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[Display omitted] • 2D GnP/MoS 2 and 3D (GnP/MoS 2)/MWNT composites are prepared by a facile, robust and ecofriendly method. • Effects of N-doping of GnPs and mass fraction of MWNTs on ORR activity are explored and rationalized. • Best synergistic ORR activity is obtained for N-doped catalyst with 3:1 2D-to-1D ratio. • Catalysts exhibit excellent stability and methanol resistance in alkaline medium. • Promising route to develop bifunctional ORR/OER catalysts. Nanocomposites have garnered attention for their potential as catalysts in electrochemical reactions vital for technologies like fuel cells, water splitting, and metal-air batteries. This work focuses on developing three-dimensional (3D) nanocomposites through aqueous phase exfoliation, non-covalent functionalization of building blocks with surfactants and polymers, and electrostatic interactions in solution leading to the nanocomposites assembly and organization. By combining molybdenum disulfide (MoS 2) layers with graphene nanoplatelets (GnPs) to form a binary 2D composite (MoS 2 /GnP), and subsequently incorporating multiwalled carbon nanotubes (MWNTs) to create ternary 3D composites, we explore their potential as catalysts for the oxygen reduction reaction (ORR) critical in fuel cells. Characterization techniques such as X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction elucidate material composition and structure. Our electrochemical studies reveal insights into the kinetics of the reactions and structure–activity relationships. Both the (MoS 2 /GnP)-to-MWNT mass ratio and nitrogen-doping of GnPs (N -GnPs) play a key role on the electrocatalytic ORR performance. Notably, the (MoS 2 / N -GnP)/MWNT material, with a 3:1 mass ratio, exhibits the most effective ORR activity. All catalysts demonstrate good long-term stability and methanol crossover tolerance. This facile fabrication method and observed trends offer avenues for optimizing composite electrocatalysts further. [ABSTRACT FROM AUTHOR]

Transition metal and heteroatom co-doped carbon nanomaterials (TM-H-C) are considered to be the most promising candidates to replace the expensive platinum-based catalysts for oxygen reduction reactions (ORR). Herein, we report a semi-closed molten salt-assisted one-step strategy for fabricating N-P-Fe-tridoped porous carbon nanotube (CNT) catalysts by using the evaporation of ZnCl2 and the catalysis of iron ions to control the heteroatoms doping process and CNT formation. The resultant densely packed porous CNT structure imparts final catalysts with an enhanced mass transfer ability for electron and ORR-involved species, ensuring a high performance in catalyzing the ORR. Significantly, the optimal catalysts show a half-wave potential of 0.89 V (vs. RHE), which is better than commercial platinum-based catalysts and most reported TM-H-C ORR catalysts. Impressively, when applied to a primary inc-oxygen (Zn–O2) battery, the synthesized catalyst comprehensively outperforms the state-of-the-art platinum-based catalyst in both its maximum power density and specific capacity. [ABSTRACT FROM AUTHOR]

Platinum-based catalysts remain the top choice for oxygen reduction reaction (ORR) in fuel cells. However, their activity and durability in the acidic medium are still under improvement. In this work, the Pt nanoclusters anchored the nitrogen-doped carbon nanotubes (Pt-NCNTs) have been synthesized by using a series process of pyrrole coating on the CNTs and subsequent pyrolysis to the chemical immersion reduction of Pt ions. The inner CNTs of Pt-NCNTs function as the nanowires offering a high-speed pathway for electron transport, and the Pt nanoclusters increases the active sites. The theoretical calculation demonstrates that the local structural defects and the uneven charge distribution induced by nitrogen-containing functional groups and porous structure are favorable to capture Pt ions for the nucleation of Pt nanoclusters. Compared with the commercial 40 wt% Pt/C (0.94 and 0.80 V), the Pt-NCNTs-1000 with Pt loading amount of 33.0 wt% owns the more positive onset potential and half-wave potential of 0.97 and 0.81 V in the sulfuric acid medium. Meanwhile, the strong attachment of Pt nanoclusters on the nitrogen-doped porous carbon layer results in a stable interface to effectively prevent the metallic species from migration and agglomeration during the electrode reactions. Therefore, the ORR current of Pt-NCNTs-1000 retained 84.3% of the initial value after 50000 s operation superior to the commercial Pt/C (64.6%). [Display omitted] • N-doped porous carbon layer coated CNT was used as support to enhance Pt deposition. • Micropores and nitrogen groups strongly anchor Pt nanoclusters deposited on NCNTs. • CNTs act as nanowires to promote charges transport of electrode reactions. • Pt-NCNTs has a good ORR activity and durability compared with commercial 40 wt% Pt/C. [ABSTRACT FROM AUTHOR]

[Display omitted] • HME was applied as an oxygen electrode of the AEM-URFCs. • Introducing 3 D CNT framework provided high ECSA of catalysts, electron transport, mass transport. • The HME_URFC exhibited superior round-trip efficiency of 55% at 20 mA cm−2 with enhanced durability and cyclability. Developing three-dimensional porous oxygen electrodes (OE) is crucial for enhancing round-trip efficiency (RTE) of anion-exchange membrane-based unitized regenerative fuel cells (AEM_URFCs). Herein, a novel OE design of AEM_URFCs is presented based on a hierarchical mesh electrode (HME) with a porous carbon nanotube (CNT) framework. The HME, featuring square-shaped macropores achieved by dispersing catalyst nanoparticles on the CNT framework enhances surface area, mass transport, and electron transport. Half-cell test demonstrated superior oxygen reduction reaction and oxygen evolution reaction activity compared to conventional electrodes. Moreover, the HME maintained stable ORR and OER activity during the stability test. In single-cell tests, the AEM_URFCs with the HME exhibited higher RTE (55% at 20 mA cm−2), surpassing the conventional electrode (52%). Furthermore, RTE was maintained at a remarkable 41% under ultrahigh current density (250 mA cm−2), which is unprecedented in the literature. The AEM_URFCs featuring the HME displayed superior cyclability over 5 cycles and durable performances under both fuel cell and water electrolysis modes. [ABSTRACT FROM AUTHOR]

