Self-standing Carbon Research Articles

General Design of Aligned-Channel Porous Carbon Electrodes for Efficient High-Current-Density Gas-Evolving Electrocatalysis.

Gas-evolving reactions (GERs) are important in many electrochemical energy conversion technologies and chemical industries. The operation of GERs at high current densities is critical for their industrial implementation but remains challenging as it poses stringent requirements on the electrodes in terms of reaction kinetics, mass transfer, and electron transport. Here the general and rational design of self-standing carbon electrodes with vertically aligned porous channels, appropriate pore size distribution, and high surface area as supports for loading a variety of catalytic species by facile electrodeposition are reported. These electrodes simultaneously possess high intrinsic activity, large numbers of active sites, and efficient transport highways for ions, gases, and electrons, resulting in significant performance improvements at high current densities in diverse GERs such as urea oxidation, hydrogen evolution, and oxygen evolution reactions, as well as overall urea/water electrolyzers. As an example, the carbon electrode decorated with Ni(OH)2 demonstrates a record-high current density of 1000mAcm-2 at 1.360V versus the reversible hydrogen electrode, largely outperforming the conventional nickel foam-based counterpart and the state-of-the-art electrodes.

Main-group element-boosted oxygen electrocatalysis of Cu-N-C sites for zinc-air battery with cycling over 5000 h

Developing highly active and durable air cathode catalysts is crucial yet challenging for rechargeable zinc-air batteries. Herein, a size-adjustable, flexible, and self-standing carbon membrane catalyst encapsulating adjacent Cu/Na dual-atom sites is prepared using a solution blow spinning technique combined with a pyrolysis strategy. The intrinsic activity of the Cu-N4 site is boosted by the neighboring Na-containing functional group, which enhances O2 adsorption and optimizes the rate-determining step of O2 activation (*O2 → *OOH) during the oxygen reduction reaction process. Meanwhile, the Cu-N4 sites are encapsulated within carbon nanofibers and anchored by the carbon matrix to form a C2-Cu-N4 configuration, thereby reinforcing the stability of the Cu centers. Moreover, the introduction of Na-containing functional groups on the carbon atoms significantly reduces the positive charge on their outer shell C atoms, rendering the carbon skeletons less susceptible to corrosion by oxygen species and further preventing the dissolution of Cu centers. Under these multi-type regulations, the zinc-air battery with Cu/Na-carbon membrane catalyst as the air cathode demonstrates long-term discharge/charge cycle stability of over 5000 h. This considerable stability improvement represents a critical step towards developing Cu-N4 active sites modified with the neighboring main-group metal-containing functional groups to overcome the durability barriers of zinc-air batteries for future practical applications.

Synergistic oxidation of levofloxacin in electro-peroxone system with enhanced in-situ N, P self-standing carbon cathode derived from Chlorella: In-situ H2O2 generation, peroxone activation and catalytic ozonation

An intrinsic N, P self-standing carbon block (NP SSCB) cathode prepared with Chlorella as a precursor was used to enhance the electro-peroxone (EP) process under acidic conditions through a temperature modulation strategy. The results exhibited that NP SSCB-800-EP had a synergistic effect on levofloxacin (LEV) degradation by 42.1% and produced in situ H2O2 up to 70 mg L−1. Quenching and EPR tests confirmed that ·OH, HO2·/O2·- and 1O2 were responsible for degradation of LEV. The quantitative results showed that EP process produced radicals in the order of 1O2> HO2·/O2·->·OH. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations under acidic conditions confirmed that pyridinic N, pyrrolic N, C-O-P and the defects were active sites for in-situ H2O2 production. Furthermore, pyridinic N, pyrrolic N and C-P-O groups contributed to the reaction of H2O2 with O3 to form HO2/O2·- and O3·- intermediates, free from overcoming the limitations associated with traditional HO2− production. Graphitic N and C3-PO were possible active sites for triggering the 1O2 and *Oad production. This work provides a new strategy for the preparation of self-standing carbon-based cathodes and achieves multiple functions of EP process under acidic conditions, presenting new insights into structure-functional relationships in carbon-based advanced oxidation processes.

