Sulfur Substitution Research Articles

Regulating the thermoelectric power factor of donor–acceptor copolymers by heavy chalcogen substitution: a first-principles study

Te substitution of sulfur (S) in PzDPP-based donor–acceptor copolymers enhances n-type power factor, while Se boosts both n-type and p-type power factors. Heavy chalcogen doping strategy shows promise for improving thermoelectric properties.

More is different: progressive β-thiolation induced-porphyrin aggregation switches singlet oxygen photosensitization.

Incorporating sulfur atoms into photosensitizers (PSs) has been well-established to populate triplet states and increase singlet oxygen (1O2) production when exposed to light. In this work, we found that progressive thiolation of porphyrin β-periphery does promote intersystem crossing (ISC) between triplets and singlets, as seen in the excited state dynamics in dichloromethane or PS nanoparticles in water. However, in the latter case, more sulfur substitution deactivates 1O2 photosensitization, in contrast to the expected trend observed in dichloromethane. This observation was further supported by photocytotoxicity studies, where 1O2 photosensitization was switched off in living cells and multicellular spheroids despite being switched on in in vivo mice models. To understand the inconsistency, we performed molecular dynamics simulation and time-dependent density functional theory calculations to investigate possible aggregation and related excited states. We found that the extent of thiolation could regulate molecular packing inside nanoparticles, which gradually lowers the energy levels of triplet states even lower than that of 1O2 and, in turn, alters their energy dissipation pathways. Therefore, this study provides new insights into the design of metal-free PSs and sheds light on the excited state dynamics in aqueous media beyond the molecular level.

Enhanced Oxygen Evolution Reaction Activity and Structural Stability of Sulfur and Manganese Substituted Co(OH)2

The search for efficient, cost-effective, and sustainable energy sources is a crucial challenge for the modern world.1, 2 In this regard, the development of effective electrocatalysts for water splitting, specifically the oxygen evolution reaction (OER), is a critical aspect of renewable energy technology.3, 4 In recent years, layered double hydroxides (LDHs) have emerged as promising materials for electrocatalysis due to their unique structural and electronic properties.5, 6 This study presents the synthesis and characterization of sulfur and manganese substituted Co(OH)2 as electrocatalysts for the oxygen evolution reaction (OER). The research employed a range of structural and physical characterization techniques, including XRD, EDX, SEM, TEM, and XPS to investigate the synthesized materials.The OER activity was measured via LSV curves in 1 M KOH solution which showed that the S-Mn-Co(OH)2 has significantly low over-potential of 250 and 275 mV for current densities of 10 and 50 mA cm-2 when compared with the Co(OH)2. Additionally, the S–Mn–Co(OH)2 catalyst demonstrated after a 15 hours treatment at 50 mA cm−2 and in 1 M KOH only an overpotential increase of 34 mV and thus excellent stability. High-resolution transmission electron microscopy (HRTEM) analysis confirmed sheet like structure, while the XPS analysis revealed an increase in electron density around the Co owing to the presence of Co2+ and Co3+ in the sample. PXRD and HRTEM analysis also showed a slight reduction in the interlayer gap, indicating further stabilization of the layered structure. Both, stabilized the layered structure and increased electron density around Co could be reason for the enhanced OER performance and be important insights into the role of cation and anion substitution for enhancing LDH OER catalysts. References S. Chu and A. Majumdar, nature, 2012, 488, 294-303.M. M. Rahman, I. Khan, D. L. Field, K. Techato and K. Alameh, Renewable Energy, 2022, 188, 731-749.Y. Feng, H. Yang, X. Wang, C. Hu, H. Jing and J. Cheng, International Journal of Hydrogen Energy, 2022.X. Liu, Y. Han, Y. Guo, X. Zhao, D. Pan, K. Li and Z. Wen, Advanced Energy and Sustainability Research, 2022, 3, 2200005.P. Shandilya, R. Sharma, R. K. Arya, A. Kumar, D.-V. N. Vo and G. Sharma, International Journal of Hydrogen Energy, 2022, 47, 37438-37475.A. Hameed, M. Batool, Z. Liu, M. A. Nadeem and R. Jin, ACS Energy Letters, 2022, 7, 3311-3328.

