Recent advances in nanomaterial-stabilized pickering foam: Mechanism, classification, properties, and applications.

Pickering foam is a type of foam stabilized by solid particles known as Pickering stabilizers. These solid stabilizers adsorb at the liquid-gas interface, providing superior stability to the foam. Because of its high stability, controllability, versatility, and minimal environmental impact, nanomaterial-stabilized Pickering foam has opened up new possibilities and development prospects for foam applications. This review provides an overview of the current state of development of Pickering foam stabilized by a wide range of nanomaterials, including cellulose nanomaterials, chitin nanomaterials, silica nanoparticles, protein nanoparticles, clay mineral, carbon nanotubes, calcium carbonate nanoparticles, MXene, and graphene oxide nanosheets. Particularly, the preparation and surface modification methods of various nanoparticles, the fundamental properties of nanomaterial-stabilized Pickering foam, and the synergistic effects between nanoparticles and surfactants, functional polymers, and other additives are systematically introduced. In addition, the latest progress in the application of nanomaterial-stabilized Pickering foam in the oil industry, food industry, porous functional material, and foam flotation field is highlighted. Finally, the future prospects of nanomaterial-stabilized Pickering foam in different fields, along with directions for further research and development directions, are outlined.

Electrochemical Hydrophobic Tri-layer Interface Rendered Mechanically Graded Solid Electrolyte Interface for Stable Zinc Metal Anode.

The aqueous zinc-ion battery is promising as grid scale energy storage device, but hindered by the instable electrode/electrolyte interface. Herein, we report the lean-water ionic liquid electrolyte for aqueous zinc metal batteries. The lean-water ionic liquid electrolyte creates the hydrophobic tri-layer interface assembled by first two layers of hydrophobic OTF- and EMIM+ and third layer of loosely attached water, beyond the classical Gouy-Chapman-Stern theory based electrochemical double layer. By taking advantage of the hydrophobic tri-layer interface, the lean-water ionic liquid electrolyte enables a wide electrochemical working window (2.93 V) with relatively high zinc ion conductivity (17.3 mS/cm). Furthermore, the anion crowding interface facilitates the OTF- decomposition chemistry to create the mechanically graded solid electrolyte interface layer to simultaneously suppress the dendrite formation and maintain the mechanical stability. In this way, the lean-water based ionic liquid electrolyte realizes the ultralong cyclability of over 10000 cycles at 20 A/g and at practical condition of N/P ratio of 1.5, the cumulated areal capacity reach 1.8 Ah/cm2 , which outperforms the state-of-the-art zinc metal battery performance. Our work highlights the importance of the stable electrode/electrolyte interface stability, which would be practical for building high energy grid scale zinc-ion battery.

Deploying Cationic Cellulose Nanofiber Confinement to Enable High Iodine Loadings Towards High Energy and High-Temperature Zn-I2 Battery.

High iodine loading and high-temperature adaptability of the iodine cathode are prerequisites to achieving high energy density at full battery level and promoting the practical application for the zinc-iodine (Zn-I2 ) battery. However, it would aggravate the polyiodide shuttle effect when employing high iodine loading and working temperature. Here, a sustainable cationic cellulose nanofiber (cCNF) was employed to confine the active iodine species through strong physiochemical adsorption to enlarge the iodine loading and stabilize it even at high temperatures. The cCNF could accommodate dual-functionality by enlarging the iodine loading and suppressing the polyiodide shuttle effect, owing to the unique framework structure with abundant surface positive charges. As a result, the iodine cathode based on the cCNF could deliver high iodine mass loading of 14.1 mg cm-2 with a specific capacity of 182.7 mAh g-1 , high areal capacity of 2.6 mAh cm-2 , and stable cycling over 3000 cycles at 2 A g-1 , thus enabling a high energy density of 34.8 Wh kg-1 and the maximum power density of 521.2 W kg-1 at a full Zn-I2 battery level. In addition, even at a high temperature of 60 °C, the Zn-I2 battery could still deliver a stable cycling.

Fluoride-Rich, Organic-Inorganic Gradient Interphase Enabled by Sacrificial Solvation Shells for Reversible Zinc Metal Batteries.

