Influence of the coagulation bath on the nanostructure of cellulose films regenerated from an ionic liquid solution.

Cellulose membranes were prepared from an EMIMAc ionic liquid solution by nonsolvent-induced phase separation (NIPS) in coagulation baths of water-acetone mixtures, ethanol-water mixtures and water at different temperatures. High water volume fractions in the coagulation bath result in a highly reproducible gel-like structure with inhomogeneities observed by small-angle neutron scattering (SANS). A structural transition of cellulose takes place in water-acetone baths at very low water volume fractions, while a higher water bath temperature increases the size of inhomogeneities in the gel-like structure. These findings demonstrate the value of SANS for characterising and understanding the structure of regenerated cellulose films in their wet state. Such insights can improve the engineering and structural tuning of cellulose membranes, either for direct use or as precursors for carbon molecular sieve membranes.

Portable and Autonomous PEDOT-Modified Flexible Paper-Based Methanol Fuel Cell Sensing Platform Applied to L1CAM Recombinant Protein Detection.

This work describes first a 5-stack direct methanol fuel cell (DMFC) based on poly(3,4-ethylenedioxythiophene)-modified paper (PEDOT/PB-DMFC), which acts as an energy source and biosensor, coupled to an electrochromic cell (EC). It is autonomous and monitors the biosensor response by color change, as appropriate for point-of-care (POC) applications. In detail, DMFC strips were developed from square Whatman paper, and the EC was made on baking paper treated with polydimethylsiloxane (PDMS). The PEDOT/PB-DMFCs operate in a passive mode with a few microliters of diluted methanol. The biosensor layer was obtained on the anode ink (a composite of EDOT, oxidized multiwalled carbon nanotubes, and carbon black with platinum and ruthenium) by electropolymerizing 3,4-ethylenedioxythiophene (EDOT), in situ, in the presence of L1CAM. Each PEDOT/PB-DMFC single cell generates a voltage in the range of 0.3-0.35 V depending on the cell, and a five-cell stack delivers a 1.5-1.6 V voltage range when fed with 0.5 M methanol. The fabricated PEDOT/PB-DMFC/biosensor was calibrated against L1CAM, showing linear responses from 1.0 × 10-12 to 1.0 × 10-8 M with a detection limit of 1.17 × 10-13 M (single cell mode). When the EC was connected to the PEDOT/PB-DMFC device, a color gradient was observed. Overall, this work opens horizons to the use of biosensors even in places with energy scarcity and offers an alternative to reducing the current energy demand.

Correction: The route for commercial photoelectrochemical water splitting: a review of large-area devices and key upscaling challenges.

Correction for 'The route for commercial photoelectrochemical water splitting: a review of large-area devices and key upscaling challenges' by António Vilanova et al., Chem. Soc. Rev., 2024, https://doi.org/10.1039/d1cs01069g.

The route for commercial photoelectrochemical water splitting: a review of large-area devices and key upscaling challenges.

Green-hydrogen is considered a "key player" in the energy market for the upcoming decades. Among currently available hydrogen (H2) production processes, photoelectrochemical (PEC) water splitting has one of the lowest environmental impacts. However, it still presents prohibitively high production costs compared to more mature technologies, such as steam methane reforming. Therefore, the competitiveness of PEC water splitting must rely on its environmental and functional advantages, which are strongly linked to the reactor design, to the intrinsic properties of its components, and to their successful upscaling. This review gives special attention to the engineering aspects and categorizes PEC devices into four main types, according to the configuration of electrodes and strategies for gas separation: wired back-to-back, wireless back-to-back, wired side-by-side, and wired separated electrode membrane-free. Independently of the device architecture, the use of concentrated sunlight was found to be mandatory for achieving competitive green-H2 production. Additionally, feasible strategies for upscaling the key components of PEC devices, especially photoelectrodes, are urgently needed. In a pragmatic context, the way to move forward is to accept that PEC devices will operate close to their thermodynamic limits at large-scale, which requires a solid convergence between academics and industry. Research efforts must be redirected to: (i) build and demonstrate modular devices with a low-cost and highly recyclable embodiment; (ii) optimize thermal and power management; (iii) reduce ohmic losses; (iv) enhance the chemical stability towards a thousand hours; (v) couple solar concentrators with PEC devices; (vi) boost PEC-H2 production through the use of organic compounds; and (vii) reach consensual standardized methods for evaluating PEC devices, at both environmental and techno-economic levels. If these targets are not met in the next few years, the feasibility of PEC-H2 production and its acceptance by industry and by the general public will be seriously compromised.

