Ultrathin Carbon Research Articles

Boosting Zn-air battery performance: Fe single-atom anchored on F, N co-doped carbon nanosheets for efficient oxygen reduction

Sluggish oxygen reduction reaction (ORR) kinetics limit the development of metal-air batteries and fuel cells, hindering overall energy conversion efficiency. Therefore, significant research has focused on cost-effective, highly active, and exceptionally stable non-precious metal ORR electrocatalysts. This study presents the synthesis of a nanohybrid material called Fe SAs/FN-CNs. It is made up of single iron atoms embedded in ultrathin porous carbon nanosheets that are co-doped with F and N. The synthesis process involves an easy one-step pyrolysis technique without additional post-treatment. The Fe SAs/FN-CNs material is designed to function as an effective zinc-air battery ORR electrocatalyst. Based on their distinctive components and structure, the optimal Fe SAs/FN-CNs exhibit outstanding catalytic efficiency and long-lasting performance in the alkaline ORR. They have an onset potential (Eonset) of 0.95 V, a half-wave potential (E0.5) of 0.85 V, a kinetic current density (JK) of 20.49 mA cm−2 at 0.8 V, and a diffusion-limited current (Jd) of 6.2 mA cm−2. In addition, a Zn-air battery made using homemade Fe SAs/FN-CNs demonstrated a power density of 197 mW cm−2, a specific capacitance of 813.5 mAh g−1, and exceptional stability. It outperformed the commercial Pt/C by operating continuously for over 147 hours at 10 mA/cm² (discharge-charge). The Fe SAs/FN-CNs nanohybrid electrocatalyst shows great potential as an electrocatalyst for various metal-air batteries.

Heterointerface of Monodispersed Ultrathin-MnO2@Amorphous Carbon to Attain Durable Lattice Oxygen Redox Chemistry through Creation of Dual Lattice Oxygens.

Lattice oxygen (OL) redox chemistry is a key to alleviating the energy and environmental crisis, but it faces challenges in activating the OL while ensuring structural stability. We disclosed herein that engineering a heterogeneous interface between ultrathin oxide and amorphous carbon can attain the durable OL redox chemistry without introducing catalytically impure sites. To this end, we proposed a green strategy to grow ∼3.9 nm-thickness wrinkled δ-MnO2 nanosheets that are rich in defects and are vertically aligned on amorphous carbon spheres. Experiments and calculations reveal that the electrons can easily migrate from the amorphous carbon to MnO2 at the δ-MnO2@C heterointerface. The heterogeneous interfaces can not only regulate the Mn-O bond and create oxygen defects in δ-MnO2 but also introduce lattice oxygen with varying reactivities. Specifically, the δ-MnO2@C structure carries more activated lattice oxygen that contributes to the enhanced activity on catalytic oxidation of bioderived 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), with a high FDCA formation rate of 1759 μmol gcat-1 h-1 and a high selectivity of 95%. The heterogeneous interface of MnO2@C also brings inert lattice oxygen, so that it manifests high structural stability during the oxidation reactions. This work deepens the fundamental understandings in the engineering of lattice oxygen for durable lattice oxygen redox chemistry and showcases an effective interface technique in creating advanced catalysts for clean sustainable energy.

Single-atom Ru modified flake g-C3N4 enhances photogenerated electron transport for rapid degradation of tetracycline antibiotics: Non-radical mechanism and ecotoxicity studies

Design of green and low-cost single-atom catalysts (SACs) with high-performance is key to moving photocatalytic degradation of antibiotics toward applications. In order to achieve SACs for large-scale manufacturing, we prepared ultrathin flake carbon nitride (FCN) by low-energy-consuming physical knockout means, and also applied an in situ growth strategy with stable and easy-operating effect to anchor the Ru element on FCN in the form of single atom. Notably, in the PMS/Vis/0.5Ru-FCN system, the degradation rate of tetracycline achieved 100 % in just five minutes, with an apparent rate constant of 0.236 min−1. Ru-FCN exhibits selective and stable determination due to narrow bandgap, unique photoresponsivity and low photogenerated carrier complexation rate. Mechanism investigation reveal that Ru-N4 sites accelerated the electron transfer between Ru-FCN and PMS, while the low oxidation state of Ru elements reduced the risk for metal corrosion. DFT calculations predict the attack sites of reactive oxygen species. This work provides a rational explanation for the charge transfer and resistance to external disturbance by Ru single atom, and it also provides a new direction to enhance the efficiency of water treatment.

