Intermediate Energy Barrier Research Articles

Atomically dispersed NiOx cluster on high-index Pt facets boost ethanol electrooxidation through long-range synergistic sites

Constructing the desired long-range dual sites to enhance the C–C bond-cleavage and CO-tolerate ability during ethanol oxidation reaction is of importance for further applications. Herein, the concept of holding atomically dispersed NiOx cluster supported on Pt-based high-index facets (NiOx/Pt) is proposed to build O-bridged Pt–Ni dual sites. Strikingly, the obtained NiOx/Pt dual sites show 4.97 times specific activity higher than that of commercial Pt/C (0.35 ​mA ​cm−2), as well as outstanding CO-tolerance and durability. The advanced electrochemical in-situ characterizations reveal that the NiOx/Pt can accelerate rapid dehydroxylation and C–C bond-cleavage over the Pt–Ni dual sites. Theoretical calculations disclose that the atomically dispersed NiOx species can lower the adsorption/reaction energy barriers of intermediates. This tactic provides a promising methodology on regulating the surface synergistic sites via engineering atomically dispersed oxide site.

Incorporation of Ag in Co9S8-Ni3S2 for Predominantly Enhanced Electrocatalytic Activities for Oxygen Evolution Reaction: A Combined Experimental and DFT Study.

Electrodeposition of abundant metals to fabricate efficient and durable electrodes indicate a viable role in advancing renewable electrochemical energy tools. Herein, we deposit Co9S8-Ag-Ni3S2@NF on nickel foam (NF) to produce Co9S8-Ag-Ni3S2@NF as a exceedingly proficient electrode for oxygen evolution reaction (OER). The electrochemical investigation verifies that the Co9S8-Ag-Ni3S2@NF electrode reveals better electrocatalytic activity to OER because of its nanoflowers' open-pore morphology, reduced overpotential (η10=125 mV), smaller charge transfer resistance, long-term stability, and a synergistic effect between various components, which allows the reactants to be more easily absorbed and subsequently converted into gaseous products during the water electrolysis route. Density functional theory (DFT) calculation as well reveals the introduction of Ag (222) surface into the Co9S8 (440)-Ni3S2 (120) structure increases the electronic density of states (DOS) per unit cell of a system and increases the electrocatalytic activity of OER by considerably lowering the energy barriers of its intermediates. This study provides the innovation of employing trimetallic nanomaterials immobilized on a conductive, continuous porous three-dimensional network formed on a nickel foam (NF) substrate as a highly proficient catalyst for OER.

Multiscale understand the tuning photocatalytic hydrogen evolution performances of BiOCl stemmed from engineered crystal facet

BiOCl photocatalyst has been extensively investigated due to unique internal electric field. However, the limited photocatalytic efficiency seriously blocks the further development of this photocatalyst. Here, using one-step hydrothermal process, we prepared the octagonal plate BiOCl, which is characterized with (110) facets. Contrasted with the ordinary BiOCl with (010) and (001) facets, the designed BiOCl-110 exbibits approximately 1.70 times and 3.15 times enhancement in photocatalytic H2 evolution, along with qualified reusability. The experimental findings collectively uncover the origin of high hydrogen production, which (110) facet greatly prolongs the lifetime of carriers, sharply increases the surface photovoltage and reasonably optimizes the carrier transport. Particularly, density functional theory simulations unveil a remarkably reduced transition between valence band maximum and conduction band minimum within BiOCl-110, resulting in a largely increased carrier extraction. Besides, the optimized free energy barriers of intermediates yield proper adsorption and desorption process in overall H2O splitting. Further ab initio molecular dynamics calculations unlock that the distinctive atomic structure on surface of the octagonal plate BiOCl serves as the inherent factor in regulating the element distribution of H2O layer on photocatalyst surface. The facet-dependent electronic structure and facet/H2O interface effects offer crucial understanding for BiOCl in highly effective hydrogen evolution.

