Tailoring Photocatalytic Water Splitting Activity of Boron Thiophene Polymer through Pore Size Engineering

Taking into account the electron-rich and visible light response of thiophene, first-principles calculations have been carried out to explore the photocatalytic activity of donor-acceptor polymers incorporating thiophene and boron. The designed honeycomb-kagome boron thiophene (BTP) polymers with varying numbers of thiophene units and fixed B center atoms are direct band gap semiconductors with tunable band gaps ranging from 2.41 eV to 1.88 eV, and show high absorption coefficients under the ultraviolet and visible regions of the solar spectrum. Fine-tuning the band edges of the BTP polymer is efficiently achieved by adjusting the pore size through the manipulation of thiophene units between the B centers. This manipulation, achieved without excessive chemical functionalization, facilitates the generation of an appropriate quantity of photoexcited electrons and/or holes to straddle the redox potential of the water. Our study demonstrates that two units between B centers of thiophene in BTP polymers enable overall photocatalytic water splitting, whereas BTP polymers with larger pores solely promote photocatalytic hydrogen reduction. Moreover, the thermodynamics of hydrogen and oxygen reduction reactions proceed either spontaneously or need small additional external biases. Our findings provide the rationale for designing metal-free and single-material polymer photocatalysts based on thiophene, specifically for achieving efficient overall water splitting

Ultrathin positively charged electrode skin for durable anion-intercalation battery chemistries

The anion-intercalation chemistries of graphite have the potential to construct batteries with promising energy and power breakthroughs. Here, we report the use of an ultrathin, positively charged two-dimensional poly(pyridinium salt) membrane (C2DP) as the graphite electrode skin to overcome the critical durability problem. Large-area C2DP enables the conformal coating on the graphite electrode, remarkably alleviating the electrolyte. Meanwhile, the dense face-on oriented single crystals with ultrathin thickness and cationic backbones allow C2DP with high anion-transport capability and selectivity. Such desirable anion-transport properties of C2DP prevent the cation/solvent co-intercalation into the graphite electrode and suppress the consequent structure collapse. An impressive PF6−-intercalation durability is demonstrated for the C2DP-covered graphite electrode, with capacity retention of 92.8% after 1000 cycles at 1 C and Coulombic efficiencies of > 99%. The feasibility of constructing artificial ion-regulating electrode skins with precisely customized two-dimensional polymers offers viable means to promote problematic battery chemistries

Ultrathin positively charged electrode skin for durable anion-intercalation battery chemistries

The anion-intercalation chemistries of graphite have the potential to construct batteries with promising energy and power breakthroughs. Here, we report the use of an ultrathin, positively charged two-dimensional poly(pyridinium salt) membrane (C2DP) as the graphite electrode skin to overcome the critical durability problem. Large-area C2DP enables the conformal coating on the graphite electrode, remarkably alleviating the electrolyte. Meanwhile, the dense face-on oriented single crystals with ultrathin thickness and cationic backbones allow C2DP with high anion-transport capability and selectivity. Such desirable anion-transport properties of C2DP prevent the cation/solvent co-intercalation into the graphite electrode and suppress the consequent structure collapse. An impressive PF6−-intercalation durability is demonstrated for the C2DP-covered graphite electrode, with capacity retention of 92.8% after 1000 cycles at 1 C and Coulombic efficiencies of > 99%. The feasibility of constructing artificial ion-regulating electrode skins with precisely customized two-dimensional polymers offers viable means to promote problematic battery chemistries

Graphene-like Carbon–Nitride Monolayer: A Potential Anode Material for Na- and K‑Ion Batteries

Presently, great attention is being directed toward the development of promising electrode materials for non-lithium rechargeable batteries which have the advantages of low cost, high energy storage density, and high rate capacity for substantial renewable energy applications. In this study, we have predicted that the C₃N monolayer is a potential electrode material for Na- and K-ion batteries by first-principle calculations. The diffusion barriers are calculated to be as small as 0.03 eV for Na and 0.07 eV for K, which could lead to a very fast diffusion on the C₃N monolayer surface, implying high mobility and cycle stability for batteries. The C₃N monolayer is predicted to allow a high storage capacity of 1072 mAh/g by the inclusion of multilayer adsorption with an average voltage of 0.13 V for Na₂C₃N and 0.26 V for K₂C₃N systems, which is more promising than previously studied anode materials. All of these results ensure that the C₃N monolayer could serve as an excellent anode material for Na- and K-ion batteries

Pt₃Ti (Ti₁₉@Pt₆₀)‑Based Cuboctahedral Core–Shell Nanocluster Favors a Direct over Indirect Oxygen Reduction Reaction