• Bifunctional OER/ORR electrocatalysts based on Fe-Ni-Co/MWCNT were synthesized. • Both the OER and the ORR activity varied with the Fe:Ni:Co ratio. • Superior bifunctional ORR/OER activity was achieved for trimetallic Fe-Ni-Co oxides. • (Fe-Ni):Co ratio close to 1 led to catalysts with the highest bifunctional ORR/OER activity. • Synergistic interactions improve the stability and selectivity of the electrocatalysts. Fabrication of efficient and cost-effective bifunctional oxygen electrocatalysts for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) remains a challenge for the development of rechargeable metal-air batteries and unitized regenerative fuel cells technologies. Herein, we report high-performance bifunctional ORR/OER electrocatalysts consisting of mixed transition metal (Fe, Co, Ni) oxide nanoparticles supported on oxidized multi-walled carbon nanotubes (MWCNT). Investigation of the ORR and OER activity of samples with different metal compositions showed that trimetallic/MWCNT composites having Fe:Ni:Co = x:x:(1-2x) ratios, with 0.25 ≤ x ≤ 0.4, exhibit highest bifunctional activity in terms of the reversible ORR/OER overvoltage at a given current density. Moreover, the trimetallic catalysts exhibited improved selectivity with respect to the reduction of O 2 to OH− compared to the bimetallic Fe-Ni, Fe-Co and Co-Ni catalysts, thus revealing synergistic interactions among the metal oxide components. Correlation of the electrocatalytic activity with the structure of the composites is discussed for the most representative cases. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract How to reduce the usage of precious metals in electrocatalysts is a big challenge for the development of fuel cells. Metal nanoclusters (NCs) are highly desirable as active catalysts, but palladium nanoclusters (Pd NCs) have been less well developed than other metal clusters, such as gold, silver and copper, owing partly to the difficulties in size-controlled synthesis. Here, based on N, N-dimethylformamide (DMF)-mediation and ligand-exchange reaction, atomically precise Pd 5 (C 12 H 25 S) 13 nanoclusters are successfully synthesized. By loading the as-prepared Pd 5 nanoclusters on multiwalled carbon nanotubes (MWCNTs) and the following pyrolysis to remove the thiolate ligands, the surface-cleaned Pd 5 clusters (Pd 5 NCs/MWCNTs) can serve as efficient electrocatalysts for the oxygen reduction reaction (ORR) and the ethanol oxidation reaction (EOR). With ultra-low mass loading of Pd (2%), the Pd 5 NCs showed higher mass and specific activities and better durability than the commercial Pd/C catalyst (5 wt%) for the ORR. At 0.8 V, the mass and specific activities of Pd 5 NCs/MWCNTs are 5.70 and 4.53 times higher than the commercial Pd/C catalyst, respectively. As for the EOR, the Pd 5 NCs/MWCNTs exhibited lower onset potential (0.39 V) and peak potential (0.81 V) than the commercial Pd/C catalyst (0.44 and 0.89 V). Electrochemical impedance spectroscopy (EIS) measurements indicated that for the EOR, the Pd 5 nanoclusters have a much smaller charge transfer resistance (R ct) than the commercial Pd/C. The high-performance electrocatalytic properties of Pd 5 NCs for the ORR and EOR could be ascribed to the relatively high surface area-to-volume ratio and high density of exposed surface atoms of the Pd 5 nanoclusters. [ABSTRACT FROM AUTHOR]

The preparation of highly efficient and cheap electrocatalysts toward oxygen reduction reaction is significant for many electrochemical cells. Here we facilely synthesized nitrogen doped carbon nanotube by pyrolyzing melamine formaldehyde resin and Fe loading on MgO. There were mainly three morphologies observed, slender bamboo-like CNT, thick bamboo-like CNT, surface smooth, hollow CNT. The content of Fe loading on MgO had little influence on morphologies of CNT, however, when no MgO as support, only carbon ribbon obtained. The MgO as support was also significant for the formation of CNT. The samples with CNT formed represented better catalytic activity than control samples with no-CNT obtained, the morphology of CNT was beneficial for catalytic process. The sample C 1 -CNT with lowest content of Fe on support represented best catalytic activity which was competitive with 20% Pt/C in half-wave potential. The C 1 -CNT also showed outstanding stability and improved selectivity towards ORR, making it a promising alternative to Pt in application of fuel cells and metal-air batteries. [ABSTRACT FROM AUTHOR]

Three-dimensional nitrogen-doped carbon (3D-NCN) has been synthesized via the ionothermal carbonization method using waste soybean dregs (SD) as the precursor. N2 adsorption/ desorption isotherms show that the as-prepared 3D-NCN formed a hierarchically porous structure with a specific BET surface area of 1093.4 m2 g-1 and a total pore volume of 1.77 cm3 g-1. The TEM images clearly show that graphene-like carbon sheets were formed on the edge of the networks. The characterization of the samples collected at different temperature indicated that salt melt plays the key role in the formation of the network structure and rich pores. When 3D-NCN is as electrocatalyst for ORR, it shows an onset potential of 0.945 V with a more positive half-wave potential (0.846 V), which is comparable to that of commercial Pt/C. In addition, the long-term cycle results show that the onset potential and half-wave potential only negatively shifted by 6 mV and 8 mV after 10,000 cycles respectively, which are smaller than those values of commercial Pt/C. Due to its high ORR activity, durability, and low-cost, producing 3D-NCN from SD in molten salt medium provides a promising approach to replace the Pt-based catalysts for use in fuel cells. [ABSTRACT FROM AUTHOR]

