Triple Doping Research Articles

[Ce3+-Pr3+-Nd3+]:CsPbI2.2Br0.8 stable energy system for photonic and electrical performance upgradation in multitudinous applications

Adopting an integrated and consolidated strategy to energy generation, conversion, and storage is linked to energy sustainability in the modern day. Current investigation explores the lanthanide triple doping mechanism coupled with temperature optimization using (cerium, praseodymium, and neodymium)-oxide to modify CsPbI2.2Br0.8 forming the stable [Ce3+-Pr3+-Nd3+]:CsPbI2.2Br0.8 (CPN:CPVSK) hetero-system. CPN:CPVSK thin films have remarkable optical output for the prolonged duration of 28 days with the band gap energy spanning around 1.64–1.67 eV. These thin films have cubic phase with the 65.44 nm average crystallite size and these thin films have excellent surficial binding without any holes or cracks. CPN:CPVSK was employed as an active light trapping material inside perovskite solar cells processed and analyzed at ambient conditions. The temperature increment from 100 to 200 °C subsequently lead to improvement in efficiency from 6.91% to 15.5% with considerable improvement in fill factor. CPN:CPVSK effectively generated pure H2 with the minor overpotential and Tafel slope values of 132 mV and 122.3 mV dec−1 while the O2 production activity was unappreciable. CPN:CPVSK is a potential material for battery application with the excellent unit capacity of 354 mA H g−1 and lower Rs of 0.44 Ω. Rare earth doped perovskite material is a sustainable, cost effective, and facile to prepare with the greater candidature for practical applications.

An appraisal of the role of lanthanide doping in stabilization and performance improvement of [Sm3+-Eu3+-Tm3+]:CsPbI2.2Br0.8 for high-performance energy systems

Energy sustainability in the present era is associated with the adoption of the integrated and consolidated approach to generate, convert, and store energy. Current investigation is demonstrative of the first exploration of the novel CsPbI2.2Br0.8 transformed by lanthanide triple doping forming [Sm3+-Eu3+-Tm3+]:CsPbI2.2Br0.8 (SET:CPVSK). Also, SET:CPVSK is the for the first time employed in multitudinous energy applications. SET:CPVSK excelled over the pristine material with the minimal alterations in the band gap energy spanning around 1.65 – 1.72 eV tracked for 28 days. With the cubic phase, SET:CPVSK thin films exhibited excellent morphology with the tighter binding to substrate. As light harvesting layers inside entirely ambient perovskite solar cells, the efficiency of the cells increased to 16.31 % from 7.49 % upon doping with an improvement in other photovoltaic features also. Electro-catalytic response of the SET:CPVSK towards hydrogen generation was magnanimous with the lower overpotential and kinetic Tafel slope of 130 mV and 116.5 mV dec−1, signifying Volmer-Heyrovsky mechanistic route. With the service life of 100 min, the developed electro-catalyst expressed sustainable output. In terms of the charge storage, the unit capacity was improved to 622.4 mAH g−1 upon doping while the other electrode can only reach up to 394.2 mAH g−1. Furthermore, the resistive response of this electrode was also appreciable with the lower equivalent series resistance (Rs) i.e. 0.41 Ω, showing auspiciousness for practical applications.

N-type semiconductor [Gd3+-Ho3+-Dy3+]:SnO2 driven functionality enhancement in energy systems associated with photovoltaic and electrochemical contraptions

Current work reports the sustainable synthesis and application of the novel n-type [Gd3+-Ho3+-Dy3+]:SnO2 semiconductor material expressing band gap energy narrowing upon lanthanide triple doping. The band gap energy of this material spanned around 3.8–3.9 eV. Rare earth doped SnO2 material has tetragonal rutile crystalline geometry, space group P42/mnm, and 59.46 nm particle size. Thin films for this material have remarkable coverage. Using this material as an electron transport layer inside all inorganic perovskite device resulted in a negligible hysteresis leading to remarkable power conversion efficiency of 14.16 %, fill factor 80 %, short circuit current 16.48 mA cm−2, and an open circuit voltage of 1.02 V [Gd3+-Ho3+-Dy3+]:SnO2 decorated nickel foam electrode expressed double layer mechanism of electrical charge storage gaining a specific capacitance of 689 F g−1 in 0.1 M NaCl electrolyte at 10 mV/s. Excellent electronic and ionic conductivity was expressed by impedance studies with equivalent series resistance (Rs) of as low as 0.11 Ω. Furthermore, the electro-catalytic water splitting results exhibited the auspicious of this material as an HER catalyst with lower overpotential and Tafel slope values of 140 mV and 125.5 mV dec−1, respectively. The developed material is a suitable candidate for advanced energy applications marked by sustainability and economic viability.