Anion Engineering for Stabilizing Li Interstitial Sites in Halide Solid Electrolytes for All-Solid-State Li Batteries.

Halide solid electrolytes (SEs) have been highlighted for their high-voltage stability. Among the halide SEs, the ionic conductivity has been improved by aliovalent metal substitutions or choosing a ccp-like anion-arranged monoclinic structure (C2/m) over hcp- or bcc-like anion-arranged structures. Here, we present a new approach, hard-base substitution, and its underlying mechanism to increase the ionic conductivity of halide SEs. The oxygen substitution to Li2ZrCl6 (trigonal, hcp) increased the ionic conductivity from 0.33 to 1.3 mS cm-1 at Li3.1ZrCl4.9O1.1 (monoclinic, ccp), while the sulfur and fluorine substitutions were not effective. A systematic comparison study revealed that the energetic stabilization of interstitial sites for Li migration plays a key role in improving the ionic conductivity, and the ccp-like anion sublattice is not sufficient to achieve high ionic conductivity. We further examined the feasibility of the oxyhalide SE for practical and all-solid-state battery applications.

Improvement of the rate capability of the Li4Ti5O12 anode material by modification of the surface composition with lithium polysulfide

Partial substitution of oxygen by sulfur was attempted using a Li/Ti rich conditions for the nominal compositions Li4Ti5O12−xSx x = 0.125–0.375. However, a much lower sulfur substitution, i.e. at dopant level, was achieved as deduced from an almost negligible increase in unit cell size observed from X-ray powder diffraction. The sulfur in the samples is mainly deposited on the surface as sulfate and Li2S2 as deduced from XPS. However, most of the nominal sulfur is lost. Interestingly, for nominal x = 0.125 a considerable improvement in performance is achieved compared to undoped LTO. The sample with x = 0.125 not only shows ∼9% higher capacity at slow cycling at C/20, but also has a remarkably better power rate behavior, with a capacity of 125 mAh g−1 at higher 2 C, compared to 79 mAh g−1 for LTO at the same rate. The significant improvement is explained by the formation of lithium polysulfide in the high-temperature reaction and the concomitant Li+ deficiency to form the spinel, causing the reduction of Ti4+ to Ti3+ and the creation of oxygen vacancies with the formation of an oxygen and lithium deficient spinel Li4−y (Ti4+)5−y (Ti3+)y O12−y. Li2S2, detected in the sample with nominal x = 0.125 by XPS and at higher nominal sulfur contents by CV, may prevent carbonation of the spinel surface while providing ionic conductivity upon reduction to Li2S, justifying its better performance. On the other hand, the contribution to capacity from both mass diffusion and the capacitive charge storage mechanism is unaffected, and therefore LTO and surface-modified LTO-S-0.125 are regarded as typical battery materials.

A Single-Component Dual Donor Enables Ultrasound-Triggered Co-release of Carbon Monoxide and Hydrogen Sulfide.

The development of dual gasotransmitter donors can not only provide robust tools to investigate their subtle interplay under pathophysiological conditions but also optimize therapeutic efficacy. While conventional strategies are heavily dependent on multicomponent donors, we herein report an ultrasound-responsive water-soluble copolymer (PSHF) capable of releasing carbon monoxide (CO) and hydrogen sulfide (H2 S) based on single-component sulfur-substituted 3-hydroxyflavone (SHF) derivatives. Interestingly, sulfur substitution can not only greatly improve the ultrasound sensitivity but also enable the co-release of CO/H2 S under mild ultrasound irradiation. The co-release of CO/H2 S gasotransmitters exerts a bactericidal effect against Staphylococcus aureus and demonstrates anti-inflammatory activity in lipopolysaccharide-challenged macrophages. Moreover, the excellent tissue penetration of ultrasound irradiation enables the local release of CO/H2 S in the joints of septic arthritis rats, exhibiting superior therapeutic efficacy without the need for any antibiotics.

