Currently, the major challenge in terms of research on K-ion batteries is to ensure that they possess satisfactory cycle stability and specific capacity, especially in terms of the intrinsically sluggish kinetics induced by the large radius of K+ ions. Here, we explore high-performance K-ion half/full batteries with high rate capability, high specific capacity, and extremely durable cycle stability based on carbon nanosheets with tailored N dopants, which can alleviate the change of volume, increase electronic conductivity, and enhance the K+ ion adsorption. The as-assembled K-ion half-batteries show an excellent rate capability of 468 mA h g−1 at 100 mA g−1, which is superior to those of most carbon materials reported to date. Moreover, the as-assembled half-cells have an outstanding life span, running 40,000 cycles over 8 months with a specific capacity retention of 100% at a high current density of 2000 mA g−1, and the target full cells deliver a high reversible specific capacity of 146 mA h g−1 after 2000 cycles over 2 months, with a specific capacity retention of 113% at a high current density of 500 mA g−1, both of which are state of the art in the field of K-ion batteries. This study might provide some insights into and potential avenues for exploration of advanced K-ion batteries with durable stability for practical applications.
The commercialization of a polymer membrane H2–O2 fuel cell and its widespread use call for the development of cost-effective oxygen reduction reaction (ORR) nonplatinum group metal (NPGM) catalysts. Nevertheless, to meet the requests for the real-world fuel cell application and replacing platinum catalysts, it still needs to address some challenges for NPGM catalysts regarding the sluggish ORR kinetics in the cathode and their poor durability in acidic environment. In response to these issues, numerous efforts have been made to study NPGM catalysts both theoretically and experimentally, developed these into the atomically dispersed coordinated metal–nitrogen–carbon (M–N–C) form over the past decades. In this review, we present a comprehensive summary of recent advancements on NPGM catalysts with high activity and durability. Catalyst design strategies in terms of optimizing active-site density and enhancing catalyst stability against demetalization and carbon corrosion are highlighted. It is also emphasized the importance of understanding the mechanisms and principles behind those strategies through a combination of theoretical modeling and experimental work. Especially, further understanding the mechanisms related to the active-site structure and the formation process of the single-atom active site under pyrolysis conditions is critical for active-site engineering. Optimizing the active-site distance is the basic principle for improving catalyst activity through increasing the catalyst active-site density. Theoretical studies for the catalyst deactivation mechanism and modeling stable active-site structures provide both mechanisms and principles to improve the NPGM catalyst durability. Finally, currently remained challenges and perspectives in the future on designing high-performance atomically dispersed NPGM catalysts toward fuel cell application are discussed.
Enhancing both the number of active sites available and the intrinsic activity of Co-based electrocatalysts simultaneously is a desirable goal. Herein, a ZIF-67-derived hierarchical porous cobalt sulfide decorated by Au nanoparticles (NPs) (denoted as HP-Au@CoxSy@ZIF-67) hybrid is synthesized by low-temperature sulfuration treatment. The well-defined macroporous–mesoporous–microporous structure is obtained based on the combination of polystyrene spheres, as-formed CoxSy nanosheets, and ZIF-67 frameworks. This novel three-dimensional hierarchical structure significantly enlarges the three-phase interfaces, accelerating the mass transfer and exposing the active centers for oxygen evolution reaction. The electronic structure of Co is modulated by Au through charge transfer, and a series of experiments, together with theoretical analysis, is performed to ascertain the electronic modulation of Co by Au. Meanwhile, HP-Au@CoxSy@ZIF-67 catalysts with different amounts of Au were synthesized, wherein Au and NaBH4 reductant result in an interesting “competition effect” to regulate the relative ratio of Co2+/Co3+, and moderate Au assists the electrochemical performance to reach the highest value. Consequently, the optimized HP-Au@CoxSy@ZIF-67 exhibits a low overpotential of 340 mV at 10 mA cm–2 and a Tafel slope of 42 mV dec–1 for OER in 0.1 M aqueous KOH, enabling efficient water splitting and Zn–air battery performance. The work here highlights the pivotal roles of both microstructural and electronic modulation in enhancing electrocatalytic activity and presents a feasible strategy for designing and optimizing advanced electrocatalysts.
Photoinduced intermolecular charge transfer (PICT) determines the voltage loss in bulk heterojunction (BHJ) organic photovoltaics (OPVs), and this voltage loss can be minimized by inducing efficient PICT, which requires energy-state matching between the donor and acceptor at the BHJ interfaces. Thus, both geometrically and energetically accessible delocalized state matching at the hot energy level is crucial for achieving efficient PICT. In this study, an effective method for quantifying the hot state matching of OPVs was developed. The degree of energy-state matching between the electron donor and acceptor at BHJ interfaces was quantified using a mismatching factor (MF) calculated from the modified optical density of the BHJ. Furthermore, the correlation between the open-circuit voltage (Voc) of the OPV device and energy-state matching at the BHJ interface was investigated using the calculated MF. The OPVs with small absolute MF values exhibited high Voc values. This result clearly indicates that the energy-state matching between the donor and acceptor is crucial for achieving a high Voc in OPVs. Because the MF indicates the degree of energy-state matching, which is a critical factor for suppressing energy loss, it can be used to estimate the Voc loss in OPVs.
