Showing papers in "Advanced Materials in 2016"
TL;DR: Current progress in this field is summarized here, especially highlighting several important bifunctional catalysts, and various approaches to improve or optimize the electrocatalysts are introduced.
Abstract: Water electrolysis is considered as the most promising technology for hydrogen production. Much research has been devoted to developing efficient electrocatalysts for hydrogen production via the hydrogen evolution reaction (HER) and oxygen production via the oxygen evolution reaction (OER). The optimum electrocatalysts can drive down the energy costs needed for water splitting via lowering the overpotential. A number of cobalt (Co)-based materials have been developed over past years as non-noble-metal heterogeneous electrocatalysts for HER and OER. Recent progress in this field is summarized here, especially highlighting several important bifunctional catalysts. Various approaches to improve or optimize the electrocatalysts are introduced. Finally, the current existing challenges and the future working directions for enhancing the performance of Co-implicated electrocatalysts are proposed.
1,963 citations
TL;DR: A nonfullerene-based polymer solar cell (PSC) that significantly outperforms fullerene -based PSCs with respect to the power-conversion efficiency and excellent thermal stability is demonstrated for the first time.
Abstract: A nonfullerene-based polymer solar cell (PSC) that significantly outperforms fullerene-based PSCs with respect to the power-conversion efficiency is demonstrated for the first time. An efficiency of >11%, which is among the top values in the PSC field, and excellent thermal stability is obtained using PBDB-T and ITIC as donor and acceptor, respectively.
1,662 citations
TL;DR: The latest successful examples of flexible and stretchable physical sensors for the detection of temperature, pressure, and strain, as well as their novel structures, technological innovations, and challenges, are reviewed.
Abstract: Flexible and stretchable physical sensors that can measure and quantify electrical signals generated by human activities are attracting a great deal of attention as they have unique characteristics, such as ultrathinness, low modulus, light weight, high flexibility, and stretchability. These flexible and stretchable physical sensors conformally attached on the surface of organs or skin can provide a new opportunity for human-activity monitoring and personal healthcare. Consequently, in recent years there has been considerable research effort devoted to the development of flexible and stretchable physical sensors to fulfill the requirements of future technology, and much progress has been achieved. Here, the most recent developments of flexible and stretchable physical sensors are described, including temperature, pressure, and strain sensors, and flexible and stretchable sensor-integrated platforms. The latest successful examples of flexible and stretchable physical sensors for the detection of temperature, pressure, and strain, as well as their novel structures, technological innovations, and challenges, are reviewed first. In the next section, recent progress regarding sensor-integrated wearable platforms is overviewed in detail. Some of the latest achievements regarding self-powered sensor-integrated wearable platform technologies are also reviewed. Further research direction and challenges are also proposed to develop a fully sensor-integrated wearable platform for monitoring human activity and personal healthcare in the near future.
1,469 citations
TL;DR: Owing to the magnetic-dielectric synergistic effect, the obtained CoNi@SiO2 @TiO2 microspheres exhibit outstanding microwave absorption performance with a maximum reflection loss of -58.2 dB and wide bandwidth of 8.1 GHz.
Abstract: The synthesis of CoNi@SiO2 @TiO2 core-shell and CoNi@Air@TiO2 yolk-shell microspheres is reported for the first time. Owing to the magnetic-dielectric synergistic effect, the obtained CoNi@SiO2 @TiO2 microspheres exhibit outstanding microwave absorption performance with a maximum reflection loss of -58.2 dB and wide bandwidth of 8.1 GHz (8.0-16.1 GHz, < -10 dB).
1,409 citations
TL;DR: Progress in nanogenerators for mechanical energy harvesting is reviewed, mainly including two key technologies: flexible piezoelectric nanognerators (PENGs) and flexible triboelectrics nanogsenerators (TENGs).
