Anion Doping Strategy Research Articles

Se-Doping on Co4S3 Cathode Based on Soft Anion Chemistry to Enhance Magnesium Storage Performance.

Rechargeable magnesium batteries (RMBs) have gradually got attention due to the high theoretical capacity, low cost and high security. However, the lack of suitable cathode materials has been a major obstacle to the development of RMBs. Transition metal sulfides (TMSs) have been studied extensively because of their high theoretical specific capacity and other advantages. However, the diffusion rate of Mg2+ in TMSs is slow and side reactions are easy to occur. In this work, soft anion doping strategy was adopted at Co4S3 cathode material. After doping the appropriate content of Se, it showed the specific capacity of 248 mAh g-1 at a current density of 100 mA g-1. The mechanism of magnesium storage was investigated by ex-situ technique. This work laid a foundation for researching cobalt-based sulfide in cathode materials of RMBs.

Mechanism of chromium poisoning on La0.5Sr0.5Co0.25Fe0.75O3 cathode and enhancing chromium tolerance using a novel anion doping strategy

Chromium poisoning the La1-xSrxCoyFe1-yO3(LSCF) cathode for solid oxide fuel cells is a severe issue that can lead to its electrochemical performance degradation. To clarify poisoning mechanism of chromium species and develop a novel anion doping strategy with enhancing chromium tolerance, the adsorption behavior of Cr species on LSCF and F-doping LSCF surface are explored by density functional theory (DFT) calculations. Our results indicate that CrO3 molecule prefers to be adsorbed on the La(Sr)O-terminated surface rather that the Co(Fe)O2-terminated LSCF(001) surface. The adsorption energies of CrO3 molecule are much larger than that of O2 molecules, implies that the CrO3 is more favorable to absorb on the LSCF surface. Bader charge analysis shows the CrO3 molecule behaves as an electron acceptor through an adsorption process. The adsorption of Cr atom is a weak physical adsorption for Sr site and La site and the Cr atom chemisorption is found to occur on hollow site and O site. In addition, F-doping efficiently improves chromium tolerance by weakening the adsorption strength of chromium species that poisons LSCF surface and this may be a feasible strategy to develop cathode for high performance solid oxide fuel cells.

Fluoride Doping Na3Al2/3V4/3(PO4)3 Microspheres As Cathode Materials for Sodium-Ion Batteries with Multielectron Redox.

Sodium-ion batteries (SIBs) are potential candidates for large energy storage usage because of the natural abundance and cheap sodium. Nevertheless, improving the energy density and cycling steadiness of SIB cathodes remains a challenge. In this work, F-doping Na3Al2/3V4/3(PO4)3(NAVP) microspheres (Na3Al2/3V4/3(PO4)2.9F0.3(NAVPF)) are synthesized via spray drying and investigated as SIB cathodes. XRD and Rietveld refinement reveal expanded lattice parameters for NAVPF compared to the undoped sample, and the successful cation doping into the Na superionic conductor (NASICON) framework improves Na+ diffusion channels. The NAVPF delivers an ultrahigh capacity of 148 mAh g-1 at 100mA g-1 with 90.8% retention after 200 cycles, enabled by the activation of V2+/V5+ multielectron reaction. Notably, NAVPF delivers an ultrahigh rate performance, with a discharge capacity of 83.6 mAh g-1 at 5000mA g-1. In situ XRD demonstrates solid-solution reactions occurred during charge-discharge of NAVPF without two-phase reactions, indicating enhanced structural stability after F-doped. The full cell with NAVPF cathode and Na+ preintercalated hard carbon anode shows a large discharge capacity of 100 mAh g-1 at 100mA g-1 with 80.2% retention after 100 cycles. This anion doping strategy creates a promising SIB cathode candidate for future high-energy-density energy storage applications.

