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A proton exchange membrane fuel cell (PEMFC) is an efficient and environmentally friendly power production technology that uses hydrogen energy. The cathodic oxygen reduction electrode is a critical component in the development of PEMFC. Most techniques deposit catalyst nanoparticles in areas that are inaccessible for catalytic processes, reducing platinum utilization. The substrate used in this study was carbon paper (CP) with a self-supporting structure. First, electrochemical acidification technology was employed to modify the CP's surface, followed by nanoparticle manufacturing and fixation on the CP in a single step by electrodeposition. The Pt/C0.5V2.24CP catalyst electrode demonstrated high-quality activity in the oxygen reduction reaction (ORR), with a homogeneous particle dispersion and particle size of around 50 nm. The mass activity and electrochemical active surface area (ECSA) of the Pt/C0.5V2.24CP catalyst electrode were 1.74 and 3.98 times higher than those of the Pt/C/CP-1 electrodes made with commercial catalysts, respectively. After 5000 cycles of accelerated durability testing (ADT), the mass activity and ECSA were 1.28 times and 6.16 times more than Pt/C/CP-1. This paper successfully proved the viability of electrodepositing Pt nanoparticles on CP following acidification, and that the electrochemical acidification methods have a positive influence on improving electrode ORR activity. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide is a promising substitute for fossil fuels because it produces non-hazardous by-products. In this work, a glassy carbon GC was anodized in sulphuric acid at +1.8 V to prepare the working electrode. It was utilized to investigate the oxygen reduction reaction (ORR) in a basic medium containing 0.1 M NaOH as a supporting electrolyte. The objective of this investigation was to synthesize hydrogen peroxide. X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), linear polarization, cyclic voltammetry (CV), and rotating disk electrode voltammetry (RDE) were performed for characterization and investigation of the catalytic properties. The RDE analysis confirmed that oxygen reduction reactions followed two electrons' process at an activated GC electrode. Hence, the prepared electrode generated hydrogen peroxide from molecular oxygen at a potential of around −0.35 V vs. Ag/AgCl (sat. KCl), significantly lower than the pristine GC surface. The transfer coefficient, standard reduction potential, and standard rate constant were estimated to be 0.75, −0.27 V, and 9.5 × 10−3 cm s−1, respectively. [ABSTRACT FROM AUTHOR]

An oxygen reduction reaction (ORR) is the key half reaction of proton exchange membrane fuel cells (PEMFCs), and is highly dependent on Pt-based nanocrystals as core electrocatalysts. Despite the exceptional ORR activity from adjusting the electronic structures of surface or near-surface atoms, several serious issues, including the corrosion of carbon supports, the preferential leaching of active metal elements, the instability of surface low-coordinated atoms and the sintering/agglomeration of nanocrystals, still exist, challenging the ORR durability of developed Pt-based ORR catalysts. From the point of view of the catalyst structure design, in this review, we summarized the state-of-the-art structural regulation strategies for improving the ORR durability of Pt-based catalysts. The current limitation of Pt-based binary catalysts for ORR electrocatalysis is firstly discussed, and the detailed strategies are further classified into the optimization of supports, metal-doped alloys, core/shell structures, intermetallics and high-entropy alloys, etc. The structure–performance relationship is detailedly explained, especially emphasizing the elimination of the above restrictions. Finally, the existing challenges and future research direction are further presented, aiming at practicing the PEMFC devices of the ultradurable Pt-based catalysts. [ABSTRACT FROM AUTHOR]

Rechargeable Zn–air batteries (ZABs) can play a significant role in the transition to a cleaner and more sustainable energy system due to their high theoretical energy density, high cell voltage, and environmental friendliness. ZAB's air cathode is the principal determinant in predicting the battery's overall performance, as it is responsible for catalyzing the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during the discharging and charging process, respectively. In this work, a detailed optimization study of the architecture of the air cathode was carried out using the benchmark bifunctional oxygen electrocatalyst (Pt/C-RuO2). The air cathode composition and architecture were optimized regarding the choice of the commercial gas diffusion layer (GDL), the effect of hot pressing the catalyst layer (CL), and the optimum pore size of the current collector. The best cathode from this study shows a maximum power density (PDmax) of 167 mW/cm2, with a round trip efficiency and a voltage gap (Egap) of 59.8% and 0.78 V, respectively, indicating the air cathodes preparation approach proposed in this work as a promising strategy for the improvement of the overall performance of ZABs. [ABSTRACT FROM AUTHOR]

The electrocatalyst of oxygen reduction reactions is one of the basic components of a fuel cell. In addition to costly Pt/C benchmark catalysts, cost-effective carbon-based catalysts have received the most attention. Enormous efforts have been dedicated to trade off the catalyst performance against the economic benefit. Optimizing composition and/or structure is a universal strategy for improving performance, but it is typically limited by tedious synthesis steps. Herein, we have found that directly introducing CNT into MOF-derived carbonaceous nanopolyhedra, i.e., introduced carbon nanotubes (CNTs) penetrated porous nitrogen-doped carbon polyhedra (NCP) dotted with cobalt nanoparticles (denoted as CNTs-Co@NCP), can optimize the catalytic activity, stability, and methanol tolerance. The hierarchical architecture combines the 0D/1D/3D Co/CNT/NCP interfaces and 1D/3D CNT/NCP junctions with the frameworks with a greatly exposed active surface, strengthened mass transport kinetics, stereoscopic electrical conductivity networks and structural robustness. The sterical self-consistency of MOF-self-assembly triggered by introduced CNTs demonstrates tactful ORR electrocatalytic activity regulation. Eventually, the CNTs-Co@NCP showed a half-wave potential (E1/2) of 0.86 V and a diffusion-limited current density (JL) of 5.94 mA/cm2 in alkaline electrolyte. The CNTs-Co@NCP was integrated into the cathode of a direct methanol fuel cell (DMFC) with an anion-exchange membrane, and an open-circuit voltage (OCV) of 0.93 V and a high power density of 46.6 mW cm−2 were achieved. This work successfully developed a catalyst with competitive ORR performance through plain parameter fine-tuning without complex material design. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cells (SOFCs) represent a breed of eco-friendly, weather-independent, decentralized power generation technologies, distinguished for their broad fuel versatility and superior electricity generation efficiency. At present, SOFCs are impeded by a lack of highly efficient oxygen reduction catalysts, a factor that significantly constrains their performance. The double perovskites LnBaCo2O5+δ (Ln = Lanthanide), renowned for their accelerated oxygen exchange and conductivity features, are widely acclaimed as a promising category of cathode catalysts for SOFCs. This manuscript offers a novel perspective on the physicochemical attributes of LnBaCo2O5+δ accumulated over the past two decades and delineates the latest advancements in fine-tuning the composition and nanostructure for SOFC applications. It highlights surface chemistry under operational conditions and microstructure as emerging research focal points towards achieving high-performance LnBaCo2O5+δ catalysts. This review offers a comprehensive insight into the latest advancements in utilizing LnBaCo2O5+δ in the field of SOFCs, presenting a clear roadmap for future developmental trajectories. Furthermore, it provides valuable insights for the application of double perovskite materials in domains such as water electrolysis, CO2 electrolysis, chemical sensors, and metal–air batteries. [ABSTRACT FROM AUTHOR]