Transpiration-mimicking wood-based microfluidic aluminum-air batteries: Green power sources for miniaturized applications

Capillary microfluidics on porous substrates emerges as an innovative platform for constructing miniaturized electronics. However, maintaining a steady flow within microfluidics remains challenging, thus limiting their practical applications. Inspired by plant transpiration, this work presents a novel wood-based microfluidic Al-air battery (μAAB) configuration driven by a photothermal evaporator (biomimetic “leaf”). Except for the Al anode, the μAAB features an all-wood design, utilizing the well-aligned microchannels of the natural wood for electrolyte transportation, partially charred wood as photothermal evaporator for flow regulating, and wood-derived self-standing carbon cathode for the oxygen reduction reaction. These components are assembled through mortise-and-tenon joints, and the resulting μAAB exhibits a remarkable peak power density of 230 mW cm−3. The superior performance stems from the boosted mass transfer, maximized electrochemical interface and minimized depletion boundary layer provided by the 3D channeled structure of the wood-derived cathode. A steady discharge for over 11 h (200 mA cm−3) is obtained via the continuous electrolyte flow which is facilitated by the photothermal evaporator in the μAAB. This work not only presents a novel concept for miniaturized microfluidic power sources but also highlights the potential of 3D wood-based microfluidics combined with solar energy utilization.

Self-Standing Porous Carbon Electrodes with Lean Electrolyte and High Areal Capacity Conditions for Rechargeable Lithium–Oxygen Batteries

Rechargeable lithium–oxygen batteries (LOBs) have the highest theoretical energy densities of all the lithium-based batteries; however, the key challenges facing them are excessing electrolyte amounts and operating at low areal capacity conditions. Thus far, few studies have investigated the performance of the LOBs under practical conditions using appropriate technological parameters. In this study, we prepared a series of carbon-black based self-standing membranes with different pore structures. The self-standing carbon membranes, which were prepared by applying a non-solvent-induced phase separation (NIPS) technique have investigated the relationship between the physicochemical properties and battery performance at low electrolyte/areal capacity ratio (E/C < 10 g/Ah) condition. As a result, the discharge capacity exhibits a clear correlation with the physicochemical property. On the other hand, the cycle number of the LOBs did not simply correlate with the total discharge capacity of the self-standing carbon electrodes. Interestingly, it is observed that the self-standing electrode mainly composed of a unique mesoporous structure exhibits superior cycle performance under small E/C conditions (E/C < 5 g/Ah). Therefore, a turbostratic morphology with a three-dimensional hexagonal array of the unique mesoporous structure is beneficial for exhibiting superior LOB performance under lean electrolyte condition (Figure 1). We believe that the results obtained in the present study give an insight into the development of a new direction for the material design of porous carbon electrodes for achieving a high LOB performance and long cycle life of practical significance. Figure 1

Growing Electrocatalytic Conjugated Microporous Polymers on Self-Standing Carbon Nanotube Films Promotes the Rate Capability of Li-S Batteries.

Lithium-sulfur (Li-S) batteries hold great promise for widespread application on account of their high theoretical energy density (2600Wh kg-1 ) and the advantages of sulfur. Practical use, however, is impeded by the shuttle effect of polysulfides along with sluggish cathode kinetics. it is reported that such deleterious issues can be overcome by using a composite film (denoted as V-CMP@MWNT) that consists of a conjugated microporous polymer (CMP) embedded with vanadium single-atom catalysts (V SACs) and a network of multi-walled carbon nanotubes (MWNTs). V-CMP@MWNT films are fabricated by first electropolymerizing a bidentate ligand designed to coordinate to V metals on self-standing MWNT films followed by treating the CMP with a solution containing V ions. Li-S cells containing a V-CMP@MWNT film as interlayer exhibit outstanding performance metrics including a high cycling stability (616mA h g-1 at 0.5 C after 1000 cycles) and rate capability (804mA h g-1 at 10 C). An extraordinary area-specific capacity of 13.2mA h cm-2 is also measured at a high sulfur loading of 12.2mg cm-2 . The underlying mechanism that enables the V SACs to promote cathode kinetics and suppress the shuttle effect is elucidated through a series of electrochemical and spectroscopic techniques.

Electrosynthesis of α-Amino Acids from NO and other NOx species over CoFe alloy-decorated Self-standing Carbon Fiber Membranes.