Multiwall carbon nanotubes (CNTs) decorated with cobalt oxide (CoO x ) nanoparticles (NPs) are prepared in various synthesis conditions to investigate their capability as oxygen reduction reaction (ORR) catalysts for fuel cells in alkaline media. The synthesis conditions include the use of protecting, reducing or complexing agents and heat treatment. Higher ORR activity is possible for smaller size of Co NPs catalysts due to the enlarged interfaces between Co species and CNTs. The addition of polyvinylpyrrolidone (PVP) as protecting agent and NaBH 4 during the preparation procedure is necessary for obtaining the highest activity since it favors the formation of lower oxidation states for Co species and the incorporation of N groups which improve ORR activity. CNTs loaded with only 1 wt.% of Co NPs prepared by a facile method using PVP, NaBH 4 and subsequent heat treatment at 500 °C under N 2 atmosphere, demonstrates both similar catalytic activity and stability than Pt/Vulcan (20 wt.% Pt on Vulcan). The synergic chemical coupling effects between CNTs and CoO x NPs and the presence of carbon material with pyridinic N and quaternary N groups formed from the protecting agent decomposition, seem to be the main factors responsible for the remarkable electrocatalytic activity. [ABSTRACT FROM AUTHOR]

Developments in fuel cell technology have led to the design of new efficient electrocatalysts for the oxygen reduction reaction (ORR). In particular, metal-nitrogen-carbon (M-N-C) catalysts are promising alternatives to conventional noble metal ORR catalysts. Since the M-N-C catalyst has lower intrinsic activity than the noble metal catalyst, M-N-C catalysts should feature large surface areas, accessibility of active sites, short mass/charge transfer lengths, and surface permeability; these properties can lead to excellent catalytic activities. In addition, carbon-based materials, such as carbon nanotubes (CNTs), can be used to effectively improve the conductivity and stability of M-N-C catalysts. However, synthesizing carbon-based metal electrocatalysts with homogeneously distributed active sites and well-controlled structures remains challenging. In this study, we designed a carbon nanotube-encapsulated hollow Co-Fe-NC electrocatalyst by combining ultrasonic spray pyrolysis and a pseudomorphic transformation to a metal-organic framework, followed by carbonization. Spray pyrolysis formed hollow spheres without additional templates, requiring no further acidic leaching steps. Pseudomorphic transformation strategies can preserve the original morphology even after transforming the material to a metal-organic framework. The prepared CoFe-NC-CNT electrocatalyst exhibited high catalytic activity (half-wave potential of 0.924 V) and excellent 4-electron ORR selectivity. [Display omitted] • CoFe-NC-CNT was prepared by combining spray pyrolysis, MOF conversion, carbonization. • Hollow structure of CoFe-NC-CNT provides high electrochemical surface area. • CNTs in CoFe-NC-CNTs increase active site density by improving metal dispersion. • CoFe-NC-CNT exhibits excellent oxygen reduction activity and durability. [ABSTRACT FROM AUTHOR]

Unitized regenerative alkaline membrane fuel cells (AMFCs) have recently attracted great attention as both an energy conversion and energy storage technology due to their low cost and high-energy storage density for renewable resources. The oxygen electrode has long been one of the primary limiting factors of reversible AMFCs due to the sluggish kinetics of the oxygen reduction and evolution reactions (ORR and OER, respectively). It is challenging to develop durable and efficient bifunctional ORR/OER electrocatalysts; in particular, few researchers have focused on the durability of the material, which is the most relevant aspect for industrial application of these catalysts. In this work, we present an optimized procedure producing a highly stable bifunctional hybrid catalyst with excellent ORR/OER activities. This catalyst comprises covalently-bonded hybrid structures of cobalt oxide nanocrystals decorated on pre-oxidized carbon nanotubes. We performed the durability test in a broad potential range, from 0.0 V to 1.9 V ( vs . RHE), which is a harsh condition under which to our knowledge no previous hybrid structure in literature has survived. We have also linked the catalyst durability to metal oxide anchoring sites and its synthesis parameters. This study provides novel perspectives for the design of carbon-based, hybrid materials and insight into the synthesis-property relationships for the next-generation electrocatalysts. [ABSTRACT FROM AUTHOR]

The serious durability concerns of carbon supported Pt electrocatalysts for oxygen reduction reaction (ORR) have strictly limited the commercialization of fuel cells. Herein, cable-like carbon nanotubes (CNTs)@SnO 2 core@shell supports with regulable electronic metal-support interaction (EMSI) are designed for Pt nanoparticles (NPs) as ORR catalysts. Impressively, the best-performing Pt-CNT@SnO 2 catalyst with optimized d- band center achieves an excellent activity (mass activity (MA) of 0.68 A mg Pt −1 at 0.9 V iR-free and peak power density of 1618 mW cm−2) and record-high durability in H 2 -O 2 fuel cells (9.2 % MA and 8 % power density loss after 5k cycles under 1.0–1.5 V) among the reported Pt-based catalysts, which is also superior to the U.S. DOE 2025 targets. Density functional theory (DFT) calculations reveal that the strong metal-support bonding interaction (SMSBI) endows much larger adhesion energy and migration barrier towards Pt atoms compared to carbon supports, leading to the extraordinarily high stability in fuel cells. [Display omitted] • The Pt-CNT@SnO 2 catalyst demonstrates the best stability among reported Pt-based ORR catalysts under high potential regions. • Strong metal-support bonding interaction (SMSBI) between Pt and SnO 2 is able to stabilize Pt NPs against migration/agglomeration. • The d -band center of Pt is optimized by regulating the electronic metal-support interaction (EMSI). [ABSTRACT FROM AUTHOR]

