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While high-entropy alloy (HEA) catalysts seem to have the potential to break linear scaling relationships (LSRs) due to their structural complexity, the weighted averaging of properties among multiple principal components actually makes it challenging to diverge from the symmetry dependencies imposed by the LSRs. Herein, we develop a 'surface entropy reduction' method to induce the exsolution of a component with weak affinity for others, resulting in the formation of few-atom-layer metal (FL-M) on the surface of HEAs. These exsolved FL-M surpass the confines of the original configurational space of conventional HEAs, and collaborate with the HEA substrate, serving as geometrically separated active sites for multiple intermediates in a complex reaction. This FL-M-covered HEA shows an outstanding performance for electrocatalytic reduction of nitrate to ammonia (NH3) with a Faradaic efficiency of 92.7%, an NH3 yield rate of 2.45 mmol h-1 mgcat.-1, and high long-term stability (>200 h). Our work achieves the precise manipulation of atomic arrangement, thereby expanding both the chemical space occupied by known HEA catalysts and their potential application scenarios.
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The pursuit of sustainable practices through the chemical recycling of polyamide wastes holds significant potential, particularly in enabling the recovery of a range of nitrogen-containing compounds. Herein, we report a novel strategy to upcycle polyamide wastes to tertiary amines with assistance of H2 in acetic acid under mild conditions (e.g., 180 ºC), which is achieved over anatase TiO2 supported Mo single atoms and Rh nanoparticles. In this protocol, the polyamide is first converted into diacetamide intermediates via acidolysis, which are subsequent hydrogenated into corresponding carboxylic acid monomers and tertiary amines in 100% selectivity. It is verified that Mo single atom and Rh nanoparticles work together to activate both amide bonds of the diacetamide intermediate, and synergistically catalyze its hydrodeoxygenation to form tertiary amine, but this catalyst is ineffective for hydrogenation of carboxylic acid. This work presents an effective way to reconstruct various polyamide wastes into tertiary amines and carboxylic acids, which may have promising application potential.
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For traditional metal complexes, intricate chemistry is required to acquire appropriate ligands for controlling the electron and steric hindrance of metal active centers. Comparatively, the preparation of single-atom catalysts is much easier with more straightforward and effective accesses for the arrangement and control of metal active centers. The presence of coordination atoms or neighboring functional atoms on the supports' surface ensures the stability of metal single-atoms and their interactions with individual metal atoms substantially regulate the performance of metal active centers. Therefore, the collaborative interaction between metal and the surrounding coordination environment enhances the initiation of reaction substrates and the formation and transformation of crucial intermediate compounds, which imparts single-atom catalysts with significant catalytic efficacy, rendering them a valuable framework for investigating the correlation between structure and activity, as well as the reaction mechanism of catalysts in organic reactions. Herein, comprehensive overviews of the coordination interaction for both homogeneous metal complexes and single-atom catalysts in organic reactions are provided. Additionally, reflective conjectures about the advancement of single-atom catalysts in organic synthesis are also proposed to present as a reference for later development.
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Chemoselective hydrogenation of quinoline and its derivatives is a significant strategy to achieve the corresponding 1,2,3,4-tetrahydroquinolines (py-THQ) for various potential applications. Here, we precisely constructed a titanium carbide supported atomically dispersed Pd catalyst (PdSA+NC/TiC) for quinoline hydrogenation, delivering above 99% py-THQ selectivity at complete conversion with an outstanding turnover frequency (TOF) of 463 h-1. AC-HAADF-STEM and XAFS demonstrate that the atomic dispersion of Pd includes Pd-Ti2C2 single atoms and Pd clusters with atomic-layer thickness. Theoretical calculation and experimental results revealed that H2 dissociation and subsequent hydrogenation rates were greatly promoted over Pd clusters. Although the adsorption of quinolines and intermediates are easier on Pd clusters than on Pd single atoms, the desorption of py-THQ is more favored over Pd single atoms than over Pd clusters. The desorption step may be the main reason for 5,6,7,8-tetrahydroquinoline (bz-THQ) and decahydroquinoline (DHQ) formation. Thus, a low reaction activity and py-THQ selectivity were received over PdSA/TiC and PdNP/TiC, respectively.
