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Aqueous K-ion batteries have attracted increasing attention. Yet, their capacity and durability are facing severe challenges. Construction of available electrolyte plays a vital role to overcome these challenges. Herein, a polymer-free CH3COOK (KAc) gel electrolyte is developed with a ultrahigh salt-water mole ratio, which can be high as 1: 1.16 (KAc: H2O). With a glassy carbon electrode, the electrochemical stability window of the gel is up to 4 V (-1.9 ~ 2.1 V vs Ag/AgCl). At room temperature , the ion conductivity is measured to be 10.9 mS cm−1, which increases to 23.5 mS cm−1 at 90 ℃ and is still 3.4 mS cm−1 at -20 ℃, indicating good temperature adaptability. Surprisingly, unlike other high-concentered electrolytes, anti-deliquescence ability of the gel is also rather good. With Raman analysis, it is found that there are almost no free water and cross-link structure among K+, Ac− and water should be formed in the gel, which is further demonstrated by density function theory (DFT) computation. Using this gel electrolyte, FeSe2 can deliver a high and reversible capacity of 250 mAh g−1 at 0.5 A g−1 as anode. Most importantly, stable solid electrolyte interphase (SEI) layer is found to be formed. It is believed that the quasi-solid state of the electrolyte together with the SEI layer can effectively suppress the reaction activity and the solvent ability of water, and hence inhibit mass loss of active materials, even the materials that store charges through phase conversion reactions.

Ti2Nb10O29 (TNO) is a suitable electrode for high-performance lithium-ion batteries and capacitors because of its large lithium storage capacity and high Li+ diffusivity. Currently, the rate or power capability of TNO-based systems is limited by the poor electronic conductivity of the material. Here we report our findings in design, synthesis, and characterization of a hierarchical N-rich carbon conductive layer wrapped TNO structure (TNO@NC) using a novel polypyrrole-chemical vapor deposition (PPy-CVD) process. It was found that carbon coating with PPy–carbon partially reduces Ti and Nb cations, forms TiN, and creates oxygen vacancies in the TNO@NC structure that further increase overall electronic and ionic conductivity. Various defect models and density functional theory (DFT) calculations are used to show how oxygen vacancies influence the electronic structure and Li-ion diffusion energy of the TNO@NC composite. The optimized TNO@NC sample shows notable rate capability in half-cells with a reversible capacity of 300 mAh g−1 at 1 C rate and maintains 211 mAh g−1 at a rate of 100 C, which is superior to that of most MxNbyOz materials. Full cell LiNi0.5Mn1.5O4 (LNMO)||TNO@NC lithium-ion batteries (LIB) and active carbon (AC)||TNO@NC hybrid lithium-ion capacitors (LIC) exhibited notable volumetric and gravimetric energy and power densities.

The size effect on the activity of a catalyst has been a focal issue since ideal catalysts were pursued, whereas that on the degradation of a catalyst, by reaction intermediates such as CO, is little discussed. We demonstrate that the dehydrogenation of methanol-d4 on supported Rh nanoclusters precovered with CO (Rh-CO clusters) was obstructed, indicated by a decreased production of CO and D2; the obstructive effect exhibits a remarkable dependence on the cluster size, with a minimum at a cluster diameter near 1.4 nm. The decreased production arose from a decreased reaction probability controlled by the increased activation energy for each dehydrogenation step (including formation of methoxy-d3), adsorption energies of CO, and repulsion from the CO array on the Rh-CO surface. The effects of these factors in deactivating the clusters varied separately with the cluster size. Consequently, the size effect on the CO poisoning should be taken into account in engineering the cluster size to optimize the catalytic performance.

Annealed Rh nanoclusters on an ordered thin film of Al2O3/NiAl(100) were shown to exhibit a promoted reactivity toward the decomposition of methanol-d4, under both ultrahigh vacuum and near-ambient-pressure conditions. The Rh clusters were grown with vapor deposition onto the Al2O3/NiAl(100) surface at 300 K and annealed to 700 K. The decomposition of methanol-d4 proceeded only through dehydrogenation, with CO and deuterium as products, on Rh clusters both as prepared and annealed. Nevertheless, the catalytic reactivity of the annealed clusters, measured with the production of either CO or deuterium per surface Rh site from the reaction, became at least 2–3 times that of the as-prepared ones. The promoted reactivity results from an altered support effect associated with an annealing-induced mass transport at the surface. Our results demonstrate a possibility to practically prepare reactive Rh clusters, regardless of the cluster size, that can tolerate an elevated reaction temperature, with no decreased reactivity.