Improved Catalytic Properties of Fluorine-Doped La0.6Sr0.4Co0.2Fe0.8O3-δ for Air Electrode with High-Performance Metal-Air Batteries

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), a perovskite material, is widely recognized as an excellent catalyst for the oxygen evolution reaction (OER). An anion doping strategy was implemented to enhance the presence of highly oxidation-active O2−/O− species crucial for the electrochemical reaction, effectively replacing oxygen. The introduction of 5 mol% fluorine to LSCF resulted in improved OER performance, comparable to that of commercial noble catalysts. Furthermore, we confirmed that fluorine-doped LSCF enhanced the oxygen reduction reaction (ORR) performance, establishing its effectiveness as a bifunctional catalyst. Moreover, when utilized as an air electrode in a homemade zinc-air battery cell, the electrochemical performance of the doped LSCF remained stable after repeated charge/discharge tests. These findings underscore the potential application of anion doping in electrochemical devices.Graphical

Anion-doped polypyrrole three-dimensional framework enables adsorption and conversion in lithium–sulfur batteries

Inhibiting the shuttle effect and propelling polysulfide conversion by introducing a suitable sulfur container has been proven as a promising strategy to enhance the cycle life of lithium-sulfur (Li–S) batteries. Here, a unique three-dimensional (3D) inter-connected framework assembled with SO42−-doped polypyrrole (PPy-SO4) nanowires is proposed. The doping SO42− anion in a polymer skeleton could confine lithium polysulfides (LiPSs) by polar-polar interaction to inhibit the shuttle effect and enhance the conductivity of PPy to accelerate polysulfide conversion. Moreover, the electrostatic coupling between SO42− anion and Li+, as well as between –N+– and Sn2−, at polypyrrole /electrolyte interface can effectively regulate the redox kinetics of polysulfide. Besides, the inter-connected framework creates a large contact surface for sulfur and high-flux paths for electron transport. Consequently, the Li–S batteries assembled with PPy-SO4/S cathode exhibit a stable capacity of 501 mAh g−1 after 350 cycles at 1C, showing a low decay rate of 0.09% per cycle. Notably, the efficiency of the anion doping strategy is further verified in the pouch cell, realizing a capacity of 480 mAh g−1 after 250 cycles. This work illustrates that anion doping with rational structural design is a feasible solution to boost the electrochemical performance of Li–S batteries.

Cl-doped CuO for electrochemical hydrogen evolution reaction and tetracycline photocatalytic degradation

Photocatalysts play a vital role in energy conversion technologies and wastewater treatment. Catalyst's electronic structure can be tuned by a simple anion doping strategy to enhance the catalytic properties. In this work, different atomic percentages of Cl‾ doped into CuO lattices were synthesized using deep eutectic solvent (DES) by increasing the molar ratio of choline chloride to urea. Here, DES act as a green solvent and, Cl‾ source in preparing catalysts. Further, catalysts' crystallinity and surface properties were analyzed through X-ray diffractometer and transmission electron microscopy. X-ray photoelectron spectroscopy confirms the presence of Cl‾ dopant in CuO lattices. Synthesized catalysts were studied for electrochemical hydrogen evolution reaction (HER) and tetracycline photocatalytic degradation. Among the synthesized electrocatalysts, 2.48 at% of Cl-doped CuO catalyst displays optimum HER activity in 1 M H2SO4 electrolyte with an overpotential of 400 mV at the current density of 10 mA cm−2 and a Tafel value of 89 mV dec−1. Moreover, the same catalyst shows 83.5% degradation of tetracycline in 240 min under the illumination of a 35 W Xe arc lamp. This work provides a simple strategy to develop a catalyst with Cl‾ doping into CuO crystal structure by DESs and enhance its HER and wastewater treatment activity.

Coupling of Oxygen Vacancies and Heterostructure on Fe3 O4 via an Anion Doping Strategy to Boost Catalytic Activity for Lithium-Sulfur Batteries.