In this study, functionalized carbon nanotube decorated with PtFeV tri-metallic electrocatalysts (PtFeV/FCNT) by different concentrations are prepared using the ethylene glycol reduction method in order to minimize electrocatalyst load and enhance the performance of the fuel cell cathodic electrode, simultaneously. The homogeneous distribution of PtFeV catalysts on the FCNT substrate and also the change in the electronic states of Pt, Fe and V elements is confirmed with characterization analyses. Electrode half-cell tests simulating the cathodic compartment of a polymer fuel cell show that the 2 mM PtFeV/FCNT electrode increases the maximum power density by about 500% compared to the commercial Pt/C 20% wt catalyst (from 4.43 to 27.31 mW/cm2). The increase in maximum power density along with the decrease in charge transfer resistance specified by the electrochemical impedance tests confirm the synergistic effects of alloying Pt with Fe and V and the application of FCNTs. In fact, in addition to the exceptional specific surface area and electrical conductivity of FCNTs, the increase in PtFeV/FCNT electrode performance can be attributed to the improved electrocatalytic activity of PtFeV tri-metallic nanoparticle alloy, resulting from the valence alterations and the Pt network compression during alloying. • Carbon nanotubes have functionalized as support of PEM fuel cells catalyst layer. • Pt-Fe-V with various concentrations were deposited on CNTs by ethylene glycol reduction. • The electrochemical performance of Pt-Fe-V/CNTs were studied by cathodic half-cell. • The modified CNTs by triple catalyst improve the performance of ORR in PEM fuel cell. • Pt-FeV/CNT improves the performance of PEMFC cathode than Pt/C up 500%. [ABSTRACT FROM AUTHOR]

To develop more efficient metal-free cathode electrocatalysts for fuel cells, novel arsenic (As)-doped, As and N-codoped carbon nanotubes are synthesized by chemical vapor deposition in this work. The as-prepared As-containing carbon nanotubes exhibit significantly enhanced activity and long-term durability for the oxygen reduction reaction (ORR) in alkaline medium, indicating that the doping of As or codoping As with other heteroatoms into carbon matrix could improve the ORR activity of carbon materials due to the changes in electronic and physical properties of carbon nanotubes evidenced by density functional theory calculations. Moreover, As-containing carbon nanotubes also display much better methanol tolerance, showing a good potential application for future fuel cells. [ABSTRACT FROM AUTHOR]

Nitrogen doped carbon nanotubes (NCNTs) with encapsulated Fe 3 C nanoparticles (Fe 3 C@NCNTs) are synthesized by a simple direct pyrolysis of melamine and ferric chloride. The characterization results reveal that Fe 3 C is mainly encapsulated in the interior of NCNTs and N species is mainly distributed on the outside surface of NCNTs. Iron and iron carbide catalyze the growth of NCNTs and are wrapped by carbon to form Fe 3 C@NCNTs. The as-prepared Fe 3 C@NCNTs catalyst exhibits superior oxygen reduction reaction (ORR) activity, excellent methanol tolerance and long-term stability in both acid and alkaline media. It is proven that the doped N is the main active site for ORR and the inner Fe 3 C with outside carbon form the synergetic active site to enhance ORR activity. The ORR mechanism of direct four electron transfer pathway is proved in acid and alkaline media. [ABSTRACT FROM AUTHOR]

PtCu/CNT alloy electrocatalysts were prepared by microwave assisted polyol synthesis. The influence of preparation pH and the presence of polyvinylpyrrolidone (PVP) as stabilizer on catalysts nanostructure and activity towards electrocatalytic oxygen reduction was evaluated. The catalysts were alloyed at 400–600 °C for 6 h in reductive atmosphere, and characterized by TEM and XRD. The XRD patterns display a positive shift in 2 θ of the Pt 111 peak, which is a good evidence for Pt–Cu alloy formation. Alloy nanoparticles already form at temperatures as low as 400 °C. Highly agglomerated PtCu nanoparticles were obtained in the absence of PVP while PVP addition resulted in dispersed and uniform nanoparticles with a mean particle size of 3.7 nm. Such small particles are a result of the considerably low temperature used during the heat treatment/alloying step. However, while Pt is nearly completely deposited on the CNTs, only smaller fractions of Cu are found in the final catalyst. A high extent of agglomeration was also noticed when the pH during polyol synthesis was increased, which is attributed to Cu-hydroxides precipitation. Pt–Cu core shell catalysts were obtained after voltammetric dealloying. Catalyst prepared at higher pH in the presence of PVP display the highest electrocatalytic activity. [ABSTRACT FROM AUTHOR]

A non-covalent functionalization for multi-walled carbon nanotubes has been used as an alternative to the damaging acid treatment. Platinum nanoparticles with similar particle size distribution have been deposited on the surface modified multi-walled carbon nanotubes. The interaction between platinum nanoparticles and multi-walled carbon nanotubes functionalized with 1-pyrenecarboxylic acid is studied and its electrochemical stability investigated. This study reveals the existence of a platinum-support interaction and leads to three main conclusions. First, the addition of 1-pyrenecarboxylic acid is improving the dispersion of platinum nanoparticles, leading to an improved electrochemical activity towards oxygen reduction reaction. Second, the investigations regarding the electrochemical stability showed that the platinum-support interaction plays an important role in improving the long-term stability by as much as 20%. Third, post-mortem microscopy analysis showed a surprising effect. During the electrochemical stability investigations concerned with carbon corrosion it was found that the multi-walled carbon nanotubes were undergoing severe structural change, transforming finally into carbon spheres. [ABSTRACT FROM AUTHOR]

