Enhanced Visible Photocatalytic Hydrogen Evolution of KN-Based Semiconducting Ferroelectrics via Band-Gap Engineering and High-Field Poling

The Effect of Multi-Fields Synergy from Electric/Light/Thermal/Force Technologies on Photovoltaic Performance of Ba0.06 Bi0.47 Na0.47 TiO3 Ferroelectric Ceramics via the Mg/Co Substitution at A/B Sites

Currently, it is widely reported that the photovoltaic effect in ferroelectric materials can be promoted by the application of a piezoelectric force, an external electric field, and intense light illumination. Here, a semiconducting ferroelectric composition is introduced, (1-x) Ba0.06 Bi0.47 Na0.47 TiO3 -xMgCoO3 (abbreviated as xMgCo, where x = 0.02-0.08), synthesized through Mg/Co ions codoping. This process effectively narrows the optical bandgaps to a spectrum of 1.38-3.06 eV. Notably, the system exhibits a substantial increase in short-circuit photocurrent density (Jsc ), by the synergy of the electric, light, and thermal fields. The Jsc can still be further enhanced by the extra introduction of a force field. Additionally, the Jsc also shows an obvious increase after the high field pre-poling. The generation of a considerable number of oxygen vacancies due to the Co2+ /Co3+ mixed valence state (in a 1:3 ratio) contributes to the reduced optimal bandgap. The integration of Mg2+ ion at the A-site restrains the loss and sustains robust ferroelectricity (Pr  = 24.1 µC cm-2 ), high polarizability under an electric field, and a significant piezoelectric coefficient (d33  = 102 pC N-1 ). This study provides a novel perspective on the physical phenomena arising from the synergy of multiple fields in ferroelectric photovoltaic materials.

Effect of Poling on Multicatalytic Performance of 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Sr0.3)TiO3 Ferroelectric Ceramic for Dye Degradation

Ferroelectric materials with a spontaneous polarization are proven to be potential multicatalysts in water remediation applications. The composition of 0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Sr_0.3)TiO₃ (BST-BZT) was examined for photocatalysis, piezocatalysis, and piezo-photocatalysis processes by degrading an azo dye named methylene blue (MB). Generally, dis-aligned dipoles restrict the catalytic activities due to which the BST-BZT powder sample was poled by the corona poling technique. Coupled piezocatalysis and photocatalysis process, i.e., the piezo-photocatalysis process has shown maximum dye degradation. There was a significant improvement in degradation efficiency by using a poled BST-BZT sample compared to the unpoled sample in all processes, thus the results suggest an extensive scope of poled ferroelectric ceramic powder in the catalysis field.

[Fe2S2-Agx]-Hydrogenase Active-Site-Containing Coordination Polymers and Their Photocatalytic H2 Evolution Reaction Properties

Three [Fe₂S₂-Ag_x]-hydrogenase active-site-containing coordination polymers (CPs), {[Fe₂S₂-Ag₁](4-cpmt)₂(CO)₆(ClO₄^-)}_n (1), {[Fe₂S₂-Ag₂](4-cpmt)₂(CO)₆(OTf^-)₂(benzene)}_n (2), and {[Fe₂S₂-Ag₂](3-cpmt)₂(CO)₆(ClO₄^-)₂}_n (3), were obtained by a direct synthesis method from ligands [FeFe](4-cpmt)₂(CO)₆ [L1; 4-cpmt = (4-cyanophenyl)methanethiolate] and [FeFe](3-cpmt)₂(CO)₆ [L2; 3-cpmt = (3-cyanophenyl)methanethiolate] with silver salts. 1-3 represent the first examples of [FeFe]-hydrogenase-based CPs. It was worth noting that the Ag-S bonding between the Ag centers and S atoms of a [Fe₂S₂] cluster produced a novel [Fe₂S₂-Ag_x] (x = 1 or 2) catalytic site in all three polymers. The results of photochemical H₂ generation experiments indicated that 2 and 3 containing [Fe₂S₂-Ag₂] active sites showed obviously improved catalytic performances compared with ligands L1 and L2 and [Fe₂S₂-Ag₁]-containing 1. This work provides a pioneering strategy for the direct synthesis of [Fe₂S₂]-based CPs or metal-organic frameworks.