Chlorine Evolution Research Articles

(Keynote) Competition of Oxygen and Chlorine Evolution on Oxide Surfaces – a Soft X-Ray and Dems Approach to Identification of Active Site

Anodic gas evolving reactions, e.g. oxygen evolution and chlorine evolution, are of fundamental importance both in energy storage as well as in electrolytic production of chemicals. Both reactions are of electrocatalytic nature, proceed in the same potential range and are catalyzed by the same types of electrode materials. While the oxygen evolution is thermodynamically favored the two electron chlorine evolution is kinetically preferred, namely at acid and neutral pH. This kinetic preference is industrially explored in chlor-alkali processes as well in chlorate electrolysis. The growing interest in electrolytic hydrogen production fueled by the popularity of the hydrogen as the likely replacement of fossil fuels brings up the question of the tolerance of the industrial anodes to presence of chlorides in the water intended for electrolytic hydrogen production. Such a tolerance can be best achieved by steering the selectivity of the anode between oxygen and chlorine evolution aiming eventually at the possibility of the sea water use in hydrogen producing water electrolysis. So far existing attempts at control the anode selectivity in presence of chlorides explore two principal approaches – pH control and surface engineering. While the pH related approach is rationalized by different pH sensitivity of each of the competing reaction the surface engineering related activities so far rely on trial and error approach. Qualitatively the selectivity may be controlled by either selectively promoting/suppressing each of the contributing reactions. While the literature lists attempts when the overall selectivity towards OER is apparently achieved by selective suppression of CER [1] more recent reports suggest that the actual selectivity is in fact controlled by the ability of the catalysts to support a lattice oxygen activating mechanism of the oxygen evolution process [2]. While these assignments are based on correlation of selectivity measurements with local structure and DFT modelling and a direct evidence of such a behavior is so far missing. This paper will document here the capability of the real-time and operando soft X-ray absorption spectroscopy [3] to provide this missing evidence. Anodic behavior of two type of ruthenium oxide electrodes in chloride free and chloride containing solutions will be documented by comparison of the nature and potential dependent population of the oxygen related intermediates formed at anode surface in the potential range of oxygen and chlorine evolution in acid media (pH=1) and combined with DEMS data to identify the active sites for each contributing electrode reaction.

Anisotropic Lens-Shaped Mesoporous Carbon with Bifunctional Dual Metal Single Atom Electrocatalyst for Na Seawater Battery

Seawater is a promising electrolyte that can replace conventional distilled water-based electrolytes in that they are affordable and abundant. In the Na seawater battery, oxygen evolution reaction and oxygen reduction reaction occur in a single electrode during the charge and discharge process respectively. To obtain high energy efficiency of the Na-seawater battery, both oxygen electrocatalytic activity should be improved. In addition, the electrochemical reaction occurring in natural seawater may be hindered by chlorine ions. Side reactions such as chlorine evolution reaction or poisoning of electrocatalyst may occur during the charge/discharge process. In this study, dual metal single atom (DSA) loaded anisotropic lens-shaped mesoporous carbon is prepared for an electrode material in a Na-seawater battery. The DSA loaded anisotropic lens-shaped mesoporous carbon is synthesized by polymer interfacial self-assembly of block copolymer (BCP, Poly(ethylene oxide)-b-polystyrene, PEO-b-PS) and immiscible homopolymer (Poly(methyl methacrylate), PMMA). During the self-assembly, pre-dissolved inorganic precursors assemble with BCPs constructing the ordered mesoporous structure. Followed by proper carbonization and chemical etching, DSA loaded anisotropic lens-shaped mesoporous carbon is prepared. Using the natural seawater, the half-cell performance on the rotating disk electrode (RDE) of DSA (Fe-Nx/Co-Nx) loaded mesoporous carbon shows the lower potential difference (EOER-EORR) than a single atom (Fe-Nx) loaded mesoporous carbon, commercial Pt/C (20 wt%) and commercial Ir/IrO catalyst. Based on the RDE result, electrocatalyst performance in seawater half-cell (Na || Seawater) exhibits a concordant result. In addition to the electrochemical results, the performance of the DSA electrocatalyst is confirmed by comparing the activities of chlorine and oxygen species on DSA model through density functional theory calculation.

