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The success of the next generation of anion-exchange membrane fuel cells (AEMFCs) depends on the development of active, reliable, and economical oxygen reduction reaction (ORR) catalysts. Here, we synthesize a series of ultra-low-cost metal-free ORR catalysts by doping a common pristine graphite precursor with chemically singular-type heteroatoms, namely I, S, N, or B, using single-step planetary ball milling technique. All doped-graphites show substantially enhanced ORR performance relative to the pristine (undoped) graphite. Among all the tested catalysts, N-graphite exhibited the highest ORR onset potential of 0.87 V vs. reversible hydrogen electrode. These results are supported by density functional theory calculations. The ORR catalysts also exhibit remarkable stability as evaluated through electrochemical tests. Most importantly, the AEMFCs prepared using these ultra-low-cost doped graphites deliver notable peak power densities with impressive voltage efficiencies, which further supports their efficacy in ORR catalysis and the broad implementation of this technology. [Display omitted] • Highly active metal-free doped-graphite catalysts for alkaline ORR are developed. • Comprehensive alkaline ORR investigation by structural and DFT modeling. • Remarkable catalyst stability is shown by electrochemical and corrosion tests. • High-performance anion-exchange membrane fuel cells using metal-free cathodes. • Ultra-low-cost ORR metal-free catalyst materials and fabrication process. [ABSTRACT FROM AUTHOR]

Iron,nitrogen-codoped carbon (FeNC) has emerged as promising alternatives to precious metals for oxygen reduction reaction (ORR). Herein, we demonstrate that the ORR activity of FeNC can be markedly enhanced by the incorporation of adjacent Fe few-atom clusters (Fe AC), where the octahedral field of Fe AC boosts the splitting of the parallelogram field of FeN 4 , and facilitates the transition from high-spin (t 2g 3e g 2) Fe(III)N 4 to medium-spin (t 2g 5e g 1) Fe(II)N 4 and hence the interaction with the π* antibonding orbitals of oxygen. This leads to a remarkable ORR performance due to optimized desorption of the OH* intermediate on FeN 4 , with a half-wave potential of +0.80 in 0.1 M HClO 4 , in comparison to that with only FeN 4 single-atom moieties. In H 2 -O 2 fuel cell tests, a high peak power density of 0.80 W cm−2 is obtained. Results from this work highlight the significance of spin engineering in the manipulation and optimization of the ORR activity of single-atom catalysts. [Display omitted] • Pyrolytic treatment of Fe-doped ZIF-8 and C 3 N 4 at controlled feed ratios. • Formation of Fe few-atom clusters (Fe AC) adjacent to Fe single atom centers (Fe SA). • Transition from high-spin Fe(III)N 4 to medium-spin Fe(II)N 4 by Fe AC. • Enhanced ORR/PEMFC performance by optimized desorption of OH* on FeN 4. [ABSTRACT FROM AUTHOR]

The metal-nitrogen-carbon (M-N-C) type oxygen reduction reaction (ORR) catalysts are promising for hydroxide exchange membrane fuel cells, but catalysts with further improved performance are challenging. Here, we report the efficient improvement of the ORR activity of M-N-C catalysts by employing highly polarizable metal cation Ag+. Ag, Fe single atomic sites embedded in concave nitrogen doped carbon (Ag 1 Fe 1 /CNC) is successfully synthesized and shows high performance towards ORR, indicating by both the ultra-high half-wave potential of 0.917 V and membrane electrolyte assembly performance of peak power density up to 1.26 W cm−2. The binding energy of the ORR intermediates on the highly polarizable Ag site in Ag 1 Fe 1 /CNC was significantly tuned by the adjacent Fe site by more than 0.2 eV, and thus leading to a low theoretical ORR overpotential of only 0.398 V. The employment of the highly polarizable metal cation brings a novel and efficient approach to construct highly active catalysts. [Display omitted] • High performance oxygen reduction reaction catalyst Ag 1 Fe 1 /CNC is synthesized. • The highly polarizable Ag site shows ultra-high catalytic activity. • The Ag sites are significantly affect by the adjacent metals. • High membrane electrolyte assembly performance is achieved by using Ag 1 Fe 1 /CNC. [ABSTRACT FROM AUTHOR]

Single-atom manganese catalysts possess high stability in the oxygen reduction reaction (ORR) due to their lower Fenton reaction activity. Here, we employ N- and S-co-coordination strategy to modulate the microstructural Mn sites towards high-efficiency ORR. The fabricated Mn-N/S-C catalyst with isolated Mn-N 2 S 2 sites demonstrates a positive half-wave potential of 0.91 V for the ORR. The fabricated zinc–air battery with Mn-N/S-C as the cathode affords a maximal power density of 193 mW cm−2 and superior output stability. Moreover, the maximal power density is increased by 1.53 times compared with S-free Mn-N-C catalyst in anion exchange membrane fuel cells (AEMFCs). Both experimental characterizations and theoretical simulations unveil that the main active sites in the Mn-N/S-C should be Mn-N 2 S 2 moiety embedded into the graphene framework (Mn-N 2 S 2 G). Further computational results demonstrate that the S atom doping and asymmetry of structure lead to higher ORR activities of ortho-Mn-N 2 S 2 G than Mn-N 4 G, Mn-N 3 SG, para-Mn-N 2 S 2 G and Mn-NS 3 G. [Display omitted] • N- and S-co-coordination to isolated Mn sites improves the catalytic activity. • The Mn-N/S-C exhibits a positive half-wave potential of 0.91 V for the ORR. • The Mn-N/S-C-based zinc–air battery affords a peak power density of 193 mW cm−2. • The Mn-N/S-C-based AEMFC affords a peak power density of 247 mW cm−2. • Ortho-Mn-N 2 S 2 G shows higher activity than Mn-N 4 G, para-Mn-N 2 S 2 G and Mn-NS 3 G. [ABSTRACT FROM AUTHOR]