The sluggish reaction kinetics and severe shutting behaviors of sulfur cathodes are the major roadblocks to realizing the practical application of lithium-sulfur (Li-S) batteries and need to be solved through designing/constructing rational sulfur hosts. Herein, an effective alternative material of Fe3 O4- x /FeP in-situ embedded in N-doped carbon-tube (Fe3 O4- x /FeP/NCT) is proposed. In this fabricated heterostructure, NCT skeleton works as a sulfur host provides physical barrier for lithium polysulfides (LiPSs), while Fe3 O4- x /FeP heterostructure with abundant oxygen vacancies provides double active centers to simultaneously accelerate e- /Li+ diffusion/transport kinetics and catalysis for LiPSs. Through the respective advantages, Fe3 O4- x /FeP/NCT exhibits synergy enhancement effect for restraining sulfur dissolution and enhancing its conversion kinetics. Furthermore, the promoted ion diffusion kinetics, enhanced electrical conductivity, and increased active sites of Fe3 O4- x /FeP/NCT are enabled by oxygen vacancies as well as the heterogeneous interfacial contact, which is clearly confirmed by experimental and first-principles calculations. By virtue of these superiorities, the constructed cathode shows excellent long-term cycling stability and a high-rate capability up to 10 C. Specially, a high areal capacity of 7.2 mAh cm-2 is also achieved, holding great promise for utilization in advanced Li-S batteries in the future.

"Mn-locking" effect by anionic coordination manipulation stabilizing Mn-rich phosphate cathodes.

High-voltage cathodes with high power and stable cyclability are needed for high-performance sodium-ion batteries. However, the low kinetics and inferior capacity retention from structural instability impede the development of Mn-rich phosphate cathodes. Here, we propose light-weight fluorine (F) doping strategy to decrease the energy gap to 0.22 eV from 1.52 eV and trigger a "Mn-locking" effect-to strengthen the adjacent chemical bonding around Mn as confirmed by density functional theory calculations, which ensure the optimized Mn ligand framework, suppressed Mn dissolution, improved structural stability and enhanced electronic conductivity. The combination of in situ and ex situ techniques determine that the F dopant has no influence on the Na+ storage mechanisms. As a result, an outstanding rate performance up to 40C and an improved cycling stability (1000 cycles at 20C) are achieved. This work presents an effective and widely available light-weight anion doping strategy for high-performance polyanionic cathodes.

Modification of the Microstructure and Transport Properties of La2CuO4−δ Electrodes via Halogenation Routes

Ruddlesden–Popper type electrodes with composition La2CuO4−δ are alternative cathode materials for solid oxide fuel cells (SOFCs); however, the undoped compound exhibits low electrical conductivity for potential applications, which is usually increased by alkaline-earth doping. A promising alternative to alkaline-earth doping is the modification of the anionic framework by halogen doping. In this study, La2CuO4−0.5xAx (A = F, Cl, Br; x = 0–0.3) compounds are prepared by a freeze-drying precursor method, using an anion doping strategy. The composition, structure, morphology and electrical properties are studied to evaluate their potential use in solid oxide fuel cells (SOFCs). The halogen-doped materials show higher electrical conductivity and improved electrocatalytic activity for oxygen reduction reactions when compared to the pristine material, with polarization resistance values 2.5 times lower, i.e., 0.20, 0.11 and 0.08 Ω cm2 for undoped, F- and Cl-doped samples, respectively, at 800 °C. Moreover, halogen doping prevents superficial copper segregation in La2CuO4−δ, making it an attractive strategy for the development of highly efficient electrodes for SOFCs.

Achieving reversible Mn2+/Mn4+ double redox couple through anionic substitution in a P2-type layered oxide cathode

P2-type Mn-based layered oxides have emerged as promising cathode materials for sodium-ion batteries (SIBs) due to their high theoretical capacity. However, the incorporation of Mn3+ cations induce severe Jahn-Teller (J-T) effect, which seriously distorts the localized lattice structure and results in insufficient battery performance. Herein, we successfully introduce reversible Mn2+/Mn4+ double redox couple into P2-type Na0.6Mg0.3Mn0.7O2 cathode with suppressed J-T effect through F anion doping strategy. The comprehensive results clearly suggest that F-substitution with an appropriate amount enlarges the interlayer spacing and reduces the band gap, resulting in accelerated charge transfer kinetics. In addition, the strong interaction between Mn and F suppresses the Mn2+ dissolution at discharged states and promotes the reversible conversion from Mn2+ to Mn4+ at charged states, leading to ameliorated J-T effect and enhanced electrochemical performance. Moreover, the oxygen redox reaction is also enhanced through F anion doping strategy. Our present study provides an effective avenue to address the J-T effect by introducing reversible Mn2+/Mn4+ double redox couple in Mn-based oxides, which is expected to revive this cathode family toward practical applications of SIBs.

