Catalytic Electron Transfer Research Articles

Multi-layer 3D Chirality and Double-Helical Assembly in a Copper Nanocluster with a Triple-Helical Cu15 Core.

Conceptually mimicking biomolecules' ability to construct multiple-helical aggregates with emergent properties and functions remains a long-standing challenge. Here we report an atom-precise 18-copper nanocluster (NC), Cu18H(PET)14(TPP)6(NCS)3 ( Cu18H ) which contains a pseudo D3-symmetrical triple-helical Cu15 core. Structurally, Cu18H may be also viewed as sandwich type of sulfur-bridged chiral copper cluster units [Cu6-Cu6-Cu6], endowing three-layered 3D chirality. More importantly, the chiral NCs are aggregated into an infinite double-stranded helix supported by intra-strand homonuclear C-H···H-Cdihydrogen contacts and inter-strand C-H/π and C-H/S interactions. The unique multi-layered 3D chirality and the double-helical assembly of Cu18H are evocative of DNA. Moreover, the collective behaviours of the aggregated NCs not only exhibit crystallization-induced emission enhancement (CIEE) and aggregation-induced emission enhancement (AIEE) effects in the deep-red region, but also efficiently catalyzes electron transfer (ET) reaction. This study thus presents that hierarchical assemblies of atomically defined copper NCs could be intricate as observed for important biomolecules like DNA with emergent properties arising from aggregated behaviours.

Multi‐layer 3D Chirality and Double‐Helical Assembly in a Copper Nanocluster with a Triple‐Helical Cu15 Core

AbstractConceptually mimicking biomolecules’ ability to construct multiple‐helical aggregates with emergent properties and functions remains a long‐standing challenge. Here we report an atom‐precise 18‐copper nanocluster (NC), Cu18H(PET)14(TPP)6(NCS)3 (Cu18H) which contains a pseudo D3‐symmetrical triple‐helical Cu15 core. Structurally, Cu18H may be also viewed as sandwich type of sulfur‐bridged chiral copper cluster units [Cu6−Cu6−Cu6], endowing three‐layered 3D chirality. More importantly, the chiral NCs are aggregated into an infinite double‐stranded helix supported by intra‐strand homonuclear C−H⋅⋅⋅H−C dihydrogen contacts and inter‐strand C−H/π and C−H/S interactions. The unique multi‐layered 3D chirality and the double‐helical assembly of Cu18H are evocative of DNA. Moreover, the collective behaviours of the aggregated NCs not only exhibit crystallization‐induced emission enhancement (CIEE) and aggregation‐induced emission enhancement (AIEE) effects in the deep‐red region, but also efficiently catalyze electron transfer (ET) reaction. This study thus presents that hierarchical assemblies of atomically defined copper NCs could be intricate as observed for important biomolecules like DNA with emergent properties arising from aggregated behaviours.

Generation of Photoinduced Phenalenyl‐Based Radicals: Towards Designing Reductive C−C Coupling Catalysis

AbstractOrganic photoredox catalysis is a versatile tool for accessing a wide range of synthetic transformations. Towards the development of a new class of organophotoredox catalysts, we have employed phenalenyl, an odd alternant hydrocarbon (OAH), for reductive C−C coupling reactions. Phenalenyl can adopt a stable open‐shell state (radical), using its non‐bonding molecular orbital. To date, chemically induced phenalenyl‐based radicals have been extensively explored in designing various intriguing organic materials and recently towards electron transfer catalysis. However, the photochemical generation of phenalenyl‐based radicals is rare. In this work, we report the photoinduced generation of phenalenyl‐based radicals with detailed mechanistic studies such as steady‐state absorption, time‐resolved transient absorption spectroscopy, and in‐situ absorption kinetic experiments to authenticate the generation of photo‐induced phenalenyl radicals. In addition, we present results demonstrating that this novel catalytic species can be applied to reductive pinacol coupling catalysis and reductive alkylation of terminal alkynes.