Surface engineering has been identified as an effective way to maximize the utilization of noble atoms and facilitate the oxygen reduction reaction. However, a cost-effective and highly durable platform for tailoring the electrocatalytic activity, is still absent. Herein, we demonstrate a new and promising catalytic material of antiperovskite-typed PdNFe 3 and construct a high performance PdNFe 3 @Pd catalyst with atomic layers of strained Pd shell. The PdNFe 3 @Pd/C catalyst presents a high mass activity (MA) of 1.14 A mg−1 Pd at 0.9 V, which is 9 and 6 times higher than those of the Pt/C and Pd/C, respectively. More importantly, the excellent performance of PdNFe 3 @Pd/C was also verified in anion-exchange membrane fuel cells and rechargeable Zn−air batteries. Density functional theory calculations reveal that the strain effect aroused by the lattice mismatch between PdNFe 3 core and Pd shell contributes to the enhanced ORR performance by optimizing the binding strength of oxygen intermediates on Pd. [Display omitted] • Demonstrating a new class of platform/core materials for constructing core-shell catalysts. • Elucidating catalytic mechanism of PdNFe 3 @Pd towards ORR. • Extraordinary catalytic performance towards oxygen reduction. [ABSTRACT FROM AUTHOR]

Supported ordered intermetallic nanoparticles are of significant interest for catalysis applications owing to their unique surface/near-surface structures and electronic properties. However, the synthesis of small-sized intermetallic catalysts with high mass activity remains a formidable challenge, as high temperatures annealing treatments are generally requisite to achieve ordered intermetallic structures but lead to undesired larger crystallites. Here, we report an industrially relevant impregnation approach for the scalable synthesis of small-sized platinum-based intermetallic nanoparticle catalysts by regulating inter-particle distance on carbon black supports to mitigate metal sintering in high-temperature annealing. We construct a library consisting of 18 binary Pt-based intermetallic nanoparticle catalysts with an average size of < 5 nm. The prepared intermetallic catalyst libraries exhibit outstanding proton-exchange-membrane fuel cells performance, including high mass activities of 1.3–1.8 A mg Pt –1, large peak power densities of 1.2–1.4 W cm–2 in H 2 -air cells, and efficient Pt utilization of ∼0.07 g kW–1 at rated power. [Display omitted] • Intermetallic compounds (IMC) have unique strain/electronic effects in catalysis. • A family of small size Pt-based IMCs was achieved by regulating inter-particle distance. • Small size and ordered IMC structure guarantee outstanding performance in fuel cell. [ABSTRACT FROM AUTHOR]

Developing efficient and durable Pt-based electrocatalysts for oxygen reduction reaction (ORR) is critical for the practical application of fuel cells but still remains challenge at present. Here we successfully synthesized a series of ternary L1 0 -PtCo x Fe 1-x (x=0.33, 0.50 and 0.67) intermetallic nanoparticles (NPs) supported on reduced graphene oxide for ORR catalysis. L1 0 -PtCo 0.50 Fe 0.50 exhibits the highest mass activity (MA) of 0.93 A mg−1 Pt at 0.9 V (1.82 times the corresponding binary L1 0 -PtCo intermetallics) and minimal activity loss (24.73 % loss in MA) after 30,000 potential cycles. By Density Functional Theory calculations, the excellent performance of ternary L1 0 -PtCo 0.50 Fe 0.50 can be ascribed to: (1) more efficient electronic structure regulation caused by dual-element driven electron transfer, which leads to more electron accumulation on Pt and weakens the over-binding of oxygen-containing species, (2) the unique two-center bridge pattern of O 2 adsorption over Pt-Fe site leads to ORR proceeding via. the dissociative mechanism, avoiding the formation of OOH*. [Display omitted] • The L1 0 −PtCo 0.50 Fe 0.50 shows efficient and stable performance for ORR catalysis. • The double-element (Co/Fe) drives more electron transfer to Pt. • The Pt-Fe sites induce ORR proceeding via. the dissociative pathway. • The effect of co-catalytic elements on boosting ORR activity was revealed. [ABSTRACT FROM AUTHOR]

We synthesized ordered mesoporous Fe/N/C with highly active Fe-N x /C sites denoted as m-FePhen-C as a non-precious metal catalyst (NPMC) for the oxygen reduction reaction in fuel cells. This was the first study that incorporated a catalyst precursor with Fe-N coordination directly in a simple block co-polymer-assisted soft-template method for the synthesis of mesoporous Fe/N/C. The synthesized catalyst (m-FePhen-C) showed a high catalytic performance comparable to that of Pt/C in half-cell tests, and a membrane electrode assembly (MEA) with an m-FePhen-C cathode exhibited 40% higher power density than did an MEA with a commercial Pt/C cathode in single-cell tests, with comparable electrode thicknesses. This result is highly meaningful in that generation of the Fe-N x /C active sites and formation of ordered mesoporous structure were achieved simultaneously in the simple soft-template-assisted process, and in that the advantages of mesoporous structure with appropriate pore size in metal-containing NPMC were elucidated for high-performance MEAs. [ABSTRACT FROM AUTHOR]

Graphitic layer encapsulated iron based nanoparticles (G@FeNPs) have recently been disclosed as an interesting type of highly active electrocatalysts for the oxygen reduction reaction (ORR). However, the complex composition of the metal-containing components and their contributions in catalysis remain unclear. As a representative catalyst of the unique encapsulated structure, a series of G@FeNPs catalysts were prepared by a high-pressure pyrolytic process with uniform and essentially identical morphologies but varied compositions. The catalysts exhibited a high onset potential of 0.85 V at 0.1 mA cm −2 in acidic media. By 57 Fe-Mössbauer spectroscopy the iron containing components were identified including α-Fe, γ-Fe, γ-Fe 2 O 3 , and Fe 3 C as well as a minor doublet component due to Fe 3+ in high spin and/or Fe 2+ in low spin state. The ORR activities are evaluated in terms of the mass specific kinetic current density found to be positively correlated with the Fe 3 C content in the range of study, indicating involvement of the encapsulated nanoparticles in the ORR catalysis. The recognition of the Fe compositions and active sites provides new insights to the confined Fe-based ORR electrocatalysts and therefore options for further development of non-precious metal materials. [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]

Tubular type carbon nanofibers (TCNFs) are prepared and used as a catalyst support material for a cathode electrode of low temperature fuel cells through structural modification. The pristine TCNF is treated by graphitization and makes partially torn-tube shape through the surface expansion by rapid thermal treatment of the oxidized graphitized TCNF. Physical properties of the TCNF group are examined, and it is confirmed that the unique ripped texture along fiber axis with graphitic structure is obtained by the surface expansion. Platinum catalysts supported on these TCNF group are prepared and evaluated. Electrochemical properties are examined via cyclic voltammograms and polarization curves for oxygen reduction reaction activity. The platinum catalyst on the surface expanded TCNF has the enhanced activity at initial and the stable performance even after accelerated durability test due to their unique structure. [ABSTRACT FROM AUTHOR]