Hydrogen Production with Seawater-Resilient Bipolar-Membrane Electrolyzers

Commercial proton exchange membrane water electrolyzers (PEMWEs) are highly efficient when operating in ultra-pure de-ionized water. However, introduction of additional ions leads to a reduction in device durability and efficiency. Chloride (Cl-) ions, typically found in high concentrations in seawater, lead to device performance issues driven in part by the chlorine evolution reaction at the anode. At the acidic anode-cation exchange layer interface, corrosive chlorine species (OCl-, HOCl, Cl-) are readily generated due to the facile kinetics of the 2-electron oxidation reaction relative to the desired 4-electron water oxidation reaction. Bipolar membrane water electrolyzers (BPMWEs), however, contain a locally basic anode-anion exchange layer interface, leading to improved thermodynamic favorability for O2 production rather than corrosive chlorine species production. Furthermore, the bipolar membrane can readily block anions and cations from accessing the desired reaction spaces. In this work, we evaluated ion transport, chloride oxidation, and durability of BPMWEs and PEMWEs operating in salt water. BPMWEs exhibit a low Faradaic efficiency of 0.005% for the oxidation of Cl− to corrosive chlorine species at the anode, compared to PEMWEs that can reach a Faradaic efficiency of up to 10% under similar conditions. In addition, BPMWEs demonstrate a device lifetime that is 140 times longer than that of PEMWEs operating in direct seawater electrolysis conditions. Failure modes for each membrane type have been investigated under both ultra-pure and impure water electrolysis conditions and are discussed in this work.

Investigation of the Impact of Chloride Contamination on Degradation in PEM Water Electrolyzer Cells

Polymer electrolyte membrane water electrolysis (PEMWE) is a promising technology for hydrogen production from renewable energy sources. However, current systems require ultra-pure water (>18 MΩ*cm) and fail in the presence of impurities like dissolved ions or chemical contaminants [1,2]. Due to the cost of purification and local scarcity of groundwater, there is a rising interest in creating electrolyzers that can function using water of inferior quality [3]. Additionally, feedwater used in offshore applications that is generated by the desalination of seawater still contains low amounts of ionic contaminants [4].Among the most detrimental impurities responsible for performance loss in PEMWE, Cl− is present in high concentrations in both, sea- and potable water [3]. Cl− can reduce the efficiency of the electrolysis process by accelerating component degradation and lower the purity of the produced hydrogen. A competing reaction between the oxygen evolution reaction (OER) and the chlorine evolution reaction (CER) results in the formation of gaseous chlorine that lowers the quality of the produced hydrogen gas. Additionally, Cl− blocking layers can form on the catalyst surfaces which result in a reduced electrochemical surface area. For PEM fuel cells, a technology facing related problems, Cl− adsorption has also been reported to accelerate the formation of hydrogen peroxide [5], promoting chemical degradation of the PFSA-based membrane.The scope of this work is to quantify the reduction of efficiency based on different Cl− concentrations in the feedwater of a PEMWE cell. Therefore, a single cell PEMWE with commercial catalyst coated membranes (CCMs) is exposed to different concentrations of Cl−. The PEMWE single cell is operated up to 100 h and investigated by various characterization techniques, including in-situ and ex-situ cell tests. Electrochemical performance characterization by means of polarization behaviour and impedance spectroscopy is carried out throughout a range of currents (0.01 A cm− 2 to 3.0 A cm− 2) at 60°C. Furthermore, the fluoride emission rate (FER) is monitored during the experiments and optical investigation of the CCMs is carried out after the tests. Based on this complementary investigation, a deeper insight into degradation phenomena associated with Cl− contamination in PEMWE cells is presented. Feng, Q.; Yuan, X.; Liu, G.; Wei, B.; Zhang, Z.; Li, H.; Wang, H. A Review of Proton Exchange Membrane Water Electrolysis on Degradation Mechanisms and Mitigation Strategies. Journal of Power Sources 2017, 366, 33–55, doi:10.1016/j.jpowsour.2017.09.006.Kuhnert, E.; Hacker, V.; Bodner, M. A Review of Accelerated Stress Tests for Enhancing MEA Durability in PEM Water Electrolysis Cells. International Journal of Energy Research 2023, 2023, 1–23, doi:10.1155/2023/3183108.Becker, H.; Murawski, J.; Shinde, D.V.; Stephens, I.E.L.; Hinds, G.; Smith, G. Impact of Impurities on Water Electrolysis: A Review. Sustainable Energy Fuels 2023, 7, 1565–1603, doi:10.1039/D2SE01517J.Bacquart, T.; Moore, N.; Wilmot, R.; Bartlett, S.; Morris, A.S.O.; Olden, J.; Becker, H.; Aarhaug, T.A.; Germe, S.; Riot, P.; et al. Hydrogen for Maritime Application—Quality of Hydrogen Generated Onboard Ship by Electrolysis of Purified Seawater. Processes 2021, 9, 1252, doi:10.3390/pr9071252.Katsounaros, I.; Meier, J.C.; Mayrhofer, K.J.J. The Impact of Chloride Ions and the Catalyst Loading on the Reduction of H2O2 on High-Surface-Area Platinum Catalysts. Electrochimica Acta 2013, 110, 790–795, doi:10.1016/j.electacta.2013.03.156.