Confinement Effects in Well-Defined Metal–Organic Frameworks (MOFs) for Selective CO2 Hydrogenation: A Review

Decarbonization has become an urgent affair to restrain global warming. CO2 hydrogenation coupled with H2 derived from water electrolysis is considered a promising route to mitigate the negative impact of carbon emission and also promote the application of hydrogen. It is of great significance to develop catalysts with excellent performance and large-scale implementation. In the past decades, metal-organic frameworks (MOFs) have been widely involved in the rational design of catalysts for CO2 hydrogenation due to their high surface areas, tunable porosities, well-ordered pore structures, and diversities in metals and functional groups. Confinement effects in MOFs or MOF-derived materials have been reported to promote the stability of CO2 hydrogenation catalysts, such as molecular complexes of immobilization effect, active sites in size effect, stabilization in the encapsulation effect, and electron transfer and interfacial catalysis in the synergistic effect. This review attempts to summarize the progress of MOF-based CO2 hydrogenation catalysts up to now, and demonstrate the synthetic strategies, unique features, and enhancement mechanisms compared with traditionally supported catalysts. Great emphasis will be placed on various confinement effects in CO2 hydrogenation. The challenges and opportunities in precise design, synthesis, and applications of MOF-confined catalysis for CO2 hydrogenation are also summarized.

The Rational Design of Reducing Organophotoredox Catalysts Unlocks Proton-Coupled Electron-Transfer and Atom Transfer Radical Polymerization Mechanisms

Photocatalysis has become a prominent tool in the arsenal of organic chemists to develop and (re)imagine transformations. However, only a handful of versatile organic photocatalysts (PCs) are available, hampering the discovery of new reactivities. Here, we report the design and complete physicochemical characterization of 9-aryl dihydroacridines (9ADA) and 12-aryl dihydrobenzoacridines (12ADBA) as strong reducing organic PCs. Punctual structural variations modulate their molecular orbital distributions and unlock locally or charge-transfer (CT) excited states. The PCs presenting a locally excited state showed better performances in photoredox defunctionalization processes (yields up to 92%), whereas the PCs featuring a CT excited state produced promising results in atom transfer radical polymerization under visible light (up to 1.21 Đ, and 98% I*). Unlike all the PC classes reported so far, 9ADA and 12ADBA feature a free NH group that enables a catalytic multisite proton-coupled electron transfer (MS-PCET) mechanism. This manifold allows the reduction of redox-inert substrates including aryl, alkyl halides, azides, phosphate and ammonium salts (Ered up to -2.83 vs SCE) under single-photon excitation. We anticipate that these new PCs will open new mechanistic manifolds in the field of photocatalysis by allowing access to previously inaccessible radical intermediates under one-photon excitation.

Electron transfer catalysis mediated by 3d complexes of redox non-innocent ligands possessing an azo function: a perspective.

It was first reported almost two decades ago that ligands with azo functions are capable of accepting electron(s) upon coordination to produce azo-anion radical complexes, thereby exhibiting redox non-innocence. Over the past two decades, there have been numerous reports of such complexes along with their structures and diverse characteristics. The ability of a coordinated azo function to accept one or more electron(s), thereby acting as an electron reservoir, is currently employed to carry out electron transfer catalysis since they can undergo redox transformation at mild potentials due to the presence of energetically accessible energy levels. The cooperative involvement of redox non-innocent ligand(s) containing an azo group and the coordinated metal centre can adjust and modulate the Lewis acidity of the latter through selective ligand-centred redox events, thereby manipulating the capacity of the metal centre to bind to the substrate. We have summarized the list of first row transition metal complexes of iron, cobalt, nickel, copper and zinc with redox non-innocent ligands incorporating an azo function that have been exploited as electron transfer catalysts to effectuate sustainable synthesis of a wide variety of useful chemicals. These include ketazines, pyrimidines, benzothiazole, benzoxazoles, N-acyl hydrazones, quinazoline-4(3)H-ones, C-3 alkylated indoles, N-alkylated anilines and N-alkylated heteroamines. The reaction pathways, as demonstrated by catalytic loops, reveal that the azo function of a coordinated ligand can act as an electron sink in the initial steps to bring about alcohol oxidation and thereafter, they serve as an electron pool to produce the final products either via HAT or PCET processes.