C-N linked donor type porphyrin derivatives: unrevealed hole-transporting materials for efficient hybrid perovskite solar cells.

A new series of Zn(II) and Cu(II)-based porphyrin complexes 5a and 5b doubly functionalised with carbazole units were developed to be used as hole-transporting materials (HTMs) in perovskite solar cells (PSCs). These complexes were obtained via a nucleophilic substitution reaction mediated by PhI(OAc)2/NaAuCl4·2H2O, or using C-N transition metal-assisted coupling. The hole extraction capability of 5a and 5b was assessed using cyclic voltammetry; this study confirmed the better alignment of the Zn(II) complex 5a with the perovskite valence band level, compared to the Cu(II) complex 5b. The optimised geometry and molecular orbitals of both complexes also corroborate the higher potential of 5a as a HTM. Photoluminescence characterisation showed that the presence of 5a and 5b as HTMs on the perovskite surface resulted in the quenching of the emission, matching the hole transfer phenomenon. The photovoltaic performance was evaluated and compared with those of reference cells made with the standard HTM spiro-OMeTAD. The optimised 5-based devices showed improvements in all photovoltaic characteristics; their open circuit voltage (Voc) reached close to 1 V and short-circuit current density (Jsc) values were 13.79 and 9.14 mA cm-2 for 5a and 5b, respectively, disclosing the effect of the metallic centre. A maximum power conversion efficiency (PCE) of 10.01% was attained for 5a, which is 65% of the PCE generated by using the spiro-OMeTAD reference. This study demonstrates that C-N linked donor-type porphyrin derivatives are promising novel HTMs for developing efficient and reproducible PSCs.

New autonomous and self-signaling biosensing device for sarcosine detection.

An early diagnosis is the gold standard for cancer survival. Biosensors have proven their effectiveness in monitoring cancer biomarkers but are still limited to a series of requirements. This work proposes an integrated power solution, with an autonomous and self-signaling biosensing device. The biorecognition element is produced in situ by molecular imprinting to detect sarcosine, a known biomarker for prostate cancer. The biosensor was assembled on the counter-electrode of a dye-sensitized solar cell (DSSC), simultaneously using EDOT and Pyrrole as monomers for the biomimetic process and the catalytic reduction of triiodide in the DSSC. After the rebinding assays, the hybrid DSSC/biosensor displayed a linear behavior when plotting the power conversion efficiency (PCE) and the charge transfer resistance (RCT) against the logarithm of the concentration of sarcosine. The latter obtained a sensitivity of 0.468 Ω/decade of sarcosine concentration, with a linear range between 1 ng/mL and 10 µg/mL, and a limit of detection of 0.32 ng/mL. When interfacing an electrochromic cell, consisting of a PEDOT-based material, with the hybrid device, a color gradient between 1 ng/mL and 10 µg/mL of sarcosine was observed. Thus, the device can be used anywhere with access to a light source, completely equipment-free, suitable for point-of-care analysis and capable of detecting sarcosine within a range of clinical interest.

Stable Cobalt-Mediated Monolithic Dye-Sensitized Solar Cells by Full Glass Encapsulation.

