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Electrochemical nitrogen reduction reaction (eNRR) offers a sustainable route for ammonia synthesis; however, current electrocatalysts are limited in achieving optimal performance within narrow potential windows. Herein, inspired by the heliotropism of sunflowers, we present a biomimetic design of Ru-VOH electrocatalyst, featuring a dynamic Ru-O-V pyramid electron bridge for eNRR within a wide potential range. In situ spectroscopy and theoretical investigations unravel the fact that the electrons are donated from Ru to V at lower overpotentials and retrieved at higher overpotentials, maintaining a delicate balance between N2 activation and proton hydrogenation. Moreover, N2 adsorption and activation were found to be enhanced by the Ru-O-V moiety. The catalyst showcases an outstanding Faradaic efficiency of 51.48% at -0.2 V (vs RHE) with an NH3 yield rate exceeding 115 µg h-1 mg-1 across the range of -0.2 to -0.4 V (vs RHE), along with impressive durability of over 100 cycles. This dynamic M-O-V pyramid electron bridge is also applicable to other metals (M = Pt, Rh, and Pd).
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Iron-nitrogen-carbon (Fe-N-C) catalysts, although the most active platinum-free option for the cathodic oxygen reduction reaction (ORR), suffer from poor durability due to the Fe leaching and consequent Fenton effect, limiting their practical application in low-temperature fuel cells. This work demonstrates an integrated catalyst of a platinum-iron (PtFe) alloy planted in an Fe-N-C matrix (PtFe/Fe-N-C) to address this challenge. This novel catalyst exhibits both high-efficiency activity and stability, as evidenced by its impressive half-wave potential (E1/2) of 0.93 V versus reversible hydrogen electrode (vs RHE) and minimal 7 mV decay even after 50,000 potential cycles. Remarkably, it exhibits a very low hydrogen peroxide (H2O2) yield (0.07%) at 0.6 V and maintains this performance with negligible change after 10,000 potential cycles. Fuel cells assembled with this cathode PtFe/Fe-N-C catalyst show exceptional durability, with only 8 mV voltage loss at 0.8 A cm-2 after 30,000 cycles and ignorable current degradation at a voltage of 0.6 V over 85 h. Comprehensive in situ experiments and theoretical calculations reveal that oxygen species spillover from Fe-N-C to PtFe alloy not only inhibits H2O2 production but also eliminates harmful oxygenated radicals. This work paves the way for the design of highly efficient and stable ORR catalysts and has significant implications for the development of next-generation fuel cells.
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The present study proposes a novel engineering concept for the customization of functionality and construction of superstructure to fabricate 2D monolayered N-doped carbon superstructure electrocatalysts decorated with Co single atoms or Co2P nanoparticles derived from 2D bimetallic ZnCo-ZIF superstructure precursors. The hierarchically porous carbon superstructure maximizes the exposure of accessible active sites, enhances electron/mass transport efficiency, and accelerates reaction kinetics simultaneously. Consequently, the Co single atoms embedded N-doped carbon superstructure (Co-NCS) exhibits remarkable catalytic activity toward oxygen reduction reaction, achieving a half-wave potential of 0.886 V versus RHE. Additionally, the Co2P nanoparticles embedded N-doped carbon superstructure (Co2P-NCS) demonstrates high activity for both oxygen evolution reaction and hydrogen evolution reaction, delivering low overpotentials of 292 mV at 10 mA cm-2 and 193 mV at 10 mA cm-2 respectively. Impressively, when employed in an assembled rechargeable Zn-air battery, the as-prepared 2D carbon superstructure electrocatalysts exhibit exceptional performance with a peak power density of 219 mW cm-2 and a minimal charge/discharge voltage gap of only 1.16 V at 100 mA cm-2. Moreover, the cell voltage required to drive an overall water-splitting electrolyzer at a current density of 10 mA cm-2 is merely 1.69 V using these catalysts as electrodes.
