Chlorine Evolution Research Articles

Chlorine evolution and char characteristics during pyrolysis upgrading of Xinjiang high chlorine coal

Xinjiang ShaErHu (SEH) coal, characterized by a high chlorine concentration exceeding 1 %, can cause severe chlorine corrosion when directly burned. To utilize this high-chlorine coal in an effective and clean way, specific pretreatments such as low-temperature pyrolysis upgrading are required. In this paper, the changes in tar, pyrolysis gas, combustion characteristics, and chlorine evolution features were analyzed during the low-temperature pyrolysis of SEH coal. The effects of increasing temperature (350 °C, 450 °C, and 550 °C) were studied. The results show that the proportion of aromatic compounds released consistently increases with temperature, reaching a peak of 80 % at 550 °C in the tar. It is noteworthy that chlorine is hardly detected in tar. The percentage of chlorine released in the pyrolysis gas remains relatively stable as the temperature rises from 350 °C to 550 °C, accounting for approximately 17.5 % of the total chlorine. The percentages of water-soluble chlorine in raw coal, char-350 °C, char-450 °C and char-550 °C are 74.3 %, 80.4 %, 82.2 %, and 55.1 % respectively. The majority of the chlorine in the char produced at 350 °C and 450 °C is inorganic, making up 68.9 % and 69.4 %, respectively. In contrast, char generated at 550 °C has 58.4 % chlorine that is primarily organic. About 40 % of the inorganic chlorine is converted to organic chlorine when the pyrolysis temperature is raised to 550 °C. This conversion likely occurs as a result of the inorganic chlorine ions combining with carbon to form C-Cl bonds. In order to effectively prevent high temperature corrosion, high-chlorine coal can be treated by pyrolysis at temperatures between 350 and 450 °C, followed by water washing and burning. This research provides a theoretical foundation for the clean and efficient use of high-chlorine coal.

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 have 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.

Novel BDD-loaded bimetallic phosphide electrodes enable interesting bifunctional seawater electrolysis

The direct electrolysis of seawater for the production of green hydrogen energy is an economically attractive approach. However, this technique confronts technical problems because to the oxygen evolution reaction (OER) weak stability and inadequate selectivity due to competition with the chlorine evolution process. This work focuses on improving the stability of the electrode and electrolysis efficiency. The phosphating NiCoP active layer with 3D porous morphology was created by electrodeposition on the B-doped diamond (BDD) as an electrode inspired by the bifunctional catalysis strategy. The successfully constructed unique cube-on-nanosheets structure in the NiCoP active layer enables the electrode to exhibit excellent electrocatalytic performance. The porous NiCoP/BDD (Por-NiCoP/BDD) electrodes showed good catalytic activity in alkaline-simulated seawater with the OER and hydrogen evolution reaction (HER) overpotentials of 400 and 261 mV, respectively, at a current density of 100 mA cm−2. More importantly, the electrode exhibits interesting stability of the catalytic performance and structural in alkaline-simulated seawater electrolysis, with the current density decaying by only 1.52 % and 4.06 % after OER and HER processes for 50 h, respectively. This work expands the valuable application scenarios of BDD electrode and provides novel ideas for the development of seawater electrolysis.

S2−-modified hetero MOF-on-MOF of Ni-MOF/Fe-MOF with efficient seawater oxidation performance

Direct seawater electrolysis offers a viable solution to the excessive consumption of fresh water resources in existing industrial electrolytic water processes. However, electrolysis efficiency and material stability are affected by electrode material corrosion caused by chlorine evolution reactions (CER) at the anode positions. In this study, the prepared S-Ni-MOF/Fe-MOF material exhibits an exceptional performance in the oxygen evolution reaction (OER) both in alkaline solution and seawater. Specifically, the material achieves low overpotentials of 281 and 279 mV in 1.0 M KOH and alkaline seawater at 100 mA cm−2 current density, and maintains stability for at least 100 h in both electrolyte solutions. The electronic structure of MOF-on-MOF was modulated through the introduction of S2−, which induced a large number of vacancies. Furthermore, the reconstruction process on the material surface was accelerated by the formation of NiOOH and FeOOH, that served as protective layers and prevented the corrosion of the electrode material by Cl−, thereby enhancing its stability in seawater. Furthermore, computational studies have indicated that the Fe-Ni active sites at the heterointerface exhibit a synergistic effect, which has been confirmed by density functional theory (DFT) calculations. These results prove that this combination significantly reduces the energy barrier associated with the OER. Consequently, the reaction process is accelerated.

