Graph Neural Network-Accelerated Multitasking Genetic Algorithm for Optimizing PdxTi1-xHy Surfaces under Various CO2 Reduction Reaction Conditions.

Palladium (Pd) hydride-based catalysts have been reported to have excellent performance in the CO2 reduction reaction (CO2RR) and hydrogen evolution reaction (HER). Our previous work on doped PdH and Pd alloy hydrides showed that Ti-doped and Ti-alloyed Pd hydrides could improve the performance of the CO2 reduction reaction compared with pure Pd hydride. Compositions and chemical orderings of the surfaces with only one adsorbate under certain reaction conditions are linked to their stability, activity, and selectivity toward the CO2RR and HER, as shown in our previous work. In fact, various coverages, types, and mixtures of the adsorbates, as well as state variables such as temperature, pressure, applied potential, and chemical potential, could impact their stability, activity, and selectivity. However, these factors are usually fixed at common values to reduce the complexity of the structures and the complexity of the reaction conditions in most theoretical work. To address the complexities above and the huge search space, we apply a deep learning-assisted multitasking genetic algorithm to screen for PdxTi1-xHy surfaces containing multiple adsorbates for CO2RR under different reaction conditions. The ensemble deep learning model can greatly speed up the structure relaxations and retain a high accuracy and low uncertainty of the energy and forces. The multitasking genetic algorithm simultaneously finds globally stable surface structures under each reaction condition. Finally, 23 stable structures are screened out under different reaction conditions. Among these, Pd0.56Ti0.44H1.06 + 25%CO, Pd0.31Ti0.69H1.25 + 50%CO, Pd0.31Ti0.69H1.25 + 25%CO, and Pd0.88Ti0.12H1.06 + 25%CO are found to be very active for CO2RR and suitable to generate syngas consisting of CO and H2.

High-throughput Compositional Screening of PdxTi1-xHy and PdxNb1-xHy Hydrides for CO2 Reduction.

Electrochemical experiments and theoretical calculations have shown that Pd-based metal hydrides can perform well for the CO2 reduction reaction (CO2RR). Our previous work on doped-PdH showed that doping Ti and Nb into PdH can improve the CO2RR activity, suggesting that the Pd alloy hydrides with better performance are likely to be found in the PdxTi1-xHy and PdxNb1-xHy phase space. However, the vast compositional and structural space with different alloy hydride compositions and surface adsorbates, makes it intractable to screen out the stable and active PdxM1-xHy catalysts using density functional theory calculations. Herein, an active learning cluster expansion (ALCE) surrogate model equipped with Monte Carlo simulated annealing (MCSA), a CO* binding energy filter and a kinetic model are used to identify promising PdxTi1-xHy and PdxNb1-xHy catalysts with high stability and superior activity. Using our approach, we identify 24 stable and active candidates of PdxTi1-xHy and 5 active candidates of PdxNb1-xHy. Among these candidates, the Pd0.23Ti0.77H, Pd0.19Ti0.81H0.94, and Pd0.17Nb0.83H0.25 are predicted to display current densities of approximately 5.1, 5.1 and 4.6 µA cm-2 at -0.5 V overpotential, respectively, which are significantly higher than that of PdH at 3.7 µA cm-2.

Metal-Doped PdH(111) Catalysts for CO2 Reduction.

PdH-based catalysts hold promise for both CO2 reduction to CO and the hydrogen evolution reaction. Density functional theory is used to systematically screen for stability, activity, and selectivity of transition metal dopants in PdH. The transition metal elements Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Ag, Cd, Hf, Ta, W, and Re are doped into PdH(111) surface with six different doping configurations: single, dimer, triangle, parallelogram, island, and overlayer. We find that several dopants, such as Ti and Nb, have excellent predicted catalytic activity and CO2 selectivity compared to the pure PdH hydride. In addition, they display good stability due to their negative doping formation energy. The improved performance can be assigned to reaction intermediates forming two bonds consisting of one C-Metal and one O-Metal bond on the PdH surface, which break the scaling relations of intermediates, and thus have stronger HOCO* binding facilitating CO2 activation.