Pt-oxygen-containing species (Pt-OCS) catalysts, in which OCS (e.g., metal-oxides) are decorated on a Pt surface, possess enhanced ethanol oxidation reaction (EOR) activity and stability compared with pure Pt and are promising in practical applications of direct ethanol fuel cells. We investigate the promotion roles of Pt-OCS electrocatalysts toward the EOR via a combination of density functional theory (DFT) calculations and experiments, providing a rational design strategy for Pt-OCS catalysts. It is revealed that Pt-AuO and Pt-SnO excel in EOR activity and stability, respectively, among the DFT screening of various Pt-OCS systems, and this is confirmed by the following experiments. Moreover, an optimized Pt-AuSnO catalyst is proposed by DFT calculations, taking advantage of both Pt-AuO and Pt-SnO. The as-prepared Pt-AuSnO catalyst delivers an EOR activity that is 9.7 times higher than that of Pt and shows desired stability. These findings are expected to elucidate the mechanistic insights into Pt-OCS materials and lead to advanced EOR electrocatalysts.

While pseudocapacitive electrodes have potential to store more energy than electrical double-layer capacitive electrodes, their rate capability is often limited by the sluggish kinetics of the Faradaic reactions or poor electronic and ionic conductivity. Unlike most transition-metal oxides, MoO2 is a very promising material for fast energy storage, attributed to its unusually high electronic and ionic conductivity; the one-dimensional tunnel is ideally suited for fast ionic transport. Here we report our findings in preparation and characterization of ultrathin MoO2 sheets with oriented tunnels as a pseudocapacitive electrode for fast charge storage/release. A composite electrode consisting of MoO2 and 5 wt % GO demonstrates a capacity of 1097 C g-1 at 2 mV s-1 and 390 C g-1 at 1000 mV s-1 while maintaining ∼80% of the initial capacity after 10,000 cycles at 50 mV s-1, due to minimal change in structural features of the MoO2 during charge/discharge, except a small volume change (∼14%), as revealed from operando Raman spectroscopy, X-ray analyses, and density functional theory calculations. Further, the volume change during cycling is highly reversible, implying high structural stability and long cycling life.

Ge is considered a promising anode candidate for Li-ion batteries (LIBs); however, its practical applicability is hindered by the relatively slow Li-ion diffusion owing to the stiffness of the diamond-like structure. Inspired by little difference in electronegativity between Ge and P, we have designed a novel layered GeP anode for LIBs, which can be readily synthesized using a mechano-chemical method and a subsequent low-temperature annealing. In particular, GeP demonstrates the best performances among all Ge-based anode materials studied, attributed to its fast Li-ion diffusion compared to Ge counterpart and a unique Li-storage mechanism that involves intercalation, conversion, and alloying, as confirmed by XRD, TEM, XPS, and Raman spectroscopy. Specially, the initial layered crystal structure of GeP can be reconstructed during charging due to its low formation energy, thus offering remarkable reversibility during cycling. Further, this study implies that the formation energy of crystal structures could be an important parameter for strategic design of large-capacity anode materials for LIBs.

With both real-world catalyst Rh/CeO2 and model-system Rh(111), we investigated how oxygen and water play effective roles in the oxidative steam-reforming (OSR) reaction of ethanol. The results sho...

Gas sensing characteristics of PdO nanoflake thin films exposed to ethanol (EtOH) at temperatures below 250 °C was studied. The PdO thin film responses distinctly to 0.15 ppm EtOH in dry air at temperatures above 100 °C. A characteristic valley-shaped response feature develops in the early stage of the exposure to EtOH at 150 °C and above. Formation of the valley feature is a result of the combined effects of two types of surface processes, which successively modify the sensor conductance in the opposite way. Dehydrogenation of adsorbed EtOH induces reduction of preadsorbed oxygen anions and the PdO substrate, resulting in the drop of the conductance. On the other hand, subsequent adsorption of EtOH and oxygen on newly growing Pd nanoclusters, which develop due to the reduction of the PdO substrate, causes the increase in the conductance. The Pd nanoclusters can be later reoxidized in the EtOH gas mixture, thereby modifying the sensing behavior of the PdO sensor. X-ray photoelectron spectroscopy (XPS), diffusive reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature programmed desorption (TPD) were used to study adspecies and gaseous species formed in the EtOH gas sensing reactions. On the basis of the characteristic electrical response and chemical characterizations, we proposed the formation mechanism for the characteristic response feature.