Abstract: Flexible nanogenerators that efficiently convert mechanical energy into electrical energy have been extensively studied because of their great potential for driving low-power personal electronics and self-powered sensors. Integration of flexibility and stretchability to nanogenerator has important research significance that enables applications in flexible/stretchable electronics, organic optoelectronics, and wearable electronics. Progress in nanogenerators for mechanical energy harvesting is reviewed, mainly including two key technologies: flexible piezoelectric nanogenerators (PENGs) and flexible triboelectric nanogenerators (TENGs). By means of material classification, various approaches of PENGs based on ZnO nanowires, lead zirconate titanate (PZT), poly(vinylidene fluoride) (PVDF), 2D materials, and composite materials are introduced. For flexible TENG, its structural designs and factors determining its output performance are discussed, as well as its integration, fabrication and applications. The latest representative achievements regarding the hybrid nanogenerator are also summarized. Finally, some perspectives and challenges in this field are discussed.
1,325 citations
TL;DR: The two new SMAs (IT-M and IT-DM) end-capped by methyl-modified dicycanovinylindan-1-one exhibit upshifted lowest unoccupied molecular orbital (LUMO) levels, and hence higher open-circuit voltages can be observed in the corresponding devices.
Abstract: Fine energy-level modulations of small-molecule acceptors (SMAs) are realized via subtle chemical modifications on strong electron-withdrawing end-groups. The two new SMAs (IT-M and IT-DM) end-capped by methyl-modified dicycanovinylindan-1-one exhibit upshifted lowest unoccupied molecular orbital (LUMO) levels, and hence higher open-circuit voltages can be observed in the corresponding devices. Finally, a top power conversion efficiency of 12.05% is achieved.
1,276 citations
TL;DR: Recent progress on the design, synthesis, and application of OER electrocatalysts based on transition-metal elements, including Co, Ni, and Fe, is summarized, and some invigorating perspectives on the future developments are provided.
Abstract: Increasing energy demands and environment awareness have promoted extensive research on the development of alternative energy conversion and storage technologies with high efficiency and environmental friendliness. Among them, water splitting is very appealing, and is receiving more and more attention. The critical challenge of this renewable-energy technology is to expedite the oxygen evolution reaction (OER) because of its slow kinetics and large overpotential. Therefore, developing efficient electrocatalysts with high catalytic activities is of great importance for high-performance water splitting. In the past few years, much effort has been devoted to the development of alternative OER electrocatalysts based on transition-metal elements that are low-cost, highly efficient, and have excellent stability. Here, recent progress on the design, synthesis, and application of OER electrocatalysts based on transition-metal elements, including Co, Ni, and Fe, is summarized, and some invigorating perspectives on the future developments are provided.
1,270 citations
TL;DR: The Li-conducting Li3PO4 SEI layer with a high Young's modulus can effectively reduce side reactions between Li metal and the electrolyte and can restrain Li dendrite growth in lithium-metal batteries during cycling.
Abstract: A Li3PO4 solid electrolyte interphase (SEI) layer is demonstrated to be stable in the organic electrolyte, even during the Li deposition/dissolution process. Thus, the Li-conducting Li3PO4 SEI layer with a high Young's modulus can effectively reduce side reactions between Li metal and the electrolyte and can restrain Li dendrite growth in lithium-metal batteries during cycling.
1,196 citations
TL;DR: Although perovskite light-emitting devices are yet to become industrially relevant, in merely two years these devices have achieved the brightness and efficiencies that organic light-EMitting diodes accomplished in two decades.
Abstract: Organic-inorganic hybrid perovskites have cemented their position as an exceptional class of optoelectronic materials thanks to record photovoltaic efficiencies of 22.1%, as well as promising demonstrations of light-emitting diodes, lasers, and light-emitting transistors. Perovskite materials with photoluminescence quantum yields close to 100% and perovskite light-emitting diodes with external quantum efficiencies of 8% and current efficiencies of 43 cd A(-1) have been achieved. Although perovskite light-emitting devices are yet to become industrially relevant, in merely two years these devices have achieved the brightness and efficiencies that organic light-emitting diodes accomplished in two decades. Further advances will rely decisively on the multitude of compositional, structural variants that enable the formation of lower-dimensionality layered and three-dimensional perovskites, nanostructures, charge-transport materials, and device processing with architectural innovations. Here, the rapid advancements in perovskite light-emitting devices and lasers are reviewed. The key challenges in materials development, device fabrication, operational stability are addressed, and an outlook is presented that will address market viability of perovskite light-emitting devices.
