate over chloride selectivity trend was found to be PVC > PVDF > PAN.

While evaluation of the complete set of charged, conductive, and hydrophobic polymers shows that a ‘one‐size‐fits‐all’ approach is not readily accessible when pursuing ion selectivity, the extraction of several general principles contribute to guiding the development of advanced materials set to further tune electrochemical separation.

Lithium has emerged as a critical raw material because of its indispensable role in the energy transition, especially in manufacturing lithium-ion batteries for electric vehicles and portable devices. However, 95% of such batteries are discarded without recycling once they reach the end of their life. When recycled, the batteries are shredded to form a black mass, which is leached by sulfuric acid. The resulting leachate contains transition cations such as nickel, cobalt, and manganese, besides Li. Thus, it is necessary to separate these elements, which is typically achieved through successive precipitation by increasing the pH of the leachate. However, this process results in a 40-60% loss of lithium which is the last element to be recovered.

Flow Electrode Capacitive Deionization (FCDI) is a very recent electromembrane desalination technology which employs flow electrodes (carbon slurries) to remove ions from saline water. We hypothesised that replacing standard cation exchange membranes with lithium-selective ones could allow for lithium recovery from brines and spent Li-ion batteries. In this talk, the journey behind the creation of Lithium Membrane Flow Capacitive Deionization (Li-MFCDI) [1] will be disclosed.

Several key challenges were addressed to optimise the FCDI/Li-MFCDI performance regarding energy efficiency and the possibility of scale-up. Polymeric lithium-selective membranes were developed [2] to overcome the limitations of ceramic membranes, which are brittle and expensive, limiting their scalability. Another challenge in FCDI and Li-MFCDI is to maintain the uninterrupted flow of carbon slurry electrodes while preventing channel blockage. In this context, the design of flow electrode channels was investigated experimentally and by computational fluid dynamics (CFD), considering the shear-thinning behaviour of flow electrodes [3]. Furthermore, innovations, including the utilisation of 3D-printed flow electrode gaskets as a substitute for the state-of-the-art computer numerical control (CNC) milled graphite current collectors, were explored to improve system scalability and efficiency. The research also assessed various operational modes under the same operating conditions to identify the most efficient operational mode for continuous and scalable desalination or lithium recovery. Finally, several different activated carbons were tested in the FCDI system to hunt out the best material for flow electrodes to enhance performance, scalability, and overall system efficiency.

Faradaic electrochemical deionization (FDI) is emerging as a transformative technology for water treatment, addressing critical challenges in conventional capacitive deionization (CDI) such as low desalination capacity, carbon anode oxidation, and co-ion expulsion effects [1]. Utilizing faradaic electrode materials—engineered by incorporating the electrochemical principles of battery electrodes—FDI employs redox and intercalation mechanisms to selectively remove ions. This innovative approach not only achieves higher desalination capacity but also offers superior energy efficiency, particularly at lower salinity levels.

In this work, we compare two advanced battery-type electrode materials for FDI: inorganic sodium-manganese oxides (NMOs) and organic polymers. NMOs, known for their open crystal structures, allow efficient ion insertion and extraction, making them ideal for Na-ion storage in aqueous systems [2]. Meanwhile, redox-active polymers like poly[N,N′-(ethane-1,2-diyl)-1,4,5,8-naphthalenetetracarboximide] (PNDIE) offer advantages in terms of low weight, stability, safety, and sustainability [3].

Our study explores two innovative FDI approaches to enhance salt removal capacity (SRC) and cycling stability:

i) All-polymer symmetric FDI cells: Utilizing buckypaper electrodes made from PNDIE, these cells achieved a superior salt removal capacity of 155.4 mg g⁻¹. The all-polymer design enhances production, reduces energy costs and promotes sustainability.

ii) Optimization of Sodium-Manganese Oxides: This study highlights the critical role of morphology and crystal structure in the desalination performance of NMOs. The mixed-phase NMO (mp-NMO) demonstrates outstanding stability, effectively mitigating the Jahn-Teller effect—a common issue in manganese oxides that can lead to stability challenges depending on the crystalline phase.