Dye-sensitized solar cells (DSSCs) emerged in the market as one of the most promising indoor photovoltaic technologies to address the need for wireless powering of low-consuming electronics and sensor nodes of the internet of things (IoT). The monolithic design structure of the cell (M-DSSCs) makes the devices simpler and cheaper, and it is straightforward for constructing in-series modules. The most efficient DSSCs reported so far are Co(III/II)-mediated liquid junction cells with acetonitrile electrolytes; however, they are mostly unstable. This study reports on highly stable cobalt-mediated M-DSSCs, passing thermal cycling tests up to 85 °C according to ISOS standard protocols. Under 1000 h of aging in the dark and under simulated solar and artificial light soaking, all tested cells improved or retained their initial power conversion efficiency. Advanced long-term stability was achieved by eliminating the extrinsic factors of degradation, such as the interaction of the cell components with the environment and electrolyte leakage. This was obtained by encapsulation of the devices using a glass-frit sealant, including the holes for filling up the liquid components of the cells. The hermeticity of the encapsulation complies with the MIL-STD-883 standard fine helium gas leakage test, and its hermeticity remained unchanged after humidity-freeze cycles according to IEC 61646. The elimination of extrinsic degradation factors allowed reliable assessment of inner factors accountable for aging. The impact of the ISOS-protocol test conditions on the intrinsic device stability and long-term photovoltaic history of the M-DSSCs is discussed.

Overview of Membrane Science and Technology in Portugal.

Membrane research in Portugal is aligned with global concerns and expectations for sustainable social development, thus progressively focusing on the use of natural resources and renewable energy. This review begins by addressing the pioneer work on membrane science and technology in Portugal by the research groups of Instituto Superior Técnico-Universidade de Lisboa (IST), NOVA School of Science and Technology-Universidade Nova de Lisboa (FCT NOVA) and Faculdade de Engenharia-Universidade do Porto (FEUP) aiming to provide an historical perspective on the topic. Then, an overview of the trends and challenges in membrane processes and materials, mostly in the last five years, involving Portuguese researchers, is presented as a contribution to a more sustainable water-energy-material-food nexus.

Graded Morphologies and the Performance of PffBT4T-2OD:PC71BM Devices Using Additive Choice.

The impact of several solvent processing additives (1-chloronaphthalene, methylnaphthalene, hexadecane, 1-phenyloctane, and p-anisaldehyde), 3% v/v in o-dichlorobenzene, on the performance and morphology of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)-2,2',5',22033,5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM)-based polymer solar cells was investigated. Some additives were shown to enhance the power conversion efficiency (PCE) by ~6%, while others decreased the PCE by ~17-25% and a subset of the additives tested completely eliminated any power conversion efficiency and the operation as a photovoltaic device. Grazing-Incidence Wide Angle X-ray Scattering (GIWAXS) revealed a clear stepwise variation in the crystallinity of the systems when changing the additive between the two extreme situations of maximum PCE (1-chloronaphthalene) and null PCE (hexadecane). Small-Angle Neutron Scattering (SANS) revealed that the morphology of devices with PCE ~0% was composed of large domains with correlation lengths of ~30 nm, i.e., much larger than the typical exciton diffusion length (~12 nm) in organic semiconductors. The graded variations in crystallinity and in nano-domain size observed between the two extreme situations (1-chloronaphthalene and hexadecane) were responsible for the observed graded variations in device performance.

Hydrogen production via aqueous-phase reforming for high-temperature proton exchange membrane fuel cells - a review.

Aqueous-phase reforming (APR) can convert methanol and other oxygenated hydrocarbons to hydrogen and carbon dioxide at lower temperatures when compared with the corresponding gas phase process. APR favours the water-gas shift (WGS) reaction and inhibits alkane formation; moreover, it is a simpler and more energy efficient process compared to gas-phase steam reforming. For example, Pt-based catalysts supported on alumina are typically selected for methanol APR, due to their high activity at temperatures of circa 200°C. However, non-noble catalysts such as nickel (Ni) supported on metal-oxides or zeolites are being investigated with promising results in terms of catalytic activity and stability. The development of APR kinetic models and reactor designs is also being addressed to make APR a more attractive process for producing in situ hydrogen. This can also lead to the possibility of APR integration with high-temperature proton exchange membrane fuel cells. The integration can result into increased overall system efficiency and avoiding critical issues faced in the state-of-the-art fuel cells integrated with methanol steam reforming.

A passive direct methanol fuel cell as transducer of an electrochemical sensor, applied to the detection of carcinoembryonic antigen.