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Hydrogen electrocatalytic reactions, including the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR), play a crucial role in a wide range of energy conversion and storage technologies. However, the HER and HOR display anomalous non-Nernstian pH dependent kinetics, showing two to three orders of magnitude sluggish kinetics in alkaline media compared to that in acidic media. Fundamental understanding of the origins of the intrinsic pH effect has attracted substantial interest from the electrocatalysis community. More critically, a fundamental molecular level understanding of this effect is still debatable, but is essential for developing active, stable, and affordable fuel cells and water electrolysis technologies. Against this backdrop, in this review, we provide a comprehensive overview of the intrinsic pH effect on hydrogen electrocatalysis, covering the experimental observations, underlying principles, and strategies for catalyst design. We discuss the strengths and shortcomings of various activity descriptors, including hydrogen binding energy (HBE) theory, bifunctional theory, potential of zero free charge (pzfc) theory, 2B theory and other theories, across different electrolytes and catalyst surfaces, and outline their interrelations where possible. Additionally, we highlight the design principles and research progress in improving the alkaline HER/HOR kinetics by catalyst design and electrolyte optimization employing the aforementioned theories. Finally, the remaining controversies about the pH effects on HER/HOR kinetics as well as the challenges and possible research directions in this field are also put forward. This review aims to provide researchers with a comprehensive understanding of the intrinsic pH effect and inspire the development of more cost-effective and durable alkaline water electrolyzers (AWEs) and anion exchange membrane fuel cells (AMFCs) for a sustainable energy future.
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Heterogeneous single-metal-site catalysts (SMSCs), often referred to as single-atom catalysts (SACs), demonstrate promising catalytic activity, selectivity, and stability across a wide spectrum of reactions due to their rationally designed microenvironments encompassing coordination geometry, binding ligands, and electronic configurations. However, the inherent disorderliness of SMSCs at both atomic scale and nanoscale poses challenges in deciphering working principles and establishing the correlations between microenvironments and the catalytic performances of SMSCs. The rearrangement of randomly dispersed single metals into homogeneous and atomic-precisely structured periodic single-metal site catalysts (PSMSCs) not only simplifies the chaos in SMSCs systems but also unveils new opportunities for manipulating catalytic performance and gaining profound insights into reaction mechanisms. Moreover, the synergistic effects of adjacent single metals and the integration effects of periodic single-metal arrangement further broaden the industrial application scope of SMSCs. This perspective offers a comprehensive overview of recent advancements and outlines prospective avenues for research in the design and characterizations of PSMSCs, while also acknowledging the formidable challenges encountered and the promising prospects that lie ahead.
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Due to the slow dynamics of mass and charge transfer at Zn|electrolyte interface, the stable operation of Zn-air batteries (ZABs) is challenging, especially at low temperature. Herein, inspired by cell membrane, a hydrophilic-hydrophobic dual modulated Zn|electrolyte interface is constructed. This amphiphilic design enables the quasi-solid-state (QSS) ZABs to display a long-term cyclability of 180 h@50 mA cm-2 at 25 °C. Moreover, a record-long time of 173 h@4 mA cm-2 at -60 °C is also achieved, which is almost threefolds of untreated QSS ZABs. Control experiments and (in situ) characterization reveal that the growth of insulating ZnO passivation layers is largely inhibited by tuned hydrophilic-hydrophobic behavior. Thus, the enhanced transfer dynamic of Zn2+ at Zn|electrolyte interface from 25 to -60 °C is attained. As an extension, the QSS Al-air batteries (AABs) with bioinspired interface also show unprecedented discharge stability of 420 h@1 mA cm-2 at -40 °C, which is about two times of untreated QSS AABs. This bioinspired-hydrophilic-hydrophobic dual modulation strategy may provide a reference for energy transform and storage devices with broad temperature adaptability.