Construction of a In2O3/ultrathin g-C3N4 S-scheme heterojunction for sensitive photoelectrochemical aptasensing of diazinon

A single semiconductor-based photoelectrochemical (PEC) aptasensor usually faces a challenge of low sensitivity due to poor solar energy utilization and a high photogenerated carrier recombination rate. Herein, an ultra-thin carbon nitride nanosheet-coated In2O3 (In2O3/CNS) S-type heterojunction-based PEC aptasensor has been established to achieve highly sensitive detection of diazinon (DZN) pesticide in water environment. Construction of S-type heterojunction induces a band shift and an electric field effect, enhancing light utilization and accelerating directional transmission of carriers, leading to outstanding PEC performance. The creation of internal electric field at interface ensures stable carrier transport. Additionally, ultrathin CNS structure can effectively shorten the transport path of carriers. The close coating of In2O3 and CNS promotes the transfer of charge. The synergistic effects amplify the sensor’s response, ultimately enabling the effective detection of DZN residue over a wide detection range (0.98 ∼ 980.0 pg mL−1), a low detection limit (0.33 pg mL−1, S/N = 3) and excellent accuracy in practical application (RSD < 5 %). This work provides a reference for the construction of a new S-type heterojunction-based PEC sensor.

Oxygen-doped Porous Ultrathin Graphitic Carbon Nitride Nanosheets for Photocatalytic Hydrogen Evolution and Rhodamine B Degradation.

Graphite phase carbon nitride (g-C3N4) is a highly promising metal-free photocatalyst. However, its applicability is restricted by low activity, due to weak quantum efficiency and small specific surface area. Exfoliating bulk crystals into porous thin-layer nanosheets and introducing element doping have been shown to improve photocatalytic efficiency, but these methods are often complex, time-consuming, and costly processes. In this study, we successfully synthesized porous oxygen-doped g-C3N4 (OCN) nanosheets utilizing a straightforward method. Our findings show that OCN have much higher light absorption and visible-light photocatalytic activity than bulk g-C3N4 (BCN) and nonporous g-C3N4 (CN). The OCN photocatalyst has a remarkable hydrogen evolution reaction (HER) rate of 8.02 mmol·g-1 h-1, which is 8 times greater than BCN. Additionally, the OCN shows a high degradation rate of 97.3% for Rhodamine B (RhB). This enhanced photocatalytic activity is ascribed to the narrow band gap and superior electron transfer capacity. Our findings suggest a potential technique for generating efficient g-C3N4 photocatalysts.

In situ growth of large-scale and ultrathin carbon nitride films shield common metal substrates from corrosion and oxidation

A centimeter-size carbon nitride (CN) film, with nanoscale thickness, is in situ deposited on various metals through the thermal condensation of melamine, achieving broad and uniform coverage, without any pre- and post-treatments. As the temperature rises, the nitrogen content in the film increases, leading to the part of CN to transform into g-C3N4. Benefit from higher Gibbs adsorption free energies of g-C3N4 with Cl- and O2 in aqueous environment, a 30 nm CN film deposited at 475 ℃ with large g-C3N4 network, minimal segregation and low internal stress enables pure metals and alloys to achieve over 90 % protection efficiency.

Boosting lactic acid photocatalytic synthesis from biomass sugars: The synergistic effect of N-doped carbon dots on ultrathin carbon nitride

The green and sustainable production of lactic acid via photocatalytic conversion of biomass-derived sugars is highly significant owing to its enhanced efficiency and reduced energy requirements. Consequently, the investigation has engineered a metal-free photocatalyst (NCDs/CCN), consisting of N-doped carbon dots (NCDs) and ultrathin carbon nitride (CCN). This catalyst has an enhanced light absorption range, facilitating a marked acceleration in the separation rate of photogenerated carriers. It has demonstrated the capability to achieve a lactic acid yield of up to 87.6 % in just 90 min with a mere 20 mg catalyst concentration in a xylose-alkali system. Electron Paramagnetic Resonance (EPR) and quenching experiments indicate that superoxide radicals (·O2−) are the primary oxidizing active species in the photocatalytic system, followed by h+, ·OH, and 1O2. DFT analysis suggests nitrogen doping enhances interaction with xylose, lowering adsorption energy and accelerating lactic acid generation, thus improving economic feasibility and sustainability.

