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  • Journal article
    Cui J, Daboczi M, Regue M, Chin Y, Pagano K, Zhang J, Isaacs MA, Kerherve G, Mornto A, West J, Gimenez S, Kim J, Eslava Set al., 2022,

    2D bismuthene as a functional interlayer between BiVO4 and NiFeOOH for enhanced oxygen-evolution photoanodes

    , Advanced Functional Materials, Vol: 32, Pages: 1-12, ISSN: 1616-301X

    BiVO4 has attracted wide attention for oxygen-evolution photoanodes in water-splitting photoelectrochemical devices. However, its performance is hampered by electron-hole recombination at surface states. Herein, partially oxidized two-dimensional (2D) bismuthene is developed as an effective, stable, functional interlayer between BiVO4 and the archetypal NiFeOOH co-catalyst. Comprehensive (photo)electrochemical and surface photovoltage characterizations show that NiFeOOH can effectively increase the lifetime of photogenerated holes by passivating hole trap states of BiVO4; however, it is limited in influencing electron trap states related to oxygen vacancies (VO). Loading bismuthene on BiVO4 photoanodes increases the density of VO that are beneficial for the oxygen evolution reaction via the formation of oxy/hydroxyl-based water oxidation intermediates at the surface. Moreover, bismuthene increases interfacial band bending and fills the VO-related electron traps, leading to more efficient charge extraction. With the synergistic interaction of bismuthene and NiFeOOH on BiVO4, this composite photoanode achieves a 5.8-fold increase in photocurrent compared to bare BiVO4 reaching a stable 3.4 (±0.2) mA cm–2 at a low bias of +0.8 VRHE or 4.7(±0.2) mA cm–2 at +1.23 VRHE. The use of 2D bismuthene as functional interlayer provides a new strategy to enhance the performance of photoanodes.
  • Journal article
    Eslava S, Hintermair U, 2021,

    Editorial: Recent advances in water splitting

    , CURRENT OPINION IN GREEN AND SUSTAINABLE CHEMISTRY, Vol: 32, ISSN: 2452-2236
  • Journal article
    Kumar S, Eslava S, 2021,

    Mechanochemically synthesized Pb-free halide perovskite-based Cs2AgBiBr6-Cu-RGO nanocomposite for photocatalytic CO2 reduction

    , Journal of Materials Chemistry A, Vol: 5/5/21, Pages: 12179-12187, ISSN: 2050-7488

    Pb-based halide perovskites have recently showed great potential in various applications such as solar cells, optoelectronics and photocatalysis. Despite their high performance, the Pb2+ toxicity along with poor stability hinders long term applications in photocatalysis. Herein, we report mechanochemically prepared Pb-free Cs2AgBiBr6 double perovskite nanoplates and their heterostructure with Cu-loaded reduced graphene oxide (Cu–RGO) for gas-phase photocatalytic CO2 reduction using water vapor as the proton source in the absence of a hole scavenger. The resulting Cs2AgBiBr6–Cu–RGO nanocomposite shows significant photocatalytic activity of 10.7 (±0.6) μmol CH4 g−1 h−1, 1.9 (±0.3) μmol CO g−1 h−1 and 1.0 (±0.2) μmol H2 g−1 h−1, with a CH4 selectivity of 93.0 (±0.5)% on an electron basis with 1 sun and a remarkable apparent quantum efficiency of 0.89 (±0.21)% at 590 nm. A further 32% enhancement in photocatalytic activity on an electron basis is achieved when the light intensity is doubled (2 suns). The high performance was attributed to their improved charge separation and suppressed electron–hole recombination, along with extended visible light absorption, better stability in a humid environment and improved CO2 adsorption. These findings support Cs2AgBiBr6 as a potential Pb-free alternative to conventional halide perovskites for photocatalytic solar-to-fuel conversion and CO2 utilization.
  • Journal article
    Schukraft GEM, Woodward RT, Kumar S, Sachs M, Eslava S, Petit Cet al., 2021,

    Hypercrosslinked polymers as a photocatalytic platform for visible-light-driven CO2 photoreduction using H2O

