Recent Development of Flexible and Stretchable Supercapacitors Using Transition Metal Compounds as Electrode Materials

Flexible and stretchable supercapacitors (FS-SCs) are promising energy storage devices for wearable electronics due to their versatile flexibility/stretchability, long cycle life, high power density, and safety. Transition metal compounds (TMCs) can deliver a high capacitance and energy density when applied as pseudocapacitive or battery-like electrode materials owing to their large theoretical capacitance and faradaic charge-storage mechanism. The recent development of TMCs (metal oxides/hydroxides, phosphides, sulfides, nitrides, and selenides) as electrode materials for FS-SCs are discussed here. First, fundamental energy-storage mechanisms of distinct TMCs, various flexible and stretchable substrates, and electrolytes for FS-SCs are presented. Then, the electrochemical performance and features of TMC-based electrodes for FS-SCs are categorically analyzed. The gravimetric, areal, and volumetric energy density of SC using TMC electrodes are summarized in Ragone plots. More importantly, several recent design strategies for achieving high-performance TMC-based electrodes are highlighted, including material composition, current collector design, nanostructure design, doping/intercalation, defect engineering, phase control, valence tuning, and surface coating. Integrated systems that combine wearable electronics with FS-SCs are introduced. Finally, a summary and outlook on TMCs as electrodes for FS-SCs are provided.

Zeolitic Imidazole Framework Sacrificial Template-Assisted Synthesis of NiCoP Nanocages Doped with Multiple Metals for High-Performance Hybrid Supercapacitors

Metal phosphides have great potential for electrochemical energy-storage devices and electrocatalysis. Although monometallic and bimetallic phosphides have been extensively studied, the preparation of more complex metal phosphides remains challenging and it is necessary to further expand the available design space. Herein, we report a universal method to dope various metal cations into NiCoP nanocages (M-NiCoP, M = Al, Cu, Cr, Zn). Interestingly, the method can also be expanded to allow the incorporation of two to four metal dopants simultaneously (AlCu-NiCoP, AlZn-NiCoP, CrZn-NiCoP, AlCrCu-NiCoP, AlCrCuZn-NiCoP). To investigate the effect of incorporating multiple dopants, AlCu-NiCoP was used as the electrode material for supercapacitors, showing enhanced capacity and cycling stability compared to Al-NiCoP, Cu-NiCoP, and NiCoP electrodes. The superior electrochemical performance is attributed to the increased number of active sites, improved ion-diffusion kinetics, and a modulated electronic structure. An aqueous hybrid supercapacitor with AlCu-NiCoP as the positive electrode and activated carbon as the negative electrode was assembled and demonstrated a high energy density of 62.8 Wh kg(-1) at a power density of 750 W kg(-1) with good cycling stability.

Atomic-level tuning of Co-N-C catalyst for high-performance electrochemical H2O2 production

Despite the growing demand for hydrogen peroxide it is almost exclusively manufactured by the energy-intensive anthraquinone process. Alternatively, H2O2 can be produced electrochemically via the two-electron oxygen reduction reaction, although the performance of the state-of-the-art electrocatalysts is insufficient to meet the demands for industrialization. Interestingly, guided by first-principles calculations, we found that the catalytic properties of the Co-N-4 moiety can be tailored by fine-tuning its surrounding atomic configuration to resemble the structure-dependent catalytic properties of metalloenzymes. Using this principle, we designed and synthesized a single-atom electrocatalyst that comprises an optimized Co-N-4 moiety incorporated in nitrogen-doped graphene for H2O2 production and exhibits a kinetic current density of 2.8 mA cm(-2) (at 0.65 V versus the reversible hydrogen electrode) and a mass activity of 155 A g(-1) (at 0.65 V versus the reversible hydrogen electrode) with negligible activity loss over 110 hours. Producing H2O2 electrochemically currently use electrocatalysts that are insufficient to meet the demands for industrialization. A single-atom electrocatalyst with an optimized Co-N4 moiety incorporated in nitrogen-doped graphene is shown to exhibit enhanced performance for H2O2 production.