Zinc metal batteries are strongly hindered by water corrosion, as solvated zinc ions would bring the active water molecules to the electrode/electrolyte interface constantly. Herein, we report a sacrificial solvation shell to repel active water molecules from the electrode/electrolyte interface and assist in forming a fluoride-rich, organic-inorganic gradient solid electrolyte interface (SEI) layer. The simultaneous sacrificial process of methanol and Zn(CF3SO3)2 results in the gradient SEI layer with an organic-rich surface (CH2OC- and C5 product) and an inorganic-rich (ZnF2) bottom, which combines the merits of fast ion diffusion and high flexibility. As a result, the methanol additive enables corrosion-free zinc stripping/plating on copper foils for 300 cycles with an average coulombic efficiency of 99.5%, a record high cumulative plating capacity of 10 A h/cm2 at 40 mA/cm2 in Zn/Zn symmetrical batteries. More importantly, at an ultralow N/P ratio of 2, the practical VO2//20 µm thick Zn plate full batteries with a high areal capacity of 4.7 mAh/cm2 stably operate for over 250 cycles, establishing their promising application for grid-scale energy storage devices. Furthermore, directly utilizing the 20 µm thick Zn for the commercial-level areal capacity (4.7 mAh/cm2) full zinc battery in our work would simplify the manufacturing process and boost the development of the commercial zinc battery for stationary storage.

Dynamic Regulation of the Interfacial pH for Highly Reversible Aqueous Zinc Ion Batteries.

An electrolyte additive, with convenient operation and remarkable functions, has been regarded as an effective strategy for prolonging the cycle life of aqueous zinc ion batteries. However, it is still difficult to dynamically regulate the unstable Zn interface during long-term cycling. Herein, tricine was introduced as an efficient regulator to achieve a pH-stable and byproduct-free interface. The functional zwitterion of tricine not only inhibits interfacial pH perturbation and parasitic reactions by the trapping effect of an anionic group (-COO-) but also simultaneously creates a uniform electric field by the electrostatic shielding effect of a cationic group (-NH2+). Such synergy accordingly eliminates dendrite formation and creates a chemical equilibrium in the electrolyte, endowing the Zn||Zn cell with long-term Zn plating/stripping for 2060 h at 5 mA cm-2 and 720 h at 10 mA cm-2. As a result, the Zn||VS2 full cell under a high cathodic loading mass (8.6 mg cm-2) exhibits exceptional capacity retention of 93% after 1000 cycles.

Construction of Multifunctional Hierarchical Biofilms for Highly Sensitive and Weather-Resistant Fire Warning.

Multifunctional biofilms with early fire-warning capabilities are highly necessary for various indoor and outdoor applications, but a rational design of intelligent fire alarm films with strong weather resistance remains a major challenge. Herein, a multiscale hierarchical biofilm based on lignocellulose nanofibrils (LCNFs), carbon nanotubes (CNTs) and TiO2 was developed through a vacuum-assisted alternate self-assembly and dipping method. Then, an early fire-warning system that changes from an insulating state to a conductive one was designed, relying on the rapid carbonization of LCNFs together with the unique electronic excitation characteristics of TiO2. Typically, the L-CNT-TiO2 film exhibited an ultrasensitive fire-response signal of ~0.30 s and a long-term warning time of ~1238 s when a fire disaster was about to occur, demonstrating a reliable fire-alarm performance and promising flame-resistance ability. More importantly, the L-CNT-TiO2 biofilm also possessed a water contact angle (WCA) of 166 ± 1° and an ultraviolet protection factor (UPF) as high as 2000, resulting in excellent superhydrophobicity, antifouling, self-cleaning as well as incredible anti-ultraviolet (UV) capabilities. This work offers an innovative strategy for developing advanced intelligent films for fire safety and prevention applications, which holds great promise for the field of building materials.

Original and liposome-modified indocyanine green-assisted fluorescence study with animal models.

Medical diagnosis heavily relies on the use of bio-imaging techniques. One such technique is the use of ICG-based biological sensors for fluorescence imaging. In this study, we aimed to improve the fluorescence signals of ICG-based biological sensors by incorporating liposome-modified ICG. The results from dynamic light scattering and transmission electron microscopy showed that MLM-ICG was successfully fabricated with a liposome diameter of 100-300 nm. Fluorescence spectroscopy showed that MLM-ICG had the best properties among the three samples (Blank ICG, LM-ICG, and MLM-ICG), as samples immersed in MLM-ICG solution achieved the highest fluorescence intensity. The NIR camera imaging also showed a similar result. For the rat model, the best period for fluorescence tests was between 10 min and 4 h, where most organs reached their maximum fluorescence intensity except for the liver, which continued to rise. After 24 h, ICG was excreted from the rat's body. The study also analyzed the spectra properties of different rat organs, including peak intensity, peak wavelength, and FWHM. In conclusion, the use of liposome-modified ICG provides a safe and optimized optical agent, which is more stable and efficient than non-modified ICG. Incorporating liposome-modified ICG in fluorescence spectroscopy could be an effective way to develop novel biosensors for disease diagnosis.