Breaking the inactivity of MXenes to drive Ampere-level selective oxygen evolution reaction in seawater

The limited activity and stability of conventional anodes in seawater have posed a significant obstacle to sustainable green hydrogen production directly from seawater via electrolysis. To address these challenges, we engineered Ti3C2Tx-MXene by incorporating iron and boron into its matrix (tagged FBT) for selective oxygen evolution reaction (OER). Positioning B underneath the top layer induces charge disparity on the Fe-sites, which influences the subsequent growth of the ZIF-67 metal-organic framework (MOF) on the MXene surface through Fe-O-Co ionic bonds. DFT calculations reveal a favorable binding energy of −2.30 eV at the heterointerface for ZIF-67 adsorption to the surface of FBT via O-Co bond, a shortened bond length of 1.94 Å, confirming the formation of ionic bonds. These ionic bonds tune the active sites for an enhanced and selective OER over chlorine evolution reaction (CER), preventing active Fe species' leaching and ensuring stability at >1.56 A cm−2 in 6 M alkaline seawater over 370 hours. Further, FBT and ZIF-67/FBT require low overpotentials of 521.2 and 508 mV, respectively, to deliver 1 A cm−2 in 6 M alkaline seawater. Our findings demonstrate a robust strategy to significantly expand the potential of MXenes from simple conductive substrates to efficient OER catalysts for seawater splitting and beyond.

Design, Reactivity, and Active Site of Atomically Dispersed Pt Catalysts for Electrochemical Chlorine Evolution Reaction

The electrochemical chlorine evolution reaction (CER) is a key anodic reaction in the chlor−alkali process for Cl2 production, on-site generation of ClO–, and Cl2-mediated electrosynthesis.1−3 For more than a half-century precious metal-based mixed metal oxides (MMOs) have been mainstays as CER catalysts, however, they intrinsically suffer from the selectivity problem arising from a parasitic oxygen evolution reaction (OER). We have recently developed a new CER catalyst based on atomically dispersed Pt sites on a carbon nanotube (Pt1/CNT), which catalyzes the CER with excellent activity and selectivity.4 The Pt1/CNT catalyst shows superior CER activity to a commercial Ru/Ir-based MMO and a Pt nanoparticle-based catalyst. Importantly, Pt1/CNT exhibits very high CER selectivity near 100% even in low Cl− concentrations (0.1 M) and neutral media, under which the OER is favored over the CER. In situ X-ray absorption spectroscopy and density functional theory calculations reveal that the CER over Pt1/CNT augments with the direct adsorption of Cl− ion on Pt, which can break the scaling relationship between CER and OER. The Pt1/CNT catalyst also shows unusual potential-dependent switching behavior of CER kinetics and rate-determining step.5 Pt1/CNT shows a reaction order of ~1.8 in the low overpotential regime, where the Volmer step is the rate-determining step (RDS). Interestingly, in the high overpotential region, the CER over Pt1/CNT proceeds with a lower reaction order and the RDS switches to the Heyrovský step. We also show that the Pt1/CNT catalyst is comprised of multiple Pt sites with different coordination environments and identify a genuine active site in Pt1/CNT catalysts for the CER.6 K. B. Karlsson and A. Cornell, Selectivity between Oxygen and Chlorine Evolution in the Chlor-Alkali and Chlorate Processes. Chem. Rev. 116, 2982–3028 (2016).S. Exner, T. Lim, and S. H. Joo, Circumventing the OCl vs. OOH Scaling Relation in the Chlorine Evolution Reaction: Beyond Dimensionally Stable Anodes. Curr. Opin. Electrochem. 34, 100979 (2022).Trasatti, Electrocatalysis: Understanding the Success of DSA. Electrochim. Acta 45, 2377–2385 (2000).Lim, G. Y. Jung, J. H. Kim, S. O. Park, J. Park, Y.-T. Kim, S. J. Kang, H. Y. Jeong, S. K. Kwak, and S. H. Joo, Atomically Dispersed Pt−N4 Sites as Efficient and Selective Electrocatalysts for the Chlorine Evolution Reaction, Nat. Commun. 11, 412 (2020).Lim, J. H. Kim, J. Kim, D. S. Baek, T. J. Shin, H. Y. Jeong, K.-S. Lee, K. S. Exner, and S. H. Joo, General Efficacy of Atomically Dispersed Pt Catalysts for the Chlorine Evolution Reaction: Potential-Dependent Switching of the Kinetics and Mechanism, ACS Catal. 11, 12232−12246 (2021).Cho, T. Lim, H. Kim, L. Meng, J. Kim, J. H. Lee, G. Y. Jung, F. Viñes, F. Illas, K. S. Exner, S. H. Joo, and C. H. Choi, Importance of Broken Geometric Symmetry of Single-Atom Pt Sites for Efficient Electrocatalysis, Nat. Commun. 14, 3233 (2023).

