•Formularized model reduction of fractional impedance spectra for batteries/ supercapacitors/fuel cells.
•Gained an insight into the characteristic time constant evolution for the joint time–frequency analysis.
•Validated the thorough model reduction of fractional impedance spectra by numerical simulations.
•Enhanced the reliability of joint time–frequency analysis for electrochemical energy devices.
Although biomass-derived carbon (biochar) has been widely used in the energy field, the relation between the carbonization condition and the physical/chemical property of the product remains elusive. Here, we revealed the carbonization condition's effect on the morphology, surface property, and electrochemical performance of the obtained carbon. An open slit pore structure with shower-puff-like nanoparticles can be obtained by finely tuning the carbonization temperature, and its unique pore structure and surface properties enable the Li-O2 battery with cycling longevity (221 cycles with 99.8% Coulombic efficiency at 0.2 mA cm-2 and controlled discharge-charge depths of 500 mAh g-1) and high capacity (16,334 mAh g-1 at 0.02 mA cm-2). This work provides a greater understanding of the mechanism of the biochar carbonization procedure under various pyrolysis conditions, paving the way for future study of energy storage devices.
With the advantage of fast charge transfer, heterojunction engineering is identified as a viable method to reinforce the anodes' sodium storage performance. Also, vacancies can effectively strengthen the Na+ adsorption ability and provide extra active sites for Na+ adsorption. However, their synchronous engineering is rarely reported. Herein, a hybrid of Co0.85Se/WSe2 heterostructure with Se vacancies and N-doped carbon polyhedron (CoWSe/NCP) has been fabricated for the first time via a hydrothermal and subsequent selenization strategy. Spherical aberration-corrected transmission electron microscopy confirms the phase interface of the Co0.85Se/WSe2 heterostructure and the existence of Se vacancies. Density functional theory simulations reveal the accelerated charge transfer and enhanced Na+ adsorption ability, which are contributed by the Co0.85Se/WSe2 heterostructure and Se vacancies, respectively. As expected, the CoWSe/NCP anode in sodium-ion battery achieves outstanding rate capability (339.6 mAh g-1 at 20 A g-1), outperforming almost all Co/W-based selenides.
Hydrogen peroxide (H2O2) production by the electrochemical 2-electron oxygen reduction reaction (2e- ORR) is a promising alternative to the energy-intensive anthraquinone process, and single-atom electrocatalysts show the unique capability of high selectivity toward 2e- ORR against the 4e- one. The extremely low surface density of the single-atom sites and the inflexibility in manipulating their geometric/electronic configurations, however, compromise the H2O2 yield and impede further performance enhancement. Herein, we construct a family of multiatom catalysts (MACs), on which two or three single atoms are closely coordinated to form high-density active sites that are versatile in their atomic configurations for optimal adsorption of essential *OOH species. Among them, the Cox-Ni MAC presents excellent electrocatalytic performance for 2e- ORR, in terms of its exceptionally high H2O2 yield in acidic electrolytes (28.96 mol L-1 gcat.-1 h-1) and high selectivity under acidic to neutral conditions in a wide potential region (>80%, 0-0.7 V). Operando X-ray absorption and density functional theory analyses jointly unveil its unique trimetallic Co2NiN8 configuration, which efficiently induces an appropriate Ni-d orbital filling and modulates the *OOH adsorption, together boosting the electrocatalytic 2e- ORR capability. This work thus provides a new MAC strategy for tuning the geometric/electronic structure of active sites for 2e- ORR and other potential electrochemical processes.