3D Printed Nitrogen-Doped Thick Carbon Architectures for Supercapacitor: Ink Rheology and Electrochemical Performance.

The 3D printing technique offers huge opportunities for customized thick-electrode designs with high loading densities to enhance the area capacity in a limited space. However, key challenges remain in formulating 3D printable inks with exceptional rheological performance and facilitating electronic/ion transport in thick bulk electrodes. Herein, a hybrid ink consisting of woody-derived cellulose nanofibers (CNFs), multiwalled carbon nanotubes (MWCNTs), and urea is formulated for the 3D printing nitrogen-doped thick electrodes, in which CNFs serve as both dispersing and thickening agents for MWCNTs, whereas urea acts as a doping agent. By systematically tailoring the concentration-dependent rheological performance and 3D printing process of the ink, a variety of gel architectures with high geometric accuracy and superior shape fidelity are successfully printed. The as-printed gel architecture is then transformed into a nitrogen-doped carbon block with a hierarchical porous structure and superior electrochemical performance after freeze-drying and annealing treatments. Furthermore, a quasi-solid-state symmetric supercapacitor assembled with two interdigitated carbon blocks obtained by a 3D printing technique combined with a nitrogen-doping strategy delivers an energy density of 0.10 mWh cm-2 at 0.56 mW cm-2 . This work provides guidance for the formulation of the printable ink used for 3D printing of high-performance thick carbon electrodes.

Microplastic remediation technologies in water and wastewater treatment processes: Current status and future perspectives.

Microplastics (MPs) are a type of contaminants produced during the use and disposal of plastic products, which are ubiquitous in our lives. With the high specific surface area and strong hydrophobicity, MPs can adsorb various hazardous microorganisms and chemical contaminants from the environment, causing irreversible damage to our humans. It is reported that the MPs have been detected in infant feces and human blood. Therefore, the presence of MPs has posed a significant threat to human health. It is critically essential to develop efficient, scalable and environmentally-friendly methods to remove MPs. Herein, recent advances in the MPs remediation technologies in water and wastewater treatment processes are overviewed. Several approaches, including membrane filtration, adsorption, chemically induced coagulation-flocculation-sedimentation, bioremediation, and advanced oxidation processes are systematically documented. The characteristics, mechanisms, advantages, and disadvantages of these methods are well discussed and highlighted. Finally, the current challenges and future trends of these methods are proposed, with the aim of facilitating the remediation of MPs in water and wastewater treatment processes in a more efficient, scalable, and environmentally-friendly way.

Low-temperature carbonized MXene/protein-based eggshell membrane composite as free-standing electrode for flexible supercapacitors.

The demerits of the carbonized eggshell membrane (EM), such as high cost, high brittleness, immutable shape and size, greatly limit its application in demanding supercapacitors as free-standing electrode. Herein, the reconstituted EM (REM) with good flexibility and excellent size-customizability is developed, which is due to their fibrous structure and abundant surface polar groups. Ti3C2 nanosheet (a typical MXene) with ultra-high electrical conductivity and good electrochemical activity is then coated on REM surface, and undergoes a low-temperature carbonization (350 °C) to prepare CREM/T. Multi-functions of Ti3C2 are exhibited: (1) constructing a conductive network on REM surface by randomly stacking to yield a high electrical conductivity of 78.1 S cm-1, (2) being as a protective mold to remain the inherent flexibility and porosity of REM during carbonization, (3) creating nanopores by inducing self-activation, and (4) yielding a large capacitance of 1729 mF cm-2 at 0.5 mA cm-2 and a high rate capability of 82 % after increasing the current density by 50 folds. Furthermore, an all-EM-based supercapacitor is fabricated with REM as the separator and CREM/T as the electrode. It delivers a high energy density of 16.1 µW h cm-2 at 1301 µW cm-2, and shows stable capacitive behaviors during bending.

Synergic Effect of Dendrite-Free and Zinc Gating in Lignin-Containing Cellulose Nanofibers-MXene Layer Enabling Long-Cycle-Life Zinc Metal Batteries.