Heterogeneous ultra-thin FeCo-LDH@Co(OH)2 nanosheets facilitated electrons transfer for oxygen evolution reaction

Developing cost efficient, robust, non-precious metal electrocatalysts for oxygen evolution reaction (OER) is a significant challenge in water splitting for renewable energy conversion. A novel electrocatalyst of heterogeneous ultra-thin FeCo-LDH@Co(OH)2 nanosheets derived from 2D Zeolitic imidazolate framework facilitated electrons transfer for OER. DFT calculation revealed that heterogeneous interfaces reduced adsorption energy barriers of intermediates in rate-determining step of OER. The CoOOH with higher CoIII valence state derived from surface reconstruction, which was detected via in-situ Raman spectroscopy, activated O ions to provide higher intrinsic activity. XPS results confirmed that electrons transfer from Co(OH)2 to FeCo-LDH accelerated alkaline OER kinetics. The FeCo-LDH@Co(OH)2–0.5 exhibited low overpotentials of 230 mV at 10 mA cm−2 and maintained long durability for 300 h. This study opened up a new method for design and synthesis of ultrathin LDHs electrocatalysts.

A pH-universal ORR catalyst with S heteroatom doping single-atom iron sites derived from a 2D flake-like MOF for superior flexible quasi-solid-state rechargeable Zn-air battery

Regulating the atomic coordination ambiance of uniformly distributed single atoms (SAs) via heteroatom doping is an up-and-coming method to facilitate the catalytic activity for oxygen reduction reactions (ORR). With the cooperative interaction of dual heteroatom doping supplied extra degrees of freedom, a greater efficiency of ORR can be realized via a reduction in intermediate energy barrier during catalytic reactions. Here, we explore a fresh approach to generate N, S co-doped Fe-SA in embedded porous carbon nanosheets/carbon nanotubes (Fe-NX@NSCST-ZL) utilizing a 2D leaf-shaped MOF as a template in this work. Taking advantage of the combined effect of carbon matrix and nanotubes as well as the abundance of Fe-NX active sites and thiophene-S, the Fe-NX@NSCST-ZL provides exceptional performance for ORRs with a half-wave potential of 0.94 V at alkaline conditions, 0.77 V at acidic conditions, and 0.74 V at neutral conditions (V vs. RHE). Furthermore, Fe-NX@NSCST-ZL-based Zn-air battery, as well as quasi solid-state flexible battery, maintain steady operation for 765 h and 30 h with a small discharge/charge interval, respectively. This work contributes perspectives on the reasonable design of economical single-atom catalysts (SACs) for applications in energy conversion that have outstanding electrocatalytic potential.

Fe and Mo dual-site single-atom catalysts for high-efficiency wide-pH hydrogen evolution and alkaline overall water splitting

The limitations of single-atom catalysts (SACs) hinder their application in wide-pH range of hydrogen evolution reaction (HER) and overall water-splitting in alkaline solution. Herein, we fabricate a rod-like Ni3S2 material wrapped by single-atom Fe-Mo co-modified CoNi-based nanosheets (FeMo@CoNi-OH/Ni3S2). The introduction of Fe-SAs and Mo-SAs into CoNi-hydroxyl compounds effectively changes their electronic structure and enhances their conductivity, thereby improving HER and OER performance. FeMo@CoNi-OH/Ni3S2 catalyst endows HER with overpotentials of 89, 176 and 177 mV in alkaline, acidic and neutral solutions, respectively, as well as good oxygen evolution reaction (OER) performance with 160 mV in alkaline to achieve 10 mA cm−2. The combination of the experiments and theoretical calculations reveals that the synergistic effect of Mo-SAs with Fe-SAs effectively reduces the intermediate energy barrier of the water dissociation step. This work contributes to the understanding of the catalytic mechanisms of dual single-atomic active sites in HER and OER processes.

