@article{Thomaz2024,

title = {Bulk and interface engineering with the combined addition of Na+ and E5+ (E = Nb5+, Ta5+) in the design of hematite photoanodes},

author = {Kelly T.C. Thomaz and Ingrid Rodríguez-Gutiérrez and Flavio L. Souza},

url = {https://www.sciencedirect.com/science/article/abs/pii/S0167577X24006098},

doi = {10.1016/j.matlet.2024.136471},

issn = {0167-577X},

year  = {2024},

date = {2024-06-00},

urldate = {2024-06-00},

journal = {Materials Letters},

volume = {365},

publisher = {Elsevier BV},

abstract = {In this letter, the synergistic effects of multiple element modification through a single polymeric precursor solution in hematite-based photoanodes using Na/Nb and Na/Ta as dopants are evaluated. Linear sweep voltammetry curves showed that the photoelectrochemical response was improved after Na/Nb (or Ta) addition. In both circumstances, an anodic shift (∼200 mV) in the onset potential was noticeable due to surface states created after Nb5+/Ta5+ segregation. The energetic loss caused by Nb (and Ta) segregation was partially restituted by NiFeOx addition due to the passivation of surface states, acting as recombination centers created by pentavalent modifiers. These combined modifications brought a three and four-fold increase for Na0.1HemNb1.5 NiFeOx and Na0.1HemTa1.0NiFeOx respectively. Charge carrier dynamics analysis studied by intensity modulated photocurrent spectroscopy revealed that the PEC enhancement in both systems is mainly associated with improved charge separation efficiency.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gomes2024,

title = {Enhanced Power Generation Using a Dual-Surface-Modified Hematite Photoanode in a Direct Glyphosate Photo Fuel Cell},

author = {Luiz Eduardo Gomes and Gustavo M. Morishita and Vitória E. M. Icassatti and Thalita F. da Silva and Amilcar Machulek Junior and Ingrid Rodríguez-Gutiérrez and Flavio L. Souza and Cauê A. Martins and Heberton Wender},

url = {https://pubs.acs.org/doi/abs/10.1021/acsami.3c18643},

doi = {10.1021/acsami.3c18643},

issn = {1944-8252},

year  = {2024},

date = {2024-04-10},

urldate = {2024-04-10},

journal = {ACS Appl. Mater. Interfaces},

volume = {16},

number = {14},

pages = {17453--17460},

publisher = {American Chemical Society (ACS)},

abstract = {Given the current and escalating global energy and environmental concerns, this work explores an innovative approach to mitigate a widely employed commercial herbicide using a direct glyphosate (Gly) photocatalytic fuel cell (PFC). The device generates power continuously by converting solar radiation, degrading and mineralizing commercial glyphosate-based fuel, and reducing sodium persulfate at the cathode. Pristine and modified hematite photoanodes were coupled to Pt/C nanoparticles dispersed in a carbon paper (CP) support (Pt/C/CP) dark cathode by using an H-type cell. The Gly/persulfate PFC shows a remarkable current and power generation enhancement after dual-surface modification of pristine hematite with segregated Hf and FeNiOx cocatalysts. The optimized photoanode elevates maximum current density (Jmax) from 0.35 to 0.71 mA cm–2 and maximum power generation (Pmax) from 0.04 to 0.065 mW cm–2, representing 102.85 and 62.50% increase in Jmax and Pmax, respectively, as compared to pristine hematite. The system demonstrated stability over a studied period of 4 h; remarkably, the photodegradation of Gly proved substantial, achieving ∼98% degradation and ∼6% mineralization. Our findings may significantly contribute to reducing Gly’s environmental impact in agribusiness since it may convert the pollutant into energy at zero bias. The proposed device offers a sustainable solution to counteract Gly pollution while concurrently harnessing solar energy for power generation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Khan2024,

title = {Triggering Synergy between p-Type Sputter-Deposited FeMnO_{\textit{x}} or FeNiO_{\textit{x}} and W-Doped BiVO_{4} for Enhanced Oxygen Evolution},

author = {Niqab Khan and Ariadne Koche and Higor Andrade Centurion and Lucas Rabelo and Jefferson Bettini and Gabriel T. dos Santos and Flavio L. Souza and Renato V. Gonçalves and Sherdil Khan},

url = {https://pubs.acs.org/doi/abs/10.1021/acsaem.3c02739},

doi = {10.1021/acsaem.3c02739},

issn = {2574-0962},

year  = {2024},

date = {2024-03-25},

urldate = {2024-03-25},

journal = {ACS Appl. Energy Mater.},

volume = {7},

number = {6},

pages = {2129--2141},

publisher = {American Chemical Society (ACS)},

abstract = {Engineering the photogenerated charge transfer through the solid–liquid interface is a key factor in boosting the solar energy conversion device performance, particularly, for BiVO4, which suffers recombination due to its short hole diffusion length and faster e–/h+ recombination. Site-selective cocatalysts have a strong potential to scavenge holes from the BiVO4 surface. However, uniform incorporation of the cocatalyst on the semiconductor surface is also challenging. This study describes simple one-step radio frequency (RF) magnetron sputtering deposition of bimetallic p-type FeMnOx and FeNiOx hole-selective cocatalysts over pure and W-doped BiVO4 particles which led to a remarkable improvement in photocatalytic O2 evolution. As compared with the pristine BiVO4 (93 μmol), the photocatalytic O2 evolution enhanced to 143 and 181 μmol per 25 mg of samples upon loading FeMnOx cocatalyst over pure and W-doped BiVO4, respectively, under solar irradiation conditions (AM 1.5 G) which were also higher than the previous literature. The enhancement in the photoactivity was attributed to the formation of controlled and site-selective p–n junctions that led to the development of built-in electric field, thereby increasing the charge transfer and suppressing the charge recombination. The band alignment was studied by the classical band bending model, which suggested FeMnOx exhibits an intense built-in electric field compared with FeNiOx, thus resulting in better O2 evolution. Our study offers a facile way to boost the photocatalytic activity of BiVO4 by uniformly loading bimetallic cocatalysts as a hole scavenger on the material surface via DC magnetron sputtering.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Verissimo2024,