1,138 citations
TL;DR: Several promising strategies, including surface engineering, chemical modification, nanostructured catalysts, and composite materials, are proposed to facilitate the future development of CO2 electroreduction.
Abstract: In view of the climate changes caused by the continuously rising levels of atmospheric CO2 , advanced technologies associated with CO2 conversion are highly desirable. In recent decades, electrochemical reduction of CO2 has been extensively studied since it can reduce CO2 to value-added chemicals and fuels. Considering the sluggish reaction kinetics of the CO2 molecule, efficient and robust electrocatalysts are required to promote this conversion reaction. Here, recent progress and opportunities in inorganic heterogeneous electrocatalysts for CO2 reduction are discussed, from the viewpoint of both experimental and computational aspects. Based on elemental composition, the inorganic catalysts presented here are classified into four groups: metals, transition-metal oxides, transition-metal chalcogenides, and carbon-based materials. However, despite encouraging accomplishments made in this area, substantial advances in CO2 electrolysis are still needed to meet the criteria for practical applications. Therefore, in the last part, several promising strategies, including surface engineering, chemical modification, nanostructured catalysts, and composite materials, are proposed to facilitate the future development of CO2 electroreduction.
1,130 citations
TL;DR: Recent progress in photocatalytic and electrocatalytic HERs using 2D TMD-based composites as catalysts is discussed.
Abstract: Hydrogen (H2) is one of the most important clean and renewable energy sources for future energy sustainability. Nowadays, photocatalytic and electrocatalytic hydrogen evolution reactions (HERs) from water splitting are considered as two of the most efficient methods to convert sustainable energy to the clean energy carrier, H2. Catalysts based on transition metal dichalcogenides (TMDs) are recognized as greatly promising substitutes for noble-metal-based catalysts for HER. The photocatalytic and electrocatalytic activities of TMD nanosheets for the HER can be further improved after hybridization with many kinds of nanomaterials, such as metals, oxides, sulfides, and carbon materials, through different methods including the in situ reduction method, the hot-injection method, the heating-up method, the hydro(solvo)thermal method, chemical vapor deposition (CVD), and thermal annealing. Here, recent progress in photocatalytic and electrocatalytic HERs using 2D TMD-based composites as catalysts is discussed.
TL;DR: The bright potential of MOF materials as emerging multifunctional materials is highlighted in some of the most important applications for gas storage and separation, optical, electric and magnetic materials, chemical sensing, catalysis, and biomedicine.
Abstract: Metal-organic frameworks (MOFs), also known as coordination polymers, represent an interesting type of solid crystalline materials that can be straightforwardly self-assembled through the coordination of metal ions/clusters with organic linkers. Owing to the modular nature and mild conditions of MOF synthesis, the porosities of MOF materials can be systematically tuned by judicious selection of molecular building blocks, and a variety of functional sites/groups can be introduced into metal ions/clusters, organic linkers, or pore spaces through pre-designing or post-synthetic approaches. These unique advantages enable MOFs to be used as a highly versatile and tunable platform for exploring multifunctional MOF materials. Here, the bright potential of MOF materials as emerging multifunctional materials is highlighted in some of the most important applications for gas storage and separation, optical, electric and magnetic materials, chemical sensing, catalysis, and biomedicine.
TL;DR: The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here and particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations.
Abstract: Sensor technology has an important effect on many aspects in our society, and has gained much progress, propelled by the development of nanoscience and nanotechnology. Current research efforts are directed toward developing high-performance gas sensors with low operating temperature at low fabrication costs. A gas sensor working at room temperature is very appealing as it provides very low power consumption and does not require a heater for high-temperature operation, and hence simplifies the fabrication of sensor devices and reduces the operating cost. Nanostructured materials are at the core of the development of any room-temperature sensing platform. The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here. Particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations. Finally, some future research perspectives and new challenges that the field of room-temperature sensors will have to address are also discussed.
TL;DR: Isolated single-atom platinum (Pt) embedded in the sub-nanoporosity of 2D g-C3 N4 as a new form of co-catalyst maximizes the atom efficiency and alters the surface trap states of g-N4, leading to significantly enhanced photocatalytic H2 evolution activity.
