Rapid Surface Reconstruction of Pentlandite by High-Spin State Iron for Efficient Oxygen Evolution Reaction.

Triggering rapid reconstruction reactions holds the potential to approach the theoretical limits of the oxygen evolution reaction (OER), and spin state manipulation has shown great promise in this regard. In this study, the transition of Fe spin states from low to high was successfully achieved by adjusting the surface electronic structure of pentlandite. In situ characterization and kinetic simulations confirmed that the high-spin state of Fe promoted the accumulation of OH- on the surface and accelerated electron transfer, thereby enhancing the kinetics of the reconstruction reaction. Furthermore, theoretical calculations revealed that the lower d-band center of high-spin Fe optimized the adsorption of active intermediates, thereby enhancing the reconstruction kinetics. Remarkably, pentlandites with high-spin Fe exhibited ultra-low overpotential (245 mV @ 10 mA cm-2 ) and excellent stability. These findings provided new insights for the design and fabrication of highly active OER electrocatalysts.

Unveiling Interfacial Effects for Efficient and Stable Hydrogen Evolution Reaction on Ruthenium Nanoparticles-Embedded Pentlandite Composites.

Heterogenous catalysis is important for future clean and sustainable energy systems. However, an urgent need to promote the development of efficient and stable hydrogen evolution catalysts still exists. In this study, ruthenium nanoparticles (Ru NPs) are in situ grown on Fe5 Ni4 S8 support (Ru/FNS) by replacement growth strategy. An efficient Ru/FNS electrocatalyst with enhanced interfacial effect is then developed and successfully applied for pH-universal hydrogen evolution reaction (HER). The Fe vacancies formed by FNS during the electrochemical process are found to be conducive to the introduction and firm anchoring of Ru atoms. Compared to Pt atoms, Ru atoms get easily aggregated and then grow rapidly to form NPs. This induces more bonding between Ru NPs and FNS, preventing the fall-off of Ru NPs and maintaining the structural stability of FNS. Moreover, the interaction between FNS and Ru NPs can adjust the d-band center of Ru NPs, as well as balance the hydrolytic dissociation energy and hydrogen binding energy. Consequently, the as-prepared Ru/FNS electrocatalyst exhibits excellent HER activity and improved cycle stability under pH-universal conditions. The developed pentlandite-based electrocatalysts with low cost, high activity, and good stability are promising candidates for future applications in water electrolysis.

Metalloborospherenes with a Stabilized Classical Fullerene-like Borospherene B40 Act as Nonlinear Optical Switches, Electron Reservoirs, Molecular Capacitors, and Molecular Reactors.

Using a new method of η5-Li and η6-Mg atoms capping the faces of the classical fullerene-like borospherene Td B40, we theoretically predict an exohedral metalloborospherene Td Mg10Li12&B40 molecule. Remarkably, a newfangled endoexo cage isomerism is proposed. Further, embedding Mg atoms in the Td B40 cage forms endohedral derivatives. Due to the intramolecular pull-push electron transfer relay, these obtained molecules possess unequal multilayered and alternant spherical charge distribution. The outer is an excess electron layer, bringing a molecular nonlinear switch character and an electron reservoir behavior with strong electron-donating and -accepting abilities. The middle (Mg2+)10(Li+)12 and the outer layers together constitute an electric double layer, presenting the behavior of a molecular capacitor where the electronic charge-discharge process occurs in the outer excess electron layer. The inner part is an empty cage B4026- with a strong negative electric field. The valence electrons of the embedded Mg atoms are transformed into new excess electrons and added in the outer excess electron layer, also exhibiting the charging behavior of the molecular capacitor. Considering the chemical reaction in the inner cage, the embedded Mg atom is ionized, forming an Mg2+ cation and 2e under the strong negative electric field; meanwhile, 2e is powerfully pushed into the outer excess electron layer. This chemical process shows a generalized Coulomb explosion, and thus the exohedral metalloborospherene molecules with cage B4026- may act as molecular reactors. The new species mark the genesis of classical fullerene-like borospherene chemistry and stimulate their applications in molecular nonlinear optical and nanoelectronics.

