Silicon (Si) is a promising anode material for lithium-ion batteries (LIBs) owing to its tremendously high theoretical storage capacity (4200 mAh g-1), which has the potential to elevate the energy of LIBs. However, Si anodes exhibit severe volume change during lithiation/delithiation processes, resulting in anode pulverization and delamination with detrimental growth of solid electrolyte interface layers. As a result, the cycling stability of Si anodes is insufficient for commercialization in LIBs. Polymeric binders can play critical roles in Si anodes by affecting their cycling stability, although they occupy a small portion of the electrodes. This review introduces crucial factors influencing polymeric binders' properties and the electrochemical performance of Si anodes. In particular, we emphasize the structure–property relationships of binders in the context of molecular design strategy, functional groups, types of interactions, and functionalities of binders. Furthermore, binders with additional functionalities, such as electrical conductivity and self-healability, are extensively discussed, with an emphasis on the binder design principle.
Conversion of solar energy into H2 by photoelectrochemical (PEC) water splitting is recognized as an ideal way to address the growing energy crisis and environmental issues. In a typical PEC cell, the construction of photoanodes is crucial to guarantee the high efficiency and stability of PEC reactions, which fundamentally rely on rationally designed semiconductors (as the active materials) and substrates (as the current collectors). In this review work, we start with a brief introduction of the roles of substrates in the PEC process. Then, we provide a systematic overview of representative strategies for the controlled fabrication of photoanodes on rationally designed substrates, including conductive glass, metal, sapphire, silicon, silicon carbide, and flexible substrates. Finally, some prospects concerning the challenges and research directions in this area are proposed.
Phase engineering is an efficient strategy for enhancing the kinetics of electrocatalytic reactions. Herein, phase engineering was employed to prepare high-performance phosphorous-doped biphase (1T/2H) MoS2 (P-BMS) nanoflakes for hydrogen evolution reaction (HER). The doping of MoS2 with P atoms modifies its electronic structure and optimizes its electrocatalytic reaction kinetics, which significantly enhances its electrical conductivity and structural stability, which are verified by various characterization tools, including X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, X-ray absorption near-edge spectroscopy, and extended X-ray absorption fine structure. Moreover, the hierarchically formed flakes of P-BMS provide numerous catalytic surface-active sites, which remarkably enhance its HER activity. The optimized P-BMS electrocatalysts exhibit low overpotentials (60 and 72 mV at 10 mA cm-2) in H2SO4 (0.5 M) and KOH (1.0 M), respectively. The mechanism of improving the HER activity of the material was systematically studied using density functional theory calculations and various electrochemical characterization techniques. This study has shown that phase engineering is a promising strategy for enhancing the H* adsorption of metal sulfides.
Silicon (Si) is widely used as a lithium-ion-battery anode owing to its high capacity and abundant crustal reserves. However, large volume change upon cycling and poor conductivity of Si cause rapid capacity decay and poor fast-charging capability limiting its commercial applications. Here, we propose a multilevel carbon architecture with vertical graphene sheets (VGSs) grown on surfaces of subnanoscopically and homogeneously dispersed Si–C composite nanospheres, which are subsequently embedded into a carbon matrix (C/VGSs@Si–C). Subnanoscopic C in the Si–C nanospheres, VGSs, and carbon matrix form a three-dimensional conductive and robust network, which significantly improves the conductivity and suppresses the volume expansion of Si, thereby boosting charge transport and improving electrode stability. The VGSs with vast exposed edges considerably increase the contact area with the carbon matrix and supply directional transport channels through the entire material, which boosts charge transport. The carbon matrix encapsulates VGSs@Si–C to decrease the specific surface area and increase tap density, thus yielding high first Coulombic efficiency and electrode compaction density. Consequently, C/VGSs@Si–C delivers excellent Li-ion storage performances under industrial electrode conditions. In particular, the full cells show high energy densities of 603.5 Wh kg-1 and 1685.5 Wh L-1 at 0.1 C and maintain 80.7% of the energy density at 3 C.
