3d Transition Metal Doping Research Articles

Improved thermodynamic properties of (Sc, V, Ti, Fe, Mn, Co, and Ni) doped NaBH4 for hydrogen storage: First-principal calculation

Sodium borohydride (NaBH4) shows promise as a hydrogen storage option, but its substantial thermodynamic stability limits its practical application. Enhancing NaBH4 by introducing transition metals is an effective approach to enhance its hydrogen-related characteristics. Nevertheless, even with the most successful additives, the temperatures needed for hydrogen release remain too elevated, exceeding 400 °C, which hinders its practical utility. Using first-principles density functional, we have investigated the potential of sodium borohydride as a hydrogen-based fuel source. Our focus has been on the stable α-phase NaBH4 structure with space group symmetry F-43m (216), aiming to understand the impact of 3d transition metal (Sc, V, Ti, Fe, Mn, Co, and Ni) doping on the structural, electronic, and dehydrogenation properties of the NaBH4 system. Furthermore, the heat of formation and desorption temperature values obtained align with the stability and volumetric capacity criteria set by the U.S. Department of Energy (DOE). Our findings indicate that doping transition metals at the Na site weakens the B–H bonds, thereby enhancing the dehydrogenation performance. Among the various systems studied, those doped with Sc and Ti exhibit the most favorable dehydrogenation properties.

Building stabilized Cu0.17Mn0.03V2O5−□·2.16H2O cathode enables an outstanding room‐/low‐temperature aqueous Zn‐ion batteries

AbstractVanadium oxide cathode materials with stable crystal structure and fast Zn2+ storage capabilities are extremely important to achieving outstanding electrochemical performance in aqueous zinc‐ion batteries. In this work, a one‐step hydrothermal method was used to manipulate the bimetallic ion intercalation into the interlayer of vanadium oxide. The pre‐intercalated Cu ions act as pillars to pin the vanadium oxide (V‐O) layers, establishing stabilized two‐dimensional channels for fast Zn2+ diffusion. The occupation of Mn ions between V‐O interlayer further expands the layer spacing and increases the concentration of oxygen defects (Od), which boosts the Zn2+ diffusion kinetics. As a result, as‐prepared Cu0.17Mn0.03V2O5−□·2.16H2O cathode shows outstanding Zn‐storage capabilities under room‐ and low‐temperature environments (e.g., 440.3 mAh g−1 at room temperature and 294.3 mAh g−1 at −60°C). Importantly, it shows a long cycling life and high capacity retention of 93.4% over 2500 cycles at 2 A g−1 at −60°C. Furthermore, the reversible intercalation chemistry mechanisms during discharging/charging processes were revealed via operando X‐ray powder diffraction and ex situ Raman characterizations. The strategy of a couple of 3d transition metal doping provides a solution for the development of superior room‐/low‐temperature vanadium‐based cathode materials.

First-principles study on the electronic, magnetic and optical properties of the novel squared SN2 monolayer with 3d transition metal doping and point vacancy

The SN2 monolayer with a square lattice (S-SN2) is a non-magnetic semiconductor. The lack of magnetism and the weak light absorption severely limit its further applications in spintronic and optoelectronic devices. Herein, we investigate the effects of 3d transition metal (Fe, Co and Ni) substitution doping and point vacancy engineering on the S-SN2 monolayer using first-principles calculations. The negative binding energies and the AIMD simulations indicate that all doped cases exhibit excellent structural stability. After doping, the diverse properties including ferromagnetic spin semiconducting behavior, non-magnetic semiconducting property, and significant ferromagnetic half-metallic character with 100 % spin polarization can be realized among these doped S-SN2 monolayers. Interestingly, the value of work function for S-SN2 monolayer can be regulated by doping from 6.55 eV for pure S-SN2 monolayer to a range of 5.11–6.89 eV for doped systems. Moreover, the visible light absorption of S-SN2 monolayer can be significantly enhanced by Fe doping, reaching a high value of about 1.2×105 cm−1. Additionally, a non-magnetic metal and a ferromagnetic half-metallic character with a large total magnetic moment of 5.93 μB can be induced in S-SN2 monolayer with a single N and S vacancy, respectively.

