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SiC/multi-walled carbon nanotube (MWCNT) composites are considered to be promising materials for high-temperature electromagnetic wave (EMW) absorption due to their strong thermal stability and tunable dielectric properties. However, the EMW absorption performance of these composites is limited by poor impedance matching. This study proposes a novel multiscale structure synergistic regulation approach to enhance EMW absorption performance, which involves constructing a heterointerface structure and a triple periodic minimal surface (TPMS) meta-structure. The addition of a SiO 2 shell as an impedance layer to the SiC/MWCNT core to improve the intrinsic impedance. Meanwhile, the heterointerface between the core-shell structure leads to multiple interface polarization, significantly enhancing EMW energy dissipation. Consequently, the effective absorption bandwidth (EAB) of SiO 2 –SiC/MWCNT composites increased from 0.88 to 4.56 GHz. Furthermore, a TPMS meta-structure, fabricated by three-dimensional (3D) printing and sol infiltration technology, is developed to further improve impedance matching with the equivalent electromagnetic effect. Simulation and experimental results demonstrate that the SiO 2 –SiC/MWCNT TPMS meta-structure exhibits broadband EMW absorption performance, with the EAB reaching 7.2 GHz. This improvement is attributed to the synergistic regulation of the heterointerface structure and TPMS meta-structure, which provides a good balance between the requirements of electromagnetic loss and impedance matching. Additionally, the composites exhibit excellent oxidation resistance, as their EAB remains almost unchanged after exposure to 1000 °C for 6 h. This research offers a new design paradigm for ultrabroadband design of the nonmagnetic high-temperature absorbing materials. [Display omitted] [ABSTRACT FROM AUTHOR]

This study aims to explore the morphology of void and compressive performances of CNTs-reinforced filament-wound risers under axial compressive loading. The porosity morphology and distribution induced by the filament winding process were measured and analyzed, revealing a transition from nearly circular to elongated voids with gradual growth in the size of the individual void as the winding angle increased. Failure modes of composite risers were comprehensively discussed to understand the progressive failure process and load-bearing capacity. The results indicated that failure mechanisms of composite risers mainly manifest as initial resin splitting at the end of the structure, cracks growing in the interwoven region and local buckling at the end of the structure, and local asymmetric buckling as winding angle increased. While the addition of CNTs enhances the brittleness of the substrate and leads to an increased probability of debonding and delamination. Furthermore, the experiment results demonstrate that the energy absorption capacity can be generally improved at larger winding angles for the composite riser with 3% and 5% of CNTs volume content. The maximum values of peak crushing load, mean crushing force, energy absorption, and specific energy absorption were observed in the circumferentially wound riser with 5% of CNTs volume content. • The shape of voids transitions with an increase in winding angle. • There is a slight sensitivity of the void content to the winding angle. • Failure mode is similar to the different composite risers with the same winding angle. • Large winding angles improve energy absorption for 1% and 5% of CNTs volume content. • Winding angle strongly affects the compressive performance but no nonlinear is observed. [ABSTRACT FROM AUTHOR]

Self-organized vertically aligned or entangled randomly-oriented carbon nanotubes films filled with ferromagnetic Fe-based phases have recently attracted a great attention for numerous applications as potential electrodes. However the large difference between their synthesis –i) methods, -ii) parameters or –iii) the specific hydrocarbons-requirement have posed many challenges in the growth-selection of one of these film-morphologies. Another important issue is the brittleness of the first type of films which is generally due to low intimate contacts between each carbon nanotube comprised in the vertically aligned films and limits their direct implementation into applications. We propose an advanced low-flow rate chemical vapour deposition approach which allows the selection of either a free-standing flexible film comprising vertically aligned carbon nanotubes filled with large quantities of Fe 3 C particles or a free-standing flexible buckypaper comprising entangled randomly-oriented carbon nanotubes films partially filled with Fe 3 C through the simple control of the evaporation temperature of the used precursors consisting of large quantities of ferrocene and very low concentrations of dichlorobenzene. The morphological, cross sectional and structural properties of the obtained nanostructures are investigated. [ABSTRACT FROM AUTHOR]

A key challenge in the fabrication of ferromagnetically filled carbon-nanotube buckypapers in the presence of Cl-radicals is the achievement of a preferential horizontal nanotube-alignment. We show that a horizontal-alignment can be achieved by tuning two main CVD parameters for a fixed dichlorobenzene concentration: the precursor-evaporation temperature and the flow rate. [ABSTRACT FROM AUTHOR]