Boron-doped CoSe2 nanowires as high-efficient electrocatalyst for hydrogen evolution reaction

High activity and stable hydrogen evolution reaction (HER) catalysts have an indispensable influence on hydrogen production. Pyrite cobalt selenide (CoSe2) is considered an excellent non-noble metal compound HER catalyst due to its low price and excellent electrical conductivity. However, the HER catalytic activity of CoSe2 is still not ideal because of the weak adsorption of hydrogen on its active Co site. The anion introduction can improve the electronic structure of the catalyst and thereby enhance the performance of HER. Here, we report that B-doped CoSe2 nanomaterials on carbon cloth (B-CoSe2/CC) were successfully synthesized. Compared with CoSe2, B-CoSe2 exhibits better HER performance in 1 M KOH. The overpotential of B-CoSe2 catalyst is only 153 mV at 10 mA cm−2. Tafel slope of B-CoSe2/CC sample is only 85 mV dec−1. In addition, B-CoSe2/CC exhibits perfect long-term durability and cycle stability. Density functional theory (DFT) calculations illustrate that the doping of B improves the intrinsic conductivity of CoSe2 and optimizes the hydrogen adsorption free energy (ΔGH*) of Se and Co sites. This work not only proposes a new anion doping strategy to improve the electronic structure of cobalt-based selenides for improved HER performance, but also provides a reference for the screening and design of other transition metal compound HER electrocatalysts.

Architecture and performance of anion-doped Co-free lithium-rich cathode material with nano-micron combined morphology

Co-free cathode materials are gradually attracted wide attention due to the low budget and environmental friendliness, but their application is still prevented by the poor rate performance and cyclic stability. Herein, the Co-free lithium-rich cathode materials (Li1.2Ni0.2Mn0.6O2, LRNMO) with a nano-micron combined morphology is prepared by a simple oxalate co-precipitation route and further modified by an anion doping strategy. It has been found that the F− anion doping can increase the content of Mn4+ in LRNMO, reduce the influence of the Jahn-Teller effect, and further impede the transition from layered phase to spinel phase. As a result, the as-obtained Li1.2Ni0.2Mn0.6O2-xFx (x = 0.04, named as F4-LRNMO) shows an optimal electrochemical performance, for instance, high discharge capacity (243 mAh g−1) with a satisfactory initial coulombic efficiency of 84.37% at 0.1C. Meanwhile, the F4-LRNMO sample also can display high capacity retention of 92.2% after 200 cycles at 1C, and a remarkably high discharge capacity of 151 mAh g−1 with capacity retention of 95.4% after 100 cycles even at high rate of 5C. In consequence, this work can not only ameliorate the defects of poor stability and low initial coulomb efficiency, but also offer a meaningful exploration for the development of Co-free lithium-rich cathode materials with high capacity and high performance-price ratio.

Engineering Electronic Structure and Band Alignment of 2D Mg(OH)2 via Anion Doping for Photocatalytic Applications.

The wide bandgap of 2D Mg(OH)2 inhibits its applications in visible-light photocatalytic applications. Besides, its mismatched band alignment to the redox potential of O2/H2O, brings about low efficacy of water-splitting performance. Therefore, to release the powder of 2D Mg(OH)2 in photocatalytic research, we explore anion doping strategies to engineer its electronic structure. Here, anion doping effects on electronic properties of 2D Mg(OH)2 are investigated by using DFT calculations for seven dopants (F, Cl, S, N, P, SO4, and PO4). We found (1) S, N and P doping remarkably reduces its band gap from 4.82 eV to 3.86 eV, 3.79 eV and 2.69 eV, respectively; (2) the band gap reduction is induced by the electron transfer to the dopant atoms; (3) F, Cl, SO4, and PO4 doping shifts its valence band to be lower than the oxidation potential of O2/H2O to render its band structure appropriate for photocatalytic water splitting. These results suggest that not only electrical conductivity of 2D Mg(OH)2 can be increased but also their band structure be aligned by using the proposed anion doping strategy. These results enable a new photocatalytic materials design approach while offering exciting possibilities in applications of high-current electrolysis, chemical gas sensing, and photocatalysis.