Sm-Eu-Tm]:CsPbI2Br1 perovskite hetero-system: Probing rare earth driven stabilization for sustainable energy conversion, generation, and storage capacity

This is the first report on the lanthanide doped cesium lead halide perovskite using triple doping mechanism for formation of the novel [Sm-Eu-Tm]:CsPbI2Br1 perovskite (SET-CPVSK) hetero-structure. SET-CPVSK remained intact in terms of opto-electronic response shown by slight alleviation in band gap from 1.63 to 1.66 eV for 28 days. It attained the characteristic black cubic phase (ABX3 crystalline orientation) when thermally treated at 200 °C. The deposited thin films were smoother and devoid of any pinholes. Planar and ambient perovskite solar cell containing SET-CPVSK absorber was 14.06 % efficient. This solar cell was also hysteresis free with 63.14 % fill factor. The profound electro-catalytic output towards O2 and H2 generation achieved with the SET-CPVSK was reflected by the lower overpotential values of 50 and 140 mV, respectively. The kinetic favorability was also disclosed by lower Tafel slope values. As a potential energy storage material, SET-CPVSK adorned electrode achieved the unit capacity of 554.4 mA H g−1 with the impressively lower equivalent series resistance (Rs) of 0.79 Ω depicting lower impedance and subsequently higher diffusion of the ions. SET-CPVSK is a sustainable energy material which has the potential to replace potentially expensive materials due to its impressive efficiency and stability.

Modulating Coordination of Iron Atom Clusters on N,P,S Triply-Doped Hollow Carbon Support towards Enhanced Electrocatalytic Oxygen Reduction.

Constructing atom-clusters (ACs) with in situ modulation of coordination environment and simultaneously hollowing carbon support are critical yet challenging for improving electrocatalytic efficiency of atomically dispersed catalysts (ADCs). Herein, a general diffusion-controlled strategy based on spatial confining and Kirkendall effect is proposed to construct metallic ACs in N,P,S triply-doped hollow carbon matrix (MACs /NPS-HC, M=Mn, Fe, Co, Ni, Cu). Thereinto, FeACs /NPS-HC with the best catalytic activity for oxygen reduction reaction (ORR) is thoroughly investigated. Unlike the benchmark sample of symmetrical N-surrounded iron single-atoms in N-doped carbon (FeSAs /N-C), FeACs /NPS-HC comprises bi-/tri-atomic Fe centers with engineered S/N coordination. Theoretical calculation reveals that proper Fe gathering and coordination modulation could mildly delocalize the electron distribution and optimize the free energy pathways of ORR. In addition, the triple doping and hollow structure of carbon matrix could further regulate the local environment and allow sufficient exposure of active sites, resulting in more enhanced ORR kinetics on FeACs /NPS-HC. The zinc-air battery assembled with FeACs /NPS-HC as cathodic catalyst exhibits all-round superiority to Pt/C and most Fe-based ADCs. This work provides an exemplary method for establishing atomic-cluster catalysts with engineered S-dominated coordination and hollowed carbon matrix, which paves a new avenue for the fabrication and optimization of advanced ADCs.

Modulating Coordination of Iron Atom Clusters on N,P,S Triply‐Doped Hollow Carbon Support towards Enhanced Electrocatalytic Oxygen Reduction