N/O-functionalized ultrathin carbon nanosheets for zinc-ion hybrid capacitors

2D carbon materials have outstanding electrical properties and rich anchoring sites, and can be used as zinc ion storage electrodes. However, it remains a formidable challenge to fabricate these materials with tunable composition by a simple synthesis strategy. Herein, folic acid-derived N/O-functionalized ultrathin carbon nanosheets are synthesized via the activation effect of nano-ZnO template. The as-fabricated FACN-800 exhibits extremely thin thickness (∼1.6 nm), hierarchically porous structure and rich N/O heteroatoms (14.9 at.% of N and 8.4 at.% of O), which is conducive to accelerate ion transport and provide additional active sites for Zn-ion storage. Thus, the optimized FACN-800 based aqueous zinc-ion hybrid capacitor delivers excellent zinc-ion storage capabilities with high specific capacity (163.6 mAh g−1 at 0.1 A g−1), admirable energy density (130.8 Wh kg−1) and ultralong cycle stability (90.3 % capacity retention over 40,000 cycles) and FACN-800 has a specific surface area of 554.3 m2 g−1. Moreover, a series of ex-situ measurements and DFT theoretical calculations further elucidate the electrochemical mechanism between zinc ion storage and N/O dopants.

Unlocking hierarchical hollow nanoblocks of NiMo sulfide with extended interlayer spacing of Mo-S units for high-performance supercapacitor

Molybdenum sulfide (MoS2) has been investigated as electrode of supercapacitor due to its unique structure. However, the restricted availability of active sites and sluggish behavior at the basal surface impede its improvement. Here we propose an unlocking hierarchical hollow strategy to synthesis the bimetallic sulfide heterostructures loaded on the ultrathin carbon (NiS/MoS2@UC). The unlocking hierarchical hollow structure and extended S-Mo layer provide interconnected channels for rapid electrolyte ion transport, while the heterojunction interface promotes the electron transfer and redox reaction. As a result, NiS/MoS2@UC − 2 exhibits a high specific capacitance of 616.7F g−1 at the current density of 1 A/g, which is approximately 10 times higher than that of MoS2@UC and 6 times higher than that of NiS@UC. Moreover, NiS/MoS2@UC − 2 demonstrates a high energy density of 7.7 Wh kg−1 at the power density of 300 W kg−1 with excellent cycling durability.

Zinc Vaporization Induced Formation of Desired Ni Nanoparticles Coated with Ultrathin Carbon Shells for Efficient Electrocatalytic H2 Production Coupling with Methanol Upgrading.

The integration of the hydrogen evolution reaction (HER) with the methanol oxidation reaction (MOR) has been demonstrated to be a viable strategy for the energy-saving generation of H2 and value-added formate, which relies primarily on highly active and cost-effective bifunctional electrocatalysts. Herein, an efficient electrocatalyst consisting of controllable Ni nanoparticles (NPs) coated with ultrathin graphitic carbon shells was obtained by the pyrolysis of a Ni-Zn metal-organic framework. Intriguingly, we found that zinc vaporization not only resulted in the relatively small Ni NPs but also ultrathin carbon shells (≤3 layers). The density functional theory simulations confirmed that these ultrathin carbon shells significantly influenced electrocatalytic activity by facilitating electron transfer from the Ni core to the carbon shell. The optimized Ni1(Zn)@C demonstrated high catalytic activity for both HER and MOR, and only a low potential of 97 mV at 10 mA cm-2 was required for HER and 1.48 V at 30 mA cm-2 for MOR. In a two-electrode electrocatalytic cell measurement, a cell voltage of 1.63 V was observed at 10 mA cm-2 in the presence of methanol, 240 mV lower than that without methanol.

Next‐Generation Ultrathin Lightweight Electrode for pH‐Universal Aqueous Flow Batteries

AbstractAqueous flow batteries (AFBs) are promising long‐duration energy storage system owing to intrinsic safety, inherent scalability, and ultralong cycle life. However, due to the thicker (3–5 mm) and heavier (300–600 g m−2) nature, the current used graphite felt (GF) electrodes still limit the volume/weight power density of AFBs. Herein, a lightweight (≈50 g m−2) and ultrathin (≈0.3 mm) carbon microtube electrode (CME) is proposed derived from a scalable one‐step carbonization of commercial cotton cloth. The unique loose woven structure composed of carbon microtube endows CME with excellent conductivity, abundant active sites, and enhanced electrolyte transport performance, thereby significantly reducing polarization in working AFBs. As a consequence, CME demonstrates excellent cycling performance in pH‐universal AFBs, including acidic vanadium flow battery (maximum power density of 632.2 mW cm−2), neutral Zn‐I2 flow battery (750 cycles with average Coulombic efficiency of 99.6%), and alkaline Zn‐Fe flow battery (energy efficiency over 70% at 200 mA cm−2). More importantly, the estimated price of CME is only 5% of GF (≈3 vs ≈60 $ m−2). Therefore, it is reasonably anticipated that the lightweight and ultrathin CME may emerge as the next generation electrode for AFBs.