Electronic properties of p-type BaSnO3 thin films

Cubic perovskite oxides are attracting wide attention for applications in electronics and optoelectronics due to their high electronic mobility, however, realization of p-type conductivity in these oxides is still a matter. Barium stannate (BaSnO3) is one of such materials, wherein low-amount of lanthanum-doping can induce an extremely high room-temperature electron mobility. In this work, anion-doping strategy was explored to realize the p-type conductivity in BaSnO3, and the underlying physics of transport was investigated. It is found that nitrogen substitution for oxygen can induce the p-type conductivity in BaSnO3 thin films. By analyzing the temperature-dependent resistance and negative magnetoresistance data, Efros-Shklovskii variable-range hopping conduction is identified as the dominant transport mechanism in p-type BaSnO3 thin films. Additionally, nitrogen-doped BaSnO3 homojunctions exhibit good rectifying and photo-response properties. This study provides an alternative strategy for realizing the p-type conductivity in stannate-based perovskite oxides, and is helpful for designing the properties of stannate-based devices.

Frequency-Agile Low-Temperature Solution-Processed Alumina Dielectrics for Inorganic and Organic Electronics Enhanced by Fluoride Doping.

The frequency-dependent capacitance of low-temperature solution-processed metal oxide (MO) dielectrics typically yields unreliable and unstable thin-film transistor (TFT) performance metrics, which hinders the development of next-generation roll-to-roll MO electronics and obscures intercomparisons between processing methodologies. Here, capacitance values stable over a wide frequency range are achieved in low-temperature combustion-synthesized aluminum oxide (AlOx) dielectric films by fluoride doping. For an optimal F incorporation of ∼3.7 atomic % F, the F:AlOx film capacitance of 166 ± 11 nF/cm2 is stable over a 10-1-104 Hz frequency range, far more stable than that of neat AlOx films (capacitance = 336 ± 201 nF/cm2) which falls from 781 ± 85 nF/cm2 to 104 ± 4 nF/cm2 over this frequency range. Importantly, both n-type/inorganic and p-type/organic TFTs exhibit reliable electrical characteristics with minimum hysteresis when employing the F:AlOx dielectric with ∼3.7 atomic % F. Systematic characterization of film microstructural/compositional and electronic/dielectric properties by X-ray photoelectron spectroscopy, time-of-fight secondary ion mass spectrometry, cross-section transmission electron microscopy, solid-state nuclear magnetic resonance, and UV-vis absorption spectroscopy reveal that fluoride doping generates AlOF, which strongly reduces the mobile hydrogen content, suppressing polarization mechanisms at low frequencies. Thus, this work provides a broadly applicable anion doping strategy for the realization of high-performance solution-processed metal oxide dielectrics for both organic and inorganic electronics applications.

Effect of Cl doping on the electrochemical performance of Sr2Fe1.5Mo0.5O6−δ cathode material for solid oxide fuel cells

In this paper, a novel Cl− anion doping strategy is proposed to modify the electrochemical performance of Sr2Fe1.5Mo0.5O6−δ (SFM) cathode for solid oxide fuel cells. A series of Cl-doped Sr2Fe1.5Mo0.5O6−x−δClx (SFMClx, x = 0, 0.1, 0.2, 0.3, 0.4) materials is synthesized by the citric acid–glycine combustion method, and the effect of Cl doping on the crystal structure and electrochemical performance is systemically investigated. The doping of Cl into the SFM leads to the lattice expansion, and the electrochemical performance of Cl-doped SFMClx cathodes is effectively improved as a result of the enhanced mobility of lattice oxygen introduced by Cl doping. The optimal composition with x = 0.2 (sample Sr2Fe1.5Mo0.5O5.8−δCl0.2, noted as SFMCl0.2) exhibits a minimum polarization resistance Rp value of 1.987 Ωcm2 at 600 °C, reduced by 38.04% compared with the SFM cathode. These results suggest that Cl doping is an effective strategy to improve the electrochemical properties of cathode for solid oxide fuel cells.