FePd and CoPd tetragonal ferromagnetic nanoparticles have recently attracted a great attention due to their large magneto-crystalline anisotropy of ∼10 8 erg/cm 3 ideal for fabrication of magnetic-arrays with giant-coercivities. However, no studies are reported on the fabrication of these alloys inside carbon nanotubes. Here we reveal the synthesis of the FePd 3 –Fe 0.037 Pd 0.963 –Fe 3 C inside carbon nanotubes by chemical vapor deposition of large quantities of ferrocene with low quantities of dichloro-cyclooctadiene-palladium and its transformation to Fe 0.438 Pd 0.561 through annealing. Instead, planar graphitic structures with embedded FePd 3 –Fe 0.037 Pd 0.963 or CoPd/CoPd 2 particles are found when large quantities of dichloro-cyclooctadiene-palladium are pyrolyzed with low quantities ferrocene or cobaltocene. [ABSTRACT FROM AUTHOR]

Polystyrene (PS) with molecular weight of 2.58 × 10 was grafted to multi-walled carbon nanotubes (MWCNTs) via covalent bonds. The modified tubes can self-assemble as regular bundles in tetrahydrofuran (THF) and benzene while unmodified ones cannot but agglomerate seriously and irregularly in the same solvents. In order to find out the role that polymer plays in self-assembly, a series of PS in different molecular weights were synthesized and grafted on the surface of MWCNTs. THF and benzene are two selective solvents because they are well compatible with PS but bad with tubes. Consequently, grafted MWCNTs show amphiphilicity in them. Solvent-philic/solvent-phobic interaction controls the self-assembly driving force. Small PS offers MWCNTs worse compatibility and poorer amphiphilicity than big PS. With amphiphilicity faded, grafted tubes lose self-assembly ability gradually. Meanwhile, degenerated compatibility cripples tubes' mobility. Therefore, both number and size of self-assemblies (SAs) decline when molecular weight of grafted PS diminishes. SAs lose their regularity and structural integrativity at the same time. Turbiscan stability index was introduced to quantify the compatibility between dispersate and solvents. Besides, a solvent-philic/solvent-phobic balance system was proposed to calculate compatibility and amphiphilicity of all the modified tubes. This model establishes a connection between compatibility, amphiphilicity, and self-assembly behaviors of modified MWCNTs. [ABSTRACT FROM AUTHOR]

Observations of lamellar like fringes in iron-carbon-filled vertically aligned carbon nanotubes (CNTs) produced by pyrolysis of ferrocene and rapid cooling methodologies (controlled quenching) have been investigated. The quantitative phase analysis of encapsulated Fe3C, γ-Fe, and α-Fe by X-ray diffraction reveals that controlling the phase-percentage leads to control of the crystal habit and of magnetic properties. Large coercivities and variable saturation magnetizations were observed. In addition, we reported a thorough study of the hysteresis behavior, the Barkhausen effect which has to be possibly associated with the formation of interfacial-defects in the crystal areas in contact with CNT layers. [ABSTRACT FROM AUTHOR]

Abstract: We have demonstrated previously that the acid-treated multi-walled carbon nanotubes (aci-MWCNTs) and taurine functionalized MWCNTs (tau-MWCNTs) induced differential pulmonary toxicity in mice after instillation exposure. In order to compare differences of cytotoxicity between the aci- and tau-MWCNTs, RAW 264.7 cells (a murine macrophage cell line) were chosen to be exposed to the aci- and tau-MWCNTs at concentrations of 0, 5, 20, 40, and 80μg/ml for 12 or 24h respectively. The results showed that although the aci- and tau-MWCNTs induced only mild decrease in cell viability to RAW 264.7 cells, the two types of MWCNTs elicited significant increase in apoptosis and decreased ability in cellular phagocytosis. Moreover, by using the specific inhibitors, we found that the scavenger receptors (SR) and caspase-9 were actively involved in the apoptosis induced by the aci- and tau-MWCNTs. The taurine functionalized MWCNTs (tau-MWCNTs) showed less cytotoxicity and apoptotic effect to RAW 264.7 cells than those of aci-MWCNTs. Taken together, the results indicated the important role of scavenger receptors and mitochondria in the apoptosis induced by MWCNTs. [Copyright &y& Elsevier]