Improved Catalytic Activity and Stability of Co9S8 by Se Incorporation for Efficient Oxygen Evolution Reaction.

Combining an excellent electrocatalytic activity with the good structural stability of Co9S8 remains challenging for the oxygen evolution reaction (OER). In this study, density functional theory was used to demonstrate the importance of moderate adsorption strength with *O and *OOH intermediate species on Co9S8 for achieving excellent electrocatalytic performances. A novel strategy was proposed to effectively optimize the *O oxidation to *OOH by introducing Se heteroatoms to adjust adsorption of the two intermediates. This process also allowed prediction of the simultaneous enhancement of the structural stability of Co9S8 due to the weak electronegativity of a Se dopant. The experimental results demonstrated that Se doping can regulate the charge density of Co2+ and Co3+ in Co9S8-xSex, leading to a substantially improved OER performance of Co9S8-xSex. As a result, our Co9S6.91Se1.09 electrode exhibited an overpotential of 271 mV at 10 mA cm-2 in a 1.0 M KOH solution. In particular, it also demonstrated an excellent stability (∼120 h) under a current density of 10 mA cm-2, indicating the potential for practical applications. Overall, the proposed strategy looks promising for regulating the electronic structures and improving the electrochemical performances of sulfide materials.

Effect of an external electric field, aqueous solution and specific adsorption on segregation of PtML/MML/Pt(111) (M = Cu, Pd, Au): a DFT study.

The oxygen reduction reaction (ORR) that occurs on the outermost layer of electrocatalysts is significantly affected by the composition and structure of the electrocatalysts. During the preparation of PtM alloy electrocatalysts, high-temperature annealing in an inert or reducing atmosphere could promote the segregation of M toward the core, forming a highly active Pt-skin structure. However, under fuel cell operating conditions, the adsorption of oxygen-containing groups could stimulate the easily dissolved M to segregate to the surface, reducing the activity and stability of the electrocatalysts. In this work, we conducted segregation energy calculation of PtM (M = Cu, Pd, Au) electrocatalysts under specific adsorption (SA), aqueous solution (AS) and an external electric field (EEF) with a density functional theory method. It was found that different factors have different effects on the segregation energy: ΔΔESA ≫ ΔΔEEEF > ΔΔEAS. The coupling effects have also been considered and compared: ΔΔESA+EEF > ΔΔESA+AS > ΔΔEEEF+AS. When including all three factors, the change of segregation energy could reach 1.63 eV. Therefore, operating conditions have a noteworthy influence on the segregation behavior of PtM ORR electrocatalysts, which should be considered in the further design of PtM ORR electrocatalysts.

The catalytic activity and mechanism of oxygen reduction reaction on P-doped MoS2.

With the approaching commercialization of proton exchange membrane fuel cell technology, developing active, non-precious metal oxygen reduction reaction (ORR) catalyst materials to replace currently used Pt-based catalysts is a necessary and essential requirement in order to reduce the overall system cost. Here, we report a single-atom doped molybdenum disulfide sheet (short as X-MoS2) catalyst for the ORR using a dispersion-corrected density functional theory method. Of all the eleven X-MoS2 (X = B, C, N, O; Al, Si, P; Ga, Ge, As, and Se) systems, only the phosphorus atom doped molybdenum disulfide (P-MoS2) has an O2 adsorption energy close to that of a Pt(111) surface. We have further explored the detailed ORR mechanism of P-MoS2. Along the four-electron reaction pathway, the reduction of OH to H2O is the rate-limiting step with the largest diffusion barrier of 0.79 eV.

Free-Standing Single-Molecule Thick Crystals Consisting of Linear Long-Chain Polymers.