Experimental and ab initio studies of the structural and optoelectronic properties of hexagonal wurtzite ZnO1-xSx alloys

The structural and optoelectronic properties of ZnO1-xSx alloys were investigated experimentally as well as theoretically. The ZnO1-xSx alloy thin films at different S concentrations (0.0 < x < 1.0) were deposited on quartz substrates by radiofrequency magnetron sputtering. The alloy composition was monitored with the help of optical emission spectroscopy. The ab initio density functional theory (DFT) based calculations were performed for the hexagonal wurtzite ZnO1-xSx system with the S compositions of x = 0.0, 0.0625, 0.125, 0.25, 0.5, 0.75, 0.875, 0.9375 and 1.0. The X-ray diffraction (XRD) and Raman spectroscopy measurements suggest the hexagonal wurtzite phase for the entire composition range. The films exhibit good crystalline quality with preferential growth along the c-axis. The linear change in the lattice parameter (c) was observed both from XRD analysis and DFT based calculations. The X-ray photoelectron spectroscopy confirms the anionic substitution of oxygen (O2−) and sulphur (S2−) in the hexagonal wurtzite lattice. Field emission scanning electron microscopy and atomic force microscopy were used to study the surface morphology. The optical properties were evaluated through transmittance spectroscopy and spectroscopic ellipsometry. The density of state calculations shows the forbidden region which confirms the semiconducting nature for all the alloy compositions. The energy band gap obtained from the respective Tauc's plots was found to vary from 2.9 to 3.6 eV with a bowing parameter of 3.2 eV. The same trend was observed in the calculated electronic band structures through DFT. The optical constants were evaluated from spectroscopic ellipsometry and the corresponding band gap values were compared with the values obtained from optical transmittance.

Biochemical and Structural Characterization of OvoATh2: A Mononuclear Nonheme Iron Enzyme from Hydrogenimonas thermophila for Ovothiol Biosynthesis.

Ovothiol A and ergothioneine are thiol-histidine derivatives with sulfur substitutions at the δ-carbon or ε-carbon of the l-histidine imidazole ring, respectively. Both ovothiol A and ergothioneine have protective effects on many aging-related diseases, and the sulfur substitution plays a key role in determining their chemical and biological properties, while factors governing sulfur incorporation regioselectivities in ovothiol and ergothioneine biosynthesis in the corresponding enzymes (OvoA, Egt1, or EgtB) are not yet known. In this study, we have successfully obtained the first OvoA crystal structure, which provides critical information to explain their C-S bond formation regioselectivity. Furthermore, OvoATh2 exhibits several additional activities: (1) ergothioneine sulfoxide synthase activity akin to Egt1 in ergothioneine biosynthesis; (2) cysteine dioxygenase activity using l-cysteine and l-histidine analogues as substrates; (3) cysteine dioxygenase activity upon mutation of an active site tyrosine residue (Y406). The structural insights and diverse chemistries demonstrated by OvoATh2 pave the way for future comprehensive structure-function correlation studies.

Physical properties of different polymorphs of sulfur doped ZnO studied in the framework of first-principles approaches