AbstractConstructing atom‐clusters (ACs) with in situ modulation of coordination environment and simultaneously hollowing carbon support are critical yet challenging for improving electrocatalytic efficiency of atomically dispersed catalysts (ADCs). Herein, a general diffusion‐controlled strategy based on spatial confining and Kirkendall effect is proposed to construct metallic ACs in N,P,S triply‐doped hollow carbon matrix (MACs/NPS−HC, M=Mn, Fe, Co, Ni, Cu). Thereinto, FeACs/NPS−HC with the best catalytic activity for oxygen reduction reaction (ORR) is thoroughly investigated. Unlike the benchmark sample of symmetrical N‐surrounded iron single‐atoms in N‐doped carbon (FeSAs/N−C), FeACs/NPS−HC comprises bi‐/tri‐atomic Fe centers with engineered S/N coordination. Theoretical calculation reveals that proper Fe gathering and coordination modulation could mildly delocalize the electron distribution and optimize the free energy pathways of ORR. In addition, the triple doping and hollow structure of carbon matrix could further regulate the local environment and allow sufficient exposure of active sites, resulting in more enhanced ORR kinetics on FeACs/NPS−HC. The zinc‐air battery assembled with FeACs/NPS−HC as cathodic catalyst exhibits all‐round superiority to Pt/C and most Fe‐based ADCs. This work provides an exemplary method for establishing atomic‐cluster catalysts with engineered S‐dominated coordination and hollowed carbon matrix, which paves a new avenue for the fabrication and optimization of advanced ADCs.

Effects of stacking layers and different doping elements on the electronic structures and quantum capacitance of graphene: A DFT study

The influence of boron (B), nitrogen (N), oxygen (O), and sulfur (S) doping on enhancing quantum capacitance were investigated through a series of the surface-doped trilayer graphene structures by using density functional theory (DFT) calculations. The quantum capacitance of monolayer models was enhanced through a single doping, a triple doping, and a vacancy defect. Our calculations suggested that the layer interactions within the trilayer models decreased the quantum capacitance but increased the stability of the doped structures. Interestingly, in the case of sulfur dopants with significantly larger atomic size than carbon, the stacking layers induced a surface distortion that could avoid the steric clashes with stacking layers and enhanced the stability. In conclusion, this work provided more realistic models of modified carbon-based electrodes for supercapacitors with more accurate information from the combined effects of doping and stacking layers.

Insight into novel triple doping (Mg, Cu, N and Mg, Cu, B) on the structural, optical, photocatalytic, and antibacterial properties of ZnO

Due to the growing worries about environmental issues, dye degradation is substantial. Besides that, it is essential to prevent illness development by creating cutting-edge antibacterial agents that can inhibit bacterial activities. Herein, we report a novel photocatalyst exhibiting visible light responsivity for the degradation of methyl violet dye and possessing antibacterial properties to mitigating the emergence of drug resistance. It is triple-doped ZnO (Mg, Cu, N-doped ZnO, and Mg, Cu, B-doped ZnO), successfully synthesized by the solid-state method. The structure crystal is hexagonal wurtzite, and the crystal size is 34.68, 30.22, and 29.47 nm for undoped ZnO, (Mg, Cu, N)-doped ZnO, and (Mg, Cu, B)-doped ZnO, respectively, according to the study of X-ray diffraction (XRD), Raman, and SEM results. The (Mg, Cu, N)- and (Mg, Cu, B)-doped ZnO have smaller particle sizes than undoped ZnO. FTIR spectra show Zn-O, Cu-O, Mg-O,and B-O stretching for synthesized samples. The formation of (Mg, Cu, N)-doped ZnO and (Mg, Cu, B)-doped ZnO also were confirmed by EDAX. PL shows the formation of peaks in UV emission (∼350 nm) and visible emission (513–519 nm and ∼646 nm) that indicate the inhibition of electron-hole recombination and oxygen vacancies in the ZnO lattice. The effective photocatalytic activity of undoped ZnO, (Mg, Cu, N)-doped ZnO, and (Mg, Cu, B)-doped ZnO achieves 80.89 %, 93.41 %, and 92.18 % decolorization of water pollutant methyl violet. The antibacterial activities of the three samples are 6.45, 6.00, and 11.90 mm, respectively.

Sc3+:Ce4+:Y3+ doped zirconia nanopowders (ScCeYSZ): Synthesis, thermal phase stability and hot corrosion behavior of spark plasma sintered body