Simultaneously promoting charge and mass transports in carved particle-in-box nanoreactor for rechargeable Zn-air battery

Fundamental understanding of fabricating promoted bi-functional electrocatalyst to achieve fast charge-transfer and smooth mass-transport in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through the rational management of catalyst composition and ingenious design of nanostructure is highly desired but still a formidable challenge. Herein, an advanced carved particle-in-box nanoreactor, composed of small Fe-Co-Ni tri-metallic alloy nanoparticles confined in porous nitrogen-doped carbon nanocage, was developed through a spatially-confined pyrolysis strategy. Tri-metal alloy could optimize the electronic structure of the catalyst, thus inducing the charge redistribution, and then regulating the adsorption and desorption energy barriers of intermediates in electrochemical reactions. Unique nano-hole design provided convenient and efficient channels for mass transfer during ORR and OER processes. Thanks to these attributes, the hybrid electrocatalyst delivered decent reversible oxygen catalytic activities, evidenced by a high half-wave potential of 0.850 V towards ORR and a low overpotential of 355 mV at 10 mA/cm2 for OER both in alkaline electrolyte. As a proof-of-concept, this as-developed carved particle-in-box nanoreactor enabled the assembled Zn-air battery to deliver a narrow potential gap of 0.735 V, a decent power density of 315 mW/cm2, a notable specific capacity of 754 mAh/gZn and excellent durability up to 165 h of continuous charge and discharge operations, thus implying the potential applications of this sophisticated catalyst model for promising energy conversion.

Strong Electron Coupling of Ru and Vacancy-Rich Carbon Dots for Synergistically Enhanced Hydrogen Evolution Reaction.

The exploitation of ingenious strategies to improve the activity and stability of ruthenium (Ru) is crucial for the advancement of Ru-based electrocatalysts. Vacancy engineering is a typical strategy for modulating the catalytic activity of electrocatalysts. However, creating vacancies directly into pure metallic Ru is difficult because of the extremely stringent conditions required and will result in instability because the integrity of the crystal structure is destroyed. In response, a compromise tactic by introducing vacancies in a Ru composite structure is proposed, and vacancy-rich carbon dots coupled with Ru (Ru@CDs) are elaborately constructed. Specifically, the vacancy-rich carbon dots (CDs) serve as an excellent platform for anchoring and trapping Ru nanoparticles, thus restraining their agglomeration and growth. As expected, Ru@CDs exhibited excellent catalytic performance with a low overpotential of 30 mV at 10 mA cm-2 in 1 m KOH, a small Tafel slope of 22 mV decade-1 , and robust stability even after 10000 cycles. The low overpotential is comparable to those of most previously reported Ru-based electrocatalysts. Additionally, spectroscopic characterizations and theoretical calculations demonstrate that the rich vacancies and the electron interactions between Ru and CDs synergistically lower the intermediate energy barrier and thereby maximize the activity of the Ru@CDs electrocatalyst.

Dual-metallic single Ru and Ni atoms decoration of MoS2 for high-efficiency hydrogen production

The limitation of single-atom catalysts hinders its promotion and application in the HER field. Herein, we fabricated a dimetallic single-atom catalyst where monoatomic Ru and Ni co-modify MoS2 using a mild method (Ru/Ni-MoS2). Experiments combined with theoretical calculations indicated that the single Ru atoms were anchored through single Ni atoms with strong electronegativity, and most of the Ru atoms coordinated with the S were distributed on the Ni atop sites. And the synergistic effect of the Ru/Ni-MoS2 with S atoms bonded with Ni as hydrogen acceptor and single-atoms Ru as hydroxyl acceptor, effectively reduced the intermediate energy barrier of the water dissociation step. The as-fabricated Ru/Ni-MoS2 exhibited a super-low overpotential of 32 mV at 10 mA cm−2 with the corresponding Tafel slope of 41 mV·dec-1 as well as negligible current attenuation over 20 h, far surpassing that of Ru-MoS2 and Ni-MoS2. This work not only provides a high-efficiency HER catalysts, but also a new idea based on electronegativity difference and bimetallic single-atom regulation to design catalyst.

Studies on chemoselective synthesis of 1,4- and 1,2-dihydropyridine derivatives by a Hantzsch-like reaction: a combined experimental and DFT study.