Various physical properties of pure and sulfur-doped zinc oxide in the germanium phosphide (GeP), cesium chloride (CsCl), and nickel arsenide (NiAs) type structures are studied using the first-principles approaches in this research. The structural characteristics of the ZnOS alloys in GeP, CsCl, and NiAs type polymorphs show a slight deviation from Vegard's law, which is consistent with the available literature. It is observed that the electronic band structures of the ZnOS alloys show an exciting impact of sulfur (S) substitution in the ZnO. The ZnOS alloys, in CsCl type structure, display their metallic character. The static dielectric constants of the GeP, CsCl, and NiAs type’s polymorphs demonstrate that with increasing S concentration, polarization is enhanced. Moreover, the CsCl type phase of the ZnOS alloys exhibits the maximum value of the static dielectric constant along with showing metallic character. The optical results highlight the potential of S-doped ZnO in these structures as the highest absorption, reflectivity, and conductivity peaks shift towards low photon energies. The examination of the absorption spectra demonstrates that GeP-type ZnOS alloys are suitable for infrared to visible regime applications. On the other hand, NiAs-type ZnOS alloys are appropriate for use in the visible light regime.

Disabling spidroin N-terminal homologs' reverse reaction unveils why its intermolecular disulfide bonds have not evolved for 380 million years

Spiders, ubiquitous predators known for their powerful silks, rely on spidroins that self-assemble from high-concentration solutions stored in silk glands, which are mediated by the NT and CT domains. CT homodimers containing intermolecular disulfide bonds enhance silk performance, promoting spider survival and reproduction. However, no NT capable of forming such disulfide bonds has been identified. Our study reveals that NT homodimers with sulfur substitution can form under alkaline conditions, shedding light on why spiders have not evolved intermolecular disulfide bonds in the NT module during their 380 million years of evolution. This discovery significantly advances our comprehension of spider evolution and silk spinning mechanisms, while also providing novel insights into protein storage, assembly, as well as the mechanisms and therapeutic strategies for neurodegenerative diseases associated with protein aggregation.

SnS-rGO heterojunction: Fabrication, characterization, and visible light-induced optoelectronic performance analysis

In this article, the orthorhombic phase of pristine SnS and SnS-rGO nanostructures with different concentrations of graphene oxide was synthesized by the co-precipitation method. The cracking of FESEM images in SnS-25rGO nanostructures shows the substitution of sulfur with the oxygen of the functional groups of graphene oxide. Also, the effect of the concentration of graphene oxide was investigated on the optoelectronic efficiency of fabricated devices. The optoelectronic characterization shows that by adding graphene oxide and increasing its concentration, the semi-circle radius in the EIS analysis and the amount of photocurrent decreased and increased, respectively. These results indicate the fast transport and transfer of electrons to the substrates and the effective separation of electron-hole pairs. Finally, the calculations showed that by increasing the concentration of graphene oxide in the SnS-rGO nanostructures, the visible-light-induced optoelectronic parameters of photosensitivity, photoresponsivity, specific detectivity, and external quantum efficiency of these nanostructures significantly improved. These parameters were obtained for the SnS-25rGO nanostructure as 204, 59.88 mA/cm2, 5.98 × 1010 jones, and 166.85, respectively, each of which increased several times compared to the optoelectronic parameters of the pristine SnS. Therefore, this multiplicity increase makes these SnS-rGO nanostructures suitable for photodetector applications.

Reactivity of bis(2‐chloroprop‐2‐enyl)sulfide in the system hydrazine hydrate/alkali: A quantum chemical insight

AbstractThe reactivity of bis(2‐chloroprop‐2‐enyl)sulfide in the system hydrazine hydrate/alkali has been studied using quantum‐chemical methods. The B2PLYP‐D2//B3LYP approach shows a good agreement between the relative values of activation barriers compared to high‐precision CBS//Q‐B3. The correction for the entropy change during the transition from the gas phase to the binary solvent hydrazine hydrate is calculated. The IEF PCM model was parameterized for hydrazine hydrate solvent. The studied reaction routes includes (i) a competition between migration of the C=C bond and dehydrochlorination of bis(2‐chloroprop‐2‐enyl)sulfide; (ii) 1,3‐prototropic rearrangements of bis (allenyl)sulfide resulting from a dehydrochlorination; (iii) the possible substitution of sulfur and chlorine atoms with hydrazine. The probable formation of the thiiranium and thiirenium cations formation in the above has also been evaluated.

