Multiple Doping Research Articles

Formation of Chemically Complex Intergranular Glass Film: An Effective Strategy to Hinder Grain Coarsening

Thermally driven grain coarsening is a commonly encountered issue in nanocrystalline ceramics, particularly in high‐temperature environments. The intergranular glass film (IGF) constitutes a crucial component of most ceramics and plays a pivotal role in the process of grain coarsening. In this study, it is proposed to impede grain coarsening by constructing a chemically complex IGF comprising multiple dopants with distinct ionic radii. Ternary dopants encompassing Al3+, Y3+, and La3+ ions are simultaneously incorporated into a ZrO2–SiO2 nanocomposite. To fabricate the nanocomposite, an amorphous precursor powder with uniformly dispersed dopants is prepared using a chemical coprecipitation method, followed by rapid hot pressing to obtain a dense bulk sample. The distribution behavior of ternary dopants at IGFs between adjacent ZrO2 nanocrystallites (NCs) is carefully examined. It is revealed that the ternary dopants coexist at the IGFs. Moreover, Si4+ ions exhibit preferential enrichment at the IGFs. Remarkably, the presence of chemically complex IGFs significantly enhances the resistance to grain coarsening in ZrO2 NCs up to 1000 °C. In these findings, valuable insights are offered for designing and fabricating nanocomposites with exceptional resistance against grain coarsening.

Sodium-Rich, Co-Ni-Free P2-Layered Manganese Oxide Cathodes for Sodium-Ion Batteries.

The rapid capacity loss attributed to irreversible phase reactions and structural instability has consistently affected the development of P2-layered cathode materials. Moreover, the introduction of costly elements such as single or multiple dopants has failed to resolve the sustainability challenges in designing an optimal Mn-based layered oxide cathode. This study proposes a Co-Ni-free, poly-elemental doping strategy (Li, Mg, and Cu) combined with high sodium content for an Mn-based P2-layered cathode designed for Na+ ion storage. In situ X-ray diffraction analysis confirms the absence of P2 - O2 phase transitions during cycling for both NLMMC87 (Na0.87Li0.1Mg0.1Mn0.7Cu0.1O2) and NLMMC77 (Na0.77Li0.1Mg0.1Mn0.7Cu0.1O2). This can be attributed to the co-substitution of the electronegative Cu element and the stabilizing dopants Li and Mg, which suppress oxygen evolution. Simultaneously, the high sodium content within the host structure promotes high reversible capacity, enhances structural stability, and minimizes internal stress due to volume changes. Moreover, NLMMC87 demonstrates a reversible capacity of 167.9mA h g-1 at 0.1 C (97% Coulombic efficiency) and maintains excellent stability across various current rates. Further investigations into the practical application of NLMMC87 in a sodium full cell will be a critical step toward realizing an ideal cathode for sodium-ion batteries.

Constructing boosted charge separation for efficient H2O2 production and pollutant degradation by highly defective ZnIn2S4/ carbon doped boron nitride

Solar-driven photocatalytic production of H2O2 as a promising environmentally-friendly approach has been applied as a chemical reagent and for enhancing photocatalytic remediation. However, this process is still limited by unsatisfactory efficiency and hard separation of photogenerated charge carriers. Herein, we design a dual pathway to improve hydrogen peroxide production by establishing a 2D/2D heterojunction between carbon-doped boron nitride (BCN) and defective zinc indium sulfide (ZIS). The introduction of multiple vacancies and dopants at the interface successfully promoted the interfacial charge transfer and peroxide generation. The Z-scheme heterojunction establishes a built-in electronic field, facilitating continuous electron accumulation and depletion, thereby inducing band bending. As a result, the optimized BCN/ZIS-30 composite (>420 nm wavelength) exhibits 925 μmol/g/h in pure water with no other additions and advances this production to 2006.1 μmol/g/h (2 times as defective ZIS and 12.1 times as BCN) under the existence of isopropanol and aeration. Mechanism investigation indicated that H2O2 is generated via a two-step electron reduction route and water oxidation reaction. The generated H2O2 successfully constructs a self-photo-Fenton system by forming hydroxyl radicals. Accompanied by strong oxygen activation ability, the photo-Fenton system also exhibits rapid degradation of antibiotics with 95 % elimination in 60 minutes. The practical applicability of this photocatalyst was demonstrated through real water remediation tests, exhibiting its effectiveness in removing antibiotics, COD, and total ammonia nitrogen, highlighting its potential for practical water treatment applications. This work provides a novel idea on constructing heterojunction materials for energy saving and water remediation.

