Lithium-sulfur (Li-S) batteries are highly regarded as the next-generation high-energy-density secondary batteries due to their high capacity and large theoretical energy density. However, the practical application of these batteries is hindered mainly by the polysulfide shuttle issue. Herein, we designed and synthesized a new lithium sulfonylimide covalent organic framework (COF) material (COF-LiSTFSI, LiSTFSI = lithium (4-styrenesulfonyl) (trifluoromethanesulfonyl)imide), and further used it to modify the common polypropylene (PP) separator of Li-S batteries. The COF-LiSTFSI with sulfonylimide anion groups features stronger electronegativity, thus can effectively facilitate the lithium ion conduction while significantly suppress the diffusion of polysulfides via the electrostatic interaction. Compared with the unmodified PP separator, the COF-LiSTFSI modified separator results in a high ionic conductivity (1.50 mS·cm⁻¹) and Li⁺ transference number (0.68). Consequently, the Li-S battery using the COF-LiSTFSI modified separator achieves a high capacity of 1229.7 mAh·g⁻¹ at 0.2 C and a low decay rate of only 0.042% per cycle after 1000 cycles at 1 C, compared with those of 941.5 mAh·g⁻¹ and 0.061% using the unmodified PP separator, respectively. These results indicate that by choosing suitable functional groups, an effective strategy for COF-modified separators could be developed for high-performance Li-S batteries.

Co-free Li-rich Mn-based layered oxides are promising candidates for next-generation lithium-ion batteries (LIBs) due to their high specific capacity, high voltage, and low cost. However, their commercialization is hindered by limited cycle life and poor rate performance. Herein, an in-situ simple and low-cost strategy with a nanoscale double-layer architecture of lithium polyphosphate (LiPP) and spinel phase covered on top of the bulk layered phase, is developed for Li_1.2Mn_0.6Ni_0.2O₂ (LMNO) using Li⁺-conductor LiPP (denoted as LMNO@S-LiPP). With such a double-layer covered architecture, the half-cell of LMNO@S-LiPP delivers an extremely high capacity of 202.5 mAh·g⁻¹ at 1 A·g⁻¹ and retains 85.3% of the initial capacity after 300 cycles, so far, the best high-rate electrochemical performance of all the previously reported LMNOs. The energy density of the full-cell assembled with commercial graphite reaches 620.9 Wh·kg⁻¹ (based on total weight of active materials in cathode and anode). Mechanism studies indicate that the superior electrochemical performance of LMNO@S-LiPP is originated from such a nanoscale double-layer covered architecture, which accelerates Li-ion diffusion, restrains oxygen release, inhibits interfacial side reactions, and suppresses structural degradation during cycling. Moreover, this strategy is applicable for other high-energy-density cathodes, such as LiNi_0.8Co_0.1Mn_0.1O₂, Li_1.2Ni_0.13Co_0.13Mn_0.54O₂, and LiCoO₂. Hence, this work presents a simple, cost-effective, and scalable strategy for the development of high-performance cathode materials.

Covalent organic frameworks (COFs) have been broadly investigated for energy storage systems. However, many COF-based anode materials suffer from low utilization of redox-active sites and sluggish ions/electrons transport caused by their densely stacked layers. Thus, it is still a great challenge to obtain COF-based anode materials with fast ions/electrons transport and thus superior rate performance. Herein, a redox-active piperazine-terephthalaldehyde (PA-TA) COF with ultra-large interlayer distance is designed and synthesized for high-rate anode material, which contains piperazine units adopting a chair-shaped conformation with the nonplanar linkages of a tetrahedral configuration. This unique structure renders PA-TA COF an ultra-large interlayer distance of 6.2 Å, and further enables it to achieve outstanding rate and cycling performance. With a high specific capacity of 543 mAh·g⁻¹ even after 400 cycles at 1.0 A·g⁻¹, it still could afford a specific capacity of 207 mAh·g⁻¹ even at a high current density of 5.0 A·g⁻¹. Our study indicates that expanding the interlayer distance of COFs by rational molecular design would be of great importance to develop high-rate electrode materials for lithium-ion batteries.

Design and synthesis of efficient photocatalysts for hydrogen production via water splitting are of great importance from both theoretical and practical viewpoints. Many metal-based semiconductors have been explored for this purpose in recent decades. Here, for the first time, an entirely carbon-based material, bulk three-dimensionally cross-linked graphene (3DG), has been developed as a photocatalyst for hydrogen production. It exhibits a remarkable hydrogen production rate of 270 μmol·h⁻¹·g_cat⁻¹ under full-spectrum light via a hot/free electron emission mechanism. Furthermore, when combined with the widely used semiconductor TiO₂ to form a TiO₂/3DG composite, it appears to become a more efficient hydrogen production photocatalyst. The composite achieves a production rate of 1, 205 μmol·h⁻¹·g_cat⁻¹ under ultraviolet–visible (UV–vis) light and a 7.2% apparent quantum efficiency at 350 nm due to the strong synergetic effects between TiO₂ and 3DG.

