Near-Atomic-Thick Bismuthene Oxide Microsheets for Flexible Aqueous Anodes: Boosted Performance upon 3D → 2D Transition

Wireless electrochemical light emission in ultrathin 2D nanoconfinements

Spatial confinement of chemical reactions or physical effects may lead to original phenomena and new properties. Here, the generation of electrochemiluminescence (ECL) in confined free-standing 2D spaces, exemplified by surfactant-based air bubbles is reported. For this, the ultrathin walls of the bubbles (typically in the range of 100-700 nm) are chosen as a host where graphene sheets, acting as bipolar ECL-emitting electrodes, are trapped and dispersed. The proposed system demonstrates that the required potential for the generation of ECL is up to three orders of magnitude smaller compared to conventional systems, due to the nanoconfinement of the potential drop. This proof-of-concept study demonstrates the key advantages of a 2D environment, allowing a wireless activation of ECL at rather low potentials, compatible with (bio)analytical systems.

Ultrathin Carbon-Coated Porous TiNb2O7 Nanosheets as Anode Materials for Enhanced Lithium Storage

TiNb₂O₇ has been considered as a promising anode material for next-generation high power lithium ion batteries for its relatively high theoretical capacity, excellent safety and long cycle life. However, the unsatisfactory electrochemical kinetics resulting from the intrinsic sluggish electron transport and lithium ion diffusion of TiNb₂O₇ limit its wide application. Morphology controlling and carbon coating are two effective methods for improving the electrochemical performance of electrode materials. Herein, an ultrathin carbon-coated porous TiNb₂O₇ nanosheet (TNO@C) is successfully fabricated by a simple and effective approach. The distinctive sheet-like porous structure can shorten the transport path of ions/electrons and provide more active sites for electrochemical reaction. The introduction of nanolayer carbon can improve electronic conductivity and increase the specific surface area of the porous TiNb₂O₇ nanosheets. Based on the above synergistic effect, TiNb₂O₇@C delivers an initial discharge capacity of 250.6 mAh g^-1 under current density of 5C and can be maintained at 206.9 mAh g^-1 after 1000 cycles with a capacity retention of 82.6%, both of which are superior to that of pure TiNb₂O₇. These results well demonstrate that TiNb₂O₇@C is a promising anode material for lithium ion batteries.

Flexible, Self-Supported Anode for Organic Batteries with a Matched Hierarchical Current Collector System for Boosted Current Density

The inherent flexibility of redox-active organic polymers and carbon-based fillers, combined with flexible current collectors (CCs) is ideal for the fabrication of flexible batteries. Herein, a one-step electrophoretic deposition of polyviologen (PV)/graphene-oxide (GO) aqueous composites onto a flexible mesh of 60 µm thick wires, 100 µm apart, is described. Notably, during electrodeposition, GO is transformed into conductive reduced GO (rGO), and nanoscopic pores are formed by self-assembly allowing charge/discharge of the redox sites over dozens of micrometers. Typically, electrodeposition of PV alone on a flat CC (FCC) is limited by its electrically insulating structure to ≈0.15 mAh cm^-2 , but the presence of rGO allows thicker active layers without loss in (dis-)charging kinetics and reaching areal capacities of ≈2 mAh cm^-2 . Remarkably, when the FCC is replaced by a mesh, the deposition of significantly more anode materials (≈5 mAh cm^-2 ) is possible, while the (dis-)charging kinetics is considerably improved. It exhibits high capacity retention at an ultrafast rate of 100 C (<3%) and excellent bending stabilities. This represents the first combination of a microscopic-CC (mesh wires) with a molecular-electronic and -ionic conductor (rGO with its pores), i.e., a hierarchical-CC system with maximized polymer thickness and minimized wire thickness. The stacking of such modified grids paves the road to further increase the areal capacity.

Reconstructed Bismuth-Based Metal-Organic Framework Nanofibers for Selective CO2 -to-Formate Conversion: Morphology Engineering

Electrochemical reduction of carbon dioxide (ERCO₂ ) is an attractive and sustainable approach to close the carbon loop. Formic acid is a high-value and readily collectible liquid product. However, the current reaction selectivity remains unsatisfactory. In this study, the bismuth-containing metal-organic framework CAU-17, with morphological variants of hexagonal prisms (CAU-17-hp) and nanofibers (CAU-17-fiber), is prepared at room temperature through a wet-chemical approach and employed as the electrocatalyst for highly selective CO₂ -to-formate conversion. An H₃ BTC-mediated morphology reconstruction is systematically investigated and further used to build a CAU-17-fiber hierarchical structure. The as-prepared CAU-17-fiber_400 electrodes give the best electrocatalytic performance in selective and efficient formate production with FE_HCOO- of 96.4 % and j_COOH- of 20.4 mA cm^-2 at -0.9 V_RHE . This work provides a new mild approach for synthesis and morphology engineering of CAU-17 and demonstrates the efficacy of morphology engineering in regulating the accessible surface area and promoting the activity of MOF-based materials for ERCO₂ .

The Metallocene Battery: Ultrafast Electron Transfer Self Exchange Rate Accompanied by a Harmonic Height Breathing

The first all-metallocene rechargeable battery consisting of poly-cobaltocenium/- and poly-ferrocene/reduced graphene oxide composites as anode and cathode was prepared. The intrinsically fast ET self-exchange rate of metallocenes was successfully combined with an efficient ion-percolation achieved by molecular self-assembly. The resulting battery materials show ideal Nernstian behavior, is thickness scalable up to >1.2 C cm^-2 , and exhibit high coulombic efficiency at ultrafast rates (200 A g^-1 ). Using aqueous LiClO₄ , the charge is carried exclusively by the anion. The ClO₄ ^- intercalation is accompanied by a reciprocal height change of the active layers. Principally, volume changes in organic battery materials during charging/discharging are not desirable and represent a major safety issue. However, here, the individual height changes-due to ion breathing-are reciprocal and thus prohibiting any internal pressure build-up in the closed-cell, leading to excellent cycling stability.