Highly Efficient Sunlight‐Driven Seawater Splitting in a Photoelectrochemical Cell with Chlorine Evolved at Nanostructured WO₃ Photoanode and Hydrogen Stored as Hydride within Metallic Cathode

Abstract

semiconductor photocatalytic particles, pure water is generally used and both reduction and oxidation reaction products, H 2 and O 2 , are formed in the same cell compartment and should be subsequently separated. [2,3] On the other hand, employing a photoelectrolysis cell with separated anodic and cathodic compartments imposes use of a supporting electrolyte with ionic conductivity large enough to avoid excessive Ohmic losses within the cell. [4,6] The choice of the appropriate electrolyte is even more important when relatively thick nanoporous film photoelectrodes with high internal photoactive surface area are employed, where too low conductivity of the electrolyte may adversely affect the amount of collected photocurrent due to uneven current distribution across the semiconductor film. [7] Consequently, in addition to pure water, also the chemicals required to prepare electrolyte for the photoelectrolysis cell will potentially constitute a nonnegligible part of the operational cost of larger scale photoelectrochemical (PEC) water splitting devices. The fact that cannot at all be neglected-extensive utilization for electrolysis of fresh water would put heavy pressure on vital water resources.Since the seawater is a free and widely abundant electrolyte, there were various attempts to use it in the PEC [8][9][10][11][12][13] and conventional electrochemical [14] devices to produce hydrogen. From the practical viewpoint, the photoelectrolysis of seawater requires at first identification of photoanode materials stable in the presence of chloride ions under highly oxidizing conditions. Only few among works reported on the PEC seawater splitting describe experiments conducted under visible light irradiation. An electrode consisting of molybdenum-doped bismuth vanadate (Mo-BiVO 4 ) reached, under simulated AM 1.5G (100 mW cm −2 ) illumination, a photocurrent of 2.2 mA cm −2 at 1 V versus RHE (reversible hydrogen electrode). [9] Loading the Mo-BiVO 4 electrode with precious metal RhO 2 catalyst was effective in limiting to ≈10% the drop of the photocurrent over a 5 h long stability test. Analysis of the photoelectrolysis A seawater splitting photoelectrochemical cell featuring a nanostructured tungsten trioxide photoanode that exhibits very high and stable photocurrents producing chlorine with average 70% Faradaic efficiency is described. Fabrication of the WO 3 electrodes on fluorine-doped tin oxide substrates involves a simple solution-based method and sequential layer-by-layer deposition with a progressively adjusted amount of structure-directing agent in the precursor and a two-step annealing. Such a procedure allows tailoring of thick, highly porous, structurally stable WO 3 films with a large internal photoactive surface area optimizing utilization of visible light wavelengths by the photoanode. With the application of an anodic potential of 0.76 V versus Ag/AgCl reference electrode (0.4 V below the thermodynamic Cl 2 /Cl − potential) in synthetic seawater, the designed WO 3 photoanodes irradiated with simulated ...

Photo-Chlorine Production with Hydrothermally Grown and Vacuum-Annealed Nanocrystalline Rutile

“…A RuO 2 /TiO 2 / n-Si photoanode hybrid has been shown to provide high yields of photo-chlorine in brine [17]. Another alternative electrode reported for use in photo-chlorine evolution is based on n-type semiconductor WO 3 films [18][19][20][21][22], with a relatively smaller band gap, better light absorption up to 500-nm wave ength, cost-effective manufacturing, and long-term stability. However, when employing effective band gap-matched LED light sources, TiO 2 -based materials become competitive and practical as there are no significant problems with spectral losses.…”

Enhanced Photoelectrochemical Water Oxidation Performance in Bilayer TiO2/α‐Fe2O3 Nanorod Arrays Photoanode with Cu : NiOx as Hole Transport Layer and Co−Pi as Cocatalyst

“…Suitable semiconductor materials are of great importance to design promising photoelectrochemical (PEC) devices. [1][2][3] In recent years, some n-type semiconductors, such as α-Fe 2 O 3 , [4,5] TiO 2 , [6,7] WO 3 , [8,9] and BiVO 4 [10,11] have been widely investigated as photoanodes due to their nontoxicity, earth abundant property, and wide spectral photoresponse sensitivity. Among these materials, α-Fe 2 O 3 is recognized as an ideal candidate for PEC solar water splitting because of its suitable bandgap (1.9-2.3 eV) for excellent capability of visible light harvesting.…”

WO3 Inversce Opal Photonic Crystals: Unique Property, Synthetic Methods and Extensive Application

“…[ 1‐2 ] Owing to these great properties, it has been widely used in environmental remediation, energy storage, electrochromic device and solar cells. [ 3‐6 ] Nevertheless, its further application is still restrained by some disadvantages including low surface area, slow electron transfer, inadequate utilization of light irradiation and high recombination of photo‐excited carriers.…”