A. Bakandritsos, R. G. Kadam, P. Kumar, G. Zoppellaro, M. Medveď, J. Tuček, T. Montini, O. Tomanec, P. Andrýsková, B. Drahoš, R. S. Varma, M. Otyepka, M. B. Gawande, P. Fornasiero, and R. Zbořil, "Mixed-Valence Single-Atom Catalyst Derived from Functionalized Graphene," ADVANCED MATERIALS, Article in press.
DOI: 10.1002/adma.201900323 IF = 21.95
Abstract: Single‐atom catalysts (SACs) aim at bridging the gap between homogeneous and heterogeneous catalysis. The challenge is the development of materials with ligands enabling coordination of metal atoms in different valence states, and preventing leaching or nanoparticle formation. Graphene functionalized with nitrile groups (cyanographene) is herein employed for the robust coordination of Cu(II) ions, which are partially reduced to Cu(I) due to graphene‐induced charge transfer. Inspired by nature's selection of Cu(I) in enzymes for oxygen activation, this 2D mixed‐valence SAC performs flawlessly in two O2‐mediated reactions: the oxidative coupling of amines and the oxidation of benzylic CH bonds toward high‐value pharmaceutical synthons. High conversions (up to 98%), selectivities (up to 99%), and recyclability are attained with very low metal loadings in the reaction. The synergistic effect of Cu(II) and Cu(I) is the essential part in the reaction mechanism. The developed strategy opens the door to a broad portfolio of other SACs via their coordination to various functional groups of graphene, as demonstrated by successful entrapment of FeIII/FeII single atoms to carboxy‐graphene.
K. Jayaramulu, F. Geyer, A. Schneemann, Š. Kment, M. Otyepka, R. Zboril, D. Vollmer, R.A. Fischer: Hydrophobic Metal–Organic Frameworks, ADVANCED MATERIALS, Article in press, 2019.
DOI: 10.1002/adma.201900820, IF = 21.95
Abstract: Metal–organic frameworks (MOFs) have diverse potential applications in catalysis, gas storage, separation, and drug delivery because of their nanoscale periodicity, permanent porosity, channel functionalization, and structural diversity. Despite these promising properties, the inherent structural features of even some of the best‐performing MOFs make them moisture‐sensitive and unstable in aqueous media, limiting their practical usefulness. This problem could be overcome by developing stable hydrophobic MOFs whose chemical composition is tuned to ensure that their metal–ligand bonds persist even in the presence of moisture and water. However, the design and fabrication of such hydrophobic MOFs pose a significant challenge. Reported syntheses of hydrophobic MOFs are critically summarized, highlighting issues relating to their design, characterization, and practical use. First, wetting of hydrophobic materials is introduced and the four main strategies for synthesizing hydrophobic MOFs are discussed. Afterward, critical challenges in quantifying the wettability of these hydrophobic porous surfaces and solutions to these challenges are discussed. Finally, the reported uses of hydrophobic MOFs in practical applications such as hydrocarbon storage/separation and their use in separating oil spills from water are summarized. Finally, the state of the art is summarized and promising future developments of hydrophobic MOFs are highlighted.
L. Mascaretti, A. Dutta, Š. Kment, V. M. Shalaev, A. Boltasseva, R. Zbořil, and A. Naldoni, "Plasmon-enhanced photoelectrochemical water splitting for efficient renewable energy storage," ADVANCED MATERIALS, Article in press.
DOI: 10.1002/adma.201805513, IF = 21.95
Abstract: Photoelectrochemical (PEC) water splitting is a promising approach for producing hydrogen without greenhouse gas emissions. Despite decades of unceasing efforts, the efficiency of PEC devices based on earth‐abundant semiconductors is still limited by their low light absorption, low charge mobility, high charge‐carrier recombination, and reduced diffusion length. Plasmonics has recently emerged as an effective approach for overcoming these limitations, although a full understanding of the involved physical mechanisms remains elusive. Here, the reported plasmonic effects are outlined, such as resonant energy transfer, scattering, hot electron injection, guided modes, and photonic effects, as well as the less investigated catalytic and thermal effects used in PEC water splitting. In each section, the fundamentals are reviewed and the most representative examples are discussed, illustrating possible future developments for achieving improved efficiency of plasmonic photoelectrodes.