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The high-current-density Zn-air battery shows big prospects in next-generation energy technologies, while sluggish O2 reaction and diffusion kinetics barricade the applications. Herein, the sequential assembly is innovatively demonstrated for hierarchically mesoporous molybdenum carbides/carbon microspheres with a tunable thickness of mesoporous carbon layers (Meso-Mo2C/C-x, where x represents the thickness). The optimum Meso-Mo2C/C-14 composites (≈2 µm in diameter) are composed of mesoporous nanosheets (≈38 nm in thickness), which possess bilateral mesoporous carbon layers (≈14 nm in thickness), inner Mo2C/C layers (≈8 nm in thickness) with orthorhombic Mo2C nanoparticles (≈2 nm in diameter), a high surface area of ≈426 m2 g-1, and open mesopores (≈6.9 nm in size). Experiments and calculations corroborate the hierarchically mesoporous Mo2C/C can enhance hydrophilicity for supplying sufficient O2, accelerate oxygen reduction kinetics by highly-active Mo2C and N-doped carbon sites, and facilitate O2 diffusion kinetics over hierarchically mesopores. Therefore, Meso-Mo2C/C-14 outputs a high half-wave potential (0.88 V vs RHE) with a low Tafel slope (51 mV dec-1) for oxygen reduction. More significantly, the Zn-air battery delivers an ultrahigh power density (272 mW cm-2), and an unprecedented 100 h stability at a high-current-density condition (100 mA cm-2), which is one of the best performances.
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Electrocatalytic carbon dioxide/carbon monoxide reduction reaction (CO(2)RR) has emerged as a prospective and appealing strategy to realize carbon neutrality for manufacturing sustainable chemical products. Developing highly active electrocatalysts and stable devices has been demonstrated as effective approach to enhance the conversion efficiency of CO(2)RR. In order to rationally design electrocatalysts and devices, a comprehensive understanding of the intrinsic structure evolution within catalysts and micro-environment change around electrode interface, particularly under operation conditions, is indispensable. Synchrotron radiation has been recognized as a versatile characterization platform, garnering widespread attention owing to its high brightness, elevated flux, excellent directivity, strong polarization and exceptional stability. This review systematically introduces the applications of synchrotron radiation technologies classified by radiation sources with varying wavelengths in CO(2)RR. By virtue of in situ/operando synchrotron radiationanalytical techniques, we also summarize relevant dynamic evolution processes from electronic structure, atomic configuration, molecular adsorption, crystal lattice and devices, spanning scales from the angstrom to the micrometer. The merits and limitations of diverse synchrotron characterization techniques are summarized, and their applicable scenarios in CO(2)RR are further presented. On the basis of the state-of-the-art fourth-generation synchrotron facilities, a perspective for further deeper understanding of the CO(2)RR process using synchrotron radiation analytical techniques is proposed.
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The development of biomimetic catalytic systems that can imitate or even surpass natural enzymes remains an ongoing challenge, especially for bioinspired syntheses that can access non-natural reactions. Here, we show how an all-inorganic biomimetic system bearing robust nitrogen-neighbored single-cobalt site/pyridinic-N site (Co-N4/Py-N) pairs can act cooperatively as an oxidase mimic, which renders an engaged coupling of oxygen (O2) reduction with synthetically beneficial chemical transformations. By developing this broadly applicable platform, the scalable synthesis of greater than 100 industrially and pharmaceutically appealing O-silylated compounds including silanols, borasiloxanes, and silyl ethers via the unprecedented aerobic oxidation of hydrosilane under ambient conditions is demonstrated. Moreover, this heterogeneous oxidase mimic also offers the potential for expanding the catalytic scope of enzymatic synthesis. We anticipate that the strategy demonstrated here will pave a new avenue for understanding the underlying nature of redox enzymes and open up a new class of material systems for artificial biomimetics.
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The local coordination environment of catalytical moieties directly determines the performance of electrochemical energy storage and conversion devices, such as Li-O2 batteries (LOBs) cathode. However, understanding how the coordinative structure affects the performance, especially for non-metal system, is still insufficient. Herein, a strategy that introduces S-anion to tailor the electronic structure of nitrogen-carbon catalyst (SNC) is proposed to improve the LOBs performance. This study unveils that the introduced S-anion effectively manipulates the p-band center of pyridinic-N moiety, substantially reducing the battery overpotential by accelerating the generation and decomposition of intermediate products Li1-3 O4 . The lower adsorption energy of discharging product Li2 O2 on NS pair accounts for the long-term cyclic stability by exposing the high active area under operation condition. This work demonstrates an encouraging strategy to enhance LOBs performance by modulating the p-band center on non-metal active sites.