title = {Dual modification on hematite to minimize small polaron effects and charge recombination for sustainable solar water splitting},

author = {Nathália C. Verissimo and Fabio A. Pires and Ingrid Rodríguez-Gutiérrez and Jefferson Bettini and Tanna E. R. Fiuza and Cleyton A. Biffe and Fabiano E. Montoro and Gabriel R. Schleder and Ricardo H. R. Castro and Edson R. Leite and Flavio L. Souza},

url = {https://pubs.rsc.org/en/content/articlelanding/2024/ta/d3ta07721g/unauth},

doi = {10.1039/d3ta07721g},

issn = {2050-7496},

year  = {2024},

date = {2024-03-12},

urldate = {2024-03-12},

journal = {J. Mater. Chem. A},

volume = {12},

number = {11},

pages = {6280--6293},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {Hematite nanostructures are strong candidates for the development of sustainable water splitting technologies. However, major challenges exist in improving charge density and minimizing charge recombination rates for a competitive photoelectrochemical performance based on hematite without compromising sustainability aspects. Here we develop a synthetic strategy to leverage earth-abundant Al3+ and Zr4+ in a dual-chemical modification to synergistically minimize small polaron effects and interfacial charge recombination. The solution-based method simultaneously induces Al3+ doping of the hematite crystal lattice while Zr4+ forms interfacial excess, creating a single-phased homogeneous nanostructured thin film. The engineered photoanode increased photocurrent from 0.7 mA cm−2 for pristine hematite up to 4.5 mA cm−2 at 1.23 V and beyond 6.0 mA cm−2 when applying an overpotential of 300 mV under simulated sunlight illumination (100 mW cm−2). The results demonstrate the potential of dual-modification design using solution-based processes to enable sustainable energy technologies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rodríguez-Gutiérrez2024,

title = {Overcoming scale-up challenges for nanostructured photoelectrodes via one-step interface engineering},

author = {Ingrid Rodríguez-Gutiérrez and Lizandra R.P. Peregrino and Karen C. Bedin and Gustavo M. Morishita and Gabriel H. Morais and Ricardo H.R. Castro and Edson R. Leite and Flavio L. Souza},

url = {https://www.sciencedirect.com/science/article/abs/pii/S036031992400243X},

doi = {10.1016/j.ijhydene.2024.01.221},

issn = {0360-3199},

year  = {2024},

date = {2024-03-00},

urldate = {2024-03-00},

journal = {International Journal of Hydrogen Energy},

volume = {58},

pages = {1138--1148},

publisher = {Elsevier BV},

abstract = {Scaling up photoelectrochemical (PEC) devices for green hydrogen production is a significant challenge that requires robust and cost-effective production methods. In this study, hematite photoelectrodes has been synthesized using a cost-effective polymeric precursor solution, resulting in homogeneous ultra-thin films (∼125 nm) with areas up to 200 cm2. We observed a substantial photocurrent drop as photoelectrode area increases, addressed by modifying the precursor solution with Hf4+. This modification improves the morphology and films adherence, leading to simultaneous grain|grain interface segregation and a modified FTO|hematite interface. As a result, film conductivity increases, reducing the photocurrent drop at larger photoelectrode areas. The improved charge separation and surface charge injection efficiencies allows a homogeneous photocurrent of 1.6 mA cm⁻2 at 1.45V across a 15.75 m2 electrode area, using less than 70 μg of photoactive material. Cost analysis study indicates that this low-energy fabrication method is a significant step forward in green hydrogen production, contributing to sustainable and efficient green hydrogen technologies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{DosSantos2024b,

title = {Nanostructured FTO/Zr-hematite interfaces for solar water-splitting applications},

author = {Gabriel T. Dos Santos and Karen C. Bedin and Tanna E.R. Fiuza and Ingrid Rodríguez-Gutiérrez and Paulo F.P. Fichtner and Flavio L. Souza and Jefferson Bettini},

url = {https://www.sciencedirect.com/science/article/abs/pii/S0169433223025473},

doi = {10.1016/j.apsusc.2023.158867},

issn = {0169-4332},

year  = {2024},

date = {2024-02-00},

urldate = {2024-02-00},

journal = {Applied Surface Science},

volume = {645},

publisher = {Elsevier BV},

abstract = {Production of green hydrogen via photoelectrochemical (PEC) processes is strategic to store and distribute solar-harvested energy. Hematite (α-Fe2O3) is a promising photoactive photoanode material candidate for PEC applications, but its synthesis as a photoanode thin film needs improvements to optimize the PEC device's performance. We have previously explored a new strategy consisting of the use of Zr4+ as a surfactant (Zr-hematite) and Ni2+ as a co-catalyst element in the synthesis of hematite photoanode thin films deposited onto a fluorine-doped tin oxide (FTO) on a glass substrate, obtaining a significant enhancement of device performance. In this work, we demonstrated how the interface and surface conditions are affected by the incorporation of Zr4+ and Ni2+. Chemical mapping performed during scanning transmission electron microscopy (STEM) analysis indicated that Zr4+ preferentially segregated at the FTO/Zr-hematite interface and grain boundaries, while Ni2+ was only present on hematite-free surfaces. The Zr4+ between the hematite and substrate interface was associated with improved back contact, facilitating electron collection and favoring electron flow through the external circuit. Structural analysis of this interface region revealed lattice distortions and strain field accumulation at the FTO/Zr-hematite interface, which differed from the expected crystal structures of the database. Additionally, local FTO/Zr-hematite energy maps showed a 2.5-nm thick interface area containing a solid mixture of SnFeOx. Moreover, a change in the electronic state of Sn and Fe on the surface of the FTO substrate and Zr-hematite grains caused by the loss of oxygen atoms was observed. NiFeOx chemical bonding was observed with Ni addition by photoelectrodeposition on the Zr-hematite-free surface. This strong interaction explains the long-term stability test without traces of photocorrosion (ion release into the solution), as demonstrated in a previous paper. These findings introduce a novel perspective for developing strategies that enable synergistic photoanode modifications toward efficient solar-to-energy conversion.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Santos2024d,