The conversion of industrial exhaust gases of nitrogen oxides into high-value products is significantly meaningful for global environment and human health. And green synthesis of amino acids is vital for biomedical research and sustainable development of mankind. Herein, we demonstrate an innovative approach for converting nitric oxide (NO) to a series of α-amino acids (over 13 kinds) through electrosynthesis with α-keto acids over self-standing carbon fiber membrane with CoFe alloy. The essential leucine exhibits a high yield of 115.4 μmol h-1 corresponding a Faradaic efficiency of 32.4 %, and gram yield of products can be obtained within 24 hours in lab as well as an ultra-long stability (>240 h) of the membrane catalyst, which could convert NO into NH2 OH rapidly attacking α-keto acid and subsequent hydrogenation to form amino acid. In addition, this method is also suitable for other nitrogen sources including gaseous NO2 or liquidus NO3 - and NO2 - . Therefore, this work not only presents promising prospects for converting nitrogen oxides from exhaust gas and nitrate-laden waste water into high-value products, but also has significant implications for synthetizing amino acids in biomedical and catalytic science.

Solid-state Li-ion batteries with carbon microfiber electrodes via 3D electrospinning

Self-standing carbon fiber electrodes hold promise for solid-state battery technology owing to their networked structures improving interparticle connectivity, robustness contributing to mechanical integrity, and surface sites confining Li dendrites. We here evaluate carbonized 3D electrospun fibers filled with polymer electrolytes as anodes in solid-state lithium half cells. Microscopic analysis of the cells demonstrates the high wettability of carbon fibers with electrolytes, promoting an intimate contact between electrolytes and fibers. Solid-state cells delivered high initial capacities up to ∼300 mAh g−1, although the latter cycles were characterized by gradual capacity fade (∼100 mAh g−1 in the 100th cycle with nearly 100% coulombic efficiency), attributed to the onset of parasitic reactions increasing the cell resistance and polarization. When these were benchmarked against similar cells but with the liquid electrolyte, it was found that Li storage in these fiber electrodes is intermediate between graphite and hard carbon in terms of lithiation voltage (vs Li/Li+), corroborating with the nature of carbon assessed by XRD and Raman analysis. These observations can contribute to further development and optimization of solid-state batteries with 3D electrospun carbon fiber electrodes.

Multi-channel cellular carbon fiber as electrode for Zn-ion hybrid capacitor with enhanced capacity and energy density

Zn-ion hybrid capacitors (ZICs) recently receive an extensive attention owning to their theoretical energy density as well as high safety. Hollow porous carbon fibers (HPCF) are used as a promising cathode for ZICs due to abundant active sites. However, it is hard to deal with the “trade-off” between defect design and graphitic degree in HPCF electrode. In this work, hollow porous carbon fiber (HPCF) cathodes are prepared via a spinning-co-foaming technique, followed by zinc oxide nanoparticles as template and activation process. The aligned channels and hierarchical cavities in HPCF wall provide a high-speed diffusion path for electrolyte penetration via capillary force. Meanwhile, due to higher exposed surface area and metal-catalytic effect of reduce zinc during pyrolysis, self-standing ZHPCF-5 exhibits a good graphitic degree (ID/IG = 0.84). Its high electrical conductivity (158.3 S m−1) provides fast electron transport. The optimized ZHPCF-5 cathode displays a capacity of 220 mAh g−1 at 0.2 A g−1 and an energy density of 224 Wh kg−1 at a 14400 W kg−1 of power density. The assembled quasi-solid-state self-standing ZIC exhibits a high capacity (153.5 mAh g−1 at 0.5 A g−1). This work finds a way to simultaneously maintain abundant defects and high electric conductivity in self-standing carbon electrode for boosting Zn2+ storage.

High-performance direct liquid fuel cells benefited from highly N-doped and defect-rich carbon paper cathode with carbon nanosheets

Persulfate is a potential oxidant in direct liquid fuel cells (DLFCs), and the commercial carbon paper (CP) can directly serve as the cathode due to strong oxidizability of persulfate. However, the poor catalytic activity and low specific surface area of CP limit the electrode performance. Herein, a defect-enriched, pyridine-N-dominated and self-standing carbon paper electrode with abundant carbon nanosheets is successfully prepared by hydrothermal treatment combined with in-situ electrochemical exfoliation. Benefitting from the integrated structure, plentiful defects and high-content pyridine-N dopants of the prepared electrode result in the superior electrocatalytic activity and long-term stability in persulfate reduction reaction. Remarkably, a membraneless DLFC with the prepared electrode as cathode and persulfate as the oxidant acquires prominent cell performance and extremely high open circuit voltage of 2.13 V. The maximum power density of the DLFC achieves 241.0 mW cm−2, far higher than those of the previously reported similar membraneless DLFCs. A three-dimensional computational model for the DLFC is developed, which is help to reveal the importance of improving the reaction kinetics and electrical conductivity for the cathode with persulfate as oxidant. A facile approach for in-situ preparation of highly N-doped CP electrode is provided to yield outstanding cell performance for low-cost DLFCs.