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

This paper reports on progress in development of electrocatalysts intended for use in seawater, which optimize the balance of competing reactions between chlorine evolution and oxygen evolution. The 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 the alkaline environment (i.e. pH 12) is γ-MnO2 [2].In this presentation, we (1) compare activities and selectivities towards the OER of electrodeposited and chemically synthesized γ-MnO2 and (2) determine how pH affects selectivity in the pH range from 11 to 13.g-MnO2 powder was synthesized using hydrothermal method. The synthesis resulted in fabrication of material with a flower-like morphology, characterized by a crystallite size of 5-15 nm and BET surface area of 75 m2/g. In parallel, MnO2 films were prepared by electrodeposition on a Pt RDE substrate, following the procedure outlined by Tsagareli et al. [3]. The electrocatalytic activity of both γ-MnO2 powder and electrodeposited MnO2 was investigated by the thin-film RDE method. The thin films of γ-MnO2 powder were obtained by drop-casting MnO2/VC ink [1] on glassy carbon substrates.We found that the shape of polarization curves on MnO2/VC films is strongly dependent on the Nafionä loading. At low Nafion loadings, we observe diffusion-limited currents, which we attribute to OH- diffusion through the Nafion. At higher Nafion loadings, neither diffusion-limited currents, nor the currents’ dependence on the rotation rate are observed. Our data indicate that at low Nafion loadings, MnO2/VC films selectively produce O2 in 0.5M NaCl at pH 12 and 13 and current densities up to 15 mA/cm2. Because of the potential effect of Nafion on the permeability of Cl- ions to the catalyst’s active sites, a set of parallel experiments is being carried out on the electrolytically deposited MnO2 films. The results of the latter experiments will be compared to those obtained on MnO2/VC films in the presentation.

A Sustainable Process for Rare Earth Electrowinning in Chloride Based Molten Salts