In the experimental process of preparing diethyl 3,5-dicarboxylate-1,4-dihydropyridine (1,4-DHP) by a Hantzsch-like reaction, it was found that a by-product named diethyl 3,5-dicarboxylate-1,2-dihydropyridine (1,2-DHP) was produced in the reaction. To discuss this phenomenon, the effects of the reaction conditions on the yield ratio of 1,4-DHP and 1,2-DHP were studied by using aromatic amines, aromatic aldehydes and ethyl propiolate as raw materials. The mechanisms for the formation of 1,4-DHP and 1,2-DHP were proposed based on the isolated intermediate named diethyl 4-((phenylamino)methylene)pent-2-enedioate generated by the Michael addition of aniline and ethyl propiolate. The transition state structures were optimized and the reaction energy barriers of intermediates in the speculated mechanisms were calculated by DFT calculations at the M062X/def2TZVP//B3LYP-D3/def-SVP level. It was found that the reaction energy barriers and dominant configurations of intermediates IM2 and IM3' are the determinants for the chemoselectivity. Together, these results demonstrate a high chemoselectivity in the synthesis of 1,4-DHPs and 1,2-DHPs by a Hantzsch-like reaction and that 1,4-DHPs and 1,2-DHPs can be easily obtained under different conditions.

Heterostructures Composed of N‐Doped Carbon Nanotubes Encapsulating Cobalt and β‐Mo2C Nanoparticles as Bifunctional Electrodes for Water Splitting

AbstractHerein, we demonstrate the use of heterostructures comprised of Co/β‐Mo2C@N‐CNT hybrids for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline electrolyte. The Co can not only create a well‐defined heterointerface with β‐Mo2C but also overcomes the poor OER activity of β‐Mo2C, thus leading to enhanced electrocatalytic activity for HER and OER. DFT calculations further proved that cooperation between the N‐CNTs, Co, and β‐Mo2C results in lower energy barriers of intermediates and thus greatly enhances the HER and OER performance. This study not only provides a simple strategy for the construction of heterostructures with nonprecious metals, but also provides in‐depth insight into the HER and OER mechanism in alkaline solution.

Heterostructures Composed of N-Doped Carbon Nanotubes Encapsulating Cobalt and β-Mo2 C Nanoparticles as Bifunctional Electrodes for Water Splitting.

Herein, we demonstrate the use of heterostructures comprised of Co/β-Mo2 C@N-CNT hybrids for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline electrolyte. The Co can not only create a well-defined heterointerface with β-Mo2 C but also overcomes the poor OER activity of β-Mo2 C, thus leading to enhanced electrocatalytic activity for HER and OER. DFT calculations further proved that cooperation between the N-CNTs, Co, and β-Mo2 C results in lower energy barriers of intermediates and thus greatly enhances the HER and OER performance. This study not only provides a simple strategy for the construction of heterostructures with nonprecious metals, but also provides in-depth insight into the HER and OER mechanism in alkaline solution.

Polyoxometalate/Lead Composite Anode for Efficient Oxygen Evolution in Zinc Electrowinning

Oxygen evolution in harsh high-acidic conditions has always been a challenge for both zinc electrowinning and hydrogen production. Lead and its alloys have met the requirements of zinc electrowinning up to now. This is the first time that a polyoxometalate/lead composite as an earth-abundant material has been investigated for use as anode in zinc electrowinning. A polyoxometalate/lead composite showed a high electrocatalytic activity and a long-term durability during an oxygen generation reaction in harsh high-acidic conditions of electrochemical accelerated corrosion tests. It could boost oxygen evolution by decreasing the Gibbs energy barriers of intermediates and showed a 10-fold higher electrochemically active surface area and one fifth of the polarization resistance compared to pure Pb. The overpotential of a Pb anode containing 1 wt % polyoxometalate was similar to that of a commercial Pb/0.75 wt % Ag anode, which implies the potential application of polyoxometalate/lead composite anodes in the hydrometallurgical industry.