In Situ Investigation on Cl- Repellency Effect of Electrolyte Additive on NiOOH for Alkaline Sea Water Splitting

Sea water splitting can produce green hydrogen by feeding abundant sea water directly without high-qualified water purification process. However, excess cation such as Mg2+ and Ca2+ in sea water absorbs on the cathode surface, and it causes the loss of active site and activity toward hydrogen evolution reaction. At the anode side, oxygen evolution reaction (OER) should be competed with chlorine evolution reaction due to huge amount of Cl- ion, so operating in high pH electrolyte at low overpotential has been suggested to increase the selectivity toward OER. To further inhibit the adsorption of Cl-, some researchers have suggested using anion additive such as PO4 3- and SO4 2- in the alkaline electrolyte, but both adsorption stability of additive anion and the interaction between anion and metal oxide catalyst are still needed to be studied.In this study, we investigated the Cl- repellency effect of additive anion in the electrolyte to NiOOH catalyst, known as state-of-the-art OER catalyst, for alkaline sea water splitting. To observe the change in adsorbate species by additive anion, we tracked the mass change of the catalyst during the reaction through in situ electrochemical quartz crystal microbalance (EQCM). Furthermore, Cl- can change (degrade) the NiOOH structure by formation of metal-chloride complex. Through in situ Raman spectroscopy, we observed the structural stability of NiOOH in presence of anion additive as well as the adsorption stability of additive anion depending on the applied potential.

Effect of pH on the Selectivity of γ-MnO2 Electrocatalysts Towards Oxygen Evolution Reaction in the Presence of Chloride Ions in Alkaline Environment

Pt-Nb anodes utilized in the cathodic protection system onboard of Naval ships generate NaOCl (and eventually Cl2) that (1) limits the materials that can be used in the vicinity of the anodes and (2) has a severe impact on living organisms in the marine environment. The environmentally-friendly oxygen evolution reaction (OER) from H2O is thermodynamically more favorable due to a lower equilibrium potential [1]. However, chlorine evolution successfully competes with the OER due to faster kinetics. One of a few catalysts that demonstrates high selectivity towards the OER in the presence of chloride ions in alkaline environment (pH 12) is g-MnO2 [2]. In this presentation, we will (1) compare activities and selectivities towards the OER of electrodeposited and chemically synthesized g-MnO2 and (2) determine how pH affects selectivity in the pH range from 8 to 12.

Unveiling the geometric site dependent activity of spinel Co3O4 for electrocatalytic chlorine evolution reaction

Spinel cobalt oxide (Co3O4), consisting of tetrahedral Co2+ (CoTd) and octahedral Co3+ (CoOh), is considered as promising earth-abundant electrocatalyst for chlorine evolution reaction (CER). Identifying the catalytic contribution of geometric Co site in the electrocatalytic CER plays a pivotal role to precisely modulate electronic configuration of active Co sites to boost CER. Herein, combining density functional theory calculations and experiment results assisted with operando analysis, we found that the CoOh site acts as the main active site for CER in spinel Co3O4, which shows better Cl− adsorption and more moderate intermediate adsorption toward CER than CoTd site, and does not undergo redox transition under CER condition at applied potentials. Guided by above findings, the oxygen vacancies were further introduced into the Co3O4 to precisely manipulate the electronic configuration of CoOh to boost Cl− adsorption and optimize the reaction path of CER and thus to enhance the intrinsic CER activity significantly. Our work figures out the importance of geometric configuration dependent CER activity, shedding light on the rational design of advanced electrocatalysts from geometric configuration optimization at the atomic level.

