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Electrochemical energy conversion and storage are central to developing future renewable energy systems. For efficient energy utilization, both the performance and stability of electrochemical systems should be optimized in terms of the electrochemical interface. To achieve this goal, it is imperative to understand how a tailored electrode structure and electrolyte speciation can modify the electrochemical interface structure to improve its properties. However, most approaches describe the electrochemical interface in a static or frozen state. Although a simple static model has long been adopted to describe the electrochemical interface, atomic and molecular level pictures of the interface structure should be represented more dynamically to understand the key interactions. From this perspective, we highlight the importance of understanding the dynamics within an electrochemical interface in the process of designing highly functional and robust energy conversion and storage systems. For this purpose, we explore three unique classes of dynamic electrochemical interfaces: self-healing, active-site-hosted, and redox-mediated interfaces. These three cases of dynamic electrochemical interfaces focusing on active site regeneration collectively suggest that our understanding of electrochemical systems should not be limited to static models but instead expanded toward dynamic ones with close interactions between the electrode surface, dissolved active sites, soluble species, and reactants in the electrolyte. Only when we begin to comprehend the fundamentals of these dynamics through operando analyses can electrochemical conversion and storage systems be advanced to their full potential., JACS Au, 2 (10), ISSN:2691-3704

Sustainable energy-conversion and chemical-production require catalysts with high activity, durability, and product-selectivity. Metal/oxide hybrid structure has been intensively investigated to achieve promising catalytic performance, especially in neutral or alkaline electrocatalysis where water dissociation is promoted near the oxide surface for (de)protonation of intermediates. Although catalytic promise of the hybrid structure is demonstrated, it is still challenging to precisely modulate metal/oxide interfacial interactions on the nanoscale. Herein, we report an effective strategy to construct rich metal/oxide nano-interfaces on conductive carbon supports in a surfactant-free and self-terminated way. When compared to the physically mixed Pd/CeO

Perovskite oxides are an important class of oxygen evolution reaction (OER) catalysts in alkaline media, despite the elusive nature of their active sites. Here, we demonstrate that the origin of the OER activity in a La1-xSrxCoO3 model perovskite arises from a thin surface layer of Co hydr(oxy)oxide (CoOxHy) that interacts with trace-level Fe species present in the electrolyte, creating dynamically stable active sites. Generation of the hydr(oxy)oxide layer is a consequence of a surface evolution process driven by the A-site dissolution and O-vacancy creation. In turn, this imparts a 10-fold improvement in stability against Co dissolution and a 3-fold increase in the activity-stability factor for CoOxHy/LSCO when compared to nanoscale Co-hydr(oxy)oxides clusters. Our results suggest new design rules for active and stable perovskite oxide-based OER materials.

Electrocatalysis is a key process for renewable energy conversion and fuel production in future energy systems. Various nanostructures have been investigated to optimize the electrocatalytic activity and realize efficient energy use. However, the long-term stability of electrocatalysts is also crucial for the sustainable and reliable operation of energy devices. Nanocatalysts are degraded by various processes during electrocatalysis, which causes critical performance loss. Recent

Despite breakthroughs in the activity of electrocatalysts for the oxygen reduction reaction (ORR), the development of nanoscale ORR electrocatalysts is still hindered by their instability. Here, to...

The impact of topological defects associated with grain boundaries (GB defects) on the electrical, optical, magnetic, mechanical and chemical properties of nanocrystalline materials1,2 is well known. However, elucidating this influence experimentally is difficult because grains typically exhibit a large range of sizes, shapes and random relative orientations3-5. Here we demonstrate that precise control of the heteroepitaxy of colloidal polyhedral nanocrystals enables ordered grain growth and can thereby produce material samples with uniform GB defects. We illustrate our approach with a multigrain nanocrystal comprising a Co3O4 nanocube core that carries a Mn3O4 shell on each facet. The individual shells are symmetry-related interconnected grains6, and the large geometric misfit between adjacent tetragonal Mn3O4 grains results in tilt boundaries at the sharp edges of the Co3O4 nanocube core that join via disclinations. We identify four design principles that govern the production of these highly ordered multigrain nanostructures. First, the shape of the substrate nanocrystal must guide the crystallographic orientation of the overgrowth phase7. Second, the size of the substrate must be smaller than the characteristic distance between the dislocations. Third, the incompatible symmetry between the overgrowth phase and the substrate increases the geometric misfit strain between the grains. Fourth, for GB formation under near-equilibrium conditions, the surface energy of the shell needs to be balanced by the increasing elastic energy through ligand passivation8-10. With these principles, we can produce a range of multigrain nanocrystals containing distinct GB defects.

