High‐Temperature One‐Step Synthesis of Efficient Nanostructured Bismuth Vanadate Photoanodes for Water Oxidation

Abstract

Bismuth vanadate (BiVO4) is a promising photoanode material for photoelectrochemical water splitting due to its well‐suited valence band edge and comparatively narrow band gap. First insights on the high‐temperature and scalable synthesis of efficient nanostructured BiVO4 photoanodes for water oxidation are provided. Nanostructured BiVO4 films with a tunable optical density and porosity ranging from 12% to 80% are synthesized in few seconds by direct deposition of flame‐made BiVO4 nanoparticle aerosols. The impact of the BiVO4 film structural properties on the photooxidation performance has been systematically investigated by a set of electrochemical and physical characterizations indicating key directions for its morphological optimization. It is found that the BiVO4 water oxidization performance is mainly determined by two competitive factors, viz., accessible surface area and carrier conductivity through the grain boundaries. Optimization of these two factors increases the photocurrent densities by more than three times resulting in ≈1.5 mA cm−2 for sulfite oxidation and ≈1 mA cm−2 for water oxidation with a FeOOH/NiOOH co‐catalyst at 1.0 V vs the reversible hydrogen electrode (RHE) under simulated 1 sun illumination. These findings provide novel insights into the structure–activity relationships of high‐temperature synthesized BiVO4 photoanodes for solar‐powered water splitting and introduce a scalable and low‐cost approach for their rapid nanofabrication.

Engineering Fractal Photonic Metamaterials by Stochastic Self‐Assembly of Nanoparticles

“…Notably, different semiconducting oxides, synthesized with the same condition, lead to similar ultra-porous fractal morphologies. [13,45] The intricacy of the nesting in these ultra-porous structures makes a structural and morphological analysis rather qualitative. A more quantitative analysis of the degree of complexity of these systems can be obtained via image processing analysis through box-counting algorithms.…”

“…Notably, different semiconducting oxides, synthesized with the same condition, lead to similar ultra‐porous fractal morphologies. [ 13,45 ]…”

From Stochastic Self‐Assembly of Nanoparticles to Nanostructured (Photo)Electrocatalysts for Renewable Power‐to‐X Applications via Scalable Flame Synthesis

“…Depending on the synthesis parameters such as atomization pressure, nature of materials, high temperature residence time, or temperature of substrates, the variety of physiochemical properties and morphologies of target nanomaterial are obtained. For example, highly porous films with fractal dimensions of ≈1.75 are obtained when materials have high melting/sintering points, and the temperature of substrates are retained low such as fractal ZnO, [49,50] TiO 2 , [25,51] or SnO 2 , [52] while larger stubby, oblong or columnar structures are achieved when the substrate temperature is high, and material has relatively low melting/ sintering temperatures such as BiVO 4 , [53] Bi 2 O 3 , [54,55] Co 3 O 4 [56] or WO 3 . [57] Fabrication of multicomponent/multiphases might be limited with the use of a single nozzle FSP as a uniformed distribution of each component in a multicomponent structure, rather than discrete individual component, is often obtained, i.e., the flexibility in tuning grain boundaries in a singlenozzle FSP system is limited.…”

“…Alternatively, a relatively dense film can be achieved if a substrate temperature is high, [132] and the substrate temperature can be easily controlled by changing a high above the burner (HAB). [53,57] For example, BiVO 4 electrode with a porosity ranging from ≈12% (a quasi-dense film) to of 80% (a porous film) were also formed when tuning the HAB (Figure 9b-e).…”

Using Flame-Assisted Printing to Fabricate Large Nanostructured Oxide Thin Film for Electrochromic Applications

“…Kun et al synthesized Li 4 Ti 5 O 12 thin film for the high-performance and flexible all-solid-state battery [14]. Tricoli et al [15] extended the use of FSP for the fabrication of EC/PEC water-splitting WO 3 and BiVO 4 electrodes. They found that the performance of direct FSP-made photoelectrodes had been greatly improved compared with those films cast with nanopowders from the FSP process.…”