Chlorine Evolution Reaction Research Articles

In situ evolved high-valence Co active sites enable highly efficient and stable chlorine evolution reaction

The chlor-alkali process is crucial in the modern chemical industry, yet it is highly energy-intensive, consuming about 4 % of global electricity due to the significant overpotential and low selectivity of existing chlorine evolution reaction (CER) electrocatalysts. Although advanced electrocatalysts have reduced the energy demands of the chlor-alkali process, they typically incorporate precious metals. Here, we introduce a novel precious metal-free electrocatalyst, (CoZn)3V2O8@C, with a hollow nanocube structure that exhibits outstanding CER performance. It features an overpotential of just 69 mV, a selectivity exceeding 90 %, and a high durability of 250 h at a current density of 10 mA/cm2, surpassing commercial dimensionally stable anodes (DSA) and some precious metal-based electrocatalysts. Comparative experiments and physical characterizations reveal that during the CER, high-valence Co evolves in situ due to the formation of adjacent Zn vacancies from the partial dissolution of Zn in (CoZn)3V2O8@C. Density functional theory further confirms that Zn vacancies can modify the electronic structure of the adjacent Co, enhancing the adsorption and activation of chloride ions, reducing the energy barrier of the reaction, and thereby improving the catalytic performance of CER.

Ru0.1Mn0.9Ox Electrocatalyst for Durable Oxygen Evolution in Acid Seawater.

Currently, direct electrolysis of seawater for green hydrogen production is primarily focused on neutral and alkaline systems. However, the precipitation of calcium and magnesium ions restricts the advancement of this technology. An acidic system can effectively address this issue. Given that Ru/Ir-based catalysts with high oxygen evolution reaction (OER) activity also exhibit high chlorine evolution reaction (CER) activity, acid seawater splitting requires anodes with higher selectivity and stability compared to the other two systems. In this study, we propose a non-precious Ru0.1Mn0.9Ox as the active anode for direct acid seawater electrolysis, which exhibits a high OER selectivity and remarkable stability for more than 1200 hours. Different from the Cl--free system, *Cl occupied on Ru sites could shift the OER active center to Mn on Ru0.1Mn0.9Ox, which prevents the lattice oxygen consumed on Ru and hinders the metal site dissolution. As the CER-insensitive catalytic center, Mn activated by the introduction of Ru can adsorb a substantial amount of *OH, creating an OER-favored local environment that inhibits CER. We introduce Cl--assisted transfer of OER active sites to CER-insensitive Mn as a fundamental strategy for achieving highly selective and durable oxygen evolution in acidic seawater.

Synergistic modification of Ti/PbO2 electrodes with metal ions (Nd, Al, Bi) and STAB surfactant for electrocatalytic treatment of desulfurization wastewater

In this study, PbO2 electrodes are modified by co-doping with different metallic elements (Nd, Al, Bi) and stearyl trimethyl ammonium bromide (STAB) using the electrodeposition method. The modified electrodes, designated as Ti/PbO2-Nd-STAB, Ti/PbO2-Al-STAB, and Ti/PbO2-Bi-STAB, are then applied in the electrochemical degradation of desulfurization wastewater. The surface morphology, crystal structure, and elemental valence of the prepared electrodes are analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Their electrochemical performance and stability are assessed by linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and accelerated life testing (ALT). The results reveal that modification with metallic elements and STAB significantly enhances the physicochemical and electrocatalytic performance of the Ti/PbO2 electrode. Among the modified electrodes, the Ti/PbO2-Nd-STAB electrode exhibits the most compact and homogeneous surface morphology, the highest oxygen evolution potential (OEP, 2.33 V vs. SCE), the lowest chlorine evolution potential (CEP, 1.44 V vs. SCE), the largest electrochemically active surface area, the lowest charge transfer resistance, the highest electrochemical stability, and a prolonged accelerated life (65 h, which is 17 h longer than that of the unmodified electrode). Further, the optimal electrochemical oxidation process parameters for desulfurization wastewater are determined as follows: current density = 50 mA/cm2, temperature = 35 ℃, electrode spacing = 3.0 cm, and stirring rate = 300 rpm. After 300 min of electrolysis, the Ti/PbO2-Nd-STAB electrode achieves a Cl− removal rate of 86.9 % and a chemical oxygen demand (COD) removal rate of 71.2 %. After 10 cycles, the Cl− and COD removal rates decrease by 2.8 % and 1.8 %, respectively. Besides, Tafel curve analysis indicates that the chlorine evolution reaction follows the Volmer-Tafel mechanism, with the recombination of adsorbed Cl− ions on the surface oxidation film being the rate-determining step. Overall, the Ti/PbO2-Nd-STAB anode exhibits immense application potential in the treatment of desulfurization wastewater.