This study aims to investigate the high-temperature phase stability and hot corrosion behavior of zirconia with triple doping of Sc3+, Ce4+ and Y3+ ions. FESEM result shows that the mean particle size of ScCeYSZ nanoparticles was 80–90 nm. Next, optimal samples regarding the highest high-temperature phase stability (1.9%Sc8.3%Ce1.8%YSZ, 1.1%Sc9.0%Ce1.8%YSZ and 0.5%Sc9.6%Ce1.8%YSZ) were consolidated at 1550 °C for 15 min via the spark plasma sintering (SPS) method. A hot corrosion test was done in the presence of 45%Na2SO4+%55V2O5 salts on three samples at 900 °C for 2 h. Also, the results of hot corrosion were compared with ceramic resulting from the nanostructured YSZ bulk sample (nanoYSZ).Based on the X-ray diffraction results, the formation of the non-transformable tetragonal phase is confirmed in the synthesized nanopowders. Also, the phase and microstructural results after hot corrosion of sintered samples show the formation of a monoclinic phase and destructive YVO4 crystals and quasi-cubic CeO2 crystals on the surface of sintered samples. The results indicated that the sample containing 1.8% scandia, 8.3% ceria, and 1.9% yttria had the highest phase stability and hot corrosion resistance (low monoclinic percentage and low leaching of stabilizer elements of Sc3+:Ce4+:Y3+ from zirconia lattice and low depth of molten salt).

Effect of Y, La, and Yb simultaneous doping on the thermal conductivity and thermoelectric performances of CaMnO3 ceramics

Triple doping of CaMnO3 in different stoichiometric proportions has been studied in bulk sintered materials. They were prepared through the classical ceramic route using planetary milling to decrease the precursors particle sizes. It has been found that particle sizes decrease with the amount of dopant, both in the precursors and in the sintered bodies. XRD patterns showed that all samples were nearly single phase, with small amounts of CaMn2O4 phase. SEM and TEM observations revealed a homogeneous distribution of dopants in the CaMnO3 phase, while EDX showed a composition close to the nominal one. However, HREM imaging has shown some dark regions in the crystallites, with different Ca(Y,La,Yb)/Mn ratios found through STEM image-chemical mapping, which points out to the coexistence of CaMnO3 and CaMn2O4–type domains in the crystallites. Electrical resistivity, absolute Seebeck coefficient and thermal conductivity have been drastically decreased with doping. The highest PF values at 800 ºC have been achieved in 0.02(Y,La,Yb) doped samples (∼ 0.37 mW/K2m), which is among the best reported values in literature. On the other hand, lattice thermal conductivity is dramatically decreased with doping due to the phonon scattering produced by the dopants, the decrease in the grain sizes, and the strains present inside the crystallites, reaching the minimum values at 800 ºC in 0.03(Y,La,Yb) doped samples (∼ 0.8 W/K m). Consequently, ZT reaches the maximum values (∼ 0.29) in 0.03(Y,La,Yb) doped samples due to their very low thermal conductivity, being higher than the best ZT reported values in the literature.

Synergistically improving luminescent properties of Eu2+, Dy3+ co-doped melilite with Bi3+ coupling

The improvement of luminescent properties is important for expanding the application of long afterglow phosphor (LAP). Here, the melilite-type Sr1·97MgSi2O7: Eu2+0.01, Dy3+0.02 LAP was studied with Bi3+ as the second co-dopant. Both photoluminescence (PL) and thermoluminescence (TL) were improved in terms of intensity and afterglow lifetime when the doping concentration of Bi3+ exceeded 2.5 mol%, and the optimized point was 3.5 mol%. As compared to the case of Eu2+ - Dy3+ double doping, the improved PL of Eu2+ - Dy3+ - Bi3+ triple doping samples was attributed to better photon absorption. The improved TL and afterglow were attributed to the synergistic strengthening density of the traps by Bi3+ and the deepening of trapping by Dy3+, if their distance was sufficient close. As a result, both TL and afterglow optimized at a concentration of 2 mol% Dy3+ - 3.5 mol% Bi3+ coupling.

Structural, thermal and electrical analysis of Tb–Gd–Sm co–doped Bi2O3–based solid solutions for intermediate–temperature solid oxide fuel cells (IT–SOFCs)

In this study, the effects of a triple doping strategy on the microstructure and electrical conductivity of Tb–Gd–Sm co–doped Bi2O3 systems were investigated. The XRD patterns generated after the conductivity measurements confirm that high–temperature conductivity tests (>700 °C) can help to stabilize the cubic δ–phase by creating a secondary annealing effect. At about 730 °C, the phase transition (α → δ) is noticeable on both the DTA curve and the conductivity plot of the sample 5Tb5Gd5Sm. The order–disorder transition is recognizable in samples 5Tb10Gd5Sm and 5Tb5Gd15Sm, resulting in two distinct conductivity regions. At 750 °C, the sample 10Tb5Gd5Sm has the highest conductivity of 0.0758 S/cm as well as the lowest activation energy of 0.27 eV.