Both approaches employ rocking-chair flow cell configurations for continuous desalination, showcasing the potential of these novel electrode materials and designs. The findings underscore their promise for efficient, sustainable brackish water desalination, offering significant contributions to global water scarcity solutions.

In proton exchange membrane water electrolyzers (PEMWE), the oxygen evolution reaction (OER) is considered the limiting process in water splitting. To date, iridium has been recognized as having the best OER performance in acidic conditions when regarding both, activity and stability. This instigated study of various Ir-based materials using different techniques, but some questions about the mechanisms are still debated [1]. Interesting insights into the redox Ir(III)/Ir(IV) reaction and the OER process can also be gained via Raman spectroscopy [2,3], and we apply this technique in our work using an ex situ [4] and in situ approach.

Since Ir is a scarce metal, its amount in electrocatalysis is reduced by the preparation of dispersed Ir NPs on different supports. When Raman spectroscopy of iridium has been reported in the literature, it has been recorded on metal foil [2], electrochemically deposited IrO_x film on GCE [3] or drop-casted samples on GCE [4], i.e. more bulk samples. The question arises whether it is possible to perform Raman measurements directly on supported Ir NPs. We made these measurements ex situ and showed that the formation of iridium oxide can be detected for degraded states. However, the relatively low loading of Ir NPs causes the low intensity of the iridium oxide bands (E_g, B_2g and A_1g vibrations). The two supports that are used in this investigation were carbon and TiO₂ (i.e. P25).

Consequently, we continued to investigate the performance of two commercial Ir-based compounds, Ir nanoparticles (Ir NPs) and rutile IrO₂, and the measurements were made on unsupported samples. Both compounds were drop-casted from suspensions on glassy carbon electrode (GCE) and activated in a 0.1 M HClO₄ electrolyte. The Raman spectrum of GCE/IrO₂ consists of three active modes at 557 cm^-1 (E_g), 728 cm^-1 (B_2g) and 746 cm^-1 (A_1g), while the fourth low-intensity B_1g mode at 145 cm^-1 [2-4] could not be identified. In the GCE/Ir NPs sample, the E_g mode appears at 552 cm^-1, while the B_2g and A_1g modes appear as an overlapping band at 724 cm^-1. Such spectrum indicates that the Ir NPs oxidize in air and the amorphous Ir-oxide forms on the surface. During the in situ Raman measurements of the GCE/Ir NPs a composed, broad band feature evolves. The previous works were carried out in different electrolytes, potential ranges and conditions [2,3] which makes it difficult to compare the results. We consequently decided to make a systematic study in three different potential ranges: 0.05 to 1.45 V_RHE , 0.05 to 1.6 V_RHE, and 1.1 to 1.6 V_RHE and in the 0.1 M HClO₄ electrolyte, which has not been used for in situ Raman spectroelectrochemical measurements before. The evolved broad bands are explored after initial, soaked and activated states. In addition, the possible perchlorate adsorption [4] at the electrode is considered.

Over the past century, humans have altered the global nitrogen cycle so drastically that managing nitrogen has emerged as a grand engineering challenge and urgent need. The emissions-intensive Haber-Bosch process for industrial fertilizer production, which converts nitrogen gas into ammonia, outpaces wastewater nitrogen removal due to fertilizer runoff and 80% of wastewater being discharged without treatment. Refining nitrate and ammonia into valuable products through reactive separations, which integrate catalysis and separations, is a useful approach for addressing both water pollution and chemical manufacturing. For example, selective membranes and adsorbents can be leveraged to control catalytic performance by tuning microenvironments near catalyst active sites. This seminar will focus on recent work designing metal electrocatalysts for selective reduction of nitrate to ammonia, along with separation of high-purity ammonia from real wastewaters. Specifically, we focus on understanding the reaction microevenionment of titanium and cobalt in multiple catalyst architectures while leveraging a systematic study of electrolyte composition on catalyst activity, selectivity, and stability. We complement these efforts with reactive separation devices that leverage electrochemical potential to drive nitrate and ammonia transport, which advances the vision of wastewater refining: producing a tunable portfolio of products from real wastewaters. 