title = {Charge dynamics in semiconductors for photoelectrochemical water splitting},

author = {Ana M.S. Santos and Ingrid Rodríguez-Gutiérrez and Gustavo M. Morishita and Ricardo M. Lopes and Flavio L. Souza},

url = {https://www.sciencedirect.com/science/article/abs/pii/S0167577X23019663},

doi = {10.1016/j.matlet.2023.135781},

issn = {0167-577X},

year  = {2024},

date = {2024-02-00},

urldate = {2024-02-00},

journal = {Materials Letters},

volume = {357},

publisher = {Elsevier BV},

abstract = {This letter focuses on monitoring alterations in the charge carrier dynamics associated with in-situ modifications into hematite photoanodes, employing advanced electrochemical techniques. A simple and scalable polymeric precursor solution, deposited by spin-coating, was employed to synthesize hematite based photoanodes. Among various modifications, Tantalum (Ta+5) shows the most promising results, yielding a hydrogen production rate of 24.0 μmol cm−2h−1 at 1.23VRHE. This is attributed to Ta5+ segregation at hematite grain surface, which facilitates the charge transport efficiency and leads to higher external quantum efficiency. Conversely, sodium (Na+) primarily increases the film thickness with limited observable effects on charge carrier dynamics, while zinc (Zn+2) adversely affects hematite performance due to its negative effect on charge separation efficiency and increased bulk recombination.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lima2023,

title = {Unraveling the impact of tetravalent and pentavalent ions on the charge dynamics of hematite photoelectrodes for solar water splitting},

author = {Brenda R. Lima and Ingrid Rodriguez-Gutierrez and Nathália C. Verissimo and Ângela Albuquerque and Gabriel T. Santos and Jefferson Bettini and Flavio L. Souza},

url = {https://www.sciencedirect.com/science/article/abs/pii/S2468519423004111},

doi = {10.1016/j.mtchem.2023.101784},

issn = {2468-5194},

year  = {2023},

date = {2023-12-00},

urldate = {2023-12-00},

journal = {Materials Today Chemistry},

volume = {34},

publisher = {Elsevier BV},

abstract = {This study focuses on understanding the impact of tetravalent (Hf4+) and pentavalent (Nb5+) ions in hematite photoelectrodes using a two-step synthesis approach. Structural, morphological, and compositional analyses confirms that Nb5+ is segregated over the hematite crystal surface while Hf4+ is allocated over the crystal surface and between the fluorine-doped tin oxide substrate (FTO)-hematite interface. Our results indicate that the modifier insertion led to substantial improvements in overall efficiency and photoelectrochemical (PEC) performance. However, it creates additional surface states, as evidenced by shifts in the anodic onset potential (Vonset) observed in the linear sweep voltammetry curves. For Nb-modified photoelectrodes, Vonset shift of ∼20 mV with respect to hematite was observed and confirmed by intensity modulated photocurrent spectroscopy (IMPS). For Hf-modified hematite, this Vonset shift is more pronounced (∼30 mV). When combined with NiFeOx, Nb5+ acted synergistically showing a 4-fold efficiency increase compared to hematite and ∼70 mV cathodic shift in the Vonset. Otherwise, NiFeOx showed no significant impact in the Hf4+ modified hematite photoelectrodes, suggesting that Hf4+ role lies in enhancing electron collection at the FTO-hematite interface. This study not only sheds light on the charge dynamics of modified hematite photoelectrodes but also provides strategies for boosting the PEC devices efficiency.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Daminelli2023,

title = {Self-Diffusion versus Intentional Doping: Beneficial and Damaging Impact on Hematite Photoanode Interfaces},

author = {Lara M. Daminelli and Ingrid Rodríguez-Gutierrez and Fabio A. Pires and Gabriel T. dos Santos and Jefferson Bettini and Flavio L. Souza},

url = {https://pubs.acs.org/doi/abs/10.1021/acsami.3c10516},

doi = {10.1021/acsami.3c10516},

issn = {1944-8252},

year  = {2023},

date = {2023-11-29},

urldate = {2023-11-29},

journal = {ACS Appl. Mater. Interfaces},

volume = {15},

number = {47},

pages = {55030--55042},

publisher = {American Chemical Society (ACS)},

abstract = {The comprehension of side effects caused by high-temperature thermal treatments in the design of (photo)electrodes is essential to achieve efficient and cost-effective devices for solar water splitting. This investigation explores the beneficial and damaging impacts of thermal treatments in the (photo)electrode design, unraveling the impact of self-diffusion and its consequences. The industrial-friendly polymeric precursor synthesis (PPS) method, which is known for its easy technological application, was chosen as the fabrication technique for hematite photoabsorbers. For substrate evaluation, two types of conductive glass substrates, aluminum borosilicate and quartz, both coated with fluorine-doped tin oxide (ABS/FTO and QTZ/FTO, respectively), were subjected to thermal treatments following the PPS protocol. Optical and structural analyses showed no significant alterations in substrate properties, whereas X-ray photoelectron spectroscopy (XPS) revealed the migration of silicon and calcium ions from the glass component to the FTO surface. This diffusion can be further mitigated by an oxide buffer layer. To track the potential ion diffusion on the photoabsorber surface and assess its effect on the photoelectrode performance, hematite was selected as the model material and deposited onto the glass substrates. From all the ions that could possibly migrate, only Si4+ and Ca2+ originating from the glass component, as well as Sn4+ from the fluorine-doped tin oxide (FTO), were detected on the surface of the hematite photoabsorber. Interestingly, the so-called “self-diffusion” of these ions did not result in any beneficial effect on the hematite photoelectrochemical response. Instead, intentional modifications showed more substantial impacts on the photoelectrochemical efficiency compared to unintentional self-diffusion. Therefore, “self-diffusion”, which can unintentionally dope the hematite, is not sufficient to significantly impact the final photocurrent. These findings emphasize the importance of understanding the true effect of thermal treatments on the photoelectrode properties to unlock their full potential in photoelectrochemical applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Pires2023,

