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The efficiency of mesoporous perovskite solar cells (mp-PSCs) is significantly influenced by favorable charge transport properties across their various interfaces. The interfaces involving compact-TiO 2 , mesoporous electron transport layer (ETL), and perovskite layer are particularly vital for high-performing devices. Our study presents a combined experimental and computational approach, specifically employing density functional theory, to explore the impact of mesoporous-ETL/perovskite interface properties on carrier transport. These properties are examined in relation to the phases and morphologies of the mesoporous layer. Different phases of TiO 2 , including anatase, rutile, and brookite, and various morphologies such as nanocubes, nanorods, and disks/clusters, were synthesized using a simple hydrothermal synthesis route. They constitute the mesoporous layer, and Cs 0.05 FA 0.84 MA 0.14 PbI 2.55 Br 0.45 is used as the perovskite absorber in mp-PSCs. The performance of the resulting mesoporous-TiO 2 (mp-TiO 2 ) device was investigated in relation to the different phases and morphologies of mp-TiO 2 . The mp-PSCs with the anatase phase as the mesoporous ETL exhibited the highest device parameters, including power conversion efficiency of 19.15%, short-circuit current density of 22.55 mA/cm 2 , fill factor of 76.50%, and open-circuit voltage of 1.11 V. The superior performance of the anatase structure is attributed to its promising band edge alignment, which results from a small negative conduction band offset compared to other phases, thereby enhancing carrier transport. This study underscores the potential of interface optimization to improve device performance. By investigating the device performance across different phases and morphologies of the mp-TiO 2 layer, we can pave the way for the design of next-generation energy devices.

A new catalyst has been developed that utilizes molybdenum oxide (MoO 3 )/nickel molybdenum oxide (NiMoO 4 ) heterostructured nanorods coupled with Pt ultrafine nanoparticles for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) toward industrial-grade water splitting. This catalyst has been synthesized using a versatile approach and has shown to perform better than noble-metals catalysts, such as Pt/C and RuO 2 , at industrial-grade current level (≥1000 mA·cm -2 ). When used simultaneously as a cathode and anode, the proposed material yields 10 mA·cm -2 at a remarkably small cell voltage of 1.55 V and has shown extraordinary durability for over 50 h. Density functional theory (DFT) calculations have proved that the combination of MoO 3 and NiMoO 4 creates a metallic heterostructure with outstanding charge transfer ability. The DFT calculations have also shown that the excellent chemical coupling effect between the MoO 3 /NiMoO 4 and Pt synergistically optimize the charge transfer capability and Gibbs free energies of intermediate species, leading to remarkably speeding up the reaction kinetics of water electrolysis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The Africa Capacity-Building Initiative is a Royal Society programme funded by the former UK Department for International Development to develop collaborative research between scientists in sub-Saharan Africa and the UK. Initially, four institutions were involved in the Chem4Energy consortium: Cardiff University in the UK and three African partners, the Kwame Nkrumah University of Science and Technology, Ghana, the University of Namibia and the University of Botswana, soon also including the Botswana International University of Science and Technology. The Chem4Energy research programme focused on 'New materials for a sustainable energy future: linking computation with experiment', aiming to deploy the synergy between state-of-the-art computational and experimental techniques to design and optimize new catalysts and semiconductor materials for renewable energy applications, based on materials that are abundant and readily available in African countries. The Chem4Energy consortium has achieved ambitious research goals, graduated seven PhD students and delivered a high-quality cross-disciplinary training programme in materials science and simulation techniques relevant to renewable energy applications. Since 2021, the extended consortium, including North-West University and the Centre for High-Performance Computing in South Africa, has remained active through an annual Chem4Energy conference series, with the sixth meeting taking place in Namibia in April 2025., Competing Interests: We declare we have no competing interests., (© 2024 The Author(s).)

Lead-free double perovskites (DPs) will emerge as viable and environmentally safe substitutes for Pb-halide perovskites, demonstrating stability and nontoxicity if their optoelectronic property is greatly improved. Doping has been experimentally validated as a powerful tool for enhancing optoelectronic properties and concurrently reducing the defect state density in DP materials. Fundamental understanding of the optical properties of DPs, particularly the self-trapped exciton (STEs) dynamics, plays a critical role in a range of optoelectronic applications. Our study investigates how Fe doping influences the structural and optical properties of Cs 2 AgBiCl 6 DPs by understanding their STEs dynamics, which is currently lacking in the literature. A combined experimental-computational approach is employed to investigate the optoelectronic properties of pure and doped Cs 2 AgBiCl 6 (Fe-Cs 2 AgBiCl 6 ) perovskites. Successful incorporation of Fe 3+ ions is confirmed by X-ray diffraction and Raman spectroscopy. Moreover, the Fe-Cs 2 AgBiCl 6 DPs exhibit strong absorption from below 400 nm up to 700 nm, indicating sub-band gap state transitions originating from surface defects. Photoluminescence (PL) analysis demonstrates a significant enhancement in the PL intensity, attributed to an increased radiative recombination rate and higher STE density. The radiative kinetics and average lifetime are investigated by the time-resolved PL (TRPL) method; in addition, temperature-dependent PL measurements provide valuable insights into activation energy and exciton-phonon coupling strength. Our findings will not only deepen our understanding of charge carrier dynamics associated with STEs but also pave the way for the design of some promising perovskite materials for use in optoelectronics and photocatalysis., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Considering the importance of physics and chemistry at material interfaces, we have explored the coupling of multinary chalcogenide semiconductor Cu 2 NiSnS 4 nanoparticles (CNTS NPs) for the first time with the noble metal (Au) to form Au-CNTS nano-heterostructures (NHSs). The Au-CNTS NHSs is synthesized by a simple facile hot injection method. Synergistic experimental and theoretical approaches are employed to characterize the structural, optical, and electrical properties of the Au-CNTS NHSs. The absorption spectra demonstrate enhanced and broadened optical absorption in the ultraviolet-visible-near-infrared (UV-Vis-NIR) region, which is corroborated by cyclic voltammetry (CV) readings. CV measurements show type II staggered band alignment, with a conduction band offset (CBO) of 0.21 and 0.23 eV at the Au-CNTS/CdS and CNTS/CdS interface, respectively. Complementary first-principles density functional theory (DFT) calculations predict the formation of a stable Au-CNTS NHSs, with the Au nanoparticle transferring its electrons to the CNTS. Moreover, our interface analysis using ultrafast transient absorption experiments demonstrate that the Au-CNTS NHSs facilitates efficient transport and separation of photoexcited charge carriers when compared to pristine CNTS. The transient measurements further reveal a plasmonic electronic transfer from the Au nanoparticle to CNTS. Our advanced analysis and findings will prompt investigations into new functional materials and their photo/electrocatalysis and optoelectronic device applications in the future.

Herein, first-principles density functional theory calculations have been employed to unravel the interfacial geometries (composition and stability), electronic properties (density of states and differential charge densities), and charge carrier transfers (work function and energy band alignment) of a TiO 2 (001)/FeS 2 (100) heterojunction. Analyses of the structure and electronic properties reveal the formation of strong interfacial Fe-O and Ti-S ionic bonds, which stabilize the interface with an adhesion energy of -0.26 eV Å -2 . The work function of the TiO 2 (001)/FeS 2 (100) heterojunction is predicted to be much smaller than those of the isolated FeS 2 (100) and TiO 2 (001) layers, indicating that less energy will be needed for electrons to transfer from the ground state to the surface to promote photochemical reactions. The difference in the work function between the FeS 2 (100) and TiO 2 (001) heterojunction components caused an electron density rearrangement at the heterojunction interface, which induces an electric field that separates the photo-generated electrons and holes. Consistently, a staggered band alignment is predicted at the interface with the conduction band edge and the valence-band edge of FeS 2 lying 0.37 and 2.62 eV above those of anatase. These results point to efficient charge carrier separation in the TiO 2 (001)/FeS 2 (100) heterojunction, wherein photoinduced electrons would transfer from the FeS 2 to the TiO 2 layer. The atomistic insights into the mechanism of enhanced charge separation and transfer across the interface rationalize the observed high photocatalytic activity of the mixed TiO 2 (001)/FeS 2 (100) heterojunction over the individual components.