    , ChemSusChem: chemistry and sustainability, energy and materials, Vol: 14, Pages: 1720-1727, ISSN: 1864-5631

    The design of robust, high‐performance photocatalysts is key for the success of solar fuel production by CO2 conversion. In this study, hypercrosslinked polymer (HCP) photocatalysts have been developed for the selective reduction of CO2 to CO, combining excellent CO2 sorption capacities, good general stabilities, and low production costs. HCPs are active photocatalysts in the visible light range, significantly outperforming the benchmark material, TiO2 P25, using only sacrificial H2O. It is hypothesized that superior H2O adsorption capacities facilitate access to photoactive sites, improving photocatalytic conversion rates when compared to sacrificial H2. These polymers are an intriguing set of organic photocatalysts, displaying no long‐range order or extended π‐conjugation. The as‐synthesized networks are the sole photocatalytic component, requiring no added cocatalyst doping or photosensitizer, representing a highly versatile and exciting platform for solar‐energy conversion.
  • Journal article
    Zhang J, Cui J, Eslava S, 2021,

    Oxygen evolution catalysts at transition metal oxide photoanodes: their differing roles for solar water splitting

    , Advanced Energy Materials, Vol: 11, Pages: 1-27, ISSN: 1614-6832

    In the field of photoelectrochemical water splitting for hydrogen production, dedicated efforts have recently been made to improve water oxidation at photoanodes, and in particular, to accelerate the poor kinetics of the oxygen evolution reaction which is a key step in achieving a viable photocurrent density for industrialization. To this end, coating the photoanode semiconductors with oxygen evolution catalysts (OECs) has been one of the most popular options. The roles of OECs have been found to be multifold, as opposed to exclusively catalytic. This review aims to unravel the complexity of the interfacial processes arising from the material properties of both semiconductors and OECs, and to rationalize the variation in findings in the literature regarding the roles of OECs. Light is also shed on some of the most useful characterization techniques that probe the dynamics of photogenerated holes, to answer some of the field's most challenging mechanistic questions. Finally, some ideas and suggestions on the design principles of OECs are proposed.
  • Journal article
    Rood SC, Pastor-Algaba O, Tosca-Princep A, Pinho B, Isaacs M, Torrente-Murciano L, Eslava Set al., 2021,

    Synergistic effect of simultaneous doping of ceria nanorods with Cu and Cr on CO oxidation and NO reduction

    , Chemistry: A European Journal, Vol: 27, Pages: 2165-2174, ISSN: 0947-6539

    Ceria particles play a key role in catalytic applications such as automotive three-way catalytic systems in which toxic CO and NO are oxidized and reduced to safe CO2 and N2, respectively. In this work, we explore the incorporation of Cu and Cr metals as dopants in the crystal structure of ceria nanorods prepared by a single-step hydrothermal synthesis. XRD, Raman and XPS confirm the incorporation of Cu and Cr in the ceria crystal lattices, offering ceria nanorods with a higher concentration of oxygen vacancies. XPS also confirms the presence of Cr and Cu surface species. H2-TPR and XPS analysis show that the simultaneous Cu and Cr co-doping results in a catalyst with a higher surface Cu concentration and a much-enhanced surface reducibility, in comparison with either undoped or singly doped (Cu or Cr) ceria nanorods. While single Cu doping enhances catalytic CO oxidation and Cr doping improves catalytic NO reduction, co-doping with both Cu and Cr enhances the benefits of both dopants in a synergistic manner employing roughly a quarter of dopant weight.
  • Journal article
    Hammond OS, Atri RS, Bowron DT, de Campo L, Diaz-Moreno S, Keenan LL, Doutch J, Eslava S, Edler KJet al., 2021,

    Structural evolution of iron forming iron oxide in a deep eutectic-solvothermal reaction

    , NANOSCALE, Vol: 13, Pages: 1723-1737, ISSN: 2040-3364
  • Journal article
    Regue M, Ahmet IY, Bassi PS, Johnson AL, Fiechter S, van de Krol R, Abdi FF, Eslava Set al., 2020,

