1,721,006 research outputs found
Industrial-scale H2O2 electrosynthesis in practical electrochemical cell systems
No full textHydrogen peroxide generated from the electrochemical reaction with oxygen is particularly interesting due to its growing demand. Although most research has focused on highly active and stable electrocatalysts for H2O2 generation, substantial challenges still impede the industry–relevant scale application of producing liquid H2O2 solution via electrochemical methods. This review emphasizes the difficulties of making highly concentrated H2O2 products without other electrolyte impurities regarding the catalyst–electrolyte interface and reactor engineering. Furthermore, we discuss the possibility of direct in-situ consumption of H2O2 to other thermo-/electrochemical oxidation reactions even at low concentrations, even with salt ions. This approach allows the electrochemical route to become more competitive in the future. © 2023 Elsevier B.V.11Nsciescopu
Recent progress in in situ/operando analysis tools for oxygen electrocatalysis
No full textFuel cell and water electrolyzer technology have been intensively investigated in the last decades toward sustainable and renewable energy conversion systems. For improved device performance and service life, nanostructured electrocatalysts on electrode have been extensively developed based on the principle of structure-activity-stability correlation. However, overall device efficiency is seriously hindered by sluggish oxygen electrocatalysis, including oxygen reduction reaction and oxygen evolution reaction. As a result, tremendous efforts have been made to construct the most active surfaces with robust durability. For knowledge-based approaches toward systematic development of highly functional nanostructures, fundamental principles within oxygen electrocatalysis should be uncovered including reaction intermediate, active site structures, and atomic dissolution from surface. However, conventional ex situ characterizations only provide a static picture of electrode surfaces without electrocatalysis. On the other hand, in situ/operando analyses allow us to directly monitor dynamics on electrode under operating conditions. In this review, we will introduce a set of in situ/operando analytical tools and summarize their contribution to fundamental researches on oxygen electrocatalysis. Taking both precious and non-precious electrocatalyst materials as examples, the most impending issues in oxygen electrocatalysis are covered with in situ/operando studies to highlight the power of in situ/operando techniques and encourage further efforts on advanced analytic techniques.11Nsciescopu
Synthesis of Heteroatom (B, N, and O)-Doped Carbons via Chlorination of a Carbonitride-Boride Mixture: Influence of Boron Addition on Structure and Electrochemical Properties of Carbon
No full textThe introduction of heteroatoms into carbon materials has been widely used to boost the surface reactivity of carbon materials, and doping of boron and/or nitrogen is one of the most powerful strategies to modify the characteristics of carbon materials. Unlike nitrogen doping that has been extensively investigated, the influence of boron doping on the synthesis of porous carbon materials has not been comprehensively understood. In this study, we successfully synthesize heteroatom (boron, nitrogen, and/or oxygen)-doped highly nanoporous carbon materials via the chlorination process of a carbonitride-boride mixture without additional treatment. Boron atoms are readily diffused from boride to adjacent carbonitride-derived carbon during the chlorination process and function as atomic welders, which are the key to construct a heteroatom-rich nanoporous carbon structure. Oxygen-rich nanoporous carbon and nitrogen-rich nanoporous carbon can be selectively synthesized by controlling the raw carbonitride precursor composition. They show superior catalytic performance in the 2e(-) and 4e(-) pathway oxygen reduction reaction, respectively.11Nsciescopu
Understanding the Roles of Sulfur Dopants in Carbonaceous Electrocatalysts for the Oxygen Reduction Reaction: The Relationship between Catalytic Activity and Work Function
No full textWe prepared a series of hollow sulfur-doped carbons with
diverse S contents through the carbonization of microporous
organic networks (MONs), which were synthesized through the
Sonogashira coupling of thiophene moieties with different
numbers of S atoms as building blocks. This preparation
method enabled the doping level to be controlled without
inducing any notable differences in textural and morphological
characteristics, and these S-doped carbons did not show any
notable differences in the chemical properties of carbon,
regardless of the sulfur content. We used these well-controlled
MON-derived carbons as a model to elucidate the role of sulfur
dopants in the oxygen reduction reaction (ORR) and to
investigate the relationship between the activities and work
functions of carbonaceous catalysts. By excluding the effect of
electrical properties of the S-doped carbon catalysts using
conducting agents, we could successfully verify that increasing
the number of dopants led to an enhancement in the ORR
activities, and the high applicability of work function as the
activity descriptor was also demonstrated. We believe that our
experimental observations will provide a deeper understanding
of carbonaceous electrocatalysts with p-block dopants, and the
investigations performed in this study are also anticipated to
serve as a rational guideline in designing carbonaceous catalysts
for various electrochemical reactions. 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei
Maximizing the Active Site Densities of Single-Atomic Fe-N-C Electrocatalysts for High-Performance Anion Membrane Fuel Cells