Modulation of magnetic and optical properties for GeS monolayer

The layered structure of GeS exhibits commendable thermal stability and holds significant promise in the realms of optoelectronics and ion batteries. But its application is limited as dilute magnetic semiconductor. Therefore, this study delves into the impact of 3d transition metal (TM = V, Cr, and Mn) doping on the magnetic and optical characteristics of two-dimensional GeS monolayer through a first-principles calculation method grounded in density functional theory. The findings elucidate that all doping systems lead to a reduction in the band gap, with the V-doped system exhibiting the most significant diminishment. After doping process, magnetic coupling emerges between the electrons in the TM-3d state and those in the S-3p state, resulting in the manifestation of magnetic semiconductor characterized by magnetic moments of 3 μB, 4 μB, and 5 μB, respectively. Comparative analysis with the pristine GeS monolayer, it reveals enhancements in optical absorptivity and refractive index within both the infrared and visible spectra of the doped systems. Notably, the V-doped system showcases superior optical properties due to its narrower band gap, facilitating more efficient electron transitions to the conduction band. Consequently, TM (TM = V, Cr, and Mn)-doped GeS monolayer hold promising potential in the realms of spintronics and optoelectronics.

Effect of 3d transition metal doping on the structural, electronic, & magnetic properties of BiCoO3 using first principles study

In this paper, the influence of 3d transition metal (TM) dopants in BiCoO3 (BCO) having C-type antiferromagnetism has been studied using first principles calculation. The value of c/a ratio is found to improve for Sc, V, Mn, Fe, Ni, Cu and Zn doping in BCO which indicates an increase in the tetragonality ratio upon introduction of these dopants in BCO. The formation energy calculations pointed out that it is easier to incorporate the TM atoms having number of d atoms lesser than that of Co (d < 7) in BCO. The electronic, and magnetic properties were studied and it was found that the electron/hole traps are introduced due to the presence of 3d TM dopant in BCO. The partial density of states reveal that V, Ni and Zn doped BCO exhibit half metallic characteristics with a lower band gap value among the other TM doped BCO systems. It was interesting to note that the presence of states in both spins at Fermi level due to Cu doping leads to a transition of BCO towards metallic behaviour in contrast to pure BCO having a clear band gap of 1.77 eV. The net magnetization was found to arise due to TM doping at Co site which may be attributed to the uncompensated Co spins and is mainly localized on the TM dopant. Successive spin polarization model (SSP model) was used to explain the net magnetization in the system due to 3d TM dopants in BCO system. The electron localization function plots also reveal that for d < 5 the electrons are localised near the TM metal ions and for d > 5 the localization impacts the near neighbouring Co ions. From this study, it is suggested that the magnetic and electronic properties of BCO system, can be tuned by 3d TM doping which has vast potential in photovoltaic and magneto-electric applications.

Sodium-Beta Alumina and Its Application in a Novel Sodium-Based Solid-State Cell Concept