title = {Selective placement of modifiers on hematite thin films for solar water splitting},

author = {Fabio A. Pires and Gabriel T. dos Santos and Jefferson Bettini and Carlos A. R. Costa and Renato V. Gonçalves and Ricardo H. R. Castro and Flavio L. Souza},

url = {https://pubs.rsc.org/en/content/articlelanding/2023/se/d3se00998j/unauth},

doi = {10.1039/d3se00998j},

issn = {2398-4902},

year  = {2023},

date = {2023-10-10},

urldate = {2023-10-10},

journal = {Sustainable Energy Fuels},

volume = {7},

number = {20},

pages = {5005--5017},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {The design of nanostructured materials for photoelectrochemical water splitting relies on a detailed understanding of the reactional bottlenecks. For hematite, a model system for photoanodes, the challenges concern poor charge transfer and separation, carrier recombination rate, and sluggish water oxidation kinetics. Several methods have been proposed to address each individually, with complex multi-step processes offered as solutions to improve overall performance. Here, we introduce a single polymeric precursor solution that enables the design of hematite (α-Fe2O3) with synergistic bulk and interfacial engineering using Ga3+, Hf4+ and NiFeOx. The solution causes Ga3+ to dope hematite lattice to reduce polaronic effects, while simultaneously induces Hf4+ enrichment at both surface and grain boundaries, improving charge separation and reducing recombination. Hf4+ also led to a refined microstructure derived from interface stabilization, which associated with Ga3+ bulk doping and NiFeOx electrodeposition resulted in a thin film with 65% of overall photoelectrode efficiency. As a consequence, the modified hematite photoanode (176 nm-thick) delivered a water oxidation photocurrent of 2.30 mA cm−2 in contrast to 0.37 mA cm−2 for the pristine system measured at 1.23 V against hydrogen reversible electrode (RHE). The results suggest the simplicity of this new polymeric solution may offer a cost-effective, scalable and versatile alternative for multiple chemical modifications in oxides beyond hematite.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Thomaz2023,

title = {Interfacial engineering of hematite photoanodes toward high water splitting performance},

author = {Kelly T.C. Thomaz and Karen C. Bedin and Ingrid Rodríguez-Gutiérrez and Nathália C. Verissimo and Jefferson Bettini and Flavio L. Souza},

url = {https://www.sciencedirect.com/science/article/abs/pii/S2468606923001557},

doi = {10.1016/j.mtener.2023.101399},

issn = {2468-6069},

year  = {2023},

date = {2023-10-00},

urldate = {2023-10-00},

journal = {Materials Today Energy},

volume = {37},

publisher = {Elsevier BV},

abstract = {Efficient and scalable photoelectrochemical water splitting electrode designs are a challenge. This study focuses on hafnium-modified hematite (X%Hf-HEM) photoanodes, prepared via spin-coating polymeric precursor solutions with varying Hf4+/Fe3+ (mol) ratios (1.0%, 3.0%, 4.0%, and 5.0%) onto fluorine-doped tin oxide substrates. Structural, morphological, and compositional analyses confirm pure hematite phases in all X%Hf-HEM samples. Increasing Hf4+ content correlated with reduced grain size, thickness, and surface roughness due to Hf4+ segregation at grain boundaries during thermal treatment. Hafnium segregation at hematite grain boundaries and hematite|fluorine-doped tin oxide interfaces is confirmed using scanning transmission electron microscopy coupled with energy dispersive spectroscopy. Notably, the 4%Hf-HEM photoanode exhibits exceptional efficiency enhancement, outperforming HEM efficiency by 4.5 times. Gas chromatography results highlight O2 and H2 evolution rates of 14.49 ± 0.09 μmol/cm2/h and 8.1 ± 0.5 μmol/cm2/h, respectively, for 4%Hf-HEM, with a H2/O2 ratio close to 2:1. The charge dynamics investigated from intensity-modulated photocurrent spectroscopy evidence the main Hf4+ effect of improving charge separation, achieving greater efficiency for 4%Hf-HEM. Shifts in valence band maximum from ultraviolet photoelectron spectroscopy measurements indicate surface state presence, supported by ηtransfer trends calculated from intensity-modulated photocurrent spectroscopy. This research presents a scalable, cost-effective approach to multiinterface photoanode development, holding promise for innovative photoelectrochemical water splitting technologies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Morishita2023,

title = {Hafnium boosts charge carrier dynamics in hematite for improved solar water splitting},

author = {Gustavo M. Morishita and Ingrid Rodríguez-Gutiérrez and Ricardo H.R. Castro and Flavio L. Souza},

url = {https://www.sciencedirect.com/science/article/abs/pii/S0167577X23003610},

doi = {10.1016/j.matlet.2023.134176},

issn = {0167-577X},

year  = {2023},

date = {2023-06-00},

urldate = {2023-06-00},

journal = {Materials Letters},

volume = {340},

publisher = {Elsevier BV},

abstract = {The work demonstrates a three-fold increase in photoelectrochemical efficiency of hematite nanorods as a result of the combination of Hafnium surface doping and the incorporation of a ZrO2 underlayer on FTO. While the ZrO2 layer reduced the electron loss from the back-injection into the FTO contact support, Hafnium surface doping did not significantly alter the hematite lattice structure. But rather, Hafnium induced nanorod diameter reduction from 32 ± 2 and 26 ± 2 nm, with a consequent increase in the active surface area. The linear sweep voltammetry measurements with 100 mW cm−2 illumination in a 500 nm photoanode thickness showed a photocurrent density of 2.07 mA cm−2 at 1.23 V in a reversible hydrogen electrode (RHE). The value contrasts with the bare hematite rods (0.75 mA cm−2), highlighting the photoanode design's role in improving solar power hydrogen production.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Centurion2023,