CdS, characterized by its comparatively narrow energy band gap (∼2.4 eV), is an appropriate material for prospective use as a photoanode in photoelectrochemical water splitting. Regrettably, it encounters several obstacles for practical and large-scale applications, including issues such as bulk carrier recombination and diminished conductivity. Here, we have tried to address these challenges by fabricating a novel photoelectrode (ZnO/CdS) composed of one-dimensional ZnO nanorods (NRs) decorated with two-dimensional CdS nanosheets (NSs). A facile two-step chemical method comprising electrodeposition along with chemical bath deposition is employed to synthesize the ZnO NRs, CdS NSs, and ZnO/CdS nanostructures. The prepared nanostructures have been investigated by UV-visible absorption spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy. The fabricated ZnO/CdS nanostructures have shown enhanced photoelectrochemical properties due to the improvement of the semiconductor junction surface area and thereby enhanced visible light absorption. The incorporation of CdS NSs has been further found to promote the rate of the charge separation and transfer process. Subsequently, the fabricated ZnO/CdS photoelectrodes achieved a photocurrent conversion efficiency 3 times higher than that of a planar ZnO NR photoanode and showed excellent performance under visible light irradiation. The highest applied bias photon-to-current conversion efficiency (% ABPE) of about ∼0.63% has been obtained for the sample with thicker CdS NSs on ZnO NRs with a photocurrent density of ∼1.87 mA/cm 2 under AM 1.5 G illumination. The newly synthesized nanostructures further demonstrate that the full photovoltaic capacity of nanomaterials is yet to be exhausted.

Hydrogels are a new class of electrolytic materials employed in zinc-air batteries due to their significant on the battery's performance. However, the effectiveness of electrolytic hydrogel is affected by factors such as water content, temperature, additives, etc. Using DMol 3 and molecular dynamics modeling techniques, this research aimed at investigating the electronic properties, effect of water content, and temperature on the binding energy, cohesive energy, and the mechanical properties of polyvinyl alcohol/cellulose-based composite hydrogel at the molecular level. The electronic optimized structures of the polymeric materials and parameters such as frontier molecular orbitals, band gap and electron density were analyzed. The results revealed that the binding energies of hydrogel polymer composite increased as the number of water molecules in the composite increased up to 60 % after which the binding energy decreased. In addition, the temperature increase led to a decrease in the binding energy of the composite. The cohesive energy density of the composite was highest at 40 % water content while higher temperatures decreased the cohesive energy density of the hydrogel. As the number of water molecules increased from 29 to 256, the tensile modulus increased from 0.707 × 10 -3 to 2.821 × 10 -3 Gpa; while the bulk modulus (K) increased in the order of K 40 > 50 > 30 > 20 > 10 respectively. These results serve as a theoretical enlightenment and a guide for experimental works in the field of energy conversion and storage devices., Competing Interests: Declaration of competing interest OFFIA-KALU NKECHI ELIZABETH reports financial support was provided by Regional Scholarship for Innovation Funds (RSIF), a flagship program of the Partnership for Skill in Applied Sciences, Engineering and Technology (PASET)., (Copyright © 2023 Elsevier Inc. All rights reserved.)

This study investigates the incorporation of Ba 2+ at a low concentration into CsPbI 2 Br, resulting in the formation of mixed CsPb 1- x Ba x I 2 Br perovskite films. Photovoltaic devices utilizing these Ba-doped CsPbI 2 Br (Ba-CsPbI 2 Br) perovskite films achieved a higher stabilized power conversion efficiency of 14.07% compared to 11.60% for pure CsPbI 2 Br films. First-principles density functional theory calculations indicate that the improved device performance can be attributed to the efficient transport of conduction electrons across the interface between Ba-CsPbI 2 Br and the TiO 2 electron transporting layer (ETL). The Ba-CsPbI 2 Br/TiO 2 interface exhibits a type-II staggered band alignment with a smaller conduction band offset (CBO) of 0.25 eV, in contrast to the CsPbI 2 Br/TiO 2 interface with a CBO of 0.48 eV. The reduced CBO at the Ba-CsPbI 2 Br/TiO 2 interface diminishes the barrier for conduction electrons to transfer from the Ba-CsPbI 2 Br layer to the TiO 2 layer, facilitating efficient charge transport.

Efficient and stable lead-free halide double perovskites (DPs) have attracted great attention for the future generation of electronic devices. Herein, we have developed a doping approach to incorporate Fe 3+ ions into the Cs 2 NaBiCl 6 crystal unit and reveal a crystallographic and optoelectronic study of the Cs 2 NaBi 1- x Fe x Cl 6 double perovskite. We report a simple solid-state mechanochemical method that has a solvent-free, one-step, green chemistry approach for the synthesis of Cs 2 NaBi 1- x Fe x Cl 6 phosphor. The analysis of powder X-ray diffraction (XRD) data determines the contraction of the lattice due to the incorporation of Fe 3+ cations, and this effect is well supported by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and solid-state nuclear magnetic resonance spectroscopy (ss-NMR). The band gap is reduced with increasing Fe content owing to the strong overlap of the Fe-3d orbitals with Cl-3p orbitals and shift of the valence band maxima (VBM) toward higher energies, as confirmed by ultraviolet photoelectron spectroscopy (UPS) and density functional theory (DFT) analyses. Photoluminescence (PL) studies of Cs 2 NaBi 1- x Fe x Cl 6 phosphors exhibit a large Stokes shift, broadband emission, and increased PL intensity more than ten times for 15% of Fe content phosphor with enhancement in the average decay lifetimes (up to 38 ns) compared to pristine Cs 2 NaBiCl 6 DP. These results indicate that the transition of dark self-trapping of excitons (STEs) into bright STEs enhances yellow emission. XRD, UV, and thermo-gravimetric analysis (TGA) confirmed that the Cs 2 NaB 1- x Fe x Cl 6 DPs have good structural and thermal stabilities. Our findings indicate that the doping of Fe 3+ cations into the Cs 2 NaBiCl 6 lattice is a constructive strategy to enhance significantly the optoelectronic properties of these phosphors.