Abstract: Isolated single-atom platinum (Pt) embedded in the sub-nanoporosity of 2D g-C3 N4 as a new form of co-catalyst is reported. The highly stable single-atom co-catalyst maximizes the atom efficiency and alters the surface trap states of g-C3 N4 , leading to significantly enhanced photocatalytic H2 evolution activity, 8.6 times higher than that of Pt nanoparticles and up to 50 times that for bare g-C3 N4 .
TL;DR: The essential components required for vitals sensors are outlined and discussed here, including the reported sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements.
Abstract: Advances in wireless technologies, low-power electronics, the internet of things, and in the domain of connected health are driving innovations in wearable medical devices at a tremendous pace. Wearable sensor systems composed of flexible and stretchable materials have the potential to better interface to the human skin, whereas silicon-based electronics are extremely efficient in sensor data processing and transmission. Therefore, flexible and stretchable sensors combined with low-power silicon-based electronics are a viable and efficient approach for medical monitoring. Flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiration rate, blood pressure, pulse oxygenation, and blood glucose have applications in both fitness monitoring and medical diagnostics. As a review of the latest development in flexible and wearable human vitals sensors, the essential components required for vitals sensors are outlined and discussed here, including the reported sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements.
TL;DR: Ultrapure blue-fluorescent molecules based on thermally activated delayed fluorescence are developed that exhibit a deep blue emission at 467 nm with a full-width at half-maximum of 28 nm and an internal quantum efficiency of ≈100%, which represent record-setting performance for blue OLED devices.
Abstract: Ultrapure blue-fluorescent molecules based on thermally activated delayed fluorescence are developed. Organic light-emitting diode (OLED) devices employing the new emitters exhibit a deep blue emission at 467 nm with a full-width at half-maximum of 28 nm, CIE coordinates of (0.12, 0.13), and an internal quantum efficiency of ≈100%, which represent record-setting performance for blue OLED devices.
TL;DR: Density function theory calculations further reveal that the different types of defects are essential for the individual electrocatalytic activity for ORR, OER, and HER, respectively.
Abstract: Defects derived by the removal of heteroatoms from graphene are demonstrated, both experimentally and theoretically, to be effective for all three basic electrochemical reactions, e.g., oxygen reduction (ORR), oxygen evolution (OER), and hydrogen evolution (HER). Density function theory calculations further reveal that the different types of defects are essential for the individual electrocatalytic activity for ORR, OER, and HER, respectively.
TL;DR: The trends indicate that hydrogels that self-heal better also achieve self- healing faster, as compared to gels that only partially self- Healing, and the potential relevance of self-Healing hydrogel to the exciting research areas of 3D/4D printing, soft robotics, and assisted health technologies is highlighted.
Abstract: Over the past few years, there has been a great deal of interest in the development of hydrogel materials with tunable structural, mechanical, and rheological properties, which exhibit rapid and autonomous self-healing and self-recovery for utilization in a broad range of applications, from soft robotics to tissue engineering. However, self-healing hydrogels generally either possess mechanically robust or rapid self-healing properties but not both. Hence, the development of a mechanically robust hydrogel material with autonomous self-healing on the time scale of seconds is yet to be fully realized. Here, the current advances in the development of autonomous self-healing hydrogels are reviewed. Specifically, methods to test self-healing efficiencies and recoveries, mechanisms of autonomous self-healing, and mechanically robust hydrogels are presented. The trends indicate that hydrogels that self-heal better also achieve self-healing faster, as compared to gels that only partially self-heal. Recommendations to guide future development of self-healing hydrogels are offered and the potential relevance of self-healing hydrogels to the exciting research areas of 3D/4D printing, soft robotics, and assisted health technologies is highlighted.
TL;DR: A two-step ligand-exchange strategy is developed, in which the long-carbon- chain ligands on all-inorganic perovskite quantum dots (QDs) are replaced with halide-ion-pair ligands.
Abstract: A two-step ligand-exchange strategy is developed, in which the long-carbon- chain ligands on all-inorganic perovskite (CsPbX3 , X = Br, Cl) quantum dots (QDs) are replaced with halide-ion-pair ligands. Green and blue light-emitting diodes made from the halide-ion-pair-capped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs.