The development of efficient non-precious metal electrocatalysts for oxygen reduction reaction (ORR) to replace Pt-based methods is crucial for the applications of fuel cells and metal–air batteries. In this study, a bimetallic M-N-C catalyst with highly dispersed dual-atom Fe/Mn-Nx sites immobilized on N-doped bamboo-like carbon nanotubes is prepared by the ball-milling and calcination of dual-MOFs as precursors. The rich N-doping and abundant M–Nx species contribute to the excellent intrinsic ORR activity of the catalyst, and the unique bamboo-like nanotubes morphology is beneficial for facilitating electron transfer and mass transport while simultaneously enabling the exposure of active sites. As expected, the optimized Z-Fe1Mn1-NC catalyst exhibits efficient ORR activity with a half-wave potential (E1/2) of 0.80 V in acid and 0.82 V in alkaline, and a higher electrochemical stability with the current density maintained at 91% (in 0.1 M KOH) and 86% (0.1 M HClO4) of its initial current density after 15 h of a chronoamperometric test at a high potential of 0.7 V. When further applied to Zn–air batteries, the catalyst also delivers a high open-circuit voltage, large power density, and outstanding rate performance. This work provides a novel means of designing dual metal M–Nx site-based M-N-C catalysts for ORR sustainable energy applications. [ABSTRACT FROM AUTHOR]

Metal-air batteries rely on the oxygen reduction reaction (ORR) for their operation. However, the ORR is kinetically slow, necessitating the use of Pt-based catalysts, which is hindered by their high cost and limited availability. Consequently, considerable efforts have been dedicated to developing metal-free catalysts for the ORR. Among these, heteroatom-doped carbons have emerged as promising candidates by manipulating their composition and microstructure. Inspired by the ancient "Pharaoh's snakes" reaction, this study utilized sugar, melamine, and a polymerizable ionic liquid as precursors to prepare heteroatom-doped carbons with the desired composition and structure. The resulting carbon catalyst exhibited an onset potential and half-wave potential in a 0.1 M KOH electrolyte that was comparable to those of a commercial Pt/C 20 wt.% catalyst, with values of 0.97 and 0.83 VRHE, respectively. Furthermore, the catalyst demonstrated excellent stability, retaining 93% of its initial current after a 10,800-s test. To evaluate its practical application, the synthesized carbon was employed as the cathode catalyst in a Zn-air battery, which achieved a maximum power density of 90 mW cm−2. This study, therefore, presents a simple yet effective method for producing metal-free heteroatom-doped carbon ORR catalysts used in various energy conversion and storage devices. [ABSTRACT FROM AUTHOR]

As energy demand increases, new energy conversion methods are also sought. In this study, two MnO2 and multiwalled carbon nanotube (MWCNT) composites were prepared and decorated with silver using magnetron sputtering, to evaluate their electrocatalytic activity towards the oxygen reduction reaction (ORR). Three nominal thicknesses of Ag layers were used, 5, 10 and 20 nm. The physicochemical characterisation was carried out using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, as well as X-ray photoelectron spectroscopy. The substrate materials (MnO2-MWCNT) were also investigated by X-ray diffraction analysis. The electrochemical studies of the ORR revealed that the activity and stability of the composite catalysts depend on the substrate material and the Ag layer thickness. [ABSTRACT FROM AUTHOR]

Efficient oxygen reduction reaction (ORR) electrocatalysts are the key to advancement of solid-state alkaline zinc–air batteries (ZAB). We demonstrate an electrocatalyst, spinel lithium-manganese oxide LiMn2O4 (LMO) by a simple hydrothermal method. Scanning electron microscope (SEM), X-ray diffraction (XRD), and Raman spectra indicate that the as-synthesized LiMn2O4 presents nanoscale irregular-shaped particles with the well-known spinel structure. The polarization curve, chronoamperometery curve, and linear scanning voltammograms of rotating disk electrode (RDE) results reveal that the as-synthesized LiMn2O4 possesses a higher electrocatalytic activity than that of electrolytic manganese dioxide for the ORR. A solid-state zinc–air cell with LiMn2O4 as the air electrode catalyst has a long voltage plateau of discharge and a discharge capacity of 188.4 mAh at a constant discharge current density of 10 mA·cm−2. In summary, spinel LiMn2O4 in which the JT effect enables electron hoping between Mn3+ and Mn4+ can be regarded as an effective robust oxygen reduction catalyst. [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]

Following the core theme of a circular economy, a novel strategy to upcycle cigarette butt waste into platinum group metal (PGM)-free metal nitrogen carbon (M-N-C) electrocatalysts for oxygen reduction reaction (ORR) is presented. The experimental route was composed of (i) the transformation of the powdered cigarette butts into carbonaceous char via pyrolysis at 450 °C, 600 °C, 750 °C and 900 °C, (ii) the porosity activation with KOH and (iii) the functionalization of the activated chars with iron (II) phthalocyanine (FePc). The electrochemical outcomes obtained by the rotating disk electrode (RRDE) technique revealed that the sample pyrolyzed at 450 °C (i.e., cig_450) outperformed the other counterparts with its highest onset (Eon) and half-wave potentials (E1/2) and demonstrated nearly tetra-electronic ORR in acidic, neutral and alkaline electrolytes, all resulting from the optimal surface chemistry and textural properties. [ABSTRACT FROM AUTHOR]

Developing efficient bifunctional electrocatalysts for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is crucial for the large-scale application of rechargeable zinc–air batteries. Perovskite oxides are attractive candidates as bifunctional electrocatalysts. Herein, Ln0.5Sr0.5CoO3-δ (Ln = La, Pr and Sm) was prepared by the sol-gel method and evaluated as bifunctional electrocatalysts for both ORR and OER. Compare with La0.5Sr0.5CoO3-δ (LSC) and Sm0.5Sr0.5CoO3-δ (SSC), Pr0.5Sr0.5CoO3-δ (PSC) demonstrated the enhanced catalytic activity towards ORR with the limiting current density of 4.19 mA cm−2 at 0.40 V vs. RHE and OER with the potential of 1.75 V vs. RHE at 10 mA cm−2 as well as the Tafel slope of 105 mV dec−1. The higher Co3+/Co2+ ratio in PSC played an essential part in boosting the bifunctional electrocatalytic activities for ORR and OER. For demonstration, rechargeable zinc–air batteries with PSC as the air electrode displayed the maximum power density of 72 mW cm−2, the low charge-discharge voltage gap (1.01 V) at 10 mA cm−2 over 80 cycles and outstanding cycling stability. This work highlights the importance of A-site cations of the perovskite oxide as a valid strategy to improve ORR and OER activities. [ABSTRACT FROM AUTHOR]