Potassium-ion batteries (KIBs) are promising energy storage devices owing to their low cost, environmental-friendly, and excellent K + diffusion properties as a consequence of the small Stoke's radius. The evaluation of cathode materials for KIBs, which are perhaps the most favorable substitutes to lithium-ion batteries, is of exceptional importance. Manganese dioxide (α-MnO 2 ) is distinguished by its tunnel structures and plenty of electroactive sites, which can host cations without causing fundamental structural breakdown. As a result of the satisfactory redox kinetics and diffusion pathways of K + in the structure, α-MnO 2 nanorods cathode prepared through hydrothermal method, reversibly stores K + at a fast rate with a high capacity and stability. It has a first discharge capacity of 142 mAh/g at C/20, excellent rate execution up to 5C, and a long cycling performance with a demonstration of moderate capacity retention up to 100 cycles. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) simulations confirm that the K + intercalation/deintercalation occurs through 0.46 K movement between Mn IV /Mn III redox pairs. First-principles density functional theory (DFT) calculations predict a diffusion barrier of 0.31 eV for K + through the 1D tunnel of α-MnO 2 electrode, which is low enough to promote faster electrochemical kinetics. The nanorod structure of α-MnO 2 facilitates electron conductive connection and provides a strong electrode-electrolyte interface for the cathode, resulting in a very consistent and prevalent execution cathode material for KIBs., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

The imino pyridine Schiff base cobalt(II) and nickel(II) complexes ( C1 and C2 ) and their functionalised γ-Fe 3 O 4 counterparts ( Fe 3 O 4 @C1 and Fe 3 O 4 @C2 ) were synthesised and characterised using IR, elemental analysis, and ESI-MS for C1 and C2 , and single crystal X-ray diffraction for C1 , while the functionalised materials Fe 3 O 4 @C1 and Fe 3 O 4 @C2 were characterized using IR, XRD, SEM, TEM, EDS, ICP-OES, XPS and TGA. Complexes C1 , C2 and the functionalised materials Fe 3 O 4 @C1 and Fe 3 O 4 @C2 were tested as catalysts for the selective transfer hydrogenation of cinnamaldehyde and all four pre-catalysts showed excellent catalytic activity. Complexes C1 and C2 acted as homogeneous catalysts with high selectivity towards the formation of hydrocinnamaldehyde (88.7% and 92.6%, respectively) while Fe 3 O 4 @C1 and Fe 3 O 4 @C2 acted as heterogeneous catalysts with high selectivity towards cinnamyl alcohol (89.7% and 87.7%, respectively). Through in silico studies of the adsorption energies, we were able to account for the different products formed using the homogeneous and the heterogeneous catalysts which we attribute to the preferred interaction of the C=C moiety in the substrate with the Ni centre in C2 (-0.79 eV) rather than the C=O (-0.58 eV).

Understanding how to catalytically break the C-H bond of aromatic molecules, such as polycyclic aromatic hydrocarbons (PAHs), is currently a big challenge and a subject of study in catalysis, astrochemistry, and planetary science. In the latter, the study of the breakdown reaction of PAHs on mineral surfaces is important to understand if PAHs are linked to prebiotic molecules in regions of star and planet formation. In this work, we employed a periodic density functional theory along with Grimme's D4 (DFT-D4) approach for studying the adsorption of a sample of PAHs (naphthalene, anthracene, fluoranthene, pyrene, coronene, and benzocoronene) and fullerene on the [010] forsterite surface and its defective surfaces (Fe-doped and Ni-doped surfaces and a MgO-Schottky vacancy) for their implications in catalysis and astrochemistry. On the basis of structural and binding energy analysis, large PAHs and fullerene present stronger adsorption on the pristine, Fe-doped, and Ni-doped forsterite surfaces than small PAHs. On a MgO-Schottky vacancy, parallel adsorption of the PAH leads to the chemisorption process (C-Si and/or C-O bonds), whereas perpendicular orientation of the PAH leads to the catalytic breaking of the aromatic C-H bond via a barrierless reaction. Spin density and charge analysis show that C-H dissociation is promoted by electron donation from the vacancy to the PAH. As a result of the undercoordinated Si and O atoms, the vacancy acts as a Frustrated Lewis Pair (FLP) catalyst. Therefore, a MgO-Schottky vacancy [010] forsterite surface proved to have potential catalytic activity for the activation of C-H bond in aromatic molecules., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Realizing photoactive and thermodynamically stable all-inorganic perovskite solar cells (PSCs) remains a challenging task within halide perovskite photovoltaic (PV) research. Here, a dual strategy for realizing efficient inorganic mixed halide perovskite PV devices based on a terbium-doped solar absorber, that is, CsPb 1- x Tb x I 2 Br, is reported, which undertakes a bulk and surface passivation treatment in the form of CsPb 1- x Tb x I 2 Br quantum dots, to maintain a photoactive γ-phase under ambient conditions and with significantly improved operational stability. Devices fabricated from these air-processed perovskite thin films exhibit an air-stable power conversion efficiency (PCE) that reaches 17.51% (small-area devices) with negligible hysteresis and maintains >90% of the initial efficiency when operating for 600 h under harsh environmental conditions, stemming from the combined effects of the dual-protection strategy. This approach is further examined within large-area PSC modules (19.8 cm 2 active area) to realize 10.94% PCE and >30 days ambient stability, as well as within low-bandgap γ-CsPb 0.95 Tb 0.05 I 2.5 Br 0.5 (E g  = 1.73 eV) materials, yielding 19.01% (18.43% certified) PCE., (© 2022 Wiley-VCH GmbH.)

In this work, we develop a photocatalyst wherein nitrogen and phosphorus co-doped carbon quantum dots are scaffolded onto TiO 2 nanoparticles (NPCQD/TiO 2 ), denoted as NPCT hereafter. The developed NPCT photocatalyst exhibits an enhanced visible light photocatalytic hydrogen production of 533 μmol h -1 g -1 compared to nitrogen doped CQD/TiO 2 (478 μmol h -1 g -1 ), phosphorus doped CQD/TiO 2 (451 μmol h -1 g -1 ) and pure CQD/TiO 2 (427 μmol h -1 g -1 ) photocatalysts. The enhanced photocatalytic activity of the NPCT photocatalyst is attributed to the excellent synergy between NPCQDs and TiO 2 nanoparticles, which results in the creation of virtual energy levels, a decrease in work function and suppressed recombination rates, thereby increasing the lifetime of photogenerated electrons. A detailed mechanism is proposed for the enhancement in visible light hydrogen production by the NPCT photocatalyst from the experimental results, Mott-Schottky plots and ultraviolet photoelectron spectroscopy results. Further, first-principles density functional theory (DFT) simulations are carried out which predict the decrease in the work function and band gap, and the increase in the density of states of NPCT as the factors responsible for the observed enhancement in visible light photocatalytic hydrogen production.

Metal sulphides, including zinc sulphide (ZnS), are semiconductor photocatalysts that have been investigated for the photocatalytic degradation of organic pollutants as well as their activity during the hydrogen evolution reaction and water splitting. However, devising ZnS photocatalysts with a high overall quantum efficiency has been a challenge due to the rapid recombination rates of charge carriers. Various strategies, including the control of size and morphology of ZnS nanoparticles, have been proposed to overcome these drawbacks. In this work, ZnS samples with different morphologies were prepared from zinc and sulphur powders via a facile hydrothermal method by varying the amount of sodium borohydride used as a reducing agent. The structural properties of the ZnS nanoparticles were analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques. All-electron hybrid density functional theory calculations were employed to elucidate the effect of sulphur and zinc vacancies occurring in the bulk as well as (220) surface on the overall electronic properties and absorption of ZnS. Considerable differences in the defect level positions were observed between the bulk and surface of ZnS while the adsorption of NaBH 4 was found to be highly favourable but without any significant effect on the band gap of ZnS. The photocatalytic activity of ZnS was evaluated for the degradation of rhodamine B dye under UV irradiation and hydrogen generation from water. The ZnS nanoparticles photo-catalytically degraded Rhodamine B dye effectively, with the sample containing 0.01 mol NaBH 4 being the most efficient. The samples also showed activity for hydrogen evolution, but with less H 2 produced compared to when untreated samples of ZnS were used. These findings suggest that ZnS nanoparticles are effective photocatalysts for the degradation of rhodamine B dyes as well as the hydrogen evolution, but rapid recombination of charge carriers remains a factor that needs future optimization., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Amakali, Živković, Warwick, Jones, Dunnill, Daniel, Uahengo, Mitchell, Dzade and de Leeuw.)