Surfactant catalyzed electron transfer mechanism in the oxidation of racemic tartaric acid by Ce(IV)

Oxidation of α-hydroxy acid, racemic tartaric acid and its kinetic studies have been carried out to establish the mechanism of oxidation. The electron transfer reaction was performed in presence of surface active agents, surfactants, a clean and green catalytic material, using Ce(IV) as the oxidant. The progress of the reaction was monitored using a spectrophotometer by recording the fall in absorbance of Ce(IV) at its λ max (wave length of maximum absorbance) of 380 nm. Disappearance of Ce(IV) is observed to be first order at constant [H + ]. Plot of log(Absorbance) against time is found to be linear in the initial stages of the reaction. The results of oxidation rates show a complex dependence of rate on [H + ]. The pseudo first order rate constants ( k ) obtained with varying substrate concentration and the plot of k obs /[substrate] vs [substrate] are observed to be excellently linear with positive slope. Plots of pseudo first order rate constants in presence of surfactant (sodium dodecyl sulphate, SDS) against the [SDS] abruptly rises in the concentration range below cmc (critical micelle concentration) after which the rate exponentially falls. Based on all the findings, Berezin model has been advanced to explain the observed kinetic phenomenon in the surfactant medium.

Single electron transfer catalysis by diphenylthiourea under visible light photoredox conditions

Diphenylthiourea, upon deprotonation and subsequent photoexcitation, has been shown to reductively cleave an aryl bromide bond, paving the way for multiple chemical transformations.

Enhanced persulfate activation by sulfur-modified Fe3O4 composites for atrazine degradation: Performance and mechanism

A novel sulfur-modified Fe3O4 composite (SF10) with excellent magnetic properties was prepared via a solvothermal method. Compared with unmodified Fe3O4, SF10 exhibited excellent performance on the activation of peroxydisulfate (PDS) for atrazine degradation and maintained good reusability. According to the quenching experiments and electron paramagnetic resonance (EPR) test, hydroxyl radical (•OH) and sulfate radical (SO4•−) were the main active species. Notably, comprehensive characterization of the morphology, crystal structure, electrochemical analysis, and surface chemical composite revealed that sulfur modification introduced pyrite and pyrrhotite phases into Fe3O4 structure to improve its catalytic activity and electron transfer capacity. Density functional theory calculations showed that sulfur modification enhanced the electron transfer from Fe3O4 to PDS and the adsorption of PDS on the catalyst surface, which was beneficial for the activation of PDS. Moreover, the surface reducing sulfur species (≡S2− and ≡S22−) acted as the electron donor for Fe(II) regeneration, driving a faster Fe(II)/Fe(III) redox cycle of SF10 for the activation of PDS. This study provides a further understanding of the synergism between sulfur and iron, and broadens the application of Fe3O4 in PDS-based advanced oxidation processes for wastewater treatment.

Bulk preparation of free‐standing single‐iron‐atom catalysts directly as the air electrodes for high‐performance zinc‐air batteries

AbstractThe keen interest in fuel cells and metal‐air batteries stimulates a great deal of research on the development of a cost‐efficient and high‐performance catalyst as an alternative to traditional Pt to boost the sluggish oxygen reduction reaction (ORR) at the cathode. Herein, we report a facile and scalable strategy for the large‐scale preparation of a free‐standing and flexible porous atomically dispersed Fe–N‐doped carbon microtube (FeSAC/PCMT) sponge. Benefiting from its unique structure that greatly facilitates the catalytic kinetics, mass transport, and electron transfer, our FeSAC/PCMT electrode exhibits excellent performance with an ORR potential of 0.942 V at −3 mA cm−2. When the FeSAC/PCMT sponge was directly used as an oxygen electrode for liquid‐state and flexible solid‐state zinc‐air batteries, high peak power densities of 183.1 and 58.0 mW cm−2 were respectively achieved, better than its powdery counterpart and commercial Pt/C catalyst. Experimental and theoretical investigation results demonstrate that such ultrahigh ORR performance can be attributed to atomically dispersed Fe–N5 species in FeSAC/PCMT. This study presents a cost‐effective and scalable strategy for the fabrication of highly efficient and flexible oxygen electrodes, provides a significant new insight into the catalytic mechanisms, and helps to realize significant advances in energy devices.

