Alkali Doped Research Articles

Deciphering the evolution of electronic and magnetic properties in alkali doped nickel oxide: An In-silico approach

In this study, we employed the DFT+U method to systematically explore the electronic, and magnetic properties of nickel oxide doped with alkali metal atoms (Li, Na, K). The Hubbard potential-U was judiciously applied to all doped compound resulting from alkali doping, and were found to exhibited half-metallic properties. A noteworthy observation was the half-metallic band gap in the spin-down channel, which exhibited a linear variation with the increasing value of the Hubbard potential. Furthermore, the total magnetic moment was discernible in the supercells, with all supercells demonstrating 100% spin polarization at the Fermi level. Consequently, the findings from this study hold significant potential for applications in spintronics, thereby paving the way for future research in this domain.

Oxidation of 5-Hydroxymethylfurfural into 2,5-Diformylfuran on Alkali Doped Ru/C Catalysts. Electron Properties of Ruthenium Species as Descriptor of Catalytic Activity.

Selective aerobic oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran has been achieved on alkali doped Ru/C catalyst. Optimization of Ru metal nanoparticles, as well as the nature and amount of the alkali dopant have been performed. The results showed that doping the Ru/C catalyst with controlled amount of potassium increases the catalytic activity, 2.5 fold with respect to the non-doped sample. Spectroscopic studies showed that these differences in activity can be attributed to a different oxidation reaction mechanism associated to the presence of electron rich Ru species in the promoted sample that facilitate the dissociation of O2, while prevents the oxidation of the metal. The Ru/C-K doped catalyst resulted very stable against leaching and metal sintering, being possible the reuse over several consecutive runs. Moreover, the catalyst could be successfully applied to the oxidation of different alcohols.

Experimental and theoretical investigation of the effect of alkali (Li, Na and K) doping on the properties of nickel oxide thin films: Comparative study

Pure and 6% alkali-doped NiO thin films (alkali A = Li, Na, K) were prepared by a sol-gel spin coating method and deposited on glass substrates. XRD analysis showed that the prepared films belonged to a cubic structure with (111) plane as preferential growth orientation for undoped and K-doped samples and (200) for Li and Na doping. An optical study based on (UV-Visible) showed that the band gap tends to decrease with alkali doping and achieves a minimal value with Na doping. The Urbach energy increases systematically with the decrease of the optical band gap. The resistivity measurements showed that alkali doping led to a significant decrease in the resistivity value. The lowest value was achieved for the 6% Na-doped sample. Structural, optical and elastic properties of pure and 6% A-doped NiO were performed using the first principal method based on density functional theory. The optimization of the geometry of the studied samples revealed that the lattice parameters changed after doping. The band structure and density of states calculations showed that undoped and alkali doped samples exhibited an indirect band gap and the doped samples had comparatively narrower band gaps. The elastic constants Cij, Bulk modulus B, Shear modulus G, Young modulus, and Poison ratio of doped and alkali-doped NiO were further investigated.

An Investigation of Superconducting Properties of Some Alkali Doped (A=Li, Na, K, Rb, Cs) Fe Based Superconductors – A First Principles Study

An Investigation of Superconducting Properties of Some Alkali Doped (A=Li, Na, K, Rb, Cs) Fe Based Superconductors – A First Principles Study

Fabrication of in situ alkali doped flexible CIGSSe solar cells by using aqueous spray deposition

Flexible Cu(In,Ga)(S,Se)2 (CIGSSe) solar cells were fabricated on stainless steel foil by using aqueous spray deposition method. Since stainless steel foil is used, external alkali doping is necessary to passivate defects in CIGSSe absorber. We investigated effects of (Na, K) co-doping and selenization temperature on solar cell performance. With co-doping of Na and K, defect states were passivated significantly and highest power conversion efficiency (PCE) was obtained. However, at higher K concentration of more than 0.5%, different growth mode of CIGSSe was observed and deep defect states were developed, decreasing PCE. In addition, selenization temperature effects were studied by varying selenization temperatures. With higher selenization temperature, defect passivation for the CIGSSe absorber was more apparent, which facilitated increase of open circuit voltage. However, short circuit current was observed to be decreased at higher selenization temperature of 570 °C. This work demonstrates in-situ alkali co-doping into CIGSSe absorber with simple and low-cost spray deposition in an air environment.

