Bi-Interlayer Strategy for Modulating NiCoP-Based Heterostructure toward High-Performance Aqueous Energy Storage Devices.

Nickel-cobalt (NiCo) phosphides (NCPs) possess high electrochemical activity, which makes them promising candidates for electrode materials in aqueous energy storage devices, such as supercapacitors and zinc (Zn) batteries. However, the actual specific capacitance and rate capability of NCPs require further improvement, which can be achieved through reasonable heterostructural design and loading conditions of active materials on substrates. Herein, novel hierarchical Bi-NCP heterogeneous structures with built-in electric fields consisting of bismuth (Bi) interlayers (electrodeposited on carbon cloth (CC)) are designed and fabricated to ensure the formation of uniform high-load layered active materials for efficient charge and ion transport. The resulting CC/Bi-NCP electrodes show a uniform, continuous, and high mass loading (>3.5 mg) with a superior capacitance reaching 1200 F g-1 at 1 A g-1 and 4129 mF cm-2 at 1 mA cm-2 combined with high-rate capability and durable cyclic stability. Moreover, assembled hybrid supercapacitors (HSCs), supercapatteries, and alkaline Zn-ion (AZBs) batteries constructed using these electrodes deliver high energy densities of 64.4, 81.8, and 319.1 Wh kg-1, respectively. Overall, the constructed NCPs with excellent aqueous energy storage performance have the potential for the development of novel transition metal-based heterostructure electrodes for advanced energy devices.

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

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

Electrodeposition of Self-Supported High-Entropy Spinel Oxides for Stable Oxygen Evolution.

Spinel oxides have attracted increasing interest due to their excellent activity in the oxygen evolution reaction (OER). However, despite the high intrinsic OER activity, their poor electrical conductivity and weak structural stability prevented their application for a long time. These shortcomings can be solved by effectively adjusting the electronic structures of spinel oxides through a high-entropy strategy. Herein, a rapid two-step method was developed to prepare self-supported high-entropy spinel-type oxides on a carbon cloth (CC) to yield (Fe0.2Co0.2Ni0.2Mn0.2Cr0.2)3O4@CC (abbreviated as FeCoNiMnCr@CC). The unique electronic structure and stable crystal configuration of the resulting FeCoNiMnCr@CC materials required only an overpotential of 287 mV for the OER at a current density of 10 mA cm-2 coupled with excellent cyclic stability. In summary, the proposed high-entropy strategy looks promising for improving the catalytic performance of spinel oxides.

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

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

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

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

Insights into high-entropy material synthesis dynamics criteria based on a thermodynamic framework.

High-entropy materials (HEMs) have attracted increasing research interests owing to their structural diversity and great potential for regulation. Numerous HEMs synthesis criteria have so far been reported but most are based on thermodynamics while a guiding basis for the synthesis of HEMs is lacking, resulting in many synthesis problems. Based on the overall thermodynamic formation criterion of HEMs, this study has explored the principles of the synthesis dynamics required based on this criterion and the influence of different synthesis kinetic rates on the final products of the reaction, filling the gap suggesting that thermodynamic criteria cannot guide the specific process changes. This will effectively provide more specific guidelines for the top-level design of material synthesis. By considering various aspects of HEMs synthesis criteria, new technologies suitable for high-performance HEMs catalysts were extracted. Also, the physical and chemical characteristics of the HEMs obtained from actual synthesis can be predicted in a better way, playing an important role in the personalized customization of HEMs with specific performance. Future development directions of HEMs synthesis were prospected for possible prediction and customization of HEMs catalysts with high performance.

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

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

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

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

Efficient fabrication of flower-like core-shell nanochip arrays of lanthanum manganate and nickel cobaltate for high-performance supercapacitors.

The low energy density issue raises serious concerns for the large-scale application of supercapacitors. However, the development and utilization of new electrode materials with a high specific capacity to improve the energy density of supercapacitors remain challenging. Herein, an LaMnO3@NiCo2O4/carbon cloth (LMO@NCO/CC) composed of a multilayer flower-like nanochip array is prepared for the first time using an efficient electrodeposition method. This novel structure exploits the high conductivity of LaMnO3/carbon cloth (LMO@CC) to provide an efficient electron transport path for the outer layer of the NiCo2O4/carbon cloth (NCO@CC) nanoarrays, broadening the potential window. Due to the unique nanostructure configuration and the strong synergistic effect of the developed LMO@NCO/CC, the prepared electrodes show excellent supercapacitor performance. At a current density of 1 A g-1, LMO@NCO/CC has a higher specific capacitance value of 942 F g-1. The application value is extended through the fabrication of asymmetric supercapacitors with a maximum energy density of 49 Wh kg-1 and excellent cycle stability (the initial capacitance value remains 106 % after 10,000 cycles of charging and discharging at a high current density of 10 A g-1). Our work paves the way for the development of next-generation electrode materials for high-performance supercapacitors.