Electrocatalytic ultrafiltration membrane reactors designed from dry-spun self-standing carbon nanotube sheets

The development of electrochemically active ultrafiltration membrane reactors offers promising perspectives to achieve simultaneous separation and degradation of persistent organic pollutants and support triggered self-cleaning of membrane materials upon surface fouling. Here, electro-responsive ultrafiltration membranes were synthesised from drawable carbon nanotubes (CNT) dry-spun as ultra-thin sheets onto preformed carbon nanofibre (CNF) supports to generate a unique class of electrically conductive and flexible ultrafiltration membranes. The pore size of the CNT-based membranes, on the order of ∼ 28 nm, was fine-tuned by controlling the dry layering and orientation of the CNT sheets to manage the membrane selectivity. The CNT-based membranes were used as effective conductive platforms to promote charge transfer during electrocatalytic degradation of acetaminophen, as a model contaminant. The CNT-based membranes, besides offering water permeance up to 2.77 × 103 L.m−2.h−1.bar−1, yielded electrocatalytic kinetic constant up to 46.5 × 10−3 min−1 during combined electrochemical reaction and ultrafiltration process, which is 1.4 to 39 times larger than previously reported values. Such high performance was maintained quite stable even after 8 reuse cycles. These results demonstrate the potential of CNT dry spinning technology for the scalable fabrication of highly permeable, but selective CNT-based membranes with remarkable electrochemical properties towards cost-effective water treatment at an exceptional reaction rate.

Hierarchical porous-structured self-standing carbon nanotube electrode for high-power lithium–oxygen batteries

Hierarchical porous-structured carbon nanotube electrode with macro-sized interconnected pores was prepared. Lithium–oxygen batteries equipped with the electrode exhibited power densities over 4.0 mW cm−2.

3D printed pure carbon-based electrodes for zinc-ion hybrid supercapacitor

Portable electronics and electric vehicles demand for high-performing, safe and low-cost energy storage devices. Recently, zinc-ion hybrid supercapacitors (ZHS) have gained considerable attention, which is due to their excellent electrochemical performance, high safety and low price. Activated carbon (AC) is one of the most commonly used materials for the cathode in ZHS. However, the lack of properly engineered hierarchical porous conducting electrodes for AC cathode has largely restricted the electrochemical performance of assembled ZHS at present. Herein, a hierarchically porous and self-standing carbon framework is developed by extrusion 3D-printing of activated carbon-Pluronic F127 ink, followed by appropriate thermal annealing to fabricate pure carbon-based electrode. Through formulating the 3D printable pastes, the ratio between the AC and F127 is shown to be crucial for affecting the electrochemical performance. The morphology, pore structure, and surface area of the thus-derived carbon cathode materials are investigated in conjunction with the performance of the zinc-ion supercapacitor. The mechanical stability is discovered to be optimized at the solid concentration range of 35%-40%. Within this range, a higher content of AC in the paste gives rise to better electrochemical performance of the zinc-ion supercapacitor, which is 323.79 mF cm −2 at 3.4 mA/cm −2 (0.1 A/g).

All-Carbon Monolithic Composites from Carbon Foam and Hierarchical Porous Carbon for Energy Storage.

We designed high-volumetric-energy-density supercapacitors from monolithic composites composed of self-standing carbon foam (CF) as the conducting matrix and embedded hierarchically organized porous carbon (PICK) as the active material. Using multiprobe scanning tunneling microscopy at selected areas, we were able to disentangle morphology-dependent contributions of the heterogeneous composite to the overall conductivity. Adding PICK is found to enhance the conductivity of the monoliths by providing additional links for the CF network, enabling high and stable performance. The resulting all-carbon CF-PICK composites were used as self-standing electrodes for symmetric supercapacitors without the need for a binder, additional conducting additive, metals as a current collector, or casting/drying steps. Supercapacitors achieved a capacitance of 181 F g-1 based on the entire mass of the monolithic electrode as well as an outstanding rate capability. Our symmetrical supercapacitors also delivered a record volumetric energy density of 19.4 mW h cm-3 when using aqueous electrolytes. Excellent cycling stability with almost quantitative retention of capacitance was found after 10,000 cycles in 6.0 M KOH as the electrolyte. Furthermore, charge-discharge testing at different currents demonstrated the fast charge-discharge capability of this material system that meets the requirements for practical applications.