The recent identification of superconductive effects in multilayer graphene systems exhibiting coexistence of rhombohedral and Bernal structural phases has attracted great attention. Complex effects have been reported in the presence of dislocations and/or solitons between graphene layers. Local magnetic fields and percolative effects have also been identified in the presence of wrinkling and disclinations. Interestingly, a recent report has also demonstrated the local stabilization of disorder-rich rhombohedral phases in low dimensional systems comprising of multiwalled carbon nanotubes modified with sulfur. In this work we identify a variation in the predicted ABA Bernal graphitic ordering of multiwalled carbon nanotubes (CNTs) fabricated in the presence of dichlorobenzene as a growth-promoter. The presented results highlight the stabilization of a high density of dislocations in samples produced by pyrolysis of low concentrations of ferrocene. We present an in-depth investigation of the dislocation-rich interfaces, especially by employing HRTEM analyses, evidencing a spontaneous local-insertion of low-dimensional atomic-lines (or solitons) into neighbouring atomic layers of curved graphene. Furthermore, by employing a methodology involving highly controllable cooling-rates and subsequential characterization through X-ray diffraction (XRD), we demonstrate a rapid migration of interstitial carbon, with relaxation of Fe3C into α-Fe and stabilization of local body centred tetragonal phases within the body centred cubic lattice of the nanowires. [ABSTRACT FROM AUTHOR]

Highly purified and uniformly distributed carbon nanotube (CNT) network is one of the key issues for developing advanced nanocomposites. However, the challenge for mitigation of the aggregation of CNT bundles during the CNT film fabrication still remained. In this work, debundling and reorganization of CNT bundles have been realized simultaneously by using a high-temperature thermal treatment. The debundling of large CNT bundles into small ones started after they were heat treated under 1400 °C and uniformly distributed CNT networks with small bundles were obtained after heat treated under 1800 °C. The tensile strength of the CNT film significantly increased by about 64% compared to the pristine film. Microstructural observations showed that the iron nanoparticles started to evaporate at 1400 °C and were completely removed at 1800 °C. Hollow amorphous carbon shells wrapped on the nanoparticles were left inside the CNT networks after the removal of the iron nanoparticles. Interestingly, these amorphous carbon shells act as carbon source for the deposition of a carbon layer on the CNT surface when the heat treatment temperature was up to 2000 °C, and they were completely consumed after being treated at 2800 °C. The microstructural evolution process of CNT bundles during heat treatment suggests the simple high-temperature treatment strategy could be applied for fabrication of highly purified CNT networks with well-distributed small bundles, enabling the development of advanced multifunctional nanocomposites in the near future. A high-temperature heat treatment is used to investigate the microstructure evolution and mechanical properties of CNT films. Benefiting from the high-purity and uniformly distributed CNT networks with small bundles after heat treated under 1800 °C, the tensile strength of the CNT film has significantly increased by ∼64% compared to the pristine film. When heat treated under 2800 °C, the hollow amorphous carbon shells are completely consumed and act as carbon source for deposition of carbon layer on the CNT surface. [Display omitted] • Debundling of large CNT bundles was observed after a high temperature treatment. • A regenerative carbon layer was deposited on CNT surface under high temperature. • The microstructural evolution of CNT networks under high temperature was proposed. [ABSTRACT FROM AUTHOR]

Highlights • CNTs and CNFs are both the nano-structured fibrous materials with excellent properties. • The dispersion of CNTs/CNFs is the decisive factor affecting the performance of composites. • The incorporation of CNTs and CNFs affects the variety performance of cement-based materials. • CNTs/CNFs-modified cement-based composites have broad application prospects. Abstract CNTs and CNFs are drawing widespread attention due to the unique structure and excellent properties, such as the mechanical property and the electrical property. It will significantly improve the cement-based composites' properties when adding CNTs/CNFs into composites. This paper briefly introduces the CNTs'/CNFs' basic properties and dispersion methods, and elucidates the properties of cement-based composites recombining CNTs/CNFs, including the mechanical property, the deformation property, the durability property, the thermal conductivities and electrical conductivities. This paper also summarizes the problems existing in present research, and gives some proposes for future study. [ABSTRACT FROM AUTHOR]