No full textIron- and nitrogen-doped carbon (Fe-N-C) catalysts have received significant attention owing to their high oxygen reduction reaction (ORR) activities, which are comparable to those of state-of-the-art Pt/C catalysts. This high ORR activity originates from the atomically dispersed Fe coordinated with the nitrogen atom (Fe-N-x) active site. Increasing the Fe-N-x active site density can enhance the ORR activity. In this study, we suggest a facile and effective method for maximizing the active site densities using a simple ZnCl2 activation method. ZnCl2 activation was applied to the metal organic framework-derived Fe-N-C catalyst that exhibits superior ORR activity compared to Pt/C and a recently reported nonprecious metal catalyst. Through various electrochemical analyses, we confirmed that this activity originates from the effectively increased active site density. The anion-exchange membrane fuel cell (AEMFC) performance was measured to confirm practical applicability, and we obtained a significantly high performance of 1076 mA cm(-2) at 0.6 V, which is significantly higher than the currently reported performance of carbon-based Fe-N-C AEMFC cathode catalysts. We demonstrate the potential of our strategy for applications in various carbon-based materials that can be used for the development of high-efficiency electrochemical energy devices.11Nsciescopu
Scaffold-like titanium nitride nanotubes with a highly conductive porous architecture as a nanoparticle catalyst support for oxygen reduction
No full textWe designed a scaffold-like porous titanium nitride (TiN) nanotube (NT) as a catalyst support for Pt to facilitate the oxygen reduction reaction. Bulk titanium nitride, which is known as an electrically conductive material, is compatible with other metals. As the size of TiN particles decreases, however, they lose their intrinsic high electrical conductivity, due to a series of nanoparticle grain boundaries acting as electron reservoirs and traps. A designed grain-boundary-free scaffold-like porous TiN NT which is analogous to the shape of the one-dimensional porous human spine exhibits high electrical conductivity in spite of having a surface area similar to that of TiN nanoparticle (NPs). The electrical conductivity of TiN NTs is ca. 30-fold higher than that of spherical TiN NPs. The electrochemical oxygen reduction measurements between porous TiN NT and TiN NPs after Pt loading clearly exhibit the superiority of TiN NT as a catalyst support. The results from various electrochemical measurements suggest that the electrocatalytic activity per site did not change from a kinetic viewpoint, but the utilization (the amount of triggered catalytic active sites) in the catalyst layer on the electrode decreased. The Pt/TiN NT composite catalyst exhibited higher activity in comparison to TiN NPs as well as conventional Pt/C catalysts. The accelerated durability test (ADT) revealed that this nanotubular supporting material dramatically enhanced the durability of the catalyst and maintained the electrochemically active surface area (ECSA) of Pt nanoparticles, thus exhibiting performance higher than that of the commercial Pt/C catalyst. X-ray spectroscopy results verified the strong metal-support interaction between Pt nanoparticles and the TiN NT support. This approach opens a reliable path for designing innovative transition-metal oxides, nitrides, or carbides as catalyst supports for use in a wide range of energy conversion applications. © 2016 American Chemical Society114151sciescopu
Functional link between surface low-coordination sites and the electrochemical durability of Pt nanoparticles
No full textA promising strategy for achieving enhanced catalytic activity involves the use of nanoscale electrocatalysts; however, their low stability remains a major challenge. Among the various performance-degradation mechanisms, atomic dissolution is known to cause severe nanoparticle deactivation. To date, the factors influencing these catalysts’ durability are not understood. Herein, we assess the role of low-coordination surface sites, focusing on the atomic dissolution of Pt nanoparticles. The density of low-coordination sites was finely controlled, and no significant size change occurred. Based on our findings, we suggest that the initial low-coordination sites trigger metal dissolution, which subsequently accelerates Pt dissolution. We believe that controlling the surface coordination number can open new routes for the design of highly durable nanoscale electrocatalysts. © 2016 Elsevier B.V.1111sciescopu
Three-Dimensional Unified Electrode Design Using a NiFeOOH Catalyst for Superior Performance and Durable Anion-Exchange Membrane Water Electrolyzers
No full textThe design of high-performance and durable electrodes for the oxygen evolution reaction (OER) is crucial for anionexchange membrane water electrolyzers (AEMWE). Herein, a threedimensional unified electrode in which nickel-iron oxyhydroxide (NiFeOOH) is directly electrodeposited on a gas diffusion layer (GDL) is developed as an AEMWE anode. Unlike conventional electrodes with a separate catalyst layer and GDL, the unified electrode comprises a single component integrating the catalyst layer with the GDL. The resulting unified electrode shows higher catalytic activity than a conventional electrode based on commercial NiFe and IrO2 and stable activity over 500 h. Investigation of the electrode parameters revealed an outstanding AEMWE performance of 3600 mA cm-2 at 1.9 V, which is the highest among many AEMWE studies. The unified AEMWE also showed durable performance at an ultrahigh current density. Therefore, unified electrode design can be considered an alternative to conventional electrodes to reduce the hydrogen production cost.11Nsciescopu
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