Wood-derived biochar as thick electrodes for high-rate performance supercapacitors

Developing effective electrodes with commercial-level active mass-loading (> 10 mg cm−2) is vital for the practical application of supercapacitors. However, high active mass-loading usually requires thick active mass layer, which severely hinders the ion/electron transport and results in poor capacitive performance. Herein, a self-standing biochar electrode with active mass-loading of ca. 40 mg cm−2 and thickness of 800 µm has been developed from basswood. The basswood was treated with formamide to incorporate N/O in the carbon structure, followed by mild KOH activation to ameliorate the pore size and introduce more O species in the carbon matrix. The as-prepared carbon monoliths possess well conductive carbon skeleton, abundant N/O dopant and 3D porous structure, which are favorable for the ion/electron transport and promoting capacitance performance. The self-standing carbon electrode not only exhibits the maximum areal/mass/volumetric specific capacitance of 5037.5 mF cm−2/172.5 F g−1/63.0 F cm−3 at 2 mA cm−2 (0.05 A g−1), but also displays excellent rate performance with 76% capacitance retention at 500 mA cm−2 (12.5 A g−1) in a symmetric supercapacitor, surpassing the state-of-art biomass-based thick carbon electrode. The assembled model can power typical electron devices including a fan, a digital watch and a logo made up of 34 light-emitting diodes for a proper period, revealing its practical application potential. This study not only puts forward a commercial-level high active mass-loading electrode from biomass for supercapacitor, but also bridges the gap between the experimental research and practical application.Graphical abstract

Thin-walled porous carbon tile-packed paper for high-rate Zn-ion capacitor cathode

Lengthened ion pathway in porous carbon cathode, especially under high mass loading and packing state, severely impeded the ion transport, thus leading to a far unsatisfactory energy/power out of Zn//C capacitors. Here, we report a novel kapok-derived quasi-2D thin-walled porous carbon tile (CT) with proper curvature and rich doping used as stacked bricks. Together with high conductivity single-walled carbon nanotubes, a porous yet relatively packed self-standing carbon cathode was constructed, which features a hierarchical ion path including short ion pathways inside thin-walled porous CTs and adequate channels “highways” caused by rational sub-micron interlayer spacing, thus leading to an excellent combination of rate and gravimetric/volumetric/areal performance at practical mass loading (12 mg cm −2 ). • A porous thin-walled layered carbon tile with proper curvature was prepared as bricks. • Porous yet packed cathode feathers hierarchical paths for fast ion/charge transfer. • High rate and gravimetric/volumetric capacity remain in high loading cathode. • The areal capacity increases linearly with the mass loading of cathode. Long ion pathway inside large-sized carbon particle or stacked 2D assembly greatly limit the electrochemical performance of practical carbon cathode (>10 mg cm −2 ) in Zn//C capacitors. Highly porous activated carbon and holy graphene can alleviate such ion-transport issue, but usually suffer from a far lower packing density and severe restacking, respectively. Herein, a kapok-derived quasi-2D thin-walled microporous carbon tile (CT) with optimized curvature and rich doping was developed and used as bricks. Assisted with single-walled carbon nanotubes (SWNTs), a porous yet relatively packed paper cathode was constructed. The unique doped thin wall (∼700 nm) can effectively shorten the ion-penetration pathways from electrolyte deep into pore structure inside CTs, and thus enlarge ion-accessible surface areas. Combined with rational sub-micron interlayer spacing among proper-curved CTs and bridged-like SWNTs, the continuous ion/charge transport “highways” are fabricated. As a result, such self-standing carbon cathode delivers outstanding rate and gravimetric/areal performance (114 mAh g −1 /1.37 mAh cm −2 ) without sacrificing volumetric capacity even at high mass loading (12 mg cm −2 ).