Single-atom catalysts (SACs) have gained substantial attention because of their exceptional catalytic properties. However, the high surface energy limits their synthesis, thus creating significant challenges for further development. In the last few years, metal-organic frameworks (MOFs) have received significant consideration as ideal candidates for synthesizing SACs due to their tailorable chemistry, tunable morphologies, high porosity, and chemical/thermal stability. From this perspective, this review thoroughly summarizes the previously reported methods and possible future approaches for constructing MOF-based (MOF-derived-supported and MOF-supported) SACs. Then, MOF-based SAC's identification techniques are briefly assessed to understand their coordination environments, local electronic structures, spatial distributions, and catalytic/electrochemical reaction mechanisms. This review systematically highlights several photocatalytic and electrocatalytic applications of MOF-based SACs for energy conversion and storage, including hydrogen evolution reactions, oxygen evolution reactions, O2/CO2/N2 reduction reactions, fuel cells, and rechargeable batteries. Some light is also shed on the future development of this highly exciting field by highlighting the advantages and limitations of MOF-based SACs.
Silicon monoxide (SiO) (silicon [Si] mixed with silicon dioxide [SiO2])/graphite (Gr) composite material is one of the most commercially promising anode materials for the next generation of high-energy-density lithium-ion batteries. The major bottleneck for SiO/Gr composite anode is the poor cyclability arising from the stress/strain behaviors due to the mismatch between two heterogenous materials during the lithiation/delithiation process. To date, a meticulous and quantitative understanding of the highly nonlinear coupling behaviors of such materials is still lacking. Herein, an electro-chemo-mechanics-coupled detailed model containing particle geometries is established. The underlying mechanism of the regulation between SiO and Gr components during electrochemical cycling is quantitatively revealed. We discover that increasing the SiO weight percentage (wt%) reduces the utilization efficiency of the active materials at the same 1 C rate charging and enhances the hindering effects of stress-driven flux on diffusion. In addition, the mechanical constraint demonstrates a balanced effect on the overall performance of cells and the local behaviors of particles. This study provides new insights into the fundamental interactions between SiO and Gr materials and advances the investigation methodology for the design and evaluation of next-generation high-energy-density batteries.
Systematic optimization of the photocatalyst and investigation of the role of each component is important to maximizing catalytic activity and comprehending the photocatalytic conversion of CO2 reduction to solar fuels. A surface-modified Ag@Ru-P25 photocatalyst with H2O2 treatment was designed in this study to convert CO2 and H2O vapor into highly selective CH4. Ru doping followed by Ag nanoparticles (NPs) cocatalyst deposition on P25 (TiO2) enhances visible light absorption and charge separation, whereas H2O2 treatment modifies the surface of the photocatalyst with hydroxyl (-OH) groups and promotes CO2 adsorption. High-resonance transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and extended X-ray absorption fine structure techniques were used to analyze the surface and chemical composition of the photocatalyst, while thermogravimetric analysis, CO2 adsorption isotherm, and temperature programmed desorption study were performed to examine the significance of H2O2 treatment in increasing CO2 reduction activity. The optimized Ag1.0@Ru1.0-P25 photocatalyst performed excellent CO2 reduction activity into CO, CH4, and C2H6 with a ~95% selectivity of CH4, where the activity was ~135 times higher than that of pristine TiO2 (P25). For the first time, this work explored the effect of H2O2 treatment on the photocatalyst that dramatically increases CO2 reduction activity.
Carbon nitrides with two-dimensional layered structures and high theoretical capacities are attractive as anode materials for sodium-ion batteries while their low crystallinity and insufficient structural stability strongly restrict their practical applications. Coupling carbon nitrides with conductive carbon may relieve these issues. However, little is known about the influence of nitrogen (N) configurations on the interactions between carbon and C3N4, which is fundamentally critical for guiding the precise design of advanced C3N4-related electrodes. Herein, highly crystalline C3N4 (poly (triazine imide), PTI) based all-carbon composites were developed by molten salt strategy. More importantly, the vital role of pyrrolic-N for enhancing charge transfer and boosting Na+ storage of C3N4-based composites, which was confirmed by both theoretical and experimental evidence, was spot-highlighted for the first time. By elaborately controlling the salt composition, the composite with high pyrrolic-N and minimized graphitic-N content was obtained. Profiting from the formation of highly crystalline PTI and electrochemically favorable pyrrolic-N configurations, the composite delivered an unusual reverse growth and record-level cycling stability even after 5000 cycles along with high reversible capacity and outstanding full-cell capacity retention. This work broadens the energy storage applications of C3N4 and provides new prospects for the design of advanced all-carbon electrodes.