Pt-based binary alloy catalysts with different structures have been designed to boost the catalytic activity of oxygen reduction reaction (ORR), however, the dissolution of the transition metals leads to insufficient catalyst durability. In order to solve this problem, a self-assembly Pt3Co superlattice catalyst is reported in this paper, which exhibits enhancement in both activity and durability towards ORR. Compared with commercial Pt catalyst, the mass activity and specific activity of Pt3Co superlattice are significantly improved. The Pt3Co superlattice dropped only 9.2% and 12.4% in the mass activity and specific activity after 5000 cycles of durability tests. Moreover, the mechanistic studies find that the improvement of the catalyst performance is mainly dominated by reducing the energy of oxygen adsorption to a more suitable energy, optimizing the electronic structure of d-band, and suppressing the leaching of Co. This work provides a strategy to prepare superlattice catalyst with great activity and durability toward ORR. [ABSTRACT FROM AUTHOR]

Single-atom catalysts are a family of heterogeneous electrocatalysts widely used in energy storage and conversion. The determination of the local structure of the active metal sites is challenging, which limits the establishment of the reliable structure-property relationship of single-atom catalysts. A carbon black-conjugated complex can be used as the model catalyst to probe the intrinsic activity of metal sites with certain local structures. In this work, we prepared carbon black-conjugated [Co(phenanthroline)Cl2], [Co(o-phenylenediamine)Cl2] and [Co(salophen)]. In these catalysts, the Co complexes with well-defined structures are anchored on the edge of carbon black by pyrazine moieties. The number of electrochemical accessible Co sites can be measured from the area of the redox peaks of pyrazine linkers in the cyclic voltammetry curve. Then, the intrinsic electrocatalytic activity of one Co site can be obtained. The catalytic performances of the three catalysts towards oxygen reduction reaction in alkaline conditions were measured. Carbon black-conjugated [Co(salophen)] showed the highest intrinsic activity with the turnover frequency of 0.72 s−1 at 0.75 V vs. the reversible hydrogen electrode. The strategy developed in this work can be used to explore and verify the possible local structure of active sites proposed for single-atom catalysts. [ABSTRACT FROM AUTHOR]

The development of cost-effective and highly efficient oxygen reduction reaction (ORR) electrocatalysts is an essential component of renewable clean energy technologies, such as fuel cells and metal/air cells, but remains a huge and long-term challenge. Here, novel heterogeneous Cu/CuO nanoparticles embedded within N-doped carbon nanosheets (Cu/CuO@NC-900) are successfully synthesized by combining a facile hydrothermal route with a solid calcination technique. Benefitting from the electronic interaction between Cu and CuO, the generated abundant highly active Cu-Nx active sites and the high conductivity of the N-doped carbon nanosheets, the resulting Cu/CuO@NC-900 material shows superior ORR performance in alkaline media, exhibiting a high half-wave potential of ~0.868 V, and a robust stability and methanol tolerance, even outperforming commercial 20 wt% Pt/C. Our study opens up a new avenue for the rational design and fabrication of efficient and durable noble-metal-free Cu-based electrocatalysts for energy conversion and storage. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is an important challenge in the development and large-scale distribution of energy conversion devices, especially low-temperature proton exchange membrane (PEM) fuel cells. In order to speed up the ORR kinetics and improve fuel cell performance, iron-doped calcium titanate (CTFO) is proposed as a cocatalyst. Fundamental physical and chemical characterizations by means of X-ray diffraction, infrared spectroscopy, and morphological and thermal analyses for the understanding of the functional features of the proposed materials were carried out. Composite catalysts containing different amounts of CTFO additive with respect to platinum (i.e., Pt:CTFO 1:0.5 and 1:1 wt:wt) were studied using a rotating disk electrode (RDE). Fuel cell tests were performed at 80 °C under 30% and 80% relative humidity. The best Pt:CTFO composite catalyst was compared to a bare Pt/C and a Pt/C:CaTiO3−δ 1:1 catalyst, revealing superior performances of the latter at high relative humidity fuel cell operation, as a combined result of an optimized electrolyte-electrode interface and improved ORR kinetics due to the inorganic additive. [ABSTRACT FROM AUTHOR]

The design and synthesis of ultra-small-sized Pt-based catalyst with specific effects for enhancing the oxygen reduction reaction (ORR) is an effective way to improve the utilization of Pt. Herein, Pt-Pd-Ni octahedra nanoparticles characterized by the ultra-small size of 4.71 nm were synthesized by a Pd seed-inducing-growth route. Initially, Pd nanocubes were synthesized under solvothermal conditions; subsequently, Pt-Ni was deposited in the Pd seed solution. The Pd seeds were oxidized into Pd2+ and combined with Pt2+ and Ni2+ in the solution and finally formed the ternary alloy small-sized octahedra. In the synthesis process of the ultra-small Pt-Pd-Ni octahedra, Pd nanocube seed played an important role. In addition, the size of the Pt-Pd-Ni octahedra could be regulated by adjusting the concentration rate of Pt-Ni. The ultra-small Pt-Pd-Ni octahedra formation by depositing Pt-Ni with a feeding ratio of 2:1 showed good ORR activity, and the high half-wave potential was 0.933 V. In addition, the Pt-Pd-Ni octahedra showed an enhanced mass activity of 0.93 A mg−1 Pt+Pd in ORR, which was 5.81 times higher than commercial Pt/C. The theoretical calculation shows that compared to Pt/C, the small-sized ternary alloy octahedra had an obvious contraction strain effect (contraction rate: 3.49%). The alloying effect affected the d-band center of the Pt negative shift. In the four-electron reaction, Pt-Pd-Ni ultra-small octahedra exhibited the lowest overpotential, resulting in the adsorption performance to become optimized. Therefore, the Pd seed-inducing-growth route provides a new idea for exploring the synthesis of small-sized nanoparticle catalysts. [ABSTRACT FROM AUTHOR]