This work describes an electrochemical sensor with a biomimetic plastic antibody film for carcinoembryonic antigen (CEA, an important biomarker in colorectal cancer), integrated in the electrical circuit of a direct methanol fuel cell (DMFC), working in passive mode and used herein as power supply and signal transducer. In detail, the sensing layer for CEA consisted of a Fluorine-doped Tin Oxide (FTO) conductive glass substrate - connected to the negative pole side of the DMFC - with a conductive poly (3,4-ethylenedioxythiophene) (PEDOT) layer and a polypyrrol (PPy) molecularly-imprinted polymer (MIP), assembled in-situ. This sensing element is then closed using a cover FTO-glass, hold in place with a clip, connected to the positive side of the DMFC. When compared with control DMFCs, the power curves of DMFC/Sensor integrated system showed decreased power values due to the MIP layer interfaced in the electrical circuit, also displaying high stability signals. The DMFC/Sensor was further calibrated at room temperature, in different medium (buffer, a synthetic physiological fluid model and Cormay® serum), showing linear responses over a wide concentration range, with a limit of detection of 0.08 ng/mL. The DMFC/Sensor presented sensitive data, with linear responses from 0.1 ng/mL to 100 µg/mL and operating well in the presence of human serum. Overall, the results obtained evidenced the possibility of using a DMFC as a transducing element in an electrochemical sensor, confirming the sensitive and selective readings of the bio (sensing) imprinted film. This integration paves the way towards fully autonomous electrochemical devices, in which the integration of the sensor inside the fuel cell may be a subsequent direction.

Cellulose-Based Carbon Molecular Sieve Membranes for Gas Separation: A Review.

In the field of gas separation and purification, membrane technologies compete with conventional purification processes on the basis of technical, economic and environmental factors. In this context, there is a growing interest in the development of carbon molecular sieve membranes (CMSM) due to their higher permeability and selectivity and higher stability in corrosive and high temperature environments. However, the industrial use of CMSM has been thus far hindered mostly by their relative instability in the presence of water vapor, present in a large number of process streams, as well as by the high cost of polymeric precursors such as polyimide. In this context, cellulosic precursors appear as very promising alternatives, especially targeting the production of CMSM for the separation of O2/N2 and CO2/CH4. For these two gas separations, cellulose-based CMSM have demonstrated performances well above the Robeson upper bound and above the performance of CMSM based on other polymeric precursors. Furthermore, cellulose is an inexpensive bio-renewable feed-stock highly abundant on Earth. This article reviews the major fabrication aspects of cellulose-based CMSM. Additionally, this article suggests a new tool to characterize the membrane performance, the Robeson Index. The Robeson Index, θ, is the ratio between the actual selectivity at the Robeson plot and the corresponding selectivity-for the same permeability-of the Robeson upper bound; the Robeson Index measures how far the actual point is from the upper bound.

Morphology, Structure, and Dynamics of Pentacene Thin Films and Their Nanocomposites with [C2 C1 im][NTf2 ] and [C2 C1 im][OTF] Ionic Liquids.

In this study, a homogeneous thin film growth of pentacene onto indium tin oxide (ITO) coated glass surfaces is explored using a high-resolution and reproducible vapor deposition methodology. Moreover, vacuum thermal evaporation of ionic liquids (ILs) ([C2 C1 im][NTf2 ] and [C2 C1 im][OTF]) onto ITO, gold/palladium (AuPd) and pentacene surfaces were performed. A greater wettability behavior of ILs is observed for surfaces containing AuPd. Sequential and simultaneous depositions of ILs and pentacene were explored. Simultaneous depositions lead to the formation of nanocomposites films, consisting of IL micro- and nanodroplets covered by pentacene layers. Plasma surface treatment was used to induce the ILs droplets coalescence and explore the dynamics and phase separation of the nanocomposites. The [C2 C1 im][OTF] droplets were found to be completely covered with pentacene, which suggests a great affinity between cation-anion pairs and the aromatic moiety. Pentacene films and their nanocomposites with ILs exhibit a typical optical band gap of Egap =1.77 eV, indicating that the nanocomposite phase domains are large enough to behavior as the bulk.

Thiophene- and Carbazole-Substituted N-Methyl-Fulleropyrrolidine Acceptors in PffBT4T-2OD Based Solar Cells.