The specific energy of Li metal batteries (LMBs) can be improved by using high-voltage cathode materials; however, achieving long-term stable cycling performance in the corresponding system is particularly challenging for the liquid electrolyte. Herein, a novel pseudo-oversaturated electrolyte (POSE) is prepared by introducing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to adjust the coordination structure between diglyme (G2) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Surprisingly, although TTE shows little solubility to LiTFSI, the molar ratio between LiTFSI and G2 in the POSE can be increased to 1:1, which is much higher than that of the saturation state, 1:2.8. Simulation and experimental results prove that TTE promotes closer contact of the G2 molecular with Li+ in the POSE. Moreover, it also participates in the formation of electrolyte/electrode interphases. The electrolyte shows outstanding compatibility with both the Li metal anode and typical high-voltage cathodes. Li||Li symmetric cells show a long life of more than 2000 h at 1 mA cm-2, 1 mAh cm-2. In the meantime, Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) cell with the POSE shows a high reversible capacity of 134.8 mAh g-1 after 900 cycles at 4.5 V, 1 C rate. The concept of POSE can provide new insight into the Li+ solvation structure and in the design of advanced electrolytes for LMBs.
The recycling of spent batteries has become increasingly important owing to their wide applications, abundant raw material supply, and sustainable development. Compared with the degraded cathode, spent anode graphite often has a relatively intact structure with few defects after long cycling. Yet, most spent graphite is simply burned or discarded due to its limited value and inferior performance on using conventional recycling methods that are complex, have low efficiency, and fail in performance restoration. Herein, we propose a fast, efficient, and “intelligent” strategy to regenerate and upcycle spent graphite based on defect-driven targeted remediation. Using Sn as a nanoscale healant, we used rapid heating (~50 ms) to enable dynamic Sn droplets to automatically nucleate around the surface defects on the graphite upon cooling owing to strong binding to the defects (~5.84 eV/atom), thus simultaneously achieving Sn dispersion and graphite remediation. As a result, the regenerated graphite showed enhanced capacity and cycle stability (458.9 mAh g-1 at 0.2 A g-1 after 100 cycles), superior to those of commercial graphite. Benefiting from the self-adaption of Sn dispersion, spent graphite with different degrees of defects can be regenerated to similar structures and performance. EverBatt analysis indicates that targeted regeneration and upcycling have significantly lower energy consumption (~99% reduction) and near-zero CO2 emission, and yield much higher profit than hydrometallurgy, which opens a new avenue for direct upcycling of spend graphite in an efficient, green, and profitable manner for sustainable battery manufacture.
The surface properties of oxidic supports and their interaction with the supported metals play critical roles in governing the catalytic activities of oxide-supported metal catalysts. When metals are supported on reducible oxides, dynamic surface reconstruction phenomena, including strong metal–support interaction (SMSI) and oxygen vacancy formation, complicate the determination of the structural–functional relationship at the active sites. Here, we performed a systematic investigation of the dynamic behavior of Au nanocatalysts supported on flame-synthesized TiO2, which takes predominantly a rutile phase, using CO oxidation above room temperature as a probe reaction. Our analysis conclusively elucidated a negative correlation between the catalytic activity of Au/TiO2 and the oxygen vacancy at the Au/TiO2 interface. Although the reversible formation and retracting of SMSI overlayers have been ubiquitously observed on Au/TiO2 samples, the catalytic consequence of SMSI remains inconclusive. Density functional theory suggests that the electron transfer from TiO2 to Au is correlated to the presence of the interfacial oxygen vacancies, retarding the catalytic activation of CO oxidation.
BiVO4 is one of the most promising photoanode materials for photoelectrochemical (PEC) solar energy conversion, but it still suffers from poor photocurrent density due to insufficient light-harvesting efficiency (LHE), weak photogenerated charge separation efficiency (ΦSep), and low water oxidation efficiency (ΦOX). Herein, we tackle these challenges of the BiVO4 photoanodes using systematic engineering, including catalysis engineering, bandgap engineering, and morphology engineering. In particular, we deposit a NiCoOx layer onto the BiVO4 photoanode as the oxygen evolution catalyst to enhance the ΦOX of Fe-g-C3N4/BiVO4 for PEC water oxidation, and incorporate Fe-doped graphite-phase C3N4 (Fe-g-C3N4) into the BiVO4 photoanode to optimize the bandgap and surface areas to subsequently expand the light absorption range of the photoanode from 530 to 690 nm, increase the LHE and ΦSep, and further improve the oxygen evolution reaction activity of the NiCoOx catalytic layer. Consequently, the maximum photocurrent density of the as-prepared NiCoOx/Fe-g-C3N4/BiVO4 is remarkably boosted from 4.6 to 7.4 mA cm-2. This work suggests that the proposed systematic engineering strategy is exceptionally promising for improving LHE, ΦSep, and ΦOX of BiVO4-based photoanodes, which will substantially benefit the design, preparation, and large-scale application of next-generation high-performance photoanodes.