SnS2 has been extensive studied as an anode material for sodium storage owing to its high theoretical specific capacity, whereas the unsatisfied initial Coulombic efficiency (ICE) caused by the partial irreversible conversion reaction during the charge/discharge process is one of the critical issues that hamper its practical applications. Hence, heterostructured SnS2/Mn2SnS4/carbon nanoboxes (SMS/C NBs) have been developed by a facial wet-chemical method and utilized as the anode material of sodium ion batteries. SMS/C NBs can deliver an initial capacity of 841.2 mAh g–1 with high ICE of 90.8%, excellent rate capability (752.3, 604.7, 570.1, 546.9, 519.7, and 488.7 mAh g–1 at the current rate of 0.1, 0.5, 1.0, 2.0, 5.0, and 10.0 A g–1, respectively), and long cycling stability (522.5 mAh g–1 at 5.0 A g–1 after 500 cycles). The existence of SnS2/Mn2SnS4 heterojunctions can effectively stabilize the reaction products Sn and Na2S, greatly prevent the coarsening of nanosized Sn0, and enhance reversible conver...

Although Pt-based anodes have shown promising electrochemical behaviors toward the ethanol oxidation reaction (EOR) in the direct ethanol fuel cell (DEFC) application, the rational design for optimizing the structures and compositions of catalysts is yet to be fully understood due largely to the lack of mechanistic insights into the catalytic reaction. Herein, we systematically investigated EOR on Pt-based binary (PtSn and PtRu) and ternary (PtSnRu) nanorods with varied atomic ratios to elucidate the effects of chemical composition and structure on the electrochemical behavior. The electrochemical results showed that Sn and Ru in the ternary PtSnRu NRs can effectively promote the EOR performance, both at 0.6 V (I06) and peak potential (Imax), as compared to binary PtSn and PtRu NRs. The enhanced activity at a low potential (I06) corresponded to the strengthened adsorption of water and ethanol on Ru site with a highly energetic d band structure; this at a high potential (Imax) was related to the oxygen-containing species on surface Sn, lowering the oxidation barriers through hydrogen-bond interactions, according to density functional theory-based calculations. The combination of electrochemical experiments on modeled binary and ternary electrodes and theoretical computation offers an effective approach to clarify the complex EOR mechanism and provides information vital to achieving the realistic design of better EOR anodes.

Beyond the physical lithium polysulfide (Li2Sx) entrapment of various 3D porous sulfur hosts, the importance of chemical interactions between sulfur host and Li2Sx on performance of Li-S batteries has recently been highlighted. However, most of these studies focus mainly on one type of chemical interaction and effective suppression of Li2Sx migration is still lacking. Here, we report a uniquely designed sulfur host that can immobilize Li2Sx through a dual chemisorption mechanism. The new sulfur host is consisted of an MXene matrix and polydopamine (PDA) overcoat, where Mxene forms a strong Ti–S bonding by the Lewis acid-base mechanism while PDA withholds Li2Sx through the polar-polar interaction. Benefited from the double chemisorption, the new cathode with a high sulfur loading of 5 mg cm−2 has been demonstrated with an initial capacity of 1001 mA h g−1 at a capacity retention of 65% over 1000 cycles at 0.2 C. Overall, this study not only presents a unique chemical mechanism to entrap Li2Sx, but also provides a new way to rationally design a practical sulfur cathode for high-performance Li-S batteries.

Nanostructured-alloy-type anodes have received great interest for high-performance lithium-ion batteries (LIBs). However, these anodes experience huge volume fluctuations during repeated lithiation/delithiation and are easily pulverized and subsequently form aggregates. Herein, an efficient method to stabilize alloy-type anodes by creating defects on the surface of the metal oxide support is proposed. As a demonstration, PPy-encapsulated SnS2 nanosheets supported on defect-rich TiO2 nanotubes were produced and investigated as an anode material for LIBs. Both experimental results and theoretical calculations demonstrate that defect-rich TiO2 provides more chemical adhesions to SnS2 and discharge products, compared to defect-poor TiO2 , and then effectively stabilizes the electrode structure. As a result, the composite exhibits an unprecedented cycle stability. This work paves the way to designing durable and active nanostructured-alloy-type anodes on oxide supports.

The use of a computation-guided method and the discovered structure–property relationship would establish a rational strategy to aid the development of ethanol oxidation reaction (EOR) catalysts for possible commercialization of direct ethanol fuel cells. Here, we investigate the promotion roles of additive metals in ternary Pt–Sn–Ag catalysts toward EOR via a combination of density functional theory calculation and experimental evidence. By calculating the EOR energetics, the promotion roles of Sn and Ag were revealed from the viewpoints of electronic and structural effects, respectively: (1) The addition of Sn and Ag on Pt essentially reduce the reaction energy and activation barrier of the second two-electron transfer process of EOR, facilitating the oxidation of acetaldehyde to acetic acid; (2) a homogeneous Pt–Sn–Ag surface configuration strengthens the adsorption energy of ethanol, thus improving the activity for ethanol oxidizing to acetaldehyde. Experimentally, various Pt–Sn–Ag nanorod catalysts ...