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Electrocatalytic reduction of CO2 into C2 products of high economic value provides a promising strategy to realize resourceful CO2 utilization. Rational design and construct dual sites to realize the CO protonation and C-C coupling to unravel their structure-performance correlation is of great significance in catalysing electrochemical CO2 reduction reactions. Herein, Cu-Cu dual sites with different site distance coordinated by halogen at the first-shell are constructed and shows a higher intramolecular electron redispersion and coordination symmetry configurations. The long-range Cu-Cu (Cu-I-Cu) dual sites show an enhanced Faraday efficiency of C2 products, up to 74.1 %, and excellent stability. In addition, the linear relationships that the long-range Cu-Cu dual sites are accelerated to C2H4 generation and short-range Cu-Cu (Cu-Cl-Cu) dual sites are beneficial for C2H5OH formation are disclosed. In situ electrochemical attenuated total reflection surface enhanced infrared absorption spectroscopy, in situ Raman and theoretical calculations manifest that long-range Cu-Cu dual sites can weaken reaction energy barriers of CO hydrogenation and C-C coupling, as well as accelerating deoxygenation of *CH2CHO. This study uncovers the exploitation of site-distance-dependent electrochemical properties to steer the CO2 reduction pathway, as well as a potential generic tactic to target C2 synthesis by constructing the desired Cu-Cu dual sites.
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Herein, we propose a platinization strategy for the preparation of Pt/X catalysts with low Pt content on substrates possessing electron-rich sites (Pt/X: X = Co3O4, NiO, CeO2, Covalent Organic Framework (COF), etc.). In examples with inorganic and organic substrates, respectively, Pt/Co3O4 possesses remarkable catalytic ability toward HER, achieving a current density at an overpotential of 500 mV that is 3.22 times higher than that of commercial Pt/C. It was also confirmed by using operando Raman spectroscopy that the enhancement of catalytic activity was achieved after platinization of the COF, with a reduction of overpotential from 231 to 23 mV at 10 mA cm-2. Density functional theory (DFT) reveals that the improved catalytic activity of Pt/Co3O4 and Pt/COF originated from the re-modulation of Ptδ+ on the electronic structure and the synergistic effect of the interfacial Ptδ+/electron-rich sites. This work provides a rapid synthesis strategy for the synthesis of low-content Pt catalysts for electrocatalytic hydrogen production.
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Heterogeneous dual-atomic-site catalysts (DACs) hold great potential for diverse applications. However, to date, the synthesis of DACs primarily relies on different atoms freely colliding on the support during synthesis, principally leading to low yields. Herein, we report a general metal ion recognition (MIR) strategy for constructing a series of DACs, including but not limited to Fe1Sn1, Fe1Co1, Fe1Ni1, Fe1Cu1, Fe1Mn1, Co1Ni1, Co1Cu1, Co2, and Cu2. This strategy is achieved by coupling target inorganometallic cations and anions as ion pairs, which are sequentially adsorbed onto a nitrogen-doped carbon substrate as the precursor. Taking the oxygen reduction reaction as an example, we demonstrated that the Fe1Sn1-DAC synthesized through this strategy delivers a record peak power density of 1.218 W cm-2 under 2.0 bar H2-O2 conditions and enhanced stability compared to the single-atom-site FeN4. Further study revealed that the superior performance arises from the synergistic effect of Fe1Sn1 dual vicinal sites, which effectively optimizes the adsorption of *OH and alleviates the troublesome Fenton-like reaction.