Nonphotocatalytic Water Splitting Process to Generate Green Electricity in Alkali Doped Zinc Oxide Based Hydroelectric Cell

Efficient nonphotocatalytic water molecule splitting and electricity generation has been obtained from alkali (Li, Na, K) doped zinc oxide (ZnO) hydroelectric cells (HECs) at room temperature. The existence of defect centers including zinc and oxygen vacancies in pure and alkali-doped ZnO has been observed by optical spectroscopy. Broadband dielectric spectroscopy has been carried out to investigate the charge transfer mechanism in the physisorbed layer of water molecules on the surface of porous ZnO HEC. Temperature dependence of dielectric relaxation was also determined to identify the reorientation dynamics of water molecules near the defect site in ZnO. Minimum activation energy for dipolar reorientation, Eₐ ∼ 128.54 kJ/mol, was calculated for the K-ZnO sample depicting easy hopping of H⁺ ions near the defect site. Maximum lattice strain induced by K doping in ZnO led to faster dipolar reorientation and easy hopping of the proton over the physisorbed layer of water molecules on the cell surface. Maximum output power, Pₒᵤₜ ∼ 5.71 mW/cm², has been delivered by K doped ZnO HEC, which is comparable to the best achieved power density by a ZnO nanoparticle-based dye-sensitized solar cell, ∼9.17 mW/cm². Zinc oxide based hydroelectric cells are a low cost, environmentally friendly solution for energy generation scarcity for the masses living in remote locations without the use of any harmful chemicals.

Highly Uniform Alkali Doped Cobalt Oxide Derived from Anionic Metal-Organic Framework: Improving Activity and Water Tolerance for CO Oxidation

A sequence of alkali metal cation-exchanged Co metal-organic frameworks(Co-MOFs), therein after denoted as M@Co-MOF, M=Na+, K+, Rb+, and Cs+, was prepared and used as the precursors to obtain the corresponding alkali doped cobalt oxide(defined as M/Co3O4, M=Na+, K+, Rb+, and Cs+) through calcination under air atmosphere. The cobalt oxide modified by uniform alkali metals exhibited a significant promotion of catalytic activity for CO oxidation. The activity of M/Co3O4 decreased in the order of Cs+>Na+>K+>Rb+. Experimental and theoretical results revealed that the anionic skeleton of Co-MOF could facilely adsorb alkali metal cations and play a crucial role in the formation of highly uniform alkali doped cobalt oxide. The further characterizations, such as temperature-programmed reduction of H2(H2-TPR), oxygen temperature-programmed desorption(O2-TPD), X-ray photoelectron spectroscopy (XPS), and in situ diffuse reflectance infrared Fourier transform(DRIFT) spectra demonstrated that the enhanced catalytic activity is originated from the interfacial electron transfer as well as weakened the Co— O bond strength, which promoted oxygen desorption from Co3O4 and formation of cobalt species with the lower valence state. The Cs/Co3O4 catalyst was maintained for 60 h without deactivation and still showed a high activity in the presence of water.

Symmetry-Induced Stability in Alkali-Doped Calcium Silicate Hydrate

CO$_2$ emissions originating from the construction industry have a significant impact on global warming where the production of ordinary Portland cement clinker is responsible for approximately 8\% of all human-made CO$_2$. Alkali doped calcium-silicate-hydrate (C-S-H) is a critical silicate material since the use of blended cements and alkali-activated materials in construction industry can substantially reduce human-made CO$_2$ emissions. However, the effect of alkali doping (Na and K) on the long-term stability and associated durability of C-S-H remains an open question. Here, using first principles quantum chemistry calculations on the model crystalline phase clinotobermorite, we show that there is a strong interplay between the thermodynamic stability of alkali doped C-S-H and the symmetry of the alkali atoms in the structure. Our results reveal that a symmetrical distribution of alkali atoms leads to a higher stability value such that stable structures with moderate alkali concentrations can be obtained provided that the alkali atoms are allowed to settle into a symmetrical distribution. We investigate the associated structural mechanisms by calculating the migration barriers of alkali atoms within the material, the electronic charge distribution in the material and the variation of basal spacing by using both computational methods and X-ray diffraction analysis.