AEMFC is becoming a prominent technology in portable energy sources. In an attempt to make it economical, non-platinum catalysts are necessary to recruit in the application. Numerous researches are accomplished on the development of platinum-free catalysts. This review summarizes the advancements in the synthesis of catalysts consisting of different components and structures. Rotating ring-disk electrode (RRDE) and fuel cell tests are commonly employed to evaluate the activity for oxygen reduction reaction (ORR) and performances of the catalysts. Here, along with the synthesis and characterization data, this information is assembled and analyzed correlating different factors. To the best of our knowledge, 13 among 203 catalysts have overcome the peak power density (PPD) threshold of 1000 mW.cm-2, which belong to the four categories i.e. Metal-Nitrogen-Carbon (M-N-C), Bimetals-Nitrogen-Carbon (MM-N-C), Transition metal oxides (TMO), and non-metallic catalysts (NMC). The improvement in catalyst's porosity, surface area, conjugation of active sites, and thereby the synthesis procedures have a great effect on the ORR activity and fuel cell performance. In addition to catalyst properties, there are several other significant factors involved such as water management, properties of anion-exchange membrane (AEM) and anion-exchange ionomer (AEI), optimized operating conditions, etc. The previously low-performing catalysts with high ORR activity cannot be ignored from the top-tier catalysts, since enormous improvements are accomplished in membrane conductivity and water management recently. [Display omitted] [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is at the core of various applications, such as fuel cells, metal-air batteries and H 2 O 2 electro-generation. Depending on the targeted application, catalysts that follow a “direct four-electron (4e − )” pathway or “two-electron (2e − )” pathway are envisaged. We have systematically investigated the impact of the electrocatalyst loading on the rotating ring-disk electrode (RRDE), on their activity and selectivity towards ORR in alkaline medium (0.1 M and 1 M KOH). Four representative catalysts, including a noble metal catalyst (commercial 20 wt% Pt/C, ETEK), metal-free catalysts (Printex carbon black and graphene), and non-noble metal catalyst (Fe/N/C), were selected because they exhibit different behaviours for ORR following a “direct four-electron (4e − )” pathway, “two-electron (2e − )” pathway, or a “series 2e − + 2e − ” pathway. The results confirmed that the catalyst loading influences the activity and the selectivity of the catalysts, with lower loadings favoring the H 2 O 2 electrogeneration, and researchers should pay attention to it. Moreover, in order to make possible comparison between results coming from different research groups, we recommend reasonable loading ranges for each type of catalyst. [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]

The preparation of ultra-small structurally ordered Pt-based intermetallic nanocrystals (< 3 nm) is still challenging due to the sintering during high temperature ordering. We report a strategy to construct size and distribution controllable Pt-based intermetallic nanocrystals based on ultra-thin metal oxide coating on Pt nanoparticles via atomic layer deposition. The area-selective and thickness controllable metal oxide coatings can not only provide metal atoms for alloying, but also prevent the sintering of Pt nanoparticles during subsequently fast ordering reduction. The prepared uniform PtZn intermetallic nanocrystals with the size of 2.50 ± 0.65 nm achieve outstanding single-cell performance with the mass activity of 0.48 A mg Pt −1 at 0.9 V and 10.42 % loss of mass activity after 30,000 voltage cycles, which is superior to commercial Pt/C. The enhanced activity and durability is attributed to the decreased binding energy of Pt-oxygen intermediates for weakly polarized surface Pt atoms and suppressed electrochemical Ostwald ripening. [Display omitted] • Uniform sub-3 nm PtZn intermetallic is synthesized by selectively coating ultra-thin ZnO on Pt nanoparticles via atomic layer deposition. • Ultra-thin ZnO coating can provide Zn atoms for alloying and prevent the sintering of nanoparticles during ordering reduction. • The enhanced activity is attributed to the decreased binding energy of Pt-oxygen intermediates for weakly polarized surface Pt atoms. • Sub-3 nm PtZn intermetallic nanocrystals with uniform size distribution suppress electrochemical Ostwald ripening in acid conditions. [ABSTRACT FROM AUTHOR]

With extensive development over the past ten years, non-precious metal (NPM) catalysts have become promising alternatives to platinum catalysts in fuel cell cathodes, but have been challenged by severe transport limitations. Hard template synthesis, also called the sacrificial support method, promises to improve transport properties introducing a sacrificial template to form mesopores. To further understand hard template transport properties, the relationship between template morphology, resulting catalyst pore structure, and overall fuel cell performance was investigated. Porous carbon materials and catalysts were synthesized using four different silica templates. Nitrogen physisorption and scanning electron microscopy were used to characterize pore diameter and morphology. The catalysts displayed pores approximately half the diameter of the template particles, and a geometric model is proposed to describe pore collapse. Catalyst electrochemical performance was characterized in membrane electrode assemblies using the hard templated materials in gas-diffusion electrodes for oxygen reduction. An optimum pore diameter was observed at approximately 9 nm. [ABSTRACT FROM AUTHOR]

The Fe-N-C single-atom catalysts (SACs) have been widely explored for oxygen reduction reaction (ORR) in fuel cells. However, how to improve the ORR activity by tailoring the electronic structure of Fe-N-C catalysts is challenging. Herein, we synthesize a Fe-Mn-N-C dual-atom catalyst (DAC) with new local structure of FeN 4 -MnN 3 moiety, and it exhibits ultralow H 2 O 2 yield and better ORR performance than Fe-N-C and Mn-N-C SACs. Importantly, the Fe-Mn-N-C-based proton-/anion- exchange membrane fuel cells present ultrahigh power densities of 1.048 W cm−2 and 1.321 W cm−2, respectively. DFT results reveal that the strain yielded by the formation of Mn-Fe bond significantly optimizes the electronic structure of the Fe-Mn-N-C, and the co-adsorption of the Fe-Mn dual-sites for *OOH not only almost completely suppresses the 2e- ORR, but also breaks the linear correlation between G OH* and G OOH* proposed by Norskov et al., which provides a new route for the design of dual- site catalysts. [Display omitted] • Fe-Mn-N-C dual-site catalyst with FeN 4 -MnN 3 moiety exhibits ultrahigh ORR activity in acidic and alkaline media. • Fe-Mn-N-C-based PEMFC and AEMFC present ultrahigh peak power densities of 1.048 W cm−2 and 1.321 W cm−2. • DFT results reveal that the Mn-Fe bond induced strain efficiently optimizes the electronic structure of the Fe-Mn-N-C. • The co-adsorption of Fe-Mn dual-sites for *OOH almost suppresses 2e- ORR, which provides a new strategy to design catalysts. [ABSTRACT FROM AUTHOR]