Three-chamber electrochemical reactor for selective lithium extraction from brine

Efficient lithium recovery from geothermal brines is crucial for the battery industry. Current electrochemical separation methods struggle with the simultaneous presence of Na+, K+, Mg2+, and Ca2+ because these cations are similar to Li+, making it challenging to separate effectively. We address these challenges with a three-chamber reactor featuring a polymer porous solid electrolyte in the middle layer. This design improves the transference number of Li+ (tLi+) by 2.1 times compared to the two-chamber reactor and also reduces the chlorine evolution reaction, a common side reaction in electrochemical lithium extraction, to only 6.4% in Faradaic Efficiency. Employing a lithium-ion conductive glass ceramic (LICGC) membrane, the reactor achieved high tLi+ of 97.5% in LiOH production from simulated brine, while the concentrations of Na+ K+, Mg2+, and Ca2+ are below the detection limit. Electrochemical experiments and surface analysis elucidated the cation transport mechanism, highlighting the impact of Na+ on Li+ migration at the LICGC interface.

Unveiling the Geometric Site Dependence of Co‐Based Spinel Oxides in the Halogen Evolution Reaction

AbstractCobalt‐based spinel oxides, such as Co3O4, have emerged as promising electrocatalysts for chlorine and bromine evolution reactions (CER and BrER) in recent years. However, the role of Co valence in determining the exceptional performance of Co3O4 for both CER and BrER remains ambiguous due to the coexistence of both octahedrally coordinated Co3+ (Co3+Oh) and tetrahedrally coordinated Co2+ (Co2+Td) sites, despite their high catalytic activity and stability. Herein, combining experiment results and electrochemical data analysis, the Co3+Oh site functions as the primary active site for CER is demonstrated. In contrast, for BrER, both Co3+Oh and Co2+Td sites exhibit good catalytic activity, with Co3+Oh sites displaying better BrER catalytic performance than Co2+Td sites. To further enhance the CER catalytic activity of the Co3+Oh site, inert Co2+Td is replaced with Cu2+ cations. As expected, CuCo2O4 featuring an optimized Co3+Oh site demonstrates an overpotential of 24 mV at a current density of 10 mA cm−2 while exhibiting exceptional stability for ≈60 h, surpassing the performance of the majority of non‐noble and even noble metal‐based electrocatalysts reported to date. Therefore, the study elucidates the significance of geometric configuration‐dependent activity in electrocatalytic halogen evolution reactions.

Lanthanide-doped enhances Ni-Sb-SnO2 orbital hybridization: Promoting efficient electrochemical ozone production and chlorine evolution reaction

The utilization of electrochemical methods for synthesizing ozone (O3) and sodium hypochlorite (NaClO) holds great promise for decomposing organic contaminants. While the Ni-Sb-SnO2 electrode demonstrates several favorable attributes, ensuring its activity and stability in practical applications remains a significant hurdle. In this study, lanthanide-doped Ni-Sb-SnO2 electrodes were prepared to explore the effects of various lanthanides on the electrochemical performance of O3 and NaClO generation. The results revealed that Nd-Ni-Sb-SnO2 exhibited exceptional ozone generation capability, achieving a Faraday efficiency of 33.6%. Additionally, Ru-Ce-Ni-Sb-SnO2 electrocatalysts for the chlorine evolution reaction (CER) yielded a remarkable Faraday efficiency of 94.3%. Theoretical calculations revealed that the incorporation of Sb and Ni as dopants played a crucial role in stabilizing reaction intermediates. Furthermore, the addition of the lanthanide element Nd enhanced the hybridization between Sn and O, leading to improved performance in the electrochemical ozone production (EOP). Additionally, doping the Ni-Sb-SnO2 electrocatalyst with Ru and Ce promoted d-f hybridization, thereby significantly increasing the Cl- adsorption capacity in the CER. Additionally, integrating a self-made continuous flow electrolyzer with the electrocatalysts facilitated efficient mass transfer, enabling the effective degradation of dyes and pesticides.