Noble metal‐based multimetallic nanoparticles (NMMNs) have attracted great attention for their multifunctional and synergistic effects, which offer numerous catalytic applications. Combined experimental and theoretical studies have enabled formulation of various design principles for tuning the electrocatalytic performance through controlling size, composition, morphology, and crystal structure of the nanoparticles. Despite significant advancements in the field, the chemical synthesis of NMMNs with ideal characteristics for catalysis, including high activity, stability, product‐selectivity, and scalability is still challenging. This review provides an overview on structure‐based classification and the general synthesis of NMMN electrocatalysts. Furthermore, postsynthetic treatments, such as the removal of surfactants to optimize the activity, and utilization of NMMNs onto suitable support for practical electrocatalytic applications are highlighted. In the end, future direction and challenges associated with the electrocatalysis of NMMNs are covered., Intriguing surface and structural properties makes noble metal‐based multimetallic nanoparticles (NMMNs) efficient catalysts for a wide‐range of electrocatalytic applications. This review provides an overview of the general preparation of electrocatalysts using NMMNs, including synthesis of NMMNs with precise control, and practical issues for applying the nanoparticles to electrocatalytic reactions.

The poor activity and stability of electrode materials for the oxygen evolution reaction are the main bottlenecks in the water-splitting reaction for H2 production. Here, by studying the activity–stability trends for the oxygen evolution reaction on conductive M1OxHy, Fe–M1OxHy and Fe–M1M2OxHy hydr(oxy)oxide clusters (M1 = Ni, Co, Fe; M2 = Mn, Co, Cu), we show that balancing the rates of Fe dissolution and redeposition over a MOxHy host establishes dynamically stable Fe active sites. Together with tuning the Fe content of the electrolyte, the strong interaction of Fe with the MOxHy host is the key to controlling the average number of Fe active sites present at the solid/liquid interface. We suggest that the Fe–M adsorption energy can therefore serve as a reaction descriptor that unifies oxygen evolution reaction catalysis on 3d transition-metal hydr(oxy)oxides in alkaline media. Thus, the introduction of dynamically stable active sites extends the design rules for creating active and stable interfaces. Understanding what underpins the activity and stability of oxygen evolution catalysts is an ongoing issue in the field of water splitting. Now, researchers show that balancing the rate of Fe dissolution and deposition over a metal hydr(oxy)oxide host yields dynamically stable Fe active sites, with the Fe–host interaction key to the performance.

Among the various renewable sources of energy, solar energy conversion systems have been regarded as a promising way to satisfy the growing energy demand. For superior solar energy conversion performance, it is important to utilize efficient photosensitizers that have excellent light-harvesting capability. In this regard, quantum dots (QDs) are promising photosensitizer candidates owing to their high absorption coefficient, band gap tunability, and potential multiple exciton generation. Here, we report an effective and straightforward approach to improve the loadings of nanocomposite PbS/CdS QDs in a mesoporous electrode, for highly efficient solar energy conversion. By controlling the surface charge of TiO2 during the successive ionic layer adsorption and reaction process, both the PbS and CdS QD loadings are distinctly increased, leading to a highly enhanced light-harvesting capability of the photoelectrodes. This enhancement is effectively applied not only for solar-to-electrical but also for solar-to-chemical energy conversion, resulting in a ∼33% increased conversion efficiency of the QD solar cells and an unprecedented photocurrent of 22.1 mA/cm2 (at 0.6 V vs. RHE) for hydrogen production from photoelectrochemical water splitting. These results provide significant insight into the application of QD photosensitizers in solar energy conversion.

Metal–organic framework (MOF)-derived carbon materials have been widely used as catalysts for a variety of electrochemical energy applications, and thermally carbonized zinc-2-methylimidazole (ZIF-8) has shown particularly high performance owing to its microporous structure with a large surface area. However, in the presence of bulky chemical species, such as triiodide, in mesoscopic dye-sensitized solar cells (DSCs), the small pore size of carbonized ZIF-8 causes a significant limitation in mass transfer and consequentially results in a poor performance. To resolve this problem, we herein report a simple strategy to enlarge the pore sizes of ZIF-8-derived carbon by increasing the dwelling time of Zn in ZIF-8 during the thermal carbonization process. A thin and uniform polydopamine shell introduced on the surface of ZIF-8, with the aim of retarding the escape of vaporized Zn species, leads to a dramatic increase in pore sizes, from the micropore to mesopore range. The porosity-tailored carbonized ZIF-8 manifests an excellent electrocatalytic performance in triiodide reduction, and when it was applied as the counter electrode of DSCs, an energy conversion efficiency of up to 9.03% is achievable, which is not only superior to that of the Pt-based counterpart but also among the highest performances of DSCs employing carbonaceous electrocatalysts.

