Electrocatalytic carbon dioxide reduction to formate is desirable but challenging. Current attention is mostly focused on tin-based materials, which, unfortunately, often suffer from limited Faradaic efficiency. The potential of bismuth in carbon dioxide reduction has been suggested but remained understudied. Here, we report that ultrathin bismuth nanosheets are prepared from the in situ topotactic transformation of bismuth oxyiodide nanosheets. They process single crystallinity and enlarged surface areas. Such an advantageous nanostructure affords the material with excellent electrocatalytic performance for carbon dioxide reduction to formate. High selectivity (~100%) and large current density are measured over a broad potential, as well as excellent durability for >10 h. Its selectivity for formate is also understood by density functional theory calculations. In addition, bismuth nanosheets were coupled with an iridium-based oxygen evolution electrocatalyst to achieve efficient full-cell electrolysis. When powered by two AA-size alkaline batteries, the full cell exhibits impressive Faradaic efficiency and electricity-to-formate conversion efficiency.

Fe−N−C single-atom catalysts (SACs) exhibit high activity for oxygen reduction reaction (ORR). However, it remains controversial how the active center mediates catalysis, and the predicted potential deviates from experimental results, hindering development of ideal SACs. Here, using first-principles calculations, we present a microkinetic model for ORR on Fe−N−C SACs, disclosing a self-adjusting mechanism induced by its intrinsic intermediate. The modeling results show that the single-atom Fe site of the FeN 4 center of Fe−N−C is covered with an intermediate OH* from 0.28 to 1.00 V. Remarkably, such OH* becomes part of the active moiety, Fe(OH)N 4 , and can optimize intermediate bindings on the Fe site, exhibiting a theoretical half-wave potential of ∼0.88 V. Partial current density analysis reveals the dominating associative path over the dissociative ones. In addition, ORR on Mn−N−C and Co−N−C SACs is unveiled. This work demonstrates the necessity of assessing the effect of intrinsic intermediates in singleatom catalysis and provides practical guidance for rational design of high-performance SACs.

Designing new materials with novel topological properties and reduced dimensionality is always desirable for material innovation. Here we report the design of a two-dimensional material, namely Be5C2 monolayer on the basis of density functional theory computations. In Be5C2 monolayer, each carbon atom binds with five beryllium atoms in almost the same plane, forming a quasi-planar pentacoordinate carbon moiety. Be5C2 monolayer appears to have good stability as revealed by its moderate cohesive energy, positive phonon modes and high melting point. It is the lowest-energy structure with the Be5C2 stoichiometry in two-dimensional space and therefore holds some promise to be realized experimentally. Be5C2 monolayer is a gapless semiconductor with a Dirac-like point in the band structure and also has an unusual negative Poisson's ratio. If synthesized, Be5C2 monolayer may find applications in electronics and mechanics.

Membranes for organic solvent nanofiltration (OSN) or solvent-resistant nanofiltration (SRNF) offer unprecedented opportunities for highly efficient and cost-competitive solvent recovery in the pharmaceutical industry. Here, we describe small-flake graphene oxide (SFGO) membranes for high-performance OSN applications. Our strategy exploits lateral dimension control to engineer shorter and less tortuous transport pathways for solvent molecules. By using La3+ as a cross-linker and spacer for intercalation, the SFGO membrane selective layer was stabilized, and size-dependent ultrafast selective molecular transport was achieved. The methanol permeance was up to 2.9-fold higher than its large-flake GO (LFGO) counterpart, with high selectivity toward three organic dyes. More importantly, the SFGO-La3+ membrane demonstrated robust stability for at least 24 hours under hydrodynamic stresses that are representative of realistic OSN operating conditions. These desirable attributes stem from the La3+ cross-linking, which forms uniquely strong coordination bonds with oxygen-containing functional groups of SFGO. Other cations were found to be ineffective.

By means of density functional theory (DFT) computations, we theoretically investigated a novel two-dimensional (2D) transition metal disulfide (TMD), namely PdS 2 monolayer. Distinguished from other 2D TMDs which adopt the ordinary 2H or 1T configuration, PdS 2 monolayer presents rather unique structural properties: each Pd atom binds to four S atoms in the same plane, and two neighboring S atoms can form a covalent S−S bond. The hybrid HSE06 DFT computations demonstrated that PdS 2 monolayer is semiconducting with an indirect band gap of 1.60 eV, which can be effectively reduced by employing a uniaxial or biaxial tensile strain. Especially, PdS 2 has a rather large hole and electron mobilities. Our results suggest that PdS 2 monolayer is rather promising for future electronics and optoelectronics.PdS 2 monolayer has distinguished strucutral properties from other transistion metal disulfides, and has also ranther high carrier mobilities. It is semiconducting with a moderate indirect band gap, which could be effectively tuned by applying a tensile strain.