    Zn-Doped Fe2TiO5 Pseudobrookite-Based Photoanodes Grown by Aerosol-Assisted Chemical Vapor Deposition

    , ACS APPLIED ENERGY MATERIALS, Vol: 3, Pages: 12066-12077, ISSN: 2574-0962
  • Journal article
    Kumar N, Kumar S, Gusain R, Manyala N, Eslava S, Ray SSet al., 2020,

    Polypyrrole-Promoted rGO-MoS2 Nanocomposites for Enhanced Photocatalytic Conversion of CO2 and H2O to CO, CH4, and H-2 Products

    , ACS APPLIED ENERGY MATERIALS, Vol: 3, Pages: 9897-9909, ISSN: 2574-0962
  • Journal article
    Temerov F, Pham K, Juuti P, Makela JM, Grachova E, Kumar S, Eslava S, Saarinen JJet al., 2020,

    Silver-Decorated TiO2 Inverse Opal Structure for Visible Light-Induced Photocatalytic Degradation of Organic Pollutants and Hydrogen Evolution

    , ACS APPLIED MATERIALS & INTERFACES, Vol: 12, Pages: 41200-41210, ISSN: 1944-8244
  • Book chapter
    Regue Grino M, Kumar S, Eslava S, 2020,

    Recent Advances in Photocatalytic Materials for Solar Fuel Production from Water and Carbon Dioxide

    , Heterogeneous Catalysis for Energy Applications, ISBN: 978-1-78801-718-3

    In recent years, photocatalysis has received significant attention because of its clean way of converting water or carbon dioxide into sustainable chemical fuels, providing promising and viable routes to overcome both renewable energy demand and global climate change. This chapter focuses on recent progress in the design and synthesis of sustainable photocatalytic materials, namely novel metal oxides, perovskites, metal–organic frameworks, metal sulfides, layered double hydroxides and plasmonic and metal-free materials. Advances in the preparation of these photocatalysts are reviewed, revealing efficient strategies to enhance their photocatalytic activity to produce hydrogen and carbon-based fuels such as carbon monoxide and methane from inexhaustible water and carbon dioxide. Emphasis is given to the strategies that maximize the visible light absorption of the solar spectrum and charge separation and transfer; for example, through forming heterojunctions of nanostructured materials. This chapter also highlights various strategies adopted for improving not only the photoconversion efficiency, but also the selectivity of certain carbon-based fuels. Adopting these advances within the scientific community will ensure more rapid progress towards high solar to fuel conversions and future commercialization of photocatalytic devices.
  • Journal article
    Schukraft GM, Woodward R, Kumar S, Sachs M, Eslava S, Petit Cet al., 2020,

    Hypercrosslinked Polymers as a Photocatalytic Platform for Visible-Light-Driven CO2 Photoreduction Using H2O

    <jats:p>The design of robust, high-performance photocatalysts is key for the success of solar fuel production <jats:italic>via</jats:italic> CO<jats:sub>2</jats:sub>conversion. Herein, we present hypercrosslinked polymer (HCP) photocatalysts for the selective reduction of CO<jats:sub>2</jats:sub> to CO, combining excellent CO<jats:sub>2</jats:sub> sorption capacities, good general stabilities, and low production costs. HCPs are active photocatalysts in the visible light range, significantly out-performing the benchmark material, TiO<jats:sub>2</jats:sub> P25, using only sacrificial H<jats:sub>2</jats:sub>O. We hypothesise that superior H<jats:sub>2</jats:sub>O adsorption capacities led to concentration at photoactive sites, improving photocatalytic conversion rates when compared to sacrificial H<jats:sub>2</jats:sub>. These polymers are an intriguing set of organic photocatalysts, displaying no long-range order or extended pi-conjugation. The as-synthesised networks are the sole photocatalytic component, requiring no co-catalyst doping or photosensitiser, representing a highly versatile and exciting platform for solar-energy conversion.</jats:p>
  • Journal article
    Kumar S, Regue M, Isaacs M, Freeman E, Eslava Set al., 2020,

    All-Inorganic CsPbBr3 nanocrystals: gram-scale mechanochemical synthesis and selective photocatalytic CO2 reduction to methane