Photodepositing CdS on the Active Cyano Groups Decorated g-C3 N4 in Z-Scheme Manner Promotes Visible-Light-Driven Hydrogen Evolution.

g-C3 N4 /CdS heterojunctions are potential photocatalysts for hydrogen production but their traditional type-II configuration generally leads to weak oxidative and reductive activity. How to construct the novel Z-scheme g-C3 N4 /CdS counterparts to address this issue remains a great challenge in this field. In this work, a new direct Z-scheme heterojunction of defective g-C3 N4 /CdS is designed by introducing cyano groups (NC-) as the active bridge sites. Experimental observations in combination with density functional theory (DFT) calculations reveal that the unique electron-withdrawing feature of cyano groups in the defective g-C3 N4 /CdS heterostructure can endow this photocatalyst with numerous advantageous properties including high light absorption ability, strong redox performance, satisfactory charge separation efficiency, and long lifetime of charge carriers. Consequently, the resultant photocatalytic system exhibits more active performance than CdS and g-C3 N4 under visible light and reaches an excellent hydrogen evolution rate of 1809.07 µmol h-1 g-1 , which is 6.09 times higher than pristine g-C3 N4 . Moreover, the defective g-C3 N4 /CdS photocatalyst maintains good stability after 40 h continuous test. This work provides new insights into design and construction of Z-scheme heterojunctions for regulating the visible-light-induced photocatalytic activity for H2 evolution.

Transforming Photocatalytic g-C3 N4 /MoSe2 into a Direct Z-Scheme System via Boron-Doping: A Hybrid DFT Study.

Z-scheme photocatalytic systems are an ideal band alignment structure for photocatalysis because of the high separation efficiency of photo-induced carriers while simultaneously preserving the strong reduction activity of electrons and oxidation activity of holes. However, the design and construction of Z-scheme photocatalysts is challenging because of the need for appropriate energy band alignment and built-in electric field. Here, we propose a novel approach to a Z-scheme photocatalytic system using density functional theory calculations with the HSE06 hybrid functional. The undesirable type-I g-C3 N4 /MoSe2 heterojunction is transformed into a direct Z-scheme system through boron doping of g-C3 N4 (B-doped C3 N4 /MoSe2 ). Detailed analysis of the total and partial density of states, work functions and differential charge density distribution of the B-doped C3 N4 /MoSe2 heterojunction shows the proper band alignment and existence of a built-in electric field at the interface, with the direction from g-C3 N4 to MoSe2 , demonstrating a direct Z-scheme heterojunction. Further investigation on the absorption spectra reveals a large enhancement of the light absorption efficiency after boron doping. The results consistently confirm that electronic structures and photocatalytic performance can be effectively manipulated by a facile boron doping. Modulating the band alignment of heterojunctions in this way provides valuable insights for the rational design of highly efficient heterojunction-based photocatalytic systems.

Coupling a Sponge Metal Fibers Skeleton with In Situ Surface Engineering to Achieve Advanced Electrodes for Flexible Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) are regarded as promising next-generation energy storage systems, however, the uncontrollable dendrite formation and serious polysulfide shuttling severely hinder their commercial success. Herein, a powerful 3D sponge nickel (SN) skeleton plus in situ surface engineering strategy, to address these issues synergistically, is reported, and a high-performance flexible LSB device is constructed. Specifically, the rationally designed spray-quenched lithium metal on the SN matrix (solid electrolyte interface (SEI)@Li/SN), as dendrite inhibitor, combines the merits of the 3D lithiophilic SN skeleton and the in situ formed SEI layer derived from the spray-quenching process, and thereby exhibits a steady overpotential within 75 mV for 1500 h at 5 mA cm-2 /10 mA h cm-2 . Meanwhile, in situ surface sulfurization of the SN skeleton hybridizing with the carbon/sulfur composite (SC@Ni3 S2 /SN) serves as efficient lithium polysulfide adsorbent to catalyze the overall reaction kinetics. COMSOL Multiphysics simulations and density functional theory calculations are further conducted to explore the underlying mechanisms. As a proof of concept, the well-designed SEI@Li/SN||SC@Ni3 S2 /SN full cell shows excellent electrochemical performance with a negative/positive ratio in capacity of ≈2 and capacity retention of 99.82% at 1 C under mechanical deformation. The novel design principles of these materials and electrodes successfully shed new light on the development of flexible LSBs.