Ceramic ozone catalytic coupling incineration ash and excess sludge recycling with ceftriaxone sodium wastewater treatment: Performance and mechanism

Highly efficient and economic treatment of wastewater sludges and wastewater containing ceftriaxone sodium (CRO) in one way is a challenging issue in the water treatment field. Therefore, a waste-recycling strategy of reasonably manufactured ceramic ozone catalyst (COC) with low cost and high value was proposed, which solved the difficult problems of sludge and incineration ash disposal and CRO removal. In view of the complex reaction among the components, the recovery heat conversion mechanism of inorganic substances forming crystalline ceramic skeleton, heavy metals solidifying stably and forming catalytic sites, and organic substances pore-forming in the whole material composition is expounded. COC has excellent catalytic performance. Under the optimal reaction conditions, the removal rate of CRO is 97.87 %, which accords with the first-order reaction kinetic model. The free radical quenching study and electron spin resonance (ESR) analysis show that the main free radical in the COC/O3 system is •O2–. The degradation intermediates in various time periods were identified by LC-MS analysis, while the degradation and transformation ways of CRO were put forward. The excellent catalytic performance can be attributed to the synergistic effect of electronic mediator CO, CC functional group adsorption and catalytic electron transfer mechanism of MgFe2O4, MnFe2O4, Fe2O3 and TiO2. In addition, COC has excellent repeatability, stability and environmental safety. The benefits of waste recycling are obvious.

Synthesis of I(III)/S(VI) reagents and their reactivity in photochemical cycloaddition reactions with unsaturated bonds

The development of novel methodologies for the introduction of the sulfoxonium group under mild conditions is appealing but remains underexplored. Herein we report the synthesis of a class of hypervalent iodine reagents with a transferrable sulfoxonium group. These compounds enable mixed iodonium-sulfoxonium ylide reactivity. These well-defined reagents are examined in visible-light-promoted cyclization reactions with a wide range of unsaturated bonds including alkenes, alkynes, nitriles, and allenes. Two distinct cyclization pathways are identified, which are controlled by the substituent of the unsaturated bond. The cycloaddition protocol features simple operation, mild reaction conditions, and excellent functional group tolerance, affording a broad range of sulfoxonium-containing cyclic structures in moderate to excellent yields. Furthermore, the sufoxonium group in the product can be transformed into diverse functional groups and structural motifs via single electron transfer and transition-metal catalysis.

Unravelling the role of transient redox partner complexes in P450 electron transfer mechanics

The molecular evolution of cytochromes P450 and associated redox-driven oxidative catalysis remains a mystery in biology. It is widely believed that sterol 14α-demethylase (CYP51), an essential enzyme of sterol biosynthesis, is the ancestor of the whole P450 superfamily given its conservation across species in different biological kingdoms. Herein we have utilized X-ray crystallography, molecular dynamics simulations, phylogenetics and electron transfer measurements to interrogate the nature of P450-redox partner binding using the naturally occurring fusion protein, CYP51-ferredoxin found in the sterol-producing bacterium Methylococcus capsulatus. Our data advocates that the electron transfer mechanics in the M. capsulatus CYP51-ferredoxin fusion protein involves an ensemble of ferredoxin molecules in various orientations and the interactions are transient. Close proximity of ferredoxin, however, is required to complete the substrate-induced large-scale structural switch in the P450 domain that enables proton-coupled electron transfer and subsequent oxygen scission and catalysis. These results have fundamental implications regarding the early evolution of electron transfer proteins and for the redox reactions in the early steps of sterol biosynthesis. They also shed new light on redox protein mechanics and the subsequent diversification of the P450 electron transfer machinery in nature.

Approaches for increasing the electrocatalitic efficiency of cytochrome P450 3A4

The electrochemically driven cytochrome P450 reactions have great promise as drug sensing device, new drug searching tool and bioreactor with broad synthetic application. In the present work, we proposed approaches for the increasing the efficiency of cytochrome P450 3A4 electrocatalysis, based on fine regulation and reproduction of nature hemeprotein catalytic cycle and electron transfer pathways on electrode. To analyze the comparative electrochemical and electrocatalytic activity, cytochrome P450 3A4 was immobilized on electrodes modified with a membrane-like synthetic surfactant, didodecyldimethylammonium bromide (DDAB). We used riboflavin, FMN and FAD as low molecular models of NADPH-dependent cytochrome P450 reductase for the improving and enhancement properties of catalytically responsible cytochrome P450 3A4-electrode. The efficiencies of electrocatalysis of erythromycin N-demethylation as well-known cytochrome P450 3A4 substrate in the case of riboflavin, FAD and FMN as electron transfer mediators were 135 ± 6, 171 ± 15 and 203 ± 10 %, respectively (in comparison with 100 ± 18 % erythromycin N-demethylation in the case of cytochrome P450 3A4-electrode as catalyst). Molecular modeling of cytochrome P450 3A4 complexes with riboflavin, FMN and FAD confirms possibility of binding isoalloxazine ring of riboflavin to the protein on the proximal side of hemeprotein, which is the place for binding of redox partners of the cytochrome P450.