The electro-oxidation of CO adsorbed on Pt nanoparticles is an important reaction in fuel cells. Despite extensive research, the underlying concept for peak multiplicity is not yet clearly understood. We investigated CO electro-oxidation features by scan-rate-dependent Tafel analysis and a model system experiment based on adsorption of 3-mercaptopropionic acid (3-MPA). The results suggest that the first main oxidation peak corresponds to the competition between OH adsorption and the interaction between adsorbed CO and OH. Modifying the Pt surface with 3-MPA can reduce the OH coverage, which in turn reduces the width of the first peak. However, the peak potential is not significantly dependent on OH coverage. Considering that the free surface is large enough for OH adsorption on Pt at high potential, the second peak shows few features that depend on OH coverage; the second peak is mainly influenced by the Pt-CO interaction.

Development of Pt-free electrocatalysts for oxygen reduction reaction (ORR) is one of the most important tasks for fuel cell commercialization. Various Mn compounds have been proposed as catalysts for ORR, but poor activity and stability necessitate further advances for their practical utilization. In this study, we demonstrate a lithium manganese phosphate-carbon composite (LMP-C) as a highly active and durable electrocatalyst for ORR in alkaline medium. LMP-C, synthesized by the solid-state method, exhibited significantly enhanced electrical conductivity and electrochemical properties, which led to a substantial increase in ORR performance. Comparison between LMP-C and the manganese phosphate-carbon composite, based on various physicochemical characterizations, revealed a high preference for the formation of the Mn3+ state on the surface of LMP-C that resulted in effective charge transfer during oxygen reduction. Moreover, the excellent stability of LMP-C was confirmed by carrying out 3000 cycles of the accelerated durability test, in which no drop in ORR performance was observed.

The durability issues of Pt catalyst should be resolved for the commercialization of proton exchange membrane fuel cells. Nanocrystal structures with high-index facets have been recently explored to solve the critical durability problem of fuel cell catalysts as Pt catalysts with high-index facets can preserve the ordered surfaces without change of the original structures. However, it is very difficult to develop effective and practical synthetic methods for Pt-based nanostructures with high-index facets. The current study describes a simple one-pot synthesis of self-assembled dendritic Pt nanostructures with electrochemically active and stable high-index facets. Pt nanodendrites exhibited 2 times higher ORR activity and superior durability (only 3.0 % activity loss after 10 000 potential cycles) than a commercial Pt/C. The enhanced catalytic performance was elucidated by the formation of well-organized dendritic structures with plenty of reactive interfaces among 5 nm-sized Pt particles and the coexistence of low- and high-index facets on the particles.

A highly active and stable non-Pt electrocatalyst for hydrogen production has been pursued for a long time as an inexpensive alternative to Pt-based catalysts. Herein, we report a simple and effective approach to prepare high-performance iron phosphide (FeP) nanoparticle electrocatalysts using iron oxide nanoparticles as a precursor. A single-step heating procedure of polydopamine-coated iron oxide nanoparticles leads to both carbonization of polydopamine coating to the carbon shell and phosphidation of iron oxide to FeP, simultaneously. Carbon-shell-coated FeP nanoparticles show a low overpotential of 71 mV at 10 mA cm–2, which is comparable to that of a commercial Pt catalyst, and remarkable long-term durability under acidic conditions for up to 10 000 cycles with negligible activity loss. The effect of carbon shell protection was investigated both theoretically and experimentally. A density functional theory reveals that deterioration of catalytic activity of FeP is caused by surface oxidation. Extende...