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The production of ammonia (NH3) from nitrogen sources involves competitive adsorption of different intermediates and multiple electron and proton transfers, presenting grand challenges in catalyst design. In nature nitrogenases reduce dinitrogen to NH3 using two component proteins, in which electrons and protons are delivered from Fe protein to the active site in MoFe protein for transfer to the bound N2. We draw inspiration from this structural enzymology, and design a two-component metal-sulfur-carbon (M-S-C) catalyst composed of sulfur-doped carbon-supported ruthenium (Ru) single atoms (SAs) and nanoparticles (NPs) for the electrochemical reduction of nitrate (NO3 -) to NH3. The catalyst demonstrates a remarkable NH3 yield rate of ~37â mg L-1 h-1 and a Faradaic efficiency of ~97 % for over 200â hours, outperforming those consisting solely of SAs or NPs, and even surpassing most reported electrocatalysts. Our experimental and theoretical investigations reveal the critical role of Ru SAs with the coordination of S in promoting the formation of the HONO intermediate and the subsequent reduction reaction over the NP-surface nearby. Such process results in a more energetically accessible pathway for NO3 - reduction on Ru NPs co-existing with SAs. This study proves a better understanding of how M-S-Cs act as a synthetic nitrogenase mimic during ammonia synthesis, and contributes to the future mechanism-based catalyst design.
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Carbono , Nitrogenasa , Azufre , Nitrogenasa/química , Nitrogenasa/metabolismo , Catálisis , Carbono/química , Azufre/química , Rutenio/química , Amoníaco/química , Amoníaco/metabolismo , Oxidación-Reducción , Nitratos/química , Nitratos/metabolismoRESUMEN
Deeply electrolytic reduction of carbon dioxide (CO2) to high-value ethylene (C2H4) is very attractive. However, the sluggish kinetics of C-C coupling seriously results in the low selectivity of CO2 electroreduction to C2H4. Herein, we report a copper-based polyhedron (Cu2) that features uniformly distributed and atomically precise bi-Cu units, which can stabilize *OCCO dipole to facilitate the C-C coupling for high selective C2H4 production. The C2H4 faradaic efficiency (FE) reaches 51% with a current density of 469.4 mA cm-2, much superior to the Cu single site catalyst (Cu SAC) (~0%). Moreover, the Cu2 catalyst has a higher turnover frequency (TOF, ~520 h-1) compared to Cu nanoparticles (~9.42 h-1) and Cu SAC (~0.87 h-1). In situ characterizations and theoretical calculations revealed that the unique Cu2 structural configuration could optimize the dipole moments and stabilize the *OCCO adsorbate to promote the generation of C2H4.
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Palladium (Pd)-based single-atom catalysts (SACs) have shown outstanding selectivity for semihydrogenation of alkynes, but most Pd single sites coordinated with highly electronegative atoms (such as N, O, and S) of supports will result in a decrease in the electron density of Pd sites, thereby weakening the adsorption of reactants and reducing catalytic performance. Constructing a rich outer-shell electron environment of Pd single-atom sites by changing the coordination structure offers a novel opportunity to enhance the catalytic efficiency with excellent alkene selectivity. Therefore, in this work, we first propose the in situ preparation of isolated Pd sites encapsulated within Al/Si-rich ZSM-5 structure using the one-pot seed-assisted growth method. Pd1@ZSM-5 features Pd-O-Al/Si bonds, which can boost the domination of d-electron near the Fermi level, thereby promoting the adsorption of substrates on Pd sites and reducing the energy barrier for the semihydrogenation of alkynes. In semihydrogenation of phenylacetylene, Pd1@ZSM-5 catalyst performs the highest turnover frequency (TOF) value of 33582 molCâC/molPd/h with 96% selectivity of styrene among the reported heterogeneous catalysts and nearly 17-fold higher than that of the commercial Lindlar catalyst (1992 molCâC/molPd/h). This remarkable catalytic performance can be retained even after 6 cycles of usage. Particularly, the zeolitic confinement structure of Pd1@ZSM-5 enables precise shape-selective catalysis for alkyne reactants with a size less than 4.3 Å.