Exploring Mg and Fe co-doped Li4Ti5O12 electrode for lithium-ion battery

Li4Ti5O12 (LTO) has been a great subject in lithium-ion battery research due to its high safety and electrochemical stability. However, the exploration of novel doping strategies to enhance its electrochemical performance remains a topic of interest. While single doping strategies have been widely investigated, co-doping strategies involving multiple dopants have only received limited attention. Here, we investigate the performance improvement of LTO through an Mg- and Fe-co-doping strategy. Fe precursors derived from steel manufacturing waste were used as dopants. Experimental results reveal that the co-doped samples exhibit enhanced capacity, cycleability, and rate capability. The theoretical analysis also provides valuable information on the electronic and structural changes induced by Mg- and Fe-co-doping, elucidating the impact on lithium-ion diffusion and storage. This approach contributes to the sustainable utilization of industrial waste and offers a low-cost method for the improvement of electrode materials.

Improving electrical and mechanical properties of cement composites by combined addition of carbon black and carbon nanotubes and steel fibers

A cost-effective cement composite material has been developed for grounding systems, utilizing carbon black, carbon nanotubes, and steel fibers as conductive dopants. The electrical conductivity, mechanical properties, and fluidity of cement composites are investigated, and the synergetic mechanism of multiple conductive dopants in cement composites is revealed based on microscopic means. The results show that the combination of carbon black, carbon nanotubes, and steel fibers facilitates the establishment of efficient conductive networks in cement composites. The addition of 5 % carbon black, 0.3 % carbon nanotubes (by weight of cement), and 0.6 % steel fibers (by volume of composite) reduced the resistivity of the cement composite from 5568 Ω·cm to 310 Ω·cm after 28 days of curing. Then, it decreased to 267 Ω·cm after natural drying in laboratory environment until the 90th day. In addition, the resistivity of cement composites varies less than 5 % in environments ranging from −20°C to 50°C. Furthermore, the compressive and flexural strengths were 30.06 MPa and 6.17 MPa, and the flow diameter was 167 mm, which provided good mechanical strength and workability for conventional engineering applications. This paves an effective way for the further application of cement composites in grounding systems.

High thermoelectric performance in hollandite-type KxTi8O16-based oxides with complex crystal structure

Thermoelectric (TE) oxides are paid great attention due to their good thermal stability, but the high lattice thermal conductivity (κL) largely impedes their further development. In this paper, a Hollandite-type structure and multiple dopants in KxTi8O16-based oxides are studied to seek for an ultralow κL. Benefited from the complex crystal structure, a relatively low κL (2.13 W m−1 K−1 at 373 K) is obtained in K1.78Ti8O16. The Ba dopant can make the [TiO6] octahedra undistorted and increase the Ti3+ amount, leading to a doubled power factor. Meanwhile, the dual-doping effect of Ba and Nb dopants can further decrease the κL to 0.85 W m−1 K−1. Thus, a competitive zT value of 0.18 is obtained in Ba1.15Ti7.2Nb0.8O16 at 1073 K. This work demonstrates that the TE performance of Hollandite-type oxides deserves to be further studied and a complex crystal structure can be designed to achieve a high zT value.