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.

Synergetic Effect of Li-Ion Concentration and Triple Doping on Ionic Conductivity of Li7La3Zr2O12 Solid Electrolyte.

Li7La3Zr2O12 (LLZO) is a promising and safe solid electrolyte for all-solid-state batteries. To achieve high ionic conductivity of LLZO, stabilizing the cubic phase and reducing Li loss during the sintering process is essential. Therefore, reducing the sintering temperature, which increases the sintering time for high-density pellets, is necessary. Herein, we investigate the change in the crystal structure, morphology, and Li ionic conductivity of LLZO pellets by triple doping with Al, Ga, and Ta and modulating the variation in initial Li concentrations. Interestingly, the proportion of the conductive cubic phase increased with increasing Li stoichiometry by 1.1 times, and this tendency was further accelerated by triple doping. The synergetic effects of triple doping and Li concentration also minimized Li loss during sintering. Accordingly, it provided a high-quality LLZO pellet with good ionic conductivity (3.6 × 10−4 S cm−1) and high relative density (97.8%). Notably, the LLZO pellet was obtained using a very short sintering process (40 min). Considering that the most time-consuming step is the sintering process for LLZO, this study can provide guidelines for the fast production and commercialization of LLZO electrolytes with high ionic conductivity.

Tunable color and energy transfer of Y2Mg3Ge3O12: Tb3+, Tm3+, Eu3+ phosphors with excellent thermal stability

Y2Mg3Ge3O12: RE3+ (RE ​= ​Tb, Eu, Tm) phosphors were prepared by solid phase method. XRD and EDS show that the samples were pure phases. The ET efficiency of Y2Mg3Ge3O12: Tb3+, Eu3+ can reach up to 96.63%, and the mechanism is d-d interaction. In Y2Mg3Ge3O12: Tb3+, Eu3+, Tm3+, the intensity of Tb3+ decreases with the increase of Eu3+ concentrations, and the intensity of Tm3+ is basically unchanged, the intensity of Eu3+ increased first and then decreased. Meanwhile, the ET efficiency can reach up to 77.53%. Moreover, the luminescence intensity at 423 ​K can still be maintained at 87–96.58% of that at the initial temperature. The value of CCT which shows a decreasing trend with increasing Eu3+ concentrations also indicates that warm white light can be obtained by triple doping of Tb3+-Eu3+-Tm3+. The above findings show that these samples are likely to be used in warm w-LEDs.

Self-Templating Synthesis of N/P/Fe Co-Doped 3D Porous Carbon for Oxygen Reduction Reaction Electrocatalysts in Alkaline Media.

The development of low-cost, highly active, and stable oxygen reduction reaction (ORR) catalysts is of great importance for practical applications in numerous energy conversion devices. Herein, iron/nitrogen/phosphorus co-doped carbon electrocatalysts (NPFe-C) with multistage porous structure were synthesized by the self-template method using melamine, phytic acid and ferric trichloride as precursors. In an alkaline system, the ORR half-wave potential is 0.867 V (vs. RHE), comparable to that of platinum-based catalysts. It is noteworthy that NPFe-C performs better than the commercial Pt/C catalyst in terms of power density and specific capacity. Its unique structure and the feature of heteroatom doping endow the catalyst with higher mass transfer ability and abundant available active sites, and the improved performance can be attributed to the following aspects: (1) Fe-, N-, and P triple doping created abundant active sites, contributing to the higher intrinsic activity of catalysts. (2) Phytic acid was crosslinked with melamine to form hydrogel, and its carbonized products have high specific surface area, which is beneficial for a large number of active sites to be exposed at the reaction interface. (3) The porous three-dimensional carbon network facilitates the transfer of reactants/intermediates/products and electric charge. Therefore, Fe/N/P Co-doped 3D porous carbon materials prepared by a facile and scalable pyrolysis route exhibit potential in the field of energy conversion/storage.

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.

