Microwave-assisted nonaqueous synthesis of WO₃nanoparticles for crystallographically oriented photoanodes for water splitting

Abstract

Nanostructured WO 3 photoanodes with crystallographic orientation along the [001] direction were fabricated via doctor blading nanoparticles synthesized through a microwave-assisted nonaqueous solgel route. Monoclinic WO 3 platelets with a size ranging from 20 to 40 nm and a thickness of 3 nm were obtained after a short reaction time of 10 minutes under microwave irradiation. The films consisted of a porous network of nanoparticles and their photoelectrochemical activity was tested. After cathodic polarization of the photoanodes in the dark which led to a significant increase of 65% of the photocurrent, the films exhibited initially a maximum photocurrent of 2.7 mA cm À2 at 1 V vs. reversible hydrogen electrode (RHE) in 3 M H 2 SO 4 under simulated AM 1.5 G illumination (100 mW cm À2 ) comparable to the best photocurrents reported for WO 3 photoanodes. However oxygen evolution measurements showed that the faradaic efficiency dropped after the cathodic polarization and other products than O 2 might be formed. In comparison to the chemical solution growth of films from molecular precursors, the use of preformed nanoparticles in the form of powders is not only more robust and easier to up-scale, but also offers many opportunities to improve the photoelectrochemical performance by tailoring the nanoparticle size, the shape, and their arrangement on the substrate.

Commercially Available WO3 Nanopowders for Photoelectrochemical Water Splitting: Photocurrent versus Oxygen Evolution

“…The photoanodes were prepared by the doctor blade method. Preparation of the slurry for doctor blading was the same as previously published . The WO 3 nanopowder (110 mg) was mixed with acetylacetone (25 μL of 10 %) in hexyl alcohol and with acetylacetone (1.25 mL of 1 %) in isopropanol.…”

“…Preparation of the slurry for doctor blading was the same as previously published. [9] The WO 3 nanopowder (110 mg) was mixed with acetylacetone (25 mLo f1 0%)i nh exyl alcohol and with acetylacetone (1.25 mL of 1%)i ni sopropanol. The mixture was sonicated for 1h and afterwards hydroxypropyl cellulose (20 mg) was added and further stirred overnight.…”

“…[9] The use of the doctor blade method for the deposition of WO 3 nanoplatelets gave access to homogeneous and nanoporous films. [9] The versatility and suitability of the methodp rompted us to examinet he photoelectrochemicala ctivity of commercially available WO 3 nanopowders.…”

A New Facile Synthesis of Tungsten Oxide from Tungsten Disulfide: Structure Dependent Supercapacitor and Negative Differential Resistance Properties

“…All the above techniques to make WO 3 nanostructures have significant advantages and disadvantages from the points of controlling the crystal growth for shape and size, processing temperature, impurities, product yield, and homogeneity. In the microwave synthesis generally Na 2 WO 4 .2H 2 O and WCl 6 are used as precursor, which are heated in microwave reactor at 180–200 °C . Fortunato and co‐workers have reported pH dependent growth of WO 3 crystal, using Na 2 WO 4 .2H 2 O as precursor and NaCl as structure‐directing agent (SDA).…”

Reply to Comment on “Commercially Available WO3 Nanopowders for Photoelectrochemical Water Splitting: Photocurrent versus Oxygen Evolution”

“…Soc., [3] because in both papers, Augustynski et al workedw ith Keggin-type polyoxometalate electrocatalysts and/or(Na)WO 3 films, while we only used commerciallya vailable WO 3 powders.If we compare now the results from the ChemPlusChem paper with our previously published paper in J. Mater.C hem. A, [4] it is obvious that in both cases the photoanodes consisted of solelyt ungsten oxide;h owever,t he microstructures differed completely.I no ne case, [4] the photoanode was composedo f crystallographically aligned, smalln anoplatelets, whereas in the other case, [1] the particles were significantly larger with a more spherical shape and also the size distribution was significantly broader.F urthermore, the two powders used for film deposition in these two papers were made by completely different synthesis procedures. To underline the sensitivity of the films to slight microstructural changes,i ti sw orth mentioning that all three commercially tested powders presented in our paper in ChemPlusChem showedd ifferent photocurrent densities, although the films had the same compositiona nd were processedi ni dentical ways.…”