Low-temperature plasma-assisted synthesis of iron and nitrogen co-doped CoFeP-N nanowires for high-efficiency electrocatalytic water splitting

Designing efficient, stable, and low-cost non-precious metal electrocatalysts is critical for gainful utilization of renewable resources and effective water splitting. The catalytic efficiency is determined by interactions between the multiple main constituent elements and dopants. However, achieving performance-boosting synergistic interactions between different species in the catalyst is challenging. This work demonstrates such effect using low-temperature plasma-enhanced hydrothermal-phosphorization synthesis of Fe, N co-doped CoFeP-N nanowires. Nickel foam was utilized as the substrate to prepare CoFe-LDH precursor by hydrothermal method and CoFeP nanoparticles were obtained by phosphorization in a tube furnace. The N element was further doped into CoFeP using a low-temperature plasma discharge. The produced CoFeP-N nanowires exhibit far superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities in an alkaline medium compared to the original CoP due to the incorporation of Fe and N elements, with overpotentials of 64 mV and 219 mV at 10 mA cm−2 respectively, and excellent cycling stability. When CoFeP-N is used as both the cathode and anode of a two-electrode water splitting device, low voltages of only 1.516 V and 1.636 V were needed to achieve current density of 10 mA cm−2 and100 mA cm−2 respectively, which are better than that of Pt/C||RuO2 and most non-precious metal-based electrocatalysts reported to date. These experimental results provide new insights and strategies for developing efficient, stable, and low-cost bifunctional water splitting electrocatalysts.

Multiple metallic dopants in nickel nanoparticles for electrocatalytic oxygen evolution

Developing efficient oxygen evolution reaction (OER) electrocatalysts is of great importance for sustainable energy conversion and storage. Ni-based catalysts have shown great potential as OER electrocatalysts, but their performance still needs to be improved. Herein, we report the multiple metal doped nickel nanoparticles synthesized via a simple oil phase strategy as efficient OER catalysts. The FeMnMoV–Ni exhibits superior OER performance with an overpotential of 220 ​mV at 10 ​mA ​cm−2 and a long-term stability of 250 ​h in 1 ​M KOH solution. In situ Raman analysis shows that the NiOOH site works as the active center and multiple metallic dopants facilitate the formation of NiOOH. Mo and V dopants promote the formation of high-valence state of Ni sites, and Mn dopants increase the electrochemical active surface area and expose more active sites. This work provides a novel strategy for catalyst design, which is critical for developing multiple metal doped catalysts.

Activating biomass carbon with metallurgical slag by pyrolysis in molten salt for high-performance supercapacitors.

Pyrolysis of sustainable biomass to advanced carbon materials for energy storage is key-enabling in energy and environmental sustainability. However, obtaining carbon materials with well-defined microstructure and composition for high-performance energy storage is extremely challenging. Herein, efficient activation of biomass carbon is realized by introducing extra metallurgical slag during pyrolysis of coconut shell in Na2CO3-K2CO3 molten salt. The molten salt guides the formation of carbon with a hierarchical honeycomb-like nanostructure, while the metallurgical slag facilitates enhanced doping of the heteroatom species, conjointly contributing to the increase of the specific surface area of carbon materials from 424 m2 g-1 to 1451 m2 g-1 and the extension of the single N dopant to multiple dopants of N, P, Zn and Co. Such adequate tuning of the microstructure and composition in the pyrolysis product increases the capacitance for supercapacitors from 30 F g-1 to 135 F g-1 at 0.5 A g-1. The results can provide new insights for the controllable upgradation of both biomass and waste industrial slag toward enhanced energy storage.

Current Development in Biomaterials-Hydroxyapatite and Bioglass for Applications in Biomedical Field: A Review.