In the development of emerging energy, proton exchange membrane fuel cells (PEMFCs) have been widely researched. Nevertheless, because of the high price and scarcity of Pt and its sluggish kinetics for oxygen reduction reaction (ORR), the preparation of highly effective cathode catalysts becomes one of the main challenges for PEMFCs in the practical application. In this study, carbon supported PtSn nanorods (NRs) with metal loading of 50 wt % and different Pt/Sn ratios of 80/20, 65/35 and 50/50 have been prepared by formic acid reduction method. The ORR performance of the catalysts can be promoted synergistically by one-dimensional (1-D) NRs and is varied with the Pt/Sn ratios. The experimental and computational efforts reveal that the Sn addition can lower the unoccupied d-band of neighboring Pt and the oxygen-containing species (OCS) on Sn can suppress their oxidation through the repulsion effect. Consequently, PtSn electrodes show the improved ORR activity; Pt50Sn50 with the highest Sn content results in the highest mass activity. On the other hand, the negatively charged OCS on Sn attracts the positively charged Pt and destructs the structures of PtSn NRs. Accordingly, Pt80Sn20 with the lowest Sn contain has the highest concentration of 1-D PtSn NRs and shows the best stability in the accelerated durability test (ADT). Our results clarify the mechanism of ORR on PtSn electrodes and suggest the importance of the precise control of atomic ratios on PtSn catalysts for the practical purpose. The findings open new perspectives about the origins of the activity and stability of the PtSn catalysts, especially for 1-D catalysts.

Atomic structures of Pt nanoclusters on graphene/Pt(111) were investigated with various techniques to probe the surface under ultrahigh-vacuum conditions and with calculations based on density-functional theory. Monolayer graphene was grown on thermal decomposition of ethylene on Pt(111) at 950 K and Pt clusters on the deposition of Pt vapor onto graphene/Pt(111) at 300 K. The graphene had two predominant domains: one had a small angle of rotation between the graphene and the underlying Pt lattice, structurally commensurate with the Pt(111) lattice (G0°), and the other was rotated about 30° with respect to the Pt lattice (G30°). G0° had a slightly corrugated structure, involving tetrahedral hybridization, and a stronger adsorption on Pt(111); in contrast, G30° was flat and weakly bound to Pt(111) via a van der Waals interaction. The grown Pt clusters were structurally ordered, having a face-centered cubic phase and growing in a (111) orientation, whereas they had correspondingly disparate nucleation modes...

Here we report a new N/S co-doped carbon nanosheets derived from a renewable natural cotton source and its performance as an anode for SIBs. The electrochemical testing shows that the new carbon anode outperforms other major carbon-based anodes in sodiation capacity (482.1 mAh g−1 at 0.1 A g−1), rate performance (375.6, 357.8, 340.5, 324.1 mAh g−1 at 1.0, 2.0, 5.0 and 10.0 A g−1, respectively) and cycling stability (351.1 mAh g−1 at 2.0 A g−1 for 600 cycles). The defects, enlarged d-spacing, reduced Na+ diffusion barrier and increased electronic conductivity of the fabricated N/S co-doped carbon nanosheets are responsible for the excellent Na + storage property, while the pseudocapacitive behavior of Na+ storage contributes to their high rate performance. This work demonstrates a low-cost path forward to fabricate high-performance carbonaceous anode materials for SIBs.

The decomposition of methanol-d4 that was adsorbed on Au–Rh bimetallic nanoclusters grown by the sequential deposition of Au and Rh vapors onto ordered thin-film Al2O3/NiAl(100) at 300 K, occurred by means of dehydrogenation and primarily on the surface Rh. Nevertheless, the surface Rh atoms were not equally reactive; their reactivity altered with both structural and electronic effects arising from the alloying. The Au deposited on Rh clusters decorated the surface and deactivated Rh by not only directly obstructing them but also by neighboring them. As the initially incorporated Au tended to aggregate around reactive low-coordinated Rh atoms, such as corner Rh atoms, the reactivity of the cluster, indicated by the CO and deuterium (D2) produced per surface Rh, decreased markedly. In contrast, the Rh deposited on Au clusters promoted their reactivity. The reactivity was sharply enhanced by a few incorporated Rh atoms, as they preferentially decorated the edge Au atoms, resulting in their lower coordination, more positive charge, higher energetic d-band centers, and high reactivity. On the reactive Rh, the scission of the O–D bond in the initial dehydrogenation of methanol-d4 became more preferential than the competing desorption. The further incorporated Rh failed to promote the reactivity, but the clusters remained more reactive than those formed by Rh clusters incorporating Au as their structuring involved an active atomic segregation that yielded more low-coordinated and reactive surface Rh.