Intrinsic Activity Identification of Noble Metal Single‐Sites for Electrocatalytic Chlorine Evolution

AbstractSingle‐atom catalysts with maximal atom‐utilization have emerged as promising alternatives for chlorine evolution reaction (CER) toward valuable Cl2 production. However, understanding their intrinsic CER activity has so far been plagued due to the lack of well‐defined atomic structure controlling. Herein, we prepare and identify a series of atomically dispersed noble metals (e.g., Pt, Ir, Ru) in nitrogen‐doped nanocarbons (M1−N−C) with an identical M−N4 moiety, which allows objective activity evaluation. Electrochemical experiments, operando Raman spectroscopy, and quasi‐in situ electron paramagnetic resonance spectroscopy analyses collectively reveal that all the three M1−N−C proceed the CER via a direct Cl‐mediated Vomer‐Heyrovský mechanism with reactivity following the trend of Pt1−N−C>Ir1−N−C>Ru1−N−C. Density functional theory (DFT) calculations reveal that this activity trend is governed by the binding strength of Cl*−Cl intermediate (ΔGCl*−Cl) on M−N4 sites (Pt<Ir<Ru) featuring distinct d‐band centers, providing a reliable thermodynamic descriptor for rational design of single metal sites toward Cl2 electrosynthesis.

Intrinsic Activity Identification of Noble Metal Single-Sites for Electrocatalytic Chlorine Evolution.

Single-atom catalysts with maximal atom-utilization have emerged as promising alternatives for chlorine evolution reaction (CER) toward valuable Cl2 production. However, understanding their intrinsic CER activity has so far been plagued due to the lack of well-defined atomic structure controlling. Herein, we prepare and identify a series of atomically dispersed noble metals (e.g., Pt, Ir, Ru) in nitrogen-doped nanocarbons (M1-N-C) with an identical M-N4 moiety, which allows objective activity evaluation. Electrochemical experiments, operando Raman spectroscopy, and quasi-in situ electron paramagnetic resonance spectroscopy analyses collectively reveal that all the three M1-N-C proceed the CER via a direct Cl-mediated Vomer-Heyrovský mechanism with reactivity following the trend of Pt1-N-C>Ir1-N-C>Ru1-N-C. Density functional theory (DFT) calculations reveal that this activity trend is governed by the binding strength of Cl*-Cl intermediate (ΔGCl*-Cl) on M-N4 sites (Pt<Ir<Ru) featuring distinct d-band centers, providing a reliable thermodynamic descriptor for rational design of single metal sites toward Cl2 electrosynthesis.

Scalable Ir-Doped NiFe2O4/TiO2 Heterojunction Anode for Decentralized Saline Wastewater Treatment and H2 Production

HighlightsIr-doped NiFe2O4 (NFI) spinel with TiO2 heterojunction overlayer brought about outstanding chlorine evolution reaction in circumneutral pH.Electroanalyses including operando X-ray absorption spectroscopy uncovered the active role of TiO2 for Cl− chemisorption.NFI/TiO2 anode boosted both NH4+-to-N2 conversion and H2 generation in wastewater, and the practical applicability was confirmed with scaled-up anodes and real wastewater.

Double-Shell Co3O4 with Rich Surface Octahedron Oxygen Vacancies for High-Selectivity Electrocatalytic Chlorine Evolution.