P. Štarha, Z. Trávníček: Non-platinum complexes containing releasable biologically active ligands, COORDINATION CHEMISTRY REVIEWS vol. 395, pp. 130-145, 2019.
DOI: 10.1016/j.ccr.2019.06.001, IF = 14.499
Abstract: Since the discovery of anticancer activity of cisplatin and other transition metal complexes, a lot of compounds have been reported as containing ligand(s) bearing its(their) own biological activity. Nowadays, the complexes containing releasable bioactive ligand(s), for which several terms (e.g., multi-targeted, multi-action or multi-modal) have been introduced, represent one of the hottest topics for the bioinorganic chemists. Herein we focused on rationally designed cytotoxic complexes of platinum-group metals, namely ruthenium, rhodium, palladium, osmium and iridium, which contain releasable bioactive ligand(s). Because a concept of multi-targeted complexes is based on a release and subsequent joint biological effect of multiple species, we concentrate especially on complexes whose fate under the (pseudo)physiological conditions is provably or most likely connected with a release of bioactive ligand(s)/substituent(s) and cytotoxic metal-containing species. Thus, the simultaneous action of the released species ensures various biological profits, such as higher cytotoxic activity, cytotoxicity at different cells (connected with the ability to overcome resistance) or modified processes connected with the mode of action, as compared with the initial complexes without bioactive ligand(s).
P.Štarha, J.Vančo and Z.Trávníček, "Platinum iodido complexes: A comprehensive overview of anticancer activity and mechanisms of action," COORDINATION CHEMISTRY REVIEWS vol. 380, pp. 103-135, 2019.
DOI: 10.1016/j.ccr.2018.09.017, IF = 14.499
Abstract: Platinum iodido complexes have long been recognized as synthetic intermediates of various platinum complexes (e.g., chlorido or carboxylato), including the world-wide used platinum-based anticancer drugs cisplatin, carboplatin and oxaliplatin. At the same time, platinum iodido complexes have been overlooked by bioinorganic chemists, because several pioneer works deemed the iodido ligand as unsuitable for the development of novel platinum-based metallotherapeutics. This was because most of platinum iodido complexes were identified as biologically and pharmacologically non-prospective as compared with the chlorido analogues. More recently, several research teams have developed various types of platinum iodido complexes as substances possessing the combination of promising chemical, physical, and especially biological properties. In particular, a number of platinum iodido complexes showed higher activity than their chlorido analogues and they exceeded even the activity of the conventional platinum-based drugs. Additionally, a lot of results have implied that relevant differences exist in the mechanism of action between platinum iodido agents, and their chlorido analogues and clinically-used platinum complexes
D. P. Dubal, K. Jayaramulu, J. Sunil, Š. Kment, P. Gomez-Romero, C. Narayana, R. Zbořil, and R. A. Fischer, "Metal–Organic Framework (MOF) Derived Electrodes with Robust and Fast Lithium Storage for Li-Ion Hybrid Capacitors," ADVANCED FUNCTIONAL MATERIALS, vol. 29, iss. 19, pp. 1900532, 2019.
DOI: 10.1002/adfm.201900532, IF = 13.325
A. Sánchez-Grande, B. de la Torre, J. Santos, B. Cirera, K. Lauwaet, T. Chutora, S. Edalatmanesh, P. Mutombo, J. Rosen, R. Zbořil, R. Miranda, J. Björk, P. Jelínek, N. Martín, D. Écija: On-Surface Synthesis of Ethynylene-Bridged Anthracene Polymers, ANGEWANDTE CHEMIE INTERNATIONAL EDITION vol. 58, iss. 20, pp. 6559-6563, 2019.
