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Efficient and selective CO 2 electroreduction into chemical fuels promises to alleviate environmental pollution and energy crisis, but it relies on catalysts with controllable product selectivity and reaction path. Here, by means of first-principles calculations, we identify six ferroelectric catalysts comprising transition-metal atoms anchored on In 2 Se 3 monolayer, whose catalytic performance can be controlled by ferroelectric switching based on adjusted d -band center and occupation of supported metal atoms. The polarization dependent activation allows effective control of the limiting potential of CO 2 reduction on TM@In 2 Se 3 (TM = Ni, Pd, Rh, Nb, and Re) as well as the reaction paths and final products on Nb@In 2 Se 3 and Re@In 2 Se 3 . Interestingly, the ferroelectric switching can even reactivate the stuck catalytic CO 2 reduction on Zr@In 2 Se 3 . The fairly low limiting potential and the unique ferroelectric controllable CO 2 catalytic performance on atomically dispersed transition-metals on In 2 Se 3 clearly distinguish them from traditional single atom catalysts, and open an avenue toward improving catalytic activity and selectivity for efficient and controllable electrochemical CO 2 reduction reaction. Electroreduction of CO 2 into chemical fuels holds promise for mitigating environmental pollution and energy crisis. This work presents a distinct design of ferroelectric catalysts with high catalytic activity and selectivity for efficient and controllable electrochemical CO 2 reduction reaction.

Epitaxial growth of atomically thin two-dimensional crystals such as transition metal dichalcogenides remains challenging, especially for producing large-size transition metal dichalcogenides bilayer crystals featuring high density of states, carrier mobility and stability at room temperature. Here we achieve in epitaxial growth of the second monolayer from the first monolayer by reverse-flow chemical vapor epitaxy and produce high-quality, large-size transition metal dichalcogenides bilayer crystals with high yield, control, and reliability. Customized temperature profiles and reverse gas flow help activate the first layer without introducing new nucleation centers leading to near-defect-free epitaxial growth of the second layer from the existing nucleation centers. A series of bilayer crystals including MoS 2 and WS 2 , ternary Mo 1−x W x S 2 and quaternary Mo 1−x W x S 2(1−y) Se 2y are synthesized with variable structural configurations and tunable electronic and optical properties. The robust, potentially universal approach for the synthesis of large-size transition metal dichalcogenides bilayer single crystals is highly-promising for fundamental studies and technological applications. Epitaxial growth of the two-dimensionally thin material flakes with effective layer number and shape calls for precise control over temperature and carrier gas. Here, authors report controlled epitaxial growth of the second layer vertically for MoS2, WS2, MoWS and MoWSSe compounds by reverse hydrogen gas flow chemical vapor epitaxy.

The hydrogenation of nitrobenzene into aniline is one of industrially important reactions, but still remains great challenge due to the lack of highly active, chemo-selective and eco-friendly catalyst. By using extensive density functional theory (DFT) calculations, herein we predict that single Pt atom decorated g-C 3 N 4 (Pt@g-C 3 N 4 ) exhibits excellent catalytic activity and selectivity for the conversion of nitrobenzene into aniline under visible light. The overall activation energy barrier for the hydrogenation of nitrobenzene on single atom Pt@g-C 3 N 4 catalyst is even lower than that of the bare Pt(111) surface. The dissociation of N–O bonds on single Pt atom is triggered by single hydrogen atom rather than double hydrogen atoms on the Pt(111) surface. Moreover, the Pt@g-C 3 N 4 catalyst exhibits outstanding chemoselectivity towards the common reducible substituents, such as phenyl,–C=C,–C≡C and–CHO groups during the hydrogenation. In addition, the doped single Pt atom can significantly enhance the photoconversion efficiency by broadening the light absorption of the pristine g-C 3 N 4 to visible light region. Our results highlight an interesting and experimentally synthesized single-atom photocatalyst (Pt@g-C 3 N 4 ) for efficient hydrogenation of nitrobenzene to aniline under a sustainable and green approach.

Scalable and sustainable solar hydrogen production through photocatalytic water splitting requires highly active and stable earth-abundant co-catalysts to replace expensive and rare platinum. Here we employ density functional theory calculations to direct atomic-level exploration, design and fabrication of a MXene material, Ti 3 C 2 nanoparticles, as a highly efficient co-catalyst. Ti 3 C 2 nanoparticles are rationally integrated with cadmium sulfide via a hydrothermal strategy to induce a super high visible-light photocatalytic hydrogen production activity of 14,342 μmol h −1 g −1 and an apparent quantum efficiency of 40.1% at 420 nm. This high performance arises from the favourable Fermi level position, electrical conductivity and hydrogen evolution capacity of Ti 3 C 2 nanoparticles. Furthermore, Ti 3 C 2 nanoparticles also serve as an efficient co-catalyst on ZnS or Zn x Cd 1− x S. This work demonstrates the potential of earth-abundant MXene family materials to construct numerous high performance and low-cost photocatalysts/photoelectrodes. Solar hydrogen production through photocatalytic water splitting requires active and stable co-catalysts to replace platinum. Here, the authors use DFT to identify Ti 3 C 2 nanoparticles as potential co-catalysts, and assess their photocatalytic hydrogen production activity.