The alkaline oxygen evolution reaction (OER) is crucial for green hydrogen production via water electrolysis. However, its industrial implementation at high current densities remains limited due to the scalability, overpotential, and stability challenges of current commercial electrocatalysts. Layered hydroxides (LH), particularly those based on abundant transition metals, are emerging as promising alternatives owing to their remarkable electrochemical properties.

In this talk, we will present the latest advances from the 2D-Chem research group (www.icmol.es/2dchem) in the synthesis and characterization of novel two-dimensional (2D) LH materials. Specifically, we have developed an industrially scalable, room-temperature, atmospheric-pressure homogeneous alkalinization synthetic pathway to produce optimized NiFe layered double hydroxide (NiFe-LDH). By leveraging the nucleophilic attack of chloride on an epoxide ring, we have achieved a low-dimensional, highly defective NiFe-LDH exhibiting pronounced cation clustering and excellent electrochemical performance. Spectroscopic studies, including in-operando XANES, EXAFS, SAXS or Raman combined with ab-initio calculations reveal the critical role of Fe clustering in lowering the energy pathway for improved catalytic activity.

Furthermore, we have extended this synthetic route to other compositions that will demonstrate the versatility of these materials beyond green hydrogen production. Indeed, in-situ XAS and PXRD studies provide further insights into the behavior of these layered materials during operation, allowing their use as precursors for metallic nanocomposites with applications in energy storage. Finally, optimized LDH and hybrid LDH-nanocarbon electrocatalysts with tailor made compositions can also play a pivotal role in alkaline electrochemical water treatment for the remediation of contaminated water systems, offering a sustainable approach for pollutant degradation and removal.

　In recent years, the utilization of renewable energy, particularly solar power, has been accelerating globally from the perspectives of both the global energy problem and the decarbonization of society. To expand the use of renewable energy, it is necessary to store energy, and hydrogen is particularly suitable for large-scale, medium- to long-term storage. In a world aiming for carbon neutrality, hydrogen is a clean energy that can be produced by electrochemically splitting water, and water electrolysis cells that enable this are being researched and developed for practical use, with simulator development being part of this effort.

　However, current simulator development involves detailed simulation environments at the particle level that represent reaction mechanisms and electrochemical phenomena. Using these as a system places a heavy burden on the calculations, making them difficult to use. When considering device requirements, there are currently no simulators available that can represent current-voltage characteristics in a simple but reasonably detailed manner.

 Therefore, we constructed a physical model of a PEM water electrolysis cell using MATLAB/Simulink, which takes into account the frequency characteristics and capacitance characteristics, and can also represent the current-voltage characteristics.

　In this study, with the cooperation of RIKEN, we measured actual data from water electrolysis cells used in distributed hydrogen systems. To express both static and dynamic characteristics, we conducted I-V measurements and FRA measurements, respectively, and performed parameter fitting using the measurement results.

　As a result, the current-voltage characteristics within the compatible range could be expressed with an accuracy of over 95%, and the electrical transient characteristics of the water electrolysis cell, such as inrush current, could be expressed qualitatively.

　Furthermore, by accurately expressing the behavior of water electrolysis cells while ensuring sufficient simulation speed as a simulation environment for the system, it became possible to verify the necessary device requirements. We expect this to be utilized in system studies using water electrolysis cells and in device prototyping using electrochemical expressions.