title = {Emerging trends of pseudobrookite Fe2TiO5 photocatalyst: A versatile material for solar water splitting systems},

author = {Higor A. Centurion and Mauricio A. Melo and Lucas G. Rabelo and Gustavo A.S. Alves and Washington Santa Rosa and Ingrid Rodríguez-Gutiérrez and Flavio L. Souza and Renato V. Gonçalves},

url = {https://www.sciencedirect.com/science/article/abs/pii/S0925838822041019},

doi = {10.1016/j.jallcom.2022.167710},

issn = {0925-8388},

year  = {2023},

date = {2023-02-00},

urldate = {2023-02-00},

journal = {Journal of Alloys and Compounds},

volume = {933},

publisher = {Elsevier BV},

abstract = {Renewable energy production from diverse sources (such as solar, wind) is essential for achieving a sustainable and CO2-free society within a short duration. Green hydrogen is regarded as the most feasible fuel for the next generation of fuel-cell electric vehicles and associated technologies. Solar water splitting is a promising strategy for green hydrogen production because it is based on renewable sources with the potential to minimize the power costs in the production of H2 via electrolysis, which presents significant barriers. Iron titanate (Fe2TiO5), a visible-light-active photocatalyst, has emerged as a possible material for designing the next generation of water splitting photoelectrodes, as it is a low-cost, plentiful, and non-toxic oxide with favorable electronic, optical, and chemical properties for this application. This review summarizes recent advances in the use of Fe2TiO5 as a semiconducting material for solar water splitting applications, covering single photocatalytic systems and heterostructures such as Fe2TiO5/TiO2, Fe2TiO5/BiVO4, and Fe2TiO5/Fe2O3. Furthermore, this perspective review discusses and highlights strategies for developing effective Fe2TiO5 based water-oxidation materials.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bedin2022b,

title = {On electron loss lowering at hematite photoelectrode interfaces},

author = {Karen C. Bedin and Ingrid Rodríguez‐Gutiérrez and Lizandra R. P. Peregrino and Lionel Vayssieres and Flavio L. Souza},

url = {https://ceramics.onlinelibrary.wiley.com/doi/abs/10.1111/jace.18460},

doi = {10.1111/jace.18460},

issn = {1551-2916},

year  = {2023},

date = {2023-01-00},

urldate = {2023-01-00},

journal = {J Am Ceram Soc.},

volume = {106},

number = {1},

pages = {79--92},

publisher = {Wiley},

abstract = {Photoelectrodes nanoscale interface design has become a key factor to enhancing their photoelectrochemical performance for water splitting by reducing the photogenerated charge recombination, thus ensuring their efficient separation, transport, and collection. In this work, hematite (α-Fe2O3) photoanodes were prepared from a simple and scalable methodology capable of synergistically mitigating the charge loss and recombination at all interfaces (i.e., fluorine-doped tin oxide/hematite, hematite/hematite, and hematite/electrolyte) and achieving overall efficiency of ∼50% for the water oxidation reaction compared to pristine photoelectrodes. The external quantum efficiency at 1.23 V versus reversible hydrogen electrode of pristine hematite was enhanced 6.7 times with the modifications of the three interfaces (Al2O3/NbH/NiFeOx). Electrochemical impedance spectroscopy and intensity-modulated photocurrent spectroscopies were applied to probe and monitor the photogenerated charge carrier dynamics revealing a substantial improvement in charge separation and collection at the back-contact interface as well as a partial mitigation of the surface states at the hematite–electrolyte interface.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Centurion2022,

title = {Constructing Particulate p–n Heterojunction Mo:SrTiO3/NiO@Ni(OH)2 for Enhanced H2 Evolution under Simulated Solar Light},

author = {Higor A. Centurion and Lucas G. Rabelo and Ingrid Rodriguez-Gutierrez and Mateus M. Ferrer and Jefferson Bettini and Heberton Wender and Liane M. Rossi and Flavio L. Souza and Renato V. Gonçalves},

url = {https://pubs.acs.org/doi/abs/10.1021/acsaem.2c02337},

doi = {10.1021/acsaem.2c02337},

issn = {2574-0962},

year  = {2022},

date = {2022-10-24},

urldate = {2022-10-24},

journal = {ACS Appl. Energy Mater.},

volume = {5},

number = {10},

pages = {12727--12738},

publisher = {American Chemical Society (ACS)},

abstract = {The global environmental issues associated with the use of fossil fuels lead to an urgent need for renewable energy sources, especially those free of CO2 emissions, such as green hydrogen. In this work, we successfully synthesized Mo-doped SrTiO3 by a molten salt method for photocatalytic hydrogen production under simulated solar light (AM 1.5G illumination). As a strategy to enhance the photocatalytic performance of Mo:SrTiO3, nickel-based nanoparticles (NiO@Ni(OH)2) were deposited onto the surface of the particles by modified magnetron sputtering to form a p–n heterojunction (HJ), resulting in the photocatalytic improvement of around 30-fold concerning pristine SrTiO3. Theoretical investigation of the electronic band structure, by DFT, reveals that the addition of Mo as a dopant leads to the formation of midgap states near the conduction band, further attributed to the photoactivity of Mo:SrTiO3 under visible-light illumination (>400 nm). The obtained structure, Mo:SrTiO3/NiO@Ni(OH)2, had its electronic behavior studied by XPS, Mott–Schottky analysis, and UV–vis spectroscopy, leading to the construction of a band diagram that confirms type-II p–n HJ formation. Remarkably, the formation of the HJ was responsible for establishing an internal electric field, which drives the photogenerated holes to the NiO@Ni(OH)2 structure, leading to the suppression of electron–hole recombination, observed by the reduction of the PL signal.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rodríguez-Gutiérrez2022b,