Post-Li-ion technologies are inevitable for solving problems connected to Li-ion cells, namely shortage of raw materials and physicochemical limits in energy density. Substitution of lithium with sodium while simultaneously replacing the liquid electrolyte with a ceramic solid electrolyte is a promising alternative.1 Sodium-beta alumina is a solid-state electrolyte with outstanding chemical, electrochemical, and mechanical properties.2 So far, high-temperature cells have been using it as a solid electrolyte.3,4 However, we recently showed that the sodium-ion conducting sodium-beta alumina solid electrolyte (BASE) is also a suitable solid electrolyte for solid-state cells operating at middle- to low temperatures. We present methods commonly used to reduce the area-specific capacity at the interfaces, stemming from the poor interaction of the rigid solid electrolyte with its adjacent electrodes. Hence, we tackle the bottleneck of middle- to low-temperature solid-state cell systems utilizing BASE, leading to enhanced cell performance.2 To increase the electrochemical performance, adjusting BASE´s properties is necessary. We showed that 3d transition metal doping tunes BASE´s properties effectively. For example, Ti4+ doping assisted a liquid sintering process, which changed the microstructure. Thus, BASE´s ionic conductivity increased by 50%. Simultaneously, we increased BASE´s fracture strength while reducing energy costs.5 Furthermore, we demonstrate the importance of proper storage conditions. We elucidate the effect of humidity on disk-shaped samples of Li-stabilized sodium-beta alumina and quantify the negative consequences of improper storage for cell systems using sodium-beta alumina. Despite detrimental effects on ionic conductivity and the chemical composition, the critical current density collapsed from the maximum of 9.1 mA cm-2, one of the highest values reported for sodium-beta alumina, to only 1.7 mA cm-2 at 25 °C. We show how impedance analysis and additional characterizations assist in clarifying occurring degradation mechanisms, namely ion exchange and subsequent buildup of surface layers.6 Combining the knowledge from previous works, we provide a proof-of-concept for a novel sodium-based solid-state cell concept utilizing sodium-beta alumina. We use sodium metal as the negative electrode, which is necessary to achieve high specific energy and the requirement to compete with existing cell systems. An environmentally friendly transition metal oxide positive electrode with high specific energy is paired with the negative electrode. A composite positive electrode ensures intra-electrode conduction while enabling a facile charge transfer due to an intimate electrolyte–electrode interface contact, leading to stable cycling over 50 cycles with good energy retention. We think that the proof-of-concept opens the door for dozens of new material combinations and enhances the utilization of sodium-beta alumina in medium- to low-temperature solid-state cell systems.All in all, the presentation points out the excellent performance and the enormous potential of sodium-beta alumina for sodium-based energy storage technologies.References Janek, J. & Zeier, W. G. A solid future for battery development. Nat. Energy 1, 1167; 10.1038/nenergy.2016.141 (2016).Fertig, M. P. et al. From High‐ to Low‐Temperature: The Revival of Sodium‐Beta Alumina for Sodium Solid‐State Batteries. Batteries & Supercaps; 10.1002/batt.202100131 (2022).Sudworth, J. The sodium/nickel chloride (ZEBRA) battery. Journal of Power Sources 100, 149–163; 10.1016/S0378-7753(01)00891-6 (2001).BASF New Business GmbH. Stationary Energy Storage. High-energy, long-duration sodium-sulfur battery (Ludwigshafen am Rhein, 2020).Dirksen, C. L., Skadell, K., Schulz, M., Fertig, M. P. & Stelter, M. Influence of 3d Transition Metal Doping on Lithium Stabilized Na-β″-Alumina Solid Electrolytes. Materials (Basel, Switzerland) 14, 5389; 10.3390/ma14185389 (2021).Fertig, M. P., Dirksen, C., Schulz, M. & Stelter, M. Humidity-Induced Degradation of Lithium-Stabilized Sodium-Beta Alumina Solid Electrolytes. Batteries 8, 103; 10.3390/batteries8090103 (2022). [Figure 1. Schematic illustrating the abstract submission´s topics. Pictures adapted from Ref. 2,6] Figure 1

Enhancement of weak magnetism of 3C–SiC by 3d-transition metal doping

Defects seem to play a very decisive role in setting up long-range magnetic order in 3C–SiC. The feeble ferromagnetic response exhibited by SiC at room temperature, known as d0 magnetism, has been attributed to defects in the system. We present the strengthening of d0 magnetism through hole doping by 3d-transition metal (TM) substitution at the Si site. The valence state of the Mn, Co, and Ni has been found to be 2+ while Cr takes a 3+ valence state. The Mn-doped system exhibits the highest Curie temperature, saturation magnetization, and spontaneous magnetization value as compared to samples with other dopants. Detailed quantitative analysis of magnetization data and electron spin resonance spectra suggests the enhancement of the d0 magnetism due to the generation of holes caused by the TM doping at the Si site. The room temperature ferromagnetic response observed in the doped samples could be explained using modified Bound Magnetic Polaron (BMP) model.

DFT computations combined with semiempirical modeling of variations with temperature of spectroscopic and magnetic properties of Gd3+-doped PbTiO3.