DOI: 10.1002/anie.201814154, IF = 12.102
Abstract: Engineering low‐band‐gap π‐conjugated polymers is a growing area in basic and applied research. The main synthetic challenge lies in the solubility of the starting materials, which precludes advancements in the field. Here, we report an on‐surface synthesis protocol to overcome such difficulties and produce poly(p‐anthracene ethynylene) molecular wires on Au(111). To this aim, a quinoid anthracene precursor with =CBr2 moieties is deposited and annealed to 400 K, resulting in anthracene‐based polymers. High‐resolution nc‐AFM measurements confirm the nature of the ethynylene‐bridge bond between the anthracene moieties. Theoretical simulations illustrate the mechanism of the chemical reaction, highlighting three major steps: dehalogenation, diffusion of surface‐stabilized carbenes, and homocoupling, which enables the formation of an ethynylene bridge. Our results introduce a novel chemical protocol to design π‐conjugated polymers based on oligoacene precursors and pave new avenues for advancing the emerging field of on‐surface synthesis.
I.S. Pieta, A. Rathi, P. Pieta, R. Nowakowski, M. Hołdynski, M. Pisarek, A. Kaminska, M.B.Gawande and R.Zboril, "Electrocatalytic methanol oxidation over Cu, Ni and bimetallic Cu-Ni nanoparticles supported on graphitic carbon nitride," APPLIED CATALYSIS B: ENVIRONMENTAL, vol. 244, pp. 272-283, 2019.
DOI: 10.1016/j.apcatb.2018.10.072, IF = 11.698
Abstract: Ni, Cu and Cu–Ni nanostructures have been fabricated and homogeneously embedded on ultrathin two-dimensional (2D) carbon nitride (g-C3N4), and the surface morphology and composition of the resulting hybrid nanostructures were studied by XRD, TEM, HRTEM-elemental mapping, Raman spectroscopy and XPS. The new hierarchical hetero-structures dropcasted on GC anodes have been visualised by SEM and their catalytic performance have been examined in methanol electrooxidation reaction (MOR) under alkaline conditions. Nanosized Ni particles dispersed finely over g-C3N4 are very active electrocatalysts with MOR onset at potential 0.35 V and charge transfer resistance 0.12 kΩ. The stability of modyfied GC electrodes, examined under chronoamperometric conditions showed that for electrode loading with 4% (wt. %) of NiO the stable current density ca. 36 A g−1 (12 A cm2) was obtained during whole experiment (up to 160 min). For all catalyst studied the curent density obtained during MOR reaction was enhanced when electrode was iluminated by UV light λ∼400 nm, and the highest value were obtained for 4% Ni/CN catalyst ca. 127 A g−1 (22 A cm2). The Cu incorporation in the hybrid material evoke loss of activity mostly due to Cu+ irreversible reduction/oxidation to Cu° and Cu2+, CuO segregation and influencing electron transfer process which results in the increasing in the redox potential. These results represent an important step towards light-enhanced electro-reactive systems and sensors in which heterojunction formation can facilitate electron-hole separation and enable more efficient energy transfer.
A.Naldoni, M. Altomare, G.Zoppellaro, N. Liu, Š.Kment, R.Zbořil and P.Schmuki, "Photocatalysis with Reduced TiO2: From Black TiO2 to Cocatalyst-Free Hydrogen Production," ACS CATALYSIS, vol. 9, iss. 1, pp. 345-364, 2019.
DOI: 10.1021/acscatal.8b04068, IF = 11.384
Abstract: Black TiO2 nanomaterials have recently emerged as promising candidates for solar-driven photocatalytic hydrogen production. Despite the great efforts to synthesize highly reduced TiO2, it is apparent that intermediate degree of reduction (namely, gray titania) brings about the formation of peculiar defective catalytic sites enabling cocatalyst-free hydrogen generation. A precise understanding of the structural and electronic nature of these catalytically active sites is still elusive, as well as the fundamental structure–activity relationships that govern formation of crystal defects, increased light absorption, charge separation, and photocatalytic activity. In this Review, we discuss the basic concepts that underlie an effective design of reduced TiO2 photocatalysts for hydrogen production such as (i) defects formation in reduced TiO2, (ii) analysis of structure deformation and presence of unpaired electrons through electron paramagnetic resonance spectroscopy, (iii) insights from surface science on electronic singularities due to defects, and (iv) the key differences between black and gray titania, that is, photocatalysts that require Pt-modification and cocatalyst-free photocatalytic hydrogen generation. Finally, future directions to improve the performance of reduced TiO2 photocatalysts are outlined.