Developing a non-platinum catalyst that effectively catalyzes the oxygen reduction reaction (ORR) is highly significant for metal–air batteries. Metal and nitrogen co-doped carbons (M-N-Cs) have emerged as alternative candidates to platinum. In this work, dual-metal Pd/Fe-N-C electrocatalysts were synthesized by the one-step pyrolysis of phytic acid, melamine, and Pd/Fe-based salts. The Pd/Fe-N-C catalyst exhibited a good catalytic ability during the ORR process and outperformed the commercial Pt/C catalyst as regards mass activity, catalytic stability, and methanol tolerance. It was found that Pd-Nx is the active center, and the synergistic effect from the Fe component introduction endowed the Pd/Fe-N-C with an excellent catalytic performance towards the ORR. When assembled into a Zn–air battery, its specific capacity was ~775 mAh gZn−1. Meanwhile, the peak power density could reach 3.85 W mgPd−1, i.e., 3.4 times that of the commercial Pt/C catalyst (1.13 W mgPt−1). This implies that the Pd/Fe-N-C catalyst has potential applications in metal–air batteries. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is a very important reaction that occurs at the cathodic side in proton exchange membrane fuel cells (PEMFCs). The high cost associated with frequently used Pt-based electrocatalysts for ORR limits the commercialization of PEMFCs. Through bifunctional and electronic effects, theoretical calculations have proved that alloying Pt with a suitable transition metal is likely to improve ORR mass activity when compared to Pt-alone systems. Herein, we demonstrate the preparation of bimetallic Pt–Fe nanoparticles supported on reduced graphene oxide sheets (RGOs) via a simple surfactant-free chemical reduction method. The present method produces PtFe/RGO catalyst particles with a 3.2 nm diameter without agglomeration. PtFe/RGO showed a noticeable positive half-wave potential (0.503 V vs. Ag/AgCl) compared with a commercial Pt/C catalyst (0.352 V vs. Ag/AgCl) with minimal Pt-loading on a glassy carbon electrode. Further, PtFe/RGO showed a higher ORR mass activity of 4.85 mA/cm2-geo compared to the commercial Pt/C (3.60 mA/cm2-geo). This work paves the way for designing noble−transition metal alloy electrocatalysts on RGO supports as high-performance electrocatalysts for ORR application. [ABSTRACT FROM AUTHOR]

The three-dimensional (3D) nanoreactor of global-local CNTs conductive network coupled with bimetallic MOFs-derived Co@N-C nanopolyhedra (denoted as gl-CNTs/Co@N-C) promotes the electrocatalytic reduction of oxygen owing to the improved mass transfer ability and stability. Here, the 1D/3D gl-CNTs/Co@N-C nanostructures with enhanced electrocatalytic properties were synthesized in one step by the direct thermolysis of Zn/Co-ZIF/MWCNTs precursor. Based on systematical optimization of the composition and structure, gl-CNTs/Co@N-C carbonaceous porous hybrids containing uniform Co nanoparticles (NPs) can not only effectively enable the conductivity but also expose more active sites. Consequently, the optimal gl-CNTs/Co@N-C nanostructure showed a significantly enhanced catalytic activity for the reduction of oxygen, the half-wave potential (E1/2) and diffusion-limited current density are 0.86 V (vs. RHE) and 5.34 mA cm−2, respectively. Moreover, this catalyst also showed long-term durability and methanol tolerance property, further highlighting the structure superiority of a precisely controllable nanoreactor. [ABSTRACT FROM AUTHOR]

Fe-N-doped carbon (Fe-N-C)-based electrocatalysts are considered to be promising alternatives to replace Pt-based catalysts for oxygen reduction reactions (ORR). Here, we reported a simple and effective approach to prepare Fe-N-C-based electrocatalysts with the shape of two-dimensional nanosheets (termed Fe/NCNSs) to enhance the ORR performance. Fe/NCNSs were prepared by the calcination of Fe/Zn dual-metal ZIFs nanosheets as precursors. Benefiting from its higher specific surface area, electrochemically active surface area, and proportion of pyridinic N and Fe-N, the optimized Fe/NCNS showed excellent ORR performance both in acidic (E1/2 = 0.725 V vs. RHE) and alkaline (E1/2 = 0.865 vs. RHE) media, being 23 mV more negative and 24 mV more positive than that of a commercial Pt/C. The optimized Fe/NCNS also exhibited long durability. In addition, the Zn-air battery with Fe/NCNS-1 and RuO2 as the air catalyst exhibited high power density (1590 mW cm−2 at a current density of 2250 mA cm−2) and superior charging/discharging durability. [ABSTRACT FROM AUTHOR]

Low-cost and highly efficient electrocatalysts for oxygen reactions are highly important for oxygen-related energy storage/conversion devices (e.g., solar fuels, fuel cells, and rechargeable metal-air batteries). In this work, a range of compositionally-tuned cerium-doped CoMn2O4 (Ce-CMO-X) spinels were prepared via oxidizing precipitation and subsequent crystallization method and evaluated as electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The Ce modification into the CMO spinels lead to the changes of surface electronic structure. And Ce-CMO-X catalysts display better electrochemical performance than that of pristine CMO spinel. Among them, Ce-CMO-18% shows the best activity. The Ce-CMO-18% processes a higher ratio of Co3+/Co2+, Mn4+/Mn3+, which is beneficial to ORR performance, while the higher content of oxygen vacancies in Ce-CMO-18% make for better OER performance. Thus, the Ce-doped CMO spinels are potential candidates as bifunctional electrocatalysts for both ORR and OER in alkaline environments. Then, the hybrid Ce-CMO-18%/MWCNTs catalyst was also synthesized, which shows further enhanced ORR and OER activities. It displays an ORR onset potential of 0.93 V and potential of 0.84 V at density of 3 mA cm−2 (at 1600 rpm), which is comparable to commercial Pt/C. The OER onset potential and potential at a current density 10 mA cm-2 are 183 mV and 341 mV. The superior electrical conductivity and oxygen functional groups at the surface of MWCNTs can facilitate the interaction between metal oxides and carbon, which promoted the OER and ORR performances significantly. [ABSTRACT FROM AUTHOR]

The effects of the electrochemical oxygen reduction reaction (ORR) on the surface of single-phase perovskite cathodes are well understood, but its potential for use in a complex system consisting of different material types is unexplored. Herein, we report how BaCO3 nanoparticles-modified La0.6Sr0.4Co0.2Fe0.8O3-δ-Gd0.2Ce0.8O2-δ (LSCF–GDC)-composite cathodes improved the electrochemical oxygen reduction kinetics for high-performing ceramic fuel cells. Both X-ray diffraction (XRD) and thermogravimetric analysis (TGA) studies reveal that BaCO3 is stable, and that it does not show any solid-state reaction with LSCF–GDC at SOFCs' required operating temperature. The electrochemical conductivity relaxation (ECR) study reveals that during the infiltration of BaCO3 nanoparticles into LSCF–GDC, the surface exchange kinetics (Kchem) are enhanced up to a factor of 26.73. The maximum power density of the NiO-YSZ anode-support cell is increased from 1.08 to 1.48 W/cm2 via surface modification at 750 °C. The modified cathode also shows an ultralow polarization resistance (Rp) of 0.027 Ω.cm2, which is ~4.4 times lower than that of the bare cathode (~0.12 Ω.cm2) at 750 °C. Such enhancement can be attributed to the accelerated oxygen surface exchange process, possibly through promoting the dissociation of oxygen molecules via the infiltration of BaCO3 nanoparticles. The density functional theory (DFT) illustrates the interaction mechanism between oxygen molecules and the BaCO3 surface. [ABSTRACT FROM AUTHOR]