Sulfur Substitution and Defect Engineering in an Unfavored MnMoO4 Catalyst for Efficient Hydrogen Evolution under Visible Light

A novel and nonstoichiometric Mn1-xMo(S,O)4-y oxysulfide catalyst with oxygen vacancies and a partial Mo6+-to-Mo4+ transition after the substitution of sulfur was synthesized for an efficient photocatalytic hydrogen evolution reaction (PHER). With appropriate sulfur substitution, a MnMoO4 semiconductor with a wide band gap was converted to Mn1-xMo(S,O)4-y with a narrow gap and a suitable band position for PHER. MnMo oxysulfide of 50 mg achieved a high PHER rate of 415.8 μmol/h under visible light, an apparent quantum efficiency (AQE) of 4.31% at 420 nm, and a solar-to-hydrogen (STH) conversion efficiency of 1.28%. Oxygen vacancies (VO) surrounded by low coordination metal atoms act as active reaction sites, which strengthen water adsorption and activation. Here, we demonstrate that sulfur substitution of MnMoO4 for lowering its wide band gap can not only disturb the strict periodicity of the lattice but also the valence states of Mn and Mo for enhancing PHER via material design.

Constructing lipid droplet-targeting photosensitizers based on coumarins with NIR emission

The development of photosensitizers (PSs) with subcellular targeting capability has raised interest for photodynamic therapy (PDT) research. In this work, two coumarin-based photosensitizers (C-S-2 and C-S-3) were designed and synthesized via expanding their π-conjugation, introducing strong electron-donor and acceptor groups, and adopting sulfur substitution strategy. These sulfured-coumarins exhibited near-infrared emission (greater than 650 nm), lipid droplet-targeting ability and obvious photocytotoxicity under laser irradiation. In particular, C-S-3 exhibited better photostability, superior lipid droplet-targeting capability, and stronger photodynamic effect on cancer cells than C-S-2.

Origin of Disseminated Gold-Sulfide Mineralization from Proximal Alteration in Orogenic Gold Deposits in the Central Sector of the Yana–Kolyma Metallogenic Belt, NE Russia

The Yana–Kolyma metallogenic belt, NE Russia, is a world-class gold belt with resources numbering ~8300 tons of gold. The belt is localized in the central part of the Verkhoyansk–Kolyma orogen, formed by a collage of diverse terranes. The Tithonian-to-Early-Cretaceous orogenic gold deposits are hosted in a sequence of Permian–Triassic and Jurassic clastic rocks and altered Late Jurassic andesite, dacite, granodiorite, trachyandesite, and trachybasalt dykes. High-fineness gold (800–900‰) in quartz veins and invisible gold in disseminated arsenian pyrite-3 (Py3) and arsenopyrite-1 (Apy1) are present in ores. Here, we present new data about microtextures; the chemical composition and stable sulfur isotopes of auriferous pyrite-3 and arsenopyrite-1 from proximal alterations in sediment-hosted (Malo–Taryn, Badran, Khangalas); and intrusion-hosted (V’yun, Shumniy) orogenic Au deposits in the central sector of the Yana–Kolyma metallogenic belt to better constrain the ore-forming process and tracking their evolution. Detailed petrography defined the following generations of pyrite: syn-sedimentary/diagenetic Py1, metamorphic Py2 and hydrothermal Py3, and Apy1. Hydrothermal Py3 and Apy1 are localized in the proximal pyrite–arsenopyrite–sericite–carbonate–quartz alteration in ore zones and make a major contribution to the economic value of the veinlet-disseminated mineralization with “invisible” gold in the orogenic deposits of the Yana–Kolyma metallogenic belt. Electron microprobe analysis (EMPA) of Py3 in both types of deposits shows concentrations of As (up to 3.16 wt%), Co, Ni, Cu, Sb, and Pb. Py3 in intrusion-hosted orogenic gold deposits reveals elevated concentrations of Co (up to 0.87 wt%), Ni (up to 3.52 wt%), and Cu (up to 2.31 wt%). The identified negative correlation between S and As indicates an isomorphic substitution of sulfur by As1−. Py3 from igneous rocks is characterized by a high degree of correlation for the pairs Fe2+→ Co2+ and Fe2+→ Ni2+. For hydrothermal Apy1, Co (up to 0.27 wt%), Ni (up to 0.30 wt%), Cu (up to 0.04 wt%), and Sb (up to 0.76 wt%) are typomorphic. According to atomic absorption spectrometry, the concentration of Au in Py3 reaches 159.5 ppm; in Apy1, it reaches 168.5 ppm. The determination of the precise site of the invisible gold within Py3 and Apy1 showed the predominance of solid-solution Au+ in the crystal lattice. The values of δ34S in Py3 and Apy1 (from −6.4 to +5.6‰, mean value of about +0.6‰), both from sediment-hosted and from intrusion-hosted deposits, display a relatively narrow range and are characteristic of the hydrothermal ore stage. Our analytical results showed no systematic differences between the chemical and stable sulfur isotope compositions of both auriferous pyrite-3 and arsenopyrite-1 from the proximal alteration in sediment-hosted (Malo–Taryn, Badran, Khangalas) and intrusion-hosted (V’yun, Shumniy) orogenic Au deposits, indicating that the primary source of sulfur, gold, and mineralizing fluids was likely from subcrustal and metamorphic systems in the Late-Jurassic-to-Early-Cretaceous Verkhoyansk–Kolyma orogen.