Organic two-dimensional (2D) crystals are fundamentally important for development of future devices. Despite that more than a half of man-made products contain polymers, 2D crystals consisting of long linear chains have yet to be explored. Here we report on the fabrication of 2D polyaniline (PANI) crystals via rational electrochemical polymerization followed by liquid-phase exfoliation. The 2D PANI is molecularly thin (∼0.8 nm) and composed of PANI chains with a number-average molecular weight of ∼31 000. The chains are parallel to each other with the benzene rings standing almost vertically to the surface, implying a face-to-face arrangement of the neighboring chains held together by abundant π-π interactions augmented with hydrogen bonds. The 2D PANI can be readily transferred to various solid surfaces and exhibit interesting electrical and optical properties, suggesting that they would be potentially useful in photoelectronic devices and other applications.

Fundamental insights into the electronic structure of zigzag MoS2 nanoribbons.

The structural and electronic properties of zigzag MoS2 nanoribbons are investigated using first-principles density functional theory. Our models are motivated by the experimental observations, in which both Mo edges are terminated by S atoms. Our calculations show that the edge can introduce some extra states into the energy gap, which lead nanoribbons to exhibit a metallic characteristic. Such extra states around the Fermi level are flat or dispersed. Through detailed analyses, we identify and discriminate them based on the major contributors. By applying an external transverse electric field, Eext the extra states around the Fermi level can shift apparently, especially for those attributed to Mo-edge atoms. It can be explained by the charge redistribution in the MoS2 nanoribbons due to Eext. In addition, the nanoribbon can be changed from metal to an n/p-type semiconductor according to different edge hydrogenation. After full edge hydrogenation, we observe a characteristic of anti-bonding orbitals between H and S atoms at the Mo-edge. Interestingly, the energy of anti-bonding orbitals and electric conductivity of nanoribbons can be tailored by Eext. The results suggest a strategy controlling the performance of MoS2 for hydrogen evolution.

Interaction of Rhodamine 6G molecules with graphene: a combined computational-experimental study.

In this work, the adsorption of Rhodamine 6G molecules on some graphene substrates is investigated using density functional theory. Some simple models, such as those of perfect graphene, defective graphene, *O/*OH modified graphene and B/N doping graphene, are constructed as substrates to simulate graphene oxide and B/N doping graphene sheets. It is demonstrated that the interactions of Rhodamine 6G molecules with graphene materials are strong. In particular, the amine group of Rhodamine 6G molecules can favor the formation of a chemical bond with some graphene substrates characterized by under-coordinated atoms. The chemical interactions would lead to significant changes in the electronic structures of graphene substrates, which have the potential to tune the electronic properties of graphene. In addition, our calculations predict that the epoxy/hydroxyl group attached to the surface of graphene could be removed by Rhodamine 6G molecules, which suggests that the reduction reaction may occur in graphene oxide upon Rhodamine 6G doping. The surface plasmon resonance spectra of R6G adsorbed on some graphene substrates are also characterized, which are well in agreement with some computational results. Therefore, combined with experimental observations, our results provide an insight into the interaction of Rhodamine 6G molecules with graphene materials.

Confinement of massless Dirac fermions in the graphene matrix induced by the B/N heteroatoms.

In this work, the systems are constructed with the defect lines of B-B or N-N dimers embedded in a graphene matrix using density functional theory. It is found that the Dirac-cone dispersions appear at the Fermi level in the bands introduced by the B or N heteroatom, linear B-B or N-N dimers, demonstrating that the carrier mobility is ∼10(6) m s(-1) which is comparable with that of the pristine graphene. Most importantly, such dimer lines act as the quasi-1-D conducting nanowires whose charge carriers are confined around the linear defects in these dimers while the charge carriers in pristine graphene are dispersed two-dimensionally. Such systems suggest that heteroatoms in graphene can indeed contribute to the Dirac cone. In addition, the type of carriers (p-type or n-type) can be manipulated using the B or N heteroatoms, respectively. This will greatly enrich the electronic properties of Dirac semimetals.

Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells.

We employed density functional theory to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt(1ML)) supported on an M surface, Pt(1ML)/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt(1ML) shell depending on the conditions. In vacuum conditions, the Pt1ML shell can be stabilized on the most of M cores except Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the Pt(ML) shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt(1ML)/M(1ML)/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt(1ML) shell were also discussed.