The development of non-noble-metal-based chlorine evolution reaction (CER) catalysts with excellent activity, kinetics, and selectivity is urgently needed but still remains a major challenge. In this study, a morphology self-evolving and surface octahedron oxygen-vacancy-generating strategy is applied at double-shell nanospheres to obtain the target hierarchical double-shell Co3O4 nanospheres with abundant surface oxygen vacancies (DS-Co3O4-OVs). The DS-Co3O4-OVs display an overpotential of only 52 mV to reach a current density of 10 mA cm-2 in which an excellent chlorine selectivity of 98.9-99.9% is attained, which is better than that of the commercial RuO2/IrO2. Furthermore, density functional theory calculations demonstrate that the involved oxygen vacancies can not only limit the lattice oxygen mechanism of the oxygen evolution reaction process but also significantly improve the kinetics of the Volmer step to enhance the CER performance. Meanwhile, the unique hierarchical double-shell nanospheres can enhance the mass feeding and promote the rate-determining step of the Krishtalik step chlorine gas desorption reaction for enhanced kinetics. The self-evolution of non-noble catalysts with surface octahedron vacancies and the related exploration of the CER mechanism may provide a novel design idea for CER catalysts.

Harnessing Iron Nitride Matrices through Incorporated Cu-Based Moieties for Chlorine Evolution Reaction

Harnessing Iron Nitride Matrices through Incorporated Cu-Based Moieties for Chlorine Evolution Reaction

Superhydrophilicity and superaerophobicity Ni/Ni3S4/1T-MoS2 for hydrazine-assisted seawater splitting

The overall hydrazine splitting (OHzS) is a promising strategy to achieve the efficient hydrogen production in seawater through replacing the slow kinetic oxygen evolution reaction (OER) and toxic chlorine evolution reaction (ClOR) by hydrazine oxidation (HzOR). We report an efficient bifunctional electrocatalyst of Ni/Ni3S4/1T-MoS2 on carbon cloth (Ni/Ni3S4/1T-MoS2/CC), which was formed from large layer spacing MoS2 and Ni3S4 with metal-Ni, and was applied as for both hydrogen evolution reaction (HER) and HzOR. The MoS2 had expanded interlayer spacing and showed 1T phase, with significantly improved conductivity and hydrophilicity, which promotes transfer process of reactants. Furthermore, the introduction of Ni/Ni3S4 on the 1T-MoS2 base surface leaded to superhydrophilic and superaerophobic properties, which makes it more conducive to the adsorption of H. The improvement of electrical conductivity induced the excellent HER and HzOR electrocatalytic properties of Ni/Ni3S4/1T-MoS2/CC, which showed an ultralow overpotential of 24 mV and working potential of 0 mV at a current density of 10 mA cm−2, respectively. Inspiringly, Ni/Ni3S4/1T-MoS2/CC also showed excellent performance in hydrazine-assisted alkaline seawater electrolysis, as well as solar panel powered electrolysis of seawater OHzS, therefore, exhibiting great potential for practical applications.

Renaissance of Chlorine Evolution Reaction: Emerging Theory and Catalytic Materials

Chlorine (Cl2) is one of the most important commodity chemicals that has found widespread utility in chemical industry. Most Cl2 is currently produced via the chlorine evolution reaction (CER) at the anode of chlor–alkali electrolyzers, for which precious group‐metal‐based mixed metal oxides (MMOs) have been used for more than half a century. However, MMOs suffer from the use of platinum‐group metals, which are costly and scarce, and the selectivity issue arises from the parasitic oxygen evolution reaction. Over the last decade, the field of CER catalysis has seen dramatic advances in both the theory and discovery of new catalysts. Theoretical approaches have enabled a fundamental understanding of CER mechanisms and provided catalyst design principles. The exploration of new materials has led to the discovery of CER catalysts other than MMOs, including non‐PGM‐based oxides, atomically dispersed single‐site catalysts, and organic molecules, with some of which following novel reaction pathways. This minireview provides an overview of the recent advances in CER electrocatalyst research and suggests future directions for this revitalized field.

Renaissance of Chlorine Evolution Reaction: Emerging Theory and Catalytic Materials.

Chlorine (Cl2) is one of the most important commodity chemicals that has found widespread utility in chemical industry. Most Cl2 is currently produced via the chlorine evolution reaction (CER) at the anode of chlor-alkali electrolyzers, for which platinum group-metal (PGM)-based mixed metal oxides (MMOs) have been used for more than half a century. However, MMOs suffer from the use of expensive and scarce PGMs and face selectivity problems due to the parasitic oxygen evolution reaction. Over the last decade, the field of CER catalysis has seen dramatic advances in both the theory and discovery of new catalysts. Theoretical approaches have enabled a fundamental understanding of CER mechanisms and provided catalyst design principles. The exploration of new materials has led to the discovery of CER catalysts other than MMOs, including non-PGM oxides, atomically dispersed single-site catalysts, and organic molecules, with some of which following novel reaction pathways. This minireview provides an overview of the recent advances in CER electrocatalyst research and suggests future directions for this revitalized field.

