Confning TiO2 Nanotubes in PECVD‑Enabled Graphene Capsules Toward Ultrafast K‑Ion Storage: In Situ TEM/XRD Study and DFT Analysis

© 2020, © 2020, The Author(s). Titanium dioxide (TiO2) has gained burgeoning attention for potassium-ion storage because of its large theoretical capacity, wide availability, and environmental benignity. Nevertheless, the inherently poor conductivity gives rise to its sluggish reaction kinetics and inferior rate capability. Here, we report the direct graphene growth over TiO2 nanotubes by virtue of chemical vapor deposition. Such conformal graphene coatings effectively enhance the conductive environment and well accommodate the volume change of TiO2 upon potassiation/depotassiation. When paired with an activated carbon cathode, the graphene-armored TiO2 nanotubes allow the potassium-ion hybrid capacitor full cells to harvest an energy/power density of 81.2 Wh kg−1/3746.6 W kg−1. We further employ in situ transmission electron microscopy and operando X-ray diffraction to probe the potassium-ion storage behavior. This work offers a viable and versatile solution to the anode design and in situ probing of potassium storage technologies that is readily promising for practical applications.[Figure not available: see fulltext.]

Biomass template derived boron/oxygen co-doped carbon particles as advanced anodes for potassium-ion batteries

Among various anode candidates for potassium-ion batteries, carbonaceous materials have attracted significant attention due to their overwhelming advantages including cost-effectiveness and environmental benignity. However, the inferior specific capacity and the sluggish reaction kinetics hinder the further development in this realm. Herein, we report biomass templated synthesis of boron/oxygen heteroatom co-doped carbon particles (BO-CPs) via direct plasma-enhanced chemical vapor deposition. With the combined advantages of abundant active sites, large accessible surface area, and functional groups, BO-CP anode exhibits high reversible specific capacity (426.5 mAh g(-1) at 0.1 A g(-1)) and excellent rate performance (166.5 mAh g(-1) at 5 A g(-1)). The K-ion storage mechanism is probed by operando Raman spectroscopy, ex situ X-ray photoelectron spectroscopy/electrochemical impedance spectroscopy, galvanostatic intermittent titration technique measurements, and theoretical simulations. The synergistic effect of boron and oxygen co-doping greatly facilitates the performance of carbon-based anode, wherein boron dopant improves the conductivity of carbon framework and the oxygen dopant affords ample active sites and thus harvests additional specific capacity. This work is anticipated to propel the development of high-performance anode materials for emerging energy storage devices.Web of Scienc

Rational Construction of a Triple-Phase Reaction Zone Using CuO-Based Heterostructure Nanoarrays for Enhanced Water Oxidation Reaction

The development of high-efficiency oxygen evolution reaction (OER) electrocatalysts for the production and conversion of clean energy is paramount yet also full of challenges. Herein, we proposed a simple and universal method to precisely fabricate the hierarchically structured CuO/TMOs loaded on Cu foil (CuO/TMOs/CF) (TMO represents Mn3O4, NiO, CoO, and CuO) nanorod-array electrodes as a highly active and stable OER electrocatalyst, employing Cu(OH)2/CF as a self-sacrificing template by the subsequent H2O2-induced chemical deposition (HiCD) and pyrolysis process. Taking CuO/Mn3O4/CF as an example, we systematically investigated its structure–performance relationship via experimental and theoretical explorations. The enhanced OER activity can be ascribed to the rational design of the nanoarray with multiple synergistic effects of abundant active sites, excellent electronic conductivity of the metallic Cu foil substrate, strong interface charge transfer, and quasi-superhydrophilic/superaerophobic property. Consequently, the optimal CuO/Mn3O4/CF presents an overpotential of 293 mV to achieve a current density of 20 mA cm–2 in 1.0 M KOH media, comparable to that of commercial RuO2 (282 mV), delivering excellent durability by the electrolysis of water at a potential of around 1.60 V [vs reversible hydrogen electrode (RHE)] without evident degeneration. This work might offer a feasible scheme for developing a hybrid nanoarray OER electrocatalyst via regulating electron transportation and mass transfer.</p

Computational Studies on Holey TMC6 (TM = Mo and W) Membranes for H2 Purification

The purification of hydrogen (H2) has been a vital step in H2 production processes such as steam&ndash;methane reforming. By first-principle calculations, we revealed the potential applications of holey TMC6 (TM = Mo and W) membranes in H2 purification. The adsorption and diffusion behaviors of five gas molecules (including H2, N2, CO, CO2, and CH4) were compared on TMC6 membranes with different phases. Though the studied gas molecules show weak physisorption on the TMC6 membranes, the smaller pore size makes the gas molecules much more difficult to permeate into h-TMC6 rather than into s-TMC6. With suitable pore sizes, the s-TMC6 structures not only show an extremely low diffusion barrier (around 0.1 eV) and acceptable permeance capability for the H2 but also exhibit considerably high selectivity for both H2/CH4 and H2/CO2 (&gt;1015), especially under relatively low temperature (150&ndash;250 K). Moreover, classical molecular dynamics simulations on the permeation process of a H2, CO2, and CH4 mixture also validated that s-TMC6 could effectively separate H2 from the gas mixture. Hence, the s-MoC6 and s-WC6 are predicted to be qualified H2 purification membranes, especially below room temperature

Bio-templated formation of defect-abundant VS 2 as a bifunctional material toward high-performance hydrogen evolution reactions and lithium − sulfur batteries