Stability of Pt near surface alloys under electrochemical conditions: a model study.

The stability is one of the key requirements for commercializing the fuel cell electrocatalysts in automotive applications. For the widely used Pt-based catalysts, it can be achieved by the formation of a stable Pt skin on the surface. Here, we employed density functional theory (DFT) to explore the stability of monolayer Pt (PtML) on various near surface alloy (NSAs) surfaces, PtML/MML/Pt(111) (M = Fe, Co, Ni, Cu; Ru, Rh, Pd, Ag; Os, Ir, Au), under various environmental conditions. Our results show that under the vacuum condition, the alloying M except Ag and Au thermodynamically prefer to stay in the subsurface and the formation of PtML on the surface is thermodynamically favored. A barrier has to be overcome for M to segregate. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathway, different M should be considered for alloying with Pt to maintain the stability of surface PtML. PtRh and PtPd are the only two systems, where the surface PtML is likely to stay intact in perchloric acid (HClO4), sulfuric acid (H2SO4), phosphoric acid (H3PO4) and alkaline solutions as well as under the oxygen reduction reaction (ORR) conditions via different pathways. PtIr should also be paid attention, which falls only during the ORR via the OOH intermediate. Our results highlight the importance of chemical environments in affecting the stability of the catalysts.

Novel hollow core-shell Zn0.5Cd0.5S@ZnIn2S4/MoS2 nanocages with Z-scheme heterojunction for enhanced photocatalysis of hydrogen generation.

The development of low-cost and efficient metal sulfide photocatalysts through morphological and structural design is vital to the advancement of the hydrogen economy. However, metal sulfide semiconductor photocatalysts still suffer from low carrier separation and poor solar-to-hydrogen conversion efficiencies. Herein, two-dimensional ZnIn2S4 nanosheets were grown on Zn0.5Cd0.5S hollow nanocages to construct Zn0.5Cd0.5S@ZnIn2S4 hollow nanocages for the first time. Novel hollow core-shell Zn0.5Cd0.5S@ZnIn2S4/MoS2 nanocages with Z-scheme heterojunction structures were obtained by incorporating MoS2 nanosheet co-catalyst via the solvothermal method. The resulting Zn0.5Cd0.5S@ZnIn2S4/MoS2 exhibited unique structural and compositional advantages, leading to remarkable photocatalytic hydrogen evolution rates of up to 8.5 mmol·h-1·g-1 without the use of any precious metal co-catalysts. This rate was 10.6-fold and 7.1-fold higher compared to pure ZnIn2S4 and Zn0.5Cd0.5S, respectively. Moreover, the optimized Zn0.5Cd0.5S@ZnIn2S4/MoS2 photocatalyst outperformed numerous reported ZnIn2S4-based photocatalysts and some ZnIn2S4-based photocatalysts based on precious metal co-catalysts. The exceptional photocatalytic performance of Zn0.5Cd0.5S@ZnIn2S4/MoS2 can be attributed to the Z-scheme heterojunction of core-shell structure that enhanced charge carrier separation and transport, as well as the co-catalytic action of MoS2. Overall, the proposed Zn0.5Cd0.5S@ZnIn2S4/MoS2 with heterojunction structure is a promising candidate for the preparation of efficient photocatalysts for solar-to-hydrogen energy conversion.

Novel amorphous FeOOH-modified Co9S8 nanosheets with enhanced catalytic activity in oxygen evolution reaction.

Efficient oxygen evolution reaction (OER) is vital for water electrolysis and advanced hydrogen energy production. However, the sluggish kinetics of this reaction require significant overpotentials, leading to high energy consumption. Therefore, developing OER electrocatalysts with exceptional performance and long-term durability is crucial for enhancing the energy efficiency and cost-effectiveness of the hydrogen production process. In this research, novel FeOOH/Co9S8 catalysts were prepared through a two-step hydrothermal reaction followed by one-step electrodeposition on nickel foam for an alkaline OER. The as-obtained catalysts possessed abundant non-homogeneous interfaces between FeOOH and Co9S8 nanosheets, conducive to optimized coordination environments of Fe and Co sites by redistributing interfacial charges. This synergy strengthened the chemisorption of oxygenated intermediates, leading to accelerated reaction kinetics, abundant active sites, and enhanced OER performance. The optimized electrocatalyst FeOOH/Co9S8-15 achieved a current density of 10 mA cm-2 at an overpotential of 248 mV and good stability for over 140 h. This study presents a novel approach for producing compelling and durable alkaline dielectric OER electrocatalysts, which will be helpful in the future manufacturing of advanced energy devices.

