7 research outputs found
Origin of the overall water splitting activity of Ta3N5 revealed by ultrafast transient absorption spectroscopy
Tantalum nitride (Ta3N5) is one of the few visible light absorbing photocatalysts capable of overall water splitting (OWS), by which the evolution of both H2 and O2 is possible. Despite favourable energetics, realizing the OWS or efficient H2 evolution in Ta3N5 prepared by the nitridation of tantalum oxide (Ta2O5) or Ta foil remains a challenge even after 15 years of intensive research. Recently our group demonstrated OWS in Ta3N5 when prepared by the short time nitridation of potassium tantalate (KTaO3). To obtain a mechanistic insight on the role of Ta precursor and nitridation time in realizing OWS, ultrafast dynamics of electrons (3435 nm probe) and holes (545 nm probe) is investigated using transient absorption spectroscopy. Electrons decay majorly by trapping in Ta3N5 prepared by the nitridation of Ta2O5, which do not show OWS. However, OWS activity in Ta3N5 prepared by 0.25 hour nitridation of KTaO3 is particularly favoured by the virtually absent electron and hole trapping. On further increasing the nitridation time of KTaO3 from 0.25 to 10 hour, trapping of both electron and hole is enhanced which concurrently results in a reduction of the OWS activity. Insights from correlating the synthesis conditions—structural defects—carrier dynamics—photocatalytic activity is of importance in designing novel photocatalysts to enhance solar fuel production
Iridium-doping as a strategy to realize visible light absorption and p-type behavior in BaTiO3
BaTiO3 is typically a strong n-type material with tuneable optoelectronic
properties via doping and controlling the synthesis conditions. It has a wide
band gap that can only harness the ultraviolet region of the solar spectrum.
Despite significant progress, achieving visible-light absorbing BTO with
tuneable carrier concentration has been challenging, a crucial requirement for
many applications. In this work, a p-type BTO with visible-light absorption is
realized via iridium doping. Detailed analysis using advanced spectroscopy
tools and computational electronic structure analysis is used to rationalize
the n- to p-type transition after Ir doping. Results offered mechanistic
insight into the interplay between the dopant site occupancy, the dopant
position within the band gap, and the defect chemistry affecting the carrier
concentration. A decrease in the Ti3+ donor levels concentration and the
mutually correlated oxygen vacancies upon Ir doping is attributed to the p-type
behavior. Due to the formation of Ir3+ or Ir4+ in-gap energy levels within the
forbidden region, the optical transition can be elicited from or to such levels
resulting in visible-light absorption. This newly developed Ir-doped BTO can be
a promising p-type perovskite-oxide with imminent applications in solar fuel
generation, spintronics and optoelectronics.Comment: 21 pages, 8 figure
Plate-like Sm2Ti2S2O5 Particles Prepared by a Flux-Assisted One-Step Synthesis for the Evolution of O-2 from Aqueous Solutions by Both Photocatalytic and Photoelectrochemical Reactions
Sm2Ti2S2O5 (STSO) is a visible-light-responsive oxysulfide semiconductor photocatalyst with applications to water splitting. In this work, plate-like STSO particles were synthesized through a flux-assisted one-step method at various temperatures. The activities of these materials during photocatalytic and photoelectrochemical O-2 evolution from aqueous solutions were investigated. Single-phase STSO with a single crystal habit was produced at 923 K, which is approximately 200 K lower than the temperatures required for previously reported methods, such as solid-state reactions and thermal sulfurization under a H2S flow. The STSO sample synthesized at the optimal temperature exhibited an AQE of 1.3 +/- 0.2% at 420 nm during photocatalytic sacrificial O-2 evolution. This efficiency is twice the values reported for specimens prepared using conventional methods. An STSO/Ti/Sn electrode fabricated by the particle transfer method generated a photoanodic current and evolved O-2 by water oxidation with a Faradaic efficiency of approximately 70 +/- 7%. The synthesis temperature yielding the highest activity was lower for photocatalytic O-2 evolution than photoelectrochemical O-2 evolution. This work demonstrates the applicability for of the flux method to the synthesis of well-crystallized oxysulfides having various particle sizes and intended for different uses