The Fe–N–C-based carbon materials, which are generally formed by high-temperature annealing, have been highlighted as a promising alternative to expensive Pt electrocatalysts for oxygen reduction reaction. However, the delicate formation of active sites remains an issue because of decomposition and transformation of the macrocycle during heat treatment. Accordingly, we developed a low-temperature and gram-scale approach to synthesizing iron phthalocyanine (Pc)-embedded two-dimensional carbon sheets by annealing at 450 °C. The low-temperature annealing process, which is motivated by the synthesis of carbon nanoribbons, is suitable for maintaining the Fe–N–C structure while enhancing coupling with carbon. Our two-dimensional carbon sheets show higher ORR activity than commercial Pt catalyst in alkaline media. Furthermore, the feasibility of real application to alkaline membrane electrolyte fuel cell is verified by superior volumetric current density. In durability point of view, the initial activity is reta...

Photoelectrochemical (PEC) cells are promising tools for renewable and sustainable solar energy conversion. Currently, their inadequate performance and high cost of the noble metals used in the electrocatalytic counter electrode have postponed the practical use of PEC cells. In this study, we report the electrochemical synthesis of nanoporous tungsten carbide and its application as a reduction catalyst in PEC cells, namely, dye-sensitized solar cells (DSCs) and PEC water splitting cells, for the first time. The method employed in this study involves the anodization of tungsten foil followed by post heat treatment in a CO atmosphere to produce highly crystalline tungsten carbide film with an interconnected nanostructure. This exhibited high catalytic activity for the reduction of cobalt bipyridine species, which represent state-of-the-art redox couples for DSCs. The performance of tungsten carbide even surpassed that of Pt, and a substantial increase (∼25%) in energy conversion efficiency was achieved when Pt was substituted by tungsten carbide film as the counter electrode. In addition, tungsten carbide displayed decent activity as a catalyst for the hydrogen evolution reaction, suggesting the high feasibility for its utilization as a cathode material for PEC water splitting cells, which was also verified in a two-electrode water photoelectrolyzer.

The effect of porous structures on the electrocatalytic activity of N-doped carbon is studied by using electrochemical analysis techniques and the result is applied to synthesize highly active and stable Fe-N-C catalyst for oxygen reduction reaction (ORR). We developed synthetic procedures to prepare three types of N-doped carbon model catalysts that are designed for systematic comparison of the porous structures. The difference in their catalytic activity is investigated in relation to the surface area and the electrochemical parameters. We found that macro- and mesoporous structures contribute to different stages of the reaction kinetics. The catalytic activity is further enhanced by loading the optimized amount of Fe to prepare Fe-N-C catalyst. In both N-doped carbon and Fe-N-C catalysts, the hierarchical porous structure improved electrocatalytic performance in acidic and alkaline media. The optimized catalyst exhibits one of the best ORR performance in alkaline medium with excellent long-term stability in anion exchange membrane fuel cell and accelerated durability test. Our study establishes a basis for rationale design of the porous carbon structure for electrocatalytic applications.

A 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.

This study was focused on elucidating the origin of the catalytic activity displayed by non-precious-metal-based oxygen reduction reaction (ORR) catalysts before and after heat treatment. Electrochemical measurements were recorded using a series of metal phthalocyanines calculated to exhibit varying oxygen adsorption energies before and after heat treatment at a temperature sufficiently high to facilitate degradation. Collectively, the results indicate that while the oxygen adsorption is germane to the catalytic activity before heat treatment, the ORR appears to proceed through a different pathway that is not dependent on adsorption energy after heat treatment. These conclusions help to explain the high catalytic activities exhibited by carbon- or nitrogen-based materials containing metal ions after heat treatment and may lead to the realization of substitutes for ORR catalysts that utilize precious transition metals.

Hollow particles of N,B co-doped carbon were synthesized at different temperatures and used as electrocatalysts for the oxygen reduction reaction (ORR). The particles were synthesized by chlorinating Ti(C 0.3 N 0.7 ) and TiB 2 powders, with the sample formed at 800 °C showing the highest ORR activity, which was comparable to a commercial Pt/C catalyst. The catalyst electron transfer number of 3.94 was close to 4, indicating high selectivity for the ORR. The excellent ORR performance arose from the particle structure that facilitated mass transport, including the hollow shape with well-developed micro and macro pores, and various active nitrogen functional groups on the surface. Boron also played an important role along with the nitrogen, improving the activity for the ORR through a synergistic effect. These properties make these materials promising for the ORR and other electrochemical applications.

We 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...

