Two-dimensional mesoporous vanadium phosphate nanosheets through liquid crystal templating method toward supercapacitor application

Abstract

Mesoporous vanadium phosphate (VOPO 4) nanosheets have been successfully synthesized through an easy and reproducible lyotropic liquid crystals (LLC) templating approach for the first time. Using the triblock copolymer (P123) as a surfactant, VOPO 4 precursor with a well-developed 2D hexagonal mesostructure can be obtained. Following complete removal of the template by calcination, crystallized VOPO 4 frameworks with less-ordered mesostructure are achieved. The as-prepared mesoporous VOPO 4 nanosheets exhibit superior pseudocapacitive performance (767 F g-1 at 0.5 A g-1) by virtue of the favorable mesostructure that gives rise to abundant easily accessible redox active sites as well as reinforced charge transfer and ion diffusion properties. The charge storage mechanism of the mesoporous VOPO 4 nanosheets has been experimentally demonstrated to be based on the reversible two-step redox reactions between V(V) and V(III) in acid medium. This advantageous LLC templating strategy is expected to open up a new route for the design of various mesoporous metal phosphates with superior electrochemical performance for utilization in energy storage devices.

Lyotropic Liquid Crystalline Mesophases Made of Salt‐Acid‐Surfactant Systems for the Synthesis of Novel Mesoporous Lithium Metal Phosphates

“…Here, we show that a better kinetic control over the metal phosphate formation could be achieved using phosphoric acid (PA, weak acid) as a phosphate source and by introducing lyotropic anions (such as phosphate related ions, H 2 PO 4 − , HPO 4 2− , and PO 4 3− ) for the assembly of surfactant molecules into micelles . PA‐non‐ionic surfactant and salt‐non‐ionic surfactant mesophases are all important in the process and need further exploration.…”

“…There have been also many preparation methods to produce mesoporous metal oxides by hard‐ or soft‐templating approaches. However, there are few methods to synthesize metal chalcogenides, metal phosphates, and metal sulphates which are highly important for applications in energy production and storage . To fully understand and control the properties of these materials, many efforts must be undertaken.…”

“…To fully understand and control the properties of these materials, many efforts must be undertaken. Recent investigations show that mesoporous materials (MMs) have many advantages in energy generation, conversion, and storage . MMs offer many advantages over their bulk counterparts, such as high surface area, size effects (both electronic and thermodynamic), reactivity in confined space, better electronic and ionic conductivity …”

“…Mesoporous metal phosphates (MMPs) are important in energy applications. Many transition metal phosphates are as good candidates as cathode materials in lithium ion batteries or supercapacitors . However, the synthesis of mesoporous lithium metal phosphates (LMPs) is still a big challenge.…”

“…Optimal kinetic control in the assembly process may have a positive impact on the development of high power energy storage systems . There are still limited number of synthetic methods for the successful synthesis of mesoporous metal phosphates (MMPs) and none for the LMPs in the literature . However, there have been attempts to control the formation kinetics in these processes using substituted phosphates .…”