The rare-earth or 3d transition metal dopants in perovskites have potential to induce interesting features, thus opening opportunities for investigations and applications. Hence, understanding some features, i.e., defect structure, site of incorporation, valence state, and mechanism of charge compensation, in a wide range of temperature is crucial for their technological applications. A comprehensive understanding of the mechanism of structural changes in PbTiO3 doped with trivalent rare-earths is significant for their potential applications in photonics. To unravel the structural changes, we utilize the density functional theory (DFT) to optimize structural data, which then serve as input for the semiempirical superposition model (SPM) analysis of spectroscopic and magnetic properties of Gd3+-doped PbTiO3. We compute the formation energies of the doped compounds with and without O-vacancy to determine the stable composition. Analysis of the Bader electron charges computed using DFT plus quantum theory of atoms in molecules enables elucidating the effects of the Gd dopant and O-vacancy on the ionic and covalent bonds and, thereby, chemical stability of the compositions. To explain and corroborate the zero-field splitting parameters (ZFSPs) measured by EMR and the lattice parameter changes obtained from XRD, we employ SPM. The optimized structures obtained from ab initio computations for various structural models of Gd3+ doped PbTiO3 are utilized as input data for SPM calculations of ZFPs. This enables theoretical analysis of variations of ZFSPs from 5 to 780 K. The results were fine-tuned by matching with available experimental EMR data for Gd3+ probes in PbTiO3 nanoparticles. Modeling has been carried out considering several possible structural models and the role of an O-vacancy around Gd3+ centers. The results show that the two-fold modeling approach, combining DFT and SPM, provides a reliable description of experimental data. Comparative analysis indicates that the Ti-site is less favorable for being replaced by Gd3+ with/without O-vacancy. This analysis confirms the plausibility of the Pb2+ site for Gd3+ dopants and sheds light on the changes of crystal structure during the phase transitions occurring in PbTiO3 with decreasing temperature.

Electronic structures and quantum capacitance of single-walled carbon nanotubes doped by 3d transition-metals: A first principles study

Supercapacitors are valued as one of the new green energy storage devices, but the low energy density limits the wide application of supercapacitors. In this paper, the effects of 3d transition metal doped on electronic structure and quantum capacitance of carbon nanotubes are investigated using DFT. The calculations show that elemental doping has caused the break-up of two degenerate states near the Fermi level, quasi-local state changes in the energy band, and the creation of new energy bands. The doping of V(Cr, Mn, Co) causes spin polarization in the energy band. The change in energy band affects the density of states near the Fermi level, effectively increasing the quantum capacitance and surface charge density of the carbon nanotube electrode. The quantum capacitance of Ni-doped carbon nanotubes is the largest, at 59.74 µF/cm2. In the range of water stability, Ti(V, Gr, Mn, Co)-CNT are suitable for use as electrode materials in symmetrical double layer supercapacitors. Sc(Fe, Cu, Zn)-CNT is suitable for use as anode materials in asymmetric double layer supercapacitors. Ni-CNT is suitable for use as a cathode material for asymmetric double layer supercapacitors. This study verifies the feasibility of 3d transition metal doping to improve the quantum capacitance of carbon nanotube electrodes.

Tuning the magnetic and electronic properties of monolayer SnS2 by 3d transition metal doping: A DFT study

Tin disulfide (SnS 2 ) is a member of the layered metal dichalcogenides family. Monolayer SnS 2 is a semiconductor with an indirect bandgap of 2.43 eV. It is a nonmagnetic semiconductor. In this article, we systematically study the electronic and magnetic properties of 3 d transition metal atom-doped monolayer SnS 2 . The spin-polarized First-principles calculations reveal that Sn-poor condition is the energetically favourable condition to substitute all the 3 d transition metal atoms into SnS 2 monolayer at the Sn-site. We observe that, in all the doped systems, the denser valence bands are filled with the hybridized impurity 3 d and S-3 p orbitals. Here we show that, Sc-doped SnS 2 is a nonmagnetic metal, and Ti and Ni-doped systems are nonmagnetic semiconductors. Single V, Cr, Mn, Fe, Co, Cu, and Zn atom doped systems with a dopant concentration of 6.25% are semiconductors with an induced magnetic moment of 1, 2, 3, 2, 1, 0.688, and 1.275 μ B , respectively. Among them, Cu and Zn-doped systems are direct bandgap semiconductors. With a dopant concentration of 4.08%, the double Fe and Co-doped SnS 2 monolayers are ferromagnetic half metals with 4 and 2 μ B , respectively. The double V, Cr, Mn and Zn-doped SnS 2 are ferromagnetic semiconductors with 2, 4, 6 and 2.56 μ B , respectively. Ferromagnetic coupling between the two identical transition metal atoms is attributed to 90° superexchange. These results emphasize the importance of 3 d transition metal doped monolayer SnS 2 for spin injection, spin polarized current generation and other spintronics device applications.