Highly effective electrocatalysts are of vital importance for advanced applications. Here we show that fully π-conjugated dense topological salophen organic frameworks with atomic dispersed tetradentate cobalt sites in-situ growth on Kejtenblack are high-efficiency and durable electrocatalyst for the oxygen reduction, with a remarkable half-wave potential of 0.959 V which surpassing that of benchmark Pt/C catalyst, and is among the highest of reported single atom electrocatalysts. The electron transfer number was 3.92–3.99 and the yield of peroxide remains below 4% in 0.40–0.95 V. When employed as a cathode electrocatalyst for zinc-air batteries, it showed a high open-circuit voltage (1.5558 V) and maximum power density (178 mWcm−2) and high specific capacity (804 mAhg zn −1). The work reported here revealed that tailoring the active centers, conjugated structures, building blocks and topologies at atomic level could synergistically enhance the ORR activity which are highly valuable for zinc–air batteries and fuel cells. [Display omitted] • Fully π-conjugated dense topological SOFs with atomic dispersed tetradentate cobalt sites were synthesized. • The synthesized CoN 2 O 2 -SOF/KB revealed superb oxygen reduction activity and highly 4-electron selectivity. • The synthesized CoN 2 O 2 -SOF/KB displayed high efficiency ORR activity with a half-wave potential of 0.959 V. • The prepared ZAB exhibits a high specific capacity of 804 mAh g−1 and maximum power density of 178 mWcm−2. [ABSTRACT FROM AUTHOR]

In the present work, graphene nanoflakes (GNFs) were grown at both low and high levels of nitrogen functionalization and subsequently put through a wet-chemical method to add iron functionalities to the surface and create active catalyst centers. No mechanical treatments are used in order to minimize the formation of defects on the GNFs and evaluate if iron-nitrogen-GNF edges or surface sites can generate catalytic activity rather than the macropore structures holding these functionalities on porous carbon black. The catalysts produced under various synthesis routes were characterized and screened for their performance as an oxygen reduction reaction (ORR) catalyst. Characterization included an electrochemical study, an examination of the carbon and nitrogen content and bonding structure, in addition to Raman analysis and the calculation of the BET surface areas. It was found that samples that were both treated with iron acetate and put through pyrolysis produced the most active samples. These samples were composed of graphitic carbon and contained a large amount of pyridinic nitrogen. Additionally, when working with GNFs generated with high levels of nitrogen, no extra nitrogen source was needed during the iron incorporation step. This study further develops the GNF-based catalyst already seen to be a suitable ORR catalyst for the polymer electrolyte membrane fuel cell. [ABSTRACT FROM AUTHOR]

Carbon xerogels represent nowadays an outstanding alternative to carbon blacks for the preparation of efficient fuel cell electrocatalysts, due to their easily tunable and well developed mesoporous structure. To further improve both activity and durability of Pt/C catalysts, the introduction of heteroatoms (such as O, N, S, P, B, etc.) in the structure of carbon materials has been proposed. In the present work, highly mesoporous carbon xerogels (CXGs) have been subjected to a sulfurization process with elemental sulfur. The insertion of S into the carbon matrix does not compromise their mesoporous structure. Pt catalysts supported on sulfurized carbon xerogels show enhanced catalytic activity towards both the methanol electro-oxidation and the oxygen electro-reduction reactions, exceeding not only the performance of the catalyst supported on the bare xerogel, but also of the catalyst supported on a commercial carbon black. The sulfurization treatment is also effective in improving the resistance of Pt/CXG catalysts towards corrosion phenomena occurring at the fuel cell cathode. [ABSTRACT FROM AUTHOR]

Graphene-like (G), multiwalled carbon nanotubes (CNTs) and active carbon (AC) have been used as carbon matrix for the synthesis of Fe/N/C catalysts for the oxygen reduction reaction. A thorough physicochemical characterization of the electrocatalysts, including X-ray photoelectronic and X-ray absorption spectroscopies, reveal that the formation of Fe/Nx ensembles is favored when the graphene-like or the CNTs are used as the carbon matrix. As a result, the catalyst prepared with the graphene matrix (Fe/N/G) records the highest activity for the ORR in the series of 3.1 A g −1 at 0.9 V. This very high ORR activity positions these catalysts as a realistic alternative to replace Pt/C cathodes in alkaline fuel cells. Moreover, using graphene as the carbon matrix endows the catalyst with very high stability during the ORR showing stable catalytic performance for the ORR even after being subjected to severe treatments of 3000 cycles up to 1.4 V. In situ IRRA spectra demonstrate that such a high stability for the ORR relates to the excellent resistance against corrosion of the graphene-based catalyst. [ABSTRACT FROM AUTHOR]

Exploring excellent catalysts for oxygen reduction reaction (ORR) with a facile and cost-effective method is desirable but remains challenging. Herein, ultra-small PtCu 3 nanoparticles (ca. 2.7 nm), immobilized on reduced graphene oxide (rGO), were synthesized via a novel and general strategy. Traceless protectant, NH 4 OH, was used to resist the aggregation of graphene oxide (GO), and the spray-freeze-drying method ensures excellent dispersion of the Pt and Cu precursors, which could not be achieved by other reported drying methods. After annealing, the nanoparticles with the highest mass loading, 52%, among reported ordered Pt-based catalysts were obtained. The PtCu 3 /rGO shows a remarkable electrocatalytic performance. Density functional theory calculations elucidate that PtCu 3 possess a lowered energy barrier of the rate-determining step, contributing to significantly improved ORR kinetics. This strategy was extended to the synthesis of other binary- and quaternary-metallic Pt-based nanoparticles, which proved its generality and applicability towards the potential commercialization of fuel cell technologies. [Display omitted] • This strategy uses a transient protectant, NH 4 OH, which successfully assists graphene oxide in resisting folding. • A novel spray-freeze-drying method ensures the mono-dispersion of Pt and Cu precursors on GO. • With ultra-small size and ordered structure of NPs, high mass loading PtCu 3 /rGO shows significant improved ORR performance. • This strategy is generally applicable, demonstrated by extending to the synthesis of other Pt-M NPs. [ABSTRACT FROM AUTHOR]