Methanol is a promising fuel for direct methanol fuel cells in portable devices. A deeper understanding of its electro-oxidation is needed for evaluating electrocatalytic performance and catalyst design. Here we provide an in-depth investigation of the cyclic voltammetry (CV) of methanol electro-oxidation. The oxidation peak in backward scan is shown to be unrelated to residual intermediate oxidation. The origin of the second oxidation peak (If2) is expected to the methanol oxidation on Pt–Ox. Electrochemical impedance spectroscopy coupled with CV reveals the origin of CV hysteresis to be a shift in the rate-determining step, from methanol dehydration to OH adsorption by water dissociation, induced by a change in Pt surface coverage with oxygenated species. The peak ratio between forward oxidation peak current (If) and backward oxidation peak current (Ib), which is If/Ib, is not related to the degree of CO tolerance but to the degree of oxophilicity indeed.

CO poisoning of Pt catalysts is one of the most critical problems that deteriorate the electrocatalytic oxidation and reduction reactions taking place in fuel cells. In general, enhancing CO oxidation properties of catalysts by tailoring the electronic structure of Pt (electronic effect) or increasing the amount of supplied oxygen species (bifunctional effect), which is the typical reactant for CO oxidation, has been performed to remove CO from the Pt surface. However, though there have been a few reports about the understanding of the electronic effect for rapid CO oxidation, a separate understanding of bifunctional modification is yet to be achieved. Herein, we report experimental investigations of CO oxidation in the absence of electronic effect and an extended concept of the bifunctional effect. A model system was prepared by blending conventional Pt/C catalysts with hydrous ruthenium oxide particles, and the CO oxidation behaviors were investigated by various electrochemical measurements, including C...

Composition-controlled and carbon-supported PdFe nanoparticles (NPs) were prepared via a modified chemical synthesis after heat-treatment at high temperature under a reductive atmosphere. This novel synthesis, which combines the polyol reduction method and hydride method, was used to obtain monodispersed PdFe NPs. In addition, to induce structural modifications, the as-prepared PdFe NPs received heat-treatment under a reductive atmosphere. Structural characterization, including high-resolution powder diffraction (HRPD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) analysis, indicated that heat-treated PdFe NPs exhibited a higher degree of alloying and surface Pd atomic composition compared with as-prepared ones. Furthermore, new crystalline phases were detected after heat-treatment. Thanks to the structural alterations, heat-treated PdFe NPs showed ∼3 and ∼18 times higher mass- and area-normalized oxygen reduction reaction (ORR) activities, respectively than commercial Pt/C. Single cell testing with heat-treated PdFe catalysts exhibited a ∼2.5 times higher mass-normalized maximum power density than the reference cell. Surface structure analyses, including cyclic voltammetry (CV), COad oxidation, and XPS, revealed that, after heat-treatment, a downshift of the Pd d-band center occurred, which led to a decrease in the affinity of Pd for oxygen species, resulting in more favorable ORR kinetics.

Platinum group metal (PGM)-free catalysts are promising candidates to supplant costly precious metal catalysts in hydrogen fuel cells and enable low-cost, commercially viable devices [1]. Recent developments in PGM-free catalysts have enabled performance comparable to Pt catalysts by some metrics [2], but durability remains a significant challenge and limits practical application of these devices [3]. To improve the durability of PGM-free catalysts, understanding and controlling atomic-scale active site structure and the corresponding degradation mechanisms is imperative [1]. Active sites in these catalysts are commonly thought to be FeN4 complexes within a graphene lattice. Many potential active site structures have been predicted by computational methods, however, and a technique capable of directly validating these models is needed to reveal the true nature of these sites and enable increased control over degradation [1]. Scanning transmission electron microscopy (STEM) is capable of resolving a wide range of materials properties down to the atomic scale, such as structure, composition, and bonding information. The characteristics of PGM-free materials makes obtaining atomic-scale information about active site structure by STEM challenging, however. These materials are often defect-rich, containing a large number of dopants, holes, etc., and a large portion of proposed active sites exist at edges of the material, all of which increase susceptibility to beam damage. Conventional high-angle annular dark-field (HAADF) STEM imaging exacerbates this problem since only a small proportion of the incident beam electrons generate signal, and this signal is most sensitive to heavy elements. A large electron dose is therefore required to obtain a sufficient signal from light elements such as carbon and nitrogen, which can result in beam-induced atomic displacements at susceptible sites when using standard accelerating voltages. As a consequence, direct structural analysis of active sites is often not possible, impeding our understanding of degradation pathways. In this talk, we will demonstrate advancements in STEM techniques that significantly enhance our ability to directly analyze atomic-scale active site structure in PGM-free materials. We utilize a recently developed dose-efficient imaging technique based on four-dimensional (4D)-STEM [4,5] to reduce the required electron dose and simultaneously increase sensitivity to light elements. To minimize beam damage at sensitive active sites, we perform this dose-efficient 4D-STEM technique in a low-voltage aberration-corrected instrument operated at 30 kV, producing an atomic-scale probe below the threshold energy for beam-induced atomic displacements at many sites. We perform these experiments on a model PGM-free catalyst that contains many monolayer regions, which is ideal for low-voltage 4D-STEM and enables experimental validation through simulations of proposed active site structures. This work demonstrates how low-voltage 4D-STEM will provide new atomic-scale insights into the structure and degradation pathways of PGM-free catalyst active sites, accelerating the development of low-cost hydrogen fuel cells. References: [1] U. Martinez et al., Adv. Mater., 31, 1806545 (2019). [2] H. T. Chung et al., Science, 357, 479 (2017). [3] Y. Shao et al., Adv. Mater., 31, 1807615 (2019). [4] K. Müller et al., Nat. Commun., 5, 5653, (2014). [5] Y. Jiang et al., Nature, 559, 343 (2018). [6] This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the Electrocatalysis Consortium (ElectroCat). Electron microscopy was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