Industrial CO2 electroreduction has received tremendous attentions for resolution of the current energy and environmental crisis, but its performance is greatly limited by mass transport at high current density. In this work, an ion-polymer-modified gas-diffusion electrode is used to tackle this proton limit. It is found that gas diffusion electrode-Nafion shows an impressive performance of 75.2% Faradaic efficiency in multicarbon products at an industrial current density of 1.16 A/cm2. Significantly, in-depth electrochemical characterizations combined with in situ Raman have been used to determine the full workflow of protons, and it is found that HCO3- acts as a proton pool near the reaction environment, and HCO3- and H3O+ are local proton donors that interact with the proton shuttle -SO3- from Nafion. With rich proton hopping sites that decrease the activation energy, a “Grotthuss” mechanism for proton transport in the above system has been identified rather than the “Vehicle” mechanism with a higher energy barrier. Therefore, this work could be very useful in terms of the achievement of industrial CO2 reduction fundamentally and practically.
Atomically-dispersed copper sites coordinated with nitrogen-doped carbon (Cu–N–C) can provide novel possibilities to enable highly selective and active electrochemical CO2 reduction reactions. However, the construction of optimal local electronic structures for nitrogen-coordinated Cu sites (Cu–N4) on carbon remains challenging. Here, we synthesized the Cu–N–C catalysts with atomically-dispersed edge-hosted Cu–N4 sites (Cu–N4C8) located in a micropore between two graphitic sheets via a facile method to control the concentration of metal precursor. Edge-hosted Cu–N4C8 catalysts outperformed the previously reported M–N–C catalysts for CO2-to-CO conversion, achieving a maximum CO Faradaic efficiency (FECO) of 96%, a CO current density of –8.97 mA cm–2 at –0.8 V versus reversible hydrogen electrode (RHE), and over FECO of 90% from –0.6 to –1.0 V versus RHE. Computational studies revealed that the micropore of the graphitic layer in edge-hosted Cu–N4C8 sites causes the d-orbital energy level of the Cu atom to shift upward, which in return decreases the occupancy of antibonding states in the *COOH binding. This research suggests new insights into tailoring the locally coordinated structure of the electrocatalyst at the atomic scale to achieve highly selective electrocatalytic reactions.
The photocatalytic conversion of CO2 into solar-powered fuels is viewed as a forward-looking strategy to address energy scarcity and global warming. This work demonstrated the selective photoreduction of CO2 to CO using ultrathin Bi12O17Cl2 nanosheets decorated with hydrothermally synthesized bismuth clusters and oxygen vacancies (OVs). The characterizations revealed that the coexistences of OVs and Bi clusters generated in situ contributed to the high efficiency of CO2–CO conversion (64.3 μmol g-1 h-1) and perfect selectivity. The OVs on the facet (001) of the ultrathin Bi12O17Cl2 nanosheets serve as sites for CO2 adsorption and activation sites, capturing photoexcited electrons and prolonging light absorption due to defect states. In addition, the Bi-cluster generated in situ offers the ability to trap holes and the surface plasmonic resonance effect. This study offers great potential for the construction of semiconductor hybrids as multiphotocatalysts, capable of being used for the elimination and conversion of CO2 in terms of energy and environment.