    , ACS Applied Energy Materials, Vol: 3, Pages: 4509-4522, ISSN: 2574-0962

    Halide perovskite CsPbBr3 has recently gained wide interest for its application in solar cells, optoelectronics and artificial photosynthesis, but further progress is needed to develop greener and more scalable synthesis procedures and for their application in humid environments. Herein, we report a fast and convenient mechanochemical synthesis of CsPbBr3 perovskite nanocrystals with scale-up capability and control over crystal size and morphology. These perovskite nanocrystals show excellent crystallinity and tunable morphologies, from nanorods to nanospheres and nanosheets, simply changing the mechanochemical reaction conditions such as ball milling time, ball size and Cs precursor. Furthermore, we explore their use for gas-phase photocatalytic CO2 reduction using water vapor as proton source. A photocatalytic conversion of CO2 and H2O(g) to 0.43 (0.03) μmol CH4 g-1 h-1, 2.25 (0.09) μmol CO g-1 h-1 and 0.08 (0.02) μmol H2 g-1 h-1 was for example achieved with CsPbBr3 nanosheets and simulated sunlight, keeping 30% of this activity over three consecutive cycles. When these CsPbBr3 nanosheets were mechanochemically prepared together with Cu-loaded reduced graphene oxide (Cu-RGO), the photocatalytic activity significantly improved to 12.7 (0.95) μmol CH4 g-1 h-1, 0.46 (0.11) μmol CO g-1 h-1 and 0.27 (0.02) μmol H2 g-1 h-1, and a 90% of this activity was retained over three consecutive cycles. The selectivity for CH4 increased to 98.5(0.93)% on an electron basis and a remarkable apparent quantum efficiency of 1.10(0.15)% at 523 nm was achieved. This enhanced activity, selectivity and stability were assigned to the better charge separation, visible light absorption, CO2 adsorption & activation, and hydrophobic character of the obtained composites. These results will contribute to the rational design and application of halide perovskites for CO2 photocatalytic reduction.
  • Journal article
    Freeman E, Kumar S, Thomas SR, Pickering H, Fermin DJ, Eslava Set al., 2020,

    PrFeO3 Photocathodes Prepared Through Spray Pyrolysis

    , CHEMELECTROCHEM, Vol: 7, Pages: 1365-1372, ISSN: 2196-0216
  • Journal article
    Rood S, Eslava S, Manigrasso A, Bannister Cet al., 2020,

    Recent advances in gasoline three-way catalyst formulation: A review

    , PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART D-JOURNAL OF AUTOMOBILE ENGINEERING, Vol: 234, Pages: 936-949, ISSN: 0954-4070
  • Book chapter
    Regue M, Kumar S, Eslava S, 2020,

    CHAPTER 4: Recent Advances in Photocatalytic Materials for Solar Fuel Production from Water and Carbon Dioxide

    , RSC Energy and Environment Series, Pages: 80-115

    In recent years, photocatalysis has received significant attention because of its clean way of converting water or carbon dioxide into sustainable chemical fuels, providing promising and viable routes to overcome both renewable energy demand and global climate change. This chapter focuses on recent progress in the design and synthesis of sustainable photocatalytic materials, namely novel metal oxides, perovskites, metal-organic frameworks, metal sulfides, layered double hydroxides and plasmonic and metal-free materials. Advances in the preparation of these photocatalysts are reviewed, revealing efficient strategies to enhance their photocatalytic activity to produce hydrogen and carbon-based fuels such as carbon monoxide and methane from inexhaustible water and carbon dioxide. Emphasis is given to the strategies that maximize the visible light absorption of the solar spectrum and charge separation and transfer; for example, through forming heterojunctions of nanostructured materials. This chapter also highlights various strategies adopted for improving not only the photoconversion efficiency, but also the selectivity of certain carbon-based fuels. Adopting these advances within the scientific community will ensure more rapid progress towards high solar to fuel conversions and future commercialization of photocatalytic devices.
  • Journal article
    Freeman E, Kumar S, Celorrio V, Park MS, Kim JH, Fermin DJ, Eslava Set al., 2019,

