In harmony: Nanoparticles of Mn3O4 and core/shell‐structured Rh/Cr2O3 as cocatalysts on the surface of a solid solution of GaN and ZnO as catalyst promote O2 and H2 evolution, respectively, under ...visible light (λ>420 nm), thereby achieving enhanced water‐splitting activity compared to analogues modified with either Mn3O4 or Rh/Cr2O3.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The coloading effect of H2 and O2 evolution cocatalysts on the overall water splitting reaction was investigated using a solid solution of GaN and ZnO (hereafter termed GaN:ZnO) as a photocatalyst. ...GaN:ZnO was modified with nanoparticulate Mn3O4, RuO2, and IrO2 as O2 evolution cocatalysts and with core/shell‐type Rh/Cr2O3 composites as H2 evolution cocatalysts. The photocatalytic activity of the coloaded samples for overall water splitting was higher than that of the samples modified with either of the O2 or H2 evolution cocatalysts alone. The activity enhancement induced by coloading was comparable for the three O2 evolution cocatalysts investigated at the optimized loading amounts. Loading of a more efficient Rh/Cr2O3 cocatalyst prepared by adsorption of Rh nanoparticles further improved the photocatalytic activity. It was concluded that a simultaneous improvement in both oxidation and reduction reactions was effective at enhancing the photocatalytic activity of GaN:ZnO, whereas the reduction reactions limited the overall reaction rate of the coloaded system more significantly.
The effects of coloading H2 and O2 evolution co‐catalysts on the photocatalytic activity of GaN:ZnO for overall water splitting were studied. The activity of GaN:ZnO was more potently limited by H2 evolution reactions whereas coloading of O2 evolution cocatalysts modestly improved photocatalytic performance.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Water splitting back reaction (stoichiometric H2 oxidation). The water formation rate for Cr2O3/Rh is strongly suppressed and negligible compared to the one for Rh. Display omitted
► Gas-phase ...photocatalytic water splitting using GaN:ZnO loaded with cocatalysts. ► H2/O2 back reaction on photocatalysts for water splitting. ► Direct evidence of suppression of the back reaction by Cr2O3 shell on Rh and Pt. ► Suppression of the back reaction enhances the net photocatalytic activity. ► Stronger suppression of the back reaction with Cr2O3/Rh than with Cr2O3/Pt.
Using silicon-based μ-reactors, we have studied the photocatalytic water splitting reaction and the catalytic back reaction on the same catalysts. GaN:ZnO without cocatalyst and loaded with Rh, Pt, Cr2O3/Rh, Cr2O3/Pt, and Rh–Cr mixed oxide has been tested for gas-phase photocatalytic water splitting. The results confirm the high activity observed in liquid-phase experiments with Cr2O3/Rh and Rh–Cr mixed oxide as cocatalysts. To investigate the reason of this enhanced activity, the back reaction was studied by reacting stoichiometric H2/O2 and monitoring the water molecules produced. The comparison of the two experiments shows that the suppression of the back reaction with the core/shell cocatalysts and the Rh–Cr mixed oxide corresponds to an increase in the net photocatalytic water splitting activity. The fact that the back reaction is not completely suppressed with Cr2O3/Pt compared to Cr2O3/Rh may be the cause of the higher net activity of the Cr2O3/Rh.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The supported mixed oxide (Rh2–y Cr y O3)/(Ga1–x Zn x )(N1–x O x ) photocatalyst, highly active for splitting of H2O, was extensively characterized for its bulk and surface properties with the ...objective of developing fundamental structure–photoactivity relationships. Raman and UV–vis spectroscopy revealed that the molecular and electronic structures, respectively, of the oxynitride (Ga1–x Zn x )(N1–x O x ) support are not perturbed by the deposition of the (Rh2–y Cr y O3) NPs. Photoluminescence (PL) spectroscopy, however, showed that the oxynitride (Ga1–x Zn x )(N1–x O x ) support is the source of excited electrons/holes and the (Rh2–y Cr y O3) NPs greatly reduce the undesirable recombination of photoexcited electron/holes by acting as efficient electron traps as well as increase the lifetimes of the excitons. High Resolution-XPS and High Sensitivity-LEIS surface analyses reveal that the surfaces of the (Rh2–y Cr y O3) NPs consist of Rh3+ and Cr3+ mixed oxide species. In situ AP-XPS help to reveal that the Rh3+ and surface N atoms are involved in water splitting. Dispersed RhO x species on the (Ga1–x Zn x )(N1–x O x ) support and on CrO x NPs were found to be the photocatalytic active sites for H2 generation and N and Zn sites from the (Ga1–x Zn x )(N1–x O x ) support are the photocatalytic active site for O2 generation. The current investigation establishes the fundamental structure–photoactivity relationships of these visible light activated photocatalysts.