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Electrochemical nitrate reduction method (NitRR) is a low-carbon, environmentally friendly, and efficient method for synthesizing ammonia, which has received widespread attention in recent years. Copper-based catalysts have a leading edge in nitrate reduction due to their good adsorption of *NO3. However, the formation of active hydrogen (*H) on Cu surfaces is difficult and insufficient, resulting in a large amount of the by-product NO2 -. In this work, Pd single atoms suspended on the interlayer unsaturated bonds of CuO atoms formed due to dislocations (Pd-CuO) were prepared by low temperature treatment, and the Pd single atoms located on the dislocations were subjected to shear stress and the dynamic effect of support formation to promote the conversion of nitrate into ammonia. The catalysis had an ammonia yield of 4.2â mol. gcat -1. h-1, and a Faraday efficiency of 90 % for ammonia production at -0.5â V vs. RHE. Electrochemical in situ characterization and theoretical calculations indicate that the dynamic effects of Pd single atoms and carriers under shear stress obviously promote the production of active hydrogen, reduce the reaction energy barrier of the decision-making step for nitrate conversion to ammonia, further promote ammonia generation.
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Lower olefins are widely used in the chemical industry as basic carbon-based feedstocks. Here, we report the catalytic system featuring isolated single-atom sites of iridium (Ir1) that can function within the entire temperature range of 300-600 °C and transform alkanes with conversions close to thermodynamics-dictated levels. The high turnover frequency values of the Ir1 system are comparable to those of homogeneous catalytic reactions. Experimental data and theoretical calculations both indicate that Ir1 is the primary catalytic site, while the coordinating C and N atoms help to enhance the activity and stability, respectively; all three kinds of elements cooperatively contribute to the high performance of this novel active site. We have further immobilized this catalyst on particulate Al2O3, and we found that the resulting composite system under mimicked industrial conditions could still give high catalytic performances; in addition, we have also developed and established a new scheme of periodical in situ regeneration specifically for this composite particulate catalyst.
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The inactivation of natural enzymes by radiation poses a great challenge to their applications for radiotherapy. Single-atom nanozymes (SAzymes) with high structural stability under such extreme conditions become a promising candidate for replacing natural enzymes to shrink tumors. Here, we report a CuN3-centered SAzyme (CuN3-SAzyme) that exhibits higher peroxidase-like catalytic activity than a CuN4-centered counterpart, by locally regulating the coordination environment of single copper sites. Density functional theory calculations reveal that the CuN3 active moiety confers optimal H2O2 adsorption and dissociation properties, thus contributing to high enzymatic activity of CuN3-SAzyme. The introduction of X-ray can improve the kinetics of the decomposition of H2O2 by CuN3-SAzyme. Moreover, CuN3-SAzyme is very stable after a total radiation dose of 500 Gy, without significant changes in its geometrical structure or coordination environment, and simultaneously still retains comparable peroxidase-like activity relative to natural enzymes. Finally, this developed CuN3-SAzyme with remarkable radioresistance can be used as an external field-improved therapeutics for enhancing radio-enzymatic therapy in vitro and in vivo. Overall, this study provides a paradigm for developing SAzymes with improved enzymatic activity through local coordination manipulation and high radioresistance over natural enzymes, for example, as sensitizers for cancer therapy.
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Cobre , Peróxido de Hidrógeno , Peroxidasa , Tolerancia a Radiación , Cobre/química , Animales , Humanos , Peróxido de Hidrógeno/química , Peróxido de Hidrógeno/metabolismo , Peroxidasa/metabolismo , Peroxidasa/química , Ratones , Línea Celular Tumoral , Catálisis/efectos de la radiación , CinéticaRESUMEN
As the most promising hydrogen evolution reaction (HER) electrocatalysts, platinum (Pt)-based catalysts still struggle with sluggish kinetics and expensive costs in alkaline media. Herein, we accelerate the alkaline hydrogen evolution kinetics by optimizing the local environment of Pt species and metal oxide heterointerfaces. The well-dispersed PtRu bimetallic clusters with adjacent MO2-x (M = Sn and Ce) on carbon nanotubes (PtRu/CNT@MO2-x) are demonstrated to be a potential electrocatalyst for alkaline HER, exhibiting an overpotential of only 75 mV at 100 mA cm-2 in 1 M KOH. The excellent mass activity of 12.3 mA µg-1Pt+Ru and specific activity of 32.0 mA cm-2ECSA at an overpotential of 70 mV are 56 and 64 times higher than those of commercial Pt/C. Experimental and theoretical investigations reveal that the heterointerfaces between Pt clusters and MO2-x can simultaneously promote H2O adsorption and activation, while the modification with Ru further optimizes H adsorption and H2O dissociation energy barriers. Then, the matching kinetics between the accelerated elementary steps achieved superb hydrogen generation in alkaline media. This work provides new insight into catalytic local environment design to simultaneously optimize the elementary steps for obtaining ideal alkaline HER performance.