Numerical simulation of the effect of gradual substitution of sulfur with selenium or tin with germanium in Cu2ZnSnS4 absorber layer on kesterite solar cell efficiency

To enhance the efficiency of kesterite Cu2ZnSnS4 solar cell, different gradient strategies are investigated. Absorber layer gradient is obtained by partial substitution of sulfur with selenium or tin with germanium. The PV Parameters are calculated using the SCAPS1D program. The effect of the front, back, and double gradient on the cell parameters was investigated. We proposed also the fully graded gap absorber layer profile. The opencircuit voltage has increased to 1.040V, the fill factor has increased to 71.69%, and the efficiency has exceeded 22.95%. In contrast to other types of gradients, the short-circuit current density remains high (Jsc= 39.7mA / cm2 ).

Boosting the sodium-ion storage capability of MoSe2 through the synergistic effect of rational sulfur substituting and carbon compositing

Molybdenum selenide (MoSe2) has been regarded as a promising anode for sodium-ion storage due to its large interlayer space, acceptable electronic conductivity, and considerable theoretical capacity, but suffers insufficient active sites and serious volume variation, leading to low reversible capacity and poor cycling lifespans. Herein, a facile one-pot hydrothermal method is developed to achieve sulfur substituting and carbon compositing simultaneously and employed to boost the sodium ion storage properties of MoSe2. The effects of sulfur substituting and carbon compositing on the redox kinetics and sodium-ion storage performance are investigated. In short, sulfur substitution mainly enhances the electronic/ionic conductivity and specific capacity of the MoSe2 by tailoring the electron structures and creating anionic vacancies. Carbon compositing mainly improves the cycling stability due to the alleviative aggregation of active materials and the prohibited active materials dissolution. As a result, the optimized MoSe2-xSx@C electrode presents 348.6 mAh g−1 at 0.1 A g−1, and can endure long-term cycling at 4 A g−1 after 600 cycles with acceptable capacity retention of 83.9%, much better than the pure MoSe2 electrode and the MoSe2-xSx electrodes. This work may provide a facile method to enhance the sodium ion storage properties of transition metal dichalcogenides.

