Improved Photocatalytic Water Splitting Activity of Highly Porous WO3 Photoanodes by Electrochemical H+ Intercalation

Abstract

WO3 photoanodes are widely used in photoelectrochemical catalysis, but typically the as-synthesized material is annealed before application. It is therefore desirable to explore less energy-intensive treatments. In this study, WO3 films of up to 3.9 μm thickness were obtained by galvanostatic anodization of tungsten foil in a neutral-pH Na2SO4 and NaF electrolyte, also containing a NaH2PO2 additive (to suppress O2 accumulation on the pore walls). Additionally, the WO3 photoanodes were modified by applying a cathodic reduction (H+ intercalation) and anodic activation treatment in-situ. XPS spectra revealed that intercalation modifies WO3 films; the amount of W5+-O and O-vacancy bonds was increased. Furthermore, subsequent activation leads to a decrease of the W5+ signal, but the amount of O-vacancy bonds remains elevated. The as-prepared and reduced (intercalated & activated) films were tested as OER photoanodes in acidic 0.1 M Na2SO4 media, under illumination with a 365 nm wavelength LED. It was observed that thinner films generated larger photocurrents. The peculiarities detected by XPS for reduced films correlate well with their improved photocatalytic activity. Photo-electrochemical impedance and intensity modulated photocurrent spectroscopies were combined with steady-state measurements in order to elucidate the effects of H+ intercalation on photoelectrochemical performance. The reduction results in films with enhanced photoexcited charge carrier generation/separation, improved conductivity, and possibly even suppressed bulk recombination. Thus, the intercalation & activation adopted in this study can be reliably used to improve the overall activity of as-synthesized WO3 photoanodes, and particularly of those that are initially poorly photoactive.

Plasma Electrolytic Oxidation Synthesis of Heterostructured TiO2/CuxO Films for Photoelectrochemical Water Splitting Applications

“…The increased currents are attributed to the photoelectrochemical process because the dark current does not change. This is an interesting phenomenon and has been observed for H + -intercalated WO 3 films in our previous research, 58 where it was attributed to vacancy/defect restructuring.…”

“…In practice this results in the emergence of a part of a semicircle at medium to low frequencies in the first quadrant of the complex coordinate plane. In previous research by our team, these semicircles were fitted to obtain k ct values when no recombination exists, 58 but such analysis is not widespread in IMPS studies.…”

Electrochemical Synthesis of a WO3/MoSx Heterostructured Bifunctional Catalyst for Efficient Overall Water Splitting

“…An electrochemical reduction-activation treatment was carried out to prove the possibility of further improving the PEC properties of the heterostructures. Specific experimental steps are summarized in Table 1, and have been described in detail recently [44,45]. The potential values were recalculated vs. RHE, and are presented as such throughout the study, unless it is stated otherwise.…”

Construction of [NbO]6−x‐xS Structure to Change Charge Density and Regulate Spontaneous Polarization to Achieve Efficient Pyro‐Photo‐Electric Water Splitting System of NaNbO3

“…Among the many existing efficient hydrogen production methods developed by researchers, photoelectrochemical (PEC) water splitting technology stands out among the many means of hydrogen production because of its economics, environmental friendliness and high efficiency as the best blueprint for converting solar energy into a green and sustainable energy source [7–10] . In order to maximize the PEC water splitting performance, much attention has been paid to the development of efficient photoanode materials, including TiO 2 , WO 3 , α‐Fe 2 O 3 , CdS, BiVO 4 [11–21] . However, the enhancement of PEC performance is still limited to the semiconductor itself, which often has some drawbacks.…”

“…[7][8][9][10] In order to maximize the PEC water splitting performance, much attention has been paid to the development of efficient photoanode materials, including TiO 2 , WO 3 , α-Fe 2 O 3 , CdS, BiVO 4 . [11][12][13][14][15][16][17][18][19][20][21] However, the enhancement of PEC performance is still limited to the semiconductor itself, which often has some drawbacks. This has led to the practical application of semiconductors in PEC water splitting being hampered by high charge recombination rates and low solar light utilization.…”