Understanding the structural origin of the competition between oxygen 2p and transition-metal 3d orbitals in oxygen-redox (OR) layered oxides is eminently desirable for exploring reversible and high-energy-density Li/Na-ion cathodes. Here, we reveal the correlation between cationic ordering transition and OR degradation in ribbon-ordered P3-Na0.6Li0.2Mn0.8O2 via in situ structural analysis. Comparing two different voltage windows, the OR capacity can be improved approximately twofold when suppressing the in-plane cationic ordering transition. We find that the intralayer cationic migration is promoted by electrochemical reduction from Mn4+ to Jahn-Teller Mn3+ and the concomitant NaO6 stacking transformation from triangular prisms to octahedra, resulting in the loss of ribbon ordering and electrochemical decay. First-principles calculations reveal that Mn4+/Mn3+ charge ordering and alignment of the degenerate eg orbital induce lattice-level collective Jahn-Teller distortion, which favors intralayer Mn-ion migration and thereby accelerates OR degradation. These findings unravel the relationship between in-plane cationic ordering and OR reversibility and highlight the importance of superstructure protection for the rational design of reversible OR-active layered oxide cathodes.
Ruthenium (Ru) has been regarded as one of the most promising alternatives to substitute Pt for catalyzing alkaline hydrogen evolution reaction (HER), owing to its inherent high activity and being the cheapest platinum-group metal. Herein, based on the idea of strong metal-support interaction (SMSI) regulation, Ru/TiN catalysts with different degrees of TiN overlayer over Ru nanoparticles were fabricated, which were applied to the alkaline electrolytic water. Characterizations reveal that the TiN overlayer would gradually encapsulate the Ru nanoparticles and induce more electron transfer from Ru nanoparticles to TiN support by the Ru-N-Ti bond as the SMSI degree increased. Further study shows that the exposed Ru-TiN interfaces greatly promote the H2 desorption capacity. Thus, the Ru/TiN-300 with a moderate SMSI degree exhibits excellent HER performance, with an overpotential of 38 mV at 10 mA cm-2. Also, due to the encapsulation role of TiN overlayer on Ru nanoparticles, it displays super long-term stability with a very slight potential change after 24 h. This study provides a deep insight into the influence of the SMSI effect between Ru and TiN on HER and offers a novel approach for preparing efficient and stable HER electrocatalysts through SMSI engineering.
The metal-organic framework (MOF) derived Ni-Co-C-N composite alloys (NiCCZ) were “embedded” inside the carbon cloth (CC) strands as opposed to the popular idea of growing them upward to realize ultrastable energy storage and conversion application. The NiCCZ was then oxygen functionalized, facilitating the next step of stoichiometric sulfur anion diffusion during hydrothermal sulfurization, generating a flower-like metal hydroxysulfide structure (NiCCZOS) with strong partial implantation inside CC. Thus obtained NiCCZOS shows an excellent capacity when tested as a supercapacitor electrode in a three-electrode configuration. Moreover, when paired with the biomass-derived nitrogen-rich activated carbon, the asymmetric supercapacitor device shows almost 100% capacity retention even after 45,000 charge-discharge cycles with remarkable energy density (59.4 Wh kg-1/263.8 µWh cm-2) owing to a uniquely designed cathode. Furthermore, the same electrode performed as an excellent bifunctional water-splitting electrocatalyst with an overpotential of 271 mV for oxygen evolution reaction (OER) and 168.4 mV for hydrogen evolution reaction (HER) at 10 mA cm-2 current density along with 30 h of unhinged chronopotentiometric stability performance for both HER and OER. Hence, a unique metal chalcogenide composite electrode/substrate configuration has been proposed as a highly stable electrode material for flexible energy storage and conversion applications.