It is very important to improve the mass activity and durability of platinum (Pt) catalysts for oxygen reduction and the oxidation of small organic molecules for fuel cell applications. A strong interaction between Pt and the support materials can change the electronic structures of platinum, enhancing catalytic activity and durability. Here, we deposited various amounts of Pt on TiN supports and characterized these catalysts using electron microscopy, H 2 uptake, XANES, XPS, and valence-band XPS. The Pt nanoparticles had very small sizes (<2 nm) with a narrow size distribution. Compared to a commercial Pt/C catalyst, the Pt surface in Pt/TiN catalysts was in a higher reduction state, and the Pt d-band center was downshifted. The results of DFT calculations confirmed that Pt could be stabilized on the TiN surface and that the Pt d-band center is downshifted relative to bulk Pt. The activity and durability of the Pt/TiN catalysts was enhanced for the oxygen reduction reaction and formic acid oxidation over that of the Pt/C catalyst. For the oxygen reduction reaction at 0.9 V (vs. RHE), the mass activity was 0.29 A/mg Pt for the 10 wt% Pt/TiN catalyst and 0.17 A/mg Pt for the Pt/C catalyst. After 5000 cycles of an accelerated durability test, the Pt/TiN exhibited a mass activity of 0.24 A/mg Pt , whereas the Pt/C catalyst exhibited a mass activity of 0.12 A/mg Pt . The Pt/TiN catalyst followed a direct pathway with fewer surface-poisoning intermediates for formic acid oxidation, which enhanced the activity of the Pt/TiN catalyst over that of the Pt/C catalyst. The modification of the electronic structure of Pt catalysts by interaction with TiN supports can significantly enhance the activity and durability of the catalyst. [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]

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]

Discovering an active and durable catalyst for oxygen reduction reaction is crucial to the commercialization of fuel cells, but remains grand challenging. Here we report, for the first time, the trace doping of early transition metal (ETM) Re into ultrathin PtNiGa nanowires (Re-PtNiGa NWs) to construct a novel catalyst integrating the superior activity, long-time durability, and high utilization efficiency of Pt atoms. Impressively, the Re-PtNiGa tetrametallic NWs present a 19.6-fold enhancement in mass activity (3.49 A mg−1 Pt) compared to commercial Pt/C catalyst and only a 10.6% loss in mass activity after 20,000 cycles of durability test. Moreover, the real fuel cell assembled by Re-PtNiGa NWs on the cathode strongly supports its great potential in fuel cells. The density functional theory calculations reveal that introduction of ETM Re into PtNiGa NWs could weaken binding strength of oxygenated species and elevate dissolution potential, well rationalizing the great enhancements in activity and durability. [Display omitted] • The trace doping of early transition metal Re into ultrathin PtNiGa nanowires to construct a novel catalyst was reported. • Ultrathin Re-PtNiGa NWs presented a 19.6-fold enhancement in mass activity(3.49 A mg−1 Pt) compared to commercial Pt/C. • The H 2 -O 2 PEMFC assembled by Re-PtNiGa NWs delivered a negligible decay (4.9%) of the output current density for 100 h. • This study revealed that doping of Re could weaken binding strength of oxygenated species and elevate dissolution potential. [ABSTRACT FROM AUTHOR]

Highlights: [•] The amide-groups are grafted over carbon surface via a simple solvothermal route. [•] Cobalt oxides of 2nm uniformly supporting on the carbon blacks were synthesized. [•] CoO x /XC N shows superior ORR activity than CoO x /XC and CoO x /XC O. [•] The enhanced ORR activity is contributed to the higher content of CoO in composite. [ABSTRACT FROM AUTHOR]

Highlights: [•] ALD is solvent-free, controlled method suitable for preparing bimetallic particles. [•] Metal location and particle size effecting catalyst activity was modified by ALD. [•] Synthetized nanoparticles have well defined surface structure. [•] The catalysts show enhanced activity for important fuel cell reactions MOR and ORR. [•] Catalyst durability in MOR is adjusted by suitable catalyst preparation parameters. [ABSTRACT FROM AUTHOR]

Highlights: [•] Good performance is obtained for PtCo alloy/Ta-doped Ti-oxide for ORR in PEMFCs. [•] High electrochemical stability is shown by PtCo/Ta-doped Ti-oxide at 1.4V RHE. [•] Oxide support shows promoting effect for ORR at intermediate temperatures (110°C). [•] Higher performance is achieved with Pt–Co/oxide vs. Pt/oxide in PEMFCs. [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]

Abstract: Graphene based non precious metal catalysts for oxygen reduction reaction (ORR) has been successfully fabricated through pyrolysis of a mixture of Fe, Co salts, polyaniline, and reduced graphene oxide (rGO). The transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), Raman spectrum and X-ray photoelectron spectroscopy (XPS) analysis''s indicated the transition metal nitrogen-containing moieties (M–N x , M=Fe or/and Co, x =2 or 4) could be embedded into the graphene sheets. The electrochemical measurements showed that the embedded M–N x moieties could act as catalytic sites and boost the activity of catalysts in both acidic and alkaline medium. The effects of Fe and Co on electrochemical properties toward ORR were also investigated, and the results showed the binary metal FeCo–N–rGO was the most active ORR catalyst. Rotating disk electrode measurements revealed that, compared to a commercial Pt/C electrocatalyst (loading: 52.6μgPtcm−2), the half-wave potential of the resultant FeCo–N–rGO was 46mV positive in alkaline medium and 119mV negative in acidic medium. In addition, the FeCo–N–rGO catalyst was much more stable and tolerant to crossover effect than Pt/C. The above superiorities make it a promising candidate for substituting Pt-based nanomaterials as a cathode catalyst for ORR in fuel cells. [Copyright &y& Elsevier]