Carbon-black-based self-standing porous electrode for 500 Wh/kg rechargeable lithium-oxygen batteries

While lithium-oxygen batteries exhibit high theoretical energy densities that by far exceed those of conventional lithium-ion batteries, there are a limited number of examples that actually demonstrate cells with high energy density. The limitation of the positive electrode with a capacity high enough to sustain repeated discharge/charge cycles under high areal capacity conditions hinders the implementation of the lithium-oxygen batteries with practically high energy density. In this study, we develop a carbon black powder-based self-standing membrane, which exhibits a discharge capacity of ~7,000 mAh/gelectrode even under high current density conditions (>0.4 mA/cm2). Using the developed self-standing carbon membrane as the positive electrode, a 500-Wh/kg class rechargeable lithium-oxygen battery was fabricated and a repeated discharge/charge cycle was demonstrated at 0.1 C-rate. The results obtained in this study provide new material research directions to realize high energy density rechargeable lithium-oxygen batteries and facilitate their future development.

Self-standing carbon nanotube aerogels with amorphous carbon coating as stable host for lithium anodes

Lithium metal anodes have a high theoretic capacity and are considered the promising electrodes for high energy density rechargeable batteries. However, the uneven deposition of lithium and lithium dendrites hinders the practical usage of lithium metal anodes. In order to solve this problem, carbon nanotube aerogels coated with amorphous carbon (AC@CNT aerogels) are used as the host, and molten lithium infuses into the carbon aerogels to obtain composite lithium metal anodes. The self-standing, porous AC@CNT aerogels provide a solid structure for lithium deposition/stripping and effectively reduce the local current density, so that lithium dendrites are suppressed and better electrochemical performances are achieved. Compared with the bare lithium metal anodes, the AC@CNT aerogel/lithium metal (AC@CNT/Li) anodes exhibit a longer cycling life of 500 h at deposition/striping capacity of 1 mAh cm−2 on symmetric cells, better cycling performance of 152 mAh g−1 at 0.1C in lithium cobalt oxide/lithium (LCO/Li) cells, and 120.3 mAh g−1 at 1 C in lithium iron phosphate/Li (LFP/Li) cells, demonstrating the potential of the AC@CNT/Li electrodes in developing high-performance lithium-metal batteries.

Multilevel structured carbon film as cathode host for Li-S batteries with superhigh-areal-capacity

The commercialization of lithium-sulfur (Li-S) battery could be accelerated by designing advanced sulfur cathode with high sulfur utilization and stable cycle life at a high sulfur loading. To allow the energy density of Li-S batteries comparable to that of commercial Li-ion batteries, the areal capacity of sulfur cathode should be above 4 mA·h·cm−2. In general, a high sulfur loading often causes rapid capacity fading by slowing electron/ion transport kinetics, catastrophic shuttle effect and even cracking the electrodes. To address this issue, herein, a multilevel structured carbon film is built by covering highly conductive CNTs and hollow carbon nanofiber together with carbon layer via chemical vapor deposition. The self-standing carbon film exhibits well-interweaved conductive network, hollow fibrous structure and abundant N, O co-doped active sites, which combine the merits of high electronic conductivity (1200·S·m−1), high porosity and polar characteristic in one host. Benefiting from this attractive multilevel structure, the obtained sulfur cathode based on the carbon film host shows an ultra-high areal capacity of 8.9 mA·h·cm−2 at 0.2 C with outstanding cyclability over 60 cycles. This work shed light on designing advanced sulfur host for Li-S batteries with high areal capacity and high cycle stability, and might make a contribution to the commercialization of Li-S batteries.

Self-supported carbon nanofibers as negative electrodes for K-ion batteries: Performance and mechanism

Self-standing carbon nanofibers (CNF) were electrospun and tested in K-ion batteries (KIB). The comparison of the electrochemical performance of KIB using potassium bis(fluorosulfonyl)imide (KFSI) and potassium hexafluorophosphate (KPF6) carbonate-based electrolytes revealed that, despite the coulombic efficiency is more readily stabilized with KFSI than with KPF6, the long-term cycling is quite the same, with a specific capacity of 200 mAh.g−1 for the CNF electrode. Post-mortem X-ray photoelectron spectroscopy analysis shows a more stable solid electrolyte interphase (SEI) for KIB employing KFSI. Finally, the K+ ion storage mechanism was investigated by combining cyclic voltammetry and operando Raman spectroscopy, showing a combination of adsorption and intercalation processes.The rate capability is, however, better with the KPF6 salt due to SEI layers formed at both CNF and K metal electrode, highlighting that full cell may lead to even superior results.