Exploration of defect structures on graphene.

For graphene obtained by chemical vapor deposition, there are large amount of defects in the crystalline structures. The carbon atoms from the feedstock can attack the graphene surface in annealing process, which may be one of the reasons affecting the structure of graphene. In order to explore some defect structures on graphene, we investigate the adsorption of carbon adatoms and vacancies on graphene using first-principles calculations. It is demonstrated that the adatoms can form strong covalent bonds with the graphene and the C-C dimmer adsorption may be the most prolific defect model. The C adatom can even fill simple vacancy of graphene. Our numerical simulations also show that the defect structures can lead to the splitting of the mid-gap peak of perfect graphene in the electronic structures. It is suggested that its conductivity would be lower than that of the perfect graphene, which can explain the low mobility of the charge carriers in some experiments.

Structure evolution and durability of Metal-Nitrogen-Carbon (M = Co, Ru, Rh, Pd, Ir) based oxygen evolution reaction electrocatalyst: A theoretical study.

Developing low-cost, high activity and stability oxygen evolution reaction (OER) catalysts is significantly important but still challenging for water electrolyzers. In this work, we calculated the OER activity and stability of Metal-Nitrogen-Carbon (MNC, M = Co, Ru, Rh, Pd, Ir) based electrocatalyst with different structures (MN4C8, MN4C10, MN4C12) using density functional theory (DFT) method. These electrocatalysts were divided into three groups based on the value of ΔG*OH, that is ΔG*OH > 1.53 eV (PdN4C8, PdN4C10, PdN4C12), ΔG*OH < 1.23 eV (RuN4C8, RuN4C10, RuN4C12, CoN4C8, CoN4C10) and 1.23 eV < ΔG*OH < 1.53 eV (RhN4C8, RhN4C10, RhN4C12, IrN4C8, IrN4C10, IrN4C12, CoN4C12), and ΔG*OH determine whether the structure evolution will appear. The results proved that MNC (M = Rh, Ir) with 1.23 eV < ΔG*OH < 1.53 eV shows higher OER activity due to moderate binding energy between reaction intermediates and MNC. Furthermore, these catalysts could maintain MNC structure without further oxidation and structural evolution under working conditions (high temperature, dynamic condition, local electric field and strong specific adsorption), therefore show excellent stability. However, MNC electrocatalyst with ΔG*OH > 1.53 eV or ΔG*OH < 1.23 eV revealed less stability under working conditions, due to their low intrinsic stability or structural evolution under working conditions, respectively. In conclusion, we proposed a comprehensive evaluation method for MNC electrocatalysts by taking ΔG*OH as the screening criterion for OER activity and stability, as well as ΔEb under working condition as descriptor of stability. This is of great significance for the design and screening of ORR, OER and HER electrocatalysts under working conditions.

Active-site-enriched dendritic crystal Co/Fe-doped Ni3S2 electrocatalysts for efficient oxygen evolution reaction.