The successful commercialization of fuel cells requires the efficient electrocatalyst to make the oxygen reduction reaction (ORR) fast because of the sluggish nature of ORR and the high cost of the platinum catalysts. In this work, we report the excellent performance of metal-free nitrogen-doped porous carbon nanosheets (NPCN) with hierarchical porous structure and a high surface area of 1436.02 m 2 g −1 for catalyzing ORR. The active NPCN is synthesized via facile high-temperature carbonization of natural ginkgo leaves followed by purification and ammonia post-treatment without using additional supporting templates and activation processes. In O 2 -saturated 0.1 M KOH solution, the resultant NPCN exhibits a high kinetic-limiting current density of 13.57 mA cm −2 at −0.25 V (vs. Ag/AgCl) approaching that of the commercial Pt/C catalyst (14 mA cm −2 ) and long-term electrochemical stability. Notably, the NPCN shows a slightly negative ORR half-wave potential in comparison with Pt/C (Δ E 1/2 = 19 mV). The excellent electrocatalytic properties of NPCN originate from the combined effect of optimal nitrogen doping, high surface area, and porous architecture, which induce the high-density distribution of highly active and stable catalytic sites. [ABSTRACT FROM AUTHOR]

To develop low-cost and efficient cathode electrocatalysts for fuel cells in acidic media, phosphorus-doped carbon nanotubes (P-CNTs) supported low Pt loading catalyst (0.85% Pt) is designed. The as-prepared Pt/P-CNTs exhibit significantly enhanced electrocatalytic oxygen reduction reaction (ORR) activity and long-term stability due to the stronger interaction between Pt and P-CNTs, which is proven by X-ray photoelectron spectroscopic analysis and density functional theory calculations. Moreover, the as-prepared Pt/P-CNTs also display much better tolerance to methanol crossover effects, showing a good potential application for future proton exchange membrane fuel cell devices. [ABSTRACT FROM AUTHOR]

Reducing the usage of noble metals, such as platinum-based catalysts for oxygen reduction reaction (ORR) is pressingly demanded towards the practical applications of proton-exchange membrane fuel cells. One promising way is to develop Pt single atom catalysts (SACs), which, however, are plagued by their preference toward two-electron ORR pathway as well as stability issue. Herein, a single-atom alloy (SAA) catalyst with platinum-cobalt (Pt-Co) dual sites encapsulated in nitrogen-doped graphitized carbon nanotubes (Pt 1 Co 100 /N-GCNT) consisting of isolated Pt atoms decorated on the surface of Co nanoparticles was reported. Based on complementary spectroscopic characterizations and first-principle calculations, we propose that the unique Pt-Co dual sites in SAA facilitates the adsorption and dissociation of oxygen, particularly for the immobilization of OOH* intermediate and the dissociation of OH* intermediate, and thus result in high-efficiency four-electron ORR pathway. Consequently, the Pt 1 Co 100 /N-GCNT SAA catalyst achieves a mass activity of 0.81 A mg–1 Pt at 0.90 V (versus the reversible hydrogen electrode) in 0.1 M HClO 4 electrolyte, outperform commercial Pt/C catalyst for 5.4 times. The superior stability of the SAA catalyst was reflected by the results from the 30,000 potential-scanning cycles combined with the post characterization of the catalyst. [Display omitted] • A single atom alloy (SAA) catalyst with well-defined platinum-cobalt (Pt-Co) dual sites was reported. • The unique Pt-Co dual sites in SAA facilitates the immobilization of OOH* intermediate and the dissociation of OH* intermediate. • The rationally designed PtCo SAA was found to have 4e- ORR activity in acidic media and exhibited high activity and durability. [ABSTRACT FROM AUTHOR]

• A facile epitaxial growth-pyrolysis tactic is proposed. • Highly porous and hollow non-noble metal carbon nanoarchitecture has been constructed. • The N-rich carbon protective layers embedded with cobalt nanoparticles boost the stability of the catalyst. • The Co@N-CNT-HC shows superior electrocatalytic activity for ORR. Fuel cells have emerged as a charming candidate for next-generation energy conversion devices. However, it is highly desired but challenging to engineer advanced non-precious oxygen reduction catalysts with highly actives and stability due to the sluggish kinetics of oxygen reduction reaction (ORR) on fuel cell cathode. Herein, a novel hybrid architecture with Co nanoparticles embedded in N-doped carbon nanotubes and hollow nanocarbon polyhedron (Co@N-CNT-HC) was constructed from core-shell ZIF-67@ZIF-8 via a facile epitaxial growth-pyrolysis process. With the Co@N-CNT-HC as the catalyst, a remarkable ORR performance is achieved in terms of a high half-wave potential of 0.84 V, a large limiting current density of 4.70 mA/cm2, and excellent long-term durability (97.8% current retention after 8 h) in alkaline medium, which outperform commercial Pt/C catalyst. Further dynamic calculations indicated that ORR follows a four-electron reaction mechanism. The enhancement activity of Co@N-CNT-HC is mainly due to the effective integration of 0D Co nanoparticles, 1D carbon nanotubes and 3D hollow nanocarbon, which synergistically strengthen the interfacial reaction kinetics of oxygen and accelerate mass/charge transfer. The strategy reported in this work provides a new insight to synthesis of low-cost and well-designed carbon hybrid electrocatalyst for ORR. [ABSTRACT FROM AUTHOR]

Abstract: The electrocatalytic performances of carbon nanotubes supported platinum (Pt/CNTs) with different Pt loadings for oxygen reduction reaction (ORR) and methanol oxidation (MOR) are studied contrastively. Pt/CNTs showed an opposite change rule along different Pt loadings for ORR and MOR, which is discussed based on the charge transportation and mass transfer. The results show that at low Pt loading, proton conduction is the key factor, which determines the MOR activity; at high Pt loading, mass transfer is crucial, which decides the ORR activity of Pt/CNT catalysts. The viewpoint proposed in this paper can guide the design and preparation of Pt based catalysts for the commercialization of direct methanol fuel cells. [Copyright &y& Elsevier]