E.C. Vermisoglou, P. Jakubec, A. Bakandritsos, M. Pykal, S. Talande, V. Kupka, R. Zbořil, M. Otyepka: Chemical Tuning of Specific Capacitance in Functionalized Fluorographene, CHEMISTRY OF MATERIALS, Article in press, 2019.
DOI: 10.1021/acs.chemmater.9b00655, IF = 10.159
Abstract: Owing to its high surface area and excellent conductivity, graphene is considered an efficient electrode material for supercapacitors. However, its restacking in electrolytes hampers its broader utilization in this field. Covalent graphene functionalization is a promising strategy for providing more efficient electrode materials. The chemistry of fluorographene is particularly attractive as it allows scalable chemical production of useful graphene derivatives. Nevertheless, the influence of chemical composition on the capacitance of graphene derivatives is a largely unexplored field in nanomaterials science, limiting further development of efficient graphene-based electrode materials. In the present study, we obtained well-defined graphene derivatives differing in chemical composition but with similar morphologies by controlling the reaction time of 5-aminoisophthalic acid with fluorographene. The gravimetric specific capacitance ranged from 271 to 391 F g–1 (in 1 M Na2SO4), with the maximum value achieved by a delicate balance between the amount of covalently grafted functional groups and density of the sp2 carbon network governing the conductivity of the material. Molecular dynamics simulations showed that covalent grafting of functional groups with charged and ionophilic/hydrophilic character significantly enhanced the ionic concentration and hydration due to favorable electrostatic interactions among the charged centers and ions/water molecules. Therefore, conductive and hydrophilic graphitic surfaces are important features of graphene-based supercapacitor electrode materials. These findings provide important insights into the role of chemical composition on capacitance and pave the way toward designing more efficient graphene-based supercapacitor electrode materials.
B. Cirera, B. de la Torre, D. Moreno, M. Ondráček, R. Zbořil, R. Miranda, P. Jelínek, D. Écija: On-Surface Synthesis of Gold Porphyrin Derivatives via a Cascade of Chemical Interactions: Planarization, Self-Metalation, and Intermolecular Coupling, CHEMISTRY OF MATERIALS vol. 31, iss. 9, pp. 3248-3256, 2019.
DOI: 10.1021/acs.chemmater.9b00125, IF = 9.89
Abstract: On-surface chemistry in ultrahigh vacuum offers complementary routes for synthesizing molecular complexes that cannot be accessed through standard solution chemistry. The presence of a surface not only imposes spatial two-dimensional restraints but also frequently acts as a source of adatoms actively participating in the chemical reactions. Here we demonstrate the formation of gold porphyrin derivatives via thermally induced chemical transformations of a fluorinated free-base porphyrin, 2H-4FTPP, on a Au(111) surface, which can rarely be accessed via standard solution chemistry protocols. We also provide an accurate description of the mechanisms of on-surface reactions and self-assembly processes, including structural and electronic characterization of intermediates and products using high-resolution scanning probe microscopy with a CO tip supported by a computational study. An initial annealing step at 500 K induces planarization of the adsorbed free base via dehydrogenation and ring-closing reactions that preserve the integrity of the C–F bonds. A second annealing step at 575 K enables metalation, producing unprecedented surface-supported gold-coordinated planarized porphyrins. A final annealing step at 625 K induces C–F and C–H activation, leading to intermolecular C–C coupling between phenyl termini to form planarized porphyrin oligomers. These results open new avenues for engineering in a stepwise manner thermally sensitive on-surface chemical reactions and metal–organic compounds that cannot be accessed in solution chemistry.