Enhancing Ru−Cl interaction via orbital hybridization effect in Ru0.4Sn0.3Ti0.3 electrode for efficient chlorine evolution

Chlorine evolution reaction (CER) is a commercially valuable electrochemical reaction used at an industrial scale. However, oxygen evolution reaction (OER) during the electrolysis process inevitably leads to the decreased efficiency of CER. It is necessary to improve the selectivity of CER by minimizing or even eliminating the occurrence of OER. Herein, a ternary metal oxide (Ru0.4Sn0.3Ti0.3) electrode was fabricated and employed as an active and robust anode for CER. The Ru0.4Sn0.3Ti0.3 electrode exhibits an excellent CER performance in 6.0 M NaCl solution, with a low potential of 1.17 V (vs. saturated calomel electrode, SCE) at 200 mA cm−2 current density, a high Cl2 selectivity of over 90 %, and robust durability after consecutive operation for 160 h under 100 mA cm−2. The maximum O2-Cl2 potential difference between OER and CER further demonstrates the high Cl2 selectivity of Ru0.4Sn0.3Ti0.3 electrode. Theoretical studies show that the strong Ru 3d−Ti 3d orbitals hybridization effect makes the d-band center (εd) of Ru 3d and Ti 3d orbitals positively and negatively shifted, respectively, endowing Ru site with enhanced Cl adsorption ability (i.e. enhanced Ru−Cl interaction) and Ru0.4Sn0.3Ti0.3 electrode with superior CER activity. This work offers valuable insights into the development of advanced electrodes for CER in practical application.

Evolution and speciation transformation of chlorine during automobile shredder residue pyrolysis

Disposal of automobile shredder residue (ASR) via pyrolysis enables the recovery of valuable products; however, the production of hazardous pollutants and low-value products is inevitable due to its high chlorine content. In this work, chlorine evolution behavior and the conversion mechanism during ASR pyrolysis between 480 and 600 °C were systematically studied. The experimental results for organic chlorine (Org-Cl) showed that released chlorinated gases were complex, and HCl only accounted for 35% of the gas phase products, while short-chain hydrocarbons with carbon atoms between two and four accounted for 52%. Chlorine was predominantly retained in the char, and Org-Cl was the primary contributor to the residual chlorine, accounting for over 50% of the char. The content of inorganic chlorine (InO-Cl) was low in the raw sample but significantly increased in the char. Through the distinction between organic and inorganic chlorine content in char, it was confirmed that Org-Cl could be converted to InO-Cl due to complex secondary reactions with metallic compounds. The conversion was favored by increasing the Org-Cl content and the temperature. Our findings clarified the evolution mechanism of chlorine and the transformation from Org-Cl to InO-Cl, thus providing guidance for chlorine regulation and the efficient recycling of metal resources.

Materials Design and System Innovation for Direct and Indirect Seawater Electrolysis.

Green hydrogen production from renewably powered water electrolysis is considered as an ideal approach to decarbonizing the energy and industry sectors. Given the high-cost supply of ultra-high-purity water, as well as the mismatched distribution of water sources and renewable energies, combining seawater electrolysis with coastal solar/offshore wind power is attracting increasing interest for large-scale green hydrogen production. However, various impurities in seawater lead to corrosive and toxic halides, hydroxide precipitation, and physical blocking, which will significantly degrade catalysts, electrodes, and membranes, thus shortening the stable service life of electrolyzers. To accelerate the development of seawater electrolysis, it is crucial to widen the working potential gap between oxygen evolution and chlorine evolution reactions and develop flexible and highly efficient seawater purification technologies. In this review, we comprehensively discuss present challenges, research efforts, and design principles for direct/indirect seawater electrolysis from the aspects of materials engineering and system innovation. Further opportunities in developing efficient and stable catalysts, advanced membranes, and integrated electrolyzers are highlighted for green hydrogen production from both seawater and low-grade water sources.