Highlights: [•] FePc/SWNT heterojunction nanowires are prepared via a self-assembly approach. [•] FePc/SWNT performs much better than Pt/C in the ORR in alkaline media. [•] DFT and experimental results are combined to understand the ORR at FePc/SWNT. [•] The O2–FePc interaction is facilitated with fast electron transfer to the surface. [ABSTRACT FROM AUTHOR]

Carbon-based nanocomposites have developed as the most promising and emerging materials in nanoscience and technology during the last several years. They are microscopic materials that range in size from 1 to 100 nanometers. They may be distinguished from bulk materials by their size, shape, increased surface-to-volume ratio, and unique physical and chemical characteristics. Carbon nanocomposite matrixes are often created by combining more than two distinct solid phase types. The nanocomposites that were constructed exhibit unique properties, such as significantly enhanced toughness, mechanical strength, and thermal/electrochemical conductivity. As a result of these advantages, nanocomposites have been used in a variety of applications, including catalysts, electrochemical sensors, biosensors, and energy storage devices, among others. This study focuses on the usage of several forms of carbon nanomaterials, such as carbon aerogels, carbon nanofibers, graphene, carbon nanotubes, and fullerenes, in the development of hydrogen fuel cells. These fuel cells have been successfully employed in numerous commercial sectors in recent years, notably in the car industry, due to their cost-effectiveness, eco-friendliness, and long-cyclic durability. Further; we discuss the principles, reaction mechanisms, and cyclic stability of the fuel cells and also new strategies and future challenges related to the development of viable fuel cells. [ABSTRACT FROM AUTHOR]

Abstract: We have fabricated Cu2−x S/carbon nanodot (C dot) electrodes for direct methanol fuel cells (DMFCs). To the best of our knowledge, this is the first time that Cu2−x S/C dot nanomaterials (NMs) were proposed to be used as a cathode catalyst for oxygen reduction reaction (ORR) in acidic media. The structural characterizations revealed that Cu2−x S alloy possessed two types of crystalline phases, such as Cu9S5 and Cu2S in the structure of Cu2−x S/C dot NMs. The onset potential of the ORR for Cu2−x S/C dot NMs is 0.92V (vs. Ag/AgCl), revealing a good ORR activity of these NMs. The Cu2−x S/C dot electrodes (mass loading: 2.26mgcm−2) provide a mean limiting density of −1.77mAcm−2 at a scan rate of 5mVs−1 and rotation rate of 3600rpm. Electrochemical impedance spectrometry (EIS) results revealed that the charge-transfer resistance (R ct) of the Cu2−x S/C dots was smaller than that of Cu2−x S/CNT. In addition, compared with Pt/C electrodes, Cu2−x S/C dot electrodes were more tolerant against MeOH poisoning. The low-cost, electrochemically stable, and highly active Cu2−x S/C dot electrode has great potential for use in DMFCs. [Copyright &y& Elsevier]

Cobalt phthalocyanine (CoPc)-impregnated functionalized multi-walled carbon nanotubes (CNTs) were used as nonprecious electrocatalysts for oxygen reduction reaction (ORR). The electrocatalysts were thermally treated at temperatures ranging from 450 to 850 °C, and the effect of pyrolysis temperature and their relationship to the electrocatalytic activity for ORR were investigated. Thermo gravimetric analysis, X-ray diffraction, and electron microscopy were used to study the thermal stability, crystal structure, and morphology of these catalysts. Cyclic voltammetry and rotating disk electrode results showed that CoPc/CNTs pyrolyzed at a temperature of 550 °C had the highest electrocatalytic activity for ORR, and the catalytic activity decreased with further increase in pyrolysis temperature. X-ray photoelectron spectroscopy showed decrease in functional groups at a temperature higher than 550 °C, correlating with the decreased catalytic activity. The result suggests that oxygen functional groups introduced by acid oxidation for anchoring the CoPc on CNT plays a major role in determining the electrocatalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: The kinetics of the oxygen reduction reaction (ORR) occurring on nitrogen-doped carbon nanotubes (NCNT) and carbon supported platinum (Pt/C) catalysts in alkaline conditions is analyzed through rotating ring disk electrode (RRDE) measurements and modeled based on typical mechanisms reported in the literature. The purely chemical intermediate reactions are found to be insensitive in the modeling of this mechanism, whereby the models can be simplified to the occurrence of parallel two and four electrochemical electron pathways. Rotating ring disk measurements are shown to be an alternative technique to split the total current density into partial currents that could be associated with the respective reaction pathways. Experimental comparisons of the NCNT and Pt/C catalysts revealed that the ORR kinetics on these materials proceeds similarly throughout two and four electron pathways. The four-electron pathway is found to be the most dominant in both catalysts. Kinetic improvements for the NCNT catalysts are observed, positioning them as promising materials for the ORR catalysis in fuel cells. [Copyright &y& Elsevier]

Abstract: The in situ ion exchange method has been employed to prepare carbon nanotubes (CNT) supported Pt electrode, in which CNT is functionalized with two-step oxidation, namely electrochemical oxidation and chemical oxidation. X-ray photoelectron spectroscopy (XPS) confirms that two-step oxidation produces more carboxylic acid groups. Transmission electron microscopy (TEM) shows that Pt nanoparticles are highly dispersed on the CNT surface. Electrochemical measurements show that the resultant Pt/CNT electrode treated by two-step oxidation exhibits the largest electrochemical surface area and the highest activity for oxygen reduction reaction (ORR) among the investigated electrodes. This can be attributed to the fact that the two-step oxidation treatment produces more carboxylic acid groups which is the determining factor for Pt loading and dispersion via ion-exchange. [Copyright &y& Elsevier]