The activation of O₂ through electrochemical reduction (ORR, oxygen reduction reaction) has shown promising results as alternative energy conversion technologies that can produce added-value chemicals from simple and abundant feedstocks. However, despite extensive efforts to develop catalytic materials with high reactivity and high selectivity, one can currently observe the lack of demonstrative performance for viable industrial applications. The deliberate surface modification of catalyst has been recently recognized as a powerful approach to design efficient and durable electrocatalysts [1]. It then becomes essential to obtain a good control over the spatial distribution of the chemical functions over the nanoobject surfaces. Recently, excellent catalytic properties towards ORR have been obtained in alkaline media of gold [2], silver [3], and platinum [4] nanoparticles when modified through the reductive grafting of rigid macrocycle calix[4]arene-tetradiazonium salts [5]. However, many fundamental questions, with important operational implications, remain open about these calixarene-modified surfaces. In particular, the conformation of the calixarene on the surface, and the structural, thermodynamic and electronic description of the interface. In addition, the C-Au bond has been poorly investigated in comparison to the S-Au bond.

Here, using spectroscopic studies coupled with computational modeling performed with density functional based tight-binding (DFTB) approaches, we investigate the interaction between calix[4]arene macrocycles and gold and platinum nanoparticles. After exploring the nature of the bond between the macrocycle and the gold surface thanks to a good agreement between measured and calculated Raman spectra, we describe the effect of calix[4]arenes on nanoparticles electrocatalytic properties [6].

Hydrogen is  a clean energy source and an important candidate to replace fossil fuels in the near future (energy transition). However, traditional hydrogen production is achieved through processes that are expensive and non-sustainable require high amounts of energy, such as carbon gasification or steam methane reforming. Waste waters are considered a cheap and abundant energy source, as they contain high amounts of organic compounds. Therefore, the hydrogen production from waste water can be a useful solution in order to reduce the energy costs associated with traditional processes. 

REGENERA project (CDTI- Misiones 2019) investigates the delocalized storage of energy from renewable energies in the form of green fuels, hydrogen and methane. This communication presents the BES-BioH₂ laboratory concept, a “Power-to-Gas” technology that aims to generate hydrogen (H₂) by using a microbial electrochemical cell. The objective is to achieve an integrated system at laboratory scale which allows the simultaneous waste water treatment, hydrogen production and biogas upgrading (achieving a purity >95% of CH₄). 

Bioelectrochemical systems (BES) combine electrochemistry with the metabolism of electroactive microorganisms for energy production. In Microbial Electrolysis Cells (MECs), electroactive bacteria grow building a biofilm on the surface of a conductive anode, which acts as electron acceptor. The electroactive microorganisms oxidize organic matter to CO₂ under anaerobic conditions and the electrons obtained in the process are transferred from the anode to the cathode through an electrical circuit [1]. The cathodic reaction is the H₂ formation through H₂O reduction under alkaline conditions. The reduction of water to hydrogen is a non-spontaneous process, so the application of an external potential is required.

This study presents the experimental results using different real waste waters (urban and industrial) and discusses on the potential of various organic substrates for hydrogen production. Thus, the energy cost for hydrogen production (kWh/kg H₂), the chemical organic demand removal rate (g/m³ day) and the hydrogen production rate (m³ hydrogen/m³ reactor) are presented in order to compare the present system with conventional system for urban waste water treatment. Finally, the study suggests main limitations and opportunities for the implementation at real scale, as the final objective of REGENERA project is the development of a prototype of 500 L capacity by the end of year 2024, with capacity to produce 1-10 Nm³H₂/day.

Conductive carbon materials gather a matchless combination of exceptional properties, highlighting their availability, relatively low-cost, lightness, sufficient stability and enormous versatility to be prepared in different sizes, shapes, conformations, porous textures and surface compositions, making them excellent candidates to be used as electrodes in various electrochemical technologies. Among them, there stand out the technologies applied in the field of water treatment, like those based on pollutants electrosorption, electrooxidation and biodegradation (in the so-called microbial electrochemical technologies (METs)). In addition, these technologies show great interest in addressing the challenges of water-energy nexus. In this context, the design of carbon properties is of paramount importance for the feasibility and optimization of these technologies. On the other hand, the availability, cost and environmental impact of these materials are key factors for their development and full-scale application.