Ultrathin carbon doped hexagonal boron nitride films for electromagnetic interference shielding in the terahertz region

We have investigated the electromagnetic interference (EMI) shielding efficiency of carbon-doped hexagonal boron nitride (hBN) films in 0.3–1.8 THz regions using transmission-based terahertz time-domain spectroscopy (THz TDS). The hBN films were synthesized on Copper foils by atmospheric pressure chemical vapor deposition (APCVD) utilizing ammonia borane (AB) powder as a precursor. Carbon doping of BN films was achieved by using the intrinsic carbon dissolved in the Copper substrate. The EMI shielding efficiencies and the optical, dielectric, and electrical properties of the films were determined using THz TDS. The Absorbance is much greater than the Reflectance indicating that absorption is the dominant mechanism of shielding in these films. These carbon-doped hBN films show a high EMI shielding effectiveness, with 99.99 % EM radiation blocked. A maximum value of 30 dB and 55 dB at 1.72 THz were observed for films with 4.5 nm and 6.5 nm thicknesses. This is equivalent to shielding efficiency per unit thickness of 6667 dB/µm and 8460 dB/µm, which is among the highest reported for 2D materials.

Regulating Spin Polarization via Axial Nitrogen Traction at Fe-N5 Sites Enhanced Electrocatalytic CO2 Reduction for Zn-CO2 Batteries.

Single Fe sites have been explored as promising catalysts for the CO2 reduction reaction to value-added CO. Herein, we introduce a novel molten salt synthesis strategy for developing axial nitrogen-coordinated Fe-N5 sites on ultrathin defect-rich carbon nanosheets, aiming to modulate the reaction pathway precisely. This distinctive architecture weakens the spin polarization at the Fe sites, promoting a dynamic equilibrium of activated intermediates and facilitating the balance between *COOH formation and *CO desorption at the active Fe site. Notably, the synthesized FeN5, supported on defect-rich in nitrogen-doped carbon (FeN5@DNC), exhibits superior performance in CO2RR, achieving a Faraday efficiency of 99 % for CO production (-0.4 V vs. RHE) in an H-cell, and maintaining a Faraday efficiency of 98 % at a current density of 270 mA cm-2 (-1.0 V vs. RHE) in the flow cell. Furthermore, the FeN5@DNC catalyst is assembled as a reversible Zn-CO2 battery with a cycle durability of 24 hours. In situ IR spectroscopy and density functional theory (DFT) calculations reveal that the axial N coordination traction induces a transformation in the crystal field and local symmetry, therefore weakening the spin polarization of the central Fe atom and lowering the energy barrier for *CO desorption.

An Enzyme-Encapsulated MOF@MOF Nanocomposite for Detecting H2O2 Derived From Superoxide Anion Released by Mitochondria of HeLa Cells.

In this work, a horseradish peroxidase (HRP)-encapsulated metal organic framework (MOF)@MOF nanocomposite is developed for detecting H2O2 converted by dismutation of superoxide anions released from live HeLa mitochondria. Initially, an HRP-polyacrylic acid cluster is incorporated on a mesoporous, peroxidase-like Cu/Co-1,4-benzenedicarboxylate (BDC) MOF platform to avoid structural change and deactivation of HRP through its interactions with MOF metal ions. Additionally, a Cu/Co-BDC(HRP)@1,3,5-benzenetricarboxyate (BTC) core-shell MOF/MOF structure, also with peroxide-like properties, serves as a protective matrix for HRP. Then, ultrathin porous carbon shells (UPCS) are adopted to improve the electrical conductivity of the MOF@MOF. The Cu/Co-BDC(HRP)@BTC|UPCS sensing platform exhibits two linear ranges of 0.05-1 µM and 1-1000 µM with a sensitivity of 172mA mM-1 cm-2 and 1.63mA mM-1 cm-2, respectively. A limit of detection of 0.057 µM, good selectivity and stability over 35 days for H2O2 detection are also achieved. After treating the mitochondrial complex with specific inhibitors, amperometric results at the sensing platform confirmed complex I and III within mitochondria as the main electron leakage sites in the electron transfer chains. Therefore, this sensing platform provides a tool that may aid in predicting and even developing treatments for some oxidative stress diseases caused by mitochondrial abnormalities.