Inorganic biomaterials, including different types of metals and ceramics are widely used in various fields due to their biocompatibility, bioactivity, and bioresorbable capacity. In recent years, biomaterials have been used in biomedical and biological applications. Calcium phosphate (CaPs) compounds are gaining importance in the field of biomaterials used as a standalone material or in more complex structures, especially for bone substitutes and drug delivery systems. The use of multiple dopants into the structure of CaPs compounds can significantly improve their in vivo and in vitro activity. Among the general information included in the Introduction section, in the first section of this review paper, the authors provided a background on the development of hydroxyapatite, methods of synthesis, and its applications. The advantages of using different ions and co-ions for substitution into the hydroxyapatite lattice and their influence on physicochemical, antibacterial, and biological properties of hydroxyapatite are also presented in this section of the review paper. Larry Hench's 45S5 Bioglass®, commercially named 45S5, was the first bioactive glass that revealed a chemical bond with bone, highlighting the potential of this biomaterial to be widely used in biomedicine for bone regeneration. The second section of this article is focused on the development and current products based on 45S5 Bioglass®, covering the historical evolution, importance of the sintering method, hybrid bioglass composites, and applications. To overcome the limitations of the original biomaterials, studies were performed to combine hydroxyapatite and 45S5 Bioglass® into new composites used for their high bioactivity and improved properties. This particular type of combined hydroxyapatite/bioglass biomaterial is discussed in the last section of this review paper.

Simultaneous Improvement of Oxygen Reduction and Catalyst Anchoring via Multiple Dopants on Mesoporous Carbon Frameworks for Flexible Al-Air Batteries.

Mesoporous carbon supported non-noble metals, as promising catalysts for boosting the oxygen reduction reaction (ORR) in metal-air batteries, usually face challenges of low activity and performance degradation caused by the catalyst detachment from carbon substrates. Herein, a one-stone-two-birds strategy is reported to simultaneously improve the ORR activity and anchor nanosized MnS catalysts on a mesoporous carbon framework via nitrogen (N) and sulfur (S) dopants (MnS/NS-C). Synchrotron-based X-ray absorption spectroscopy (XAS) confirms the existence of Mn-N and Mn-S bonds, which firmly anchor active MnS nanoparticles. Density functional theory (DFT) calculations reveal that the N, S codoping lowers the d-band center of Mn and optimizes ORR intermediate adsorption. An excellent ORR performance (the onset and half-wave potential of 1.07 and 0.91 V) and long-term durability are achieved for MnS/NS-C in alkaline media. The flexible Al-air battery, using MnS/NS-C as the cathode catalyst, shows a power density of 134.6 mW cm-2 in comparison to the Pt/C-based counterpart of 106.2 mW cm-2. This study constructs a stable interaction with non-noble catalysts and carbon substrates for enhancing catalytic activity and durability in metal-air batteries.

Synergy effects of Tb/Y/Zn for structural stability of high-voltage LiCoO2 cathode material

As a popular cathode material in rechargeable lithium-ion batteries, lithium cobalt oxide (LiCoO2) is required to achieve high-level safety with high energy density to meet the ever-increasing energy demand for energy storage devices. The method of lifting the operating voltage of LiCoO2 to release more capacity for higher energy density usually causes severe structural instability at the deeply delithiated state, resulting in capacity fade and limited lifespan. Herein, we present a series of zinc, yttrium and terbium modified LiCoO2 through solid-state reaction to tackle this long-term issue of structure destruction cycling at high voltages. Compared with the mediocre electrochemical performance of LiCoO2 doped with single elements of Zn, Y and Tb, respectively, the dual-doped LiCoO2 exhibits better structural stability and capacity retention at high voltages. Furthermore, the prepared Zn–Y–Tb ternary-doped LiCoO2 exhibits excellent electrochemical capability with a discharge capacity of 185mAh/g after 100 cycles and capacity retention of 98% at 4.55 V. These multiple dopants synergistically maintain structural integrity after 300 cycles and effectively promote the cycle stability of lithium cobalt oxide cathode material at high voltages.