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Rh
y
Cr
2−
y
O
3
/(Ga
1−
x
Zn
x
)(N
1−
x
O
x
) photocatalysts immobilized in polytetrafluoroethylene (PTFE) membranes has been investigated for the design of novel reaction sites. In the case of ...hydrophobic PTFE membranes, the Rh
y
Cr
2−
y
O
3
/(Ga
1−
x
Zn
x
)(N
1−
x
O
x
) photocatalyst simultaneously evolved both H
2
and O
2
, even from an aqueous AgNO
3
solution as sacrificial reagent. This indicates that water vapor was split into H
2
and O
2
by the Rh
y
Cr
2−
y
O
3
/(Ga
1−
x
Zn
x
)(N
1−
x
O
x
) photocatalyst particles in the hydrophobic pores of PTFE.
Graphical Abstract
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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 ∼10 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.
A gradual size control of poly(N-vinyl-2-pyrrolidone)-protected Rh nanoparticles (PVP-Rh NPs) was successfully achieved in the range of 1.7–7.7 nm by tuning the pH value and the reaction temperature ...of the ethylene glycol (EG) solution; smaller NPs were formed at higher pH and at higher temperature. This trend can be interpreted by the change in the nucleation rate caused by tuning the pH value and/or the temperature of the solution. When the size tuned PVP-Rh NPs were applied for use as cocatalysts in a photocatalyst (solid solution of GaN and ZnO (Ga1–x Zn x )(N1–x O x )) for overall water splitting under visible light, it was demonstrated that smaller Rh cores gave higher activity than the larger ones.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Core–shell‐structured nanoparticles, consisting of a noble metal or metal oxide core and a chromia (Cr2O3) shell, were studied as promoters for photocatalytic water splitting under visible light. ...Core nanoparticles were loaded by impregnation, adsorption or photodeposition onto a solid solution of gallium nitride and zinc oxide (abbreviated GaN:ZnO), which is a particulate semiconductor photocatalyst with a band gap of approximately 2.7 eV, and a Cr2O3 shell was formed by photodeposition using a K2CrO4 precursor. Photodeposition of Cr2O3 on GaN:ZnO modified with a noble metal (Rh, Pd and Pt) or metal oxide (NiOx, RuO2 and Rh2O3) co‐catalyst resulted in enhanced photocatalytic activity for overall water splitting under visible light (λ>400 nm). This enhancement in activity was primarily due to the suppression of undesirable reverse reactions (H2–O2 recombination and/or O2 photoreduction) and/or protection of the core component from chemical corrosion, depending on the core type. Among the core materials examined, Rh species exhibited relatively high performance for this application. The activity for visible‐light water splitting on GaN:ZnO modified with an Rh/Cr2O3 core–shell configuration was dependent on both the dispersion of Rh nanoparticles and the valence state. In addition, the morphology of the Cr2O3 photodeposits was significantly affected by the valence state of Rh and the pH at which the photoreduction of K2CrO4 was conducted. When a sufficient amount of K2CrO4 was used as the precursor and the solution pH ranged from 3 to 7.5, Cr2O3 was successfully formed with a constant shell thickness (≈2 nm) on metallic Rh nanoparticles, which resulted in an effective promoter for overall water splitting.
Breaking up is hard to do: Photodeposition of chromia onto nanoparticulate co‐catalysts (metals or metal oxides) onto a GaN:ZnO solid solution to form a core–shell configuration resulted in enhanced activity for photocatalytic overall water splitting under visible light (see figure).
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
PDF