Plate-like Sm2Ti2S2O5 Particles Prepared by a Flux-Assisted One-Step Synthesis for the Evolution of O-2 from Aqueous Solutions by Both Photocatalytic and Photoelectrochemical Reactions
Sm2Ti2S2O5 (STSO) is a visible-light-responsive oxysulfide semiconductor photocatalyst with applications to water splitting. In this work, plate-like STSO particles were synthesized through a flux-assisted one-step method at various temperatures. The activities of these materials during photocatalytic and photoelectrochemical O-2 evolution from aqueous solutions were investigated. Single-phase STSO with a single crystal habit was produced at 923 K, which is approximately 200 K lower than the temperatures required for previously reported methods, such as solid-state reactions and thermal sulfurization under a H2S flow. The STSO sample synthesized at the optimal temperature exhibited an AQE of 1.3 +/- 0.2% at 420 nm during photocatalytic sacrificial O-2 evolution. This efficiency is twice the values reported for specimens prepared using conventional methods. An STSO/Ti/Sn electrode fabricated by the particle transfer method generated a photoanodic current and evolved O-2 by water oxidation with a Faradaic efficiency of approximately 70 +/- 7%. The synthesis temperature yielding the highest activity was lower for photocatalytic O-2 evolution than photoelectrochemical O-2 evolution. This work demonstrates the applicability for of the flux method to the synthesis of well-crystallized oxysulfides having various particle sizes and intended for different uses
Plate-like Sm<sub>2</sub>Ti<sub>2</sub>S<sub>2</sub>O<sub>5</sub> Particles Prepared by a Flux-Assisted One-Step Synthesis for the Evolution of O<sub>2</sub> from Aqueous Solutions by Both Photocatalytic and Photoelectrochemical Reactions
Sm<sub>2</sub>Ti<sub>2</sub>S<sub>2</sub>O<sub>5</sub> (STSO) is
a visible-light-responsive oxysulfide semiconductor photocatalyst
with applications to water splitting. In this work, plate-like STSO
particles were synthesized through a flux-assisted one-step method
at various temperatures. The activities of these materials during
photocatalytic and photoelectrochemical O<sub>2</sub> evolution from
aqueous solutions were investigated. Single-phase STSO with a single
crystal habit was produced at 923 K, which is approximately 200 K
lower than the temperatures required for previously reported methods,
such as solid-state reactions and thermal sulfurization under a H<sub>2</sub>S flow. The STSO sample synthesized at the optimal temperature
exhibited an AQE of 1.3 ± 0.2% at 420 nm during photocatalytic
sacrificial O<sub>2</sub> evolution. This efficiency is twice the
values reported for specimens prepared using conventional methods.
An STSO/Ti/Sn electrode fabricated by the particle transfer method
generated a photoanodic current and evolved O<sub>2</sub> by water
oxidation with a Faradaic efficiency of approximately 70 ± 7%.
The synthesis temperature yielding the highest activity was lower
for photocatalytic O<sub>2</sub> evolution than for photoelectrochemical
O<sub>2</sub> evolution. This work demonstrates the applicability
of the flux method to the synthesis of well-crystallized oxysulfides
having various particle sizes and intended for different uses
Enhancement of Charge Separation and Hydrogen Evolution on Particulate La<sub>5</sub>Ti<sub>2</sub>CuS<sub>5</sub>O<sub>7</sub> Photocathodes by Surface Modification
Particulate La<sub>5</sub>Ti<sub>2</sub>CuS<sub>5</sub>O<sub>7</sub> (LTC) photocathodes prepared
by particle transfer show a positive onset potential of 0.9 V vs RHE
for the photocathodic current in photoelectrochemical (PEC) H<sub>2</sub> evolution. However, the low photocathodic current imposes
a ceiling on the solar-to-hydrogen energy conversion efficiency of
PEC cells based on LTC photocathodes. To improve the photocurrent,
in this work, the surface of Mg-doped LTC photocathodes was modified
with TiO<sub>2</sub>, Nb<sub>2</sub>O<sub>5</sub>, and Ta<sub>2</sub>O<sub>5</sub> by radio frequency reactive magnetron sputtering. The
photocurrent of the modified Mg-doped LTC photocathodes was doubled
because these oxides formed type-II heterojunctions and extended the
lifetimes of photogenerated charge carriers. The enhanced photocathodic
current was attributed to hydrogen evolution at a positive potential
of +0.7 V vs RHE. This work opens up possibilities for improving PEC
hydrogen evolution on particulate photocathodes based on surface oxide
modifications and also highlights the importance of the band gap alignment