Abstract: The development of non-noble metal catalysts is of great interest due to their significant potential application in both fuel cell systems and metal–air batteries, particularly when considering long term commercial deployment. In this regard, novel Co-N-S/C non-noble metal catalysts supported on carbon, are synthesized in this study using a solvent-milling method followed by heat-treatment at elevated temperatures. Pyridine is used as the nitrogen-rich ligand for Co-N x precursor complex formation. The morphology and composition of the catalyst are characterized by X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM) as well as X-ray photoelectron spectroscopy (XPS). Several catalysts containing different amounts of Co are also synthesized. The optimal Co content is found to be in the range of 10–15wt% nominal, in terms of catalytic oxygen reduction reaction (ORR) activity. This catalyst shows high electroactivity for the ORR with a high stability in alkaline media. Using rotating disk electrode measurements, and Koutechy–Levich analysis, the overall electron transfer number in the catalyzed ORR is found to be 3.8–4.0, suggesting the catalyzed ORR is a four-electron transfer process from O2 to H2O. [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: An effective method is developed for preparing highly dispersed CeO2 nanoparticles on a Pt/C catalyst synthesized by a continuous two-step process as a cathode material in low-temperature fuel cell. The XRD patterns of the 20Pt–10CeO2/C catalyst reveal that both crystalline Pt and CeO2 phases coexist. The HR-TEM images show that Pt and CeO2 nanoparticles have average particle sizes of approximately 3.4nm and 4.2nm, respectively, with quite a narrow distribution between 3nm and 5nm. Based on the analysis of the polarization curves for the ORR, the optimum proportion of CeO2 into the 20Pt/C catalyst is 10wt%. In the ORR and single cell tests, the 20Pt–10CeO2/C catalyst shows higher performance than the commercial 20Pt/C catalyst, owing to the oxygen storage capacity of CeO2 and its ability to exchange oxygen rapidly with oxygen in the buffer. In the accelerated stability tests, the 20Pt–10CeO2/C catalyst has a better durability compared to the commercial 20Pt/C catalyst due to the existence of CeO2, which prevents the agglomeration and dissolution of Pt nanoparticles on the carbon support, extending the life of the catalyst. [Copyright &y& Elsevier]

Abstract: Iron-based catalysts for the oxygen reduction reaction (ORR) were produced by pyrolysis of iron-acetate and Ketjenblack® carbon with varying amounts of 2,2′-bipyridine in a closed, constant-volume vessel. The total surface nitrogen content detected by XPS varied from 0.6 to 2.2at% when the nitrogen precursor loading was varied from 1.5 to 11.3wt%. The amount of nitrogen in the Fe-pyridinic form is estimated to vary between 0.12 and 0.24at%, correlating to catalytic activity (current density) variation from 0.07 to 1.9mAcm−2 at a catalyst loading of 0.5mgcm−2. These results support the theory that iron associated with pyridinic nitrogen is a component of the catalytic active site responsible for oxygen reduction. [Copyright &y& Elsevier]

The factors that control the electrocatalytic activity for the oxygen reduction reaction (ORR) in fuel cells have been investigated systematically with the low cost carbon-supported Pd100−x Co x (0≤ x ≤50) nanoalloys. The Pd100−x Co x /C samples have been prepared by a solution-based reduction procedure and annealed at 350 and 500°C. While the catalytic activity of the as-prepared samples decreases monotonously with nominal Co content due to poor alloying and instability, a volcano type dependence of the activity on Co content with the maximum at around a nominal Co content of 25at% Co or an actual Co content of about 10at% in the Pd lattice (degree of alloying) is found for the samples annealed at 350 and 500°C due to the influence of both the degree of alloying and variations in crystallite size. Below 30at% nominal Co content, the catalytic activity of the annealed samples increases with increasing nominal Co content due to both a decreasing crystallite size and increasing degree of alloying. For 30–50at% nominal Co content, the catalytic activity decreases with Co content due to increasing degree of alloying as the crystallite size remains constant. The durability of the catalyst increases with annealing due to both an increase in the degree of alloying and crystallite size. [Copyright &y& Elsevier]

Abstract: Hollow core mesoporous shell (HCMS) carbon has been explored for the first time as a cathode catalyst support in direct methanol fuel cells (DMFCs). The HCMS carbon consisting of discrete spherical particles possesses unique structural characteristics including large specific surface area and mesoporous volume and well-developed interconnected void structure, which are highly desired for a cathode catalyst support in low temperature fuel cells. Significant enhancement in the electrocatalytic activity toward oxygen reduction reaction has been achieved by the HCMS carbon-supported Pt nanoparticles compared with carbon black Vulcan XC-72-supported ones in the DMFC. In addition, much higher power was delivered by the Pt/HCMS catalysts (i.e., corresponding to an enhancement of ca. 91–128% in power density compared with that of Pt/Vulcan), suggesting that HCMS carbon is a unique cathode catalyst support in direct methanol fuel cell. [Copyright &y& Elsevier]

• A novel cactus-like NiCo 2 S 4 @NiFe LDH hollow sphere has been developed. • The strong electronic interactions of heterointerface greatly enhance the electronic transfer. • The outer NiFe LDH is capable of protecting inner NiCo 2 S 4 to reduce its corrosion. • The NiCo 2 S 4 @NiFe LDH achieves a small potential gap of only 0.667 V in 0.1 M KOH. The high-performance non-precious electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial to the practical application of fuel cells and metal-air batteries. Herein, a novel cactus-like NiCo 2 S 4 @NiFe LDH hollow sphere assembled by one-dimensional (1D) NiFe LDH nanowires and two-dimensional (2D) NiFe LDH nanosheets on the NiCo 2 S 4 hollow spheres is prepared by a facile hydrothermal method. The outer NiFe LDH nanowires and NiFe LDH nanosheets can effectively suppress the collapse and corrosion of inner NiCo 2 S 4 hollow structure during long-term stability tests. The integration of the effective OER electrocatalyst NiFe LDH into NiCo 2 S 4 to form heterostructures, as well as the strong electronic interaction between NiCo 2 S 4 and NiFe LDH, can greatly boost both ORR and OER activities. Due to the above merits, the NiCo 2 S 4 @NiFe LDH achieves remarkably a small potential gap (ΔE = Ej=10-E 1/2) of only 0.667 V. This work offers a facile strategy to design efficient catalysts with heterostructures. [ABSTRACT FROM AUTHOR]