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The application of electrochemical hydrodechlorination has been impeded due to the low utilization and activity of Pd catalyst. Herein, a series of Pd catalysts were prepared via the controllable evolution of Zn state during the pyrolysis of ZIF-8 nanosheet. Various forms of Pd with different chemical surroundings were generated upon the combined use of galvanic displacement and ion exchange process. Electrocatalytic hydrodechlorination of 4-chlorophenol was performed and the electrocatalytic hydrodechlorination efficiency of Pd/CN reaches 100% within 3 h at extra low Pd concentration. The coexistence of zero-valent Pd (Pd0) and nitrogen coordinated Pd (Pd-N) was verified by XAFS which provide multiple active sites for focusing on adsorbing H* and cracking C-Cl respectively. The synergetic effect between different chemical state of Pd for efficient hydrodechlorination of chloroaromatics and scheme for dexterous preparation of Pd based electrocatalyst are proposed and discussed.
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Low-nuclear site catalysts with dual atoms have the potential for applications in energy and catalysis chemistry. Understanding the formation mechanism of dual metal sites is crucial for optimizing local structures and designing desired binuclear sites catalysts. In this study, we demonstrate for the first time the formation process of dual atoms through the pyrolysis of the interface of a double framework using Zn atoms in metal-organic frameworks and Co atoms in covalent organic frameworks. We unambiguously revealed that the cooling stage is the key point to form the binuclear sites by employing the in situ synchrotron radiation X-ray absorption spectrum technique. The binuclear site catalysts show higher activity and selectivity than single dispersed atom catalysts for electrocatalytic oxygen reduction. This work guides us to synthesize and optimize the various binuclear sites for extensive catalytic applications.
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Full understanding to the origin of the catalytic performance of a supported nanocatalyst from the points of view of both the active component and support is significant for the achievement of high performance. Herein, based on a model electrocatalyst of single-iridium-atom-doped iron (Fe)-based layered double hydroxides (LDH) for oxygen evolution reaction (OER), we reveal the first completed origin of the catalytic performance of such supported nanocatalysts. Specially, besides the activity enhancement of Ir sites by LDH support, the stability of surface Fe sites is enhanced by doped Ir sites: DFT calculation shows that the Ir sites can reduce the activity and enhance the stability of the nearby Fe sites; while further finite element simulations indicate, the stability enhancement of distant Fe sites could be attributed to the much low concentration of OER reactant (hydroxyl ions, OH- ) around them induced by the much fast consumption of OH- on highly active Ir sites. These new findings about the interaction between the main active components and supports are applicable in principle to other heterogeneous nanocatalysts and provide a completed understanding to the catalytic performance of heterogeneous nanocatalysts.
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The greatest challenge for lithium-sulfur (Li-S) batteries application is the development of cathode hosts to address the low conductivity, huge volume change, and shuttling effect of sulfur or lithium polysulfides (LiPs). Herein, we demonstrate a composite host to circumvent these problems by confining sub-nanometric manganous oxide clusters (MOCs) in nitrogen doped mesoporous carbon nanosheets. The atomic structure of MOCs is well-characterized and optimized via the extended X-ray absorption fine structure analysis and density functional theory (DFT) calculations. Benefiting from the unique design, the assembled Li-S battery displays remarkable electrochemical performances including a high reversible capacity (990 mAh g-1 after 100 cycles at 0.2 A g-1) and a superior cycle life (60% retention over 250 cycles at 2 A g-1). Both the experimental results and DFT calculations demonstrate that the well-dispersed MOCs could significantly promote the chemisorption of LiPs, thus greatly improving the capacity and rate performance.