Utilizing supported single atoms as catalysts presents an opportunity to reduce the usage of critical raw materials such as platinum, which are essential for electrochemical reactions such as hydrogen oxidation reaction (HOR). Herein, we describe the synthesis of a Pt single electrocatalyst inside single-walled carbon nanotubes (SWCNTs) via a redox reaction. Characterizations via electron microscopy, X-ray photoelectron microscopy, and X-ray absorption spectroscopy show the single-atom nature of the Pt. The electrochemical behavior of the sample to hydrogen and oxygen was investigated using the advanced floating electrode technique, which minimizes mass transport limitations and gives a thorough insight into the activity of the electrocatalyst. The single-atom samples showed higher HOR activity than state-of-the-art 30% Pt/C while almost no oxygen reduction reaction activity in the proton exchange membrane fuel cell operating range. The selective activity toward HOR arose as the main fingerprint of the catalyst confinement in the SWCNTs.
Transition-metal oxyhydroxides are attractive catalysts for oxygen evolution reactions (OERs). Further studies for developing transition-metal oxyhydroxide catalysts and understanding their catalytic mechanisms will benefit their quick transition to the next catalysts. Herein, Mo-doped CoOOH was designed as a high-performance model electrocatalyst with durability for 20 h at 10 mA cm-2. Additionally, it had an overpotential of 260 mV (glassy carbon) or 215 mV (nickel foam), which was 78 mV lower than that of IrO2 (338 mV). In situ, Raman spectroscopy revealed the transformation process of CoOOH. Calculations using the density functional theory showed that during OER, doped Mo increased the spin-up density of states and shrank the spin-down bandgap of the 3d orbits in the reconstructed CoOOH under the electrochemical activation process, which simultaneously optimized the adsorption and electron conduction of oxygen-related intermediates on Co sites and lowered the OER overpotentials. Our research provides new insights into the methodical planning of the creation of transition-metal oxyhydroxide OER catalysts.
Metallic lithium (Li) is considered the “Holy Grail” anode material for the next-generation of Li batteries with high energy density owing to the extraordinary theoretical specific capacity and the lowest negative electrochemical potential. However, owing to inhomogeneous Li-ion flux, Li anodes undergo uncontrollable Li deposition, leading to limited power output and practical applications. Carbon materials and their composites with controllable structures and properties have received extensive attention to guide the homogeneous growth of Li to achieve high-performance Li anodes. In this review, the correlation between the behavior of Li anode and the properties of carbon materials is proposed. Subsequently, we review emerging strategies for rationally designing high-performance Li anodes with carbon materials, including interface engineering (stabilizing solid electrolyte interphase layer and other functionalized interfacial layer) and architecture design of host carbon (constructing three-dimension structure, preparing hollow structure, introducing lithiophilic sites, optimizing geometric effects, and compositing with Li). Based on the insights, some prospects on critical challenges and possible future research directions in this field are concluded. It is anticipated that further innovative works on the fundamental chemistry and theoretical research of Li anodes are needed.
Efficient photocatalytic reduction of CO2 to high-calorific-value CH4, an ideal target product, is a blueprint for C1 industry relevance and carbon neutrality, but it also faces great challenges. Herein, we demonstrate unprecedented hybrid SiC photocatalysts modified by Fe-based cocatalyst, which are prepared via a facile impregnation-reduction method, featuring an optimized local electronic structure. It exhibits a superior photocatalytic carbon-based products yield of 30.0 µmol g-1 h-1 and achieves a record CH4 selectivity of up to 94.3%, which highlights the effectiveness of electron-rich Fe cocatalyst for boosting photocatalytic performance and selectivity. Specifically, the synergistic effects of directional migration of photogenerated electrons and strong π-back bonding on low-valence Fe effectively strengthen the adsorption and activation of reactants and intermediates in the CO2 → CH4 pathway. This study inspires an effective strategy for enhancing the multielectron reduction capacity of semiconductor photocatalysts with low-cost Fe instead of noble metals as cocatalysts.