Sulfur Mismatch Substitution in Layered Double Hydroxides as Efficient Oxygen Electrocatalysts for Flexible Zinc–Air Batteries

AbstractAlthough layered double hydroxides (LDHs) are extensively investigated for oxygen electrocatalysis, their development is hampered by their limited active sites and sluggish reaction kinetics. Here, sulfur mismatch substitution of NiFe–LDH (S–LDH) is demonstrated, which are in‐situ deposited on nitrogen‐doped graphene (S–LDH/NG). This atomic‐level sulfur incorporation leads to the construction of the tailored topological microstructure and the modulated electronic structure for the improved catalytic activity and durability of bifunctional electrocatalysts. The combined computational and experimental results clarify that the electron transfer between the sulfur anion and Fe3+ generates the high‐valence Fe4+ species, while the mismatch substitution of the sulfur anion induces the metallic conductivity, an increased carrier density, and the reduced reaction barrier. Consequently, the as‐fabricated Zn–air battery achieves a high power density of 165 mW cm‐2, a large energy density of 772 Wh kgZn‐1 at 5 mA cm‐2, and long cycle stability for 120 h, demonstrating its real‐life operation.

17% efficiency for linear-shaped ADA-type nonfullerene acceptors enabled by 3D reticulated molecular packing

The fundamental principles governing photovoltaic properties of nonfullerene acceptors (NFAs) are essential for developing high-performance polymer solar cells. In this work, using three heteroheptacene-based acceptors (M-series) as model compounds, we systematically study the implication of heteroatoms in the heteroheptacene core on the molecular packing, morphology, optoelectronic, photophysical, and photovoltaic properties of the NFAs. It is found that replacing the oxygen atoms at the inner positions of the heteroheptacene core with sulfur atoms leads to the molecular packing mode change from a linear two-dimensional (2D) brickwork structure to a three-dimensional (3D) reticulated motif, which facilitates the formation of a desirable active layer with nanostructured phase separation morphology and improved charge transport. Meanwhile, the down-shifted highest occupied molecular orbital energy level of M36 induced by the sulfur substitution, matches better with that of polymer donor PM6 thereby leading to more efficient exciton dissociation and charge transfer. As a result, the best-performing photovoltaic device based on M36 affords an outstanding efficiency of 17%, which is among the highest values reported for all the ADA-type NFAs. Our work reveals the important role of the heteroatoms in the heteroheptacene core in constructing the 3D network of ADA-type NFAs, and the structure-property relationships herein shall provide an important guidance for designing high-performance NFAs.

How to dope the basal plane of 2H-MoS2 to boost the hydrogen evolution reaction?

Molybdenum disulfide (MoS2) is considered one of the most likely materials that could be turned into low-cost hydrogen evolution reaction (HER) catalysts to replace noble metals in acidic solutions. However, several challenges prevent MoS2 from being truly applicable, including limited number of active sites (typically only the edges are active) and poor conductivity. In this work, we perform an extensive density functional theory (DFT) screening of substitutional doping as a possibility to activate the otherwise inert basal surface. We assess 17 Earth abundant elements for molybdenum doping and 5 elements for sulfur substitution. Systematically determining the preference of the metallic dopants to be located on the edges rather than in the basal plane, we reveal that most dopants are much more likely to be incorporated at the edges, suggesting that advanced synthesis methods are required to obtain basal-plane doped catalysts. The latter may, however, feature many more active sites per MoS2 formula unit, motivating our study on the properties of such substitutionally doped surfaces. For the first time for such a screening study, we explore not only the formation of H*, but also of OH* and H2O* to explore the reactivity of the solvent. Two additional phenomena that could hinder the hydrogen production at these sites are investigated, namely H2S release and the (local) segregation/dispersion tendency of the dopants in the basal surface. Moreover, to assess the electrocatalytic activity, we take the electrochemical potential explicitly into account via grand canonical DFT. Compared with pristine MoS2 nanosheets, our results show that most doping elements significantly enhanced the electrocatalytic activity. Considering all assessed factors, we identify the most promising systems: Dimers of Ti, Zr and Hf and the substitution of S by P are predicted to lead to stable active sites on the basal plane with overpotentials of about 0.2 V.