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Proton-exchange membrane fuel cells (PEMFCs) are limited by their extreme sensitivity to trace-level CO impurities, thus setting a strict requirement for H2 purity and excluding the possibility to directly use cheap crude hydrogen as fuel. Herein, we report a proof-of-concept study, in which a novel catalyst comprising both Ir particles and Ir single-atom sites (IrNP @IrSA -N-C) addresses the CO poisoning issue. The Ir single-atom sites are found not only to be good CO oxidizing sites, but also excel in scavenging the CO molecules adsorbed on Ir particles in close proximity, thereby enabling the Ir particles to reserve partial active sites towards H2 oxidation. The interplay between Ir nanoparticles and Ir single-atom centers confers the catalyst with both excellent H2 oxidation activity (1.19â W cm-2 ) and excellent CO electro-oxidation activity (85â mW cm-2 ) in PEMFCs; the catalyst also tolerates CO in H2 /CO mixture gas at a level that is two times better than that of the current best PtRu/C catalyst.
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Phenoxyl radical was generally suggested as the intermediate during copper-catalyzed aerobic oxygenation of phenols. However, the substrate-dependent selectivity has not been well interpreted, due to insufficient characterization of the radical intermediate under reaction conditions. When studying the CuCl-LiCl-catalyzed aerobic phenol oxidation, we obtained EPR spectra of phenoxyl radicals generated by oxidizing phenols with the preactivated catalyst. Upon correlation to the selectivity of benzoquinone, the hyperfine coupling constant of para-site proton (aH, para) was found to be better than the Hammett constant. The catalysis mechanism was studied based on EPR detection and the reaction results of phenoxyl radicals under N2 or O2 atmosphere. It appeared that the chemoselectivity depended on the attack of activated dioxygen on phenoxyl radicals, and the activation of dioxygen by [CunCln+1]- (n = 1, 2, 3) was suggested as the rate-determining step. Understanding of the substrate-dependent selectivity contributed to predicting the chemoselectivity in the aerobic oxidation of phenols.
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The development of high-efficiency electrocatalysts for large-scale water splitting is critical but also challenging. In this study, a hierarchical CoMoSx chalcogel was synthesized on a nickel foam (NF) through an in situ metathesis reaction and demonstrated excellent activity and stability in the electrocatalytic hydrogen evolution reaction and oxygen evolution reaction in alkaline media. The high catalytic activity could be ascribed to the abundant active sites/defects in the amorphous framework and promotion of activity through cobalt doping. Furthermore, the superhydrophilicity and superaerophobicity of micro-/nanostructured CoMoSx /NF promoted mass transfer by facilitating access of electrolytes and ensuring fast release of gas bubbles. By employing CoMoSx /NF as bifunctional electrocatalysts, the overall water splitting device delivered a current density of 500â mA cm-2 at a low voltage of 1.89â V and maintained its activity without decay for 100â h.
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Maximizing the platinum utilization in electrocatalysts toward oxygen reduction reaction (ORR) is very desirable for large-scale sustainable application of Pt in energy systems. A cost-effective carbon-supported carbon-defect-anchored platinum single-atom electrocatalysts (Pt1 /C) with remarkable ORR performance is reported. An acidic H2 /O2 single cell with Pt1 /C as cathode delivers a maximum power density of 520â mW cm-2 at 80 °C, corresponding to a superhigh platinum utilization of 0.09â gPt kW-1 . Further physical characterization and density functional theory computations reveal that single Pt atoms anchored stably by four carbon atoms in carbon divacancies (Pt-C4 ) are the main active centers for the observed high ORR performance.
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Strong metal-support interaction (SMSI) has been regarded as one of the most important concepts in heterogeneous catalysis, which has been almost exclusively discussed in metal/oxide catalysts. Here, we show that gold/molybdenum carbide (Au/MoC x) catalysts feature highly dispersed Au overlayers, strong interfacial charge transfer between metal and support, and excellent activity in the low-temperature water-gas shift reaction (LT-WGSR), demonstrating the active SMSI state. Subsequent oxidation treatment results in strong aggregation of Au nanoparticles, weak interfacial electronic interaction, and poor LT-WGSR activity. The two interface states can be transformed into each other by alternative carbonization and oxidation treatments. This work reveals the active SMSI effect in metal/carbide catalysts induced by carbonization, which opens a new territory for this important concept.