Neodymium production has become increasingly important due to use of neodymium–iron–boron (NdFeB) magnets in green energy, consumer technology and defense applications. The state-of-the-art practice features a neodymium fluoride and lithium fluoride molten salt with a consumable carbon anode converting dissolved neodymium oxide and carbon to neodymium metal and CO2.1-2 The anode effect results in PFCs and CO emissions, which make the current neodymium electrowinning process unsustainable.3-4 Some attempts have been made to electrolyze the chloride salt of neodymium to produce chlorine at the anode. Chlorine is a value-added product which neither consumes the anode nor produces other deleterious GHGs. Additionally, the chloride of neodymium can be non-carbothermically produced through a spontaneous reaction with hydrochloric acid, producing only water as a side product. However, a common problem in chloride rare earth electrowinning is the low Coulombic efficiency (10-50%) obtained in lab-scale and pilot-scale efforts.5 The neodymium chloride electrolysis process notoriously encounters a two-step reduction producing an intermediate divalent (Nd2+) oxidation state which is stable in the chloride media.6-7 The intermediate neodymium species diffuses away from the cathode leading to Coulombic efficiency loss. Additionally, the kinetics of the chlorine evolution reaction (CER) in chloride molten salts are known to be relatively sluggish, causing significant anodic overpotentials which elevate the specific energy consumption during electrowinning. Furthermore, electrowinning from molten salts often produces spongy or dendritic deposits of metal requiring energy-intensive purification. In this talk, we will address all aforementioned technical hurdles and report on our efforts achieving high Coulombic efficiency (~85%), and compact deposits with superior as-electrowon neodymium metal purity (>99 wt.%). Furthermore, we will report the development of a new anode which catalyzes chlorine evolution, lowering the anodic overpotential considerably during electrolysis at high current densities of practical interest for electrowinning. Specific energy consumption is calculated for some example cases and found to be between 2.1 and 3.5 kWh/kg representing a significant improvement over the conventional oxyfluoride process. Figure 1

Enabling Rhenium Electrodeposition in Water-in-Salt Electrolytes through Isolated Anodic Reactions

Perfluorosulfonic Acid (PFSA)/Polytetrafluoroethylene (PTFE) copolymer and cation-exchange membranes were used to elongate the use water-in-salt electrolytes for rhenium electrodeposition. Water-in-salt electrolytes are a common technique used to minimize the amount of free water in solution by including high concentrations of salts, thus solvating the water molecules and lowering activity of the solution. This expands the electrochemical window in which deposition is possible and minimizes unnecessary hydrogen evolution reactions (HER) in the electrodeposition system by reducing available protons.Lithium chlorine (LiCl) is a common salt for this purpose due to low costs. However, in the LiCl electrolyte, the necessary oxygen evolution reaction (OER) competes with chlorine evolution, which increases water activity and is visually identifiable with a color change from clear to yellow. When chloride ions are depleted, further deposition is no longer possible, and the electrolyte breaks down.A solution to this issue is using membranes to isolate the anode and cathode, thus preventing the chlorine evolution reaction from occurring. Since rhenium is a system with a small electrochemical window, possible oxide intermediates, and an overpotential for hydrogen evolution, the system requires the use of a stable water-in-salt electrolyte for elongated deposition.In this experiment, three membranes were examined to compare the impact on rhenium depositions in an H-cell. To compare the impact of each membrane, the change of pH of the DI side of the H-cell was monitored across time alongside the volume changes on both sides of the H-cell as a function of time due to LiCl inclusion. The quality and thicknesses of the coatings was examined by SEM as well as the impact on the morphologies of the rhenium of the deposits between each of the membranes.

Polymorphic Engineering of MnO2 Structure as a Diffusion Blocking Layer for Selective Seawater Electrolysis

The water splitting via renewable energy is one of the sustainable process to generate the future clean energy in form of hydrogen. One of the key challenge for the large-scale water electrolysis is the availability of pure water. The sweater can be consider as an alternate feedstock for the large-scale water electrolysis. However, the presence of undesirable components like chlorides, bromides etc. are the potential challenge to make the use of seawater as a facile feedstock. As per the electrochemical potentials, chlorine evolution reaction (CER) along with the oxygen evolution reaction (OER) at the anode is one of the primary existing challenge in seawater electrolysis. Where thermodynamics favour OER and kinetic benefits, the CER process with two-electron transfers reaction. As of now, precious noble metal catalysts such as ruthenium and iridium-based oxides have been explored as a catalyst for seawater electrolysis. However, their high cost does not recommend the use of these catalysts for the large-scale production and limits its commercialization. Here, we are exploring the non-precious Mn based catalyst for OER vs. CER and make make seawater electrolysis as a commercial favourable process. We have explored various polymorphs of MnO2, such as α, β, γ, and δ-MnO2, considering the MnO2 as diffusion blocking layer for the selective OER process during the seawater electrolysis. The polymorphic engineering provide the window to tune the catalytic properties to make it selective towards the OER. Further, the results suggest that α- and β-MnO2 are OER selective however, the γ-, and δ- MnO2 are CER selective. We have identified the reaction mechanism using various electrochemical tools and shown the structure-activity-selectivity trends for the polymorphic structure of MnO2.