Design of CoSbyOx/Ti electrocatalyst via facile thermal decomposition method for durable and high temperature chlorine evolution reaction in acidic media

Developing stable and cost-effective electrodes for the anode compartment of chlor-alkali process to drive the chlorine evolution reaction (CER) has remained as a challenge. This study introduces CoSbyOx/Ti as a durable and non-precious anode electrocatalyst synthesized via facile and scalable thermal decomposition method. This novel electrode permanently conducts CER for 240 h under 100 mA.cm−2 at 70 °C in 4 M NaCl (pH=2) with an overpotential of only 498 mV and a high selectivity of 92.2 % toward CER. From XRD results, crystalline CoSb2O6 forms above 600 °C and acts as active and stable phase during CER. From XPS analysis, a combination of Co3+ and Co2+ forms on the surface of the electrode; the content of Co3+ species increases after CER which can reduce structural defects and hence improve the stability of the structure. We further shed more light on the degradation mechanism of this type of electrodes by performing additional 240 h durability test under accelerated condition of 1000 mA.cm−2. Observations indicate a failure mechanism that is probably a combination of deactivation of the electrode and catalyst detachment in accelerated conditions.

Iron and phosphorus dual-doped NiMoO4 with nanorod structure as efficient oxygen evolution catalyst in alkaline seawater

Hydrogen production by electrolysis of seawater is more in line with the new era of green chemistry than electrolysis of freshwater, but the high cost and the accompanying chlorine evolution hinder the development of the process. In this study, the growth of transition metal elements Fe as well as P double-doped NiMoO4 with nanorod-like nanostructures on Ni foam (Fe/P–NiMoO4@NF) is feasible. The optimized Fe/P–NiMoO4@NF material exposes more active sites, which exhibits excellent oxygen evolution reaction (OER) activity in alkaline seawater. At a current density of 10 mA cm−2, the operating potential is only 1.35 V and operating potential of 1.54 V at 100 mA cm−2 is obtained with Tafel slopes as small as 13.16 mV dec−1. The enhanced activity is attributed to the exposure of more active sites and faster charge transfer due to double doping of Fe and P. And the catalyst exhibited relatively good durability, which could be maintained at 50 mA cm−2 for 24 h at a constant voltage of 1.60 V without IR-compensation. The experiment result shows that the doped P smoothly covers on the surface the catalyst, making the surface metal compound on the nickel foam is resistant to seawater corrosion. Density Functional Theory (DFT) shows that double doping of Fe and P can increase the electron transfer rate and enhance the adsorption energy of water. This work provides a new and simple double doping strategy for the development of high-performance catalysts with controllable morphology for seawater splitting.

Ruthenium Oxide Clusters Immobilized in Cationic Vacancies of 2D Titanium Oxide for Chlorine Evolution Reaction

The development of dimensionally stable anodes (DSAs) has made the chlorine evolution reaction (CER) the most important industrial anode reaction since the 1960s. However, the preparation of DSA depends on the extensive use of precious metals, Ru and Ir, which are expensive and scarce. Herein, a cationic defect adsorption–oxidation anchoring strategy to immobilize oxidized sub‐nano ruthenium clusters on 2D low‐crystallinity titanium oxide (2D TiOx) substrate is reported. Through the metal oxide−support interaction, the 2D TiOx alters the electronic structure of ruthenium oxide (RuOx), improving its activity, selectivity, and stability for CER. Specifically, the mass activity of the RuOx/2D TiOx electrode is 26.5 and 143.5 times higher than that of the state‐of‐the‐art commercial RuO2 and DSA, respectively, at an overpotential of 100 mV. Moreover, the selectivity of the RuOx/2D TiOx electrode to CER is approximately 96.5%, and it exhibits remarkable durability lasting for over 210 h. Therefore, the 2D TiOx substrate holds significant potential for improving the dispersion, active site density, and atomic utilization of oxidized sub‐nano noble metal clusters.