Activating the pseudocapacitance of multiple-doped carbon foam via long-term charge-discharge circulation

Carbon-based supercapacitors, featuring superior power density and stability, are strongly desired for electrical vehicles, yet suffered from their low energy densities. Recently, incorporating pseudo-capacitive constituents into the carbon matrix has been emerged as a prevailing method to increase its capacitance, while usually accompanied with declined stability. Herein, we employed a triple doping strategy to fabricate boron, nitrogen, and oxygen co-doped graphite foam (BNO-GF). The multiple dopants trigger a favorable initial specific capacitance of BNO-GF. Interestingly, the specific capacitance of the BNO-GF increases along with the charge-discharge circulation. An enhancement of the capacitance (∼40 %), entirely the pseudocapacitance, was further determined. Detailed structural characterization further determines a merging of the defective domains during cycles. With an amplifying disordering, these merged defective domains contribute a boosted pseudocapacitance. Meanwhile, the carbon framework maintains the structural integrity, without scarifying stability. This work provides a novel route to activate the carbon materials towards superior pseudocapacitance.

High Throughput Studies of Li-La-Zr-O Garnet Solid Electrolytes

Development of next-generation Li-ion batteries has increasingly focused on all-solid batteries employing either ceramic, polymer, or glass electrolytes in order to address shortcomings in currently commercialized liquid electrolyte Li-ion batteries including safety, limited lifetime, and lower energy densities resulting from instability with respect to Li metal anodes.[1] Lithium lanthanum zirconium oxide (LLZO) is a leading candidate for solid Li-batteries due to its high Li-ion conductivity, stability in air and against Li metal, and compatibility with high-voltage cathodes.[2],[3] Despite significant progress being made, our understanding of LLZO is limited by the relatively small number of compositions which have been studied; especially considering the leading contender is a pseudo-quaternary oxide (Ga-doped LLZO) and many studies are now utilizing multiple dopants.[4] Herein, we have applied a high-throughput methodology for synthesizing, characterizing, and testing sets of 64 LLZO electrolytes at the mg-scale. We employ a citrate sol-gel synthesis method whereby reagent solutions are dispensed across a well-plate to give a composition gradient. After drying the samples and burning off the citrates, the resulting powders are pressed into pellets using a custom-made 64-pellet die and the pellets are sintered at the desired temperature. The high-throughput characterization techniques utilized include powder X-ray diffraction, electrochemical impedance spectrometry and electrochemical cycling in order to test electrolyte stability; with each method performed on up to 64 samples simultaneously.Using our methodology, we have studied over 700 samples to produce a full phase stability diagram for the Li-La-Zr-O pseudoternary system. We find that within the Li-La-Zr-O system, there is significant solubility of Li into the La2Zr2O7 pyrochlore structure commonly found as an impurity in LLZO synthesis due to lithium loss. We also find that LLZO appears as both tetragonal and cubic forms throughout the system, with the cubic LLZO appearing in an extremely restricted region that is difficult to access as pure phase due to lithium loss, while excess lithium leads to the tetragonal LLZO. Li conductivity measurements show that both cubic and tetragonal undoped LLZO have similar bulk conductivities, but there is only a limited region near the formal Li7La3Zr2O12 composition where grain boundary conductivity is high. Our methodology is also applied to a comprehensive doping study where over 40 different dopants are evaluated and promising dopants are tested in co-doped compositions. [1] D. Aurbach et al., Electrochimica Acta 2004, 50, 247-254. [2] Q. Liu, et al., J. Power Sources 2018, 389, 120-134. [3] T. Thompson, et al., ACS Energy Letters 2017, 2, 462-468. [4] F. Zheng, et al., J. Power Sources 2018, 389, 198-213.

Extraordinary thermoelectric performance, thermal stability and mechanical properties of n-type Mg3Sb1.5Bi0.5 through multi-dopants at interstitial site

Mg3Sb2-based thermoelectric materials have attracted much interest since the discovery of their excellent n-type thermoelectric performance with excess Mg content and proper dopant. Herein, we proposed a doping diagram for Mg3Sb2-based material in a binary parameters space of electronegativity difference and atomic radius difference of extrinsic elements with Mg atom. Based on this doping diagram, we designed a multiple interstitial doped TMx:Mg3Sb1.5Bi0.5 (TM = CrMnFeCoCu) material, and achieved a high dimensionless figure of merit value of 0.76 at room temperature and 1.83 at 500 °C, respectively. The multiple interstitial dopants significantly suppress the formation of Mg vacancy, which is of great importance in protecting the electrical transport channel and improving the thermal stability. Besides, the mechanical properties are also enhanced due to the random distribution of elements in the matrix, impeding the migration of dislocations. Our work verifies the benefits of maximized sub-lattice disordering through the multi-elements doping strategy in the Mg3Sb1.5Bi0.5 material.