In spite of large improvements in RDE, shaped nanoparticles do not exhibit substantial improvement in electrochemical devices, which requiresadditional steps in research aimed to development of more active nanoscale materials. The effect of nanoparticle size, surface mophology, composition and near-surface composition, shape, architecture, nature and porosity of the support will be thoroughly addressed. The main emphasis will be placed on the atomic precision approach that offers a new direction in the catalyst development. While hollow structures greatly diminish buried non-functional precious metal atoms, their uncommon geometry provides a pathway for tailoring physical and chemical properties. These structures can address some of the major design criteria for advanced nanoscale electrocatalysts, namely, high surface-to-volume ratio, 3D surface molecular accessibility, and optimal precious metal utilization, including durability and selectivity.

The impact of topological defects associated with grain boundaries (GB defects) on the electrical, optical, magnetic, mechanical and chemical properties of nanocrystalline materials

Transition metal dichalcogenides, especially MoS

Demand on the practical synthetic approach to the high performance electrocatalyst is rapidly increasing for fuel cell commercialization. Here we present a synthesis of highly durable and active intermetallic ordered face-centered tetragonal (fct)-PtFe nanoparticles (NPs) coated with a "dual purpose" N-doped carbon shell. Ordered fct-PtFe NPs with the size of only a few nanometers are obtained by thermal annealing of polydopamine-coated PtFe NPs, and the N-doped carbon shell that is in situ formed from dopamine coating could effectively prevent the coalescence of NPs. This carbon shell also protects the NPs from detachment and agglomeration as well as dissolution throughout the harsh fuel cell operating conditions. By controlling the thickness of the shell below 1 nm, we achieved excellent protection of the NPs as well as high catalytic activity, as the thin carbon shell is highly permeable for the reactant molecules. Our ordered fct-PtFe/C nanocatalyst coated with an N-doped carbon shell shows 11.4 times-higher mass activity and 10.5 times-higher specific activity than commercial Pt/C catalyst. Moreover, we accomplished the long-term stability in membrane electrode assembly (MEA) for 100 h without significant activity loss. From in situ XANES, EDS, and first-principles calculations, we confirmed that an ordered fct-PtFe structure is critical for the long-term stability of our nanocatalyst. This strategy utilizing an N-doped carbon shell for obtaining a small ordered-fct PtFe nanocatalyst as well as protecting the catalyst during fuel cell cycling is expected to open a new simple and effective route for the commercialization of fuel cells.

This experiment was carried out to figure out the growth and yield of waxy corn after cultivating the hairy vetch which was mostly used as a green manure crop. The waxy corn showed the growth and yield efficiency relative to conventional culture after the hairy vetch was returned to as the green manure and the amount of nitrogen fertilizer increased, and the LAI was similar to the conventional culture when less than 18 kg. Length of ear slightly decreased compared to 188 mm of conventional culture when the hairy vetch was used as the green manure and the amount of nitrogen fertilizer was less than 9 kg, but the length of ear increased relative to the conventional culture when the amount of applied nitrogen fertilizer was more than 18 kg. The highest 100-kernel weight was 35.4 g with the hairy vetch and 27 kg of nitrogen fertilizer treatment. The lowest 100-kernel weight was 27.4 g with the hairy vetch and 0 kg of nitrogen fertilizer treatment. Quantity with the hairy vetch and 9 kg of the nitrogen fertilizer treatment was similar the conventional culture. Suger content with the hairy vetch and more than 18 kg of the nitrogen fertilizer treatment was higher than the conventional culture. Thickness of pericarp showed no difference among treatments.