Boundary layer chemical vapour synthesis is a fabrication approach which exploits random fluctuations within the viscous boundary layer established between a laminar flow of pyrolyzed ferrocene and a rough substrate, to yield iron filled radial carbon nanotubes (CNTs). The key feature of this method is the significant enhancement of the encapsulated nanowire-length, which has been explained in terms of the diffusion gradient established at the open-tip of growing CNTs. In this work, we carried out a statistical investigation on the possible relationship between the width of the inner-CNT-cavity and the nanowire diameter within radially grown iron filled CNTs. A systematic analysis of nanowire-continuity allowed for the identification of particularly high filling rates, with nanowire-lengths up to 20 μm and an almost complete filling of the CNT-capillary. Two types of contact-modes could be identified between the catalyst particles and the CNTs: the first type, in which the catalyst-diameter is comparable with the width of the inner CNT-cavity (full catalyst encapsulation), and the second type, in which the base particle is found to be not fully encapsulated (i.e. only partially encapsulated within the inner CNT-cavity). The observed CNT/catalyst-base interactions resemble those reported in recent studies for tangential and intermediate-tangential growth-modes occurring after nanotube-cap nucleation. Comparative statistical analyses performed on other types of Fe-filled CNT films (flower-like structures and buckypaper) obtained by pyrolysis of ferrocene or ferrocene/dichlorobenzene mixtures are further discussed. [ABSTRACT FROM AUTHOR]

Fe nanoparticles immobilized on polyaniline-covered carbon nanotube (CNT) surfaces (Fe NPs–PANI/CNT) are prepared by reducing FeCl 3 in the mixing solution of aniline and CNT. Significantly, the structure of such composites can be effectively optimized by pretreating FeCl 3 with sodium citrate (CA). In the absence of CNTs, we found these two routes have large differences in reduction behaviors and different PANI states with varied conductivities. Therefore, the self-assembly mechanism in the preparation is proposed and the controlled self-assembly manner in the pretreating route is disclosed. Under acid condition, both catalysts demonstrate high oxygen reduction reaction (ORR) activity with four-electron pathway, and high electrochemical durability, revealing a promising application in the proton exchange membrane fuel cells. However, the high Tafel slopes relating to the surface red-ox couple and porous conductivity are still the main obstacles to improve their ORR dynamic, and more efforts on these aspects are needed to drive non-noble catalyst application in future. [ABSTRACT FROM AUTHOR]

The growth control of α-Fe inside multiwall carbon nanotubes has challenged researchers for more than a decade owing to the coexistence of this phase with Fe3C and γ-Fe. Previously, long heating treatments of 20 h have been used to decompose the encapsulated Fe-phases in C and Fe; however, these methods were limited by an unusual oxidation process leading to nanotube decomposition. In this letter, we report an alternative chemical vapour deposition approach that through an accurate control of the ferrocene-vapour flow-rate allows to achieve the direct encapsulation of 95% of α-Fe without additional heating treatments. [ABSTRACT FROM AUTHOR]

• The curing residual stress is beneficial for the compression strength of composite risers. • The effect of curing process parameters on the compressive strength was not significant. • The addition of nano-reinforced particles reduces the curing residual stresses. • The performance of the composite riser is enhanced with the increase of nanoparticle content. • The addition of nano-reinforced particles affects the failure mode of the composite riser. The present study is dedicated to the numerical analysis of progressive failure damage in multiangle nano-reinforced filament wound risers, with due consideration for process-induced residual stresses. Utilizing a multi-model coupling strategy, we introduce an integrated methodology predicated upon the time-varying material characteristics at a macroscopic scale. Initially, the process-induced residual stresses are anticipated via a sequential coupled numerical simulation methodology based on the time-varying attributes of the material. Subsequently, the curing residual stresses serve as the initial stress for the composite wound riser to prognosticate its axial compressive strength, grounded in the progressive damage model. Finally, the multiparametric effects on the strength properties of the composite risers are further investigated to reveal the intrinsic mechanism. The numerical findings evince that curing-induced residual stress retards both fiber and matrix failure while augmenting the axial compressive strength of the composite riser. Furthermore, the escalation in nanoparticle content diminishes the process-induced residual stresses. Additionally, the incorporation of 5 % nanoparticles yields an enhancement in the strength of the composite risers by approximately 16.26 % relative to those devoid of nanoparticles. [ABSTRACT FROM AUTHOR]