Enhancement in oxygen transfer rate of CuMn2O4 oxygen carrier via selective dopants: Role of dopant effects on O migration for chemical looping combustion

Chemical looping combustion technology has been widely studied because this platform can convert fossil fuels efficiently into sustainable energy with an in situ carbon capture capability. The redox property of the oxygen carrier (usually a transition metal oxide) plays a critical role in determining the kinetics of the combustion process. This study investigated computationally and experimentally methane oxidation on spinel structure of Mn–Cu bimetallic oxygen carriers due to its facile oxygen uncoupling (Mn and Cu) with high durability in the reduction cycle. Our simulation predicted that the mechanism of complete methane oxidation on CuMn2O4 involved two competitive rate-limiting steps: 1) thermodynamic controlled step of CH2O* formation (CH3O* + O → CH2O* + OH) and 2) kinetic controlled step of CO formation (CHO* + O → CO* + OH). Multiple dopants (Co, Cr, Fe, Ni, Ti, V, and Zn) to the activation barriers of the rate-limiting steps were tested to enhance the performance of oxygen carriers by improving the oxygen transfer rate. Ni-doped CuMn2O4 and V-doped CuMn2O4 showed promising results computationally (significant decrease in ∆E of rate limiting steps). The enhanced oxygen transfer rate of Ni-doped CuMn2O4 was confirmed experimentally. On the other hand, experimentally, V-doped CuMn2O4 provided a lower oxygen transfer rate than the other CuMn2O4 materials, which is inconsistent with the computational predictions. Computation studies showed that the lower oxygen transfer rate stems from the hindrance of O migration by surface V dopants; surface V atom energetically hampers O migration from the subsurface to the top surface. This behavior adversely affects the oxygen transfer rate, resulting in a lower net oxygen transfer rate. These results suggest that the effects of dopants on O migration should be carefully considered when designing enhanced oxygen carriers using a dopant strategy.

Preparation of Mineral Admixture from Iron Tailings with Steel Slag-Desulfurization Ash and Its Application to Concrete.

Iron tailing solid waste not only has a high annual output but also has a low comprehensive utilization rate. Low utilization rate of iron tailings seriously restricts the development of comprehensive utilization of solid waste. In order to prepare an iron tailings-based ternary solid waste admixture and to verify its application to concrete, first, the effect of solid waste synergy on the strength of an iron tailings-steel slag-desulfurization ash admixture (ISD) system was investigated. Second, the effect of chemical activator dosing on the strength of an ISD system was studied and the mechanism of chemical activator action on the ISD system was investigated by thermogravimetric analysis (TG-DTA) Then, the effect of this admixture on the strength of concrete was studied. Finally, the mechanism of the effect of this admixture on the strength of concrete was clarified by mercury intrusion porosimetry (MIP) and backscattering electron tests (BSE). The results showed that the 7 d and 28 d compressive strengths of the ISD admixture were significantly higher than those of iron tailings single admixture. The 7 d and 28 d compressive strengths of the ISD system reached 24.9 MPa and 36.1 Mpa, respectively, when the ratio of iron tailings:steel slag:desulfurization ash = 1:1:1. Na2SiO3 is suitable for the early strength agent of the ISD admixture, but the amount of admixture should not exceed 0.6% of the admixture. TG-DTA shows that Na2SiO3 is enhancing the early strength of the ISD system by promoting the consumption of Ca(OH)2 in the ISD system to produce C-S-H. However, in the late reaction of the ISD system, Na2SiO3 inhibits the late strength development of the ISD system by suppressing Ca(OH)2 production. Concrete with ISD dosing of 30% or less meets the C40 requirement. MIP and BSE show that ISD provides a filling effect to concrete, but also causes a reduction in the active reactants of concrete and the combined effect of microfilling and active effects affects the strength development of ISD concrete. This study provides a theoretical and scientific basis for the preparation of iron tailings-based ternary solid waste dopants, and, in addition, the study promotes the consumption of iron tailings solid waste and the development of multiple solid waste dopants.

