Density Functional Theory Study of the Hydrogenation of Carbon Monoxide over the Co (001) Surface: Implications for the Fischer–Tropsch Process

The increasing demand for renewable fuels and sustainable products has encouraged growing interest in the development of active and selective catalysts for the conversion of carbon monoxide into desirable products. The Fischer–Tropsch process consists of the reaction of a synthesis gas mixture containing carbon monoxide and hydrogen (syngas), which are polymerized into liquid hydrocarbon chains, often using a cobalt catalyst. Here, first-principles calculations based on the density functional theory (DFT) are used to investigate the reaction mechanism of the Fischer–Tropsch synthesis over the Co (001) surface. The most energetically favorable adsorption configurations of the species involved in the carbon monoxide hydrogenation process are identified, and the possible elementary steps of hydrogenation and their related transition states are explored using the Vienna Ab initio simulation package (VASP). The results provide the mechanisms for the formation of CH4, CH3OH and C2H2 compounds, where the calculations suggest that CH4 is the dominant product. Findings from the reaction energies reveal that the preferred mechanism for the hydrogenation of carbon monoxide is through HCO and cis-HCOH, and the largest exothermic reaction energy in the CH4 formation pathway is released during the hydrogenation of cis-HCOH (−0.773 eV). An analysis of the kinetics of the hydrogenation reactions indicates that the CH production from cis-HCOH has the lowest energy barrier of just 0.066 eV, and the hydrogenation of CO to COH, with the largest energy barrier of 1.804 eV, is the least favored reaction kinetically

Thermodynamic and Kinetic Study of Carbon Dioxide Hydrogenation on the Metal-Terminated Tantalum-Carbide (111) Surface: A DFT Calculation

The need to reduce our reliance on fossil fuels and lessen the environmentally harmful effects of CO2 have encouraged investigations into CO2 hydrogenation to produce useful products. Transition metal carbides exhibit a high propensity towards CO2 activation, which makes them promising candidates as suitable catalysts for CO2 hydrogenation. Here, we have employed calculations based on the density-functional theory to investigate the reaction network for CO2 hydrogenation to product molecules on the tantalum-terminated TaC (111) surface, including two routes from either HCOOH* or HOCOH* intermediates. Detailed calculations of the reaction energies and energy barriers along multiple potential catalytic pathways, along with the exploration of all intermediates, have shown that CH4 is the predominant product yielded through a mechanism involving HCOOH, with a total exothermic reaction energy of −4.24 eV, and energy barriers between intermediates ranging from 0.126 eV to 2.224 eV. Other favorable products are CO and CH3OH, which are also produced via the HCOOH pathway, with total overall reaction energies of −2.55 and −2.10 eV, respectively. Our calculated thermodynamic and kinetic mechanisms that have identified these three predominant products of the CO2 hydrogenation catalyzed by the TaC (111) surface explain our experimental findings, in which methane, carbon monoxide, and methanol have been observed as the major reaction products

Computational studies of the adsorption of hydrazine on Cu surfaces

This thesis presents a comprehensive computational study of the molecular and dissociative adsorption of hydrazine (N2H4) on low-index perfect and defective copper surfaces, using the density functional theory calculations with long-range dispersion correction (DFT-D2). Firstly, we have studied the adsorption of hydrazine on low-index planar copper surfaces, where (111) is found to be the most stable surface, whilst (110) surface is the least stable. DFT-D2 calculations with a correction for the van der Waals interactions result in significant enhancement of molecule-substrate binding. Secondly, DFT-D2 has been used to simulate the interaction of hydrazine with low-index defect-containing copper surfaces. We have studied three types of defects at the surfaces: monoatomic steps, Cu-adatoms and vacancies, where our calculations show that the adsorption energy increases as the coordination of the adsorption sites decreases, with the strongest adsorption energy found on the stepped (110) surface. Thirdly, we have investigated the arrangement of multiple hydrazine molecules upon adsorption onto the Cu(111) surface, showing that the main contributors to the assembly of the hydrazine layers are the binding interactions between the adsorbates and the substrate and the organisation of the N2H4 monolayers is primarily due to the long-range interactions. Furthermore, we have simulated the dissociative adsorption of hydrazine on the planar and stepped Cu(111) surfaces. We found that hydrazine prefers to form NH2 via N–N bond decoupling, where the NH2 molecule reacts fairly easily with co-adsorbed NH2 to form NH3, as well as with N2Hx (x=1–4) by subtracting hydrogen to produce NH3 and N2 molecules. Finally, we have constructed a microkinetic model to develop our understanding of the catalytic process of N2H4 dissociation on the planar Cu(111) surfaces. The temperature programmed reaction and batch reactor simulations were simulated, showing that the NH3 and N2 are the dominant gaseous products, while H2 is the minor gaseous product

Electrochemically Engineered Lanthanum Nickelate as a Promising Transparent Hole Transport Layer for Bulk Heterojunction Polymer Solar Cells: An Experimental and DFT Study