Tuning the sulfide interface of MnCo2O4-based nanostructures enables efficient water/seawater electrolysis

Hydrogen generation through water electrolysis is greatly dependent on the development of energy and time-efficient techniques to construct stable and active electrocatalysts for oxygen evolution reaction (OER). Currently, major research focuses on producing hydrogen through direct seawater electrolysis instead of fresh water to build a sustainable society. However, competitive reactions such as chlorine evolution reaction (CIER) beyond OER and electrode erosion issues make seawater electrolysis more difficult. Here, we report an interfacial engineering strategy that constructs a MnCo2O4@CoS hybrid structure by sulfurization of the spinal MnCo2O4 nanowires. The hybrid structure demonstrates an excellent OER performance in electrolytes containing alkaline and saltwater. Specifically, the prepared catalyst needs overpotentials of 205 mV and 225 mV to deliver a current density of 10 mA cm−2 in 1 M KOH and alkaline seawater when used as OER electrocatalysts. This should be noted that the CoS layer on the surface of MnCo2O4 nanowires not only acts as a Cl‾ protective layer to impede electrode erosion and CIER but also provides metallic ions with a higher valence state to enhance the intrinsic catalytic activity of water oxidization. Thus, this type of electrocatalyst could represent a favorable choice, carrying substantial implications for hydrogen-based economies and environmental enhancement.

Coordination Environment and Distance Optimization of Dual Single Atoms on Fluorine-Doped Carbon Nanotubes for Chlorine Evolution Reaction.

The chlorine evolution reaction (CER) is a crucial anode reaction in the chlor-alkali industrial process. Precious metal-based dimensionally stable anodes (DSAs) are commonly used as catalysts for CER but are constrained by their high cost and low selectivity. Herein, a Pt dual singe-atom catalyst (DSAC) dispersed on fluorine-doped carbon nanotubes (F-CNTs) is designed for an efficient and robust CER process. The prepared Pt DSAC demonstrates excellent CER activity with a low overpotential of 21 mV to achieve a current density of 10 mA cm-2 and a remarkable mass activity of 3802.6 A gpt-1 at an overpotential around 30 mV, outperforming those of commercial DSA and Pt single-atom catalysts. The excellent CER performance of Pt DSAC is attributed to the high atomic utilization and improved intrinsic activity. Notably, introducing fluorine atoms on CNTs increases the oxidation and chlorination resistance of Pt DSAC, and reduces the demetalization ratio of Pt atoms, resulting in excellent long-term CER stability. Theoretical calculations reveal that several Pt DSAC configurations with optimized first-shell ligands and interatomic distance display lower energy barriers for Cl intermediates generation and weaker ionic Pt-Cl bond interaction, which are favorable for the CER process.

Coordination Environment and Distance Optimization of Dual Single Atoms on Fluorine‐Doped Carbon Nanotubes for Chlorine Evolution Reaction

AbstractThe chlorine evolution reaction (CER) is a crucial anode reaction in the chlor‐alkali industrial process. Precious metal‐based dimensionally stable anodes (DSA) are commonly used as catalysts for CER but are constrained by their high cost and low selectivity. Herein, a Pt dual singe‐atom catalyst (DSAC) dispersed on fluorine‐doped carbon nanotubes (F‐CNTs) is designed for an efficient and robust CER process. The prepared Pt DSAC demonstrates excellent CER activity with a low overpotential of 21 mV to achieve a current density of 10 mA cm−2 and a remarkable mass activity of 3802.6 A gpt−1 at an overpotential around 30 mV, outperforming those of commercial DSA and Pt single‐atom catalyst. The excellent CER performance of Pt DSAC is attributed to the high atomic utilization and improved intrinsic activity. Notably, introducing fluorine atoms on CNTs increases the oxidation and chlorination resistance of Pt DSAC, and reduces the demetalization ratio of Pt atoms, resulting in excellent long‐term CER stability. Theoretical calculations reveal that several Pt DSAC configurations with optimized first‐shell ligands and interatomic distance display lower energy barriers for Cl intermediates generation and weaker ionic Pt−Cl bond interaction, which are favorable for the CER process.