T. Malina, K. Poláková, J. Skopalík, V. Milotová, K. Holá, M. Havrdová, K.B. Tománková, V. Čmiel, L. Šefc, R. Zbořil: Carbon dots for in vivo fluorescence imaging of adipose tissue-derived mesenchymal stromal cells, CARBON, Article in press, 2019.
DOI: 10.1016/j.carbon.2019.05.061, IF = 7.466
Abstract: Tissue regeneration based on stem cell therapy is one of the most rapidly developing fields of modern medicine. Several properties of human mesenchymal stromal cells (MSCs), such as tropism toward a tumor or injury site, make them promising candidates for regenerative medicine, targeted therapy, or treating injured tissues. However, to fully understand the role of stem cells in therapeutic function, their visualization in vivo is essential. Here, we describe, for the first time, the use of biocompatible quaternized carbon dots (QCDs) as a novel stem-cell tracking probe for in vivo fluorescence imaging of transplanted human MSCs. By studying the in vitro cytotoxicity, intracellular distribution, and precise uptake mechanism, we showed that QCDs had a high biocompatibility and excellent fluorescence properties after 24 h incubation with MSCs. Further to demonstrate the in vivo feasibility of the system, QCD-labeled MSCs (100 μg/mL of QCDs, 24 h incubation time) were transplanted subcutaneously into an immunodeficient mouse and visualized by optical in vivo imaging. The labeled cells were strongly fluorescent, allowing their semi-quantitative detection. Moreover, the homing of intravenously transplanted QCD-labeled MSCs into the solid tumor was clearly shown. The results demonstrated that QCD-labeling of human MSCs is a highly promising approach for in vivo tracking during stem cell therapy.
H.Barès, A.Bakandritsos, M.Medveď, J.Ugolotti, P.Jakubec, O.Tomanec, S.Kalytchuk, R.Zbořil and M.Otyepka, "Bimodal role of fluorine atoms in fluorographene chemistry opens a simple way toward double functionalization of graphene," CARBON vol. 145, pp. 251-258, 2019.
DOI: 10.1016/j.carbon.2019.01.059, IF = 7.466
Abstract: Photo-triggered and double functionalization of graphene without use of aggressive photo-generated radicals is a challenging task in two-dimensional chemistry. This was here-in achieved by unravelling the bimodal role of fluorine atoms in fluorographene chemistry: (i) they rendered graphene's double bonds susceptible to reaction with a photo-activated diene and (ii) allowed nucleophilic substitution on F-bonded carbons. Theoretical calculations indicated that the presence of F atoms in the vicinity of sp2 carbon domains significantly increased bond polarization, turning the otherwise unfeasible on pristine graphene photo-cycloaddition into a very efficient functionalization strategy. Following this strategy, we prepared new graphene derivatives densely and homogeneously covered by functional groups. Furthermore, photo-induced cycloaddition following amine nucleophilic substitution on fluorographene enabled preparation of a bis-functionalized graphene derivative. The reported procedure paves the way toward unexplored graphene derivatives not attainable through known graphene chemistries, which can be utilized in many applications such as dual read-out sensors, drug delivery systems, catalysis, and energy storage.
M. Černík, J. Nosek, J.Filip, J. Hrabal, D.W. Elliott and R.Zbořil, "Electric-field enhanced reactivity and migration of iron nanoparticles with implications for groundwater treatment technologies: Proof of concept," WATER RESEARCH, vol. 154, pp. 361–369, 2019.