Alkaline Electrolysis with an Ion-Solvating Membrane

The paper presents a membrane based alkaline electrolyzer comparable in performance to the PEM electrolyzer. The need for energy efficient as well as cost efficient electrolyzers is obvious in the transition to a sustainable energy system. The PEM electrolyzer has recently gained high popularity with outstanding rate capability, efficiency and lifetime. The key to the success of the PEM electrolyzer is the thin proton exchange membrane, which allows for low internal resistance in a zero-gap configuration. The down-side of it is high cost due in part to noble metal catalysts and expensive coatings of cell components to limit contact resistance in the acidic environment. The extensive use of noble metals is not only costly; especially the need for iridium for the anode catalyst most likely limits large scale roll-out due to the low availability of this element. The alkaline electrolyzer, on the other hand, does not depend on noble metals. It represents a proven and robust technology, but in its traditional form, it suffers from low rate capability, and a bulky construction with a footprint an order of magnitude larger than that of the PEM electrolyzer. An alkaline ion conducting membrane with properties comparable to those of the proton exchange membrane could change that and make the alkaline system very competitive. The game-changer anion exchange membrane is the dream and the search for a suitable material is ongoing (often as fuel cell research). However, the materials still lack in terms of either conductivity or durability when compared to proton exchange membranes. We propose the use of an ion-solvating membrane instead. It has no side chains terminated by quaternary ammonium ions, but a polymer backbone with affinity to aqueous KOH, with which the membrane is imbibed. The principle is similar to that of polybenzimidazole (PBI) imbibed with phosphoric acid in high-temperature PEM fuel cells[1], and the work was initiated using meta-PBI imbibed with aqueous KOH [2-6] . With this system, a performance of 2-3 A cm-2 at 2 V has been demonstrated without the use of noble metals [7]. With the ongoing development of the electrodes, further improvement is expected. The long term stability of the membrane has not been proven, and meta-PBI is, although surprisingly stable in hot 6 M KOH, not stable enough for long term operation. Other ion-solvating membrane materials within the PBI family and apart are being studied. [1] Q. Li, J. O. Jensen, R. F. Savinell and N. J. Bjerrum. High temperature proton exchange membranes based on polybenzimidazoles for fuel cells. Progress in Polymer Science 34 449-477 (2009) [2] D. Aili, M. K. Hansen, R. F. Renzaho, Q. Li, E. Christensen, J. O. Jensen and N. J. Bjerrum. Heterogeneous anion conducting membranes based on linear and crosslinked KOH doped polybenzimidazole for alkaline water electrolysis. J. Membrane Sci. 447 424–432 (2013) [3] J. O. Jensen, D. Aili, M. K. Hansen, Q. Li, N. J. Bjerrum and E. Christensen. A Stability Study of Alkali Doped PBI Membranes for Alkaline Electrolyzer Cells. ECS Trans. 64 (3) 1175-1184 (2014) [4] D. Aili, K. J. Jankova, Q. Li, N. J. Bjerrum, J. O. Jensen. The stability of poly(2,2’-(m-phenylene)-5,5’-bibenzimidazole) membranes in aqueous potassium hydroxide. J. Membrane Sci. 492, 422-429 (2015) [5] M. R. Kraglund, D. Aili, K. Jankova, E. Christensen, Q. Li, and J. O. Jensen. Zero-gap alkaline water electrolysis using ion-solvating polymer electrolyte membranes at reduced KOH concentrations. J. Electrochem. Soc. 163 (11) (2016) F3125-F3131 [6] D. Aili, A. G. Wright, M. R. Kraglund, K. Jankova, S. Holdcroft and J. O. Jensen. Towards a stable ion-solvating polymer electrolyte for advanced alkaline water electrolysis. J. Mater. Chem. A. 5 (10) (2017) 5055-5066 [7] M. R. Kraglund, M. Carmo et al. Advanced alkaline polymer electrolyte membrane electrolysis using ion-solvating membranes. In manuscript.

