Tandem Dual-Site PbCu Electrocatalyst for High-Rate and Selective Glycine Synthesis at Industrial Current Densities

Direct electrosynthesis of high-value amino acids from carbon and nitrogen monomers remains a challenge. Here, we design a tandem dual-site PbCu electrocatalyst for efficient amino acid electrosynthesis. Using oxalic acid (H2C2O4) and hydroxylamine (NH2OH) as the raw reactants, for the first time, we have realized the flow-electrosynthesis of glycine at the industrial current density of 200 mA cm–2 with Faradaic efficiency over 78%. In situ ATR-FTIR spectroscopy characterizations reveal a favorable tandem pathway on the dual-site catalyst. Specifically, the Pb site drives the highly selective electroreduction of H2C2O4 to form glyoxylic acid, and the Cu site accelerates the fast hydrogenation of oxime to form a glycine product. A glycine electrosynthesis (GES)-formaldehyde electrooxidation (FOR) assembly is further established, which synthesizes more valuable chemicals (HCOOH, H2) while minimizing energy consumption. Altogether, we introduce a new strategy to enable the one-step electrosynthesis of high-value amino acid from widely accessible monomers

Oxygen Vacancies Confined in Ultrathin Indium Oxide Porous Sheets for Promoted Visible-Light Water Splitting

Finding an ideal model for disclosing the role of oxygen vacancies in photocatalysis remains a huge challenge. Herein, O-vacancies confined in atomically thin sheets is proposed as an excellent platform to study the O-vacancy–photocatalysis relationship. As an example, O-vacancy-rich/-poor 5-atom-thick In₂O₃ porous sheets are first synthesized via a mesoscopic-assembly fast-heating strategy, taking advantage of an artificial hexagonal mesostructured In-oleate complex. Theoretical/experimental results reveal that the O-vacancies endow 5-atom-thick In₂O₃ sheets with a new donor level and increased states of density, hence narrowing the band gap from the UV to visible regime and improving the carrier separation efficiency. As expected, the O-vacancy-rich ultrathin In₂O₃ porous sheets-based photoelectrode exhibits a visible-light photocurrent of 1.73 mA/cm², over 2.5 and 15 times larger than that of the O-vacancy-poor ultrathin In₂O₃ porous sheets- and bulk In₂O₃-based photoelectrodes

Atomically Thick Bismuth Selenide Freestanding Single Layers Achieving Enhanced Thermoelectric Energy Harvesting

Thermoelectric materials can realize significant energy savings by generating electricity from untapped waste heat. However, the coupling of the thermoelectric parameters unfortunately limits their efficiency and practical applications. Here, a single-layer-based (SLB) composite fabricated from atomically thick single layers was proposed to optimize the thermoelectric parameters fully. Freestanding five-atom-thick Bi₂Se₃ single layers were first synthesized via a scalable interaction/exfoliation strategy. As revealed by X-ray absorption fine structure spectroscopy and first-principles calculations, surface distortion gives them excellent structural stability and a much increased density of states, resulting in a 2-fold higher electrical conductivity relative to the bulk material. Also, the surface disorder and numerous interfaces in the Bi₂Se₃ SLB composite allow for effective phonon scattering and decreased thermal conductivity, while the 2D electron gas and energy filtering effect increase the Seebeck coefficient, resulting in an 8-fold higher figure of merit (<i><i>ZT</i></i>) relative to the bulk material. This work develops a facile strategy for synthesizing atomically thick single layers and demonstrates their superior ability to optimize the thermoelectric energy harvesting

Defect-Mediated Electron–Hole Separation in One-Unit-Cell ZnIn₂S₄ Layers for Boosted Solar-Driven CO₂ Reduction