This contribution revises the carbon properties that determine their performance in electrochemical water treatment applications. Particularly, the influence of microstructure, porosity and surface chemistry on the electrochemical properties of carbons (conductivity, stability, electrochemical double layer, electron transfer, etc.) is analyzed. Furthermore, advances in strategies and tools to control and optimize these properties are discussed. Finally, recent findings on carbon properties stimulating microbial extracellular electron transfer for METs are summarized. In this respect, recent studies demonstrate that certain oxygen surface groups can promote anchorage and/or electron transfer with electroactive bacteria; whereas nanoscale (bacteria-inaccessible) porosity remarkably enhances the microbially derived electrical current. Among different carbon materials, electroactive biochar is proposed as a good candidate for large-scale environmental applications of METs.

Among the electrochemical advanced oxidation processes (EAOPs) for wastewater treatment, which exhibit high effectiveness combined with green deployment, some of them primarily rely on the efficiency of anode materials in generating potent oxidants like hydroxyl radicals (•OH). Hence, the development of novel, cost-effective nickel-manganese-based anodes has been investigated in this work, aiming to revolutionize the electro-oxidation of organic pollutants. Key to this endeavor is the use of 3D porous conductive substrates, akin to those employed in redox-flow batteries and water electrolyzers. These substrates are crucial for maximizing the electrode-electrolyte interactions and facilitating efficient flow-through designs, thereby significantly boosting the EAOPs performance. The synthesis, characterization, and optimization of these Ni-Mn-based electrodes, including their physicochemical structure and electrochemical properties, have been studied. It has been found that by employing Ni-Mn-based materials as the active material and utilizing the high surface area of 3D substrates such as nickel foam and graphite felt, our electrodes achieved a remarkable 100% removal of phenol, coupled with an 80% reduction in chemical oxygen demand (COD), thus marking a significant advancement over traditional anodes. Comparative analyses with boron-doped diamond (BDD) and dimensionally stable anode (DSA) highlight the superior activity and efficiency of our anodes. Further, a detailed mechanistic study was undertaken to elucidate the electrochemical pathways and interactions. This investigation reveals an enhanced generation of hydroxyl radicals and other oxidizing species on the anode surface, justifying the observed degradation efficiency. The implications of these findings are substantial in the field of wastewater treatment. Developing our Ni-Mn oxides not only sets a new benchmark in pollutant degradation efficiency but also offers valuable insights into the electrochemical mechanisms underpinning EAOPs.

The water crisis is a major concern at global scale, which underscores the need for alternative freshwater resources. In this context, urban wastewater is one of the main targets to feed regenerated water for many applications, but it faces challenges from persistent pharmaceuticals resistant to conventional treatments. Advanced methods like electrochemical advanced oxidation processes (EAOPs), particularly the electro-Fenton (EF) process, offer a highly promising performance [1]. However, limitations such as narrow pH range and low H₂O₂ yields must be addressed by developing new electrocatalysts and heterogeneous catalysts.

This work addresses these issues through two innovations: (1) Electrocatalysts for highly selective two-electron oxygen reduction reaction (2e^– ORR) to generate H₂O₂ in situ, and (2) advanced heterogeneous catalysts with enhanced H₂O₂ activation efficiency.

In EF, 3.0 to 15.0 mM H₂O₂ is sufficient to purify wastewater [2], making the electrochemical 2e^– ORR with a gas-diffusion electrode (GDE) an attractive alternative to the industrialized anthraquinone process to synthesize H₂O₂. Tin (Sn) exhibits strong O₂ adsorption under alkaline conditions [3]; accordingly, Sn-doped carbon materials are demonstrated to have outstanding H₂O₂ selectivity (98%) and high H₂O₂ production efficiency at near-neutral pH, with an electron transfer number of 2.04. Nitrogen-doped carbons, optimized for pyrrolic nitrogen content, delivered superior H₂O₂ yields (reaching 18 mg h^–1 cm^–2) compared to commercial GDEs.