Ethylbenzene to styrene over alkali doped TiO2-ZrO2 with CO2 as soft oxidant

Oxidative dehydrogenation of ethylbenzene (EB) to styrene monomer (SM) over alkali metal (Na, K) doped TiO2-ZrO2 (TZ) has been studied. The EB and CO2 conversions observed over alkali doped TZ are higher than that of non-doped TZ. The enhanced CO2 conversion compared with non-doped counterparts is attributed to improved basicity, formation of TiZrO4 phase with increased CO2 affinity and insertion of K or Na into the lattice which affects the binding energy of “O” in turn providing more labile oxygen species. Alkali doping also effected in fine tuning the surface acid base properties. Moreover, these K and Na doped binary metal oxides system showed high surface area of 256m2/g and 199m2/g respectively. There was a 10-fold increase in the CO2 conversions in case of the doped TZ compared to non-doped TZ increasing the stability of the catalyst by decreasing coking on the surface of the catalyst in spite of the high conversions.

(Invited) A Stability Study of Alkali Doped PBI Membranes for Alkaline Electrolyzer Cells

Polybenzimidazole membranes in a linear, a crosslinked and a thermally cured form were subjected to aging in 6 M aqueous KOH at 85 ºC for periods of up to 176 days. The aged membranes were characterized with respect to weight loss, mechanical properties and ionic conductivity. The area specific conductivity was similar to a commercial Zirfon membrane and suitable for a water electrolyzer. Some chemical degradation was seen during the aging period, but the crosslinked and the cured materials were both integral after 176 days of aging. A simplified electrolyzer test cell was operated successfully.

Invited: A Stability Study of Alkali Doped PBI Membranes for Alkaline Electrolyzer Cells

Alkaline fuel cells and electrolyzers are attracting increasing interest. This is to a large extent due to the broad selection of catalyst materials not based on resource limited and expensive noble metals. The first fuel cells in practical use were Francis Thomas Bacon’s based on an alkaline electrolyte. The system has been quite successful with good oxygen kinetics, but the electrolyte suffers from carbonization when operated in normal CO2containing air and this has limited the application to space technology and similar niches. The alkaline electrolyzer on the other hand has been the state of art commercial choice for decades and the carbonization problem is absent since oxygen is produced, not consumed. However, the demand for high voltage efficiency has been limited and the alkaline electrolyzer has been optimized in the direction of robustness and long lifetime instead. Today it has become obvious that an energy system based on renewable energy will need conversion of a large amount of electrical energy to fuel for storage and for transport. We believe that from a materials perspective the alkaline electrolyzer has the strongest potential for meeting the manufacturing cost targets given, but voltage efficiency and rate capability must be improved significantly.One important component with room for improvement is the electrolyte which traditionally fills a gap of up to several mm between the electrodes. The resistance can be much reduced if a thin anion conducting membrane or a porous diaphragm is used instead in direct contact with both electrodes (zero gap). In proton exchange membrane (PEM) electrolyzers proton conducting membranes like in PEM fuel cells have been very successful, but for the equivalent anion exchange membranes a similar conductivity has not yet been demonstrated; in contrast it is typically about an order of magnitude lower, which is insufficient [1].The aromatic fluorine free polymer polybenzimidazole (PBI) has been very successful as a high temperature fuel cell membrane when doped with phosphoric acid [2] and it has been shown by Xing and Savadogo [3] that it can also be doped with potassium hydroxide and serve as electrolyte for alkaline fuel cells. See figure 1.In this work the stability of PBI doped with aqueous KOH was studied after storage in 6 M KOH at 85 °C for up to 176 days, i.e. close to half a year [4]. The pristine polymer was supplied by Danish Power Systems ApS and solution cast from DMAc. Three different variants of the PBI were used. 1) The pristine linear PBI, 2) PBI crosslinked by dibromoparaxylene and 3) PBI thermally cured at 350°C.Tensile strength and elastic modulus decreased somewhat during storage, but all membranes remained integral throughout the entire storage period with the exception of the linear untreated sample which disintegrated when handled after the full 176 days. A gradual weight loss was seen for all membranes but the effect was much reduced for the crosslinked and the cured pieces. The thermally cured membrane lost less that 10 mass %. Viscosity measurement on the linear PBI (the only one soluble) showed a decreasing molecular weight over time of storage. The materials were also examined by IR, NMR and TGA.Finally, electrolysis tests were made including comparison with a commercial diaphragm material (Zirfon). The conductivity of the alkali doped PBI samples was around 0.05 S cm-2 at 85°C, while that of Zirfon was ca. 0.2 S cm-2, but since Zirfon is much thicker to ensure a low bubble point pressure the practical area specific resistances were more or less equal and the cells showed very similar polarization characteristics.[1] G. Merle, M. Wessling and K. Nijmeijer. J. Membrane Sci. 377 (2011) 1– 35[2] Q. F. Li, J. O. Jensen, R. F. Savinell and N. J. Bjerrum. Prog. Polym. Sci. 34(2009) 449[3] B. Xing, O. Savadogo, Electrochemistry Communications 2(2000) 697-702[4] D. Aili, M. K. Hansen, R.F. Renzaho, Q. F. Li, E. Christensen, J. O. Jensen and N. J..Bjerrum. J. Membrane Sci. 447 (2013) 424–432