Lanthanum nickelate (LNO) was grown on the FTO-coated glass slide by employing the chronoamperometry method and used as a hole transport layer (HTL) in bulk heterojunction polymer solar cells (BHJ PSC). The electrodeposition parameters, including deposition time, potential magnitude, and electrolyte condition, were changed to obtain LNO thin films providing appropriate energy levels as HTL. The electrochemical, morphological, optical, and structural characteristics of electrochemically produced LNO samples were compared to those of the sample prepared via the sol-gel procedure. The LNO sample prepared by applying -1.18 V, while the electrolyte was stirring, exhibited significantly better electrochemical and optical properties. The fabricated PSC using this sample provided a considerably higher (45.3%) power conversion efficiency (PCE) than the PSC prepared based on an LNO thin film acquired by the sol-gel method. The superior performance of the BHJ PSC was ascribed to the increased electroactive surface area (1.341 cm2), improved charge mobility (2.30×10-6 cm2.V-1.s-1), and reduced charge recombination probabilities. A short circuit current of 13.24 mA.cm2, an open circuit voltage of about 0.64 V, a fill factor of 70%, an external quantum efficiency of 75.3%, and a PCE of 5.9% was demonstrated by the best fabricated PSC, surpassing the reference device with PEDOT:PSS HTL. Moreover, the prepared PSC exhibited remarkable ambient stability, maintaining 84% of its initial PCE after 450 h of aging. The agreement between DFT calculations and experimental results confirmed that LNO possesses the optical and elastic characteristics required to improve the efficiency and stability of PSCs as HTL

TiO2 nanoarrays modification by a novel Cobalt-heteroatom doped graphene complex for photoelectrochemical water splitting: An experimental and theoretical study

Different graphene structures have received much attention due to their unique chemical and electron properties. In this report, we use heteroatom-doped graphene to coordinate Co2+ for use in photoelectrochemical cells. Flower-like TiO2 photoelectrode morphology was used as a semiconductor. Its surface was covalently modified with Co2+ coordinated nitrogen and sulfur-doped graphene quantum dot (S, N-GQD). S, N-GQD was used to improve visible light absorption and electron transport properties. Also, cobalt ions were coordinated with pyridinic nitrogen in the GQD structure and, like the cobalt-bipyridine complexes, acted as a catalyst for the water oxidation reaction. The modified photoelectrode significantly improved cell performance and resulted in a photocurrent density of 1.141 mA/cm2. To study the electronic structure of the compounds in more detail, we also used density functional theory (DFT) calculations. The obtained results confirmed the effective interactions of cobalt and S, N-GQD, and showed the energy levels and band gaps in agreement with the experimental results. This study led to the presentation of a new and robust strategy to improve the optical and catalytic performance of TiO2 nanoarrays in photoelectrochemical cells

A First-Principles Study of CO2 Hydrogenation on a Niobium-Terminated NbC (111) Surface

Density functional theory calculations are used to investigate the electronic properties and catalytic activity of an Nb-terminated NbC (111) surface towards CO2 hydrogenation to gain insight into the mechanisms related to CO2 hydrogenation to other products. The results show that the formations of CH4, CH3OH, and CO are favored in comparison to other compounds, with CH4 being the dominant product. In addition, the reaction energies reveal that the preferred mechanism for CO2 hydrogenation is thorough HCOOH. As promising materials for the reduction of greenhouse gases, transition-metal carbides, which are highly active in the hydrogenation of CO2, are mainly considered. In this regard, the reaction mechanism of CO2 hydrogenation to useful products on the Nb-terminated NbC (111) surface is investigated by applying density functional theory calculations. The computational results display that the formation of CH4, CH3OH, and CO are more favored than other compounds, where CH4 is the dominant product. In addition, the findings from reaction energies reveal that the preferred mechanism for CO2 hydrogenation is thorough HCOOH*, where the largest exothermic reaction energy releases during the HCOOH* dissociation reaction (2.004 eV). The preferred mechanism of CO2 hydrogenation towards CH4 production is CO2*→t,c-COOH*→HCOOH*→HCO*→CH2O*→CH2OH*→CH2*→CH3*→CH4*, where CO2*→t,c-COOH*→HCOOH*→HCO*→CH2O*→CH2OH*→CH3OH* and CO2*→t,c-COOH*→CO* are also found as the favored mechanisms for CH3OH and CO productions thermodynamically, respectively. During the mentioned mechanisms, the hydrogenation of CH2O* to CH2OH* has the largest endothermic reaction energy of 1.344 eV

Experimental and density functional theory studies of laminar double-oxidized graphene oxide nanofiltration membranes

