Sol-gel synthesis of highly reproducible WO3 photoanodes for solar water oxidation

Abstract

Although monoclinic WO 3 is widely studied as a prototypical photoanode material for solar water splitting, limited success, hitherto, in fabricating WO 3 photoanodes that simultaneously demonstrate high efficiency and reproducibility has been realized. The difficulty in controlling both the efficiency and reproducibility is derived from the ever-changing structures/compositions and chemical environments of the precursors, such as peroxytungstic acid and freshly prepared tungstic acid, which render the fabrication processes of the WO 3 photoanodes particularly uncontrollable. Herein, a highly reproducible sol-gel process was developed to establish efficient and translucent WO 3 photoanodes using a chemically stable ammonium metatungstate precursor. Under standard simulated sunlight of air mass 1.5 G, 100 mW cm −2 , the WO 3 photoanode delivered photocurrent densities of ca. 2.05 and 2.25 mA cm −2 at 1.23 V versus the reversible hydrogen electrode (RHE), when tested in 1 mol L −1 H 2 SO 4 and CH 3 SO 3 H, respectively. Hence, the WO 3 photoanodes fabricated herein are one of the WO 3 photoanodes with the highest performance ever reported. The reproducibility of the fabrication scheme was evaluated by testing 50 randomly selected WO 3 samples in 1 mol L −1 H 2 SO 4 , which yielded an average photocurrent density of 1.8 mA cm −2 at 1.23 V RHE with a small standard deviation. Additionally, the effectiveness of the ammonium metatungstate precursor solution was maintained for at least 3 weeks, when compared with the associated upper-limit values of peroxytungstic and tungstic acid-based precursors after 3 d. This study presents a key step to the future development of WO 3 photoanodes for efficient solar water splitting.

Material Design and Surface/Interface Engineering of Photoelectrodes for Solar Water Splitting

“…The IPCE curves of photoelectrodes actually reflect the yields of solar photons being absorbed by semiconductors and converted into current. [ 12 ] By considering the associated three elemental steps in PEC water splitting, the IPCE can be expressed in the following formulawhere η abs is the light absorption efficiency, η sep is the bulk charge separation efficiency, and η inj is the surface charge injection efficiency, respectively.…”

“…The IPCE curves of photoelectrodes actually reflect the yields of solar photons being absorbed by semiconductors and converted into current. [12] By considering the associated three elemental steps in PEC water splitting, the IPCE can be expressed in the following formula…”

Engineering the heterogeneous interfaces of inverse opals to boost charge transfer for efficient solar water splitting

“…3e, f. The TFF inverse opal photoelectrode displayed a smaller arc radius at high frequencies of the Nyquist plots, suggesting lower charge transfer resistance (R ct ) [36,37]. Furthermore, the R ct values were obtained from the equivalent circuit model based on the EIS data (Fig.…”

Photo-assisted decoration of Ag-Pt nanoparticles on Si photocathodes for reducing overpotential toward enhanced photoelectrochemical water splitting

“…In recent decades, the development of sustainable and renewable energies has been urgently needed worldwide due to the significantly increased consumption of fossil fuels and dramatically growing environmental pollution. Among various energy sources, photoelectrochemical (PEC) water splitting, which can directly convert solar energy into chemical energy stored in H 2 and O 2 , is a promising method [1][2][3][4][5]. The semiconductor photoelectrodes play a crucial role in the overall performance of PEC water splitting.…”