Developing a highly efficient catalyst with lower Pt content for the oxygen reduction reaction (ORR) is highly sought for fuel cell applications. The potential applicability of a cuboctahedral core–shell (Ti₁₉@Pt₆₀) nanocluster (NC) toward ORR activity has been investigated and compared with that of a pure Pt NC (Pt₇₉). The energetic stability, thermal stability, and dissolution limit of Ti₁₉@Pt₆₀ NCs has been investigated for their possible synthesis and practical usages. Thermodynamic and kinetic parameters are explored to find out the most favored ORR pathway and product selectivity on the Ti₁₉@Pt₆₀ NC. Rate-determining steps (*O₂ activation and *OH formation) are highly improved over the Ti₁₉@Pt₆₀ NC with respect to the cuboctahedral Pt NC (Pt₇₉), pure metal (Pt, Pd, and Ag), and alloy (Pt₃M; M = Ni, Co, Ti) based catalysts. Our detailed investigation reveals that the *O₂-induced structural changes favor direct *O₂ dissociation on the Ti₁₉@Pt₆₀ NC surface. Further, we find that a dual mechanism (ligand effect and charge transfer) plays an important role to improve the ORR activity. The results obtained in this study provide fundamental insight into the role of a core–shell NC toward ORR activity

High-energy-density dual-ion battery for stationary storage of electricity using concentrated potassium fluorosulfonylimide

Graphite dual-ion batteries represent a potential battery concept for large-scale stationary storage of electricity, especially when constructed free of lithium and other chemical elements with limited natural reserves. Owing to their non-rocking-chair operation mechanism, however, the practical deployment of graphite dual-ion batteries is inherently limited by the need for large quantities of electrolyte solutions as reservoirs of all ions that are needed for complete charge and discharge of the electrodes. Thus far, lithium-free graphite dual-ion batteries have employed moderately concentrated electrolyte solutions (0.3–1 M), resulting in rather low cell-level energy densities of 20–70 Wh kg^−1. In this work, we present a lithium-free graphite dual-ion battery utilizing a highly concentrated electrolyte solution of 5 M potassium bis(fluorosulfonyl)imide in alkyl carbonates. The resultant battery offers an energy density of 207 Wh kg^−1, along with a high energy efficiency of 89% and an average discharge voltage of 4.7 V.ISSN:2041-172

Cation-selective two-dimensional polyimine membranes for high-performance osmotic energy conversion

Two-dimensional (2D) membranes are emerging candidates for osmotic energy conversion. However, the trade-off between ion selectivity and conductivity remains the key bottleneck. Here we demonstrate a fully crystalline imine-based 2D polymer (2DPI) membrane capable of combining excellent ionic conductivity and high selectivity for osmotic energy conversion. The 2DPI can preferentially transport cations with Na+ selectivity coefficient of 0.98 (Na+/Cl− selectivity ratio ~84) and K+ selectivity coefficient of 0.93 (K+/Cl− ratio ~29). Moreover, the nanometer-scale thickness (~70 nm) generates a substantially high ionic flux, contributing to a record power density of up to ~53 W m−2, which is superior to most of nanoporous 2D membranes (0.8~35 W m−2). Density functional theory unveils that the oxygen and imine nitrogen can both function as the active sites depending on the ionization state of hydroxyl groups, and the enhanced interaction of Na+ versus K+ with 2DPI plays a significant role in directing the ion selectivity

Porous Dithiine-Linked Covalent Organic Framework as a Dynamic Platform for Covalent Polysulfide Anchoring in Lithium-Sulfur Battery Cathodes

Dithiine linkage formation via a dynamic and self-correcting nucleophilic aromatic substitution reaction enables the de novo synthesis of a porous thianthrene-based two-dimensional covalent organic framework (COF). For the first time, this organo-sulfur moiety is integrated as a structural building block into a crystalline layered COF. The structure of the new material deviates from the typical planar interlayer π-stacking of the COF to form undulated layers caused by bending along the C-S-C bridge, without loss of aromaticity and crystallinity of the overall COF structure. Comprehensive experimental and theoretical investigations of the COF and a model compound, featuring the thianthrene moiety, suggest partial delocalization of sulfur lone pair electrons over the aromatic backbone of the COF decreasing the band gap and promoting redox activity. Postsynthetic sulfurization allows for direct covalent attachment of polysulfides to the carbon backbone of the framework to afford a molecular-designed cathode material for lithium-sulfur (Li-S) batteries with a minimized polysulfide shuttle. The fabricated coin cell delivers nearly 77% of the initial capacity even after 500 charge-discharge cycles at 500 mA/g current density. This novel sulfur linkage in COF chemistry is an ideal structural motif for designing model materials for studying advanced electrode materials for Li-S batteries on a molecular level