Enhanced Activities in Alkaline Hydrogen and Oxygen Evolution Reactions on MoS2 Electrocatalysts by In-Plane Sulfur Defects Coupled with Transition Metal Doping.

2D transition metal disulfides (TMDs) are promising and cost-effective alternatives to noble-metal-based catalysts for hydrogen production. Activation of the inert basal plane of TMDs is crucial to improving the catalytic efficiency. Herein, introduction of in-plane sulfur vacancies (Sv ) and 3d transition metal dopants in concert activates the basal planes of MoS2 (M-Sv -MoS2 ) to achieve high activities in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Acetate introducing mild wet chemical etching removes surface S atoms facilitating subsequent cation exchange between the exposed Mo atoms and targeted metal ions in solution. Density-functional theory calculation demonstrates that the exposed 3d transition metal dopants in MoS2 basal planes serve as multifunctional active centers, which not only reduce ΔGH* but also accelerate water oxidation. As a result, the optimal Ni-Sv -MoS2 and Co-Sv -MoS2 electrocatalysts show excellent stability and alkaline HER and OER characteristics such as low overpotentials of 101 and 190mV at 10mA cm-2 , respectively. The results reveal a strategy to activate the inert MoS2 basal planes by defect and doping co-engineering and the technique can be extended to other types of TMDs for high-efficiency electrocatalysis beyond water splitting.

3d‐Transition metal doped two-dimensional SnTe: Modulation of thermoelectric properties

Newly explored hexagonal phase of two-dimensional (2D) SnTe has been shown to be thermodynamically as well as dynamically stable and it exhibits high thermoelectric performance. In this study, we mainly investigate the effect in terms of electrical and thermal transport properties due to 3d-transition metal (TM) doping in 2D-SnTe. Based on first-principles calculations and Boltzmann transport theory, our study encompasses that both V and Mn doped SnTe exhibit moderate intrinsic carrier mobility because of lower elastic constant and higher carrier effective mass. Furthermore, the incorporation of V and Mn in the atomic layer of SnTe slightly enhances the Seebeck coefficient than pristine. While calculating thermal transport coefficient, V and Mn doping show a significant reduction in lattice thermal conductivity than pristine 2D SnTe due to enhanced phonon-phonon scattering strength, and as a result, we achieve very high zT ~ 2.24 at 900 K for Mn-doped SnTe. The replacement of Sn by cost-effective and environmentally-friendly 3d-TM with enhanced thermoelectric performance by 5%, would be beneficial during the energy crisis.

Tuning the magnetic and electronic properties of MoI3 monolayer by 3d transition metal doping: A first-principles study

Two-dimensional (2D) materials with intrinsic magnetism have sparked a lot of attention due to their potential applications in spintronics. Recently, monolayer molybdenum triiodide (MoI3), which is a member of the transition metal trihalides (MX3) family, has been predicted to be a stable bipolar ferromagnetic semiconductor (BFMS) with intrinsic magnetism. By means of first-principle calculations based on the GGA + Ueff approach, we modified MoI3 through substitutional doping with 3d transition metal (TM) atoms to improve its spintronic properties. We focused on the study of structural, electronic and magnetic properties of the pristine and 3d TM (TM = Sc, Ti, V, Cr, and Mn) doped MoI3 systems. Our findings reveal that substitutional doping of MoI3 monolayers with Sc and Ti atoms changes their electronic character from a BFMS to a ferromagnetic semiconductor, while V- and Cr-doped MoI3 monolayers result in half semiconducting properties (HSC). More interestingly, the Mn-doped MoI3 monolayer reveals a half-metallic character with enhanced magnetism and sustains these properties even under spin–orbit coupling (SOC). In addition, robust ferromagnetism and high mean-field Curie temperatures were found in all doped systems, especially in the V-doped MoI3 monolayer. By exhibiting these unique electronic and magnetic properties, these TM-doped MoI3 systems could serve as potential candidates for spintronic applications.

3d Transition metal doping induced charge rearrangement and transfer to enhance overall water-splitting on Ni3S2 (101) facet: a first-principles calculation study.