To overcome the drawbacks of the single N-doped carbon materials, the further development of dual-heteroatoms (N and S) co-doped electrocatalysts is highly anticipated. Herein, N, S-doping and Fe-based carbon materials were synthesized by pyrolyzing a metal–organic framework (MIL-88) with the addition of N-/N, and S-containing ligands (chitosan and L-Cysteine) in the case of iron salt. The resulting electrocatalyst heat-treated at 850 °C (FeNSC-850) displays superior oxygen reduction reaction (ORR) performances to MIL-88-850, with an overall electron transfer number of 3.97 and a minor yield of HO2- (<2.6%). In addition to the comparable activity to commercial Pt/C in catalyzing the ORR in alkaline solution, the FeNSC-850 also shows higher stability, with a slight decline in half-wave potential (∆E1/2 = 15 mV) after 5000-cycle scanning of cyclic voltammetry. In view of the multiple Fe-based active sites, the additional S doping within FeNSC-850 creates more FeSx active sites for boosting the ORR performances in alkaline solution. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is paid much more attention because of the high overpotential required for driving the four-electron process in the field of storage and sustainable energy conversion, including fuel cell applications. In this paper, PtCo nanoparticles encapsulated on carbon supports were prepared by a simple modified polyol method with ethylene glycol. Structural as well as electrochemical characterizations illustrated that the PtCo/C electrocatalysts had a minimum particle size of 4.8 nm, which is close to the commercial 40 wt% Pt/JM. Moreover, the electrochemical measurements indicated that ORR activity was competitive with the commercial 40 wt% Pt/JM catalyst. The synthesis method is a critical way to produce PtCo/C catalysts for use in polymer electrolyte membranes in fuel cells (PEMFCs). [ABSTRACT FROM AUTHOR]

In this study, Ag-MnxOy/C composite catalysts deposited on reduced graphene oxide (rGO) and, for the first time on N-doped graphene oxide (NGO), were prepared via a facile synthesis method. The influence of the carbon support material on the activity and stability of the oxygen reduction reaction (ORR) and on the tolerance to ethanol in alkaline medium was focused and investigated. The physicochemical properties of the Ag-MnxOy/C catalysts were analyzed by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), Brunauer–Emmett–Teller (BET) method, atomic absorption spectroscopy (AAS), inductively coupled plasma-mass spectrometry (ICP-MS), and thermogravimetric gas analysis (TGA). Electrochemical characterization was performed by rotating disk electrode (RDE) experiments. The results show that the active manganese species MnO2 was assembled as nanorods and nanospheres on rGO and NGO, respectively. Ag was assumed to be present as very small or amorphous particles. Similar redox processes for Ag-MnxOy/rGO and Ag-MnxOy/NGO were examined via cyclic voltammetry. The Ag-MnxOy/rGO resulted in a more negative diffusion limiting current density of −3.01 mA cm−2 compared to Ag-MnxOy/NGO. The onset potential of approximately 0.9 V vs. RHE and the favored 4-electron transfer pathway were independent of the support material. Ag-MnxOy/NGO exhibited a higher ORR stability, whereas Ag-MnxOy/rGO showed a better ethanol tolerance. [ABSTRACT FROM AUTHOR]

This review considers the features of the catalysts with different nanoparticle structures architecture transformation under the various pre-treatment types. Based on the results of the publications analysis, it can be concluded that the chemical or electrochemical activation of bimetallic catalysts has a significant effect on their composition, microstructure, and catalytic activity in the oxygen reduction reaction. The stage of electrochemical activation is recommended for use as a mandatory catalyst pre-treatment to obtain highly active de-alloyed materials. The literature is studied, which covers possible variants of the structural modification under the influence of thermal treatment under different processing conditions. Additionally, based on the literature data analysis, recommendations are given for the thermal treatment of catalysts alloyed with various d-metals. [ABSTRACT FROM AUTHOR]

The development of high-performance non-noble metal-based oxygen electrocatalysts is crucial for the practical application of zinc–air batteries. Most of them suffer from low intrinsic activity and poor stability, failing to meet the needs of practical applications. Here, we report an efficient and durable bifunctional oxygen electrocatalyst of Fe@Fe-SAC composite (SAC stands for single atoms on carbon). A facile and ease-to-scale-up process synthesizes it. Fe single-atom and Fe nanoparticles are anchored on nitrogen-doped porous carbon, with the latter encapsulated by the graphitic shell. It exhibits appealing activity and durability in a basic electrolyte, requiring a half-wave potential of 0.805 V for oxygen reduction reaction (ORR) and an overpotential of only 348 mV to deliver a current density of 10 mA cm−2 for oxygen evolution reaction (OER). Both activities are comparable to the corresponding benchmarking electrocatalyst of Pt/C for ORR and IrO2 for OER. The superior activities are attributed to the strong electronic interaction between metal single-atom and nanoparticles. The favorable stability is ascribed to the physical encapsulation of carbon coatings on nanoparticles. This work presents a feasible scheme for designing and large-scale preparation of high-performance non-noble metal-based bifunctional oxygen electrocatalysts. [ABSTRACT FROM AUTHOR]

Hydrogen fuel cell technology is an essential component of a green economy. However, it is limited in practicality and affordability by the oxygen reduction reaction (ORR). Nanoscale silver particles have been proposed as a cost-effective solution to this problem. However, previous computational studies focused on clean and flat surfaces. High-index surfaces can be used to model active steps presented in nanoparticles. Here, we used the stable stepped Ag(322) surface as a model to understand the ORR performance of steps on Ag nanoparticles. Our density functional theory (DFT) results demonstrate a small dissociation energy barrier for O2 molecules on the Ag(322) surface, which can be ascribed to the existence of low-coordination number surface atoms. Consequently, the adsorption of OOH* led to the associative pathway becoming ineffective. Alternatively, the unusual dissociative mechanism is energetically favored on Ag(322) for ORR. Our findings reveal the importance of the coordination numbers of active sites for catalytic performance, which can further guide electrocatalysts' design. [ABSTRACT FROM AUTHOR]