This work studied a coagulation–flocculation system using ferric hydroxide and poly acrylamide flocculant to find the effective condition to remove the radionuclides of Co, Mn, Sb, Ru, and Sr remaining in solution after Cs removal by adsorption for the treatment of radioactive waste seawater generated in a disastrous nuclear power plant accident like Fukushima Daiichi. The coagulation–flocculation mechanism was studied, and the performance characteristics of the coagulation–flocculation system was evaluated in views of decontamination yield of the elements, residual turbidity of treated solution, settling speed of flocs, and generated total floc volume, etc. The total removal yield of target radio nuclides of Co, Mn, Sb, and Ru was more than 99% in seawater at pH 8.

Methanol crossover critically restricts the practical application of direct methanol fuel cells (DMFCs). To resolve this crucial difficulty from the standpoint of electrocatalysis, an electrode material having high activity for the oxygen reduction reaction and low activity for the methanol oxidation reaction compared to widely used Pt-based electrodes is needed for DMFC cathodes. In this research carbon-supported Pd-rich Pd–Pt bimetallic nanoparticle electrocatalysts with 60 wt.% metal content were prepared for this purpose by sodium borohydride reduction of metal chlorides. The physical features of the prepared nanoparticles were investigated by transmission electron microscopy, energy dispersive X-ray spectroscopy, atomic absorption spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption near edge spectroscopy. Methanol tolerance was tested by means of rotating disk electrode (RDE) voltammetry using oxygen-saturated methanol-containing electrolyte solutions as the anode fuel for DMFC unit cell performance tests. In the RDE measurements, Pd-rich electrocatalysts (carbon-supported Pd19Pt1 nanoparticles) showed excellent methanol tolerance compared with Pd-free Pt electrocatalyst. When Pd19Pt1 nanoparticles were used as a DMFC cathode catalyst, unit cell performance tests showed that the i-V curves of the Pd19Pt1 electrocatalyst decreased slightly with increasing methanol concentration, while that of the Pt electrocatalyst decreased rapidly. The results in a liquid-feed DMFC unit cell test were in good agreement with the methanol tolerant characteristics identified in the RDE measurements.

Ion transport is an important issue in electrochemical-based energy conversion and storage devices. Ion transport at the interface of the electrode and electrolyte is critical for performance. However, there is little understanding of the interface phenomena based on ion transport properties. Here, the proton transport behavior in a Nafion membrane (electrolyte) and that of an ionomer in the catalyst layer (electrode/electrolyte interface) was investigated simultaneously by electrochemical impedance spectroscopy. Our study indicates that the proton transport behavior in the catalyst layer is different from that in membrane. To elucidate the interface phenomena, we analyzed the Nafion electrolyte and proton behavior by molecular dynamics (MD). On the basis of the MD results, we modified the catalyst with a hybrid of inorganic Pt catalyst and organic 3-mercaptopropionic acid to promote a positive interfacial reaction between the electrolyte and electrode, which resulted in improved proton transport and perf...

Structure effects of NiS and Ni3S2 nanoparticles were investigated for their electrocatalytic activity in the hydrogen evolution reaction in both acid and alkaline media. Owing to the different atomic configurations and crystalline structures, there is a hydrogen adsorption energy difference, which induces a difference in the activity. From density functional theory calculations and experimental observations, the importance of designing an electrocatalyst with an appropriate atomic configuration is evident.

We report on the facile synthesis of porous silicon structure via magnesiothermic reduction followed by coating of the surface with TiSi2. These modifications not only showed significant promise in overcoming the drastic volume change during charge and discharge cycles but also in improving the relatively low conductivity of silicon. The synthesized porous structure with a highly electrically conductive coating layer significantly enhanced the electrochemical performance in terms of cyclic stability and rate capability. The TiSi2 coating layer, which has good electrical conductivity and physical strength, enhances the conductivity and maintains the Si structure during cycling. This combination of porous structure via magnesiothermic reduction and highly conductive TiSi2 coating provides a synergistic effect, which can be seen in the improvements in electrochemical performance. This synthesis demonstrates a promising method for producing high capacity anode materials for next generation LIBs.