The electrochemical decomposition of water plays a critical role in green and sustainable energy. However, the development of efficient and low-cost non-noble metal catalysts to overcome the high potential of the anodic oxygen evolution reaction (OER) is still challenging. In this work, electrocatalysts with high OER activity were obtained by doping Co/Fe bimetals into Ni3S2 (CF-NS) via a simple single-step hydrothermal method by adjusting the doping ratio of bimetals. A series of characterization studies revealed that the introduction of a Co/Fe co-dopant increased the number of active sites and improved the electroconductibility, while optimizing the electronic structure of Ni3S2. Meanwhile, Fe-induced high valence Ni contributed to the production of an OER active phase NiOOH. The unique dendritic crystal morphology facilitated the disclosure of the active sites and the expansion of mass transfer channels. The optimized sample required a low overpotential of 146 mV to obtain a current density of 10 mA cm-2 in 1.0 M KOH solution. The optimized sample also operated stably for at least 86 h. In sum, the proposed method looks very promising for designing efficient, stable, and low-cost non-precious metal catalysts with high conductivity and multiple active sites, useful for future synthesis of transition metal sulfide catalysts.

Electron-ion conjugation sites co-constructed by defects and heteroatoms assisted carbon electrodes for high-performance aqueous energy storage.

Rapid preparation strategies of carbon-based materials with a high power density and energy density are crucial for the large-scale application of carbon materials in energy storage. However, achieving these goals quickly and efficiently remains challenging. Herein, the rapid redox reaction of concentrated H2SO4 and sucrose was employed as a means to destroy the perfect carbon lattice to form defects and insert large numbers of heteroatoms into the defects to rapidly form electron-ion conjugated sites of carbon materials at room temperature. Among prepared samples, CS-800-2 showed an excellent electrochemical performance (377.7 F g-1, 1 A g-1) and high energy density in 1 M H2SO4 electrolyte owing to its large specific surface area and a significant number of electron-ion conjugated sites. Additionally, CS-800-2 exhibited desirable energy storage performance in other aqueous electrolytes containing various metal ions. The theoretical calculation results revealed increased charge density near the carbon lattice defects, and the presence of heteroatoms effectively reduced the adsorption energy of carbon materials toward cations. Accordingly, the constructed "electron-ion" conjugated sites comprising defects and heteroatoms on the super-large surface of carbon-based materials accelerated the pseudo-capacitance reactions on the material surface, thereby greatly enhancing the energy density of carbon-based materials without sacrificing power density. In sum, a fresh theoretical perspective for constructing new carbon-based energy storage materials was provided, promising for future development of high-performance energy storage materials and devices.

Reasonably optimized structure of iron-doped cobalt hydroxylfluoride for high-performance supercapacitors.

Cobalt hydroxylfluoride (CoOHF) is an emerging supercapacitor material. However, it remains highly challenging to effectively enhance the performance of CoOHF, which is limited by its poor electron and ion transport ability. In this study, the intrinsic structure of CoOHF was optimized through Fe doping (CoOHF-xFe, where x represents the Fe/Co feeding ratio). As indicated by the experimental and theoretical calculation results, the incorporation of Fe effectively enhances the intrinsic conductivity of CoOHF and optimizes its surface ion adsorption capacity. Moreover, since the radius of Fe is slightly larger than that of Co, the space between the crystal planes of CoOHF increases to a certain extent, and the ability to store ions is consequently enhanced. The optimized CoOHF-0.06Fe sample exhibits the maximum specific capacitance (385.8 F g-1). The asymmetric supercapacitor with activated carbon achieves a high energy density of 37.2 Wh kg-1 at a power density of 1600 W kg-1, and a full hydrolysis pool is successfully driven by the device, indicating great application potential. This study lays a solid basis for the application of hydroxylfluoride to a novel generation of supercapacitors.

Prediction of future breakthroughs in materials synthesis and manufacturing techniques: a new perspective of synthesis dynamics theory.

The continuous development of different kinds of materials plays a significant role in social productivity. However, the lack of a complete synthesis kinetic theory has resulted in the absence of scientific guidance for the emergence of advanced manufacturing technologies, limiting the research and production of new types of materials. The present work aims at obtaining the basic form of the diffusion flux-driving force equation through the concept of ion diffusion so as to establish a synthesis kinetic theory. Using this theory, the scientific principles of existing synthesis technologies are summarized, and the key directions that future manufacturing technologies need to break through are proposed as well. Based on a comprehensive analysis of this theory, the feasible directions are discussed, providing strong support for the early realization of targeted design and manufacturing of new materials with specific functions.