A Facile Strategy to Construct Amorphous Spinel‐Based Electrocatalysts with Massive Oxygen Vacancies Using Ionic Liquid Dopant

AbstractOxygen vacancies are demonstrated to be beneficial to various electrocatalytic reactions. However, integrating oxygen vacancies into an amorphous catalyst with a large specific surface area, and investigating its effect on the oxygen evolution reaction remains a great challenge. Herein, oxygen vacancies are introduced into an amorphous N, P, and F tri‐doped CoFe2O4 using ionic liquid as a dopant. Simultaneously, ultrafine MoS2 nanoclusters are anchored onto its surface to increase the specific surface area. The vacancy‐rich MoS2/NPF‐CoFe2O4 exhibits an overpotential of 250 mV and a small Tafel slope of 41 mV dec−1, which is the best spinel‐based oxygen evolution reaction (OER) electrocatalysts so far. The excellent performance is attributed to massive oxygen vacancies, amorphous structure, large surface area, and synergistic coupling effects among active species. Density‐functional theory calculations reveal that the electronic structure of the catalyst can be modulated in the presence of heteroatoms and MoS2 nanoclusters, and then the energy barriers of intermediates are decreased as well, which enhances the OER performance. This design not only provides a simple strategy to construct amorphous structures with abundant oxygen vacancies using ionic liquid‐dopants, but also presents an in‐depth insight into the OER mechanism in alkaline solution.

Electronic Modulation of Electrocatalytically Active Center of Cu7S4 Nanodisks by Cobalt-Doping for Highly Efficient Oxygen Evolution Reaction.

Cu-based electrocatalysts have seldom been studied for water oxidation because of their inferior activity and poor stability regardless of their low cost and environmentally benign nature. Therefore, exploring an efficient way to improve the activity of Cu-based electrocatalysts is very important for their practical application. Modifying electronic structure of the electrocatalytically active center of electrocatalysts by metal doping to favor the electron transfer between catalyst active sites and electrode is an important approach to optimize hydrogen and oxygen species adsorption energy, thus leading to the enhanced intrinsic electrocatalytic activity. Herein, Co-doped Cu7S4 nanodisks were synthesized and investigated as highly efficient electrocatalyst for oxygen evolution reaction (OER) due to the optimized electronic structure of the active center. Density-functional theory (DFT) calculations reveal that Co-engineered Cu7S4 could accelerate electron transfer between Co and Cu sites, thus decrease the energy barriers of intermediates and products during OER, which are crucial for enhanced catalytic properties. As expected, Co-engineered Cu7S4 nanodisks exhibit a low overpotential of 270 mV to achieve current density of 10 mA cm-2 as well as decreased Tafel slope and enhanced turnover frequencies as compared to bare Cu7S4. This discovery not only provides low-cost and efficient Cu-based electrocatalyst by Co doping, but also exhibits an in-depth insight into the mechanism of the enhanced OER properties.

Transition Metal Ion‐Induced High Electrocatalytic Performance of Conducting Polymer for Oxygen and Hydrogen Evolution Reactions

AbstractHere, it is discovered that the conductive polymers with heteroatoms, such as polypyrrole (PPy) and polyaniline (PANI), are electroactive for hydrogen evolution reaction (HER) or oxygen evolution reaction (OER) in alkaline media. Density functional theory calculations demonstrate that the heteroatoms in the conducting polymers, such as N, can induce the formation of the electrocatalytic active centers (EACs). For further enhancement of performance, the transition metal ion (TMI)‐doped conductive polymers (such as Co(II)‐doped PPy and Fe(III)‐doped PANI) supported on nickel foam are developed as low‐cost and high‐performance electrocatalysts for HER or OER. Here, it is demonstrated that the TMN bonds in TMI‐doped conductive polymer can efficiently create high EACs and obviously lower energy barriers of intermediates and products of HER or OER. The experimental results show that the TMI‐doped conductive polymer exhibits significantly improved electrocatalytic performance, such as low onset potential, high electrocatalytic activity, and excellent long‐term durability. The results suggest the great promise of developing a new family of TMI‐doped conducting polymers as low‐cost and high‐performance electrocatalysts for HER and OER in alkaline media.

Selective arc-discharge synthesis of Dy2S-clusterfullerenes and their isomer-dependent single molecule magnetism.