Cost-efficient bifunctional electrocatalysts with good stability and high activity are in great demand to replace noble-metal-based catalysts for overall water-splitting. Ni3S2 has been considered a suitable electrocatalyst for either the hydrogen evolution reaction (HER) or the oxygen evolution reaction (OER) owing to its good conductivity and stability, but high performance remains a challenge. Based on density functional theory calculations, we propose a practical 3d-transition-metal (TM = Mn, Fe and Co) doping to enhance the catalytic performance for both HER and OER on the Ni3S2 (101) facet. The enhancement originates from TM-doping-induced charge rearrangement and charge transfer, which increases the surface activity and promotes catalytic behavior. In particular, Mn-doped Ni3S2 shows good bifunctional catalytic activity because it possesses more active sites, reduced hydrogen adsorption free energy (ΔG H*) for HER and low overpotential for OER. Importantly, this work not only provides a feasible means to design efficient bifunctional electrocatalysts for overall water-splitting but also provides insights into the mechanism of improving catalytic behavior.

Tuning the magnetic and electronic properties of monolayer VI3 by 3d transition metal doping: A first-principles study

Two-dimensional (2D) materials with robust magnetism have drawn immense attention for their promising applications in spintronics. Recently, intrinsic ferromagnetic vanadium triiodide (VI3) has been synthesized experimentally. To enhance its spintronic property, we modified VI3 by interstitial doping with 3d transition metals (TM) and used first-principles calculations to investigate the geometric structure, formation energy, electronic property, and magnetism of pristine VI3 and 3d TM-doped VI3 monolayer. Among eight transition metal (Sc-, Ti-, V-, Cr-, Mn-, Fe-, Co-, and Ni-) doped VI3 materials, four of them (Ti-, V-, Mn-, and Ni-doped VI3) show robust magnetism with full spin polarization near the Fermi energy. Our research demonstrates that Ti-doped VI3 results in half-metallic semiconductor properties (HMS), while V-doped VI3 and Ni-doped VI3 result in half-semiconductor properties (HSC). Surprisingly, Mn-doped VI3 exhibits an unusual bipolar magnetic semiconductor property (BMS). This unique combination of strong ferromagnetism and 100% spin polarization with a half-metallic, half-semiconductor, or bipolar semiconductor property renders 3d TM-doped VI3 as potential candidates for next generation semiconductor spintronic applications. These spin-polarized materials will be extremely useful for spin-current generation and other spintronic applications.

Spin Polarization Properties of Two Dimensional GaP3 Induced by 3d Transition-Metal Doping.

The electronic structure and spin polarization properties of monolayer GaP3 induced by transition metal (TM) doping were investigated through a first-principles calculation based on density functional theory. The calculation results show that all the doped systems perform spin polarization properties, and the Fe–doped system shows the greatest spin polarization property with the biggest magnetic moment. Based on the analysis from the projected density of states, it was found that the new spin electronic states originated from the p–d orbital couplings between TM atoms and GaP3 lead to spin polarization. The spin polarization results were verified by calculating the spin density distributions and the charge transfer. It is effective to introduce the spin polarization in monolayer GaP3 by doping TM atoms, and our work provides theoretical calculation supports for the applications of triphosphide in spintronics.

Activated edge of single layered TiO2 nanoribbons through transition metal doping and strain approaches for hydrogen production

The tunable electronic structures and hydrogen evolution reaction ability of single-layered TiO2 nanoribbons were investigated with 3d transition-metal doping and uniaxial strain. Surprisingly, both surface and inner oxygen atoms in nanoribbon can be effectively activated by Cr doping for hydrogen production. Its hydrogen adsorption free energy was reduced to 0.1 eV, much close to that of Pt metal. The binding capacity of inner oxygen with adsorbed hydrogen was related to its py+z band center level. Moreover, the dependence of amendatory hydrogen adsorption ability on the band center level was also proposed to understand the mechanism of strain engineering. These insights provide a potential approach for achieving high hydrogen production activity in oxide nanomaterials.