Uncontrollable zinc dendrite growth and parasitic reactions have greatly hindered the development of high energy and long life rechargeable aqueous zinc-ion batteries. Herein, the synergic effect of a bifunctional lignin-containing cellulose nanofiber (LCNF)-MXene (LM) layer to stabilize the interface of zinc anode is reported. On one hand, the LCNF provides enough strength (43.7 MPa) at relative low porosity (52.2%) to enable the diffusion limited dendrite suppression, while, on the other hand, the MXene serves as a zinc gating layer, facilitating the zinc ion mobility, restricting the active water/anions from degradation in the electrode/electrolyte interface, and epitaxially guiding zinc deposition along (002) plane. Benefiting from the synergic effect of diffusion limited dendrite suppression and zinc gate, the LM layer enabled a high coulombic efficiency (CE) of 98.9% with a low overpotential of 43.1 mV at 1 mA cm-2 in Zn//Cu asymmetric cells. More importantly, Zn//MnO2 full cells with the LM layer achieve a high-capacity retention of 90.0% for over 1000 cycles at 1 A g-1 , much higher than the full cell without the protective layer (73.9% over 500 cycles). The work provides a new insight in designing a dendrite-free zinc anode for long-cycle-life batteries.

Lignin-containing cellulose nanofibers made with microwave-aid green solvent treatment for magnetic fluid stabilization.

Lignin-containing cellulose nanofibers (LCNFs), prepared from energy cane bagasse (ECB) using microwave-assisted natural deep eutectic solvent (MW-NADES) pretreatment combined with microfluidization, are utilized as stabilizing agents for magnetic particles (MNPs) in magnetorheological fluids (MRFs). The as-prepared LCNFs helped suspend negatively charged MNPs in MRFs effectively due to the presence of physically entangled network of LCNFs and the electrostatic repulsion between LCNFs and MNPs. Consequently, the presence of LCNFs increased the viscosity, yield stress and dynamic moduli of MRFs within the entire magnetic field range (0-1 T). Moreover, the as-developed LCNF-MRFs exhibited superior magnetorheological properties, i.e., widely controllable viscosity, yield stress and dynamic moduli, rapid magnetic response, good reversibility and outstanding cycling stability. This work demonstrates the sustainable, ultrafast production of LCNFs from cellulosic biomass using MW-NADES for MRF stabilization, paving the way for the development of high-performance, and eco-friendly MRFs.

Lignocellulose-based free-standing hybrid electrode with natural vessels-retained, hierarchically pores-constructed and active materials-loaded for high-performance hybrid oxide supercapacitor.

Lignocellulose including cellulose, lignin, and hemicellulose could be extracted from wood, and has been used to prepare carbon electrode. However, complicated extraction greatly increases preparation cost. To achieve maximum utilization of lignocellulose and avoid complicated extraction, wood with porous structure and good mechanical strength is used as carbon precursor. Additionally, chemical activation is commonly used to create micropores to provide high capacitance, but it brings in natural structure destruction, and generation of wastewater during pickling. Moreover, to achieve desirable energy density, multi-step strategy with long duration is required for loading active materials on carbonized lignocellulose (CL). Herein, a one-step method is developed to prepare a free-standing hybrid CL electrode (CLE) by using Lewis acid in three aspects: (1) as structure protection agent, (2) as activating agent, (3) as active materials donor, which bypasses pickling and further avoids the generation of wastewater. Additionally, natural vessels in wood can not only provide large space for active materials loading, but also act as rapid ions diffusion way, simultaneously confining active materials detachment. Benefiting from the synergistic effect of porous structure and Lewis acid, this work not only makes full utilization of lignocellulose, but also makes CLE exhibit excellent performance in hybrid oxide supercapacitor.

Production of lignin-containing cellulose nanofibers using deep eutectic solvents for UV-absorbing polymer reinforcement.

Lignin-containing cellulose nanofibers (LCNFs) from energy cane bagasse (ECB), were prepared using microwave assisted deep eutectic solvent (MV-DES) treatment in combination with ultrasonication. The yield of lignocellulose is up to 45.2 % with 81.0 % delignification under the optimal reaction condition (110 ℃, 30 min). The resulting LCNF exhibited a highly entangled network, which was caused by the binder role of lignin between cellulose nanofibers. The addition of LCNFs improved the stability of the polyanionic cellulose (PAC) film-forming suspension, which was confirmed by the increased zeta potential and viscosity values. The LCNF / PAC films showed tunable mechanical and UV-resistant properties, depending on the amount and type of LCNFs. PAC films with the addition of 5 % LCNFs (PEF-5 %) showed good mechanical properties (a tensile strength of 55.8 MPa with a 26.3 % strain to break) and high UV protection ability (a UV-transmittance of 2.9 %).