We successfully report a liquid-liquid chemical reduction and hydrothermal synthesis of a highly stable columbite-tantalite electrocatalyst with remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance in acidic media. The reduced Fe 0.79 Mn 0.21 Nb 0.16 Ta 0.84 O 6 (CTr) electrocatalyst shows a low overpotential of 84.23 mV at 10 mA cm -2 and 103.7 achieved at 20 mA cm -2 current density in situ for the HER and OER, respectively. The electrocatalyst also exhibited low Tafel slopes of 104.97 mV/dec for the HER and 57.67 mV/dec for the OER, verifying their rapid catalytic kinetics. The electrolyzer maintained a cell voltage of 1.5 V and potential-time stability close to that of Pt/C and RuO 2 . Complementary first-principles density functional theory calculations identify the Mn sites as most active sites on the Fe 0.75 Mn 0.25 Ta 1.875 Nb 0.125 O 6 (100) surface, predicting a moderate Gibbs free energy of hydrogen adsorption (Δ G H* ≈ 0.08 eV) and a low overpotential of η = 0.47 V. The |Δ G Mn H *| = 0.08 eV on the Fe 0.75 Mn 0.25 Ta 1.875 Nb 0.125 O 6 (100) surface is similar to that of the well-known and highly efficient Pt catalyst (|Δ G Pt H *| ≈ 0.09 eV).

Zinc phosphides (ZnP 2 and Zn 3 P 2 ) are emerging absorber materials for photovoltaic applications owing to their abundancy and non-toxic nature. Herein, we provide a comprehensive characterisation of the surface structure, composition, stabilities, morphology, and electronic properties of both bare and hydrated/hydroxylated low-Miller index surfaces of β-ZnP 2 by means of density functional theory (DFT) calculations. Mechanistic insights into the fundamental aspects of water adsorption and dissociation, including the adsorption geometries, energetics, and structural parameters along the reaction path are systematically characterised. The stabilities of the surfaces under dry and wet conditions are discussed in detail and the predicted phase diagrams for the water adsorption are presented. Using calculated surface energies, we have derived the equilibrium morphology of the β-ZnP 2 nanocrystals under vacuum and upon hydration or hydroxylation. Atomic-level insights into the origin of the incipient oxidation of β-ZnP 2 surfaces are provided through analysis of Bader charges, which reveal that the Zn sites to which H 2 O and OH species are bound undergo oxidation due to the transfer of charge to the adsorbed species. Adsorption-induced changes to the electronic properties before and after hydration/hydroxylation were characterised by the work function and partial density of states. The results highlight the need for protection of β-ZnP 2 nanocrystals against possible oxidation in the presence of water through post-synthesis organic functionalisation.

Zinc phosphide (Zn 3 P 2 ) is an ideal absorber candidate for solar cells thanks to its direct bandgap, earth-abundance, and optoelectronic characteristics, albeit it has been insufficiently investigated due to limitations in the fabrication of high-quality material. It is possible to overcome these factors by obtaining the material as nanostructures, e.g. via the selective area epitaxy approach, enabling additional strain relaxation mechanisms and minimizing the interface area. We demonstrate that Zn 3 P 2 nanowires grow mostly defect-free when growth is oriented along the [100] and [110] of the crystal, which is obtained in nanoscale openings along the [110] and [010] on InP(100). We detect the presence of two stable rotated crystal domains that coexist in the structure. They are due to a change in the growth facet, which originates either from the island formation and merging in the initial stages of growth or lateral overgrowth. These domains have been visualized through 3D atomic models and confirmed with image simulations of the atomic scale electron micrographs. Density functional theory simulations describe the rotated domains' formation mechanism and demonstrate their lattice-matched epitaxial relation. In addition, the energies of the shallow states predicted closely agree with transition energies observed by experimental studies and offer a potential origin for these defect transitions. Our study represents an important step forward in the understanding of Zn 3 P 2 and thus for the realisation of solar cells to respond to the present call for sustainable photovoltaic technology.

Lead-free double perovskites have emerged as stable and non-toxic alternatives to Pb-halide perovskites. Herein, the synthesis of Fe-doped Cs 2 AgBiCl 6 lead-free double perovskites are reported that display blue emission using an antisolvent method. The crystal structure, morphology, optical properties, band structure, and stability of the Fe-doped double perovskites were investigated systematically. Formation of the Fe-doped Cs 2 AgBiCl 6 double perovskite is confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. XRD and thermo-gravimetric analysis (TGA) shows that the Cs 2 AgBiCl 6 double perovskite has high structural and thermal stability, respectively. Field emission scanning electron microscopy (FE-SEM) analysis revealed the formation of dipyramidal shape Cs 2 AgBiCl 6 crystals. Furthermore, energy-dispersive X-ray spectroscopy (EDS) mapping shows the overlapping of Cs, Bi, Ag, Fe, and Cl elements and homogenous incorporation of Fe in Cs 2 AgBiCl 6 double perovskite. The Fe-doped Cs 2 AgBiCl 6 double perovskite shows a strong absorption at 380 nm. It extends up to 700 nm, suggesting that sub-band gap states transition may originate from the surface defect of the doped perovskite material. The radiative kinetics of the crystals was studied using the time-correlated single-photon counting (TCSPC) technique. Lattice parameters and band gap value of the Fe-doped Cs 2 AgBiCl 6 double perovskites predicted by the density functional theory (DFT) calculations are confirmed by XRD and UV/Visible spectroscopy analysis. Time-dependent photo-response characteristics of the Fe-doped Cs 2 AgBiCl 6 double perovskite show fast response and recovery time of charge carriers. We believe that the successful incorporation of Fe in lead-free, environmentally friendly Cs 2 AgBiCl 6 double perovskite can open a new class of doped double perovskites with significant potential optoelectronics devices fabrication and photocatalytic applications., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Cu2ZnGeSe4 (CZGSe) is a promising earth-abundant and non-toxic semiconductor material for large-scale thin-film solar cell applications. Herein, we have employed a joint computational and experimental approach to characterize and assess the structural, optoelectronic, and heterojunction band offset and alignment properties of a CZGSe solar absorber. The CZGSe films were successfully prepared using DC-sputtering and e-beam evaporation systems and confirmed by XRD and Raman spectroscopy analyses. The CZGSe films exhibit a bandgap of 1.35 eV, as estimated from electrochemical cyclic voltammetry (CV) measurements and validated by first-principles density functional theory (DFT) calculations, which predicts a bandgap of 1.38 eV. A fabricated device based on the CZGSe as a light absorber and CdS as a buffer layer yields power conversion efficiency (PCE) of 4.4% with VOC of 0.69 V, FF of 37.15, and Jsc of 17.12 mA cm-2. Therefore, we suggest that interface and band offset engineering represent promising approaches to improve the performance of CZGSe devices by predicting a type-II staggered band alignment with a small conduction band offset of 0.18 eV at the CZGSe/CdS interface.