    Strategies for deposition of LaFeO3 photocathodes: improving photocurrent with a polymer template

    , Sustainable Energy and Fuels, Vol: 4, Pages: 884-894, ISSN: 2398-4902

    Renewable and sustainable alternatives to fossil fuels are needed to limit the impact of global warming. Using metal oxide semiconductors as photoelectrodes within photoelectrochemical cell devices, in which solar energy can be stored and ultimately used for electricity generation, is one such alternative. LaFeO3 (LFO) has been shown to be an active photocathode on illumination of visible light but is restricted by low surface area and relatively low photocurrents achieved. The work herein utilizes a spin coating deposition method with a solution of nitrate precursors combined with non-ionic polymeric surfactant (Triton X-100). This allowed for the formation of a uniform porous LFO film of high coverage on a fluorine-doped tin oxide coated substrate, through directing growth and preventing particle aggregation during film fabrication. These porous LFO films achieved an enhanced photocurrent of -161±6 µA cm-2 at +0.43 VRHE, in addition to a remarkable high onset potential of +1.4 VRHE for cathodic photocurrent. It was additionally shown that this attained film quality and activity was superior to other film fabrication methods such as doctor blading and spray pyrolysis. With this polymer templating method for LFO films, not only are higher photocurrents achieved but there are also added benefits such as better charge separation, higher efficiencies, higher specific electrochemically-active surface area and improved stability.
  • Journal article
    Regue M, Sibby S, Ahmet IY, Friedrich D, Abdi FF, Johnson AL, Eslava Set al., 2019,

    TiO2 photoanodes with exposed {010} facets grown by aerosol-assisted chemical vapor deposition of a titanium oxo/alkoxy cluster

    , JOURNAL OF MATERIALS CHEMISTRY A, Vol: 7, Pages: 19161-19172, ISSN: 2050-7488
  • Journal article
    Zhang J, Eslava S, 2019,

    Understanding charge transfer, defects and surface states at hematite photoanodes

    , SUSTAINABLE ENERGY & FUELS, Vol: 3, Pages: 1351-1364, ISSN: 2398-4902
  • Journal article
    Poli I, Hintermair U, Regue M, Kumar S, Sackville EV, Baker J, Watson TM, Eslava S, Cameron PJet al., 2019,

    Graphite-protected CsPbBr3 perovskite photoanodes functionalised with water oxidation catalyst for oxygen evolution in water

    , Nature Communications, Vol: 10, Pages: 1-10, ISSN: 2041-1723

    Metal-halide perovskites have been widely investigated in the photovoltaic sector due to their promising optoelectronic properties and inexpensive fabrication techniques based on solution processing. Here we report the development of inorganic CsPbBr3-based photoanodes for direct photoelectrochemical oxygen evolution from aqueous electrolytes. We use a commercial thermal graphite sheet and a mesoporous carbon scaffold to encapsulate CsPbBr3 as an inexpensive and efficient protection strategy. We achieve a record stability of 30 h in aqueous electrolyte under constant simulated solar illumination, with currents above 2 mA cm−2 at 1.23 VRHE. We further demonstrate the versatility of our approach by grafting a molecular Ir-based water oxidation catalyst on the electrolyte-facing surface of the sealing graphite sheet, which cathodically shifts the onset potential of the composite photoanode due to accelerated charge transfer. These results suggest an efficient route to develop stable halide perovskite based electrodes for photoelectrochemical solar fuel generation.
  • Conference paper
    Zhang Y, Kumar S, Marken F, Krasny M, Roake E, Eslava S, Dunn S, Da Como E, Bowen CRet al., 2019,

    Pyro-electrolytic water splitting for hydrogen generation

    , 4th International Conference on Nanogenerator and Piezotronics (NGPT), Publisher: ELSEVIER SCIENCE BV, Pages: 183-191, ISSN: 2211-2855
  • Conference paper
    Kumar S, Poli I, Isaacs MA, Regue M, Eslava Set al., 2019,

    Mechanochemical synthesis of all-Inorganic CsPbBr3 nanorods and their use in selective photocatalytic hydrogenation of CO2