title = {Advances in Engineered Metal Oxide Thin Films by Low-Cost, Solution-Based Techniques for Green Hydrogen Production},

author = {Ingrid Rodríguez-Gutiérrez and Karen Cristina Bedin and Beatriz Mouriño and João Batista Souza Junior and Flavio L. Souza},

url = {https://www.mdpi.com/2079-4991/12/12/1957},

doi = {10.3390/nano12121957},

issn = {2079-4991},

year  = {2022},

date = {2022-06-00},

urldate = {2022-06-00},

journal = {Nanomaterials},

volume = {12},

number = {12},

publisher = {MDPI AG},

abstract = {Functional oxide materials have become crucial in the continuous development of various fields, including those for energy applications. In this aspect, the synthesis of nanomaterials for low-cost green hydrogen production represents a huge challenge that needs to be overcome to move toward the next generation of efficient systems and devices. This perspective presents a critical assessment of hydrothermal and polymeric precursor methods as potential approaches to designing photoelectrodes for future industrial implementation. The main conditions that can affect the photoanode’s physical and chemical characteristics, such as morphology, particle size, defects chemistry, dimensionality, and crystal orientation, and how they influence the photoelectrochemical performance are highlighted in this report. Strategies to tune and engineer photoelectrode and an outlook for developing efficient solar-to-hydrogen conversion using an inexpensive and stable material will also be addressed.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bedin2022,

title = {Solution chemistry back-contact FTO/hematite interface engineering for efficient photocatalytic water oxidation},

author = {Karen Cristina Bedin and Beatriz Mouriño and Ingrid Rodríguez-Gutiérrez and João Batista Souza Junior and Gabriel Trindade dos Santos and Jefferson Bettini and Carlos Alberto Rodrigues Costa and Lionel Vayssieres and Flavio L. Souza},

url = {https://www.sciencedirect.com/science/article/abs/pii/S1872206721639736},

doi = {10.1016/s1872-2067(21)63973-6},

issn = {1872-2067},

year  = {2022},

date = {2022-05-00},

urldate = {2022-05-00},

journal = {Chinese Journal of Catalysis},

volume = {43},

number = {5},

pages = {1247--1257},

publisher = {Elsevier BV},

abstract = {This work describes a simple yet powerful scalable solution chemistry strategy to create back-contact rich interfaces between substrates such as commercial transparent conducting fluorine-doped tin oxide coated glass (FTO) and photoactive thin films such as hematite for low-cost water oxidation reaction. High-resolution electron microscopy (SEM, TEM, STEM), atomic force microscopy (AFM), elemental chemical mapping (EELS, EDS) and photoelectrochemical (PEC) investigations reveal that the mechanical stress, lattice mismatch, electron energy barrier, and voids between FTO and hematite at the back-contact interface as well as short-circuit and detrimental reaction between FTO and the electrolyte can be alleviated by engineering the chemical composition of the precursor solutions, thus increasing the overall efficiency of these low-cost photoanodes for water oxidation reaction for a clean and sustainable generation of hydrogen from PEC water-splitting. These findings are of significant importance to improve the charge collection efficiency by minimizing electron-hole recombination observed at back-contact interfaces and grain boundaries in mesoporous electrodes, thus improving the overall efficiency and scalability of low-cost PEC water splitting devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rodríguez-Gutiérrez2022,

title = {On the Effect of Thermal Processing on Sn Diffusion and Efficiency Enhancement in Hematite/FTO Photoanodes},

author = {Ingrid Rodríguez-Gutiérrez and Beatriz Mouriño and André L. M. Freitas and Carlos A. R. Costa and Elcio L Pires and Renato V. Gonçalves and Lionel Vayssieres and Flavio L. Souza},

url = {https://iopscience.iop.org/article/10.1149/2162-8777/ac6114/meta},

doi = {10.1149/2162-8777/ac6114},

issn = {2162-8777},

year  = {2022},

date = {2022-04-01},

urldate = {2022-04-01},

journal = {ECS J. Solid State Sci. Technol.},

volume = {11},

number = {4},

publisher = {The Electrochemical Society},

abstract = {The frequently underestimated effects of “in air” thermal treatment processing conditions such as temperature, duration, and heating and cooling rates in the design and efficiency of photoelectrodes fabricated for academic studies onto the most common commercial transparent conductive glass substrate i.e. fluorine-doped tin oxide (FTO) were investigated by XRD, XPS, SEM, conductive AFM, electrochemical impedance spectroscopy (EIS) as well as direct current (DC) and photoelectrochemical (PEC) measurements. The PEC response of Hematite photoanode thin films consisting of short nanorods thermally treated at 400 °C and 800 °C upon fast or extended time conditions is inhibited by factors such as crystallinity, Sn diffusion, or substrate integrity. A “fast” thermal treatment in air at 750 °C provided the best synergy between charge transfer resistance, Sn-diffusion from the FTO substrate, nanorod dimensions, reduced recombination, improved charge separation and minimized substrate damage. This study does offer valuable fundamental and practical insights for a better understanding of the benefits and drawbacks of photoelectrode thermal processing, which is critical for the improvement of the PEC performance-reproducibility relationship for FTO-based solar water splitting systems and devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Melo2022,

title = {Binary Transition Metal NiFeO_{x} and CoFeO_{x} Cocatalysts Boost the Photodriven Water Oxidation over Fe_{2}TiO_{5} Nanoparticles},

author = {Mauricio A. Melo and Higor A. Centurion and Giovanna Machado and Flavio L. Souza and Renato V. Gonçalves},