Transition metal chalcogenides have nowadays garnered burgeoning interest owing to their fascinating electronic and catalytic properties, thus possessing great implications for energy conversion and storage applications. In this regard, their controllable synthesis in a large scale at low cost has readily become a focus of research. Herein we report diatomite-template generic and scalable production of VS2 and other transition metal sulfides targeting emerging energy conversion and storage applications. The conformal growth of VS2 over diatomite template would endow them with defect-abundant features. Throughout detailed experimental investigation in combination with theoretical simulation, we reveal that the enriched active sites/sulfur vacancies of thus-derived VS2 architectures would pose positive impacts on the catalytic performance such in electrocatalytic hydrogen evolution reactions. We further show that the favorable electrical conductivity and highly exposed sites of VS2 hold promise for serving as sulfur host in the realm of Li−S batteries. Our work offers new insights into the templated and customized synthesis of defect-rich sulfides in a scalable fashion to benefit multifunctional energy applications

In situ construction of CoSe2@vertical-oriented graphene arrays as self-supporting electrodes for sodium-ion capacitors and electrocatalytic oxygen evolution

Transitional metal dichacogenides (TMDs) have stimulated an increasing research and technological attention due to their unique properties, holding great promise for emerging energy storage and conversion applications. However, tailorable and efficient synthesis of TMDs to garner the electrochemical and electrocatalytic performance of thus-derived electrodes has by far remained challenging. Herein we demonstrate a versatile synthetic strategy to in situ grow CoSe 2 @vertically-oriented graphene (VG) hierarchical architecture on carbon fiber cloth (CC) via combined steps of plasma-enhanced chemical vapor deposition and wet chemistry. Such self-supporting and flexible CoSe 2 @VG/CC arrays possess significant implications for pseudocapacitive Na storage and electrocatalytic O 2 evolution (OER). When evaluated as an anode material for sodium-ion hybrid capacitors, full cells comprising a CoSe 2 @VG/CC anode and AC cathode enable a favorable cyclic stability at 0.5 A g −1 for 1800 cycles in the potential range of 0.5-3.3 V, harvesting a high energy and power density of 116 Wh kg −1 and 7298 W kg −1 . In addition, CoSe 2 @VG/CC array also exhibits an excellent OER performance with a low overpotential of 418 mV and Tafel slope of 82 mV dec −1 on a basis of experimental exploration and theoretical simulation

Enhanced Kinetics Harvested in Heteroatom Dual-Doped Graphitic Hollow Architectures toward High Rate Printable Potassium-Ion Batteries

© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Carbonaceous materials have emerged as promising anode candidates for potassium-ion batteries (PIBs) due to overwhelming advantages including cost-effectiveness and wide availability of materials. However, further development in this realm is handicapped by the deficiency in their in-target and large-scale synthesis, as well as their low specific capacity and huge volume expansion. Herein the precise and scalable synthesis of N/S dual-doped graphitic hollow architectures (NSG) via direct plasma enhanced chemical vapor deposition is reported. Thus-fabricated NSG affording uniform nitrogen/sulfur co-doping, possesses ample potassiophilic surface moieties, effective electron/ion-transport pathways, and high structural stability, which bestow it with high rate capability (≈100 mAh g−1 at 20 A g−1) and a prolonged cycle life (a capacity retention rate of 90.2% at 5 A g−1 after 5000 cycles), important steps toward high-performance K-ion storage. The enhanced kinetics of the NSG anode are systematically probed by theoretical simulations combined with operando Raman spectroscopy, ex situ X-ray photoelectron spectroscopy, and galvanostatic intermittent titration technique measurements. In further contexts, printed NSG electrodes with tunable mass loading (1.84, 3.64, and 5.65 mg cm−2) are realized to showcase high areal capacities. This study demonstrates the construction of a printable carbon-based PIB anode, that holds great promise for next-generation grid-scale PIB applications

Rapid Adsorption Enables Interface Engineering of PdMnCo Alloy/Nitrogen-Doped Carbon as Highly Efficient Electrocatalysts for Hydrogen Evolution Reaction

The catalytic performance of Pd-based catalysts has long been hindered by surface contamination, particle agglomeration, and lack of rational structural design. Here we report a simple adsorption method for rapid synthesis (∼90 s) of structure-optimized Pd alloy supported on nitrogen-doped carbon without the use of surfactants or extra reducing agents. The material shows much lower overpotential than 30 wt % Pd/C and 40 wt % Pt/C catalysts while exhibiting excellent durability (80 h). Moreover, unveiled by the density functional theory (DFT) calculation results, the underlying reason for the outstanding performance is that the PdMnCo alloy/pyridinic nitrogen-doped carbon interfaces weaken the hydrogen-adsorption energy on the catalyst and thus optimize the Gibbs free energy of the intermediate state (Δ<i>G</i>_H*), leading to a remarkable electrocatalytic activity. This work also opens up an avenue for quick synthesis of a highly efficient structure-optimized Pd-based catalyst

Rapid Adsorption Enables Interface Engineering of PdMnCo Alloy/Nitrogen-Doped Carbon as Highly Efficient Electrocatalysts for Hydrogen Evolution Reaction

The catalytic performance of Pd-based catalysts has long been hindered by surface contamination, particle agglomeration, and lack of rational structural design. Here we report a simple adsorption method for rapid synthesis (∼90 s) of structure-optimized Pd alloy supported on nitrogen-doped carbon without the use of surfactants or extra reducing agents. The material shows much lower overpotential than 30 wt % Pd/C and 40 wt % Pt/C catalysts while exhibiting excellent durability (80 h). Moreover, unveiled by the density functional theory (DFT) calculation results, the underlying reason for the outstanding performance is that the PdMnCo alloy/pyridinic nitrogen-doped carbon interfaces weaken the hydrogen-adsorption energy on the catalyst and thus optimize the Gibbs free energy of the intermediate state (Δ<i>G</i>_H*), leading to a remarkable electrocatalytic activity. This work also opens up an avenue for quick synthesis of a highly efficient structure-optimized Pd-based catalyst