Rapid single-step synthesis of porous carbon from an agricultural waste for energy storage application.

Single-step synthesis of porous carbon (PC) from biomass is a challenge via microwave heating, because biomass rarely absorbs the microwave energy. Herein, wheat-straw-derived char, as a good microwave absorber, was used to achieve rapidly single-step synthesis of PC from an agricultural waste (wheat straw). KOH was used to generate abundant micropores in the PCs. High heating rate caused by microwave heating combined with the pyrolysis gases resulted in the formation of meso-/macropores. A series of post-oxidation reactions between active sites in the PCs and oxygen in the air led to the doping of oxygen-containing chemical groups. Consequently, the obtained PC possessed a high specific surface area of 1905 m2 g-1, a balanced pore distribution with abundant micropores (0.62 cm3 g-1), considerable content of meso-/macropores (0.53 cm3 g-1), and an oxygen-enriched structure (oxygen content up to 21.6%). These characteristics not only contributed to the achievement of a high specific capacitance of 268.5 F g-1 at 0.5 A g-1 for the resultant supercapacitor, but also resulted in an excellent rate capability with a high capacitance retention of 81.2% at 10 A g-1 in a gel electrolyte (polyvinyl alcohol/LiCl). This supercapacitor can extract a high energy density of 21.5 W h kg-1 at 0.5 A g-1 and a high power density of 7.2 kW kg-1 at 10 A g-1.

Fast microwave self-activation from chitosan hydrogel bead to hierarchical and O, N co-doped porous carbon at an air-free atmosphere for high-rate electrodes material.

As ZnCl2 is a good microwave absorber, it was usually used as an porogen to produce porous carbon from biomass by microwave heating. In this study, a facile microwave self-activation with the absence of ZnCl2 was proposed to produce chitosan-hydrogel-bead-based porous carbons (CPC-Air) for a short duration of 10 min. KOH was used as a substitute for the typically used NaOH to form chitosan-based hydrogen beads. During microwave irradiation, KOH acted as a chemical porogen to generate abundant micropores with a pore volume of 0.39 cm3 g-1 in CPC-Air, while water wrapped in hydrogel beads was transformed into steam, serving as a physical porogen to form a considerable content of mesopores (41.8%) and creating a air-free atmosphere. Microwave irradiation led to fast pyrolysis of chitosan, generating meso-/macropores. Combined with self-activation process, it resulted in a high defects degree in CPC-Air. Nitrogen with a high content of 3.4% remained in CPC-Air after self-activation. In addition, a significantly high oxygen content of 17.5% was introduced by the post-oxidation in air atmosphere. Consenquently, the proposed approach can produce a hierarchical and O, N co-doped CPC material with a high defects degree at air-free atmosphere, and with comparable electrochemical properties but with much simpler process and less production duration than the conventional method using ZnCl2. Particularly, owing to the combined effects of those characteristics in CPCs, an excellent rate capability was achieved in the prepared electrode, demonstrating an ultra-high capacitance retention of 87.5% when the current load was increased from 0.5-10 A g-1. The supercapacitor prepared by this electrode can deliver the energy densities of 17.3-20.6 W h kg-1 and the power densities of 0.5-9.0 kW kg-1.

Fast Microwave Synthesis of Hierarchical Porous Carbons from Waste Palm Boosted by Activated Carbons for Supercapacitors.

The synthesis of biomass-derived porous carbons (PCs) for supercapacitors by conventional two-steps method (chemical activation after carbonization) is complicated and time-consuming. In this study, we present a one-step microwave activation strategy to prepare hierarchically PCs from waste palm boosted by activated carbons (ACs). ACs with various specific surface areas (14, 642, and 1344 m²·g-1) were used for the first time to fast absorb microwave energy for converting waste palm into hierarchically PCs, that is, PC1, PC2, and PC3, respectively. The morphological and structural characterizations of PCs were studied. Also, the electrochemical performances of supercapacitors based on PCs as electrodes were further investigated. The results showed that the PC (PC1) boosted by AC with the lowest specific surface area possessed a porous structure (containing micro-, meso-, and macro- pores) with the largest specific surface area (1573 m²·g-1) and the highest micropore volume (0.573 cm³·g-1), as well as the suitable mesoporosity (29.69%). The as-prepared PC1 supercapacitor even in a gel electrolyte (PVA/LiCl) exhibited a high specific capacitance of 226.0 F·g-1 at 0.5 A·g-1 and presented excellent charge-discharge performance with an energy density of 72.3 Wh·kg-1 at a power density of 1.4 kW·kg-1 and 50.0 Wh·kg-1 at 28.8 kW·kg-1. Moreover, this promising method exhibited a simple, rapid, and cost-effective preparation of carbon materials from renewable biomass for energy storage applications.