Chlorine-anion doping induced multi-factor optimization in perovskties for boosting intrinsic oxygen evolution

The oxygen evolution reaction (OER) plays a crucial role in many electrochemical energy technologies, and creating multiple beneficial factors for OER catalysis is desirable for achieving high catalytic efficiency. Here, we highlight a new halogen-chlorine (Cl)-anion doping strategy to boost the OER activity of perovskite oxides. As a proof-of-concept, proper Cl doping at the oxygen site of LaFeO3 (LFO) perovskite can induce multiple favorable characteristics for catalyzing the OER, including rich oxygen vacancies, increased electrical conductivity and enhanced Fe-O covalency. Benefiting from these factors, the LaFeO2.9-δCl0.1 (LFOCl) perovskite displays significant intrinsic activity enhancement by a factor of around three relative to its parent LFO. This work uncovers the effect of Cl-anion doping in perovskites on promoting OER performance and paves a new way to design highly efficient electrocatalysts.

Cover Feature: Fluoride‐Based Anion Doping: A New Strategy for Improving the Performance of Protonic Ceramic Conductors of the Form BaZrO3 (ChemElectroChem 10/2020)

The Cover Feature illustrates the enhanced mobility of ionic charge carriers after substitution of F− on the O2− site. Interestingly, weakened chemical bonds were observed between the cations (A or B site) and the oxygen ions by the anion doping strategy resulting in an improved oxygen mobility in the lattice. This finding suggests that targeted anion doping is a promising strategy for the development of a new generation of electrolyte materials. More information can be found in the Aricle by J. Gao et al.

Boosting the reactivity of Ni2+/Ni3+ redox couple via fluorine doping of high performance Na0.6Mn0.95Ni0.05O2-xFx cathode

Though P2-type Na-Mn-Ni-O cathodes with low cost and environmental benign have been extensively investigated, it is still challenging to fulfill practical application with limited cycle stability and low operating potential. However, the research of the reactive Ni2+/Ni3+ redox pair that enable both high working potential and high reversible capacity was almost ignored. And traditional cationic doping mainly focusses on crystal modulation and structure stabilization. In this study, an anion doping strategy (F-doping) was carried out to further boost the activity of Ni2+. The multi-function including structural parameter modulation and robust Ni-F bond significantly promote the activation of Ni2+/Ni3+ and advance the respective working potential. Related reaction kinetics and structural evolution were also investigated to elucidate the F-doping mechanism. The Na0.6Mn0.95Ni0.05O1.95F0.05 with appropriate F content could deliver a high capacity of 80.76 mA h g−1 at 2C with 75.0% retained after 960 cycles. The excellent rate capability and full cell performance also demonstrate the high potential. This study may provide a new sight for the development of P2-type layered Na-Mn-Ni-O cathode, which could be extended to other oxides cathode.

Sulfur-Doped CoO Nanoflakes with Loosely Packed Structure Realizing Enhanced Oxygen Evolution Reaction.

The development of active and inexpensive electrocatalysts for the oxygen evolution reaction (OER) to promote water splitting has always been a major challenge. Cobalt-based oxides and sulfides have been actively investigated due to their low cost and high activity. However, the lower intrinsic conductivity of cobalt oxide and the inferior stability of cobalt sulfides still limit their practical application. Herein, CoO was chosen for a proof-of-concept study in which the anion-doping strategy was used to obtain an excellent catalyst. Sulfur incorporation optimizes the charge-transfer properties and active sites of sulfur-doped CoO (S-CoO) and thus gives rise to improved catalytic activity. Besides sulfur doping, the stable framework of the cobalt oxide was well maintained, and thus high stability of S-CoO throughout the reaction process was ensured.