Density functional theory (DFT) has provided deep atomic-level insights into the adsorption behavior of aromatic molecules on solid surfaces. However, modeling the surface phenomena of large molecules on mineral surfaces with accurate plane wave methods (PW) can be orders of magnitude more computationally expensive than localized atomic orbitals (LCAO) methods. In the present work, we propose a less costly approach based on the DFT-D4 method (PBE-D4), using LCAO, to study the interactions of aromatic molecules with the {010} forsterite (Mg 2 SiO 4 ) surface for their relevance in astrochemistry. We studied the interaction of benzene with the pristine {010} forsterite surface and with transition-metal cations (Fe 2+ and Ni 2+ ) using PBE-D4 and a vdW-inclusive density functional (Dion, Rydberg, Schröder, Langreth, and Lundqvist (DRSLL)) with LCAO methods. PBE-D4 shows good agreement with coupled-cluster methods (CCSD(T)) for the binding energy trend of cation complexes and with PW methods for the binding energy of benzene on the forsterite surface with a difference of about 0.03 eV. The basis set superposition error (BSSE) correction is shown to be essential to ensure a correct estimation of the binding energies even when large basis sets are employed for single-point calculations of the optimized structures with smaller basis sets. We also studied the interaction of naphthalene and benzocoronene on pristine and transition-metal-doped {010} forsterite surfaces as a test case for PBE-D4. Yielding results that are in good agreement with the plane wave methods with a difference of about 0.02-0.17 eV, the PBE-D4 method is demonstrated to be effective in unraveling the binding structures and the energetic trends of aromatic molecules on pristine and transition-metal-doped forsterite mineral surfaces. Furthermore, PBE-D4 results are in good agreement with its predecessor PBE-D3(BJM) and with the vdW-inclusive density functionals, as long as transition metals are not involved. Hence, PBE-D4/CP-DZP has been proven to be a robust theory level to study the interaction of aromatic molecules on mineral surfaces.

Ternary Cu 2 SnS 3 (CTS) is an attractive nontoxic and earth-abundant absorber material with suitable optoelectronic properties for cost-effective photoelectrochemical applications. Herein, we report the synthesis of high-quality CTS nanoparticles (NPs) using a low-cost facile hot injection route, which is a very simple and nontoxic synthesis method. The structural, morphological, optoelectronic, and photoelectrochemical (PEC) properties and heterojunction band alignment of the as-synthesized CTS NPs have been systematically characterized using various state-of-the-art experimental techniques and atomistic first-principles density functional theory (DFT) calculations. The phase-pure CTS NPs confirmed by X-ray diffraction (XRD) and Raman spectroscopy analyses have an optical band gap of 1.1 eV and exhibit a random distribution of uniform spherical particles with size of approximately 15-25 nm as determined from high-resolution transmission electron microscopy (HR-TEM) images. The CTS photocathode exhibits excellent photoelectrochemical properties with PCE of 0.55% (fill factor (FF) = 0.26 and open circuit voltage (Voc) = 0.54 V) and photocurrent density of -3.95 mA/cm 2 under AM 1.5 illumination (100 mW/cm 2 ). Additionally, the PEC activities of CdS and ZnS NPs are investigated as possible photoanodes to create a heterojunction with CTS to enhance the PEC activity. CdS is demonstrated to exhibit a higher current density than ZnS, indicating that it is a better photoanode material to form a heterojunction with CTS. Consistently, we predict a staggered type-II band alignment at the CTS/CdS interface with a small conduction band offset (CBO) of 0.08 eV compared to a straddling type-I band alignment at the CTS/ZnS interface with a CBO of 0.29 eV. The observed small CBO at the type-II band aligned CTS/CdS interface points to efficient charge carrier separation and transport across the interface, which are necessary to achieve enhanced PEC activity. The facile CTS synthesis, PEC measurements, and heterojunction band alignment results provide a promising approach for fabricating next-generation Cu-based light-absorbing materials for efficient photoelectrochemical applications., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Sodium-ion batteries (SIBs) can develop cost-effective and safe energy storage technology for substantial energy storage demands. In this work, we have developed manganese oxide (α-MnO 2 ) nanorods for SIB applications. The crystal structure, which is crucial for high-performance energy storage, is examined systematically for the metal oxide cathode. The intercalation of sodium into the α-MnO 2 matrix was studied using the theoretical density functional theory (DFT) studies. The DFT studies predict Na ions' facile diffusion kinetics through the MnO 2 lattice with an attractively low diffusion barrier (0.21 eV). When employed as a cathode material for SIBs, MnO 2 showed a moderate capacity (109 mAh·g -1 at C/20 current rate) and superior life cyclability (58.6% after 800 cycles) in NaPF 6 /EC+DMC (5% FEC) electrolyte. It shows a much higher capacity of 181 mAh·g -1 (C/20 current rate) in NaClO 4 /PC (5% FEC) electrolyte, though it suffers fast capacity fading (11.5% after 800 cycles). Our findings show that high crystallinity and hierarchical nanorod morphology of the MnO 2 are responsible for better cycling performance in conjunction with fast and sustained charge-discharge behaviors.

Cu 2 SrSnS 4 (CSTS) is a promising alternative candidate to Cu 2 ZnSnS 4 (CZTS) for single- or multi-junction photovoltaics (PVs) owing to its efficient light-absorbing capability, earth-abundant, nontoxic constituents, and suitable defect properties. However, as a novel absorber material, several fundamental properties need to be characterized before further progress can be made in CSTS photovoltaics. In this letter, hybrid density functional theory (DFT) calculations have been used to comprehensively characterize for the first time, the electronic structure, band alignment, and optical properties of CSTS. It is demonstrated that CSTS possesses the ideal electronic structure (direct band gap of 1.98 eV and small photocarrier effective masses) and optical properties (high extinction coefficient and wide absorption) suitable for photovoltaic applications. Simulated X-ray photoelectron spectroscopy (XPS) valence band spectra using variable excitation energies show that Cu-3d electronic state dominates the valence band maximum of CSTS. Furthermore, the vacuum-aligned band diagram between CSTS and other common absorbers (CZTS, CIGS, CdTe) and the common n-type partner materials (CdS, ZnO) was constructed, which indicate staggered type-II band alignment at the CSTS/CdS and CSTS/ZnO interfaces. Based on these results, interface band offset engineering and alternative device architectures are suggested to improve charge carrier separation and power conversion efficiencies of CSTS.

Mixed-halide CsPbI 2 Br perovskite is promising for efficient and thermally stable all-inorganic solar cells; however, the use of conventional antisolvent methods and additives-based hole-transporting layers (HTLs) currently hampers progress. Here, we have employed hot-air-assisted perovskite deposition in ambient condition to obtain high-quality photoactive CsPbI 2 Br perovskite films and have extended stable device operation using metal cation doping and dopant-free hole-transporting materials. Density functional theory calculations are used to study the structural and optoelectronic properties of the CsPbI 2 Br perovskite when it is doped with metal cations Eu 2+ and In 3+ . We experimentally incorporated Eu 2+ and In 3+ metal ions into CsPbI 2 Br films and applied dopant-free copper(I) thiocyanate (CuSCN) and poly(3-hexylthiophene) (P3HT)-based materials as low-cost hole transporting layers, leading to record-high power conversion efficiencies of 15.27% and 15.69%, respectively, and a retention of >95% of the initial efficiency over 1600 h at 85 °C thermal stress., Competing Interests: The authors declare no competing financial interest., (© 2021 American Chemical Society.)

Considering the significance of hexagonal copper thiocyanate (β-CuSCN) in several optoelectronic technologies and applications, it is essential to investigate its electronic structure and surface properties. Herein, we have employed density functional theory (DFT) calculations to characterise the band structure, density of states, and the energy-dependent X-ray photoelectron (XPS) valence band spectra at variable excitation energies of β-CuSCN. The surface properties in the absence and presence of dimethyl sulfoxide (DMSO), a solvent additive for improving perovskite solar cells' power conversion efficiency, have also been systematically characterised. β-CuSCN is shown to be an indirect band gap material ( E g = 3.68 eV) with the valence band edge demonstrated to change from being dominated by Cu-3 d at soft X-ray ionisation photon energies to Cu-3 p at hard X-ray ionisation photon energies. The adsorption energy of dimethyl sulfoxide (DMSO) on the (100) and (110) β-CuSCN surfaces is calculated at -1.12 and -0.91 eV, respectively. The presence of DMSO on the surface is shown to have a stabilisation effect, lowering the surface energy and tuning the work function of the β-CuSCN surfaces, which is desirable for organic solar cells to achieve high power conversion efficiencies.