Interstitial atom-doped NiFe alloy as pre-catalysts boost direct seawater oxygen evolution

NiFe-based materials are excellent OER electrocatalysts. However, it is difficult to stabilize anions and cations during reconstruction, which also leads to the problem of high valence metals at low levels and poor stability in direct seawater. Herein, we propose the strategy of using interstitial P atom-doped NiFe alloys (P4.8-NiFe ANs-400) as pre-catalysts to stabilize anions and cations, thereby promoting the formation of abundant high-valent metal species and excellent activity and stability in direct seawater. The reconstructed P4.8-NiFe ANs-400 catalyst generates a large amount of high-valence transition metal Ni4+, which contributed to its low overpotential (214 mV) and long-term stability (100 h) in a seawater electrolyte at 100 mA cm−2. Experiments and theoretical calculations show that the interstitially doped P atoms share the charge around the Fe and the active Ni sites, optimizing the free energy of the OER intermediate and making the chlorine evolution reaction (CER) difficult to proceed.

Ru rich Ru-Mn-O phases for selective suppression of chlorine evolution in sea water electrolysis

Limits of steering selectively gas evolving reaction on Ru rich oxide phases in Ru-Mn-O system were investigated by combined theoretical and experimental approach. Ru1-xMnxO2 materials of single phase nature conforming to the rutile structure were prepared by the spray freeze - freeze drying approach and tested for activity in oxygen and chlorine evolution reactions. The overall electrocatalytic activity of the prepared materials increases with increasing Mn content. In this manner also increases the selectivity towards oxygen evolution in acidic chloride containing solutions. Closer analysis shows that the amount of evolved oxygen (for a given electrode material) is practically independent of the chloride concentration. This is illustrated by the order of the oxygen evolution reaction with respect to chloride concentration being close to 0 in the whole range of the prepared Ru-Mn-O phases. The high selectivity towards oxygen evolution reaction coincides with low tendency of Ru-Mn-O phases to evolve oxygen via lattice oxygen activation (LOER). The experimental behavior is further confirmed by DFT analysis of the reactivity of the Ru-Mn-O surfaces.

The electrochemical kinetics of chloride oxidation over multi-metallic Pt-Ni-Co electrodes affected by metal deposition method and electrode support

Platinum, nickel, and cobalt oxides were coated on different electrode supports (graphite, stainless steel mesh, Ti foil and Ni form) by multistep electrode deposition method. Scanning electron microscopy, X-Ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammetry and linear sweep voltammetry were used to characterize electrodes. Results showed that the deposition process, such as applied current and deposition time, and the substrates influenced electrode morphology and electrochemical chlorine generation capability. Porous structure and Co3O4 crystalline could promote chloride oxidation on electrode surface. Graphite substrate exhibited the benefit of chloride oxidation and 0.6A × 20 s× 30 is the optimal deposition condition for electrode fabrication. The 0.6A × 20 s× 30-G electrode has the lowest chlorine evolution potential, largest difference in water oxidation and chloride oxidation potential, and the smallest transfer coefficient (α), meaning that this electrode is more favorable to chloride oxidation than other electrodes. Moreover, a mechanism of chlorine generation has been proposed in this study, indicating that chlorine radicals were formed on electrode surface. The high chlorine generation capability and good durability of Pt-Ni-Co-G electrode has the potential for application in water treatment process, such as disinfection and inorganic or organic pollutants decontamination.

Treatment of aniline-containing wastewater by electrochemical oxidation using Ti/RuO2 anode: the influence of process parameters and reaction mechanism.

Aniline detected in many industrial wastewater is a refractive organic pollutant with strong biological toxicity to aquatic organisms and humans. In this research, electrochemical oxidation process with Ti/RuO2 as the anode has been used to degrade aniline-containing wastewater on a laboratory scale. The influence of anode materials, electrolyte, NaCl concentration, current density, and aniline initial concentration on COD removal, ICE, and Ep were studied. The results showed that Cl- addition in the electrolyte is essential to promote aniline degradation efficiency and avoid the anode being passivated. Furthermore, decreasing the current density, increasing Cl- concentration, and initial aniline concentration are beneficial to increase current efficiency and reduce energy consumption. Although the addition of SO42- has a restriction on the active chlorine evolution process, the conductivity increased, which resulted in the reduction of energy consumption. At last, the aniline degradation mechanism in the presence of chloride ions was summed up and proposed based on the literature.