url = {https://aces.onlinelibrary.wiley.com/doi/abs/10.1002/cnma.202100510},

doi = {10.1002/cnma.202100510},

issn = {2199-692X},

year  = {2022},

date = {2022-04-00},

urldate = {2022-04-00},

journal = {ChemNanoMat},

volume = {8},

number = {4},

publisher = {Wiley},

abstract = {Although achieving a perfect match between a cocatalyst and a photocatalyst is challenging, it is a key factor to maximize the production of solar fuels. Herein, the nanostructured binary transition metal oxides NiFeOx and CoFeOx, loaded through magnetron sputtering deposition, were employed as cocatalysts for Fe2TiO5 nanoparticles, applied to the oxygen production from solar water splitting. After the coverage of Fe2TiO5 with exceptionally small CoFeOx and NiFeOx nanoparticles, the O2 evolution boosted from 7.0 (pure Fe2TiO5) to 56.0 and 63.0 μmol, respectively, under visible light irradiation. To the best of our knowledge, these performance enhancements are the highest reported for the particulate Fe2TiO5 photocatalyst, so far. The improvements result from the alleviation of charge transfer resistance at the solid/liquid interface, as the binary metal oxides aid the charge carriers separation at the heterojunctions and improve the kinetics of the water oxidation reaction.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{SouzaJunior2021b,

title = {On the relevance of understanding and controlling the locations of dopants in hematite photoanodes for low-cost water splitting},

author = {Joao B. Souza Junior and Flavio L. Souza and Lionel Vayssieres and Oomman K. Varghese},

url = {https://pubs.aip.org/aip/apl/article-abstract/119/20/200501/1065135/On-the-relevance-of-understanding-and-controlling?redirectedFrom=fulltext},

doi = {10.1063/5.0066931},

issn = {1077-3118},

year  = {2021},

date = {2021-11-15},

urldate = {2021-11-15},

volume = {119},

number = {20},

publisher = {AIP Publishing},

abstract = {Successful large-scale implementation of solar fuel technologies relies on cost, performance, and reliability of materials, devices, and infrastructures. Earth-abundant, low-cost, easily recyclable, and environmentally benign light absorbers are desired for renewable fuel generation technologies, such as solar photoelectrochemical (PEC) water splitting. Hematite is considered an ideal material for PEC oxygen evolution reaction, which is a critical component in the overall water splitting process for hydrogen fuel generation. However, intrinsic and operational limitations have prevented hematite-based PEC devices from reaching their highest theoretical solar-to-hydrogen efficiency of 15%–17%. Literature clearly shows that no single approach can eliminate these limitations. An overall fundamental understanding of the effect of dopant addition as well as their physical locations and functions within the photoelectrode, in both as-synthesized form and under operating conditions, is of critical importance to unleash the tremendous potentials of hematite-based PEC systems. In this short perspective, the concept of effective doping (i.e., increase of charge carrier density) up to the limit of dopant segregation at the grain boundaries to lower the charge recombination is discussed. Based on relevant theoretical and experimental data from the literature on the effects of surface-to-bulk doping as well as dopant segregation at the grain boundaries on hematite photoelectrode performance, we discuss here the views on the necessity of understanding these processes and their individual and synergistic effects to unravel a simple yet powerful approach to design and develop highly efficient hematite photoanodes for clean hydrogen generation using water and sunlight.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rodriguez-Gutierrez2021,

title = {An intensity modulated photocurrent spectroscopy study of the role of titanium in thick hematite photoanodes},

author = {Ingrid Rodriguez-Gutierrez and Joao B. Souza Junior and Edson R. Leite and Lionel Vayssieres and Flavio L. Souza},

url = {https://pubs.aip.org/aip/apl/article-abstract/119/7/071602/1023062/An-intensity-modulated-photocurrent-spectroscopy?redirectedFrom=fulltext},

doi = {10.1063/5.0060483},

issn = {1077-3118},

year  = {2021},

date = {2021-08-16},

urldate = {2021-08-16},

volume = {119},

number = {7},

publisher = {AIP Publishing},

abstract = {In this Letter, the role of Ti addition in thick hematite mesoporous photoanodes was elucidated by performing intensity modulated photocurrent spectroscopy (IMPS) monitoring its charge carrier dynamics during water oxidation. Interface engineering associated with doping of hematite is crucial to develop highly efficient thick photoanodes. Photoelectrochemical data recorded under front- and back-side illumination show that Ti insertion mitigates the collection deficit faced by hematite due to an energy barrier decrease between the grains and a change in the surface chemistry. IMPS reveals that Ti clearly influences the hematite film performance by increasing the charge separation efficiency due to its segregation at the hematite interface. However, Ti insertion does not enhance the kinetics of water oxidation at the solid–liquid interface. These facts indicate that Ti mainly affects the hematite electronic properties instead of accelerating the surface processes. This comprehensive understanding of the electronic transport and charge carrier dynamics in Ti:hematite photoanodes enables the control and design of better interfaces for more efficient photoelectrochemical water splitting.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nakajima2021,

title = {Improving Thermodynamic Stability of nano-LiMn_{2}O_{4} for Li-Ion Battery Cathode},

author = {Kimiko Nakajima and Flavio L. Souza and Andre L. M. Freitas and Andrew Thron and Ricardo H. R. Castro},