For H₂O₂ activation, Cu/NC and FeCu/NC catalysts derived from MOFs exhibited great performance. Cu/NC enabled the effective pollutant mineralization at pH 6–8, being superior to the EF process with soluble Fe²⁺ at pH 3. The core-shell structure of FeCu/NC minimized metal leaching and extended catalyst lifespan. This brought about an accelerated Fe(II) regeneration, achieving 100% removal of lisinopril within 75 min.

This research shows significant progress in the development of sustainable EF systems, integrating the efficient electrogeneration and activation of H₂O₂, which allows addressing the problem of pharmaceutical pollutants in wastewater.

Water issues represents one of the biggest challenges of the 21st century. The United Nations has addressed Sustainable Development Goal (SDG) to answers the water crisis. The increase of water demand in the different sectors (agriculture, industry and household), and the water stress that is globally rising in the meantime, are responsible for this critical issue. To face it, the water reuse approach is more and more considered. However, before reusing wastewater there is the need to completely remove emerging pollutants (e.g., pharmaceuticals, pesticides, personal care products) since they are not eliminated by the bioprocesses typically applied in plants. Still, wastewater contains valuable chemicals (e.g., phosphate, magnesium) that could be recovered in the meantime. Electrochemical systems can tune the removal and recovery steps by playing on the applied potential/current, in contrast with chemical processes. They also offer the advantages of operating several unit operations (separation and conversion technologies) without the need for chemicals addition and within the same reactor design. Moreover, vector of energy could be electrogenerated (e.g., hydrogen (H2)). This presentation will focus on case studies implementing electro-precipitation, electro-sorption and electro-reduction/-oxidation for resource recovery in wastewater under microfluidic conditions.

Feeding long-term sustainability to our planet is becoming a major must, given the urgent need to preserve our natural resources, reduce pollution and protect the natural ecosystems. Sustainable development holds on three pillars, namely environmental sustainability and protection, economic viability, and social equity. Among them, the former receives great attention and it is build up on reducing carbon emissions and footprint, packaging waste, water usage, and other negative environmental impacts. New paradigm towards green chemistry, sustainability, and circular economy in the chemical sciences must be developed, in order to better employ, reuse, and recycle the materials employed in every aspect of modern life. Following this approach, electrochemical reactions have found technological applications in various fields, including electrochemical synthesis, energy storage, and environmental remediation [1]. Sustainability and electrochemistry are therefore closely related. In this talk, the utilization of electrochemical tools together with bio-based or sustainable materials is presented.

First, the exploration of new synthetic routes to reduce the toxicity of residual monomer and other chemicals employed (initiators, surfactants) during the fabrication of polymer hydrogels, one of the most promising groups of biomaterials, is required. With a similar approach to the previously developed "green" and clean production of polymer nanogels, largely used in biomedicine, based on the recourse to high energy irradiation, electrochemical advanced oxidation technologies were used to crosslink hydrogels of poly(vinylpyrrolidone)(PVP) by means of electrogenerated hydroxyl radicals. This facile electrosynthesis route showed that the kind of radicals strongly drives the transformation of the architecture of linear, inert polymer chains into a functionalized nanogel (with -COOH and succinimide groups), more suitable for further conjugation [2-4].

Second, the conversion of bio-based polymers such as chitosan and agarose, into eco-friendly carbonaceous electrodes is described, as a suitable choice for promoting sustainability due to their low cost and high activity/selectivity [5-6]. The use of mesoporous carbon supports both reduce the amount of noble metals employed as electrocatalysts and enhance the accessibility of reactants to the active sites. On the one hand, excellent electrocatalytic performance of N-doped chitosan-derived carbons and large surface area agarose-derived carbons are responsible of the high efficiencies achieved (above 95%), allowing the fast destruction of pharmaceutical residues in electro-Fenton treatment. On the other hand, chitosan-derived mesoporous carbons served as optimal supports for PtCu electrocatalysts, evidencing an increased activity of both the four-electron ORR and the methanol oxidation reaction as compared to commercial supported Pt and PtCu catalysts, which is attributed to the good balance achieved between micro/mesoporosity.