MXene is a promising energy storage material for miniaturized microbatteries and microsupercapacitors (MSCs). Despite its superior electrochemical performance, only a few studies have reported MXene-based ultrahigh-rate (>1000 mV s−1) on-paper MSCs, mainly due to the reduced electrical conductance of MXene films deposited on paper. Herein, ultrahigh-rate metal-free on-paper MSCs based on heterogeneous MXene/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)-stack electrodes are fabricated through the combination of direct ink writing and femtosecond laser scribing. With a footprint area of only 20 mm2, the on-paper MSCs exhibit excellent high-rate capacitive behavior with an areal capacitance of 5.7 mF cm−2 and long cycle life (>95% capacitance retention after 10,000 cycles) at a high scan rate of 1000 mV s−1, outperforming most of the present on-paper MSCs. Furthermore, the heterogeneous MXene/PEDOT:PSS electrodes can interconnect individual MSCs into metal-free on-paper MSC arrays, which can also be simultaneously charged/discharged at 1000 mV s−1, showing scalable capacitive performance. The heterogeneous MXene/PEDOT:PSS stacks are a promising electrode structure for on-paper MSCs to serve as ultrafast miniaturized energy storage components for emerging paper electronics.
Electrocatalytic CO2-to-formate conversion is considered an economically viable process. In general, Zn-based nanomaterials are well-known to be highly efficient electrocatalysts for the conversion of CO2 to CO, but seldom do they exhibit excellent selectivity toward formate. In this article, we demonstrate that a heterointerface catalyst ZnO/ZnSnO3 with nanosheet morphology shows enhanced selectivity with a maximum Faradaic efficiency (FE) of 86% at −0.9 V versus reversible hydrogen electrode and larger current density for the conversion of CO2 to formate than pristine ZnO and ZnSnO3. In particular, the FEs of the C1 products (CO + HCOO−) exceed 98% over the potential window. The experimental measurements combined with theoretical calculations revealed that the ZnO in ZnO/ZnSnO3 heterojunction delivers the valence electron depletion and accordingly optimizes Zn d-band center, which results in moderate Zn–O hybridization of HCOO* and weakened Zn–C hybridization of competing COOH*, thus greatly boosting the HCOOH generation. Our study highlights the importance of charge redistribution in catalysts on the selectivity of electrochemical CO2 reduction.
Porous aromatic framework 1 (PAF-1) is an extremely representative nanoporous organic framework owing to its high stability and exceptionally high surface area. Currently, the synthesis of PAF-1 is catalyzed by the Ni(COD)2/COD/bpy system, suffering from great instability and high cost. Herein, we developed an in situ reduction of the Ni(II) catalytic system to synthesize PAF-1 in low cost and high yield. The active Ni(0) species produced from the NiCl2/bpy/NaI/Mg catalyst system can effectively catalyze homocoupling of tetrakis(4-bromophenyl)methane at the room temperature to form PAF-1 with high Brunauer–Emmett–Teller (BET)-specific surface area up to 4948 m2 g−1 (Langmuir surface area, 6785 m2 g−1). The possible halogen exchange and dehalogenation coupling mechanisms for this new catalytic process in PAF's synthesis are discussed in detail. The efficiency and universality of this innovative catalyst system have also been demonstrated in other PAFs' synthesis. This work provides a cheap, facile, and efficient method for scalable synthesis of PAFs and explores their application for high-pressure storage of Xe and Kr.
Fe-based Prussian blue (Fe-PB) cathode material shows great application potential in sodium (Na)-ion batteries due to its high theoretical capacity, long cycle life, low cost, and simple preparation process. However, the crystalline water and vacancies of Fe-PB lattice, the low electrical conductivity, and the dissolution of metal ions lead to limited capacity and poor cycling stability. In this work, a perylene tetracarboxylic dianhydride amine (PTCDA) coating layer is successfully fabricated on the surface of Fe-PB by a liquid-phase method. The aminated PTCDA (PTCA) coating not only increases the specific surface area and electronic conductivity but also effectively reduces the crystalline water and vacancies, which avoids the erosion of Fe-PB by electrolyte. Consequently, the PTCA layer reduces the charge transfer resistance, enhances the Na-ion diffusion coefficient, and improves the structure stability. The PTCA-coated Fe-PB exhibits superior Na storage performance with a first discharge capacity of 145.2 mAh g−1 at 100 mA g−1. Long cycling tests exhibit minimal capacity decay of 0.027% per cycle over 1000 cycles at 1 A g−1. Therefore, this PTCA coating strategy has shown promising competence in enhancing the electrochemical performance of Fe-PB, which can potentially serve as a universal electrode coating strategy for Na-ion batteries.