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Despite the extensive development of non-noble metals for the N-alkylation of amines with alcohols, the exploitation of catalysts with high selectivity, activity, and stability still faces challenges. The controllable modification of single-atom sites through asymmetric coordination with a second heteroatom offers new opportunities for enhancing the intrinsic activity of transition metal single-atom catalysts. Here, we prepared the asymmetric N/P hybrid coordination of single-atom Co1-N3P1 by absorbing the Co-P complex on ZIF-8 using a concise impregnation-pyrolysis process. The catalyst exhibits ultrahigh activity and selectivity in the N-alkylation of aniline and benzyl alcohol, achieving a turnover number (TON) value of 3480 and a turnover frequency (TOF) value of 174-h. The TON value is 1 order of magnitude higher than the reported catalysts and even 37-fold higher than that of the homogeneous catalyst CoCl2(PPh3)2. Furthermore, the catalyst maintains its high activity and selectivity even after 6 cycles of usage. Controlling experiments and isotope labeling experiments confirm that in the asymmetric Co1-N3P1 system, the N-alkylation of aniline with benzyl alcohol proceeds via a transfer hydrogenation mechanism involving the monohydride route. Theoretical calculations prove that the superior activity of asymmetric Co1-N3P1 is attributed to the higher d-band energy level of Co sites, which leads to a more stable four-membered ring transition state and a lower reaction energy barrier compared to symmetrical Co1-N4.
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The chemical recycling of polyester wastes is of great significance for sustainable development, which also provides an opportunity to access various oxygen-containing chemicals, but generally suffers from low efficiency or separation difficulty. Herein, we report anatase TiO2 supported Ru and Mo dual-atom catalysts, which achieve transformation of various polyesters into corresponding diols in 100% selectivity via hydrolysis and subsequent hydrogenation in water under mild conditions (e.g., 160 °C, 4 MPa). Compelling evidence is provided for the coexistence of Ru single-atom and O-bridged Ru and Mo dual-atom sites within this kind of catalysts. It is verified that the Ru single-atom sites activate H2 for hydrogenation of carboxylic acid derived from polyester hydrolysis, and the O-bridged Ru and Mo dual-atom sites suppress hydrodeoxygenation of the resultant alcohols due to a high reaction energy barrier. Notably, this kind of dual-atom catalysts can be regenerated with high activity and stability. This work presents an effective way to reconstruct polyester wastes into valuable diols, which may have promising application potential.
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The heteroatom substitution is considered as a promising strategy for boosting the redox kinetics of transition metal compounds in hybrid supercapacitors (HSCs) although the dissimilar metal identification and essential mechanism that dominate the kinetics remain unclear. It is presented that d-p orbital hybridization between the metal and electrolyte ions can be utilized as a descriptor for understanding the redox kinetics. Herein, a series of Co, Fe and Cu heteroatoms are respectively introduced into Ni3Se4 cathodes, among them, only the moderate Co-substituted Ni3Se4 can hold the optimal d-p orbital hybridization resulted from the formed more unoccupied antibonding states π*. It inevitably enhances the interfacial charge transfer and ensures the balanced OH- adsorption-desorption to accelerate the redox kinetics validated by the lowest reaction barrier (0.59â eV, matching well with the theoretical calculations). Coupling with the lower OH- diffusion energy barrier, the prepared cathode delivers ultrahigh rate capability (~68.7 % capacity retention even the current density increases by 200â times), and an assembled HSC also presents high energy/power density. This work establishes the principles for determining heteroatoms and deciphers the underlying effects of the heteroatom substitution on improving redox kinetics and the rate performance of battery-type electrodes from a novel perspective of orbital-scale manipulation.