Enhancement of the electrochemical properties of commercial coconut shell-based activated carbon by H2O dielectric barrier discharge plasma.

Commercial coconut shell-based activated carbon (CSAC) has low specific capacitance and specific capacitance retention owing to its undeveloped pore structure and low proportion of heteroatoms. In this study, dielectric barrier discharge plasma was used to enhance the specific capacitance and rate capability of CSAC. H2O was used as an excited medium to introduce oxygen functional groups. The physico-chemical properties of CSAC and CSAC modified by H2O plasma (HCSAC) were revealed by automated surface area and pore size analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Electrochemical work was applied to investigate the electrochemical properties of CSAC and HCSAC. The results obtained showed that plasma modification improved the specific capacitance of CSAC by 64.8% (current density, 1 A g-1; electrolyte, 6 M KOH solution) within 100 s. This result is ascribed to the oxygen functional groups introduced to the surface of CSAC. It can also improve the hydrophilicity and wettability of the carbon surface leading to an increase from 76.7% to 84.6% in specific capacitance retention. Furthermore, H2O plasma modification can introduce oxygen functional groups without destroying the initial pore structures of CSAC. In summary, we provide a simple, fast, environment-friendly modification method to enhance the electrochemical properties of CSAC.

Preparation of lignin-based porous carbon with hierarchical oxygen-enriched structure for high-performance supercapacitors.

The biomass-based porous carbon produced by the conventional two-step method (carbonization followed by chemical activation) has a high production cost and an undeveloped mesopore/macropore structure. In this study, lignin was successfully converted into porous carbon (LPC) in one step by microwave heating combined with the use of humidified nitrogen. The obtained LPC had abundant micropores (0.70 cm-3·g-1), hierarchical pore distribution (mesopore ratio: 65.8%), and an oxygen-enriched chemical structure (surface oxygen content: 16.5%). These characteristics provided a high energy density (23.0 kW·kg-1 at 10 A·g-1) and excellent rate capability of the prepared supercapacitor in a gel electrolyte (polyvinyl alcohol/LiCl), leading to a high specific capacitance of 173 F·g-1 at 0.5 A·g-1, and 71.1% at 10 A·g-1 remains. The prepared supercapacitor could deliver a high power density of 1.1 kW·kg-1 at the maximum energy density. The obtained results demonstrate the feasibility of the proposed energy-saving cost-effective preparation approach to obtain a high-performance supercapacitor with a low production cost.

Rapid microwave activation of waste palm into hierarchical porous carbons for supercapacitors using biochars from different carbonization temperatures as catalysts.

A rapid, simple and cost-effective approach to prepare hierarchical porous carbons (PCs) for supercapacitors is reported by microwave activation of abundant and low-cost waste palm, biochar (BC) and KOH. BCs from waste palm at different carbonization temperatures (300-700 °C), as catalysts and microwave receptors, were used here for the first time to facilitate the conversion of waste palm into hierarchical PCs. As a result, the high-graphitization PC obtained at a BC carbonization temperature of 300 °C (PC-300) possessed a high surface area (1755 m2 g-1), a high pore volume (0.942 cm3 g-1) and a moderate mesoporosity (37.79%). Besides their high-graphitization and hierarchical porous structure, the oxygen doping in PC-300 can also promote the rapid transport of electrolyte ions. The symmetric supercapacitor based on the PC-300 even in PVA/LiCl gel electrolyte exhibited a high specific capacitance of 164.8 F g-1 at a current density of 0.5 A g-1 and retained a specific capacitance of 121.3 F g-1 at 10 A g-1, demonstrating a superior rate capacity of 73.6%. Additionally, the PC-300 supercapacitor delivered a high energy density of 14.6 W h kg-1 at a power density of 398.9 W kg-1 and maintained an energy density of 10.8 W h kg-1 at a high power density of 8016.5 W kg-1, as well as an excellent cycling stability after 2000 cycles with a capacitance retention of 92.06%.