Influence of mono- and triple (Cr–La–Ba) doping on the mechanical, optical and gas diffusion properties of corundum

The effect of triple doping with chromium, lanthanum and barium on the mechanical, degassing and gas diffusion properties of fine-crystalline corundum synthesized in a supercritical water fluid was studied. The influence of chromium monodoping on the mechanical and optical properties of fine-crystalline corundum was also investigated. It was found that even small amounts of dopants of lanthanum and chromium during triple and monodoping of corundum significantly improve its mechanical properties (increase the abrasive ability) and reduce it several times the content of volatile gas-liquid impurities, which contributes to increase transparency of the resulting ceramics. The role of the interaction of a chromium impurity with oxygen vacancies in corundum on the increase in the static strength of crystals was suggested. The diffusion coefficients of water in doped corundum were determined. Comparison of the degassing and diffusion properties of corundum doped with La, Cr, Ba with undoped corundum and corundum doped with lanthanum was carried out. The results obtained contribute to the creation of new materials based on doped corundum with high abrasive, luminescent, and gas diffusion characteristics.

Proposal of a Facile Method to Fabricate a Multi-Dope Multiwall Carbon Nanotube as a Metal-Free Electrocatalyst for the Oxygen Reduction Reaction

In this study, a one-pot, low-temperature synthesis method is considered for the fabrication of heteroatom dope multiwall carbon nanotubes (MWCNT). Doped MWCNT is utilized as an effective electrocatalyst for oxygen reduction reaction (ORR). Single, double, and triple doping of boron, nitrogen and sulfur elements are utilized as the dopants. A reflux system with temperature of 180 °C is implemented in the doping procedure. Actually, unlike the previous studies in which doping on the carbon structures was performed using a furnace at temperatures above 700 °C, in this green and sustainable method, the triple doping on MWCNT is conducted at atmospheric pressure and low temperature. The morphology and structure of the fabricated catalysts were evaluated by Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Raman spectroscopy. According to the results, the nanoparticles were encapsulated in the carbon nanotubes. Aggregated clusters of the sulfur in the case of S-MWCNT are considerable. Cyclic voltammetry (CV), rotating disk electrode, linear sweep voltammetry (LSV), and chronoamperometry electrochemical tests are employed for assessing the oxygen reduction activity of the catalysts. The results illustrate that by using this doping method, the onset potential shifts to positive values towards the oxidized MWCNT. It can be deduced that by doping the N, B, and S atoms on MWCNTs, the defects in the CNT structure, which serve as active sites for ORR application, increase. The N/S/B-doped graphitic layers have a more rapid electron transfer rate at the electrode/electrolyte interface. Thus, this can improve the electrochemistry performance and electron transfer of the MWCNTs. The best performance and electrochemical activity belonged to the NB-MWCNT catalyst (−0.122 V vs. Ag/AgCl). Also, based on the results gained from the Koutecky–Levich (KL) plot, it can be said that the ORR takes place through the 4 e− pathway.

Improved microstructure and significantly enhanced dielectric properties of Al3+/Cr3+/Ta5+ triple-doped TiO2 ceramics by Re-balancing charge compensation.

The charge compensation mechanism and dielectric properties of the (AlxCr0.05−x)Ta0.05Ti0.9O2 ceramics were studied. The mean grain size slightly changed with the increase in the Al3+/Cr3+ ratio, while the porosity was significantly reduced. The dielectric permittivity of the co-doped Cr0.05Ta0.05Ti0.9O2 ceramic was as low as ε′∼ 103, which was described by self-charge compensation between Cr3+–Ta5+, suppressing the formation of Ti3+. Interestingly, ε′ can be significantly increased (6.68 × 104) by re-balancing the charge compensation via triple doping with Al3+ in the Al3+/Cr3+ ratio of 1.0, while a low loss tangent (∼0.07) was obtained. The insulating grains of [Cr0.053+Ta0.055+]Ti0.94+O12 has become the semiconducting grains for the triple-doped Alx3+[Cr0.05−x3+Ta0.05−x5+][Tax5+Tix3+Ti0.9+x4+]O12+3x/2. Considering an insulating grain with low ε′ of the Cr0.05Ta0.05Ti0.9O2 ceramic, the electron-pinned defect-dipoles and interfacial polarization were unlikely to exist supported by the first principles calculations. The significantly enhanced ε′ value of the triple-doped ceramic was primarily contributed by the interfacial polarization at the interface between the semiconducting and insulating parts, which was supported by impedance spectroscopy. This research gives an underlying mechanism on the charge compensation in the Al3+/Cr3+/Ta5+-doped TiO2 system for further designing the dielectric and electrical properties of TiO2-based ceramics for capacitor applications.