Investigating Water and Ion Transport in a Novel Cell Design for Seawater Electrolysis

With increasing concerns about the climate change associated with the carbon dioxide emission from utilizing traditional fuels, hydrogen has become a preferred low-carbon energy carrier. For hydrogen to truly be a clean source of energy, it must be produced from a renewable source of energy through water electrolysis. Theoretically, for each kilogram of hydrogen to be produced 9 kg of high-purity water need to be consumed, thus the enormous use of clean water for H2 production may worsen the shortage of fresh water in many parts of the world.Owing to its abundance, seawater has received great attention in the field of hydrogen production; however, there are many challenges associated with the direct use of seawater for electrolysis. In traditional systems, the seawater is first deionized by reverse osmosis (RO) before being fed to the electrolyzer. The RO system adds complexity to the system and requires energy to be expended for the deionization. Therefore, modern systems have aimed to directly electrolyze seawater, but this comes with it own issues including electrode corrosion, scaling from the ions present in saline water, environmental concerns associated with competitive chlorine evolution reaction, and increased membrane resistance limiting the overall performance of saline water electrolysis. Several strategies have been proposed to overcome these challenges including developing selective electrocatalysts, blocking strategy, pH buffer strategy, etc.This project sought to overcome the issues with direct seawater utilization by designing a cell that is driven by osmotic separation, but does not require an external power source. In this device, high concentration acid/base concentrations are maintained in contact with another compartment containing seawater. The acid/base reservoirs act as draw solutions, taking water passively from seawater due to their differences in osmotic pressure. This talk will focus on the cell design and operation, and include both experimental and modeling results. The rate of water transport with various cell operating configurations was quantified alongside the rate of chloride ion crossover through the anion exchange membrane. New methods for chloride mitigation were explored – including cell operating conditions, membrane design and absorption. Multiple cell configurations will be shown and strategies for reducing the cell operating voltage will be discussed.

Atomically Dispersed Ru-doped Ti4O7 Electrocatalysts for Chlorine Evolution Reaction with a Universal Activity.

Chlorine has been supplied by the chlor-alkali process that deploys dimensionally stable anodes (DSAs) for the electrochemical chlorine evolution reaction (ClER). The paramount bottlenecks have been ascribed to an intensive usage of precious elements and inevitable competition with the oxygen evolution reaction. Herein, a unique case of Ru2+-O4 active motifs anchored on Magnéli Ti4O7 (Ru-Ti4O7) via a straightforward wet impregnation and mild annealing is reported. The Ru-Ti4O7 performs radically active ClER with minimal deployment of Ru (0.13 wt%), both in 5 m NaCl (pH 2.3) and 0.1 m NaCl (pH 6.5) electrolytes. Scanning electrochemical microscopy demonstrates superior ClER selectivity on Ru-Ti4O7 compared to the DSA. Operando X-ray absorption spectroscopy and density functional theory calculations reveal a universally active ClER (over a wide range of pH and [Cl-]), through a direct adsorption of Cl- on Ru2+-O4 sites as the most plausible pathway, together with stabilized ClO* at low [Cl-] and high pH.

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.