url = {https://pubs.acs.org/doi/abs/10.1021/acs.chemmater.0c04305},

doi = {10.1021/acs.chemmater.0c04305},

issn = {1520-5002},

year  = {2021},

date = {2021-06-08},

urldate = {2021-06-08},

journal = {Chem. Mater.},

volume = {33},

number = {11},

pages = {3915--3925},

publisher = {American Chemical Society (ACS)},

abstract = {Nanomaterials can exhibit improved electrochemical performance in cathode applications, but their inherently high surface areas cause unconventional instability, leading to capacity fading after a limited number of battery cycles. This is because of their high surface reactivity, which makes them more susceptible to phenomena such as grain growth, sintering, solubilization, and phase transformations. Thermodynamically, these can be attributed to an increased contribution of interfacial enthalpies to the total free energy of the system. The lack of experimental data on the interfacial thermodynamics of lithium-based materials has hindered strategies to mitigate such degradation mechanisms. In this study, interfacial energies of LiMn2O4 nanoparticles were directly measured for the first time using calorimetry, and the possibility of thermodynamically manipulating both surface and grain boundary energies using a dopant (scandium) was explored. We show that undoped LiMn2O4 nanoparticles have a surface energy of 0.85 J/m2, which is significantly lower than that of LiCoO2. Moreover, introducing scandium further lowered the LiMn2O4 surface energy, leading to a demonstrated improved stability against coarsening and reactivity to water, which can potentially result in more stable cathode materials for battery applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{deLima2021b,

title = {Unveiling the dopant segregation effect at hematite interfaces},

author = {Felipe C. de Lima and Gabriel R. Schleder and João B. Souza Junior and Flavio L. Souza and Fabrício B. Destro and Roberto H. Miwa and Edson R. Leite and Adalberto Fazzio},

url = {https://pubs.aip.org/aip/apl/article-abstract/118/20/201602/40343/Unveiling-the-dopant-segregation-effect-at?redirectedFrom=fulltext},

doi = {10.1063/5.0049914},

issn = {1077-3118},

year  = {2021},

date = {2021-05-17},

urldate = {2021-05-17},

volume = {118},

number = {20},

publisher = {AIP Publishing},

abstract = {Understanding the effects of atomic structure modification in hematite photoanodes is essential for the rational design of high-efficiency functionalizations. Recently, it was found that interface modification with Sn/Sb segregates considerably increases hematite photocatalytic efficiency. However, the understanding of the different electronic effects of these modifications at the atomic level is still lacking. This Letter describes the segregation effects of two different dopants–Sn and Sb–on both the solid–solid (grain boundaries) and solid–liquid interfaces (surfaces) of hematite. Within an ab initio approach, we quantitatively extract the potential barrier reduction on polycrystalline interfaces due to the dopant, which causes an increase in the inter-grain electron transport. Concomitantly, the dopants' segregation on hematite surfaces results in a decrease in the oxygen vacancy formation energy. Such vacancies lead to the experimentally observed rise of the flatband potential. The comprehension of the electronic effects of dopants on both types of interfaces explains the experimental peak efficiency of interface-modified hematite with dopant segregates, also enabling the control and design of interfaces for different higher-efficiency applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Freitas2021,

title = {Insights on Thickness-Dependent Charge Transfer Efficiency Modulated by Ultrasonic Treatment in Hematite Photoanodes},

author = {Andre L. M. Freitas and Aryane Tofanello and Flavio L. Souza and Yat Li},

doi = {10.1021/acs.jpcc.0c11397},

issn = {1932-7455},

year  = {2021},

date = {2021-05-13},

urldate = {2021-05-13},

journal = {J. Phys. Chem. C},

volume = {125},

number = {18},

pages = {9981--9989},

publisher = {American Chemical Society (ACS)},

abstract = {The comprehension of the solid–liquid interface associated with the poor charge carrier dynamic of hematite has prevented its commercial application as a photoanode in a photoelectrochemical cell. The development of a low-cost and scalable strategy to overcome such drawbacks is still being pursued by the scientific community. Here, a simple surface modification of hematite photoanode designed with different thicknesses was carried out by employing an ultrasonic treatment (UST) process. UST creates an inhomogeneous defect distribution based on the solid–liquid energetics. The thicker photoanodes (H-4h) showed that the mechanical process can contribute to removing unstable layers, creating favorable sites for oxygen evolution without compromise the solid–solid interface. The UST approach for H-2h has promoted surface states pinning and possibly increased the stress between hematite and FTO. The effects on thinner photoanodes (H-2h) can drastically create polarized states that enhance surface trapping states, reducing the photogenerated charge lifetime. The outcome findings reveal that the surface hydroxylation might be extremely dependent on the electrode thickness. This study indicates that the UST approach is an efficient tool to boost the performance of thicker photoanodes, as desired for practical applications. Thus, for thinner layers, the stress induced at the hematite–FTO interface can be aggravated by mechanical treatment overcoming the beneficial effects at the solid–liquid interface. In fact, hydroxylation conducted via the sonication process is highly recommended for designing thicker films.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Carminati2021,

title = {Challenges and prospects about the graphene role in the design of photoelectrodes for sunlight-driven water splitting},

author = {Saulo A. Carminati and Ingrid Rodríguez-Gutiérrez and Andreia de Morais and Bruno L. da Silva and Mauricio A. Melo and Flavio L. Souza and Ana F. Nogueira},

url = {https://pubs.rsc.org/en/content/articlehtml/2021/ra/d0ra10176a},

doi = {10.1039/d0ra10176a},

issn = {2046-2069},

year  = {2021},

date = {2021-04-16},

urldate = {2021-04-16},

journal = {RSC Adv.},

volume = {11},

number = {24},

pages = {14374--14398},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {Graphene and its derivatives have emerged as potential materials for several technological applications including sunlight-driven water splitting reactions. This review critically addresses the latest achievements concerning the use of graphene as a player in the design of hybrid-photoelectrodes for photoelectrochemical cells. Insights about the charge carrier dynamics of graphene-based photocatalysts which include metal oxides and non-metal oxide semiconductors are also discussed. The concepts underpinning the continued progress in the field of graphene/photoelectrodes, including different graphene structures, architecture as well as the possible mechanisms for hydrogen and oxygen reactions are also presented. Despite several reports having demonstrated the potential of graphene-based photocatalysts, the achieved performance remains far from the targeted benchmark efficiency for commercial application. This review also highlights the challenges and opportunities related to graphene application in photoelectrochemical cells for future directions in the field.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}