10 research outputs found
Experimental and theoretical investigation of Prussian blue-type catalysts for artificial photosynthesis
Cobalt Hexacyanoferrate on BiVO4 Photoanodes for Robust Water Splitting
The efficient integration of photoactive and catalytic materials is key to promoting photoelectrochemical water splitting as a sustainable energy technology built on solar power. Here, we report highly stable water splitting photoanodes from BiVO4 photoactive cores decorated with CoFe Prussian blue-type electrocatalysts (CoFe-PB). This combination decreases the onset potential of BiVO4 by,similar to 0.8 V (down to 0.3 V vs reversible hydrogen electrode (RHE)) and increases the photovoltage by 0.45 V. The presence of the catalyst also leads to a remarkable 6-fold enhancement of the photocurrent at 1.23 V versus RHE, while keeping the light-harvesting ability of BiVO4. Structural and mechanistic studies indicate that CoFe-PB effectively acts as a true catalyst on BiVO4. This mechanism, stemming from the adequate alignment of the energy levels, as showed by density functional theory calculations, allows CoFe-PB to outperform all previous catalyst/BiVO4 junctions and, in addition, leads to noteworthy long-term stability. A bare 10-15% decrease in photocurrent was observed after more than 50 h of operation under light irradiation
Boosting Photoelectrochemical Water Oxidation of Hematite in Acidic Electrolytes by Surface State Modification
State-of-the-art water-oxidation catalysts (WOCs) in acidic electrolytes usually contain expensive noble metals such as ruthenium and iridium. However, they too expensive to be implemented broadly in semiconductor photoanodes for photoelectrochemical (PEC) water splitting devices. Here, an Earth-abundant CoFe Prussian blue analogue (CoFe-PBA) is incorporated with core-shell FeO/FeTiO type II heterojunction nanowires as composite photoanodes for PEC water splitting. Those deliver a high photocurrent of 1.25 mA cm at 1.23 V versus reversible reference electrode in acidic electrolytes (pH = 1). The enhancement arises from the synergic behavior between the successive decoration of the hematite surface with nanolayers of FeTiO and then, CoFe-PBA. The underlying physical mechanism of performance enhancement through formation of the FeO/FeTiO/CoFe-PBA heterostructure reveals that the surface states' electronic levels of hematite are modified such that an interfacial charge transfer becomes kinetically favorable. These findings open new pathways for the future design of cheap and efficient hematite-based photoanodes in acidic electrolytes
Experimental and theoretical investigation of Prussian blue-type catalysts for artificial photosynthesis
A Database of the Structural and Electronic Properties of Prussian Blue, Prussian White, and Berlin Green Compounds through Density Functional Theory
Prussian blue and its related compounds
are formed by cheap and
abundant metals and have shown their importance in the generation
of new fuels by renewable sources. To optimize these compounds it
is important to understand their electronic structure and thus establish
robust structure–activity relationships. To this end, we employed
theoretical simulations based on density functional theory, employing
functionals of different degree of complexity, including pure generalized
gradient approximation (GGA) and GGA+U functionals, which introduce
self-interaction correction terms through the Hubbard parameter, and
compared those to the hybrid functionals HSE03 and HSE06. With this
robust setup, we can identify an appropriate computational scheme
that provides the best compromise between computational demand
and accuracy. A complete database considering Berlin green and
Prussian blue and white for all alkaline cations is presented
Versatile Nature of Oxygen Vacancies in Bismuth Vanadate Bulk and (001) Surface
Bismuth vanadate (BiVO4) has emerged as one of the most promising
photoanode materials for solar fuel production. Oxygen vacancies play a pivotal role in the
photoelectrochemical efficiency, yet their electronic nature and contribution to n-type
conductivity are still under debate. Using first-principles calculations, we show that oxygen
vacancies in BiVO4 have two distinguishable geometric configurations characterized by
either undercoordinated, reduced VIVO3 and BiIIO7 subunits or a VIV−O−VIV/V bridge
(split vacancy), quenching the oxygen vacancy site. While both configurations have similar
energies in the bulk, the (001) subsurface acts like an energetic sink that stabilizes the split
oxygen vacancy by ∼1 eV. The barrierless creation of a bridging V2O7 unit allows for
partial electron delocalization throughout the near-surface region, consistent with recent
experimental observations indicating that BiVO4(001) is an electron-rich surface
Level Alignment as Descriptor for Semiconductor/Catalyst Systems in Water Splitting: The Case of Hematite/Cobalt Hexacyanoferrate Photoanodes