Stable and efficient chlorine evolution reaction with atomically dispersed Ru on surface tensile strained TiO2

Developing highly efficient and selective electrocatalysts for the chlorine evolution reaction (CER) in the chloralkali industry is of great importance. Here, we report the discovery of a new electrocatalyst for CER consisting of atomically dispersed Ru sites on surface tensile strained TiO2 (Ru-S-TiO2). The single-atom Ru species were stabilized on the strained TiO2 surface by strong metal-support interactions. The Ru-S-TiO2 is highly efficient, initiating CER at only 5 mV above the ECER, and has shown excellent stability for over 100 hours. It exhibited >95 % CER selectivity even in acidic media with low Cl− concentrations (0.2 M). Our results demonstrate that the strong metal-support interactions between the atomically dispersed Ru species and the strained TiO2 surface are crucial for the high catalytic activity, selectivity, and stability of Ru-S-TiO2 for CER. Ru-S-TiO2 holds great promise as a viable alternative to existing mixed metal oxides-based electrocatalysts for CER in the chloralkali industry.

Selective chlorine evolution reaction using Pt-RuO2 electrocatalysts in brackish water and seawater at circum-neutral pH and its application to seawater desalination

Precious metal-based mixed metal oxides have been widely used as catalysts for the chlorine evolution reaction (CER). However, a concurrent oxygen evolution reaction (OER) leads to insufficient selectivity for CER at circum-neutral pH. Herein, nanoparticulate Pt-RuO2 (PRO) is synthesized with various Pt/Ru ratios at sub-boiling temperatures, followed by post-annealing. The synthetic conditions significantly influence the physicochemical properties (crystalline structures, morphologies, surface areas, double-layer capacitance, and charge transfer resistance) and the electrocatalytic activities of CER in NaCl solutions (0.137 and 0.5 M) and seawater (with a salinity of 3.6 g L–1). Among PRO-x@y samples (where x is the mole fraction of Pt in the mixed Pt and Ru precursor solutions, and y is the annealing temperature [°C]), PRO-0.2@800 and PRO-0.8@500 show remarkable faradaic efficiencies (FEs) for CER (CER-FE). Despite their similar FEs (CER-FEs of approximately 95 % and 99 %, and OER-FEs of 4–6 % and <1 %, for PRO-0.2 and PRO-0.8, respectively), the Pt-rich PRO requires less potential for the same current density (J) and exhibits excellent stability at J = 800 mA cm–2 over 250 h in seawater at circum-neutral pH. The optimized PRO electrode is further used for seawater desalination and simultaneous production of HClO, achieving FEs of ∼100 %. Finally, various electrochemical analyses are conducted to elucidate the CER mechanism.

Theoretical study on the carbon nanomaterial-supported Pt complex electrocatalysts for efficient and selective chlorine evolution reaction.

Chlorine is an important chemical which has long been produced in chlor-alkali process using dimensionally stable anodes (DSA). However, some serious drawbacks of DSA inspire the development of alternative anodes for chlorine evolution reaction (CER). In this study, we focused on the graphene- and carbon nanotube-supported platinum tetra-phenyl porphyrins as electrocatalysts for CER, which have been theoretically investigated based on density functional theory. Our results reveal that the supported substrates possess potential CER electrocatalytic activity with very low thermodynamic overpotentials (0.012-0.028 V) via Cl* pathway instead of ClO*. The electronic structures analyses showed that electron transfer from the support to the adsorbed chlorine via the Pt center leads to strong Pt-Cl interactions. Furthermore, the supported electrocatalysts exhibited excellent selectivity toward CER because of high overpotentials and reaction barriers of oxygen evolution process. Therefore, our results may pave the way for designing CER electrocatalyst utilizing emerging carbon nanomaterials.

Enabling direct seawater electrolysis by redox-inactive amphiphilic amines via chloride sequestration

Sustainable hydrogen production requires large amounts of treated freshwater and precious metals. Direct electrolysis of seawater without additional electrolytes can be a practical approach to address these limitations, however, it usually suffers from kinetically favored chlorine evolution reaction (CER), which is detrimental to an electrolysis system. We report that organocatalytic amphiphilic diamines play a crucial role in preventing the generation of chlorine gas. The feasibility of direct seawater electrolysis was demonstrated with pH-responsive organic amines, which can self-assemble under neutral and acidic conditions. Electrochemical analysis of our electrolysis in saline solutions revealed that (electro)chemical stability of amphiphilic diamines was responsible for preventing CER and hypochlorite formation. Our findings may have significant implications for the chemical industry and energy sectors as the world transitions towards renewable energy sources.