DOI: 10.1016/j.watres.2019.01.058, IF = 7.051
Abstract: The extensive use of nanoscale zero-valent iron (nZVI) particles for groundwater treatment has been limited, in part, because of their non-selective reactivity and low mobility in aquatic environments. Herein, we describe and explore progressive changes in the reactivity and migration of aqueous dispersed nZVI particles under an applied DC electric field. Due to the applied electric field with an intensity of about 1 V cm–1, the solution oxidation-reduction potential (ORP) remained as low as –200 mV for at least 32 days, which was in agreement with the persistence of the reduced iron species (mainly Fe(II)), and led to substantially prolonged reactivity of the original nZVI. The treatment of chlorinated ethenes (DCE>PCE>TCE) was markedly faster, individual CHC compounds were eliminated with the same kinetics and no lesser-chlorinated intermediates were accumulated, following thus the direct dechlorination scheme. When nZVI-dispersion flows towards the anode through vertical laboratory columns filled with quartz sand, significant enhancement of nZVI migration was recorded because of lower extent of nanoparticle aggregation and increased repulsion forces between the nanoparticles and the surface of silica dioxide. The results of this study have significant consequences for groundwater remediation, mainly for the treatment of slowly degradable DCE in real CHC contaminated groundwater, where it could improve the reactivity, the longevity and the migration of nZVI particles.
D.D.Chronopoulos, M. Medveď, P.Błoński, Z. Nováček, P.Jakubec, O.Tomanec, A.Bakandritsos, V.Novotná, R.Zbořil and M.Otyepka, "Alkynylation of graphene via the Sonogashira C–C cross-coupling reaction on fluorographene," CHEMICAL COMMUNICATIONS, vol. 55, iss. 8, pp. 1088–1091, 2019.
DOI: 10.1039/c8cc08492k, IF = 6.29
Abstract: We report successful grafting of alkynyl groups onto graphene via the Sonogashira reaction between fluorographene and terminal alkynes. Theoretical calculations revealed that fluorographene can efficiently bind and oxidize the palladium catalyst on electrophilic sites activated by fluorine atoms. This paves the way towards conductive and mechanically robust 3D covalent networks.
L. Stadler, M. Homafar, A. Hartl, S. Najafishirtari, M. Colombo, R.Zboril, P. Martin, M.B.Gawande, J. Zhi and O. Reiser, "Recyclable Magnetic Microporous Organic Polymer (MOP) Encapsulated with Palladium Nanoparticles and Co/C Nanobeads for Hydrogenation Reactions," ACS SUSTAINABLE CHEMISTRY & ENGINEERING, vol. 7, iss. 2, pp. 2388–2399, 2019.
DOI: 10.1021/acssuschemeng.8b05222, IF = 6.14
Abstract: Microporous organic polymers (MOPs) encapsulated with palladium nanoparticles (NPs) and immobilized on magnetic Co/C nanobeads show excellent activity in hydrogenation reactions of alkenes, alkynes, and nitro arenes with turnover frequencies (TOFs) up to 3000 h–1. The magnetic core of the nanobeads ensures an easy and fast recyclability for at least six consecutive runs by applying an external magnet to recapture the catalyst. The catalytic system reported here uses cross-linked toluene as a polymer structure and is readily prepared via a cost-efficient and versatile synthesis based on commercially available starting materials. The novel catalysts combine the advantages of a heterogeneous magnetic support with MOPs that prevent NPs from agglomeration or deactivation. In addition, the advantages of palladium NPs as exceedingly active catalyst due to their high surface-area-to-volume ratio are exploited. Furthermore, the polymeric structure can easily be varied by the change of the aromatic monomer. Introducing hydroxyl groups by 2,2′-biphenol as the monomer into the MOP, the leaching of palladium and cobalt from the catalyst can be reduced to a minimum.
M. Magro, D. Baratella, E. Bonaiuto, J. de Almeida Roger, G. Chemello, S. Pasquaroli, L. Mancini, I. Olivotto, G.Zoppellaro, J.Ugolotti, C. Aparicio, A.P. Fifi, G. Cozza, G. Miotto, G. Radaelli, D. Bertotto, R.Zboril and F.Vianello, "Stealth Iron Oxide Nanoparticles for Organotropic Drug Targeting," BIOMACROMOLECULES, vol. 20, iss. 3, pp. 1375–1384, 2019.