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The electrochemical reduction reaction of carbon dioxide (CO2RR) to carbon monoxide (CO) is the basis for the further synthesis of more complex carbon-based fuels or attractive feedstock. Single-atom catalysts have unique electronic and geometric structures with respect to their bulk counterparts, thus exhibiting unexpected catalytic activities. A nitrogen-anchored Zn single-atom catalyst is presented for CO formation from CO2RR with high catalytic activity (onset overpotential down to 24â mV), high selectivity (Faradaic efficiency for CO (FECO ) up to 95 % at -0.43â V), remarkable durability (>75â h without decay of FECO ), and large turnover frequency (TOF, up to 9969â h-1 ). Further experimental and DFT results indicate that the four-nitrogen-anchored Zn single atom (Zn-N4 ) is the main active site for CO2RR with low free energy barrier for the formation of *COOH as the rate-limiting step.
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Heterogeneous nano-electrocatalysts doped with nonmetal atoms have been studied extensively based on the so-called dopant-based active sites, while little attention has been paid to the stability of these dopants under working conditions. In this work, we reveal significantly, when the redox working potential is too low negatively or too high positively, the active sites based on these dopants actually tend to collapse. It means that some previously observed "remarkable catalytic performance" actually originated from some unknown active sites formed in situ. Take the Bi-F for the CO2RR as an example, results show that the observed remarkable activity and stability were not directly from F-based active sites, but the defective Bi sites formed in situ after the dopant leaching. Such a fact is unveiled from several heteroatom-doped nanocatalysts for four typical reactions (CO2RR, HER, ORR, and OER). This work provides insight into the role of dopants in electrocatalysis.
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Nanosized Pt catalysts are the catalyst-of-choice for proton exchange membrane fuel cell (PEMFC) anode, but are limited by their extreme sensitivity to CO in parts per million (ppm) level, thereby making the use of ultrapure H2 a prerequisite to ensure acceptable performance. Herein, we confront the CO poisoning issue by bringing the Ir/Rh single atom sites to synergistically working with their metallic counterparts. In presence of 1000 ppm CO, the catalyst represents not only undisturbed H2 oxidation reaction (HOR) catalytic behavior in electrochemical cell, but also unparalleled peak power density at 643 mW cm-2 in single cell, 27-fold in mass activity of the best PtRu/C catalysts available. Pre-poisoning experiments and surface-enhanced Raman scattering spectroscopy (SERS) and calculation results in combine suggest the presence of adjacent Ir/Rh single atom sites (SASs) to the nanoparticles (NPs) as the origin for this prominent catalytic behavior. The single sites not only exhibit superb CO oxidation performance by themselves, but can also scavenge the CO adsorbed on approximated NPs via supplying reactive OH* species. We open up a new route here to conquer the formidable CO poisoning issue through single atom and nanoparticle synergistic catalysis, and pave the way towards a more robust PEMFC future.
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Revealing key factors that modulate the regioselectivity in heterogeneous hydroformylation requires identifying and monitoring the dynamic evolution of the truly active center under real reaction conditions. However, unambiguous in situ characterizations are still lacking. Herein, we elaborately construct a series of Rh-POPs catalysts for propylene hydroformylation which exhibited tunable regioselectivity. Multi-technique approaches reveal the unique microenvironment of the diverse HRh(CO)(PPh3-frame)2 sites with distinct P-Rh-P bite angles ranging from 90° to 120° and 158° to 168°, respectively. In situ time-resolved XAFS, FT-IR, and quasi-in situ Solid-state NMR experiments combined with DFT calculations explain the dynamic evolution of the electronic and coordinate state of the distinct active sites induced by hemilabile PPh3-frame ligands and further disclose the regulatory mechanism of regioselectivity. These state-of-the-art techniques and multiscale analysis advance the understanding of how hemilabile coordination influences regioselectivity and will provide a new thought to modulate the regioselectivity in future industrial processes.