With calculations based on density-functional theory (DFT) we investigated the adsorption of a single Au atom and a dimer on thin θ-Al2O3(001) films supported on NiAl(100). The interaction of the Au adsorbates with the surface was shown to depend on the thickness of the film. The adsorption energy for an Au atom on θ-Al2O3(001)/NiAl(100) of film thickness ≤four atomic layers was significantly enhanced—over three times that on a bulk θ-Al2O3(001) surface, and accompanied with a shortened Au-oxide bond and an uplifted Au-binding Al. The strong Au-surface interaction involved a decreased work function of θ-Al2O3(001)/NiAl(100) and consequently drove charge to transfer from the substrate to the adsorbed Au atom; the charge was transferred from NiAl, through alumina, on monolayer θ-Al2O3(001)/NiAl(100), but directly from alumina on thicker layers. For an Au dimer, both upright (end-on) and flat-lying (side-on) geometries existed. The flat-lying dimer was preferred on mono- and tri-layer alumina films, having a greater adsorption energy but a weakened Au–Au bond, whereas the upright geometry prevailed for films of other thickness, having a weaker adsorption energy and being less charged, similar to that on a bulk θ-Al2O3(001) surface. The results imply an opportunity to control the properties and morphologies of metal clusters supported on an oxide film by tuning its thickness.

The development of Pt-based bimetallic catalysts for ethanol oxidation reaction (EOR) is an important subject to enhance the performance of the promising and clean direct ethanol fuel cells (DEFCs). In this study, we thoroughly investigated EOR activity on Pt and its bimetallic catalysts PtM (M = Au, Ag and Sn) with different degrees of oxophilicity. The computational results found that EOR on Pt-based catalysts prefers the sequence of CH3CH2OH* → CH3CH2O* → CH3CHO* to form the main product of acetaldehyde and rate-determining step is controlled in the initial O H bond cleavage. The foreign elements M can reduce the barrier to some extents. Additionally, their surface oxygen containing species (OCS) can further lower the barrier to better enhance EOR activity. Among those PtM, PtSn has the highest oxophilicity and the most abundant surface OCS, which can most effectively lower the barrier. Thus, the computational study predicted that PtSn shows the best EOR activity through bifunctional mechanism. Experimentally, PtM nanorods with varied surface OCS have been synthesized, characterized and applied for electrochemical tests. The enhanced EOR activity was observed on the PtM with significant amount of surface OCS. The computational and experimental efforts concluded that the oxophilicity plays an important role for the enhanced EOR activity, attributable to the highly active surface OCS.

While T-Nb2O5 has been frequently reported to display an exceptionally fast rate of Li-ion storage (similar to a capacitor), the detailed mechanism of the energy storage process is yet to be unraveled. Here we report our findings in probing the nature of the ultrafast Li-ion storage in T-Nb2O5 using both experimental and computational approaches. Experimentally, we used in operando Raman spectroscopy performed on a well-designed model cell to systematically characterize the dynamic evolution of vibrational band groups of T-Nb2O5 upon insertion and extraction of Li ions during repeated cycling. Theoretically, our model shows that Li ions are located at the loosely packed 4g atomic layers and prefer to form bridging coordination with the oxygens in the densely packed 4h atomic layers. The atomic arrangement of T-Nb2O5 determines the unique Li-ion diffusion path topologies, which allow direct Li-ion transport between bridging sites with very low steric hindrance. The proposed model was validated by computati...

While several proton-conducting anode materials have shown excellent tolerance to sulfur poisoning, the mechanism is still unclear due largely to the inability to probe miniscule amounts of sulfur-containing species using conventional surface characterization techniques. Here we present our findings in unraveling the mechanism of water-mediated sulfur tolerance of a proton conductor under operating conditions empowered by surface-sensitive, operando surface-enhanced Raman spectroscopy (SERS) coupled with impedance spectroscopy. Contrary to the conventional view that surface-adsorbed sulfur is removed mainly by oxygen anions, it is found that -SO4 groups on the surface of the proton conductor are converted to SO2 by a water-mediated process, as confirmed by operando SERS analysis and density functional theory (DFT)-based calculations. The combination of operando SERS performed on a model electrode and theoretical computation offers an effective approach to investigate into complex mechanisms of electrode processes in various electrochemical systems, providing information vital to achieve the rational design of better electrode materials.