DOI: 10.1021/acs.biomac.8b01750, IF = 5.738
Abstract: The ability of peculiar iron oxide nanoparticles (IONPs) to evade the immune system was investigated in vivo. The nanomaterial was provided directly into the farming water of zebrafish (Danio rerio) and the distribution of IONPs and the delivery of oxytetracycline (OTC) was studied evidencing the successful overcoming of the intestinal barrier and the specific and prolonged (28 days) organotropic delivery of OTC to the fish ovary. Noteworthy, no sign of adverse effects was observed. In fish blood, IONPs were able to specifically bind apolipoprotein A1 (Apo A1) and molecular modeling showed the structural analogy between the IONP@Apo A1 nanoconjugate and high-density lipoprotein (HDL). Thus, the preservation of the biological identity of the protein suggests a plausible explanation of the observed overcoming of the intestinal barrier, of the great biocompatibity of the nanomaterial, and of the prolonged drug delivery (benefiting of the lipoprotein transport route). The present study promises novel and unexpected stealth materials in nanomedicine.
X. Yang, S. Wang, X. Zhuang, O.Tomanec, R.Zboril, D.Y.W. Yu and A.L. Rogach, "Polypyrrole and Carbon Nanotube Co-Composited Titania Anodes with Enhanced Sodium Storage Performance in Ether-Based Electrolyte," ADVANCED SUSTAINABLE SYSTEMS, Article in press, 2019.
Abstract: In terms of applications for sodium‐ion batteries, titania shows several compelling features, such as environmental availability, favorable sodiation potential, and long cycle lifespan, but it also possesses several drawbacks such as the low utilization and low initial coulombic efficiency (ICE). A double‐fold carbon incorporation strategy of improving titania anode materials, namely coating titania nanoparticles with polypyrrole (PPY) and integrating them into a carbon nanotube (CNT) network, is introduced. This treatment not only ensures direct contact of individual titania nanoparticles with the conductive components in the composite but also builds a 3D interconnecting CNT framework to facilitate both mass and charge transfer. The TiO2/PPY/CNT composite delivers reversible capacity of 252 and 201 mAh g−1 at 0.1 and 1 C, respectively; achieves an ICE of 70%, which is the highest value so far, in an ether‐based electrolyte; and retains nearly 80% of its capacity in a 3000‐cycle test. Co‐compositing titania with PPY and CNT guarantees both efficient electrical connection of active materials and resilience against cycling, and this strategy is feasible for various electrode materials which usually need carbon incorporation to improve capacity and stabilize cycling.
M. Poornajar, N. T. Nguyen, H.-J. Ahn, M. Büchler, N. Liu, S.Kment, R.Zboril, J. E. Yoo and P.Schmuki, "Fe2O3 Blocking Layer Produced by Cyclic Voltammetry Leads to Improved Photoelectrochemical Performance of Hematite Nanorods," SURFACES vol. 2, iss. 1, pp. 131-144, 2019.
Abstract: Hematite is a low band gap, earth abundant semiconductor and it is considered to be a promising choice for photoelectrochemical water splitting. However, as a bulk material its efficiency is low because of excessive bulk, surface, and interface recombination. In the present work, we propose a strategy to prepare a hematite (α-Fe2O3) photoanode consisting of hematite nanorods grown onto an iron oxide blocking layer. This blocking layer is formed from a sputter deposited thin metallic iron film on fluorine doped tin oxide (FTO) by using cyclic voltammetry to fully convert the film into an anodic oxide. In a second step, hematite nanorods (NR) are grown onto the layer using a hydrothermal approach. In this geometry, the hematite sub-layer works as a barrier for electron back diffusion (a blocking layer). This suppresses recombination, and the maximum of the incident photon to current efficiency is increased from 12% to 17%. Under AM 1.5 conditions, the photocurrent density reaches approximately 1.2 mA/cm2 at 1.5 V vs. RHE and the onset potential changes to 0.8 V vs. RHE (using a Zn-Co co-catalyst).