Li–CO2/O2 batteries, a promising energy storage technology, not only provide ultrahigh discharge capacity but also capture CO2 and turn it into renewable energy. Their electrochemical reaction pathways' ambiguity, however, creates a hurdle for their practical application. This study used copper selenide (CuSe) nanosheets as the air cathode medium in an environmental transmission electron microscope to in situ study Li–CO2/O2 (mix CO2 as well as O2 at a volume ratio of 1:1) and Li–O2 batteries as well as Li–CO2 batteries. Primary discharge reactions take place successively in the Li–CO2/O2–CuSe nanobattery: (I) 4Li+ + O2 + 4e- → 2Li2O; (II) Li2O + CO2 → Li2CO3. The charge reaction proceeded via (III) 2Li2CO3 → 4Li+ + 2CO2 + O2 + 4e-. However, Li–O2 and Li–CO2 nanobatteries showed poor cycling stability, suggesting the difficulty in the direct decomposition of the discharge product. The fluctuations of the Li–CO2/O2 battery's electrochemistry were also shown to depend heavily on O2. The CuSe-based Li–CO2/O2 battery showed exceptional electrochemical performance. The Li–CO2/O2 battery offered a discharge capacity apex of 15,492 mAh g-1 and stable cycling 60 times at 100 mA g-1. Our research offers crucial insight into the electrochemical behavior of Li–CO2/O2, Li–O2, and Li–CO2 nanobatteries, which may help the creation of high-performance Li–CO2/O2 batteries for energy storage applications.
The supercritical CO2 (sCO2) power cycle could improve efficiencies for a wide range of thermal power plants. The sCO2 turbine generator plays an important role in the sCO2 power cycle by directly converting thermal energy into mechanical work and electric power. The operation of the generator encounters challenges, including high temperature, high pressure, high rotational speed, and other engineering problems, such as leakage. Experimental studies of sCO2 turbines are insufficient because of the significant difficulties in turbine manufacturing and system construction. Unlike most experimental investigations that primarily focus on 100 kW- or MW-scale power generation systems, we consider, for the first time, a small-scale power generator using sCO2. A partial admission axial turbine was designed and manufactured with a rated rotational speed of 40,000 rpm, and a CO2 transcritical power cycle test loop was constructed to validate the performance of our manufactured generator. A resistant gas was proposed in the constructed turbine expander to solve the leakage issue. Both dynamic and steady performances were investigated. The results indicated that a peak electric power of 11.55 kW was achieved at 29,369 rpm. The maximum total efficiency of the turbo-generator was 58.98%, which was affected by both the turbine rotational speed and pressure ratio, according to the proposed performance map.
Iron-based pyrophosphates are attractive cathodes for sodium-ion batteries due to their large framework, cost-effectiveness, and high energy density. However, the understanding of the crystal structure is scarce and only a limited candidates have been reported so far. In this work, we found for the first time that a continuous solid solution, Na4-αFe2+α/2(P2O7)2 (0 ≤ α ≤ 1, could be obtained by mutual substitution of cations at center-symmetric Na3 and Na4 sites while keeping the crystal building blocks of anionic P2O7 unchanged. In particular, a novel off-stoichiometric Na3Fe2.5(P2O7)2 is thus proposed, and its structure, energy storage mechanism, and electrochemical performance are extensively investigated to unveil the structure–function relationship. The as-prepared off-stoichiometric electrode delivers appealing performance with a reversible discharge capacity of 83 mAh g-1, a working voltage of 2.9 V (vs. Na+/Na), the retention of 89.2% of the initial capacity after 500 cycles, and enhanced rate capability of 51 mAh g-1 at a current density of 1600 mA g-1. This research shows that sodium ferric pyrophosphate could form extended solid solution composition and promising phase is concealed in the range of Na4-αFe2+α/2(P2O7)2, offering more chances for exploration of new cathode materials for the construction of high-performance SIBs.
Graphitic carbon nitride (g-C3N4) is a highly recognized two-dimensional semiconductor material known for its exceptional chemical and physical stability, environmental friendliness, and pollution-free advantages. These remarkable properties have sparked extensive research in the field of energy storage. This review paper presents the latest advances in the utilization of g-C3N4 in various energy storage technologies, including lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, potassium-ion batteries, and supercapacitors. One of the key strengths of g-C3N4 lies in its simple preparation process along with the ease of optimizing its material structure. It possesses abundant amino and Lewis basic groups, as well as a high density of nitrogen, enabling efficient charge transfer and electrolyte solution penetration. Moreover, the graphite-like layered structure and the presence of large π bonds in g-C3N4 contribute to its versatility in preparing multifunctional materials with different dimensions, element and group doping, and conjugated systems. These characteristics open up possibilities for expanding its application in energy storage devices. This article comprehensively reviews the research progress on g-C3N4 in energy storage and highlights its potential for future applications in this field. By exploring the advantages and unique features of g-C3N4, this paper provides valuable insights into harnessing the full potential of this material for energy storage applications.