Enhancing arsenic (III) removal by integrated electrocatalytic oxidation and electrosorption reactions on nano-textured bimetal composite of iron oxyhydroxide and manganese dioxide polymorphs (α-, γ-, β-, and ε-MnxFe1−xO)

A composite electrode of manganese oxide (MnO2) incorporated with iron oxide (α-FeOOH) was synthesized for arsenite (As(III)) oxidation and subsequent arsenate (As(V)) electrosorption. The crystal structure and chemical state of MnO2 polymorphs were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and BET surface area. The redox couple of Mn(III)/Mn(IV) mediated the catalytic electron transfer with respect to As(III)/As(V) redox equilibrium. The Mn site contributed a high diffusive current to the redox capacitance, meanwhile the Fe site better provided the double-layer capacitive deionization for arsenic species. Electrolysis of arsenite under constant anodic potential mode (+1.0 V vs. Ag/AgCl) enabled assess the performance of the electrodes. Among the polymorphs, γ-Mn0.2Fe0.8O exhibited the best arsenic adsorption capacity of 48 mg-As g−1, compared to that of α-FeOOH NPs (15 mg-As g−1) and γ-MnO2 (7 mg-As g−1), based on multilayer Langmuir adsorption model.

Cloning and Organelle Expression of Bamboo Mitochondrial Complex I Subunits Nad1, Nad2, Nad4, and Nad5 in the Yeast Saccharomyces cerevisiae.

Mitochondrial respiratory complex I catalyzes electron transfer from NADH to ubiquinone and pumps protons from the matrix into the intermembrane space. In particular, the complex I subunits Nad1, Nad2, Nad4, and Nad5, which are encoded by the nad1, nad2, nad4, and nad5 genes, reside at the mitochondrial inner membrane and possibly function as proton (H+) and ion translocators. To understand the individual functional roles of the Nad1, Nad2, Nad4, and Nad5 subunits in bamboo, each cDNA of these four genes was cloned into the pYES2 vector and expressed in the mitochondria of the yeast Saccharomyces cerevisiae. The mitochondrial targeting peptide mt gene (encoding MT) and the egfp marker gene (encoding enhanced green fluorescent protein, EGFP) were fused at the 5′-terminal and 3′-terminal ends, respectively. The constructed plasmids were then transformed into yeast. RNA transcripts and fusion protein expression were observed in the yeast transformants. Mitochondrial localizations of the MT-Nad1-EGFP, MT-Nad2-EGFP, MT-Nad4-EGFP, and MT-Nad5-EGFP fusion proteins were confirmed by fluorescence microscopy. The ectopically expressed bamboo subunits Nad1, Nad2, Nad4, and Nad5 may function in ion translocation, which was confirmed by growth phenotype assays with the addition of different concentrations of K+, Na+, or H+.

Cathode catalyst selection for enhancing oxygen reduction reactions of microbial fuel cells: COF-300@NiAl-LDH/GO and Ti3AlC2/NiCoAl-LDH

In this study, a cathode catalyst for microbial fuel cells (MFCs) was successfully prepared by a simple step-by-step hydrothermal method. Graphene oxide (GO) and layered double hydroxide (LDH) composite substrate and three-dimensional covalent organic framework materials (COF-300) grown vertically on the surface were observed. (003), (006), (012), (018), (110) were the obvious crystal plane of the composite COF-300@NiAl-LDH/GO. C, O, N, Ni, Na, Al and other elements existed on the surface of the composite. The maximum power density produced by COF-300@NiAl-LDH/GO-MFC was 481.69 mW/m2, which was 1.22 times of Ti3AlC2/NiCoAl-LDH-MFC (393.82 mW/m2) and 2.21 times of Ti3AlC2-MFC (217.73 mW/m2). The maximum voltage of COF-300@NiAl-LDH/GO-MFC was 518 mV and it could remain stable within 8 days. GO was used as the substrate to improve the conductivity; LDH was used to enhance the catalytic activity and electron transfer rate; The three-dimensional bulk COF-300 attached to the surface enhanced the surface area and catalytic properties; The above jointly promoted oxygen reduction reaction of cathode, so as to improve MFC performances.