We studied the structural and morphological evolution of Rh clusters on an ordered ultrathin alumina film grown on NiAl(100) in annealing processes, under ultrahigh vacuum conditions and with various surface probe techniques. The Rh clusters, prepared on vapor deposition of Rh onto the alumina film at 300 K, had an fcc phase and grew in the (100) orientation, the annealing altered the cluster structure little&mdash, the lattice parameter decreased by a factor &lt, 2%&mdash, but the cluster morphology significantly. With elevated temperature, small clusters (diameter &le, 1.5 nm) decreased little in size, in contrast, large clusters (diameter &ge, 2.0 nm) varied in a complex manner&mdash, their mean diameter decreased to about 1.5 nm on annealing to 450 K, despite their similar height, while it increased to above 2.0 nm at temperature &ge, 570 K. This atypical decrease in size was governed predominantly by energetics. Such a reduced size enhanced the total surface area as well as the reactivity of the clusters toward methanol decomposition, so increased the production of D2 (H2) and CO from decomposed methanol-d4 (or methanol). The result implies a higher temperature tolerance for Rh clusters on the alumina film and a practical approach to prepare small Rh clusters with high reactivity.

SnS nanoparticles (SnS NPs) electrostatically anchored on a 3D N-doped graphene (3DNG) network exhibit the best cycling performance reported so far for SnS-based anodes. The stronger affinity of 3DNG to SnS NPs and to the discharge product compared to pure graphene is the fundamental reason for achieving a stable electrode architecture during cycling.

In this study, the reaction mechanism and electrochemical properties of carbon-supported PtSn nanomaterials including nanoparticles and nanowires (NWs) toward the oxygen reduction reaction (ORR) have been investigated computationally and experimentally. Segregation energy calculations were applied to screen the unique thermodynamic stability of PtSn under ORR operation. Materials chemistry processing was further utilized to tailor the morphologies of PtSn NWs that have shown promoted ORR stability when compared to Pt NWs (24 vs. 83% decay during durability tests of 10 000 cycles). Additionally, these PtSn NWs with a Pt rich inner core and an Sn rich outer shell structure also showed an enhancement in ORR activity from electrochemical tests. The enhanced performance, which has been rationalized by computation and various experimental techniques of high resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, can be attributed to Sn and its oxides inducing change of electronic structures and the morphological effects, which not only reduce oxophilicity and the d-band center of surface Pt but also stabilize the structure during the durability test.

The interaction of CO molecules adsorbed on Au–Rh bimetallic nanoclusters supported on an ordered thin film of Al2O3/NiAl(100) was studied, primarily with infrared reflection absorption spectroscopy and density-functional-theory calculations. The bimetallic clusters, grown by sequential deposition of vapor Au and Rh onto the Al2O3/NiAl(100) surface at 300 K, had diameters of 1.2–3.0 nm and heights of 0.4–1.2 nm; they had a fcc phase and grew in the orientation (100). The infrared absorption line for CO adsorbed on Au sites (COAu) of the bimetallic clusters at 110 K was narrow (centered about 2100 cm−1) and intense, which results largely from the small adsorption energy and large dipole moment of COAu, whereas that on Rh sites (CORh) was broad (1880–2100 cm−1) and weak, which contrasts also with its counterpart on pure Rh clusters. Upon increasing the temperature to remove COAu, the absorption line for CORh narrowed and the intensity increased; at 300 K, the line width decreased by 30–40% and the absorption intensity was enhanced by 40–60%. The former arose, after the desorption of COAu, from a decreased CO–CO interaction and inhomogeneous broadening; the latter corresponded to an enhanced dipole moment of CORh, attributed to a promoted charge transfer from the CORh-binding Rh to the neighboring Au and consequently increased charge donated from CORh to Rh. The varied IR absorption for adsorbed CO can thus serve as an indicator for the charge transfer between the components in bimetallic clusters.

Self-organized alloying of Au with Rh in nanoclusters on an ordered thin film of Al2O3/NiAl(100) was investigated via various surface probe techniques under ultrahigh-vacuum conditions and calculations based on density-functional theory. The bimetallic clusters were formed on the sequential deposition of vapors of Au and Rh onto Al2O3/NiAl(100) at 300 K. The formation was more effective on the oxide seeded with Rh, since all post-deposited Au joined the pregrown Rh clusters; for metal deposition in the reverse order, some separate Rh clusters were formed. The contrasting behavior is rationalized through the easier nucleation of Rh on the oxide surface, due to the stronger Rh-oxide and Rh-Rh bonds. The alloying in the clusters proceeded, regardless of the order of metal deposition, toward a specific structure: an fcc phase, (100) orientation and Rh core-Au shell structure. The orientation, structural ordering and lattice parameters of the Au-Rh bimetallic clusters resembled Rh clusters, rather than Au clusters, on Al2O3/NiAl(100), even with Rh in a minor proportion. The Rh-predominated core-shell structuring corresponds to the binding energies in the order Rh-Rh > Rh-Au > Au-Au. The core-shell segregation, although active, was somewhat kinetically hindered, since elevating the sample temperature induced further encapsulation of Rh. The bimetallic clusters became thermally unstable above 500 K, for which both Rh and Au atoms began to diffuse into the substrate. Moreover, the electronic structures of surface elements on the bimetallic clusters, controlled by both structural and electronic effects, show a promising reactivity.