A method for the selective synthesis of sulfide clusterfullerenes Dy2S@C2n is developed. Addition of methane to the reactive atmosphere reduces the formation of empty fullerenes in the arc-discharge synthesis, whereas the use of Dy2S3 as a source of metal and sulfur affords sulfide clusterfullerenes as the main fullerene products along with smaller amounts of carbide clusterfullerenes. Two isomers of Dy2S@C82 with Cs(6) and C3v(8) cage symmetry, Dy2S@C72-Cs(10528), and a carbide clusterfullerene Dy2C2@C82-Cs(6) were isolated. The molecular structure of both Dy2S@C82 isomers was elucidated by single-crystal X-ray diffraction. SQUID magnetometry demonstrates that all of these clusterfullerenes exhibit hysteresis of magnetization, with Dy2S@C82-C3v(8) being the strongest single molecule magnet in the series. DC- and AC-susceptibility measurements were used to determine magnetization relaxation times in the temperature range from 1.6 K to 70 K. Unprecedented magnetization relaxation dynamics with three consequent Orbach processes and energy barriers of 10.5, 48, and 1232 K are determined for Dy2S@C82-C3v(8). Dy2S@C82-Cs(6) exhibits faster relaxation of magnetization with two barriers of 15.2 and 523 K. Ab initio calculations were used to interpret experimental data and compare the Dy-sulfide clusterfullerenes to other Dy-clusterfullerenes. The smallest and largest barriers are ascribed to the exchange/dipolar barrier and relaxation via crystal-field states, respectively, whereas an intermediate energy barrier of 48 K in Dy2S@C82-C3v(8) is assigned to the local phonon mode, corresponding to the librational motion of the Dy2S cluster inside the carbon cage.

Effective dissipation: Breaking time-reversal symmetry in driven microscopic energy transmission.

At molecular scales, fluctuations play a significant role and prevent biomolecular processes from always proceeding in a preferred direction, raising the question of how limited amounts of free energy can be dissipated to obtain directed progress. We examine the system and process characteristics that efficiently break time-reversal symmetry at fixed energy loss; in particular for a simple model of a molecular machine, an intermediate energy barrier produces unusually high asymmetry for a given dissipation. We relate the symmetry-breaking factors found in this model to recent observations of biomolecular machines.

FeOOH/Co/FeOOH Hybrid Nanotube Arrays as High-Performance Electrocatalysts for the Oxygen Evolution Reaction.

Herein, we developed FeOOH/Co/FeOOH hybrid nanotube arrays (HNTAs) supported on Ni foams for oxygen evolution reaction (OER). The inner Co metal cores serve as highly conductive layers to provide reliable electronic transmission, and can overcome the poor electrical conductivity of FeOOH efficiently. DFT calculations demonstrate the strong electronic interactions between Co and FeOOH in the FeOOH/Co/FeOOH HNTAs, and the hybrid structure can lower the energy barriers of intermediates and thus promote the catalytic reactions. The FeOOH/Co/FeOOH HNTAs exhibit high electrocatalytic performance for OER, such as low onset potential, small Tafel slope, and excellent long-term durability, and they are promising electrocatalysts for OER in alkaline solution.

FeOOH/Co/FeOOH Hybrid Nanotube Arrays as High‐Performance Electrocatalysts for the Oxygen Evolution Reaction

AbstractHerein, we developed FeOOH/Co/FeOOH hybrid nanotube arrays (HNTAs) supported on Ni foams for oxygen evolution reaction (OER). The inner Co metal cores serve as highly conductive layers to provide reliable electronic transmission, and can overcome the poor electrical conductivity of FeOOH efficiently. DFT calculations demonstrate the strong electronic interactions between Co and FeOOH in the FeOOH/Co/FeOOH HNTAs, and the hybrid structure can lower the energy barriers of intermediates and thus promote the catalytic reactions. The FeOOH/Co/FeOOH HNTAs exhibit high electrocatalytic performance for OER, such as low onset potential, small Tafel slope, and excellent long‐term durability, and they are promising electrocatalysts for OER in alkaline solution.