The type and loading level of oxygen-containing functional groups on graphene oxide (GO) nanosheets significantly affect the size and alignment of nanochannels formed between the GO nanosheets and the separation performance of laminar GO membranes. Here, we demonstrate how double-oxidation of GO leads to the higher surface charge of GO nanosheets, the formation of highly stable water-based GO solution, more-ordered deposition of GOs on the polyethersulfone membrane through the pressure-assisted self-assembly method, and the formation of highly durable GO membranes possessing smoother surface morphology and higher antifouling properties. A multi-technique investigation was applied to follow the physicochemical difference between GO and double-oxidized GO, and the physical stability and separation performance of the corresponding membranes using experimental and computational studies. The double-oxidized GO-based membranes provided a significantly high water flux of 230 L/(m2.h) in 2.5 bar transmembrane pressure, excellent rejection of 99.9% for methylene blue (MB) dye, and outstanding separation performance stability over time. In contrast, GO membranes showed rejection of 81.5% for MB, and their separation performance diminished significantly over time. The antifouling properties of double-oxidized GO membranes were substantially higher (∼ four times) due to their higher negative surface charge and smoother surface morphology. The density functional theory (DFT) was used to gain insight into the interactions between the functional groups and the reasoning for the higher mechanical stability of double-oxidized GO membranes. Results revealed that the formation energy of GO decreases by increasing the number density of functional groups. It was also found that a higher number of carboxyl groups at the edges of the double-oxidized GO leads to higher hydrogen bonding, higher binding energy, and a more stable GO-membrane structure

TiO2 nanoarrays modification by a novel Cobalt-heteroatom doped graphene complex for photoelectrochemical water splitting: an experimental and theoretical study

Different graphene structures have received much attention due to their unique chemical and electron properties. In this report, we use heteroatom-doped graphene to coordinate Co2+ for use in photoelectrochemical cells. Flower-like TiO2 photoelectrode morphology was used as a semiconductor. Its surface was covalently modified with Co2+ coordinated nitrogen and sulfur-doped graphene quantum dot (S, N-GQD). S, N-GQD was used to improve visible light absorption and electron transport properties. Also, cobalt ions were coordinated with pyridinic nitrogen in the GQD structure and, like the cobalt-bipyridine complexes, acted as a catalyst for the water oxidation reaction. The modified photoelectrode significantly improved cell performance and resulted in a photocurrent density of 1.141 mA/cm2. To study the electronic structure of the compounds in more detail, we also used density functional theory (DFT) calculations. The obtained results confirmed the effective interactions of cobalt and S, N-GQD, and showed the energy levels and band gaps in agreement with the experimental results. This study led to the presentation of a new and robust strategy to improve the optical and catalytic performance of TiO2 nanoarrays in photoelectrochemical cells

Investigating the efficacy of functionalized graphene oxide with polyhedral oligomeric silsesquioxane as an effective additive in sustainable ionic liquid-based electrolytes for dye-sensitized solar cells through experimental and DFT studies

The focus of the study has been on the first-ever use of functionalized graphene oxide with polyhedral oligomeric silsesquioxane (FGO-POSS) as an effective additive to ionic liquid-based electrolytes in dye-sensitized solar cells (DSSCs). The electrolytes consisted of binary ionic liquids (ILs), 1-ethyl-3-methylimidazolium iodide (EMII), and 1-butyl-3-methylimidazolium iodide (BMII). Different concentrations of the efficient additive FGO-POSS, ranging from 0% to 1%, were incorporated into the electrolytes. Under highly controlled conditions, a series of reactions was conducted to synthesize FGO-POSS. By reacting graphene oxide (GO) with L-phenylalanine, initially, GO-L-phenylalanine was obtained. In the next phase, GO-L-Phenylalanine reacted with SSQ-[3-(2-Aminoethyl) amino] propyl-Heptaisobutyl substituted to modify its structure with polyhedral oligomeric silsesquioxane (POSS). The ILs, namely EMII, and BMII, were synthesized using the scientific methodologies detailed in the referenced articles. Furthermore, BMII was functionalized with CuI (BMICuI⁻₂) through a specific procedure. Five types of electrolytes were prepared to be employed in DSSCs using prepared ILs and FGO-POSS, and their results were reported to show the electrical and gelatin features of these types of electrolytes. According to this study's findings, using FGO-POSS as an innovative and efficient additive in ILs-based environmentally sustainable nanocomposite electrolytes in an amount of 0.75 wt% increased the value of the short circuit current density (JSC) from 9.433 mA.cm⁻² to 15.592 mA.cm⁻², the open circuit voltage (VOC) from 0.738 V to 0.762 V, and the overall efficiency (η) increased from 4.965 to 8.303 %. The FGO-POSS and ILs, EMII, and BMICuI⁻₂ boost electron transport and electrolyte conductivity, resulting in increased JSC, VOC, and η. Results of the density functional theory (DFT) calculation indicated that the adsorption of the FGO-POSS electrolyte additives on the TiO₂ electrode surface produces midgap states in the band gap of TiO₂, resulting in the reduction of the total bandgap and less barrier electron transfer and a redshift in the adsorption edge and enhancement of DSSCs' efficiency