Sodium ion batteries (SIBs) have been considered a promising alternative to lithium ion batteries for large-scale energy storage. However, their inferior electrochemical performances, especially cyclability, become the major challenge for further development of SIBs. Large volume change and sluggish diffusion kinetics are generally considered to be responsible for the fast capacity degradation. Here we report the strong chemical bonding of nanostructured Sb2S3 on sulfur-doped graphene sheets (Sb2S3/SGS) that enables a stable capacity retention of 83% for 900 cycles with high capacities and excellent rate performances. To the best of our knowledge, the cycling performance of the Sb2S3/SGS composite is superior to those reported for any other Sb-based materials for SIBs. Computational calculations demonstrate that sulfur-doped graphene (SGS) has a stronger affinity for Sb2S3 and the discharge products than pure graphene, resulting in a robust composite architecture for outstanding cycling stability. Our stu...

Manganese oxides of different structures, especially α-MnO2, have been extensively studied as electrodes for pseudocapacitors. However, the poor stability associated with intercalation of proton has been the main obstacle to their commercial applications. To effectively mitigate this problem, it is necessary to fully understand the energy storage mechanism of the MnO2 phases. In this study, δ phase MnO2 has been synthesized through controllable electroplating on architectural Ga-doped ZnO (GZO) bones, demonstrating a high specific capacitance of 1068 F g−1 and high stability (slight performance drop focus on the first 2000 cycles and then remained relatively constant in the subsequent 13,000 cycles). The charge storage mechanism of the δ-MnO2 coated GZO has been carefully investigated under this extreme reaction condition. Results suggest that the amount of charge stored in the electrode material correlates well with the amount of Na+ inserted into the electrode material from the electrolyte. It is also noted that no spectral features corresponding to H+ insertion were detected during cycling when the sample was probed using in operando Raman spectroscopy. Therefore, for layered δ-MnO2, a charge storage mechanism of Na+ intercalation/deintercalation dominated, accompanied by interlayer spacing expansion/contraction, was proposed. Moreover, theoretical calculations also confirmed that the insertion of Na+ is more energetically favorable than H+ at all sites of the interlayer in δ-MnO2, offering a rational explanation of the proposed mechanism and the observed excellent stability.

The surface of Ptshell–Rucore nanocatalysts was modified with an atomic-scaled Au cluster of different sizes by a polyol reduction technique using sequence and composition control. Our results, combining the structure, surface chemical analysis, and density functional theory calculation, elucidate that these clusters reduced the oxidation current of carbon monoxide to a maximum extent of ∼53%; consequently, the anti-CO poisoning factor of the NCs was doubled by increasing the Au/Pt ratios from 0 to 15 at%. Such substantial improvement is caused by steric shielding and the electron localization field that reject the sorption of electronegative ligands/molecules at the NC surface by Au clusters. Most importantly, this work clarifies the mechanistic insights of the charge relocation at core–shell nanoparticles by subnanoscaled cluster intercalation and the impacts of cluster size for the chemical durability of catalysts in fuel cell applications.

Ru–Pd nanoparticles (NPs) with Pt atomic cluster modification were synthesized using polyol reactions with a sequence design. Such modification resulted in the formation of Ru in the inner core and Pd on the outer shell structure (Rucore–Pdshell) via transmetalation between the Pt ion and Pd atom followed by thermal reduction. The Pt modified Rucore–Pdshell NPs improve the on-set potential by 0.041 volt and reduce Pt loading to less than ∼2%, as compared with that of carbon supported Pt NPs. For the optimum case, the MA (current degradation) of Ru–Pd NPs is improved (suppressed) by ∼345% (18.1%) in the accelerated degradation test (ADT) at 0.85 volt (vs. RHE) for 5000 cycles by intercalating Pt clusters (2 to 9 at%) in the NP surface. These improvements are attributed to the electron localization and reinforcement by surface Pt clusters, which facilitated the oxygen reduction activity and chemical durability of NPs.

In this study, we have investigated the oxygen reduction reaction (ORR) activity and durability of Co-based catalysts mechanistically. CoPt/C catalysts with a Pt loading of 7 wt% and Au modification have been prepared and shown excellent ORR performance. The various as-prepared CoPt/C and CoPtAu/C catalysts have about 2.6–9.2 times higher mass activity than commercial Pt/C. The mechanistic insight obtained by density functional theory calculations has shown that the enhanced activity is attributable to the fact that Co-based catalysts can easily dissociate surface O2* without the high-barrier protonation step and efficiently remove the dissociated O*. The improved stability, 1000th decay = 14.6%, corresponds to the fact that the core Au can resist the shrinkage of surface Pt during the accelerated durability test.