Proton exchange membrane (PEM) fuel cells using Pt-based materials as electrocatalysts have achieved a decent performance, represented by the launched Toyota Mirai vehicle. The ideal PEM fuel cells consume stored pure hydrogen and air. However, SO2, as a primary air contaminant, may be fed along with air at the cathode, leading to Pt site deactivation. Therefore, it is important to improve the SO2 tolerance of catalysts for the stability of the oxygen reduction reaction (ORR). In this work, we develop the Pt/C-TiO2 catalyst against SO2 poisoning during ORR. Impressively, the hybrid Pt/C-TiO2 catalyst with 20 mass % TiO2 shows the best ORR and anti-toxic performance: the kinetic current density of ORR is 20.5% higher and the degradation rate after poisoning is 50% lower than Pt/C. The interaction between Pt and TiO2 as well as the abundant hydroxyl groups on the surface of TiO2 are both revealed to account for the accelerated removal of poisonous SO2 on Pt surfaces. [ABSTRACT FROM AUTHOR]

The development of non-precious metal electrocatalysts towards oxygen reduction reaction (ORR) is crucial for the commercialisation of polymer electrolyte fuel cells. In this work, cobalt-containing nitrogen-doped porous carbon materials were prepared by a pyrolysis of mixtures of saccharides, cobalt nitrate and dicyandiamide, which acts as a precursor for reactive carbon nitride template and a nitrogen source. The rotating disk electrode (RDE) experiments in 0.1 M KOH solution showed that the glucose-derived material with optimised cobalt content had excellent ORR activity, which was comparable to that of 20 wt% Pt/C catalyst. In addition, the catalyst exhibited high tolerance to methanol, good stability in short-time potential cycling test and low peroxide yield. The materials derived from xylan, xylose and cyclodextrin displayed similar activities, indicating that various saccharides can be used as inexpensive and sustainable precursors to synthesise active catalyst materials for anion exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

Transition metal (TM) single atomic catalysts (MSAC-N-C) derived from doped zeolite imidazolate frameworks (ZIF-8) are considered attractive oxygen reduction reaction (ORR) catalysts for fuel cells and metal-air batteries due to their advantages of high specific surface area, more active catalytic sites, adjustable pore size, and coordination topology features. This review provides an updated overview of the latest advances of MSAC-N-C catalysts derived from ZIF-8 precursors in ORR electrocatalysis. Particularly, some key challenges, including coordination environments regulation of catalysis center in MSAC-N-C, the active sites loading optimization and synergistic effects between TM nanoclusters/nanoparticles and the single atoms on MSAC-N-C catalysis activity, as well as their adaptability in various devices, are summarized for improving future development and application of MSAC-N-C catalysts. In addition, this review puts forward future research directions, making it play a better role in ORR catalysis for fuel cells and metal air batteries. [ABSTRACT FROM AUTHOR]

Unmodified natural silicates (bentonite, kaolin, clinoptilolite and diatomites) were tested as adsorbents for the organic pollutants in water tables using Methylene Blue (MB) as the model adsorbate. Among the selected materials, bentonite adsorbed as much as 237 mg/g, confirming its excellent suitability for pollutant removal. Spectral evidence confirmed successful MB immobilization at the bentonite surface. Furthermore, the thermal treatment of MB-saturated adsorbent in an inert atmosphere at 700 °C produced a carbon/silicate composite. EDX confirmed the formation of the nitrogen-doped carbon overlay on the silica scaffold and the obtained composite material was probed as an electrode material for oxygen reduction in an alkaline solution. Reduction proceeded via a two-electron mechanism with the main product being HO2−, a known nucleophile, which was subsequently used to degrade/demethylate MB. The composite showed a considerable 70% MB removal rate after an hour of electrochemical treatment. The synergy between the processes of adsorption of MB and the surface-generated HO2− dictates the efficiency of the method and points to a possible route for spent adsorbent reuse in the form of a durable product for environmental protection. [ABSTRACT FROM AUTHOR]

Hollow Pt-based nanoparticles are known to possess the properties of high electrocatalytic activity and durability. Nonetheless, their practical applications as catalytic materials are limited because of the requirement for exhaustive preparation. In this study, we prepared carbon-supported hollow PtNix (x = the moles of the Ni precursor to the Pt precursor in the catalyst preparation step) catalysts using a one-step preparation method, which substantially reduced the complexity of the conventional method for preparing hollow Pt-based catalysts. In particular, this hollow structure formation mechanism was proposed based on extensive characterizations. The prepared catalysts were examined to determine if they could be used as electrocatalysts for the oxygen reduction reaction (ORR). Among the investigated catalysts, the acid-treated hollow PtNi3/C catalyst demonstrated the best ORR activity, which was 3 times higher and 2.3 times higher than those of the commercial Pt/C and acid-treated particulate PtNi3/C catalysts, respectively. [ABSTRACT FROM AUTHOR]

We report here, a strategy to prepare Pt/Pd nanoparticles decorated with Co-N-C materials, where Co-N-C was obtained via pyrolysis of ZIF-67 directly. As-prepared Pt/Pd/Co-N-C catalysts showed excellent ORR performance, offered with a higher limit current density (6.6 mA cm−2) and similar half-wave potential positive (E1/2 = 0.84 V) compared with commercial Pt/C. In addition to an ORR activity, it also exhibits robust durability. The current density of Pt/Pd/Co-N-C decreased by only 9% after adding methanol, and a 10% current density loss was obtained after continuous testing at 36,000 s. [ABSTRACT FROM AUTHOR]

To evaluate supports' effects on catalytic activity toward the oxygen reduction reaction (ORR), a simple and controlled chemical synthesis, involving the hot injection of metal precursors, was developed to produce bimetallic PtNi nanoparticles (75 wt.% Pt and 25 wt.% Ni), supported on carbon nanotubes (CNTs) and carbon nanofibers (CNFs). The synthesized electrocatalyst was characterized using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and scanning transmission electron microscopy (STEM). To determine the catalytic activity, an electrochemical evaluation of the synthesized catalysts in an acidic medium was performed using cyclic voltammetry (CV), CO stripping, and rotating disk electrode (RDE) tests. The presence of Pt and Ni in the nanoparticles was confirmed by EDS and XRD. Based on the STEM micrographs, the average particle size was 30 nm. Compared to the commercial Pt/C catalyst, the PtNi/CNT catalyst exhibited higher specific activity and slightly lower mass activity toward ORR in a 0.1 M HClO4 electrolyte solution. [ABSTRACT FROM AUTHOR]