In this work, African maize cobs (AMC) were used as a rich biomass precursor to synthesize carbon material through a chemical activation process for application in electrochemical energy storage devices. The carbonization and activation were carried out with concentrated Sulphuric acid at three different temperatures of 600, 700 and 800 °C, respectively. The activated carbon exhibited excellent microporous and mesoporous structure with a specific surface area that ranges between 30 and 254 m 2 ·g -1 as measured by BET analysis. The morphology and structure of the produced materials are analyzed through Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Boehm titration, X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. X-ray photoelectron spectroscopy indicates that a considerable amount of oxygen is present in the materials. The functional groups in the activated carbon enhanced the electrochemical performance and improved the material's double-layer capacitance. The carbonized composite activated at 700 °C exhibited excellent capacitance of 456 F g -1 at a specific current of 0.25 A g -1 in 6 M KOH electrolyte and showed excellent stability after 10,000 cycles. Besides being a low cost, the produced materials offer good stability and electrochemical properties, making them suitable for supercapacitor applications.

Large-scale deployment of thin-film photovoltaics will be facilitated through earth-abundant components. Herein, selective area epitaxy and lateral overgrowth epitaxy are explored for the growth of zinc phosphide (Zn 3 P 2 ), a promising earth-abundant absorber. The ideal growth conditions are elucidated, and the nucleation of single-crystal nanopyramids that subsequently evolve towards coalesced thin-films is demonstrated. The zinc phosphide pyramids exhibit room temperature bandgap luminescence at 1.53 eV, indicating a high-quality material. The electrical properties of zinc phosphide and the junction with the substrate are assessed by conductive atomic force microscopy on n-type, p-type and intrinsic substrates. The measurements are consistent with the p-type characteristic of zinc phosphide. Overall, this constitutes a new, and transferrable, approach for the controlled and tunable growth of high-quality zinc phosphide, a step forward in the quest for earth-abundant photovoltaics., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

CuBi 2 O 4 exhibits significant potential for the photoelectrochemical (PEC) conversion of solar energy into chemical fuels, owing to its extended visible-light absorption and positive flat band potential vs the reversible hydrogen electrode. A detailed understanding of the fundamental electronic structure and its correlation with PEC activity is of significant importance to address limiting factors, such as poor charge carrier mobility and stability under PEC conditions. In this study, the electronic structure of CuBi 2 O 4 has been studied by a combination of hard X-ray photoemission spectroscopy, resonant photoemission spectroscopy, and X-ray absorption spectroscopy (XAS) and compared with density functional theory (DFT) calculations. The photoemission study indicates that there is a strong Bi 6s-O 2p hybrid electronic state at 2.3 eV below the Fermi level, whereas the valence band maximum (VBM) has a predominant Cu 3d-O 2p hybrid character. XAS at the O K-edge supported by DFT calculations provides a good description of the conduction band, indicating that the conduction band minimum is composed of unoccupied Cu 3d-O 2p states. The combined experimental and theoretical results suggest that the low charge carrier mobility for CuBi 2 O 4 derives from an intrinsic charge localization at the VBM. Also, the low-energy visible-light absorption in CuBi 2 O 4 may result from a direct but forbidden Cu d-d electronic transition, leading to a low absorption coefficient. Additionally, the ionization potential of CuBi 2 O 4 is higher than that of the related binary oxide CuO or that of NiO, which is commonly used as a hole transport/extraction layer in photoelectrodes. This work provides a solid electronic basis for topical materials science approaches to increase the charge transport and improve the photoelectrochemical properties of CuBi 2 O 4 -based photoelectrodes., Competing Interests: The authors declare no competing financial interest.

The unique structural merits of heterostructured nanomaterials including the electronic interaction, interfacial bonding and synergistic effects make them attractive for fabricating highly efficient optoelectronic devices. Herein, we report the synthesis of MnO 2 nanorods and a rGO/MnO 2 nano-heterostructure using low-cost hydrothermal and modified Hummers' methods, respectively. Detailed characterization and confirmation of the structural and morphological properties are done via X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). Compared to the isolated MnO 2 nanorods, the rGO/MnO 2 nano-heterostructure exhibits impressive field emission (FE) performance in terms of the low turn-on field of 1.4 V μm -1 for an emission current density of 10 μA cm -2 and a high current density of 600 μA cm -2 at a relatively very low applied electric field of 3.1 V μm -1 . The isolated MnO 2 nanorods display a high turn-on field of 7.1 for an emission current density of 10 μA cm -2 and a low current density of 221 μA cm -2 at an applied field of 8.1 V μm -1 . Besides the superior FE characteristics of the rGO/MnO 2 nano-heterostructure, the emission current remains quite stable over the continuous 2 h period of measurement. The improvement of the FE characteristics of the rGO/MnO 2 nano-heterostructure can be ascribed to the nanometric features and the lower work function (6.01 and 6.12 eV for the rGO with 8% and 16% oxygen content) compared to the isolated α-MnO 2 (100) surface ( Φ = 7.22 eV) as predicted from complementary first-principles electronic structure calculations based on density functional theory (DFT) methods. These results suggest that an appropriate coupling of rGO with MnO 2 nanorods would have a synergistic effect of lowering the electronic work function, resulting in a beneficial tuning of the FE characteristics., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

To improve the constraints of kesterite Cu 2 ZnSnS 4 (CZTS) solar cell, such as undesirable band alignment at p-n interfaces, bandgap tuning, and fast carrier recombination, cadmium (Cd) is introduced into CZTS nanocrystals forming Cu 2 Zn 1- x Cd x SnS 4 through cost-effective solution-based method without postannealing or sulfurization treatments. A synergetic experimental-theoretical approach was employed to characterize and assess the optoelectronic properties of Cu 2 Zn 1- x Cd x SnS 4 materials. Tunable direct band gap energy ranging from 1.51 to 1.03 eV with high absorption coefficient was demonstrated for the Cu 2 Zn 1- x Cd x SnS 4 nanocrystals with changing Zn/Cd ratio. Such bandgap engineering in Cu 2 Zn 1- x Cd x SnS 4 helps in effective carrier separation at interface. Ultrafast spectroscopy reveals a longer lifetime and efficient separation of photoexcited charge carriers in Cu 2 CdSnS 4 (CCTS) nanocrystals compared to that of CZTS. We found that there exists a type-II staggered band alignment at the CZTS (CCTS)/CdS interface, from cyclic voltammetric (CV) measurements, corroborated by first-principles density functional theory (DFT) calculations, predicting smaller conduction band offset (CBO) at the CCTS/CdS interface as compared to the CZTS/CdS interface. These results point toward efficient separation of photoexcited carriers across the p-n junction in the ultrafast time scale and highlight a route to improve device performances., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

We report the synthesis of two-dimensional porous ZnO nanosheets, CuSCN nanocoins, and ZnO/CuSCN nano-heterostructure thin films grown on fluorine-doped tin oxide substrates via two simple and low-cost solution chemical routes, i.e., chemical bath deposition and successive ionic layer adsorption and reaction methods. Detail characterizations regarding the structural, optoelectronic, and morphological properties have been carried out, which reveal high-quality and crystalline synthesized materials. Field emission (FE) investigations performed at room temperature with a base pressure of 1 × 10 -8 mbar demonstrate superior FE performance of the ZnO/CuSCN nano-heterostructure compared to the isolated porous ZnO nanosheets and CuSCN nanocoins. For instance, the turn-on field required to draw a current density of 10 μA/cm 2 is found to be 2.2, 1.1, and 0.7 V/μm for the ZnO, CuSCN, and ZnO/CuSCN nano-heterostructure, respectively. The observed significant improvement in the FE characteristics (ultralow turn-on field of 0.7 V/μm for an emission current density of 10 μA/cm 2 and the achieved high current density of 2.2 mA/cm 2 at a relatively low applied electric field of 1.8 V/μm) for the ZnO/CuSCN nano-heterostructure is superior to the isolated porous ZnO nanosheets, CuSCN nanocoins, and other reported semiconducting nano-heterostructures. Complementary first-principles density functional theory calculations predict a lower work function for the ZnO/CuSCN nano-heterostructure (4.58 eV), compared to the isolated ZnO (5.24 eV) and CuSCN (4.91 eV), validating the superior FE characteristics of the ZnO/CuSCN nano-heterostructure. The ZnO/CuSCN nanocomposite could provide a promising class of FE cathodes, flat panel displays, microwave tubes, and electron sources., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