Ultrathin Porous Carbon Nitride Anchored with Pt Nanoclusters for Synergistic Enhancement of Hydrogen Production in Alkaline Photocatalytic Polyester Reforming.

Photocatalytic reforming (PR) of polyester waste, fueled by renewable sources like solar energy, offers a sustainable method for producing clean H2 and valuable by-products under mild conditions. The design of high-performance photocatalyst plays a pivotal role in determining the efficacy of an alkaline polyester PR system, influencing H2 generation activity and selectivity. Here, ultrathin porous carbon nitride nanosheets (UP-CN) loaded with Pt nanoclusters (Pt NCs, average diameter of 1.7nm) with uniform Pt NCs distribution are introduced. The resulting Pt NCs/UP-CN catalyst can accelerate charge and mass transfer while providing additional active sites, achieving superior H2 generation rates of 11.69mmol gcat -1 h-1 and 2923mmol gPt -1 h-1 under AM 1.5 light, which nine times higher than that of Pt nanoparticles-bulk graphitic carbon nitride composite (1.29mmol gcat -1 h-1 and 258mmol gPt -1 h-1) as counterpart. This performance also surpasses that of previously reported carbon nitride-based and TiO2-based photocatalysts. Moreover, the density functional theory calculations reveal a significant reduction in the energy barrier for the water dissociation step (H2O + * → *H + OH) at the interface between UP-CN and anchored Pt NCs, showcasing the synergistic effect between Pt NCs and UP-CN. This catalytic system also exhibits universality across various polyester plastics.

Atomically dispersed nickel-bismuth dual-atom sites for high rate electrochemical CO2 reduction

We report a diatomic-site catalyst configuration constituted by Ni-N3 and Bi-N4 embedded in ultrathin nitrogenated carbon nanosheets (Ni/Bi-N-C) which showed dramatically improved activity and selectivity for the conversion of CO2 to CO. Specifically, the catalyst exhibited high CO Faradaic efficiency (FECO) of above 90 % over a wide potential window from −0.76 to −2.22 versus reversible hydrogen electrode with the maximum CO partial current density up to 312 mA cm−2 in a flow cell, and coupled with robust durability. Ni/Bi-N-C-based membrane electrode assembly (MEA) device presented ultrahigh FECO of 95.7 % at 750 mA and over 100 h of continuous operation without decay under constant current density of 100 mA cm−2. Mechanistic studies and density functional theory calculations reveal that regulating the CO2RR catalytic performance via nearby Ni and Bi active sites can potentially break the activity benchmark of the single metal counterparts because the neighboring Ni and Bi active sites work in synergy to decrease the reaction barrier for the formation of *COOH and desorption of *CO. This work presents an efficient combination of two metal atomic sites which was designed by optimizing the interaction between the atomic sites and key reaction intermediates, resulting in the high-rate electrocatalytic CO2 reduction.

Biomass Derived Self-Doped Carbon Nanosheets Enable Robust Hole Transport Layers with Ion Buffer for Perovskite Solar Cells.

The diffusion of iodine species and lead leakage during device degradation represent the main obstacles restricting the commercial application of perovskite solar cells (PSCs). Cobalt loaded ultrathin carbon nanosheets (Co(III)-CNS) derived from biomass are prepared as ion buffer material to construct robust hole transport layers (HTLs). The carbon nanosheets containing trivalent cobalt ions can facilitate the oxidation of the hole transport material while preserving the structural integrity and electrical properties of HTLs under thermal stress, thereby ensuring efficient carrier transport. The two-dimensional ultrathin graphitized lamellar structure of Co(III)-CNS is conducive to alleviate the corrosive effects of the outward diffusion of iodine species on HTLs and silver electrodes, while avoiding irreversible degradation of PSCs. With the improvement of HTL composition and the related interfaces, Co(III)-CNS doped devices can maintain intact device structure under thermal stress and remain above 80% of the original power conversion efficiency (PCE) after thermal aging at 85 oC for 720 h. Notably, the chemical interactions between heteroatoms of self-doped carbon nanosheets and the mobile lead ions can effectively alleviate lead leakage and avoid the potential impacts of device degradation on ecosystem. Ultimately, the Co(III)-CNS doped PSCs with enhanced thermal stability exhibit a champion PCE of 22.32%.