Dispersion coding of ENZ media via multiple photonic dopants

Epsilon-near-zero (ENZ) media are opening up exciting opportunities to observe exotic wave phenomena. In this work, we demonstrate that the ENZ medium comprising multiple dielectric photonic dopants would yield a comb-like dispersion of the effective permeability, with each magnetic resonance dominated by one specific dopant. Furthermore, at multiple frequencies of interest, the resonant supercouplings appearing or not can be controlled discretely via whether corresponding dopants are assigned or not. Importantly, the multiple dopants in the ENZ host at their magnetic resonances are demonstrated to be independent. Based on this platform, the concept of dispersion coding is proposed, where photonic dopants serve as “bits” to program the spectral response of the whole composite medium. As a proof of concept, a compact multi-doped ENZ cavity is fabricated and experimentally characterized, whose transmission spectrum is manifested as a multi-bit reconfigurable frequency comb. The dispersion coding is demonstrated to fuel a batch of innovative applications including dynamically tunable comb-like dispersion profiled filters, radio-frequency identification tags, etc.

Configuration Sensitivity of Electrocatalytic Oxygen Reduction Reaction on Nitrogen-Doped Graphene.

As one of the most promising nonprecious metal catalysts for the oxygen reduction reaction (ORR), the structure of the active site on nitrogen-doped carbon materials is still under debate. Here, we report that the sensitivity of the ORR on the local configuration of multiple nitrogen dopants may be overlooked. Combining global structure searching with density functional theory calculations, we established the structure-activity relationship for 19 and 298 possible configurations of graphitic nitrogen-doped graphene with N content of 2 and 3%, respectively. It was revealed that the stability cannot be a screener to determine the major contributor to the activity. 77.5% of current density is contributed by the active configuration with 4.59% population on the graphene containing 3% nitrogen. It unambiguously demonstrates the configuration sensitivity of N-doped graphene for ORR and opens a new window to identifying the optimal structure of N-doped carbons for various applications.

Enhancing capacity of lithium spinel via chlorination and triple doping with transition metals for next generation lithium based batteries

Lithium spinel (LiMn2O4) possesses a lower theoretical specific capacity compared to layered oxide cathodes (LiCoO2, LiNi0.33Mn0.33Co0.33O2, etc.) but offers an environmentally safe alternative by eliminating the cobalt used in current cathodes. LiMn2O4 requires dopants to increase the operating voltage, maximize energy density, and be competitive with current cathodes. Through a modified Pechini method, this is demonstrated with multiple dopants. The process and spinel structure enable multiple transition metal dopants (nickel, iron, and cobalt) to be added on the Mn site, which increases the specific capacity up to 110 mAh g−1 when charging up to 5.25 V. Chlorine doping in LiMn2O4 expands the lattice from 8.189 to 8.215 Å, allowing for the insertion and removal of additional lithium when cycling down to 2 V. This results in a nearly two fold increase in specific capacity to 200 mAh g−1 when discharging at 0.5 mA cm−2. However, cycling between 5.25 V and 2 V with standard liquid electrolytes increases cell resistance from 63 to 314 Ω due to instability of the electrolyte at voltages greater than 4.5 V. The chlorinated spinel is then paired with a >5 V stable Li6.75La2.75Ca0.25Zr1.5Nb0.5O12 garnet to validate 5 V cycling, achieving 190 mAh g−1 for 5 cycles with limited specific capacity decay.