RESUMEN
Photoelectrochemical (PEC) devices that use semiconductors to absorb solar light for water splitting offer a promising way toward the future scalable production of renewable hydrogen fuels. However, the charge recombination in the photoanode/electrolyte (solid/liquid) junction is a major energy loss and hampers the PEC performance from being efficient. Here, we show that this problem is addressed by the conformal deposition of an ultrathin p-type NiO layer on the photoanode to create a buried p/n junction as well as to reduce the charge recombination at the surface trapping states for the enlarged surface band bending. Further, the in situ formed hydroxyl-rich and hydroxyl-ion-permeable NiOOH enables the dual catalysts of CoO(x) and NiOOH for the improved water oxidation activity. Compared to the CoO(x) loaded BiVO4 (CoO(x)/BiVO4) photoanode, the â¼6 nm NiO deposited NiO/CoO(x)/BiVO4 photoanode triples the photocurrent density at 0.6 V(RHE) under AM 1.5G illumination and enables a 1.5% half-cell solar-to-hydrogen efficiency. Stoichiometric oxygen and hydrogen are generated with Faraday efficiency of unity over 12 h. This strategy could be applied to other narrow band gap semiconducting photoanodes toward the low-cost solar fuel generation devices.
RESUMEN
The effect of cobalt doping into a manganese oxide (tetragonal spinel Mn3O4) nanoparticle cocatalyst up to Co/(Co + Mn) = 0.4 (mol/mol) on the activity of photocatalytic water oxidation was studied. Monodisperse â¼10 nm CoyMn1-yO (0 ≤y≤ 0.4) nanoparticles were uniformly loaded onto photocatalysts and converted to CoxMn3-xO4 nanoparticles through calcination. 40 mol% cobalt-doped Mn3O4 nanoparticle-loaded Rh@Cr2O3/SrTiO3 photocatalyst exhibited 1.8 times-higher overall water splitting activity than that with pure Mn3O4 nanoparticles. Investigation on the band structure and electrocatalytic water oxidation activity of CoxMn3-xO4 nanoparticles revealed that the Co doping mainly contributes to the improvement of water oxidation kinetics on the surface of the cocatalyst nanoparticles.
RESUMEN
SnNb2O6 has arisen as a candidate for photoanodes for solar water splitting. CoOx cocatalyst-loaded SnNb2O6 showed a stable, high anodic photocurrent with an incident photon-to-current conversion efficiency (IPCE) of 18% at 0.6 VRHE and a half-cell solar-to-hydrogen (HC-STH) efficiency of 0.39% at 0.6 VRHE.
RESUMEN
TiO2 (band gap = 3.0 eV) and SrTiO3 (band gap = 3.2 eV) codoped with nickel and either tantalum or niobium ions showed photocatalytic activities for O2 evolution from an aqueous silver nitrate solution and H2 evolution from an aqueous methanol solution under visible light irradiation (lambda > 420 nm). The visible-light responses were due to the charge-transfer transition from the electron donor levels formed by the 3d orbitals of doped Ni2+ to the conduction bands of the host materials. Codoping of a tantalum or niobium ion made the absorption intensity in the visible light region strong for TiO2 doped with nickel ions, resulting in the enhancement of the photocatalytic activity for O2 evolution under visible light irradiation. SrTiO3 codoped with nickel and tantalum showed higher activity for H2 evolution than SrTiO3 doped with only nickel. This is due to the fact that codoped Ta5+ ions played a role in charge compensation, resulting in the suppression of the formation of Ni3+ ions, which are expected to trap photogenerated electrons.