Ni single atoms on carbon nitride for visible-light-promoted full heterogeneous dual catalysis

Visible-light-driven organic transformations are of great interest in synthesizing valuable fine chemicals under mild conditions. The merger of heterogeneous photocatalysts and transition metal catalysts has recently drawn much attention due to its versatility for organic transformations. However, these semi-heterogenous systems suffered several drawbacks, such as transition metal agglomeration on the heterogeneous surface, hindering further applications. Here, we introduce heterogeneous single Ni atoms supported on carbon nitride (NiSAC/CN) for visible-light-driven C-N functionalization with a broad substrate scope. Compared to a semi-heterogeneous system, high activity and stability were observed due to metal-support interactions. Furthermore, through systematic experimental mechanistic studies, we demonstrate that the stabilized single Ni atoms on CN effectively change their redox states, leading to a complete photoredox cycle for C-N coupling.Y

Direct Synthesis of Intermetallic PlatinumAlloy Nanoparticles Highly Loaded on Carbon Supports for Efficient Electrocatalysis

© 2020 American Chemical Society. Compared to nanostructured platinum (Pt) catalysts, ordered Pt-based intermetallic nanoparticles supported on a carbon substrate exhibit much enhanced catalytic performance, especially in fuel cell electrocatalysis. However, direct synthesis of homogeneous intermetallic alloy nanocatalysts on carbonaceous supports with high loading is still challenging. Herein, we report a novel synthetic strategy to directly produce highly dispersed MPt alloy nanoparticles (M = Fe, Co, or Ni) on various carbon supports with high catalyst loading. Importantly, a unique bimetallic compound, composed of [M(bpy)(3)](2+) (bpy = 2,2'-bipyridine) and [PtCl6](2-) anion, evenly decomposes graphene oxide on carbon surface and forms uniformly sized intermetallic nanoparticles with a nitrogen-doped carbon protection layer. The excellent oxygen reduction reaction (ORR) activity and stability of the representative reduced graphene oxide (rGO)-supported L1(0)-FePt catalyst (37 wt %-FePt/rGO), exhibiting 18.8 times higher specific activity than commercial Pt/C catalyst without degradation over 20 000 cycles, well demonstrate the effectiveness of our synthetic approach toward uniformly alloyed nanoparticles with high homogeneity11sci

Direct Synthesis of Intermetallic Platinum-Alloy Nanoparticles Highly Loaded on Carbon Supports for Efficient Electrocatalysis

© 2020 American Chemical Society. Compared to nanostructured platinum (Pt) catalysts, ordered Pt-based intermetallic nanoparticles supported on a carbon substrate exhibit much enhanced catalytic performance, especially in fuel cell electrocatalysis. However, direct synthesis of homogeneous intermetallic alloy nanocatalysts on carbonaceous supports with high loading is still challenging. Herein, we report a novel synthetic strategy to directly produce highly dispersed MPt alloy nanoparticles (M = Fe, Co, or Ni) on various carbon supports with high catalyst loading. Importantly, a unique bimetallic compound, composed of [M(bpy)(3)](2+) (bpy = 2,2'-bipyridine) and [PtCl6](2-) anion, evenly decomposes graphene oxide on carbon surface and forms uniformly sized intermetallic nanoparticles with a nitrogen-doped carbon protection layer. The excellent oxygen reduction reaction (ORR) activity and stability of the representative reduced graphene oxide (rGO)-supported L1(0)-FePt catalyst (37 wt %-FePt/rGO), exhibiting 18.8 times higher specific activity than commercial Pt/C catalyst without degradation over 20 000 cycles, well demonstrate the effectiveness of our synthetic approach toward uniformly alloyed nanoparticles with high homogeneity11sci

Electrochemically generated electrophilic peroxo species accelerates alkaline oxygen evolution reaction

Introducing a new redox cycle into (electro)catalysts can activate reactants, enabling novel functionality. Here, we report that early transition metals (TMs) with vacant d orbitals (d0-oxoanions) directly participate in and accelerate the alkaline oxygen evolution reaction (OER) via a redox cycle associated with early TM-peroxo species [M-(O2)2−]. Interestingly, the metal-peroxo cycles both induced by hydrogen peroxide (H2O2) and OER intermediates have similar characteristics, making it possible to modulate the OER performance using d0-oxoanions that react with H2O2 as enhancers. This principle was successfully integrated into practical electrolysis systems with the anode side extended to typical OER catalysts. Among them, tungstate-modified iron-nickel (oxy)hydroxide (W/FeNiOOH) exhibited current densities of 7.87 and 4.26 A cmgeo−2 at 2.0 Vcell in water electrolysis while running in 1.0 M KOH and 1.0 wt % K2CO3 electrolyte, respectively. Our finding provides universal platforms demonstrating a controllable strategy toward electrochemical oxygen activation using the electrophilic peroxo cycle. © 2023 Elsevier Inc.11Nsciescopu