Nickel single-atom synergistic iron-nitrogen sites for efficient CO2 electroreduction at a wide potential range

Recently, diatomic site catalysts (DASCs) by introducing a second metal active site have become a research focus in electrochemical CO2 reduction reaction (eCO2RR), as can regulate electronic structure of metal centers and optimize reaction free energies. However, hitherto the studies on the origin of the outstanding performance of DASCs and the accurate identification of active centers are not still clear. Herein, we designed a nickel–iron diatomic site catalyst by loading highly dispersed iron phthalocyanine (FePc) on a nickel single-atom with ultrathin porous nitrogen-doped carbon nanosheet substrate (denoted as FePc/M-LNi-NC). Experimental and calculational results prove that the synergistic catalysis of FePc and carbon nanosheet based Ni single-atom endowed FePc/M-LNi-NC achieving excellent CO2 reduction performance with a maximum CO Faradaic efficiency of 98.8 % at –0.8 V vs. RHE. In particular, the current density of FePc/M-LNi-NC at −1.0 V vs. RHE in an H-type cell (−20.9 mA/cm2) is 5.6 times that of FePc (3.7 mA/cm2). Compared with M-LNi-NC, the potential range of FePc/M-LNi-NC when FECO above 95 % expands from 0.31 to 0.43 V. Density functional theory calculations reveal that the Fe site in FePc/M-LNi-NC has a lower free energy change for *COOH formation (ΔG*COOH) and CO desorption (ΔGCO) than Ni site, thus exhibits higher electrocatalytic activity. Furthermore, the ΔG*COOH on FePc/M-LNi-NC declines from 0.78 to 0.08 eV compared to M-LNi-NC, and the ΔGCO lowers from 1.36 to 0.33 eV compared to FePc, thus FePc/M-LNi-NC achieves high performance for eCO2RR at a wide potential range.

Ultra-thin DLC diaphragm-based optical fiber sensor achieving a highly sensitive and broadband acoustic response.

In the design of an extrinsic Fabry-Perot interferometer (EFPI) acoustic sensor, broadband response and high-sensitivity sensing are usually conflicting and need to be carefully balanced. Here, we present a novel, to the best of our knowledge, optical fiber acoustic sensor based on an ultra-thin diamond-like carbon (DLC) film, fabricated using the plasma-enhanced chemical vapor deposition method, and transferred by a surface-energy-assisted method. The sensor exhibits a broadband response ranging from 200 Hz to 100 kHz, maintains an average sensitivity of 457.3 mV/Pa within the range of 6 to 30 kHz, and can detect weak acoustic signals down to 3.23 µPa/Hz1/2@16.19 kHz. The combination of an ultra-thin DLC film with a relatively high Young's modulus and internal stresses results in a trade-off between high sensitivity and a broadband response. This performance demonstrates that our sensor is among the most advanced in the EFPI acoustic sensor family, with significant potential for applications such as photoacoustic spectroscopy, defect diagnosis, and bio-imaging.

Ultrathin Carbon Shell Protecting Copper Sites to Boost Anodic Hydrogen Production via Low-Potential Formaldehyde Oxidation.

The oxidation of aldehydes on a copper-based electrocatalyst within a small potential window can produce hydrogen at the anode, thus offering a bipolar hydrogen production system. However, the inherent activity and stability of Cu-based electrocatalysts for aldehyde oxidation are still not satisfactory in practical application. Herein, by coating an ultrathin carbon shell on the copper sphere, an effective and stable formaldehyde oxidation reaction (FOR) can be realized to produce H2 at a very low potential. FOR needs only a potential of 0.13 V (vs RHE) to reach a current density of 100 mA cm-2. By coupling FOR with hydrogen evolution reaction (HER), hydrogen is generated simultaneously at both the cathode and the anode. The Faraday efficiency of H2 at the bipolar state is close to 100%. In a flow cell, it needs a low cell voltage of 0.1 V to reach a current density of 100 mA cm-2. Moreover, it can be operated steadily for more than 30 h at high current density. The carbon shell acts as an armor to protect the Cu(0) sites, avoid the oxidation of copper, and keep the catalyst activity for a long time in the electrolytic process. Experimental and theoretical calculation results indicate that electron transfer occurs at the interface between the copper core and ultrathin carbon shell. The ultrathin carbon-coated Cu reduces the reaction energy barrier, making the C-H bond more easily fractured and facilitating H coupling to generate H2. This study provides a basic principle for the design of copper-based electrocatalysts with long durability and activity.