Finally, one of the most appealing and recent trends in the application of biopolymers in electrochemical water treatment is reported. The co-generation of freshwater and sustainable energy in a closed loop where the solar energy is used not only for water purification treatment with porous materials like hydrogels, but also for thermoelectric power generation, by means of material transpiration and diffusion processes. The photothermal electricity production is promoted by hydrogels based on biopolymers such as alginate (ALG) and thermosensistive materials like poly(N-isopropylacrylamide) (PNIPAAm). ALG-PNIPAAm bio-hydrogel, modified with conducting polymer (CP), as thermal absorber component, was used to obtain freshwater from seawater desalination under sunlight. Higher evaporation rates (> 4 kg/h*m²) have been observed in the presence of lineal CP, if compared with nanoparticles of CP [7-8]. Impedance measurements elucidate the ion diffusion dynamics within the hydrogel, directly correlating this behavior to enhanced power generation; these results revealed that the presence of hydrophilic groups (─OH, ─SO₃H), present in the CP backbone, promotes the capillary flow of the electrolyte during the sunlight irradiation. The doped CP molecules facilitate a fast ion transport thanks to a good balance between the material hydrophilicity and the interconnected pores.

Electrocatalysis is increasingly important in water treatment for its efficiency and eco-friendliness, and materials play important role in performance. In this work, we synthesized an efficient single-atom Co-N/C catalyst for electrocatalytic dehalogenation, which provided more active sites and a faster charge transfer rate. Co-N/C effectively removed florfenicol (FLO) over a broad pH range, with rate constants that were 3.5 and 2.1 times higher than those of N/C and commercial Pd/C, respectively. The defluorination and dechlorination efficiencies were 67.6 and 95.6%, respectively, with extremely low Co leaching (6 μg L^-1) and low energy consumption (22.7 kWh kg^-1). H* and direct electron transfer were the primary causes of dehalogenation. The Co-N/C was minimally affected by pH, co-existing ions, and water quality, maintaining a high removal rate (>90%) after ten cycles [1]. To enhance H* production, the phosphorus-doped cobalt nitrogen carbon catalyst (Co-NP/C) was prepared for electrocatalytic dechlorination, which had high catalytic activity in a wide pH range (3-11). The introduction of phosphorus was found enhanced the electron density of cobalt and regulated the electron transfer.

We further developed the heterogeneous electro-Fenton process based on dual-functional cathodes. The catalyst composed of nitrogen-doped carbon nanotubes encapsulating zero-valent iron (Fe@N-C) was synthesized, which demonstrated superior degradation of sulfamethazine (SMT) under mildly alkaline conditions. The primary reactive species generated by Fe@N-C were H* and singlet oxygen (¹O₂), with hydroxyl radicals (∙OH) playing a supportive role [2]. Additionally, the catalyst with boron and nitrogen co-doped carbon nanotubes encapsulating zero-valent iron (Fe@BN-C) was fabricated, which significantly increased the selectivity for H₂O₂ to 94%, and H₂O₂ was directionally converted to ¹O₂ via surface ∙OH. Theoretical calculations confirmed the confinement effect of Fe⁰ overcame the rate-limiting step for H₂O₂ formation, achieving high efficiency and selectivity for ¹O₂ transformation[3].

Traditional free radicals-dominated electrochemical advanced oxidation processes (EAOPs) and sulfate radical-based advanced oxidation processes (SR-AOPs) are limited by pH dependence and weak reusability, respectively. To address these shortcomings, electro-enhanced activation of peroxymonosulfate (PMS) was proposed. Firstly, a novel perovskite-Ti₄O₇ composite anode activating PMS (E-PTi-PMS) system achieved an ultra-efficient removal rate (k = 0.467 min^-1) of carbamazepine (CBZ). The electric field expedited the decomposition and utilization of PMS, promoting the generation of radicals and expanding the formation pathway of ¹O₂. This system presented superiorities over wide pH (3-10) and less dosage of PMS (1 mM), expanding the pH adaptability and reducing the cost of EAOPs [4].