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

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

Two-step fabrication of lanthanum nickelate and nickel oxide core-shell dandelion-like materials for high-performance supercapacitors.

LaNiO3 and NiO are promising materials for supercapacitor applications. However, it is still challenging to design special structures based on these materials to improve the electrochemical performances of supercapacitor electrodes. In this work, a two-step method with low cost and convenient operation was developed to prepare dandelion-shaped LaNiO3/NiO (CSD-LaNiO3/NiO) with core-shell structure. The as-obtained CSD-LaNiO3/NiO showed high conductivity due to the core LaNiO3, which helped to provide an efficient electron transmission path for the shell NiO, producing a strong synergistic effect. The results of electrochemical properties of CSD-LaNiO3/NiO, LaNiO3 and NiO samples revealed the superior specific capacitance of CSD-LaNiO3/NiO (326.8 F g-1) at 1 A g-1 compared to LaNiO3 (166.5 F g-1) and NiO (44.2 F g-1). The as-obtained CSD-LaNiO3/NiO material was then mixed with activated carbon and assembled into an asymmetric supercapacitor, which exhibited a wide potential window of 1.8 V, energy density of 30.4 Wh kg-1 at 1800 W kg-1, and specific capacity retention of 97.7% after 3000 cycles. In sum, the as-obtained core-shell nanostructure prepared by the proposed synthesis method is very promising for future development of high-performance supercapacitors.

Coaxial cable-like dual conductive channel strategy in polypyrrole coated perovskite lanthanum manganite for high-performance asymmetric supercapacitors.

Perovskite transition metal oxides are promising materials for supercapacitor electrodes due to their high theoretical capacities. However, these materials still suffer from poor conductivity, low specific capacitance, and moderate cycle stability, restraining their practical applications. In this study, LaMnO3@CC-PPy materials were prepared by two-step electrodeposition based on the inspiring design of coaxial cables. To this end, electrochemically active LaMnO3 was first grown on carbon cloth (CC) with good flexibility and conductivity and then followed by further coating with polypyrrole (PPy) layer. The best PPy load was identified by adjusting the deposition time. The resulting LaMnO3@CC-PPy electrodes showed excellent specific capacitance reaching 862F g-1 at 1 A g-1 with retention rate of 75% at high current density of 10 A g-1, indicative of excellent rate performance. The cycle stability of the electrodes also improved after 3000 cycles at 10 A g-1 with a retention rate reaching 66%. To assemble asymmetric supercapacitor (ASC) devices, NiCo2O4@CC cathodes were prepared by electrodeposition. Ultra-high energy density of about 73 Wh kg-1 and good cycle stability were recorded with the devices. The high performance of the as-obtained materials was attributed to the existence of internal and external double electric channels, as well as the abundant internal space. These features ensured good conductivity, rapid charge transfer, and fast ion diffusion, thereby significantly improving the overall material cycle stability. In sum, these findings look promising for future preparation of high-performance perovskite supercapacitors.

Oxygen-vacancy abundant alpha bismuth oxide with enhanced cycle stability for high-energy hybrid supercapacitor electrodes.

Bi2O3 is an outstanding electrode material due to its high theoretical specific capacity. Hence, the synthesis of δ-Bi2O3 materials with high oxygen-vacancy contents could improve their electrochemical performances but causes easy conversion to α-Bi2O3 with low oxygen-vacancy contents, leading to poor cycling stability and limited practical applications. To overcome these problems, an effective strategy for constructing high oxygen vacancies α-Bi2O3 on activated carbon fiber paper (ACFP) is developed in this study. To this end, ACFP/Bi(OH)3 is first synthesized by the solvothermal method and then converted to ACFP/α-Bi2O3 by in situ electrochemical activation. The proposed innovative electrochemical method quickly and easily introduces oxygen vacancies while preserving the three-dimensional structure, thereby promoting the charge transfer and ions diffusion in ACFP/α-Bi2O3. Consequently, the specific capacity of ACFP/α-Bi2O3 reaches 906C g-1 at 1 A g-1, and the capacity retention remains above 70% after 3000 cycles, a value higher than that of δ-Bi2O3 (45%). Furthermore, the hybrid supercapacitor device assembled by ACFP/α-Bi2O3 delivers a maximum energy density of 114.9 Wh kg-1 at 900 W kg-1 and outstanding cycle stability with 73.56 % retention after 5500 cycles. In sum, the proposed ACFP/α-Bi2O3 with high performance and good stability looks promising for use as bismuth-based anode materials in supercapacitors and aqueous batteries.