The smart choice of polyoxometalates (POMs) and the design of POM@carbon-based composites are promising tools for producing active electrocatalysts for both the oxygen reduction (ORR) and the oxygen evolution reactions (OER). Hence, herein, we report the preparation, characterization and application of three composites based on doped, multi-walled carbon nanotubes (MWCNT_N6) and three different POMs (Na12[(FeOH2)2Fe2(As2W15O56)2]·54H2O, Na12[(NiOH2)2Ni2(As2W15O56)2]·54H2O and Na14[(FeOH2)2Ni2(As2W15O56)2]·55H2O) as ORR and OER electrocatalysts in alkaline medium (pH = 13). Overall, the three POM@MWCNT_N6 composites showed good ORR performance with onset potentials between 0.80 and 0.81 V vs. RHE and diffusion-limiting current densities ranging from −3.19 to −3.66 mA cm−2. Fe4@MWCNT_N6 and Fe2Ni2@MWCNT_N6 also showed good stability after 12 h (84% and 80% of initial current). The number of electrons transferred per O2 molecule was close to three, suggesting a mixed regime. Moreover, the Fe2Ni2@MWCNT_N6 presented remarkable OER performance with an overpotential of 0.36 V vs. RHE (for j = 10 mA cm−2), a jmax close to 135 mA cm−2 and fast kinetics with a Tafel slope of 45 mV dec−1. More importantly, this electrocatalyst outperformed not only most POM@carbon-based composites reported so far but also the state-of-the-art RuO2 electrocatalyst. Thus, this work represents a step forward towards bifunctional electrocatalysts using less expensive materials. [ABSTRACT FROM AUTHOR]

New highly active electrocatalysts were obtained by depositing bimetallic Pt-Cu nanoparticles on the surface of an N-doped carbon support. The structural–morphological characteristics and electrochemical behavior of the catalysts were studied. Using current stress testing protocols, their resistance to degradation was assessed in comparison with that of a commercial Pt/C material. A combined approach to catalyst synthesis that consists in alloying platinum with copper and doping the support makes it possible to obtain catalysts with a uniform distribution of bimetallic nanoparticles on the carbon surface. The obtained catalysts exhibit high activity and durability. [ABSTRACT FROM AUTHOR]

In addition to C, H and O, some biomass is also rich in mineral elements. The recovery and utilization of special mineral elements is of great significance to prepare functional materials and alleviate the current energy shortage. Herein, we describe a facile strategy for making full use of the chemical composition (C, Fe) and special structure of red blood cells (RBCs) from waste pig blood to fabricate a dual metal (Fe, Co)-nitrogen (N)-doped porous carbon catalyst by pyrolysis of a mixture of RBCs biomass, cobaltous acetate, and melamine. The porous catalyst displays a comparable activity for oxygen reduction reaction (ORR) to that of commercial Pt/C catalyst, with a half-wave potential of 0.821 VvsRHE in alkaline media and 0.672 VvsRHE in acid electrolyte. Especially, the as-prepared catalyst shows excellent methanol tolerance and stability in both acidic and alkaline electrolytes, which is superior to commercial Pt/C catalysts. The excellent ORR activity of FeCo-N/C(RBC) can be ascribed to the porous morphology and the cooperation between metal and nitrogen species. This work provides a novel idea of exploiting the composition of renewable biomass to modulate the activity and stability of carbon-based ORR catalysts. [ABSTRACT FROM AUTHOR]

Opening up electrocatalysts for oxygen reduction reaction (ORR) is essential for practical application in fuel cells and metal-air batteries; however, how to make the catalysts with both good performance and low cost is difficult. Recently, research on the ORR of molybdenum disulfide-based catalysts in alkaline electrolytes has been on the rise. However, the development of MoS2 catalyst for acidic ORR is still in its infancy. Herein, without using reductant and morphology control reagent, we firstly obtained flowerball-like MoS2/Vulcan XC-72R (VC) nanocomposites via hydrothermal method. The designed composite exhibits a nearly 4e− ORR process with 0.78 and 0.92 V onset potentials in 0.1 M KOH and HClO4, respectively. Furthermore, the flowerball-like composite shows utmost electrochemical stability judging by 87 and 80% current retention for about 5.5 h either in alkaline or acid media, long term durability for continuous 10,000 cycles, and stronger resistance to methanol than the commercial Pt/C catalyst. The abundant Mo edges as catalytic active centers of flowerball-like structure, high electron conductivity, and enhanced mass transport in either alkaline or acidic electrolyte are favorable for catalytic performance. The prepared catalyst provides great potential for the substitution of noble metal based catalysts in fuel cells and metal-air batteries. [ABSTRACT FROM AUTHOR]

In order to fill the research gap of high metal loading of high performance PtNi alloy catalysts, a PtNi/C alloy nano-catalyst with metal loading more than 50 wt.% and core-shell like structure was prepared by ethylene glycol reduction, high temperature annealing, and acid pickling. The electrochemical test results showed that the prepared PtNi alloy catalyst had excellent electrochemical activity: the electrochemical surface area (ECSA) was 63.8 m2·gPt−1, and the mass activity (MA) was 0.574 A·mgPt−1, which is 2.73 times greater than those of the Pt/C JM (Johnson Matthey) catalyst. The durability of the PtNi/C catalyst was further investigated. After 30 K cycles of accelerated durability test, the ECSA and MA of the PtNi/C alloy catalyst decreased by 10.2% and 31.2%, respectively. The PtNi/C alloy catalyst prepared in this study has excellent catalytic activity and overcomes the problem of insufficient durability of traditional alloy catalysts and has the potential for large-scale commercial application. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) at the cathode is a fundamental process and functions a pivotal role in fuel cells and metal-air batteries. However, the electrochemical performance of these technologies has been still challenged by the high cost, scarcity, and insufficient durability of the traditional Pt-based ORR electrocatalysts. Heteroatom-doped nanocarbon electrocatalysts with competitive activity, enhanced durability, and acceptable cost, have recently attracted increasing interest and hold great promise as substitute for precious-metal catalysts (e.g., Pt and Pt-based materials). More importantly, three-dimensional (3D) porous architecture appears to be necessary for achieving high catalytic ORR activity by providing high specific surface areas with more exposed active sites and large pore volumes for efficient mass transport of reactants to the electrocatalysts. In this review, recent progress on the design, fabrication, and performance of 3D heteroatom-doped nanocarbon catalysts is summarized, aiming to elucidate the effects of heteroatom doping and 3D structure on the ORR performance of nanocarbon catalysts, thus promoting the design of highly active nanocarbon-based ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

Herein, a promising method to prepare efficient N-doped porous carbon-supported Fe2O3 nanoparticles (Fe2O3/N-PCs) ORR electrocatalysts is presented. The porous carbon was derived from a biomass i.e., mulberry leaf through a cost-effective approach. The existence of diverse compounds containing carbon, oxygen, nitrogen and sulfur in mulberry leaf benefit the formation and uniform dispersion of Fe2O3 nanoparticles (NPs) in the porous carbon. In evaluating the effects of the carbon support on the Fe2O3 NPs towards the ORR, we found that the sample of Fe2O3/N-PCs-850 (Fe2O3/N-PCs obtained at 850 °C) with high surface area of 313.8 m2·g-1 exhibits remarkably superior ORR activity than that of materials acquired under other temperatures. To be specific, the onset potential and reduction peak potential of Fe2O3/N-PCs-850 towards ORR are 0.936 V and 0.776 V (vs. RHE), respectively. The calculated number of electron transfer n for the ORR is 3.9, demonstrating a near four-electron-transfer process. Furthermore, it demonstrates excellent longtime stability and resistance to methanol deactivation compared with Pt/C catalyst. This study provides a novel design of highly active ORR electrocatalysts from low-cost abundant plant products. [ABSTRACT FROM AUTHOR]

