A Building Block Approach to Photochemical Water-Splitting Catalysts Based on Layered Niobate Nanosheets

Abstract

We present a modular approach to the synthesis of nanostructured catalysts for photochemical splitting of water into hydrogen and oxygen. The catalysts are built from exfoliated, semiconducting niobate nanosheets derived from the layered perovskite HCa 2 Nb 3 O 10 . The latter is a catalyst for photochemical evolution of hydrogen from water under UV irradiation. After chemical modification with 3-aminopropyltrimethoxysilane (APS), IrO 2 or Pt particles can be attached to the nanosheets to produce various two-component nanostructures that were fully characterized with transmission electron microscopy and ultraviolet and infrared spectroscopy. Cyclic voltammetry was used to determine the onset potentials for O 2 and H 2 evolution. At pH ) 14, the observed values are in the range +0.61 to +1.24 V (NHE, water oxidation) and -1.36 to -1.62 V (NHE, water reduction). Under UV irradiation, all catalysts evolve hydrogen from water without any sign of deactivation for 5 h. The highest quantum efficiency of 3.49% is observed for a structure with Pt directly grown onto the nanosheets. No O 2 is evolved, which we attribute to the adsorption of O 2 to the catalyst surface. For Pt-[HCa 2 Nb 3 O 10 ], this process starts to shut down H 2 evolution after 9 h of constant irradiation, but the activity can be restored to >60% by evacuating the catalyst dispersion and purging it with Ar. Catalysts assembled from preformed citrate-coated Pt nanoparticles are slightly less active for H 2 evolution and so are catalysts that use the linker aminoethyl-aminoundecanetrimethoxysilane (AEAUS) instead of APS. The activity of IrO 2 -APS-[Ca 2 Nb 3 O 10 ] is lowest among two component catalysts, near the activities of the pure or APSmodified nanosheets. On the basis of XPS data, IrO 2 in this catalyst undergoes photochemical reduction to Ir(0) upon UV irradiation.

Niobate Nanosheets as Catalysts for Photochemical Water Splitting into Hydrogen and Hydrogen Peroxide

“…5,12,[24][25][26][27][28] As we reported before, dispersions of individual nanosheets are able to evolve H 2 from water under UV light, but no oxygen. [29][30][31] We now find that hydrogen evolution with the niobate sheets is coupled with stoichiometric formation of peroxide, according to eq 2. This peroxide does not form via reduction of O 2 (eq 3), since irradiation experiments conducted in the presence of O 2 mostly lead to free H 2 O 2 and only to small amounts of coordinated peroxide.…”

“…29 However, evacuating the atmosphere above the solution and then flushing with Ar gas temporarily restores the H 2 evolution rate to 60% of the original activity, as shown in Figure 2B.…”

Building Niobate Nanoparticles with Hexaniobate Lindqvist Ions

“…Figure 6(a) portrays a SEM image of (AgNb) 0.75 (SrTi) 0. 25 O 3 NPs that were annealed at 650°C for 24 h. It is apparent that changes in morphology and particle size of these NPs were rare after annealing, as were changes in composition based on the EDS spectrum of a single NP [ Figure 6 The (AgNb) 1-x (SrTi) x O 3 solid solutions, when x is less than 0.9, retains an orthorhombic crystal structure with almost consistent lattice parameters, [4,5] as do the as-prepared (AgNb) 1-x …”

Effect of H2/CO2 mixture gas treatment temperature on the activity of LaNiO3 catalyst for hydrogen production from formaldehyde aqueous solution under visible light

“…If we can synthesize a catalyst to produce hydrogen from water by harvesting sunlight, it could be a key to solve these problems. However, most of developed photocatalysts capable of splitting water can work only in the ultraviolet region [1][2][3][4][5][6][7]. To effectively utilize the visible light that accounts for 43% of the solar spectrum [8], it is therefore necessary to develop a visible-light responsive photocatalyst, and substantial efforts have been made in recent years to explore such a material.…”