We investigated the role of metal atomization and solvent decomposition into reductive species and carbon clusters in the phase formation of transition-metal carbides (TMCs; namely, Co3C, Fe3C, TiC, and MoC) by pulsed laser ablation of Co, Fe, Ti, and Mo metals in acetone. The interaction between carbon s–p-orbitals and metal d-orbitals causes a redistribution of valence structure through charge transfer, leading to the formation of surface defects as observed by X-ray photoelectron spectroscopy. These defects influence the evolved TMCs, making them effective for hydrogen and oxygen evolution reactions (HER and OER) in an alkaline medium. Co3C with more oxygen affinity promoted CoO(OH) intermediates, and the electrochemical surface oxidation to Co3O4 was captured via in situ/operando electrochemical Raman probes, increasing the number of active sites for OER activity. MoC with more d-vacancies exhibits strong hydrogen binding, promoting HER kinetics, whereas Fe3C and TiC with more defect states to trap charge carriers may hinder both OER and HER activities. The results show that the assembled membrane-less electrolyzer with Co3C‖Co3C and MoC‖MoC electrodes requires ~2.01 and 1.99 V, respectively, to deliver a 10 mA cm−2 with excellent electrochemical and structural stability. In addition, the ascertained pulsed laser synthesis mechanism and unit-cell packing relations will open up sustainable pathways for obtaining highly stable electrocatalysts for electrolyzers.
Layered-type transition metal (TM) oxides are considered as one of the most promising cathodes for K-ion batteries because of the large theoretical gravimetric capacity by low molar mass. However, they suffer from severe structural change by de/intercalation and diffusion of K+ ions with large ionic size, which results in not only much lower reversible capacity than the theoretical capacity but also poor power capability. Thus, it is important to enhance the structural stability of the layered-type TM oxides for outstanding electrochemical behaviors under the K-ion battery system. Herein, it is investigated that the substitution of the appropriate Ti4+ contents enables a highly enlarged reversible capacity of P3-type KxCrO2 using combined studies of first-principles calculation and various experiments. Whereas the pristine P3-type KxCrO2 just exhibits the reversible capacity of ~120 mAh g−1 in the voltage range of 1.5–4.0 V (vs. K+/K), the ~0.61 mol K+ corresponding to ~150 mAh g−1 can be reversible de/intercalated at the structure of P3-type K0.71[Cr0.75Ti0.25]O2 under the same conditions. Furthermore, even at the high current density of 788 mA g−1, the specific capacity of P3-type K0.71[Cr0.75Ti0.25]O2 is ~120 mAh g−1, which is ~81 times larger than that of the pristine P3-type KxCrO2. It is believed that this research can provide an effective strategy to improve the electrochemical performances of the cathode materials suffered by severe structural change that occurred during charge/discharge under not only K-ion battery system but also other rechargeable battery systems.
The use of lithium–sulfur batteries under high sulfur loading and low electrolyte concentrations is severely restricted by the detrimental shuttling behavior of polysulfides and the sluggish kinetics in redox processes. Two-dimensional (2D) few layered black phosphorus with fully exposed atoms and high sulfur affinity can be potential lithium–sulfur battery electrocatalysts, which, however, have limitations of restricted catalytic activity and poor electrochemical/chemical stability. To resolve these issues, we developed a multifunctional metal-free catalyst by covalently bonding few layered black phosphorus nanosheets with nitrogen-doped carbon-coated multiwalled carbon nanotubes (denoted c-FBP-NC). The experimental characterizations and theoretical calculations show that the formed polarized P–N covalent bonds in c-FBP-NC can efficiently regulate electron transfer from NC to FBP and significantly promote the capture and catalysis of lithium polysulfides, thus alleviating the shuttle effect. Meanwhile, the robust 1D-2D interwoven structure with large surface area and high porosity allows strong physical confinement and fast mass transfer. Impressively, with c-FBP-NC as the sulfur host, the battery shows a high areal capacity of 7.69 mAh cm−2 under high sulfur loading of 8.74 mg cm−2 and a low electrolyte/sulfur ratio of 5.7 μL mg−1. Moreover, the assembled pouch cell with sulfur loading of 4 mg cm−2 and an electrolyte/sulfur ratio of 3.5 μL mg−1 shows good rate capability and outstanding cyclability. This work proposes an interfacial and electronic structure engineering strategy for fast and durable sulfur electrochemistry, demonstrating great potential in lithium–sulfur batteries.