Anion exchange membrane based on alkali doped poly(2,5-benzimidazole) for fuel cell

The properties of alkali doped poly(2,5-benzimidazole) membrane with different alkali doping levels for fuel cell application are reported in this work. The alkali doping level played an important role for the ion conductivity of the membrane. The ion conductivity significantly increased with alkali doping level. The ion conductivity also increased with the temperature. The ion conductivity of the alkali doped ABPBI membrane (alkali doping level = 0.37), reached to 2.3 × 10 − 2 S cm − 1 at room temperature and 7.3 × 10 − 2 S cm − 1 at 100 °C. The water uptake of the alkali doped ABPBI membrane was increased from 9.1% to 19.2% with increasing alkali doping level at room temperature. The alkali doped poly(2,5-benzimidazole) membrane also showed excellent ion conducting stability and thermal stability as compared with the known quaternized anion exchange membranes.

Doping-enhanced hyperpolarizabilities of silicon clusters: A global ab initio and density functional theory study of Si10 (Li, Na, K)n (n = 1, 2) clusters

A global theoretical study of the (hyper)polarizabilities of alkali doped Si(10) is presented and discussed. First, a detailed picture about the low lying isomers of Si(10)Li, Si(10)Na, Si(10)K, Si(10)Li(2), Si(10)Na(2), and Si(10)K(2) has been obtained in a global manner. Then, the microscopic first (hyper)polarizabilities of the most stable configurations have been determined by means of ab initio methods of high predictive capability such as those based on the Møller-Plesset perturbation and coupled cluster theory, paying extra attention to the (hyper)polarizabilities of the open shell mono-doped systems Si(10)Li, Si(10)Na, Si(10)K, and the influence of spin contamination. These results were used to assess the performance of methods of low computational cost based on density functional theory (DFT) in the reliable computation of these properties in order to proceed with an in-depth study of their evolution as a function of the alkali metal, the cluster composition, and the cluster structure. The most interesting outcomes of the performed (hyper)polarizability study indicate that while alkali doping leaves the per atom polarizability practically unaffected, influences dramatically the hyperpolarizabilities of Si(10). The lowest energy structures of the mono-doped clusters are characterized by significantly enhanced hyperpolarizabilities as compared to the analogue neutral or charged bare silicon clusters Si(10) and Si(11), while, certain patterns governed by the type and the number of the doping agents are followed. The observed hyperpolarizability increase is found to be in close connection with specific cluster to alkali metal charge transfer excited states and to the cluster structures. Moreover, an interesting correlation between the anisotropy of the electron density, and the hyperpolarizabilities of these systems has been observed. Finally, it is important to note that the presented method assessment points out that among the various DFT functionals used in this work, (B3LYP, B3PW91, BhandHLYP, PBE0, CAM-B3LYP, LC-BLYP, LC-BPW91) only B3PW91 and PBE0 out of the seven provided a consistent quantitative performance for both polarizabilities and hyperpolarizabilities with respect to the ab initio methods utilized here. On the other hand, the long range corrected functionals LC-(U)BLYP and LC-(U)BPW91 (μ = 0.47) failed to supply quantitatively accurate hyperpolarizability results in all the studied clusters while the CAM-(U)B3LYP functional performs satisfactory only in the case of the Na and K doped systems.