The residual surfactant organic molecules on electrocatalysts are expected to enhance the tolerance to specific anion adsorption, whereas the surfactants have been generally regarded as contaminants that block active surfaces. In this study, the Pt nanoparticles with adsorbed surfactants were prepared, and their electrochemical characteristics at various phosphoric acid concentrations were studied by the half-cell test. The third-body effect was experimentally confirmed by the single-cell test with a phosphoric acid-doped polybenzimidazole membrane.

Schwannomas are tumors that arise from Schwann cells. Although schwannomas can occur almost anywhere in the body where nerve cells are present, they rarely occur in the head and neck region, including the oral and maxillofacial region. Cystic changes in schwannomas are extremely rare. This report is on a case of schwannoma with cystic changes that occurred in the pterygomandibular space.A 46-year-old woman presented with a complaint of limited mouth opening and pain on the left side of the mandible for 3 months. On panoramic radiography, radiolucency was seen on the left mandibular ramus. On enhanced computed tomography, a 4 × 3 cm cystic mass was found along the inner side of the left mandibular ramus area. Magnetic resonance imaging showed a multiseptated, well-demarcated cystic lesion on the inner side of the mandibular ramus on the left side. Under general anesthesia, the tumor was excised. The final diagnosis was schwannoma with cystic changes. Lower lip hypoesthesia occurred postoperatively. At the 1-year postoperative follow-up, maximum mouth opening was increased to 44 mm, and lip hypoesthesia was improved.

Nitrogen-doped porous carbon materials have been highlighted as promising alternatives to high-cost platinum in various electrochemical energy applications. However, protocols to generate effective pore structure are still challenging, which hampers mass production and utilization of carbon materials. Here, we suggest a facile and effective method for hierarchical porous carbon by a single-step carbonization of coffee waste (CW) with ZnCl2. The CW, which is one of the most earth-abundant organic waste, can be successfully converted to nitrogen-doped porous carbon. It shows outstanding oxygen reduction activity and durability comparable to the state-of-the-art platinum, and the half-wave potential is also comparable to the best metal-free electrocatalysts in alkaline media. Finally, we apply it to counter electrode of dye-sensitized solar cell, whose photovoltaic efficiency surpasses the one made with conventional platinum electrode. We demonstrate the feasibility of our strategies for highly efficient, ch...

Demands for sustainable production of hydrogen are rapidly increasing because of environmental considerations for fossil fuel consumption and development of fuel cell technologies. Thus, the development of high‐performance and economical catalysts has been extensively investigated. In this study, a nanoporous Mo carbide electrode is prepared using a top‐down electrochemical process and it is applied as an electrocatalyst for the hydrogen evolution reaction (HER). Anodic oxidation of Mo foil followed by heat treatment in a carbon monoxide (CO) atmosphere forms a nanostructured Mo carbide with excellent interconnections, and these structural characteristics lead to high activity and durability when applied to the HER. Additionally, characteristic behavior of Mo is observed; metallic Mo nanosheets form during electrochemical anodization by exfoliation along the (110) planes. These nanosheets are viable for chemical modification, indicating their feasibility in various applications. Moreover, the role of carbon shells is investigated on the surface of the electrocatalysts, whereby it is suggested that carbon shells serve as a mechanical barrier against the oxidative degradation of catalysts that accompanies unavoidable volume expansion.

Fuel cells are one of the promising energy-conversion devices due to their high efficiency and zero emission. Although recent advances in electrocatalysts have been achieved using various material designs such as alloys, core@shell structures, and shape control, many issues still remain to be resolved. Especially, material design issues for high durability and high activity are recently accentuated owing to severe instability of nanoparticles under fuel-cell operating conditions. To address these issues, fundamental understanding of functional links between activity and durability is timely urgent. Here, the activity and durability of nanoscale materials are summarized, focusing on the nanoparticle size effect. In addition to phenomenological observation, two major degradation origins, including atomic dissolution and particle size increase, are discussed related to the activity decrease. Based on the fundamental understanding of nanoparticle degradation, recent promising strategies for durable Pt-based nanoscale electrocatalysts are introduced and the role of each design for durability enhancement is discussed. Finally, short comments related to the future direction of nanoparticle issues are provided in terms of nanoparticle synthesis and analysis.