Operando Identification of the Chemical and Structural Origin of Li-Ion Battery Aging at Near-Ambient Temperature

© 2020 American Chemical Society. Integrated with heat-generating devices, a Li-ion battery (LIB) often operates at 20-40 degrees C higher than the ordinary working temperature. Although macroscopic investigation of the thermal contribution has shown a significant reduction in the LIB performance, the molecular level structural and chemical origin of battery aging in a mild thermal environment has not been elucidated. On the basis of the combined experiments of the electrochemical measurements, Cs-corrected electron microscopy, and in situ analyses, we herein provide operando structural and chemical insights on how a mild thermal environment affects the overall battery performance using anatase TiO2 as a model intercalation compound. Interestingly, a mild thermal condition induces excess lithium intercalation even at near-ambient temperature (45 degrees C), which does not occur at the ordinary working temperature. The anomalous intercalation enables excess lithium storage in the first few cycles but exerts severe intracrystal stress, consequently cracking the crystal that leads to battery aging. Importantly, this mild thermal effect is accumulated upon cycling, resulting in irreversible capacity loss even after the thermal condition is removed. Battery aging at a high working temperature is universal in nearly all intercalation compounds, and therefore, it is significant to understand how the thermal condition contributes to battery aging for designing intercalation compounds for advanced battery electrode materials11sci

Operando Identification of the Chemical and Structural Origin of Li-Ion Battery Aging at Near-Ambient Temperature

© 2020 American Chemical Society. Integrated with heat-generating devices, a Li-ion battery (LIB) often operates at 20-40 degrees C higher than the ordinary working temperature. Although macroscopic investigation of the thermal contribution has shown a significant reduction in the LIB performance, the molecular level structural and chemical origin of battery aging in a mild thermal environment has not been elucidated. On the basis of the combined experiments of the electrochemical measurements, Cs-corrected electron microscopy, and in situ analyses, we herein provide operando structural and chemical insights on how a mild thermal environment affects the overall battery performance using anatase TiO2 as a model intercalation compound. Interestingly, a mild thermal condition induces excess lithium intercalation even at near-ambient temperature (45 degrees C), which does not occur at the ordinary working temperature. The anomalous intercalation enables excess lithium storage in the first few cycles but exerts severe intracrystal stress, consequently cracking the crystal that leads to battery aging. Importantly, this mild thermal effect is accumulated upon cycling, resulting in irreversible capacity loss even after the thermal condition is removed. Battery aging at a high working temperature is universal in nearly all intercalation compounds, and therefore, it is significant to understand how the thermal condition contributes to battery aging for designing intercalation compounds for advanced battery electrode materials11sci

Controlling Multiple Active Sites on Pd-CeO2 for Sequential C-C Cross-coupling and Alcohol Oxidation in One Reaction System

Ceria (CeO2)-supported metal catalysts have been widely utilized for various single-step chemical transformations. However, using such catalysts for a multistep organic reaction in one reaction system has rarely been achieved. Here, we investigate multiple active sites on Pd-CeO2 catalysts and optimize them for a multistep reaction of C-C cross-coupling and alcohol oxidation. Atomic-level imaging and spectroscopic studies reveal that metallic Pd-0 and Pd-CeO2 interface are active sites on Pd-CeO2 for C-C cross-coupling and oxidation, respectively. These active sites are controlled under the structural evolution of Pd-CeO2 during reductive heat-treatments. Accordingly, we found that optimally reduced Pd-CeO2 catalysts containing similar to 1.5 nm-sized Pd nanoclusters with both sites in balance are ideal for multistep chemical transformations in one reaction system. Our strategy to design supported metal catalysts leads to one-pot sequential synthetic protocols for pharmaceutical building blocks.11Nsciescopu