Enhanced electrolytic production of hypochlorous acid using phosphorus-modified carbon felt electrodes: A study in disinfectant synthesis

In this study, we fabricated phosphorus-modified carbon felt electrode anodes for chloride oxidation in saline solutions to produce HClO via electrocatalysis, forming a compound fungicide saline applicable for debridement and disinfection. A low-cost phosphorus-modified carbon felt electrode (P@CF) with high chlorine evolution reaction activity was synthesized to address the reduced efficiency of CER and the solution's pH increase. Heteroatoms P and O were introduced into the carbon felt by phosphoric acid activation followed by heat treatment. The maximum active chlorine concentration on the P@CF electrode could reach 616.8 mg/L in 60 min under the optimal synthesis conditions of a phosphoric acid mass fraction of 30%, a phosphoric acid impregnation time of 3 h, and a heat treatment temperature of 300 °C. The active chlorine concentration was 1.8 times higher on the P@CF electrode compared to the original carbon felt electrode. The optimal reaction conditions for the generation of active chlorine were as follows: salt concentration of 9 g/L, voltage of 7 V, and electrode spacing of 2 cm as verified by response surfaces. This electrolysis reaction follows one-stage reaction kinetics. Subsequently, the disinfection efficacy of the produced disinfectants was examined. The prepared disinfectant was also compared to a commercially available hypochlorite disinfectant, showing similar disinfection effects on E. coli for both.

Rapid electrodeposition synthesis of partially phosphorylated cobalt iron phosphate for application in seawater overall electrolysis

To obtain hydrogen energy from seawater, it is of utmost importance to design an efficient bifunctional electrocatalyst that can be produced on a large scale and in a rapid manner. In this work, iron cobalt phosphate (CoFe-EP/NF) for long-term efficient and stable seawater electrolysis were rapidly synthesized by a simple electrodeposition. The study showed that metal phosphides/phosphates provided additional active sites for the catalysts for hydrogen evolution reaction (HER, 160 mV at 100 mA/cm2) and oxygen evolution reaction (OER, 266 mV at 100 mA/cm2), in alkaline seawater electrolyte (1 M KOH + seawater), respectively. Notably, the presence of phosphate groups facilitates the transformation of cobalt-iron metal phosphates into the truly reactive substance CoOOH, which improves the OER kinetics. In addition, the phosphate layer formed after catalyst activation avoids the occurrence of chlorine evolution reaction (CER) by shielding the adsorption of Cl−, thus enhancing the corrosion resistance and enabling long-term stable operation in seawater. The two-electrode overall seawater electrolysis easily reaches 100 mA/cm2 at 1.68 V and exhibit a long-term durability of more than 100 h. This study offers a viable approach for the synthesis of electrocatalysts with high activity and corrosion resistance, which is vital for the practical realization of large-scale seawater electrolysis.

Photoelectrochemical Synthesis of Hydrogen Peroxide from Saline Water via the Two-Electron Water Oxidation Reaction.

Hydrogen peroxide (H2O2) production on the anode is more valuable than oxygen and chlorine evolution for photoelectrochemical saline water splitting. In this work, by the introduction of bicarbonate (HCO3-), H2O2 is produced from saline water (2 M KHCO3 + 0.5 M NaCl aqueous solution) via the two-electron water oxidation reaction by a photoanode of bismuth vanadate (BiVO4). Furthermore, the Faradaic efficiency (FE) and accumulation for H2O2 are improved by coating antimony tetroxide (Sb2O4) on BiVO4. A H2O2 FE of 26% at 1.54 V vs RHE is obtained by Sb2O4/BiVO4 and 49 ppm of H2O2 is accumulated after a 135 min chronoamperometry. Similar to that in KHCO3 pure water solution, infrared spectroscopy and electrochemical analysis confirm that HCO3- plays a surface-mediating role in the formation of H2O2 in KHCO3 saline water solution. The presence of HCO3- in the electrolyte is able to not only increase the photocurrent density but also effectively inhibit the chlorine evolution reaction.