There is a growing demand for hybrid supercapacitor systems to overcome the energy density limitation of existing-generation electric double layer capacitors (EDLCs), leading to next generation-Ⅱ supercapacitors with minimum sacrifice in power density and cycle life. Here, an advanced graphene-based hybrid system, consisting of a graphene-inserted Li₄Ti₅O₁₂ (LTO) composite anode (G–LTO) and a three-dimensional porous graphene–sucrose cathode, has been fabricated for the purpose of combining both the benefits of Li-ion batteries (energy source) and supercapacitors (power source). Graphene-based materials play a vital role in both electrodes in respect of the high performance of the hybrid supercapacitor. For example, compared with the theoretical capacity of 175 mA·h·g^–1 for pure LTO, the G–LTO nanocomposite delivered excellent reversible capacities of 207, 190, and 176 mA·h·g^–1 at rates of 0.3, 0.5, and 1 C, respectively, in the potential range 1.0–2.5 V vs. Li/Li⁺; these are among the highest values for LTO-based nanocomposites at the same rates and potential range. Based on this, an optimized hybrid supercapacitor was fabricated following the standard industry procedure; this displayed an ultrahigh energy density of 95 Wh·kg^–1 at a rate of 0.4 C (2.5 h) over a wide voltage range (0–3 V), and still retained an energy density of 32 Wh·kg^–1 at a high rate of up to 100 C, equivalent to a full discharge in 36 s, which is exceptionally fast for hybrid supercapacitors. The excellent performance of this Li-ion hybrid supercapacitor indicates that graphene-based materials may indeed play a significant role in next-generation supercapacitors with excellent electrochemical performance.

Graphene mesh electrodes (GMEs) with good conductivity and transparency have been fabricated by the standard industrial photolithography and O₂ plasma etching process using graphene solutions. Organic photovoltaic (OPV) cells using GMEs as the transparent electrodes with a blend of poly-(3-hexylthiophene)/phenyl-C₆₁-butyric acid methyl ester (P3HT/PC₆₁BM) as the active layer have been fabricated and exhibit a power conversion efficiency (PCE) of 2.04%, the highest PCE for solution-processed graphene transparent electrode-based solar cells reported to date.

A series of inkjet printing processes have been studied using graphene-based inks. Under optimized conditions, using water-soluble single-layered graphene oxide (GO) and few-layered graphene oxide (FGO), various high image quality patterns could be printed on diverse flexible substrates, including paper, poly(ethylene terephthalate) (PET) and polyimide (PI), with a simple and low-cost inkjet printing technique. The graphene-based patterns printed on plastic substrates demonstrated a high electrical conductivity after thermal reduction, and more importantly, they retained the same conductivity over severe bending cycles. Accordingly, flexible electric circuits and a hydrogen peroxide chemical sensor were fabricated and showed excellent performances, demonstrating the applications of this simple and practical. The results show that graphene materials—which can be easily produced on a large scale and possess outstanding electronic properties—have great potential for the convenient fabrication of flexible and low-cost graphene-based electronic devices, by using a simple inkjet printing technique.

Flexible organic field-effect transistors (OFETs) using solution-processable functionalized graphene for all the electrodes (source, drain, and gate) have been fabricated for the first time. These OFETs show performance comparable to corresponding devices using Au electrodes as the source/drain electrodes on SiO₂/Si substrates with Si as the gate electrode. Also, these devices demonstrate excellent flexibility without performance degradation over severe bending cycles. Furthermore, inverter circuits have been designed and fabricated using these all-graphene-electrode OFETs. Our results demonstrate that the long-sought dream for all-carbon and flexible electronics is now much closer to reality.

An arc-discharge method using a buffer gas containing carbon dioxide has been developed for the efficient and large-scale synthesis of few-layered graphene. The resulting samples of few-layered graphene, well-dispersed in organic solvents such as N, N-dimethylformamide (DMF) and 1, 2-dichlorobenzene (o-DCB), were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), and thermal gravimetric analysis (TGA). The electrical conductivity and transparency of flexible films prepared using a direct solution process have also been studied.

A novel hybrid material prepared from graphene and poly (3, 4-ethyldioxythiophene) (PEDOT) shows excellent transparency, electrical conductivity, and good flexibility, together with high thermal stability and is easily processed in both water and organic solvents. Conductivities of the order of 0.2 S/cm and light transmittance of greater than 80% in the 400–1800 nm wavelength range were observed for films with thickness of tens of nm. Practical applications in a variety of optoelectronic devices are thus expected for this transparent and flexible conducting graphene-based hybrid material.