A Combinatorial Chemistry Method for Fast Screening of Perovskite-Based NO Oxidation Catalyst

A fast parallel screening method based on combinatorial chemistry (combichem) has been developed and applied in the screening tests of perovskite-based oxide (PBO) catalysts for NO oxidation to hit a promising PBO formulation for the oxidation of NO to NO₂. This new method involves three consecutive steps: oxidation of NO to NO₂ over a PBO catalyst, adsorption of NOx onto the PBO and K₂O/Al₂O₃, and colorimetric assay of the NOx adsorbed thereon. The combichem experimental data have been used for determining the oxidation activity of NO over PBO catalysts as well as three critical parameters, such as the adsorption efficiency of K₂O/Al₂O₃ for NO₂ (α) and NO (β), and the time-average fraction of NO included in the NOx feed stream (ξ). The results demonstrated that the amounts of NO₂ produced over PBO catalysts by the combichem method under transient conditions correlate well with those from a conventional packed-bed reactor under steady-state conditions. Among the PBO formulations examined, La_0.5Ag_0.5MnO₃ has been identified as the best chemical formulation for oxidation of NO to NO₂ by the present combichem method and also confirmed by the conventional packed-bed reactor tests. The superior efficiency of the combichem method for high-throughput catalyst screening test validated in this study is particularly suitable for saving the time and resources required in developing a new formulation of PBO catalyst whose chemical composition may have an enormous number of possible variations

Mesoporous Ge/GeO₂/Carbon Lithium-Ion Battery Anodes with High Capacity and High Reversibility

We report mesoporous composite materials (m-GeO₂, m-GeO₂/C, and m-Ge-GeO₂/C) with large pore size which are synthesized by a simple block copolymer directed self-assembly. m-Ge/GeO₂/C shows greatly enhanced Coulombic efficiency, high reversible capacity (1631 mA h g^–1), and stable cycle life compared with the other mesoporous and bulk GeO₂ electrodes. m-Ge/GeO₂/C exhibits one of the highest areal capacities (1.65 mA h cm^–2) among previously reported Ge- and GeO₂-based anodes. The superior electrochemical performance in m-Ge/GeO₂/C arises from the highly improved kinetics of conversion reaction due to the synergistic effects of the mesoporous structures and the conductive carbon and metallic Ge

Direct O–O Coupling Promoted the Oxygen Evolution Reaction by Dual Active Sites from Ag/LaNiO₃ Interfaces

The development of highly active oxygen evolution reaction (OER) electrocatalysts is one of the most important issues for advanced water electrolysis technology with high energy efficiency. However, according to the conventional adsorbate evolution mechanism (AEM), the OER activity is theoretically limited with high overpotential by the scaling relationship in binding energies of the reaction intermediates. We propose an attractive strategy to promote OER activity by direct O–O coupling at the interfacial active sites for Ag (x) nanoparticles decorated on La1–xNiO3 perovskite electrocatalysts (Ag/LNO-x). The overpotential of the Ag/LNO-0.05 was 315 mV at a current density of 10 mA cm–2geo, which was much lower than that of other Ag/LNO-x (x = 0, 0.3, and 0.5) and commercial iridium oxide (IrO2, 398 mV) electrocatalysts. The theoretical calculation revealed that the improved OER electrocatalytic activity of Ag/LNO-x originated from a change in the reaction mechanism at the interfacial active sites. At the interface, oxygen evolution via the dual-site mechanism with direct O–O coupling becomes more favorable than that via the conventional AEM. Finally, due to the formation of the interfacial active sites, the synthesized Ag/LNO-0.05 electrocatalyst showed significantly enhanced OER activity, which was 20 times higher mass activity before and 74 times after an accelerated durability test than that of the IrO2 electrocatalyst

Advanced Hybrid Supercapacitor Based on a Mesoporous Niobium Pentoxide/Carbon as High-Performance Anode

Recently, hybrid supercapacitors (HSCs), which combine the use of battery and supercapacitor, have been extensively studied in order to satisfy increasing demands for large energy density and high power capability in energy-storage devices. For this purpose, the requirement for anode materials that provide enhanced charge storage sites (high capacity) and accommodate fast charge transport (high rate capability) has increased. Herein, therefore, a preparation of nanocomposite as anode material is presented and an advanced HSC using it is thoroughly analyzed. The HSC comprises a mesoporous Nb₂O₅/carbon (m-Nb₂O₅–C) nanocomposite anode synthesized by a simple one-pot method using a block copolymer assisted self-assembly and commercial activated carbon (MSP-20) cathode under organic electrolyte. The m-Nb₂O₅–C anode provides high specific capacity with outstanding rate performance and cyclability, mainly stemming from its enhanced pseudocapacitive behavior through introduction of a carbon-coated mesostructure within a voltage range from 3.0 to 1.1 V (<i>vs</i> Li/Li⁺). The HSC using the m-Nb₂O₅–C anode and MSP-20 cathode exhibits excellent energy and power densities (74 W h kg^–1 and 18 510 W kg^–1), with advanced cycle life (capacity retention: ∼90% at 1000 mA g^–1 after 1000 cycles) within potential range from 1.0 to 3.5 V. In particular, we note that the highest power density (18 510 W kg^–1) of HSC is achieved at 15 W h kg^–1, which is the highest level among similar HSC systems previously reported. With further study, the HSCs developed in this work could be a next-generation energy-storage device, bridging the performance gap between conventional batteries and supercapacitors

Facile Synthesis of Nb₂O₅@Carbon Core–Shell Nanocrystals with Controlled Crystalline Structure for High-Power Anodes in Hybrid Supercapacitors

Hybrid supercapacitors (battery-supercapacitor hybrid devices, HSCs) deliver high energy within seconds (excellent rate capability) with stable cyclability. One of the key limitations in developing high-performance HSCs is imbalance in power capability between the sluggish Faradaic lithium-intercalation anode and rapid non-Faradaic capacitive cathode. To solve this problem, we synthesize Nb₂O₅@carbon core–shell nanocyrstals (Nb₂O₅@C NCs) as high-power anode materials with controlled crystalline phases (orthorhombic (<i>T</i>) and pseudohexagonal (<i>TT</i>)) <i>via</i> a facile one-pot synthesis method based on a water-in-oil microemulsion system. The synthesis of ideal <i>T</i>-Nb₂O₅ for fast Li⁺ diffusion is simply achieved by controlling the microemulsion parameter (<i>e.g.,</i> pH control). The <i>T</i>-Nb₂O₅@C NCs shows a reversible specific capacity of ∼180 mA h g^–1 at 0.05 A g^–1 (1.1–3.0 V <i>vs</i> Li/Li⁺) with rapid rate capability compared to that of <i>TT</i>-Nb₂O₅@C and carbon shell-free Nb₂O₅ NCs, mainly due to synergistic effects of (i) the structural merit of <i>T</i>-Nb₂O₅ and (ii) the conductive carbon shell for high electron mobility. The highest energy (∼63 W h kg^–1) and power (16 528 W kg^–1 achieved at ∼5 W h kg^–1) densities within the voltage range of 1.0–3.5 V of the HSC using <i>T</i>-Nb₂O₅@C anode and MSP-20 cathode are remarkable