The stabilization of γ-Fe inside carbon nanotubes (CNTs) and its magnetic-coupling with α-Fe or Fe 3 C has attracted a great interest for the possible control of the hysteresis-loss processes in magnetic hyperthermia. Being interested in exploring further the stabilization-dynamics of this phase (γ-Fe), we have performed novel investigations on the fabrication and manipulation of filled CNTs films (buckypapers) with major focus on the effects of vapour-flow- and cooling-rate synthesis-parameters. X-ray diffractograms (XRD) and Rietveld refinements evidence an unusual stabilization of γ-Fe upon cooling, with a maximum relative abundance of 26 % after a slow-cooling step of 30 min. In-situ post-growth manipulation of the CNT-structure, in presence of tris(tetramethylcyclopentadienyl)‑gadolinium (III), allows for a particularly efficient functionalization of the CNT-walls, with in-situ surface-deposition of an amorphous Gd-phase. The rapid-cooling approach employed in the post-growth Gd-functionalization-step is found to have beneficial effects on the γ-Fe stabilization, with an enhanced relative abundance of 30 %, as extracted from Rietveld refinements. Extended characterization through magnetometry, evidence a dependence of the coercive-field value on both cooling and flow-rate parameters. The reported dataset confirms the existence of a magnetic-coupling within the encapsulated nanocrystals, with the unit-cell-volume being in the order of 45.9 Å3. [Display omitted] • We report a novel investigation on the fabrication and manipulation of filled CNTs. • New insights on the effects of flow- and cooling-rate CVD-parameters are presented. • We show an unusual stabilization of γ-Fe upon-cooling. • Tris(tetramethylcyclopentadienyl)Gd(III) was employed for the CNT-functionalization. • A dependence of the coercive-field value on both cooling and flow-rate is shown. [ABSTRACT FROM AUTHOR]

Epoxy‐amine system is a type of important matrix material for preparation of carbon fiber composites. The amidation of carbon nanotubes (CNTs) has been widely developed for enhancing the mechanical properties of the epoxy resin matrix. However, the various amino‐functionalized CNTs will produce different effect in the same epoxy matrix due to the diversity in reactivity, compatibility, and dispersion stability. In this paper, the amino‐functionalized multiwalled carbon nanotubes (MWCNTs‐NH2) were prepared through surface grafting ethylenediamine and diethyltoluenediamine (DETDA; designated as MWCNTs‐EDA and MWCNTs‐DETDA), and dispersed into epoxy resin matrix in which the DETDA was also used as curing agent. Compared with MWCNTs‐EDA, the MWCNTs‐DETDA showed a better dispersion state and stability in the epoxy resin, and had a relatively small impact on the curing behavior of epoxy matrix. After adding 0.5 wt% MWCNTs‐DETDA, the unidirectional T700 carbon fiber composites exhibited the significantly enhanced interlaminar shear strength and flexural properties due to the uniform dispersion of MWCNTs‐DETDA and the modified interface bonding. The results indicated that the chemical compatibility between MWCNTs‐NH2 and resin matrix can exert an important influence on the microstructure, curing behavior, thermo‐mechanical properties, and mechanical properties of the epoxy resin and the resulting carbon fiber composites. POLYM. COMPOS., 39:E733–E744, 2018. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

To drive the Fe-based application for the Oxygen Reduction Reaction (ORR) in alkali media, this work found the Carbon Nanotube supported Fe-Polyaniline (Fe-PANI/CNT) catalyst from controlled Molecular Self-assembly (MS) method is comparable to the commercial Pt/C catalyst in mass current density and ORR stability, but with large gap on specific current density. This can be due to that the controlled MS method help establish the most active site of Fe-N coordination in the PANI pore, whose hydrophilic state inhibits O 2 transfer and whose poor conductivity restricts O 2 utilization jointly. In the meanwhile, we revealed that the enormous impact of OH adsorption (OH ad ) on ORR activity and stability, exhibiting negative results on the Pt/C catalyst but beneficial results for Fe-based catalysts, especially in the “indirect 2e+2e pathway” relating to the inner and outer-sphere electron transfer processes. All these progress facilitate the clarification for the structure-catalysis and encourage preparation towards controlled MS methods. [ABSTRACT FROM AUTHOR]