Metal-Based Nanocatalysts via a Universal Design on Cellular Structure.

Metal-based nanocatalysts supported on carbon have significant prospect for industry. However, a straightforward method for efficient and stable nanocatalysts still remains extremely challenging. Inspired by the structure and comptosition of cell walls and membranes, an ion chemical bond anchoring, an in situ carbonization coreduction process, is designed to obtain composite catalysts on N-doped 2D carbon (C-N) loaded with various noble and non-noble metals (for example, Pt, Ru, Rh, Pd, Ag, Ir, Au, Co, and Ni) nanocatalysts. These 2 nm particles uniformly and stably bond with the C-N support since the agglomeration and growth are suppressed by anchoring the metal ions on the cell wall and membrane during the carbonization and reduction reactions. The Pt@C-N exhibits excellent catalytic activity and long-term stability for the hydrogen evolution reaction, and the relative overpotential at 100 mA cm-2 is only 77 mV, which is much lower than that of commercial Pt/C and Pt single-atom catalysts reported recently.

Boosting fast energy storage by synergistic engineering of carbon and deficiency.

Exploring advanced battery materials with fast charging/discharging capability is of great significance to the development of modern electric transportation. Herein we report a powerful synergistic engineering of carbon and deficiency to construct high-quality three/two-dimensional cross-linked Ti2Nb10O29-x@C composites at primary grain level with conformal and thickness-adjustable boundary carbon. Such exquisite boundary architecture is demonstrated to be capable of regulating the mechanical stress and concentration of oxygen deficiency for desired performance. Consequently, significantly improved electronic conductivity and enlarged lithium ion diffusion path, shortened activation process and better structural stability are realized in the designed Ti2Nb10O29-x@C composites. The optimized Ti2Nb10O29-x@C composite electrode shows fast charging/discharging capability with a high capacity of 197 mA h g-1 at 20 C (∼3 min) and excellent long-term durability with 98.7% electron and Li capacity retention over 500 cycles. Most importantly, the greatest applicability of our approach has been demonstrated by various other metal oxides, with tunable morphology, structure and composition.

Defect Promoted Capacity and Durability of N-MnO2- x Branch Arrays via Low-Temperature NH3 Treatment for Advanced Aqueous Zinc Ion Batteries.

Defect engineering (doping and vacancy) has emerged as a positive strategy to boost the intrinsic electrochemical reactivity and structural stability of MnO2 -based cathodes of rechargeable aqueous zinc ion batteries (RAZIBs). Currently, there is no report on the nonmetal element doped MnO2 cathode with concomitant oxygen vacancies, because of its low thermal stability with easy phase transformation from MnO2 to Mn3 O4 (≥300 °C). Herein, for the first time, novel N-doped MnO2- x (N-MnO2- x ) branch arrays with abundant oxygen vacancies fabricated by a facile low-temperature (200 °C) NH3 treatment technology are reported. Meanwhile, to further enhance the high-rate capability, highly conductive TiC/C nanorods are used as the core support for a N-MnO2- x branch, forming high-quality N-MnO2- x @TiC/C core/branch arrays. The introduced N dopants and oxygen vacancies in MnO2 are demonstrated by synchrotron radiation technology. By virtue of an integrated conductive framework, enhanced electron density, and increased surface capacitive contribution, the designed N-MnO2- x @TiC/C arrays are endowed with faster reaction kinetics, higher capacity (285 mAh g-1 at 0.2 A g-1 ) and better long-term cycles (85.7% retention after 1000 cycles at 1 A g-1 ) than other MnO2 -based counterparts (55.6%). The low-temperature defect engineering sheds light on construction of advanced cathodes for aqueous RAZIBs.