Tuning electronic structure of ZnO nanowires via 3d transition metal dopants for improved photo-electrochemical water splitting: An ab initio study

ZnO nanowires have been proposed as potential photo-anode materials for photo-electrochemical water splitting due to their low toxicity, simple synthesis and easy modification routes. However, ZnO suffers from low PEC activity and photo-corrosion eff ;ects, and therefore, application of ZnO nanowires in PEC water splitting still awaits development of effective design and synthesis strategies to improve its PEC efficiencies to commercially viable levels. Here, we present ab initio Density Functional Theory calculations considering 3d transition metal doping as a potential route towards attainment of ZnO nanowires with superior PEC activity. Our results show that the stability of 3d transition metal dopants in ZnO NWs is dependent on the d character of the transition metal dopant as well as their concentration and doping site, with most transition metal atoms being energetically most favorable at the Zn substitutional site both in O-rich and Zn-rich conditions considered. Specifically, we find all 3d transition metal dopants in ZnO NW under O-rich conditions as well as Sc, Ti and V under Zn-rich conditions have negative formation energies at the considered dopant concentrations of 1−6 atm. %, indicating that these dopants can readily be incorporated into ZnO NWs at thermodynamic equilibrium conditions. The electronic properties of Ti and V at 2% and 4% dopant concentration, respectively, yield a staggered band-structure configuration, while Sc, Cr, Mn, Co, Ni, and Cu dopants in ZnO NWs induce band-edge states. In addition, 3d TM dopants induces significant red-shift of the absorption edge of ZnO NW due to reduction in band gap, and are projected to improve visual light harvesting capabilities. Finally, the band alignment relative to the redox potential of water revealed that the valence band maximum of Sc, V, Ni and Cu doped ZnO NWs remains strongly positive above the oxidation potential of O2/H2O, while their reduction potential remain negative below the reduction potential of H+/H2, favouring PEC applications.

Role of 3d transition metal doping in determining the electronic structure and properties of small magnesium clusters: a DFT-based comparison of neutral and cationic states

We have carried out density functional theory calculation to study the evolution of geometric, energetic and electronic properties of Mgn (n = 2–10) clusters. The dispersion corrected ωB97X-D functional is found to be more efficient over the B3LYP + D3 method in determination of accurate structure and energetics of the gas phase small Mgn clusters. We have found that Mg4 possesses the smallest possible three-dimensional geometry and is the most stable cluster among the Mgn clusters studied here. We have therefore selected Mg4 cluster as a host for the doping of 3d transition metal (TM) atom to study the structural, electronic and magnetic properties of these TMMg30,+ clusters. MnMg3 and NiMg3+ clusters are found to be the most stable neutral and cationic TMMg3 clusters, respectively. The NBO and DOS analyses have shown that the stability of the TMMg30,+ clusters is governed by the charge transfer processes as well as the nature of interaction of the atomic orbitals. These studies also confirm that the neutral doped clusters exhibit covalent-like bonding while ionic type bonding is present in cationic clusters. Larger charge gains by the charge deficient TM cations from the Mg atoms in TMMg3+ make them relatively stable over the neutral clusters. The DOS and molecular orbital analyses reveal that the 3d orbitals of the dopant TM atoms actively participate in electronic charge transfer processes by maintaining their individuality in TMMg3 clusters, whereas they remain silent in this regard in case of TMMg3+ clusters. In both these cases, the TM0,+(3d) orbitals play the crucial role of tuning the magnetic moment. Therefore, the overall electronic structure and properties of TMMg30,+ clusters depend solely on the TM(3d) orbitals, which is governed by the charge transfer processes characterized by the charge state of the cluster. Graphical abstract

Increasing the photocatalytic properties of monolayer black phase GeSe by 3d transition metal doping: From ultraviolet to infrared absorption

Improving photocatalytic efficiency is one of the most challenging tasks of photocatalysts in the environmental purification. While most photocatalysis made of two-dimensional (2D) materials only response to ultraviolet (UV) and/or visible light (VL), GeSe can absorb most solar spectrum because of its narrow band gap. However, its absorption efficiency is still not high enough for applications. In this work, using first principles study, the photocatalytic performance of 3d transition metal (TM) (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) doped monolayer GeSe were investigated. The results indicate that Sc doped GeSe demonstrates excellent photocatalytic activity under solar spectrum. The reason is that doping Sc can improve the optical absorption efficiency in the infrared (IR) region, suppress the recombination rate of carriers, and enhance the oxidizability of photogenerated holes. This work provides an important guidance for developing GeSe-based full solar spectrum photocatalysis.