Metal oxides are promising for photoelectrochemical (PEC) water splitting due to their robustness and low cost. However, poor charge carrier transport impedes their activity, particularly at low-bias voltage. Here we demonstrate the unusual effectiveness of phosphorus doping into bismuth vanadate (BiVO 4 ) photoanode for efficient low-bias PEC water splitting. The resulting BiVO 4 photoanode shows a separation efficiency of 80% and 99% at potentials as low as 0.6 and 1.0 V RHE , respectively. Theoretical simulation and experimental analysis collectively verify that the record performance originates from the unique phosphorus-doped BiVO 4 configuration with concurrently mediated carrier density, trap states, and small polaron hopping. With NiFeO x cocatalyst, the BiVO 4 photoanode achieves an applied bias photon-to-current efficiency of 2.21% at 0.6 V RHE . The mechanistic understanding of the enhancement of BiVO 4 properties provides key insights in trap state passivation and polaron hopping for most photoactive metal oxides. While photoelectrochemical water splitting produces fuel from solar energy, a large fraction of photoanode photoexcited charge carriers cannot be extracted efficiently at low bias voltages. Here, authors improve the charge transport in P-doped BiVO 4 by mediating polaron hopping and trap states.

Lead (Pb) free non-toxic perovskite solar cells have become more important in the commercialization of the photovoltaic devices. In this study the structural, electronic, optical and mechanical properties of Pb-free inorganic metal halide cubic perovskites CsBX 3 (B = Sn, Ge; X = I, Br, Cl) for perovskite solar cells are simulated using first-principles Density Functional Theory (DFT). These compounds are semiconductors with direct band gap energy and mechanically stable. Results suggest that the materials have high absorption coefficient, low reflectivity and high optical conductivity with potential application in solar cells and other optoelectronic energy devices. On the basis of the optical properties, one can expect that the Germanium (Ge) would be a better replacement of Pb as Ge containing compounds have higher optical absorption and optical conductivity than that of Pb containing compounds. A combinational analysis of the electronic, optical and mechanical properties of the compounds suggests that CsGeI 3 based perovskite is the best Pb-free inorganic metal halide semiconductor for the solar cell application. However, the compound with solid solution of CsGe(I 0.7 Br 0.3 ) 3 is found to be mechanically more ductile than CsGeI 3 . This study will also guide to obtain Pb-free organic perovskites for optoelectronic devices.

Two-dimensional (2D) atomic crystal superlattices integrate diverse 2D layered materials enabling adjustable electronic and optical properties. However, tunability of the interlayer gap and interactions remain challenging. Here we report a solution based on soft oxygen plasma intercalation. 2D atomic crystal molecular superlattices (ACMSs) are produced by intercalating O 2 + ions into the interlayer space using the plasma electric field. Stable molecular oxygen layer is formed by van der Waals interactions with adjacent transition metal dichalcogenide (TMD) monolayers. The resulting interlayer gap expansion can effectively isolate TMD monolayers and impart exotic properties to homo-(MoS 2 [O 2 ] x ) and hetero-(MoS 2 [O 2 ] x /WS 2 [O 2 ] x ) stacked ACMSs beyond typical capacities of monolayer TMDs, such as 100 times stronger photoluminescence and 100 times higher photocurrent. Our potentially universal approach to tune interlayer stacking and interactions in 2D ACMSs may lead to exotic superlattice properties intrinsic to monolayer materials such as direct bandgap pursued for future optoelectronics. Two-dimensional (2D) atomic crystal superlattices offer technological opportunities beyond the reach of existing materials. Here, the authors produce 2D atomic crystal molecular superlattices by intercalating O 2 molecules into the interlayer space of 2D materials using a soft plasma strategy.

Developing of lead-free double perovskites have drawn significant interest for photovoltaics and optoelectronics as the materials have the potential to avoid toxicity and instability issues associated with lead-based organometallic perovskites. In this study, we report the optoelectronic properties of a new group of non-toxic lead-free organic-inorganic halide double perovskites composed of caesium (Cs), methylammonium (MA) or formamidinium (FA) with bismuth (Bi) and metal copper (Cu). We perform density functional theory investigations to calculate the structural, electronic and optical properties of 18 Pb-free compounds, ABiCuX 6 [A = Cs 2 , (MA) 2 , (FA) 2 , CsMA, CsFA, MAFA; X = I, Br, Cl] to predict their suitability in photovoltaic and optoelectronic applications. We found that the considered compounds are semiconductors with a tunable band gap characteristics that are suitable for some devices like light emitting diodes. In addition to this, the high dielectric constant, high absorption, high optical conductivity and low reflectivity suggest that the materials have the potential in a wide range of optoelectronic applications including solar cells. Furthermore, we predict that the organic-inorganic hybrid double perovskite (FA) 2 BiCuI 6 is the best candidate in photovoltaic and optoelectronic applications as the material has superior optical and electronic properties.

Active sites identification in metal-free carbon materials is crucial for developing practical electrocatalysts, but resolving precise configuration of active site remains a challenge because of the elusive dynamic structural evolution process during reactions. Here, we reveal the dynamic active site identification process of oxygen modified defective graphene. First, the defect density and types of oxygen groups were precisely manipulated on graphene, combined with electrocatalytic performance evaluation, revealing a previously overlooked positive correlation relationship between the defect density and the 2 e - oxygen reduction performance. An electrocatalytic-driven oxygen groups redistribution phenomenon was observed, which narrows the scope of potential configurations of the active site. The dynamic evolution processes are monitored via multiple in-situ technologies and theoretical spectra simulations, resolving the configuration of major active sites (carbonyl on pentagon defect) and key intermediates (*OOH), in-depth understanding the catalytic mechanism and providing a research paradigm for metal-free carbon materials. Active sites identification in metal-free carbon materials is crucial for developing practical electrocatalysts. Here the authors report a dynamic active site evolution phenomenon on oxygen modified defective graphene during electrochemical H2O2 production.