Synergistic Doping and Intercalation: Realizing Deep Phase Modulation on MoS2 Arrays for High-Efficiency Hydrogen Evolution Reaction.

A synergistic N doping plus PO4 3- intercalation strategy is used to induce high conversion (ca. 41 %) of 2H-MoS2 into 1T-MoS2 , which is much higher than single N doping (ca. 28 %) or single PO4 3- intercalation (ca. 10 %). A scattering mechanism is proposed to illustrate the synergistic phase transformation from the 2H to the 1T phase, which was confirmed by synchrotron radiation and spherical aberration TEM. To further enhance reaction kinetics, the designed (N,PO4 3- )-MoS2 nanosheets are combined with conductive vertical graphene (VG) skeleton forming binder-free arrays for high-efficiency hydrogen evolution reaction (HER). Owing to the decreased band gap, lower d-band center, and smaller hydrogen adsorption/desorption energy, the designed (N,PO4 3- )-MoS2 /VG electrode shows excellent HER performance with a lower Tafel slope and overpotential than N-MoS2 /VG, PO4 3- -MoS2 /VG counterparts, and other Mo-base catalysts in the literature.

Coupled Biphase (1T-2H)-MoSe2 on Mold Spore Carbon for Advanced Hydrogen Evolution Reaction.

Performance breakthrough of MoSe2 -based hydrogen evolution reaction (HER) electrocatalysts largely relies on sophisticated phase modulation and judicious innovation on conductive matrix/support. In this work the controllable synthesis of phosphate ion (PO43- ) intercalation induced-MoSe2 (P-MoSe2 ) nanosheets on N-doped mold spore carbon (N-MSC) forming P-MoSe2 /N-MSC composite electrocatalysts is realized. Impressively, a novel conductive N-MSC matrix is constructed by a facile mold fermentation method. Furthermore, the phase of MoSe2 can be modulated by a simple phosphorization strategy to realize the conversion from 2H-MoSe2 to 1T-MoSe2 to produce biphase-coexisted (1T-2H)-MoSe2 by PO43- intercalation (namely, P-MoSe2 ), confirmed by synchrotron radiation technology and spherical aberration-corrected TEM (SACTEM). Notably, higher conductivity, lower bandgap and adsorption energy of H+ are verified for the P-MoSe2 /N-MSC with the help of density functional theory (DFT) calculation. Benefiting from these unique advantages, the P-MoSe2 /N-MSC composites show superior HER performance with a low Tafel slope (≈51 mV dec-1 ) and overpotential (≈126 mV at 10 mA cm-1 ) and excellent electrochemical stability, better than 2H-MoSe2 /N-MSC and MoSe2 /carbon nanosphere (MoSe2 /CNS) counterparts. This work demonstrates a new kind of carbon material via biological cultivation, and simultaneously unravels the phase transformation mechanism of MoSe2 by PO43- intercalation.

Tailoring Bandgap of Perovskite BaTiO3 by Transition Metals Co-Doping for Visible-Light Photoelectrical Applications: A First-Principles Study.

The physical and chemical properties of V-M″ and Nb-M″ (M″ is 3d or 4d transition metal) co-doped BaTiO3 were studied by first-principles calculation based on density functional theory. Our calculation results show that V-M″ co-doping is more favorable than Nb-M″ co-doping in terms of narrowing the bandgap and increasing the visible-light absorption. In pure BaTiO3, the bandgap depends on the energy levels of the Ti 3d and O 2p states. The appropriate co-doping can effectively manipulate the bandgap by introducing new energy levels interacting with those of the pure BaTiO3. The optimal co-doping effect comes from the V-Cr co-doping system, which not only has smaller impurity formation energy, but also significantly reduces the bandgap. Detailed analysis of the density of states, band structure, and charge-density distribution in the doping systems demonstrates the synergistic effect induced by the V and Cr co-doping. The results can provide not only useful insights into the understanding of the bandgap engineering by element doping, but also beneficial guidance to the experimental study of BaTiO3 for visible-light photoelectrical applications.