The effect of defects on electron–hole separation is not always clear and is sometimes contradictory. Herein, we initially built clear models of two-dimensional atomic layers with tunable defect concentrations, and hence directly disclose the defect type and distribution at atomic level. As a prototype, defective one-unit-cell ZnIn₂S₄ atomic layers are successfully synthesized for the first time. Aberration-corrected scanning transmission electron microscopy directly manifests their distinct zinc vacancy concentrations, confirmed by positron annihilation spectrometry and electron spin resonance analysis. Density-functional calculations reveal that the presence of zinc vacancies ensures higher charge density and efficient carrier transport, verified by ultrafast photogenerated electron transfer time of ∼15 ps from the conduction band of ZnIn₂S₄ to the trap states. Ultrafast transient absorption spectroscopy manifests the higher zinc vacancy concentration that allows for ∼1.7-fold increase in average recovery lifetime, confirmed by surface photovoltage spectroscopy and PL spectroscopy analysis, which ensures promoted carrier separation rates. As a result, the one-unit-cell ZnIn₂S₄ layers with rich zinc vacancies exhibit a carbon monoxide formation rate of 33.2 μmol g^–1 h^–1, roughly 3.6 times higher than that of the one-unit-cell ZnIn₂S₄ layers with poor zinc vacancies, while the former’s photocatalytic activity shows negligible loss after 24 h photocatalysis. This present work uncovers the role of defects in affecting electron–hole separation at atomic level, opening new opportunities for achieving highly efficient solar CO₂ reduction performances

Highly Efficient and Exceptionally Durable CO₂ Photoreduction to Methanol over Freestanding Defective Single-Unit-Cell Bismuth Vanadate Layers

Unearthing an ideal model for disclosing the role of defect sites in solar CO₂ reduction remains a great challenge. Here, freestanding gram-scale single-unit-cell <i>o</i>-BiVO₄ layers are successfully synthesized for the first time. Positron annihilation spectrometry and X-ray fluorescence unveil their distinct vanadium vacancy concentrations. Density functional calculations reveal that the introduction of vanadium vacancies brings a new defect level and higher hole concentration near Fermi level, resulting in increased photoabsorption and superior electronic conductivity. The higher surface photovoltage intensity of single-unit-cell <i>o</i>-BiVO₄ layers with rich vanadium vacancies ensures their higher carriers separation efficiency, further confirmed by the increased carriers lifetime from 74.5 to 143.6 ns revealed by time-resolved fluorescence emission decay spectra. As a result, single-unit-cell <i>o</i>-BiVO₄ layers with rich vanadium vacancies exhibit a high methanol formation rate up to 398.3 μmol g^–1 h^–1 and an apparent quantum efficiency of 5.96% at 350 nm, much larger than that of single-unit-cell <i>o</i>-BiVO₄ layers with poor vanadium vacancies, and also the former’s catalytic activity proceeds without deactivation even after 96 h. This highly efficient and spectrally stable CO₂ photoconversion performances hold great promise for practical implementation of solar fuel production

Partially Oxidized SnS₂ Atomic Layers Achieving Efficient Visible-Light-Driven CO₂ Reduction

Unraveling the role of surface oxide on affecting its native metal disulfide’s CO₂ photoreduction remains a grand challenge. Herein, we initially construct metal disulfide atomic layers and hence deliberately create oxidized domains on their surfaces. As an example, SnS₂ atomic layers with different oxidation degrees are successfully synthesized. <i>In situ</i> Fourier transform infrared spectroscopy spectra disclose the COOH* radical is the main intermediate, whereas density-functional-theory calculations reveal the COOH* formation is the rate-limiting step. The locally oxidized domains could serve as the highly catalytically active sites, which not only benefit for charge-carrier separation kinetics, verified by surface photovoltage spectra, but also result in electron localization on Sn atoms near the O atoms, thus lowering the activation energy barrier through stabilizing the COOH* intermediates. As a result, the mildly oxidized SnS₂ atomic layers exhibit the carbon monoxide formation rate of 12.28 μmol g^–1 h^–1, roughly 2.3 and 2.6 times higher than those of the poorly oxidized SnS₂ atomic layers and the SnS₂ atomic layers under visible-light illumination. This work uncovers atomic-level insights into the correlation between oxidized sulfides and CO₂ reduction property, paving a new way for obtaining high-efficiency CO₂ photoreduction performances