TL;DR: Li dendrite-free growth is achieved by employing glass fiber with large polar functional groups as the interlayer of Li metal anode and separator to uniformly distribute Li ions.
Abstract: Li dendrite-free growth is achieved by employing glass fiber with large polar functional groups as the interlayer of Li metal anode and separator to uniformly distribute Li ions. The evenly distributed Li ions render the dendrite-free Li deposits at high rates (10 mA cm(-2)) and high lithiation capacity (2.0 mAh cm(-2)).
TL;DR: Recent advances in soft materials, devices, and integrated systems are reviewes, with representative examples that highlight the utility of soft bioelectronics for advanced medical diagnostics and therapies.
Abstract: Flexible and stretchable electronics and optoelectronics configured in soft, water resistant formats uniquely address seminal challenges in biomedicine. Over the past decade, there has been enormous progress in the materials, designs, and manufacturing processes for flexible/stretchable system subcomponents, including transistors, amplifiers, bio-sensors, actuators, light emitting diodes, photodetector arrays, photovoltaics, energy storage elements, and bare die integrated circuits. Nanomaterials prepared using top-down processing approaches and synthesis-based bottom-up methods have helped resolve the intrinsic mechanical mismatch between rigid/planar devices and soft/curvilinear biological structures, thereby enabling a broad range of non-invasive, minimally invasive, and implantable systems to address challenges in biomedicine. Integration of therapeutic functional nanomaterials with soft bioelectronics demonstrates therapeutics in combination with unconventional diagnostics capabilities. Recent advances in soft materials, devices, and integrated systems are reviewes, with representative examples that highlight the utility of soft bioelectronics for advanced medical diagnostics and therapies.
TL;DR: Extremely efficient sky-blue organic electroluminescence with external quantum efficiency of ≈37% is achieved in a conventional planar device structure using a highly efficient thermally activated delayed fluorescence emitter based on the spiroacridine-triazine hybrid.
Abstract: Extremely efficient sky-blue organic electroluminescence with external quantum efficiency of ≈37% is achieved in a conventional planar device structure, using a highly efficient thermally activated delayed fluorescence emitter based on the spiroacridine-triazine hybrid and simultaneously possessing nearly unitary (100%) photoluminescence quantum yield, excellent thermal stability, and strongly horizontally oriented emitting dipoles (with a horizontal dipole ratio of 83%).
TL;DR: A unique type of pH/H2 O2 dual-responsive intelligent nanoscale delivery system based on albumin-coated MnO2 is presented, which is capable of modulating the tumor microenvironment by relieving hypoxia.
Abstract: A unique type of pH/H2 O2 dual-responsive intelligent nanoscale delivery system based on albumin-coated MnO2 is presented, which is capable of modulating the tumor microenvironment (TME) by relieving hypoxia. Additionally, TME-responsive size changes enable effective intratumor diffusion. A highly effective combined photodynamic and chemotherapy is realized with these nanoparticles in a mouse tumor model.
TL;DR: As an emerging class of porous crystalline materials, covalent organic frameworks (COFs) are excellent candidates for various applications and can serve as ideal platforms for capturing CO2 to mitigate the dilemma caused by the greenhouse effect.
Abstract: As an emerging class of porous crystalline materials, covalent organic frameworks (COFs) are excellent candidates for various applications. In particular, they can serve as ideal platforms for capturing CO2 to mitigate the dilemma caused by the greenhouse effect. Recent research achievements using COFs for CO2 capture are highlighted. A background overview is provided, consisting of a brief statement on the current CO2 issue, a summary of representative materials utilized for CO2 capture, and an introduction to COFs. Research progresses on: i) experimental CO2 capture using different COFs synthesized based on different covalent bond formations, and ii) computational simulation results of such porous materials on CO2 capture are summarized. Based on these experimental and theoretical studies, careful analyses and discussions in terms of the COF stability, low- and high-pressure CO2 uptake, CO2 selectivity, breakthrough performance, and CO2 capture conditions are provided. Finally, a perspective and conclusion section of COFs for CO2 capture is presented. Recent advancements in the field are highlighted and the strategies and principals involved are discussed.