Abstract: The development of new cost-effective cathode catalysts with high methanol tolerance and at a high catalyst loading is highly desirable for the direct methanol fuel cell. The Pd3Pt1 bimetallic alloy nanoparticles highly loaded on different carbon supports, including Vulcan XC-72R carbon, single and multi-walled carbon nanotubes (SWCNTs/MWCNTs) and ordered mesoporous carbon (OMC), have been prepared by a modified polyol reduction route. The activities of the catalysts for the oxygen reduction reaction (ORR) have been studied based on the rotating disk and ring-disk electrode (RDE/RRDE) techniques in pure and methanol-containing electrolytes. X-ray diffraction indicates that all the Pd3Pt1/C nanoparticles evidence a single-phase fcc disordered structure. The mean particle size of Pd3Pt1 alloy nanoparticles on different supports is ca. 4–5nm even at a metal loading of 50wt%. Among various carbons supported catalysts, the highest ORR activity, found on the OMC-supported Pd3Pt1 catalyst, even surpasses that on the commercial Pt/C catalyst. Kinetic analysis reveals that the ORR on the Pd3Pt1/OMC catalyst predominantly undergoes a four-electron process, leading to water formation. Furthermore, the Pd3Pt1/OMC catalyst exhibited a higher methanol tolerance during the ORR than the commercial Pt/C catalyst; ensuring a higher ORR performance while diminishing Pt utilization. [Copyright &y& Elsevier]

Abstract: A carbon nanotube/perovskite composite material was developed as material for air electrodes in fuel cells or zinc-air batteries. For this purpose, carbon nanotubes were directly grown on the perovskite La0.6Sr0.4CoO3 impregnated with Fe solution which acted as substrate. The synthesis was carried out in a fluidised bed reactor. The carbon source was acetylene. The influence of the temperature on the growth of carbon nanotubes and on the stability of the perovskite was investigated. All samples contained multi-wall carbon nanotubes; however, at a temperature above 675 °C the perovskite was reduced by hydrogen originating from acetylene. The samples with the intact perovskite were further processed to air electrodes to catalyze the oxygen reduction reaction. These electrodes showed an improved performance compared to electrodes made of acetylene black and perovskites. [Copyright &y& Elsevier]

Abstract: The efficiency of fuel cells suffers from the high activation polarisation at the cathode, where the oxygen reduction reaction takes place. In order to improve the performance, air electrodes composed of carbon nanotubes (CNTs) and the perovskite La0.6Sr0.4CoO3 are produced by two different methods and investigated. In the first method CNTs are directly grown on the perovskite and in the second method CNTs and perovskite are combined by ultrasonic mixing. Their catalytic activity towards oxygen reduction in alkaline solution is evaluated by polarisation curves and electrochemical impedance spectroscopy. Best performance shows the electrode composed of 25wt% CNTs, 55wt% La0.6Sr0.4CoO3 and 20wt% PTFE as binder, produced by ultrasonic mixing. The Nyquist plot of this electrode displays two potential-dependent semi-circles, accounting for processes on the catalyst surface and for processes depending on the morphology of the electrode. [Copyright &y& Elsevier]

Nanostructured FeS dispersed onto N, S dual-doped carbon nanotube–graphene composite support (FeS/N,S:CNT–GR) was prepared by a simple synthetic method. Annealing an ethanol slurry of Fe precursor, thiourea, carbon nanotube, and graphene oxide at 973 K under N2 atmosphere and subsequent acid treatment produced FeS nanoparticles distributed onto the N, S-doped carbon nanotube–graphene support. The synthesized FeS/N,S:CNT–GR catalyst exhibited significantly enhanced electrochemical performance in the oxygen reduction reaction (ORR) compared with bare FeS, FeS/N,S:GR, and FeS/N,S:CNT with a small half-wave potential (0.827 V) in an alkaline electrolyte. The improved ORR performance, comparable to that of commercial Pt/C, could be attributed to synergy between the small FeS nanoparticles with a high activity and the N, S-doped carbon nanotube–graphene composite support providing high electrical conductivity, large surface area, and additional active sites. [ABSTRACT FROM AUTHOR]

The construction of optimized biological fuel cells requires a cathode which combines the longevity of a microbial catalyst with the current density of an enzymatic catalyst. Laccase-secreting fungi were grown directly on the cathode of a biological fuel cell to facilitate the exchange of inactive enzymes with active enzymes, with the goal of extending the lifetime of laccase cathodes. Directly incorporating the laccase-producing fungus at the cathode extends the operational lifetime of laccase cathodes while eliminating the need for frequent replenishment of the electrolyte. The hybrid microbial–enzymatic cathode addresses the issue of enzyme inactivation by using the natural ability of fungi to exchange inactive laccases at the cathode with active laccases. Finally, enzyme adsorption was increased through the use of a functionally graded coating containing an optimized ratio of titanium dioxide nanoparticles and single-walled carbon nanotubes. The hybrid microbial–enzymatic fuel cell combines the higher current density of enzymatic fuel cells with the longevity of microbial fuel cells, and demonstrates the feasibility of a self-regenerating fuel cell in which inactive laccases are continuously exchanged with active laccases. [ABSTRACT FROM AUTHOR]