Transition metal perovskite chalcogenides are attractive solar absorber materials for renewable energy applications. Herein, we present the first-principles screened hybrid density functional theory analyses of the structural, elastic, electronic and optical properties of the two structure modifications of strontium zirconium sulfide (needle-like α-SrZrS 3 and distorted β-SrZrS 3 phases). Through the analysis of the predicted electronic structures, we show that both α- and β-SrZrS 3 materials are direct band gaps absorbers, with calculated band gaps of 1.38, and 1.95 eV, respectively, in close agreement with estimates from diffuse-reflectance measurements. A strong light absorption in the visible region is predicted for the α- and β-SrZrS 3 , as reflected in their high optical absorbance (in the order of 10 5 cm -1 ), with the β-SrZrS 3 phase showing stronger absorption than the α-SrZrS 3 phase. We also report the first theoretical prediction of effective masses of photo-generated charge carriers in α- and β-SrZrS 3 materials. Predicted small effective masses of holes and electrons at the valence, and conduction bands, respectively, point to high mobility (high conductivity) and low recombination rate of photo-generated charge carriers in α- and β-SrZrS 3 materials, which are necessary for efficient photovoltaic conversion.

We report the field emission properties of two-dimensional SnSe nanosheets (NSs) and Au/SnSe nano-heterostructure (NHS) prepared by a simple and economical route of one-pot colloidal and sputtering technique. Field Emission Scanning Electron Microscope (FESEM) analysis reveal surface protrusions and morphology modification of the SnSe NSs by Au deposition. By decorating the SnSe NSs with Au nanoparticles, significant improvement in field emission characteristics were observed. A significant reduction in the turn-on field from 2.25 V/µm for the SnSe NSs to 1.25 V/µm for the Au/SnSe NHS was observed. Emission current density of 300 µA/cm 2 has been achieved at an applied field of 4.00 and 1.91 V/µm for SnSe NSs and Au/SnSe NHS, respectively. Analysis of the emission current as a function of time also demonstrated the robustness of the present Au/SnSe NHS. Consistent with the experimental data, our complementary first-principles DFT calculations predict lower work function for the Au/SnSe NHS compared to the SnSe NSs as the primary origin for improved field emission. The present study has evidently provided a rational heterostructure strategy for improving various field emission related applications via surface and electronic modifications of the nanostructures.

Zinc phosphide (Zn 3 P 2 ) is a novel earth-abundant photovoltaic material with a direct band gap of 1.5 eV. Herein, the incipient oxidation mechanism of the (001), (101), and (110) Zn 3 P 2 surfaces in the presence of oxygen and water, which severely limits the fabrication of efficient Zn 3 P 2 -based photovoltaics, has been investigated in detail by means of dispersion-corrected density functional theory (DFT-D3) calculations. The fundamental aspects of the oxygen and water adsorption, including the initial adsorption geometries, adsorption energies, structural parameters, and electronic properties, are presented and discussed. A chemical picture and origin of the initial steps of Zn 3 P 2 surface oxidation are proposed through analyses of Bader charges, partial density of states, and differential charge density isosurface contours. The results presented show that while water interacts weakly with the Zn ions on the Zn 3 P 2 surfaces, molecular and dissociative oxygen species interact strongly with the (001), (101), and (110) surface species. The adsorption of oxygen is demonstrated to be characterized by a significant charge transfer from the interacting surface species, causing them to be oxidized from Zn 2+ to Zn 3+ formal oxidation states. Preadsorbed oxygen species are shown to facilitate the O-H bond activation of water towards its dissociation, with the adsorbed hydroxide species (OH - ) demonstrated to draw a significant amount of charges from the interacting surface sites. Despite the fact that the semiconducting nature of the different Zn 3 P 2 surfaces is preserved, we observe noticeable adsorption induced changes in their electronic structures, with the covered surface exhibiting smaller band gaps than the naked surfaces. The present study demonstrates the importance of the oxygen-water/solid interface to understand the oxidation mechanism of Zn 3 P 2 in the presence of oxygen and water at the molecular level. The study also highlights the need for Zn 3 P 2 nanoparticles to be protected against possible oxidation in the presence of oxygen and moisture via in situ functionalization, wherein the Zn 3 P 2 nanoparticles are exposed to a vapour of organic functional molecules immediately after synthesis.

Accurate prediction of the structures, stabilities, and electronic structures of hybrid inorganic/organic systems is an essential prerequisite for tuning their electronic properties and functions. Herein, the interface chemistry between the 4-aminothiophenol (4ATP) molecule and the (001), (101), and (110) surfaces of zinc phosphide (Zn 3 P 2 ) has been investigated by means of first-principles density functional theory calculation with a correction for van der Waals interactions. In particular, the atomic-level insights into the fundamental aspects of the 4ATP adsorption, including the lowest-energy adsorption configurations, binding energetics, structural parameters, and electronic properties are presented and discussed. The 4ATP molecule is demonstrated to bind most strongly onto the least stable Zn 3 P 2 (001) surface ( E ads = -1.91 eV) and least strongly onto the most stable Zn 3 P 2 (101) surface ( E ads = -1.21 eV). Partial density of states analysis shows that the adsorption of 4ATP on the Zn 3 P 2 surfaces is characterized by strong hybridization between the molecule's sulfur and nitrogen p-orbitals and the d-orbitals of the interacting surface Zn ions, which gave rise to electron density accumulation around the centers of the newly formed Zn-S and Zn-N chemical bonds. The thermodynamic crystal morphology of the nonfunctionalized and 4ATP-functionalized Zn 3 P 2 nanoparticles was obtained using Wulff construction based on the calculated surface energies. The stronger binding of the 4ATP molecule onto the less stable (001) and (110) surfaces in preference to the most stable (101) facet resulted in the modulation of the Zn 3 P 2 nanocrystal shape, with the reactive (001) and (110) surfaces becoming more pronounced in the equilibrium morphology., Competing Interests: The author declares no competing financial interest., (Copyright © 2020 American Chemical Society.)

We report a phase-pure kesterite Cu 2 ZnSnS 4 (CZTS) thin films, synthesized using radio frequency (RF) sputtering followed by low-temperature H 2 S annealing and confirmed by XRD, Raman spectroscopy and XPS measurements. Subsequently, the band offsets at the interface of the CZTS/CdS heterojunction were systematically investigated by combining experiments and first-principles density functional theory (DFT) calculations, which provide atomic-level insights into the nature of atomic ordering and stability of the CZTS/CdS interface. A staggered type II band alignment between the valence and conduction bands at the CZTS/CdS interface was determined from Cyclic Voltammetry (CV) measurements and the DFT calculations. The conduction and valence band offsets were estimated at 0.10 and 1.21 eV, respectively, from CV measurements and 0.28 and 1.15 from DFT prediction. Based on the small conduction band offset and the predicted higher positions of the VB max and CB min for CZTS than CdS, it is suggested photogenerated charge carriers will be efficient separated across the interface, where electrons will flow from CZTS to the CdS and and vice versa for photo-generated valence holes. Our results help to explain the separation of photo-excited charge carriers across the CZTS/CdS interface and it should open new avenues for developing more efficient CZTS-based solar cells.