Hydrochar-mediated photocatalyst Fe3O4/BiOBr@HC for highly efficient carbamazepine degradation under visible LED light irradiation

• Hydrochar-mediated Fe 3 O 4 /BiOBr@HC was synthesized by a hydrolysis method. • Efficient carbamazepine removal benefited from synergistic effect of Fe 3 O 4 and HC. • Faster charge separation and more active species generation occurred with help of HC. • Active species include superoxide radicals, hydroxyl radicals, and photogenerated holes. • Three degradation pathways were proposed to indirectly verify the role of active species. Construction of composite photocatalysts with high charge transfer efficiency and fast surface catalytic reaction has recently gained huge interest. In this work, a hydrochar microsphere-mediated photocatalyst Fe 3 O 4 /BiOBr@HC with rapid surface catalytic reaction and electron transfer was fabricated. Under visible-LED-light irradiation, removal of refractory analgesic carbamazepine (CBZ) and total organic carbon (TOC) reached 100% and 67.41%, respectively, by Fe 3 O 4 /BiOBr@HC20% within 40 min, demonstrating the excellent photocatalytic activity compared to other photocatalysts. The narrower band gap (2.02 eV) of Fe 3 O 4 /BiOBr@HC obviously improved the visible light absorption. The hydrochar with abundant surface oxygen functional groups provided more active oxygen species ·O 2 – (4.05 µM) and ·OH (107.8 nM), and acted as an electron bridge to promote the electron transfer of BiOBr and Fe 3 O 4 . Eleven main CBZ intermediates were identified and three degradation pathways were proposed to illustrate the contribution of superoxide radicals, hydroxyl radicals, and photogenerated holes to the photodegradation of CBZ. Furthermore, five-cycle reusing experiments revealed that Fe 3 O 4 /BiOBr@HC composite catalysts have excellent reusability and stability, indicating that they have a promising application future.

Radical Aza-Heck Cyclization of Imidates via Energy Transfer, Electron Transfer, and Cobalt Catalysis.

A radical aza-Heck cyclization has been developed to afford functionally rich products with four contiguous C-heteroatom bonds. This multi-catalytic strategy provides rapid syntheses of dense, medicinally relevant motifs by enabling the conversion of alcohol-derived imidates to heteroatom-rich fragments containing vinyl oxazolines/oxazoles, allyl amines, β-amino alcohols/halides, and combinations thereof. Mechanistic insights of this process show how three distinct photocatalytic cycles cooperate to enable: (1) imidate radical generation by energy transfer, (2) dehydrogenation by Co catalysis, and (3) catalyst turnover by electron transfer.

Mo2C@C nanofibers film as durable self-supported electrode for efficient electrocatalytic hydrogen evolution

Self-supported electrocatalytic thin films consist 3D conducting network and well-embedded electrocatalysts, which endows the advantage in mass flow kinetics and durability for large-scale water splitting. Synthesis of such self-supported electrode still remains a big challenge due to the difficulty in the control over the 3D conducting network and the simultaneous growth of catalyst with well attachment on the conducting fibers. Herein, a self-supported Mo2C@carbon nanofibers (Mo2C@C NF) film has been successfully fabricated with outstanding electrocatalytic performance under optimized pyrolysis temperature and precursors mass ratio conditions. During the carbonation process, the Mo2C nanoparticles (∼16 nm) were simultaneously grown and well dispersed on the inter-connected carbon nanofibers, which formed a 3D conducting network. The as-formed 3D carbon network was strong enough to support direct electrocatalytic application without additional ink or supporting substrates. This particular electrode structure facilitated easy access to the active catalytic sites, electron transfer, and hydrogen diffusion, resulting in the high hydrogen evolution reaction activity. A low overpotential of 86 mV was needed to achieve 10 mA cm−2 current density with outstanding kinetics metric (Tafel 43 mV dec−1) in 1 M KOH. Additionally, the self-supported Mo2C@C NF film, a binder-free electrode, exhibited extraordinary stability of more than 340 h.