Designing affordable high efficient oxygen reaction (ORR/OER) electrocatalyst is a major task for promoting sustainable energy conversion batteries (such as Zn-air batteries and fuel cells). Herein, a bifunctional oxygen reaction electrocatalyst with excellent activity and stability constructed using the peasecod-like N-doped carbon nanotubes (N/CNT) in situ confinement encapsulate bimetallic FeCu alloy (FeCu–N/C). The bimetallic FeCu alloy embedded into N/CNT that inhibits serious polymerization of copper, increases Fe/Cu–N bimetallic active sites, improves conductivity, reduces the energy barrier of oxygen reaction and speeds up reaction kinetics, thus obtaining efficient ORR/OER performance. The optimal FeCu–N/C electrocatalyst reveal more positive half-wave potential for ORR, smaller overpotential for OER and lower ORR/OER potential gap than those of commercial grade Pt/C, IrO 2 and many reported catalysts. Moreover, the zinc-air batteries constructed using FeCu–N/C as the air electrode indicate the high power density and excellent stability. The alkaline anion exchange membrane fuel cells assembled with FeCu–N/C as cathode also exhibit enhanced power density compared to single metal-based catalysts (Fe–N/C and Cu–N/C). This work demonstrates potential use of FeCu–N/C for energy conversion and storage applications, provides a new sight for the reasonable design of bifunctional oxygen reaction electrocatalysts. Image 1 • A bifunctional oxygen reaction catalyst constructed using FeCu alloy encapsulated in peasecod-like N-rich carbon nanotubes. • The FeCu alloy increases Fe/Cu-N bimetallic active sites, conductivity and electrocatalytic oxygen reaction activity. • The FeCu 0.3 -N/C exhibited the low ORR/OER potential gap (△ E) of 0.777 V and extraordinary stability. • The FeCu 0.3 -N/C reveals superb cathode catalytic activity in zinc-air batteries and anion exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

• Etching of KMnO 4 could well tune the pyridinic-N content and defects of N-CNT. • Etching of KMnO 4 significantly improved the ORR performance of N-CNT. • This catalyst even outperformed the commercial Pt/C in Zn-air battery. • The second nearest carbon atom to the pyridinic-N at the edge was the real active site. Increasing the number of active sites is critical for developing N-doped carbon electrocatalysts towards oxygen reduction reaction (ORR) in fuel cells and metal-air batteries applications. Herein, we prepared N-doped carbon nanotubes (N-CNT) with enriched pyridinic N and abundant defects resulted from the etching of KMnO 4 of the precursor (polypyrrole). It was observed that the content of pyridinic N could be well controlled by regulating the etching time. The resultant catalyst displayed a superior ORR activity compared commercial Pt/C in an alkaline solution, which was further confirmed by home-made Zn-air batteries. Density functional theory (DFT) computations showed that the superior catalytic activity originated from the second nearest carbon atom to the pyridinic-N at the edge. This work provides a simple etching approach to alter the N configuration and the amount of defects in N-doped CNT, which can be extended to many other energy conversion materials. [ABSTRACT FROM AUTHOR]

SYNOPSIS TOC Hierarchical structured Fe 3 C/Co/N-doped carbon nanotubes were rationally designed and controllable synthesized by a novel and efficient multi-step approach. Benefiting from the unique structural and composition characteristics, the catalysts exhibited excellent electrochemical performance for oxygen reduction reaction in alkaline electrolyte, even better than commercial Pt/C. This introduced synthesis approach can open up new opportunities for the design and synthesis of other MOF assemblies and their derivatives with high performance, not only in the energy field, but also in other frontiers. • Hierarchically porous Fe 3 C/Co/N-doped carbon nanotubes are designed and prepared. • The components effects on the electro activity have been systematically studied. • It is a general way for the preparation of other catalysts with high performances. It is critical and challenging for preparing nonprecious metal catalysts with high catalytic performance in fuel cells and metal-air batteries. In this work, we developed an efficient multistep approach to synthesize metal-organic framework (MOF)@Fe-Phen nanotube-derived composite electrocatalyst (CNCo-n@Fe-x), which consisted of N-riched mesoporous carbon nanotubes with high graphitization degree and uniformly distributed active sites (Co, Fe 3 C, N-C, Fe-Nx, and Co-Nx). Experimental results indicated that the bimetallic doping was superior to a single metal. Benefiting from the unique hierarchical structure and the synergies among the active sites also the high conductivity, as expected, the composite nanotubes exhibited excellent electrochemical performance for oxygen reduction reaction in alkalinity electrolyte, even better than the commercial Pt/C catalyst. More importantly, when used for constructing the air electrode of the Zn-air battery, CNCo-5@Fe-2 nanotubes also displayed high performance. [ABSTRACT FROM AUTHOR]

• An overview of the state-of-the-art in oxygen reduction reaction is presented. • In-depth discussion of carbon dots and their practical applications in fuel cell. • An analysis of recent progress in carbon nanotubes applied on a fuel cell. Proton exchange membrane fuel cell (PEMFC) is receiving strong attention in sustainable energy conversion and storage systems. Its high efficiency, low emission, and environmental friendliness enable hydrogen fuel cell electric vehicle (FCEV) for day to day transportation. High costs, limited durability and inefficient oxygen reduction reaction (ORR) have been identified as key challenges for the widespread commercial success of fuel cell transportation vehicles. ORR is constrained by slow kinetics of cathode catalyst and must be improved by suitable nanoengineering of low-cost electrocatalysts. Replacing platinum group metals with carbon-based non-precious metal is a promising solution. Recently, advances in zero-dimensional carbon dots are showing promise for challenging energy-oriented issues. In addition, the one-dimensional carbon nanotubes are also found suitable for efficient ORR. However, carbon-based electrocatalyst showing improved performance in electrochemical measurements are not up to the expectation in the practical application of FCEV. This review highlights the advancement and future opportunities for improving performance of ORR using carbon dots and carbon nanotubes nanostructures. We discussed the application of carbon dots and carbon nanotubes in the fuel cell. Their corresponding electrochemical performance was presented. Followed by, practical application of carbon nanotubes in the real operating condition of PEMFC was discussed. Finally, the current status and future target of FCEV were comprehensively addressed. [ABSTRACT FROM AUTHOR]