Facilitating Electrochemical Ozone Production and Chlorine Evolution Reaction by Synergistic Effect of Multicomponent Metal Oxides

AbstractThe concomitant degradation of organic contaminants using green oxidants, NaClO and O3, exhibits great potential to mitigate the deleterious impact of organic pollutants. In this work, the electrochemical ozone production (EOP) and chlorine evolution reaction (CER) performed by highly active electrocatalysts composed of Ce‐Ni‐Sb‐SnO2 and Ru‐Ir‐Ce‐Ni‐Sb‐SnO2, respectively, are presented. Ce‐Ni‐Sb‐SnO2 exhibits high selectivity with a 43.9% Faraday efficiency in EOP. Incorporating Ru and Ir in Ru‐Ir‐Ce‐Ni‐Sb‐SnO2 improves CER performance, achieving outstanding Faraday efficiency of up to 98.3%. Additionally, it achieves a low overpotential of ≈80 mV at 10 mA cm−2 with 0.3 m NaCl (pH = 6). Theoretical calculations reveal the significant impact of multicomponent oxides on reaction intermediate adsorption. Ce, Ni, Sb doping on SnO2 enhances O2 and O3 adsorption for optimal EOP performance, while Ru and Ir doping on Ce‐Ni‐Sb‐SnO2 enhances Cl adsorption, boosting CER performance. Further investigations into the decomposition of pesticides and antibiotics demonstrate that the collaborative impact of O3 and NaClO elicits a significantly more robust kinetic degradation rate in comparison to their individual influences. This work aims to shed light on the synthesis of multicomponent metal oxides as potential precursors for the cost‐effective preparation of O3 and NaClO for electrochemical advanced oxidation processes.

Ru-Doped Co3O4 Nanoparticles as Efficient and Stable Electrocatalysts for the Chlorine Evolution Reaction.

The electrochemical chlorine evolution reaction (CER) is one of the most important electrochemical reactions. Typically, iridium (Ir)- or ruthenium (Ru)-based mixed metal oxides have been used as electrocatalysts for the CER due to their high activities and durabilities. However, the scarcity of Ir and Ru has indicated the need to develop alternative earth-abundant transition-metal-based CER catalysts. In this study, we report a Co3O4 nanoparticle (NP) catalyst synthesized by a hydrothermal method. Furthermore, Ru was successfully incorporated into the Co3O4 NPs (RuxCo3-xO4 NPs) for further improvement of catalytic performance in chlorine generation. Electrokinetic analyses combined with in situ X-ray absorption near-edge structure (XANES) results suggested an identical CER mechanism for the Co3O4 NPs and RuxCo3-xO4 NPs. Various characterization techniques demonstrated that the homogeneous substitution of Ru4+ ions into the Co3+ octahedral sites enhanced the structural disorder and changed the electronic state of Co3O4, resulting in additional exposed active sites. Remarkably, the Ru0.09Co2.91O4 NP electrode exhibited outstanding stability for more than 150 h even at a high current density of 500 mA/cm2, which shows its commercial viability for active chlorine generation.

Membrane fouling mitigation and EPS reduction by CNTs-TiO2-PEDOT modified anode-membrane in Membrane Electro-Bioreactor (MEBR) treating mariculture wastewater

Membrane Electro-Bioreactor (MEBR), with dual function of electrochemical in-situ membrane fouling mitigation and pollutants removal by chlorine evolution reaction (CIER), has emerged as a promising technology of treating mariculture wastewater. However, the fouling control mechanism regarding extracellular polymeric substance (EPS) variations and related microbial community is still unclear. In this study, MEBR was developed with conducting anode-membrane modified by CNTs-TiO2-PEDOT for fouling resistant and ammonia/nitrite removal. The CIER electroactivity was enhanced that onset potential negatively shifted from 1.12 to 0.98 V vs. SCE (saturated calomel electrode). Ammonia removal rate (71.49 mgN/(L·day)) was 176.8 % higher and nitrite was significantly reduced in MEBR than MBR at HRT of 45 min. Membrane fouling was mitigated in MEBR that operation duration was extended by 40 % compared with MBR. The EPS of cake layer on the membrane surface rather than the biofilters was found the main fouling contributor. The significant reduction in LB-EPSp (65.4 %) in MEBR (33.8 % in MBR) was the dominant factor contributing to membrane fouling alleviation, which highly depended on the relative abundance of Hyphomonas and Hirschia. This study will be beneficial for fouling control in seawater treatment.