The demand for lithium-ion batteries (LIBs) is driven largely by their use in electric vehicles, which is projected to increase dramatically in the future. This great success, however, urgently calls for the efficient recycling of LIBs at the end of their life. Herein, we describe a froth flotation-based process to recycle graphite—the predominant active material for the negative electrode—from spent LIBs and investigate its reuse in newly assembled LIBs. It has been found that the structure and morphology of the recycled graphite are essentially unchanged compared to pristine commercial anode-grade graphite, and despite some minor impurities from the recycling process, the recycled graphite provides a remarkable reversible specific capacity of more than 350 mAh g−1. Even more importantly, newly assembled graphite‖NMC532 cells show excellent cycling stability with a capacity retention of 80% after 1000 cycles, that is, comparable to the performance of reference full cells comprising pristine commercial graphite.
Metal-organic frameworks recently have been burgeoning and used as precursors to obtain various metal–nitrogen–carbon catalysts for oxygen reduction reaction (ORR). Although rarely studied, Mn–N–C is a promising catalyst for ORR due to its weak Fenton reaction activity and strong graphitization catalysis. Here, we developed a facile strategy for anchoring the atomically dispersed nitrogen-coordinated single Mn sites on carbon nanosheets (MnNCS) from an Mn-hexamine coordination framework. The atomically dispersed Mn–N4 sites were dispersed on ultrathin carbon nanosheets with a hierarchically porous structure. The optimized MnNCS displayed an excellent ORR performance in half-cells (0.89 V vs. reversible hydrogen electrode (RHE) in base and 0.76 V vs. RHE in acid in half-wave potential) and Zn–air batteries (233 mW cm−2 in peak power density), along with significantly enhanced stability. Density functional theory calculations further corroborated that the Mn–N4–C12 site has favorable adsorption of *OH as the rate-determining step. These findings demonstrate that the metal-hexamine coordination framework can be used as a model system for the rational design of highly active atomic metal catalysts for energy applications.
SnO2 has been extensively investigated as an anode material for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) due to its high Na/K storage capacity, high abundance, and low toxicity. However, the sluggish reaction kinetics, low electronic conductivity, and large volume changes during charge and discharge hinder the practical applications of SnO2-based electrodes for SIBs and PIBs. Engineering rational structures with fast charge/ion transfer and robust stability is important to overcoming these challenges. Herein, S-doped SnO2 (S–SnO2) quantum dots (QDs) (≈3 nm) encapsulated in an N, S codoped carbon fiber networks (S–SnO2–CFN) are rationally fabricated using a sequential freeze-drying, calcination, and S-doping strategy. Experimental analysis and density functional theory calculations reveal that the integration of S–SnO2 QDs with N, S codoped carbon fiber network remarkably decreases the adsorption energies of Na/K atoms in the interlayer of SnO2–CFN, and the S doping can increase the conductivity of SnO2, thereby enhancing the ion transfer kinetics. The synergistic interaction between S–SnO2 QDs and N, S codoped carbon fiber network results in a composite with fast Na+/K+ storage and extraordinary long-term cyclability. Specifically, the S–SnO2–CFN delivers high rate capacities of 141.0 mAh g−1 at 20 A g−1 in SIBs and 102.8 mAh g−1 at 10 A g−1 in PIBs. Impressively, it delivers ultra-stable sodium storage up to 10,000 cycles at 5 A g−1 and potassium storage up to 5000 cycles at 2 A g−1. This study provides insights into constructing metal oxide-based carbon fiber network structures for high-performance electrochemical energy storage and conversion devices.
Ammonia serves as a crucial chemical raw material and hydrogen energy carrier. Aqueous electrocatalytic nitrogen reduction reaction (NRR), powered by renewable energy, has attracted tremendous interest during the past few years. Although some achievements have been revealed in aqueous NRR, significant challenges have also been identified. The activity and selectivity are fundamentally limited by nitrogen activation and competitive hydrogen evolution. This review focuses on the hurdles of nitrogen activation and delves into complementary strategies, including materials design and system optimization (reactor, electrolyte, and mediator). Then, it introduces advanced interdisciplinary technologies that have recently emerged for nitrogen activation using high-energy physics such as plasma and triboelectrification. With a better understanding of the corresponding reaction mechanisms in the coming years, these technologies have the potential to be extended in further applications. This review provides further insight into the reaction mechanisms of selectivity and stability of different reaction systems. We then recommend a rigorous and detailed protocol for investigating NRR performance and also highlight several potential research directions in this exciting field, coupling with advanced interdisciplinary applications, in situ/operando characterizations, and theoretical calculations.