Lithium-bearing brines are an increasingly attractive source of Li for extraction. One extraction mechanism is the removal of Li from the fluid phase through the precipitation of zabuyelite (Li 2 CO 3 ). The chemistry of the brine plays an important role in this process because ions in solution can compete for the components of the Li-carbonate phase. Here we explore the effect of different brine components on the precipitation of zabuyelite using experiments and computational simulations. Crystals formed in all solutions showed morphological evidence for potential transformation from a precursor phase. Our study indicates that Ca 2+ and SO 4 2- are incorporated into the precipitated zabuyelite crystals. Sulfate also interacts directly with specific surfaces on the growing crystal and is expected to form ion pairs with Li + in solution. Similarly, Na + appears to form ion pairs in solution with the carbonate ion, slowing nucleation of zabuyelite in the experiments. K + and Cl - may interact with the growing zabuyelite crystals but do not appear to affect zabuyelite nucleation and growth times. These experiments highlight the importance of understanding the solution chemistry on zabuyelite formation in order to predict the efficiency of extraction processes and the purity of the solids., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

Molybdenum disulfide (MoS 2 ) and related transition metal chalcogenides can replace expensive precious metal catalysts such as Pt for the hydrogen evolution reaction (HER). The relations between the nanoscale properties and HER activity of well-controlled 2H and Li-promoted 1T phases of MoS 2 , as well as an amorphous MoS 2 phase, have been investigated and a detailed comparison is made on Mo-S and Mo-Mo bond analysis under operando HER conditions, which reveals a similar bond structure in 1T and amorphous MoS 2 phases as a key feature in explaining their increased HER activity. Whereas the distinct bond structure in 1T phase MoS 2 is caused by Li + intercalation and disappears under harsh HER conditions, amorphous MoS 2 maintains its intrinsic short Mo-Mo bond feature and, with that, its high HER activity. Quantum-chemical calculations indicate similar electronic structures of small MoS 2 clusters serving as models for amorphous MoS 2 and the 1T phase MoS 2 , showing similar Gibbs free energies for hydrogen adsorption (ΔG H* ) and metallic character., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The interfacial interaction of U 3 Si 2 with water leads to corrosion of nuclear fuels, which affects various processes in the nuclear fuel cycle. However, the mechanism and molecular-level insights into the early oxidation process of U 3 Si 2 surfaces in the presence of water and oxygen are not fully understood. In this work, we present Hubbard-corrected density functional theory (DFT + U ) calculations of the adsorption behavior of water on the low Miller indices of the pristine and defective surfaces as well as water dissociation and accompanied H 2 formation mechanisms. The adsorption strength decreases in the order U 3 Si 2 {001} > U 3 Si 2 {110} > U 3 Si 2 {111} for both molecular and dissociative H 2 O adsorption. Consistent with the superior reactivity, dissociative water adsorption is most stable. We also explored the adsorption of H 2 O on the oxygen-covered U 3 Si 2 surface and showed that the preadsorbed oxygen could activate the OH bond and speed up the dissociation of H 2 O. Generally, we found that during adsorption on the oxygen-covered, defective surface, multiple water molecules are thermodynamically more stable on the surface than the water monomer on the pristine surface. Mixed molecular and dissociative water adsorption modes are also noted to be stable on the {111} surface, whereas fully dissociative water adsorption is most stable on the {110} and {001} surfaces., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

Molybdenum disulfide (MoS 2 ) is a highly promising catalyst for the hydrogen evolution reaction (HER) to realize large-scale artificial photosynthesis. The metallic 1T'-MoS 2 phase, which is stabilized via the adsorption or intercalation of small molecules or cations such as Li, shows exceptionally high HER activity, comparable to that of noble metals, but the effect of cation adsorption on HER performance has not yet been resolved. Here we investigate in detail the effect of Li adsorption and intercalation on the proton reduction properties of MoS 2 . By combining spectroscopy methods (infrared of adsorbed NO, 7 Li solid-state nuclear magnetic resonance, and X-ray photoemission and absorption) with catalytic activity measurements and theoretical modeling, we infer that the enhanced HER performance of Li x MoS 2 is predominantly due to the catalytic promotion of edge sites by Li., Competing Interests: The authors declare no competing financial interest.

Binary II-V semiconductors are highly optically active materials, possess high intrinsic mechanical and chemical durability, and have electronic properties ideal for optoelectronic applications. Among them, zinc diphosphide (ZnP 2 ) is a promising earth-abundant absorber material for solar energy conversion. We have investigated the structural, mechanical, and optoelectronic properties of both the tetragonal (α) and monoclinic (β) phases of ZnP 2 using standard, Hubbard-corrected and screened hybrid density functional theory methods. Through the analysis of bond character, band gap nature, and absorption spectra, we show that there exist two polymorphs of the β phase (denoted as β 1 and β 2 ) with distinct differences in the photovoltaic potential. While β 1 exhibits the characteristics of metallic compounds, β 2 is a semiconductor with predicted thin-film photovoltaic absorbing efficiency of almost 10%. The α phase is anticipated to be an indirect gap material with a calculated efficiency limited to only 1%. We have also analysed and gained insights into the electron localization function, projected density of states and projected crystal orbital Hamilton populations for the analogue bonds between the α and β-ZnP 2 . In light of these calculations, a number of previous discrepancies have been solved and a solid ground for future employment of zinc diphosphides in photovoltaics has been established.

Transition metal dichalcogenides (TMDs), such as MoS2 and WS2, are promising alternative non-noble metal catalysts to drive the electrocatalytic H2 evolution reaction (HER). However, their catalytic performance is inherently limited by the small number of active sites as well as their poor electrical conductivity. Here, we grow vertically aligned 2H-WS2 on different substrates to expose their edge sites for the HER and introduce a scalable approach to tune these active sites via defect engineering. In a thermal hydrogen treatment procedure, sulfur vacancies and metallic tungsten nanoparticles are formed. The extent of desulfurization, and thus the HER activity, can be tuned via controlling the H2 annealing conditions. The obtained W/WS2-x electrocatalysts are evaluated experimentally and theoretically to arrive at a better understanding of how to modify the inherently inert 2H-WS2 for more efficient HER.

We present a Hubbard-corrected density functional theory (DFT+U) study of the adsorption and reduction reactions of oxygen on the pure and 25% Ca-doped LaMnO3 (LCM25) {100} and {110} surfaces. The effect of oxygen vacancies on the adsorption characteristics and energetics has also been investigated. Our results show that the O2 adsorption/reduction process occurs through the formation of superoxide and peroxide intermediates, with the Mn sites found to be generally more active than the La sites. The LCM25{110} surface is found to be more efficient for O2 reduction than the LCM25{100} surface due to its stronger adsorption of O2, with the superoxide and peroxide intermediates shown to be energetically more favorable at the Mn sites than at the Ca sites. Moreover, oxygen vacancy defect sites on both the {100} and {110} surfaces are shown to be more efficient for O2 reduction, as reflected in the higher adsorption energies calculated on the defective surfaces compared to the perfect surfaces. We show from Löwdin population analysis that the O2 adsorption on the pure and 25% Ca-doped LaMnO3 surfaces is characterized by charge transfer from the interacting surface species into the adsorbed oxygen πg orbital, which results in weakening of the O-O bonds and its subsequent reduction. The elongated O-O bonds were confirmed via vibrational frequency analysis.