Electro-oxidation of ammonia nitrogen using W, Ti-doped IrO2 DSA as a treatment method for mariculture and livestock wastewater.

Animal farming wastewater is one of the most important sources of ammonia nitrogen (NH4+-N) emissions. Electro-oxidation can be a viable solution for removing NH4+-N in wastewater. Compared with other treatment methods, electro-oxidation has the advantages of i) high removal efficiency, ii) smaller size of treatment facilities, and iii) complete removal of contaminant. In this study, a previously prepared DSA (W, Ti-doped IrO2) was used for electro-oxidation of synthetic mariculture and livestock wastewater. The DSA was tested for chlorine evolution reaction (CER) activity, and the reaction kinetics was investigated. CER current efficiency reaches 60-80% in mariculture wastewater and less than 20% in livestock wastewater. In the absence of NH4+-N, the generation of active chlorine follows zero-order kinetics and its consumption follows first-order kinetics, with cathodic reduction being its main consumption pathway, rather than escape or conversion to ClO3-. Cyclic voltammetry experiments show that NH4+-N in the form of NH3 can be oxidized directly on the anode surface. In addition, the generated active chlorine combines with NH4+-N at a fast rate near the anode, rather than in the bulk solution. In electrolysis experiments, the NH4+-N removal rate in synthetic mariculture wastewater (30-40mg/L NH4+-N) and livestock wastewater (~ 450mg/L NH4+-N) is 112.9g NH4+-N/(m2·d) and 186.5g NH4+-N/(m2·d), respectively, which is much more efficient than biological treatment. The specific energy consumption (SEC) in synthetic mariculture wastewater is 31.5 kWh/kg NH4+-N, comparable to other modified electro-catalysts reported in the literature. However, in synthetic livestock wastewater, the SEC is as high as 260 kWh/kg NH4+-N, mainly due to the suppression of active chlorine generation by HCO3- and the generation of NO3- as a by-product. Therefore, we conclude that electro-oxidation is suitable for mariculture wastewater treatment, but is not recommended for livestock wastewater. Electrolysis prior to urea hydrolysis may enhance the treatment efficiency in livestock wastewater.

Enthralling Anodic Protection by Molybdate on High-Entropy Alloy-Based Electrocatalyst for Sustainable Seawater Oxidation.

Efficient and sustainable seawater electrolysis is still limited due to the interference of chloride corrosion at the anode. The designing of suitable electrocatalysts is one of the crucial ways to boost electrocatalytic activity. However, the approach may fall short as achieving high current density often occurs in chlorine evolution reaction (CER)-dominating potential regions. Thereby, apart from developing an OER-active high-entropy alloy-based electrocatalyst, the present study also offers a unique way to protect anode surface under high current density or potential by using MoO4 2- as an effective inhibitor during seawater oxidation. The wide variation of d-band center of high-entropy alloy-based electrocatalyst allows great oxygen evolution reaction (OER) proficiency exhibiting an overpotential of 230mV at current density of 20mA cm-2. Besides, the electrocatalyst demonstrates impressive stability over 500h at high current density of 1 A cm-2 or at a high oxidation potential of 2.0V versus RHE in the presence of a molybdate inhibitor. Theoretical and experimental studies reveal MoO4 2- electrostatically accumulated at anode surface due to higher adsorption ability, thereby creating a protective layer against chlorides without affecting OER.

Routes to Avoiding Chlorine Evolution in Seawater Electrolysis: Recent Perspective and Future Directions

Routes to Avoiding Chlorine Evolution in Seawater Electrolysis: Recent Perspective and Future Directions