We studied the adsorption and lateral interactions of CO molecules on Rh nanoclusters supported on an ordered thin film of Al2O3/NiAl(100) with varied surface probe techniques under ultra-high vacuum conditions and with density-functional-theory (DFT) calculations. The Rh clusters were grown with vapor deposition onto the Al2O3/NiAl(100) surface at 300 K; with increasing deposition, their mean diameter evolved from 1.0 to 3.5 nm and their height from 0.4 to 0.8 nm. The initial adsorption energy (for sparse CO coverage) and the number of adsorbed CO per surface site on the Rh clusters increased with decreasing cluster size. The former effect results from the surface structure and expanded lattice parameter of small Rh clusters, whereas the latter effect involves not only the initial adsorption energy but also altered lateral interactions among CO molecules. In contrast with CO on Rh single crystals, CO on small clusters adsorbed with their axes tilted from the surface normal, weakening the CO–CO repulsive interactions for CO coverage over a wide range. The saturated density of CO on clusters of diameter near 1.0 nm and height near 0.4 nm is 2–3 times that of large clusters (diameter ≥ 3.5 nm) or a Rh(100) surface. The CO–CO repulsive interactions on small clusters became effective at large CO densities, given that the onset of desorption of CO at saturation was 100 K lower than that of large clusters.

Pt and Rh nanoclusters, grown on deposition of Pt and Rh vapors onto graphene/Pt(111), show separate reactivity toward the decomposition of methanol-d4. The Pt (Rh) clusters had a mean diameter 2.0-3.5 nm (2.1-4.0 nm) and height 0.45-0.94 nm (0.41-0.9 nm) evolving with the coverage; they were structurally ordered, having an fcc phase and growing in (111) orientation, and had lattice constants similar to their bulk values. Methanol-d4 on the Pt clusters did not decompose but desorbed mostly, disparate from that on Pt(111) surface; the disparity arose as the adsorption energies of methanol-d4 on most surface sites of the Pt clusters became smaller than their single crystal counterpart. This size effect, nevertheless, did not apply on the Rh clusters, despite their similar atomic stacking; the Rh clusters showed a reactivity similar to that of the Rh(111) surface because the adsorption energies of methanol-d4 on both Rh clusters and Rh(111) are comparable. The distinct size dependence was rationalized through their electronic structures and charge distribution of Fukui function mapping. Our results suggest that reactive transition metals do not necessarily become more reactive while they are scaled down to nanoscale; their reactivity evolves with their size in a manner largely dependent on their electronic nature.

The surface structures and compositions of Au-Rh bimetallic nanoclusters on an ordered thin film of Al2O3/NiAl(100) were investigated, primarily with infrared reflection absorption spectra and temperature-programmed desorption of CO as a probe molecule under ultrahigh-vacuum conditions and calculations based on density-functional theory. The bimetallic clusters were formed by sequential deposition of vapors of Au and Rh onto Al2O3/NiAl(100) at 300 K. Alloying in the clusters was active and proceeded toward a specific structure-a fcc phase, (100) orientation, and Rh core-Au shell structure, regardless of the order of metal deposition. For Au clusters incorporating deposited Rh, the Au atoms remained at the cluster surface through position exchange and became less coordinated; for deposition in reverse order, deposited Au simply decorated the surfaces of Rh clusters. Both adsorption energy and infrared absorption intensity were enhanced for CO on Au sites of the bimetallic clusters; both of them are associated with the bonding to Rh and also a decreased coordination number of CO-binding Au. These enhancements can thus serve as a fingerprint for alloying and atomic inter-diffusion in similar bimetallic systems.

Organometal-trihalide-perovskite-based solar cells have exhibited high efficiencies when incorporated into mesoscopic NiO (NiOnc) hole-transport layers. The integration of a NiOnc-perovskite heterojunction provides an inorganic alternative as a p-type contact material with efficient hole extraction for perovskite-based solar cells. Herein the origin of such highly efficient carrier transport is studied in terms of electronic, chemical and transport properties of a NiOnc-perovskite heterojunction with X-ray photoelectron spectra, ultraviolet photoelectron spectra, near-edge X-ray absorption fine structure spectra, a scanning transmission X-ray microscope, and calculations of electronic structure. A pronounced chemical redox reaction is found at an NiOnc-perovskite heterojunction such that PbI2 is oxidized to PbO with subsequent formation of hole-dopant CH3NH3PbI3–2δOδ at the heterojunction. The generation of hole-doping CH3NH3PbI3–2δOδ induced by the redox reaction at the NiOnc/perovskite heterojunction plays a significant role to facilitate the carrier transport, and thus enhances the photovoltaic efficiencies.