The realization of artificial photosynthesis may depend on the efficient integration of photoactive semiconductors and catalysts to promote photoelectrochemical water splitting. Many efforts are currently devoted to the processing of multicomponent anodes and cathodes in the search for appropriate synergy between light absorbers and active catalysts. No single material appears to combine both features. Many experimental parameters are key to achieve the needed synergy between both systems, without clear protocols for success. Herein, we show how computational chemistry can shed some light on this cumbersome problem. DFT calculations are useful to predict adequate energy‐level alignment for thermodynamically favored hole transfer. As proof of concept, we experimentally confirmed the limited performance enhancement in hematite photoanodes decorated with cobalt hexacyanoferrate as a competent water‐oxidation catalyst. Computational methods describe the misalignment of their energy levels, which is the origin of this mismatch. Photoelectrochemical studies indicate that the catalyst exclusively shifts the hematite surface state to lower potentials, which therefore reduces the onset for water oxidation. Although kinetics will still depend on interface architecture, our simple theoretical approach may identify and predict plausible semiconductor/catalyst combinations, which will speed up experimental work towards promising photoelectrocatalytic systems
Cobalt Hexacyanoferrate on BiVO<sub>4</sub> Photoanodes for Robust Water Splitting
The efficient integration
of photoactive and catalytic materials is key to promoting photoelectrochemical
water splitting as a sustainable energy technology built on solar
power. Here, we report highly stable water splitting photoanodes from
BiVO<sub>4</sub> photoactive cores decorated with CoFe Prussian blue-type
electrocatalysts (<b>CoFe-PB</b>). This combination decreases
the onset potential of BiVO<sub>4</sub> by ∼0.8 V (down to
0.3 V vs reversible hydrogen electrode (RHE)) and increases the photovoltage
by 0.45 V. The presence of the catalyst also leads to a remarkable
6-fold enhancement of the photocurrent at 1.23 V versus RHE, while
keeping the light-harvesting ability of BiVO<sub>4</sub>. Structural
and mechanistic studies indicate that <b>CoFe-PB</b> effectively
acts as a true catalyst on BiVO<sub>4</sub>. This mechanism, stemming
from the adequate alignment of the energy levels, as showed by density
functional theory calculations, allows <b>CoFe-PB</b> to outperform
all previous catalyst/BiVO<sub>4</sub> junctions and, in addition,
leads to noteworthy long-term stability. A bare 10–15% decrease
in photocurrent was observed after more than 50 h of operation under
light irradiation
Boosting Photoelectrochemical Water Oxidation of Hematite in Acidic Electrolytes by Surface State Modification
State-of-the-art water-oxidation catalysts (WOCs) in acidic electrolytes
usually contain expensive noble metals such as ruthenium and iridium.
However, they too expensive to be implemented broadly in semiconductor
photoanodes for photoelectrochemical (PEC) water splitting devices. Here,
an Earth-abundant CoFe Prussian blue analogue (CoFe-PBA) is incorporated
with core–shell Fe2O3/Fe2TiO5 type II heterojunction nanowires as composite
photoanodes for PEC water splitting. Those deliver a high photocurrent
of 1.25 mA cm−2 at 1.23 V versus reversible reference electrode in acidic
electrolytes (pH = 1). The enhancement arises from the synergic behavior
between the successive decoration of the hematite surface with nanolayers
of Fe2TiO5 and then, CoFe-PBA. The underlying physical mechanism of
performance enhancement through formation of the Fe2O3/Fe2TiO5/
CoFe-PBA heterostructure reveals that the surface states’ electronic levels
of hematite are modified such that an interfacial charge transfer becomes
kinetically favorable. These findings open new pathways for the future design
of cheap and efficient hematite-based photoanodes in acidic electrolytes
Boosting Photoelectrochemical Water Oxidation of Hematite in Acidic Electrolytes by Surface State Modification
State-of-the-art water-oxidation catalysts (WOCs) in acidic electrolytes usually contain expensive noble metals such as ruthenium and iridium. However, they too expensive to be implemented broadly in semiconductor photoanodes for photoelectrochemical (PEC) water splitting devices. Here, an Earth-abundant CoFe Prussian blue analogue (CoFe-PBA) is incorporated with core-shell FeO/FeTiO type II heterojunction nanowires as composite photoanodes for PEC water splitting. Those deliver a high photocurrent of 1.25 mA cm at 1.23 V versus reversible reference electrode in acidic electrolytes (pH = 1). The enhancement arises from the synergic behavior between the successive decoration of the hematite surface with nanolayers of FeTiO and then, CoFe-PBA. The underlying physical mechanism of performance enhancement through formation of the FeO/FeTiO/CoFe-PBA heterostructure reveals that the surface states' electronic levels of hematite are modified such that an interfacial charge transfer becomes kinetically favorable. These findings open new pathways for the future design of cheap and efficient hematite-based photoanodes in acidic electrolytes