TL;DR: A new trimethylaluminum vapor-based crosslinking method to render the nanocrystal films insoluble is applied, coupled with the natural confinement of injected charges within the perovskite crystals, facilitates electron-hole capture and gives rise to a remarkable electroluminescence yield.
Abstract: The preparation of highly efficient perovskite nanocrystal light-emitting diodes is shown. A new trimethylaluminum vapor-based crosslinking method to render the nanocrystal films insoluble is applied. The resulting near-complete nanocrystal film coverage, coupled with the natural confinement of injected charges within the perovskite crystals, facilitates electron-hole capture and give rise to a remarkable electroluminescence yield of 5.7%.
TL;DR: Halloysite nanotubes are a promising mesoporous media for catalytic nanoparticles that may be seeded on the tube surface or synthesized exclusively in the lumens, providing enhanced catalytic properties, especially at high temperatures.
Abstract: Halloysite is an alumosilicate tubular clay with a diameter of 50 nm, an inner lumen of 15 nm and a length of 600-900 nm. It is a natural biocompatible nanomaterial available in thousands of tons at low price, which makes it a good candidate for nanoarchitectural composites. The inner lumen of halloysite may be adjusted by etching to 20-30% of the tube volume and loading with functional agents (antioxidants, anticorrosion agents, flame-retardant agents, drugs, or proteins) allowing for formulations with sustained release tuned by the tube end-stoppers for hours and days. Clogging the tube ends in polymeric composites allows further extension of the release time. Thus, antioxidant-loaded halloysite doped into rubber enhances anti-aging properties for at least 12 months. The addition of 3-5 wt% of halloysite increases the strength of polymeric materials, and the possibility of the tube's orientation promises a gradient of properties. Halloysite nanotubes are a promising mesoporous media for catalytic nanoparticles that may be seeded on the tube surface or synthesized exclusively in the lumens, providing enhanced catalytic properties, especially at high temperatures. In vitro and in vivo studies on biological cells and worms indicate the safety of halloysite, and tests for efficient adsorption of mycotoxins in animals' stomachs are also carried out.
TL;DR: Two-dimensional (2D) transition-metal dichalcogenide (TMD) nanosheets have emerged as a fascinating new class of materials for catalysis, attractive for understanding the fundamental principles of electro- and photocatalysis, as well as for developing highly efficient, renewable, and affordable catalysts for large-scale production of hydrogen.
Abstract: Two-dimensional (2D) transition-metal dichalcogenide (TMD) nanosheets have emerged as a fascinating new class of materials for catalysis. These nanosheets are active for several important catalysis reactions including hydrogen evolution from water. The rich chemistry of TMDs combined with numerous strategies that allow tuning of their electronic properties make these materials very attractive for understanding the fundamental principles of electro- and photocatalysis, as well as for developing highly efficient, renewable, and affordable catalysts for large-scale production of hydrogen. Recent developments are highlighted and important challenges in using TMDs as catalysts are also discussed.
TL;DR: A white light-emitting diode (0.33, 0.33) is fabricated using perovskite quantum dot/silica composites and is shown to have greatly improved stability.
Abstract: A white light-emitting diode (0.33, 0.33) is fabricated using perovskite quantum dot/silica composites. It is shown to have greatly improved stability.
TL;DR: A carbonized plain-weave silk fabric is fabricated into wearable and robust strain sensors, which can be stretched up to 500% and show high sensitivity in a wide strain range.
Abstract: A carbonized plain-weave silk fabric is fabricated into wearable and robust strain sensors, which can be stretched up to 500% and show high sensitivity in a wide strain range. This sensor can be assembled into wearable devices for detection of both large and subtle human activities, showing great potential for monitoring human motions and personal health.
TL;DR: This approach yields N-CNS with a high nitrogen content and comparable oxygen reduction reaction catalytic activities to commercial Pt/C catalysts in alkaline media.
Abstract: Nitrogen-doped porous carbon nanosheets (N-CNS) are synthesized by hydrothermal carbon coating of g-C3 N4 nanosheets followed by high-temperature treatment in N2 . g-C3 N4 serves as a template, nitrogen source, and porogen in the synthesis. This approach yields N-CNS with a high nitrogen content and comparable oxygen reduction reaction catalytic activities to commercial Pt/C catalysts in alkaline media.