Highly-efficient catalysts for the oxygen reduction reaction (ORR) have been extensively investigated for the development of proton exchange membrane fuel cells (PEMFCs). The state-ofthe- art Pt/C catalysts suffer from high price, limited accessibility of Pt, sluggish reaction kinetics, as well as undesirable long-term durability. Engineering ultra-small noble metal clusters with high surface-to-volume ratios and robust stabilities for ORR represents a new avenue. After a simple introduction regarding the significance of ORR and the recent development of noble metal clusters, the general ORR mechanism in both acidic and basic media is firstly discussed. Subsequently, we will summarize the recent efforts employing Pt, Au, Ag, Pd and Ru clusters, as well as the alloyed bi-metallic clusters for acquiring highly efficient catalysts to enhance both the activity and stability of ORR. Molecular noble metal clusters with definitive composition to reveal the relevant ORR mechanism will be particularly highlighted. Finally, the current challenges, the future outlook, as well as the perspectives in this booming field will be proposed, featuring the great opportunities and potentials to engineering noble metal clusters as highly-efficient and durable cathodic catalysts for fuel cell applications. [ABSTRACT FROM AUTHOR]

Ag4Bi2O5/MnO2 nano-sized material was synthesized by a co-precipitation method in concentrated KOH solution. The morphology characterization indicates that MnO2 nanoparticles with a size of 20 nm are precipitated on the surface of nano Ag4Bi2O5, forming a structure like corn on the cob. The obtained material with 60% Mn offers slightly higher initial potential (0.098 V vs. Hg/HgO) and limiting current density (-5.67 mA cm-2) at a rotating speed of 1600 rpm compared to commercial Pt/C (-0.047 V and -5.35 mA cm-2, respectively). Furthermore, the obtained material exhibits superior long-term durability and stronger methanol tolerance than commercial Pt/C. The remarkable features suggest that the Ag4Bi2O5/MnO2 nano-material is a very promising oxygen reduction reaction catalyst. [ABSTRACT FROM AUTHOR]

Development of inexpensive and robust electrocatalysts towards oxygen reduction reaction (ORR) is crucial for the cost-affordable manufacturing of metal-air batteries and fuel cells. Here we show that cross-linked CoMoO4 nanosheets and reduced graphene oxide (CoMoO4/rGO) can be integrated in a hybrid material under one-pot hydrothermal conditions, yielding a composite material with promising catalytic activity for oxygen reduction reaction (ORR). Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used to investigate the efficiency of the fabricated CoMoO4/rGO catalyst towards ORR in alkaline conditions. The CoMoO4/rGO composite revealed the main reduction peak and onset potential centered at 0.78 and 0.89 V (vs. RHE), respectively. This study shows that the CoMoO4/rGO composite is a highly promising catalyst for the ORR under alkaline conditions, and potential noble metal replacement cathode in fuel cells and metal-air batteries. [ABSTRACT FROM AUTHOR]

Metal-organic framework (MOF) materials can be used as precursors to prepare non-precious metal catalysts (NPMCs) for oxygen reduction reaction (ORR). Herein, we prepared a novel MOF material (denoted as Co-bpdc) and then combined it with multi-walled carbon nanotubes (MWCNTs) to form Co-bpdc/MWCNTs composites. After calcination, the cobalt ions from Co-bpdc were converted into Co nanoparticles, which were distributed in the graphite carbon layers and MWCNTs to form Co-bpdc/MWCNTs. The prepared catalysts were characterized by TEM (Transmission electron microscopy), XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), BET (Brunauer-Emmett-Teller), and Raman spectroscopy. The electrocatalytic activity was measured by using rotating disk electrode (RDE) voltammetry. The catalysts showed higher ORR catalytic activity than the commercial Pt/C catalyst in alkaline solution. Co-bpdc/MWCNTs-100 showed the highest ORR catalytic activity, with an initial reduction potential and half-wave potential reaching 0.99 V and 0.92 V, respectively. The prepared catalysts also showed superior stability and followed the 4-electron pathway ORR process in alkaline solution. [ABSTRACT FROM AUTHOR]

We report a facile synthetic method for the preparation of a terpyridine-containing imine-rich graphene (IrGO-Tpy) using an acid-catalyzed dehydration reaction between graphene oxide (GO) and 40-(aminophenyl)-2,20':'602"-terpyridine. Owing to the presence of terpyridine ligands, cobalt ions (Co2+) were readily incorporated into the IrGO-Tpy structures, affording a metal complex, denoted IrGo-Tpy-Co. Cyclic voltammetry and linear sweep voltammetry measurements confirm the noticeable oxygen reduction reaction (ORR) activities of the IrGo-Tpy and IrGo-Tpy-Co electroacatalysts in alkaline electrolytes, along with the additional merits of high selectivity, excellent long-term durability, and good resistance to methanol crossover. In addition, a remarkable improvement in the ORR performance was observed for IrGO-Tpy-Co compared with that of IrGo-Tpy, arising from the significant contribution of the cobalt-terpyridine complex in facilitating the ORR process. [ABSTRACT FROM AUTHOR]

In the current work, heteroatom-doped graphene materials containing different atomic ratios of nitrogen and sulphur were employed as electrocatalysts for the oxygen reduction reaction (ORR) in acidic and alkaline media. To this end, the hydrothermal route and different chemical reducing agents were employed to synthesize the catalytic materials. The physicochemical characterization of the catalysts was performed by several techniques, such as X-ray diffraction, Raman spectroscopy and elemental analysis; meanwhile, the electrochemical performance of the materials toward the ORR was analyzed by linear sweep voltammetry (LSV), rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques. The main results indicate that the ORR using heteroatom-doped graphene is a direct four-electron pathway, for which the catalytic activity is higher in alkaline than in acidic media. Indeed, a change of the reaction mechanism was observed with the insertion of N into the graphenic network, by the rate determining step changes from the first electrochemical step (formation of adsorbed OOH) on glassy carbon to the removal of adsorbed O (Oad) from the N-graphene surface. Moreover, the addition of sulphur atoms into the N-graphene structure increases the catalytic activity toward the ORR, as the desorption of Oad is accelerated. [ABSTRACT FROM AUTHOR]