• Cross-linked multi-atom Pt anchored on a Zn, Fe and N co-doped carbon catalyst is prepared. • The MAC-Pt/ZnFe -N- C catalyst shows 100 % exposure of surface Pt atoms. • The MAC-Pt/ZnFe -N- C catalyst exhibits remarkable catalytic activity and stability for the oxygen reduction reaction. • A fuel cell assembled by this catalyst delivers a maximal power output of 1.02 W cm−2 at 0.035 mg Pt cm−2 at the cathode. Although single-atom catalysts (SACs) are drawing wide attention because they offer properties that differ from those of conventional nanoparticle (NP)-based catalysts, the lack of neighboring metal centers to cooperate in catalysis limits their actual application in many important chemical processes. Here, we report the synthesis of multi-atom Pt catalyst that consists of cross-linked Pt-Pt metal centers stabilized by atomically dispersed ZnFe -N- C support through Pt-N bonds. XAFS analysis reveals that each Pt atom in the multi-atom Pt catalyst coordinates with ∼2.6 N atoms and ∼4.3 Pt atoms. This novel catalyst combines the merits of SACs and NPs, resulting in 100 % exposure of surface Pt atoms and excellent stability and fuel cell performance. With an ultralow Pt loading of 0.035 mg cm−2 at the cathode, the fuel cell delivers a 1.02 W cm-2 maximal power output. DFT calculations revealed that the strongly coupled Pt-N bond is critical for stabilizing the cross-linked Pt. [ABSTRACT FROM AUTHOR]

• Atomically dispersed bimetallic FeCu coordinated with N-CNTs, FeCu/N-CNTs, are developed. • FeCu/N-CNTs show PA enhance activity and stability for ORR at elevated temperatures. • PA/PBI cells based on FeCu/N-CNTs cathode show a high and stable power performance at 230 degrees. • DFT calculation verifies the promotion mechanism of phosphate on bimetallic FeCu for ORR. Phosphate poisoning of Pt electrocatalysts is one of the major barriers that constrains the performance of phosphoric acid-doped polybenzimidazole (PA/PBI) membrane fuel cells. Herein, we developed new atomically dispersed bimetallic FeCu coordinated with nitrogen-doped carbon nanotubes (FeCu/N-CNTs) as Pt-free oxygen reduction reaction (ORR) electrocatalysts. The cell with FeCu/N-CNTs cathodes delivers a peak power density of 302 mWcm−2 at 230℃, similar to that using Pt/C electrocatalysts (1 mg Pt cm−2) but with a much better stability. In contrast to phosphate poisoning of Pt/C, FeCu/N-CNTs show PA enhanced activities. DFT calcualtions indicate that phosphate promotion effect results from the stronger binding of phosphate on Cu sites, which decreases the activation energy barrier for the cleavage of the O 2 double bond and provides local protons to facilitate the proton-coupled electron transfer ORR. The results also show that FeCu/N-CNTs have a much better activity for ORR as comapre to Fe single atom catalysts coordinated with nitrogen-doped carbon nanotubes, Fe/N-CNTs. This study demonstrates the promising potential of bimetallic FeCu/N-CNTs as true Pt-free, highly active and durable cathodes for PA/PBI based high temperature polymer electrolyte fuel cells. [ABSTRACT FROM AUTHOR]

• Carbon-supported Pt-based materials with Matryoshka-like structure are proposed as ORR catalysts. • The catalyst has 3.4 times higher mass activity than commercial Pt/C in half-cell. • Pt@Cu IL Pd/C-based polymer electrolyte membrane fuel cells show high and stable performance. Electrochemical catalysts with a core-shell structure have received much attention because of their enhanced efficiency and activity. Among them, those with a CuPd alloy core exhibit better activity than the ones with a single metal Pd core, which is known to be an excellent core-material. However, the superior performance of previously reported Pt catalysts with CuPd core has only been observed in half-cells, and was not reflected or even expanded to single-cells. We report catalysts having a Matryoshka-like structure with a Pt outer-layer, Cu interlayer, and Pd core for oxygen reduction reaction. This catalyst has 3.4 times higher Pt mass activity than the commercial Pt/C in half-cells, and also performs better in single-cells at only 0.056 mg Pt cm−2. Particularly, the stability of this catalyst satisfies the 2020 DOE target, and electrochemical surface area loss during the stability test is only 40 % for this catalyst, while that of Pt/C is 80 %. [ABSTRACT FROM AUTHOR]

• Metal-organic frameworks (MOFs) are emergent compounds extensively used as sacrificial templates. • The review summarizes the current advances of hetero-doped (Fe, Co, P, S, N) nanostructures derived from MOFs. • These nanomaterials, are classified as 0D, 1D, 2D and 3D morphologies, and discussed for the very important ORR. • The correlation between the characteristic properties of MOFs and the derived nanomaterials is investigated. • Controlled electronic structures, extrinsic/intrinsic structures and interface (edge) properties are discussed for ORR. This review summarizes the current advances of hetero-doped (Fe, Co, P, S, N) nanostructures derived from MOFs (metal-organic frameworks) for the oxygen reduction reaction (ORR) electrocatalysis. These nanomaterials are classified as: 0D (polyhedrons, hollow and core-shell structures), 1D (nanotubes and nanorods), 2D (nanosheets), and 3D (honeycomb like frameworks) morphologies. It is thoroughly discussed the critical and very important pathway of ORR, which occurs in electrochemical devices such as fuel cells and metal-air batteries (high energy capacity, excellent conversion efficiency and low environmental impact). Emphasis is given on the mechanistic studies devoted to both the nanostructure formation from MOFs and the morphology-activity relationship of transition-metal anchored carbon nanostructures transformed from MOFs. Controlled electronic structures, extrinsic/intrinsic structures and interface (edge) properties are also discussed for the ORR performance, providing a useful preparation approach for carbon doped with heteroatoms by rationally designing MOF precursors. As a result of the ongoing flexibility of these frameworks, the doped carbon based electrocatalysts present enhanced ORR performance, which expands their applications (except for fuel cells) in other energy conversion and storage devices like supercapacitors and metal ion batteries. [ABSTRACT FROM AUTHOR]