• The salt freeze-thaw resistance of concrete is better when the MWCNTs content is low. • Air content and void specific surface area are most closely related to the change of compressive strength of MWCNTs-FAC. • The average chord length and void spacing factor have the greatest influence on the damage of MWCNTs-FAC. This paper aims to investigate the primary and secondary effects of different void structure parameters (air content, specific surface area, spacing factor, and average chord length of voids) on the macroscopic damage of multi-walled carbon nanotube-fly ash concrete (MWCNTs-FAC) under the coupling action of sulfate attack and freeze-thaw cycles. Through coupling tests of sulfate attack and freeze-thaw cycles, as well as X-ray computed tomography (CT) scanning tests, analyzed how MWCNTs-FAC differ in their compressive strength and damage quantity as a function of the number of coupling cycles. The effect of different void structure parameters of MWCNTs-FAC on the compressive strength and the damage quantity was also discussed using the grey correlation entropy analysis. The results show that the addition of MWCNTs can effectively improve the salt freeze-thaw resistance of concrete. When the MWCNTs content is 0.05 wt%, MWCNTs-FAC has the best improvement effect of salt freeze-thaw resistance. When the content of MWCNTs remains constant, the compressive strength of MWCNTs-FAC decreases, and the damage quantity increases as the air content, spacing factor, and average chord length of voids increase. The effect of specific surface area on the macroscopic damage of MWCNTs-FAC is exactly the reverse. Under salt freeze-thaw conditions, air content and specific surface area are two major factors influencing compressive strength, whereas average chord length and spacing factor are the main elements influencing damage quantity. [ABSTRACT FROM AUTHOR]

The appearance of coexisting ferromagnetic and superconductive phenomena in graphite‑sulfur and amorphous carbon‑sulfur composites has recently attracted an important attention. In this work we propose a novel re-investigation of the carbon‑sulfur doping mechanism performed by employing carbon nanotube networks (cm-scale buckypapers) and graphene-oxide films as host-materials. In the buckypaper-case, the presence of multiple sulfidation processes involving formation of 1) carbon‑sulfur and 2) metal-sulfide phases was demonstrated. Presence of carbon‑sulfur bonding was identified by employing both Raman spectroscopy and X-ray photoelectron spectroscopy. The conductive and magnetic properties of the sulfur-rich areas within the buckypaper were also investigated. An enhanced carbon‑sulfur bonding was then identified in sulfur-doped graphene-oxide films. In this latter case we demonstrate an almost complete annihilation of ferromagnetic-signals. ESR-spectroscopy of this second-type of system revealed the appearance of a paramagnetic transition for g ~ 2.08 at T ~ 77 K, possibly originating from the carbon‑sulfur bonding. A weak enhancement in the diamagnetic component could be interestingly detected below T ~ 60 K as a consequence of sulfur doping, after subtraction of the percolative ferromagnetic signals. [Display omitted] • We investigate carbon-sulfur doping by employing CNT- networks and graphene-oxide as host-materials. • In the buckypaper-case, formation of carbon-sulfur and metal-sulfide phases was demonstrated. • The conductive and magnetic properties of the sulfur-rich areas were investigated. • Carbon-sulfur bonding was identified also in sulfur-doped graphene-oxide films • Annihilation of ferromagnetic-signals is demonstrated, with appearance of a paramagnetic transition for g~2.08 (T~77K) • A weak enhancement in the diamagnetic component could be interestingly detected below T ~ 60K [ABSTRACT FROM AUTHOR]

Abstract: This paper established an in-situ synthesis strategy that the mixing solution of aniline, CNTs and CoCl2 was directly reduced to prepare polyaniline-cobalt-carbon nanotube (PANI-Co-CNT) electrocatalyst. Furthermore, this strategy was effectively modified by pretreating CoCl2 precursor with citric acid (CA), forming 2-4nm cobalt nanoparticles uniformly distributed on PANI-CNT support with porous structure. The control experiments revealed various PANI states in the growth stage, further proposing the self-assembly mechanisms in these two routes with and without CA pretreatment. These two PANI-Co-CNT electrocatalysts were also checked by oxygen reduction reaction (ORR) in acid environment, to corroborate their basically 4-electron processes. Inspiringly, the large activity and stability for the pretreated route could be comparable with those of the advanced electrocatalysts. All these progresses lay a bottom-up approach for future electrocatalysts. [Copyright &y& Elsevier]