    , National Meeting of the American-Chemical-Society (ACS), Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
  • Journal article
    Rood SC, Ahmet HB, Gomez-Ramon A, Torrente-Murciano L, Reina TR, Eslava Set al., 2019,

    Enhanced ceria nanoflakes using graphene oxide as a sacrificial template for CO oxidation and dry reforming of methane

    , APPLIED CATALYSIS B-ENVIRONMENTAL, Vol: 242, Pages: 358-368, ISSN: 0926-3373
  • Journal article
    Walsh D, Zhang J, Regue M, Dassanayake R, Eslava Set al., 2019,

    Simultaneous Formation of FeOx Electrocatalyst Coating within Hematite Photoanodes for Solar Water Splitting

    , ACS APPLIED ENERGY MATERIALS, Vol: 2, Pages: 2043-2052, ISSN: 2574-0962
  • Journal article
    Castresana PA, Martinez SM, Freeman E, Eslava S, Di Lorenzo Met al., 2019,

    Electricity generation from moss with light-driven microbial fuel cells

    , ELECTROCHIMICA ACTA, Vol: 298, Pages: 934-942, ISSN: 0013-4686
  • Journal article
    Jo W-K, Kumar S, Eslava S, Tonda Set al., 2018,

    Construction of Bi2WO6/RGO/g-C3N4 2D/2D/2D hybrid Z-scheme heterojunctions with large interfacial contact area for efficient charge separation and high-performance photoreduction of CO2 and H2O into solar fuels

    , APPLIED CATALYSIS B-ENVIRONMENTAL, Vol: 239, Pages: 586-598, ISSN: 0926-3373
  • Journal article
    Regue M, Armstrong K, Walsh D, Richards E, Johnson AL, Eslava Set al., 2018,

    Mo-doped TiO2 photoanodes using [Ti4Mo2O8(OEt)(10)](2) bimetallic oxo cages as a single source precursor

    , SUSTAINABLE ENERGY & FUELS, Vol: 2, Pages: 2674-2686, ISSN: 2398-4902
  • Journal article
    Park MS, Walsh D, Zhang J, Kim JH, Eslava Set al., 2018,

    Efficient hematite photoanodes prepared by hydrochloric acid-treated solutions with amphiphilic graft copolymer

    , JOURNAL OF POWER SOURCES, Vol: 404, Pages: 149-158, ISSN: 0378-7753
  • Journal article
    Poli I, Baker J, McGettrick J, De Rossi F, Eslava S, Watson T, Cameron PJet al., 2018,

    Screen printed carbon CsPbBr3 solar cells with high open-circuit photovoltage

    , JOURNAL OF MATERIALS CHEMISTRY A, Vol: 6, Pages: 18677-18686, ISSN: 2050-7488
  • Journal article
    Zhang J, Garcia-Rodriguez R, Cameron P, Eslava Set al., 2018,

    Role of cobalt-iron (oxy)hydroxide (CoFeOx) as oxygen evolution catalyst on hematite photoanodes

    , Energy and Environmental Science, Vol: 11, Pages: 2972-2984, ISSN: 1754-5692

    Photoelectrochemical solar water splitting into hydrogen and oxygen offers an elegant and potentially efficient way to store solar energy in the chemical bonds of hydrogen, but the oxygen evolution rate is quite limited. The deposition of an oxygen evolution catalyst on the photoanode can enhance oxygen evolution, although the precise interplay between the semiconductor and the catalyst remains poorly understood and unoptimized. In this work, we use a combination of electrochemical approaches, including photoelectrochemical impedance spectroscopy and intensity modulated photocurrent spectroscopy, to unravel the nature of the interactions between different loadings of an electrocatalyst (CoFeOx) and a hematite (α-Fe2O3) semiconductor. A thin layer of CoFeOx mainly reduces surface charge recombination, while an extremely thin layer enhances charge transfer kinetics. Moreover, an interlayer of GaOx modifies the surface state distribution and increases the charge transfer rate even further. These findings point to new opportunities for understanding and manipulating complex photoanodes for oxygen evolution.

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