Porous carbons with edge-sited Fe-N 4 species were successfully prepared from Fe-containing abundant biomass, which shows superior electrocatalytic oxygen reduction performance, as well higher power/energy density and stability than commercial Pt/C in Zn-air battery. The theoretical calculations indicate that O 2 molecule adsorbs on edged Fe-N 4 sites with an energetically favorable side-on configuration with elongated O O bond, boosting the subsequent dissociation pathway with a direct 4e− reaction route. • Edge-sited Fe-N 4 atomic species are formed by pyrolysis of abundant Fe-containing biomass. • The microstructures of Fe-N 4 species are revealed by advanced HAADF-STEM, XANES, and Mössbauer techniques. • The ORR activity of edge-sited Fe-N 4 species is promoted by elongating O O bond. • The Zn-air battery using edge-sited Fe-N 4 species shows a high specific capacity and power density as well as long-life over 200 h. • The density functional calculations are employed to explain the origin of improved activity from the electronic structure. The development of low-cost, efficient, and stable electrocatalysts toward the oxygen reduction reaction (ORR) is urgently demanded for scalable applications in fuel cells or zinc-air batteries (ZABs), but still remains a challenge. Herein, carbon materials with edge-sited Fe-N 4 atomic species (E-FeNC) were synthesized from pyrolysis of abundant Fe-containing biomass using silica spheres as hard template. The E-FeNC delivers remarkable ORR performance with a half-wave potential of 0.875 V (vs. reversible hydrogen electrode (RHE)), much better than Pt/C (0.859 V), attributed to atomically dispersed Fe-N 4 moieties nearby graphitic edges. The density functional calculations reveal that O 2 molecule adsorbs on Fe-N 4 sites with an energetically favorable side-on configuration with elongated O O bond rather than end-on form, boosting the subsequent dissociation pathway with a direct 4e reaction route. Using E-FeNC as cathode catalyst, the primary ZAB exhibits high specific capacity of 710 mA h g−1 and power density of 151.6 mW cm−2. The rechargeable ZAB by coupling E-FeNC and NiFe layered double hydroxide (LDH) demonstrates long-term capacity retention over 200 h, superior to that using noble Pt/C and RuO 2. This unique carbon material with atomically dispersed metal sites opens up an avenue for the design and engineering of electrocatalysts for energy conversion systems. [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]

• 3D mesoporous Co-N-C nanosheets network enwrapping Co nanohybrids were prepared. • The nanohybrids possess high content of Co-N 4 -type single-atom sites (>5 wt%). • The synergy of the two Co species lets the nanohybrids show superior ORR activity. • Such nanohybrids manifest better electrocatalytic stability than Pt/C catalyst. • The contributions of atomic and nanoscaled Co species were determined. Metal-nitrogen-codoped carbon (M-N-C) nanostructures are promising electrocatalysts for oxygen reduction reaction (ORR). Despite the great progress that has been achieved, synthesizing three-dimensional porous nanoarchitectures derived from Co-N-C nanosheets or related nanohybrids with high content (> 5 wt%) of exposed single-atom sites remains a challenge. Herein, novel three-dimensional mesoporous Co-N-C nanosheets network enwrapping small amount of Co nanoparticles nanohybrids are fabricated by molten-salt template-assisted pyrolysis of Co-folic acid precursors and chemical etching. In the obtained nanohybrids, the content of single-atom-like Co (SA-Co%) is 7.4 wt% < SA-Co%<19.4 wt%. Due to the unique mesoporous nanosheets network structure and efficient synergy of atomic and nanoscaled Co species, such nanohybrids manifest enhanced ORR activity with a half-wave potential of 0.85 V, outperforming pure Co-N-C, Pt/C and most of other reported catalysts. Moreover, their stability exceeds that of Pt/C. This work will lead to the optimization of M-N-C nanostructures and accelerate their applications in fuel cells. [ABSTRACT FROM AUTHOR]

• Improvement of weakly ferromagnetic Fe-N-C catalyst performance in the ORR under an external magnetic field is demonstrated. • The presence of an external magnetic field yields higher selectivity towards the 4e− ORR. • Additional treatment of Fe-N-C catalysts in reductive conditions boosts their activity. • Fe in reduced state contributes to higher activity of pyrolyzed Fe-N-C catalysts. • Immobilization of a multicopper oxidase enzyme on Fe-N-C catalysts provides attractive materials for enzymatic biofuel cells. Electrocatalysis can be enhanced either by using more active catalysts or by means of external process intensifications exploiting different energy types. The improvement of oxygen reduction reaction (ORR) efficiency by using an external magnetic field is technologically practical yet poorly scrutinized. An iron/nitrogen/sulfur-co-doped carbon gel (Fe-N-C/S) is studied as a non-precious metal catalyst for the ORR under an external magnetic field generated by a permanent magnet. The application of a magnetic field enhances the ORR process in both acidic and alkaline environments and yields higher selectivity towards 4e− electroreduction of O 2. To elucidate the origin of the observed phenomena and show the role of the catalyst's components, samples either free of sulfur (Fe-N-C) or iron (N-C/S) are studied as references. Moreover, the highly porous carbon gel constitutes an attractive substrate for enzyme immobilization. Modification of the catalyst with laccase (a multicopper oxidase enzyme) additionally strengthens the efficiency of O 2 electroreduction. [ABSTRACT FROM AUTHOR]

A mononuclear Mn/N-codoped graphene catalyst shows excellent electrochemical ORR performance in alkaline electrolyte. • Atomically dispersed manganese was embedded onto nitrogen-doped graphene. • Mn@NG shows ORR performance with E 1/2 of ∼0.82 V vs RHE in 0.1 M KOH. • The MnN 4 moiety embedded into graphene is the active center for efficient ORR. Rational design and preparation of earth-abundant materials with high-efficiency oxygen reduction reaction (ORR) performance is pivotal for fuel cells. Here, an atomically dispersed Mn- and nitrogen-codoped graphene material (Mn@NG) is developed by a facile high-temperature annealing and subsequent acid-leaching strategy. The atomically dispersion of manganese in Mn@NG is confirmed by aberration-corrected electron microscopy with atomic resolution and the main structure of MnN 4 moiety is resolved by X-ray absorption spectroscopy. The Mn@NG catalyst shows an onset potential and half-wave potential of 0.95 and 0.82 V vs RHE in 0.1 M KOH solution, respectively. Theoretical calculations manifest that MnN 4 moiety embedded into graphene is the active center for efficient ORR, on which the theoretical overpotential is 0.63 V, lower than that on graphitic-N (1.18 V), pyridinic-N (1.58 V), MnN 3 -G (1.48 V), MnN 3 O-G (2.33 V), and Mn 3 O 4 (001) surface (0.86 V). [ABSTRACT FROM AUTHOR]