Alkali Doped Poly(vinyl alcohol) (PVA) for Anion-exchange Membrane Fuel Cells: Ionic Conductivity, Chemical Stability and FT-IR Characterizations

Novel alkaline solid polymer electrolyte membranes have been successfully prepared for poly(vinyl alcohol) (PVA), poly(vinyl alcohol)/poly(vinylpyrrolidone)(PVA/PVP) and poly(vinyl alcohol)/poly(ethylene glycol) dimethyl ether (PVA/PEGDE) by KOH doping. The ionic conductivity(σ) of the membranes was investigated as a function of cross-linking time, blending composition and water content. FT-IR spectroscopy was used for clarifying the conducting mechanism. In particular, the chemical stability of the membranes was investigated toward base treatment with elevated temperature at different KOH concentrations for potential fuel cell applications. The measured conductivity of the membrane ranged from 2.75 to 4.73×10−4 S cm-1 at room temperature for KOH doped PVA and, was greatly enhanced high up to 2 ×10-3 S cm-1 by addition of PVP and 1.5 ×10-3 S cm-1 by addition of PEGDE. The obtained membranes exhibited excellent chemical stability to high concentration base treatment (10M KOH) at elevated temperature of 120oC.

Alkali Doped Poly(vinyl alcohol) for Anion-Exchange Membrane Fuel Cells

not Available.

Optical Properties of Alkali Doped Group IV Nano Materials

AbstractOptical properties of sodium and other alkali metals (lithium & potassium) incorporated into nano hosts of group 4 elements (carbon, silicon & germanium) were investigated as candidates for solid state light emitting materials. First, optical properties were calculated by quantum mechanical simulations using TDDFT method. Results of the simulations indicate that alkali doped group 4 nano hosts exhibit optical transitions in and around the visible range whereas, undoped nano hosts do not have any at similar wavelengths. Some combinations of alkali dopant and nano host give rise to multiple transitions in the visible. One of the simulated combinations, Li dopant and carbon nano host was chosen to be synthesized for experimental verification. Optical absorption and emission characteristics of the synthesized material were measured and compared with those obtained from quantum mechanical calculations. Both the wavelength and the relative intensity of the measured optical transitions were found to be in good agreement with the results of the calculations. Alkali metals which have good light emission characteristics can be combined with group 4 indirect semiconductors to obtain new nano materials which have interesting optical properties in the visible.

New alkali doped pillared carbon materials designed to achieve practical reversible hydrogen storage for transportation.

We propose a new generation of materials to maximize reversible H2 storage at room temperature and modest pressures (<20 bars). We test these materials using grand canonical Monte Carlo simulations with a first-principles-derived force field and find that the Li pillared graphene sheet system can take up 6.5 mass% of H2 (a density of 62.9 kg/m(3) at 20 bars and room temperature. This satisfies the DOE (Department of Energy) target of hydrogen-storage materials for transportation. We also suggest ways to synthesize these systems. In addition we show that Li-doped pillared single-wall nanotubes can lead to a hydrogen-storage capacity of 6.0 mass% and 61.7 kg/m(3) at 50 bars and room temperature storage, which is close to the DOE target.

The Measurements of Photostimulated Luminescence in Alkali Doped BaFBr:Eu2☎ at Liquid Nitrogen Temperature

Considerable increase of the photostimulated luminescence (PSL) intensity and red shift of the excitation spectrum was obtained by alkali doping of BaFBr:Eu2☎ crystals [1]. The band of the FA(Br−) centers about 0.1 eV shifted to low energy side against the “normal” F(Br−) centers. The FA(Br−) centers are destroyed after heating to 330 K.

Superconducting Properties of Alkali Doped C60 Prepared by Precipitation from Liquid Methylamine or Ammonia

Abstract An extremely convenient method of preparing alkali doped face-centered cubic phases of C60 consists of the partial solubilization of the constituent materials in liquid ammonia or monomethylamine followed by precipitation and annealing. The preparation and properties of Rb3C60, K3C60 and Rb2CsC60 prepared in this manner from monomethylamine are decribed. When attempting to prepare Rb2NaC60 from liquid ammonia, one obtains a phase separated material, consisting of the energetically more stable superconducting Rb3C60 and nonsuperconducting NaxC60. This sample exhibits a very sharp superconducting transition temperature at 26.3 K. The decrease in Tc with respect to that of pure-phase Rb3C60 is explained as the result of the decrease in density of states in Josephson-like junctions formed between the two phases. This composition displays a large volume fraction of superconductivity, and all measurements of superconducting parameters are extremely well defined, implying high phase purity of the Rb3C60...