Lead-free thin film capacitors, simultaneously possessing a large energy storage density, ultrahigh efficiency and an extra wide working temperature range, are desirable in applications. In this work, A2Bi4Ti5O18 (A = Ba and Sr) thin films were successfully deposited onto Pt/Ti/SiO2/Si by chemical solution deposition. A large energy storage density (Ure) of 37.1 and 17.2 J cm−3 and a high efficiency (η) of 91.5% and 80.8% were achieved in Ba2Bi4Ti5O18 and Sr2Bi4Ti5O18 thin films, respectively. Moreover, these two thin films show excellent thermal abilities under an extra wide working temperature range from −100 °C to 180 °C. Additionally, high cycling fatigue endurance with a variation of the energy storage density of less than 3.7% and efficiency less than 2.1% after 2 × 108 charge–discharge cycles is obtained for these two thin films. These results indicate that A2Bi4Ti5O18 thin film capacitors have strong potential applications in equipment in harsh working environments.

Lead-free A2Bi4Ti5O18 thin film capacitors (A = Ba and Sr) with large energy storage density, high efficiency, and excellent thermal stability

Investigation on a new multiferroic compound KBiFe2O5: Structural, optical, electrical and magnetic properties

Rhombohedral BiFeO3 thick films integrated on Si with a giant electric polarization and prominent piezoelectricity

Ferroelectrics have ignited great interest in the field of photoelectrochemistry due to the built-in electric field assisted charge separation and switchable polarization. However, low photocurrent density limits their potential application. Herein, a photoelectrochemical study of optimized ferroelectric BiFeO3 film shows that positive and negative polarization by applying an external field may lead to enhancement of the p-type light response or reverse it to an n-type light response, and the BiFeO3 film may serve as either a photoanode or photocathode depending on the polarization conditions. Nevertheless, the low photocurrent density indicates that the unique switchable spontaneous polarization of ferroelectrics has not been fully exploited, which is due to severe charge recombination at the interfaces of the domain walls rather than recombination inside the domains. In order to take full advantage of charge separation by the spontaneous polarization field of ferroelectric materials, appropriate interface/domain wall engineering is necessary.

Exploration of the intrinsic factors limiting the photocurrent density in ferroelectric BiFeO3 thin film

Multiferroic BiFeO3 (BFO) thin films with a thickness larger than 400 nm are grown on solution-derived LaNiO3 coated Si substrates via chemical solution deposition. The prepared BFO/LaNiO3/Si thin films are strongly (00l)-oriented with a distorted rhombohedral structure of R3c symmetry. The effects of the annealing temperature within the temperature range of 500–650 °C on the microstructures and properties are investigated. With an annealing temperature increasing to 600 °C, the (00l) orientation is enhanced and the grain size is increased, whereas a higher annealing temperature will lead to the deterioration of the orientation and microstructures. The annealing temperature dependent dielectric, leakage and ferroelectric properties are investigated, showing excellent properties for the low temperature annealed BFO thin films. The mechanisms about annealing temperature effects are discussed. The results will provide an effective route to realize the integration of large-area BFO thin films on Si wafers by an all-solution approach with low cost.

BiFeO3(00l)/LaNiO3/Si thin films with enhanced polarization: an all-solution approach

BiFeO3 (short for BFO) thin films with different grain sizes were fabricated via sol–gel spin-coating method. The effects of grain size on leakage behavior, dielectric, ferroelectric, piezoelectric properties and domain structure of BFO thin films have been investigated systematically. The X-ray diffraction results show that BFO thin films are rhombohedral distortion perovskite structure. Compared with the films annealed at 550 °C, the grain size of BFO thin films annealed at 600 °C is larger and the roughness is less, and the crystallinity and purity are higher. The leakage current density of BFO thin films with larger grain size is much lower than that of the films with smaller grain size. It is found that the conduction behavior of BFO thin films with smaller grain size transforms from Ohmic to space-charge-limited current and Fowler–Nordheim tunneling conduction as electric field increases. But there is the only transition from Ohmic conduction to space-charge-limited conduction for the thin films with larger grain size as electric field increase. The room temperature dielectric constant and remnant polarization of BFO thin films with larger grain size are higher than that of the films with smaller grain size. The ferroelectric domain size increases with the increase of grain size so that the ferroelectric polarization in BFO thin films with larger grain size enhances. Moreover, it is found that there are negatively charged “tail to tail” domain wall in BFO thin films with smaller grain size and positively charged “head to head” domain wall in the sample with larger grain size. The majority carriers including positively charged hole or oxygen vacancy assemble on negatively charged “tail to tail” domain wall in p-type BFO thin films with smaller grain size and result in relative higher leakage current. The piezoelectric coefficient of the films with larger grain size is much higher than that of the sample with smaller grain size.

The effects of grain size on electrical properties and domain structure of BiFeO3 thin films by sol–gel method

The broad employment of water electrolysis for hydrogen (H2) production is restricted by its large voltage requirement and low energy conversion efficiency because of the sluggish oxygen evolution reaction (OER). Herein, we report a strategy to replace OER with a thermodynamically more favorable reaction, the partial oxidation of formaldehyde to formate under alkaline conditions, using a Cu3Ag7 electrocatalyst. Such a strategy not only produces more valuable anodic product than O2 but also releases H2 at the anode with a small voltage input. Density functional theory studies indicate the H2C(OH)O intermediate from formaldehyde hydration can be better stabilized on Cu3Ag7 than on Cu or Ag, leading to a lower C-H cleavage barrier. A two-electrode electrolyzer employing an electrocatalyst of Cu3Ag7(+)||Ni3N/Ni(-) can produce H2 at both anode and cathode simultaneously with an apparent 200% Faradaic efficiency, reaching a current density of 500 mA/cm2 with a cell voltage of only 0.60 V. 

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Dual hydrogen production from electrocatalytic water reduction coupled with formaldehyde oxidation via a copper-silver electrocatalyst

Electrocatalytic dual hydrogenation of organic substrates with a Faradaic efficiency approaching 200%

https://doi.org/10.1016/j.isci.2022.104064

Guodong Li

Papers

The effects of grain size on electrical properties and domain structure of BiFeO3 thin films by sol–gel method

Dual hydrogen production from electrocatalytic water reduction coupled with formaldehyde oxidation via a copper-silver electrocatalyst

Electrocatalytic dual hydrogenation of organic substrates with a Faradaic efficiency approaching 200%

Near-infrared light photocatalysis enabled by a ruthenium complex-integrated metal–organic framework via two-photon absorption