The impact of fullerene side chain functionalization with thiophene and carbazole groups on the device properties of bulk-heterojunction polymer:fullerene solar cells is discussed through a systematic investigation of material blends consisting of the conjugated polymer poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)-2,2';5',2″;5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD) as donor and C60 or C70 fulleropyrrolidines as acceptors. The photovoltaic performance clearly depended on the molecular structure of the fulleropyrrolidine substituents although no direct correlation with the surface morphology of the photoactive layer, as determined by atomic force microscopy, could be established. Although some fulleropyrrolidines possess favorable lowest unoccupied molecular orbital levels, when compared to the standard PC71BM, they originated OPV cells with inferior efficiencies than PC71BM-based reference cells. Fulleropyrrolidines based on C60 produced, in general, better devices than those based on C70, and we attribute this observation to the detrimental effect of the structural and energetic disorder that is present in the regioisomer mixtures of C70-based fullerenes, but absent in the C60-based fullerenes. These results provide new additional knowledge on the effect of the fullerene functionalization on the efficiency of organic solar cells.

Tailoring the Anodic Hafnium Oxide Morphology Using Different Organic Solvent Electrolytes.

Highly ordered anodic hafnium oxide (AHO) nanoporous or nanotubes were synthesized by electrochemical anodization of Hf foils. The growth of self-ordered AHO was investigated by optimizing a key electrochemical anodization parameter, the solvent-based electrolyte using: Ethylene glycol, dimethyl sulfoxide, formamide and N-methylformamide organic solvents. The electrolyte solvent is here shown to highly affect the morphological properties of the AHO, namely the self-ordering, growth rate and length. As a result, AHO nanoporous and nanotubes arrays were obtained, as well as other different shapes and morphologies, such as nanoneedles, nanoflakes and nanowires-agglomerations. The intrinsic chemical-physical properties of the electrolyte solvents (solvent type, dielectric constant and viscosity) are at the base of the properties that mainly affect the AHO morphology shape, growth rate, final thickness and porosity, for the same anodization voltage and time. We found that the interplay between the dielectric and viscosity constants of the solvent electrolyte is able to tailor the anodic oxide growth from continuous-to-nanoporous-to-nanotubes.

Different agglomeration properties of PC61BM and PC71BM in photovoltaic inks - a spin-echo SANS study.

Fullerene derivatives are used in a wide range of applications including as electron acceptors in solution-processable organic photovoltaics. We report agglomeration of fullerene derivatives in optically opaque solutions of PC61BM and PC71BM, with concentrations ranging from 30 mg mL-1 up to 90 mg mL-1, in different solvents with relevance to organic photovoltaics, using a novel neutron scattering technique, Spin-Echo Small Angle Neutron Scattering (SESANS). From SESANS, agglomerates with correlation lengths larger than 1 µm are found in some PC61BM solutions, in contrast no agglomerates are seen in PC71BM solutions. These results clearly show that PC71BM is fundamentally more soluble than PC61BM in the solvents commonly used in photovoltaic inks and corroborating similar observations previously achieved using other experimental techniques. Computer models are presented to study the energetics of solution and agglomeration of both species, ascribing the difference to a kinetic effect probably related to the larger anisotropy of PC71BM. Also, this work showcases the power of SESANS to probe agglomerates of fullerene derivatives in completely opaque solutions for agglomerates of the order of one to several microns.

The impact of phenyl-phenyl linkage on the thermodynamic, optical and morphological behavior of carbazol derivatives.

The impact of structural differentiation between phenylcarbazoles (PhC, mCP, CBP, TCB) and phenylamines (TPA, BDB, TPB, TDAB) on the phase equilibria, optical spectrum, band gap, and thin-film morphology is evaluated and discussed. The carbazolyl units lead to a lower electronic conjugation contributing to a wide band gap when compared with the diphenylamine analogs. The fusion and sublimation equilibria indicate that entropic contribution is the key factor for the distinguished melting behavior and solid-phase volatility between phenylcarbazole derivatives and phenylamine analogs. The molecular differentiation between the two classes of compounds is not reflected in the crystal packing and intermolecular interactions. However, compared with the diphenylamino groups, the incorporation of carbazolyl moieties contributes to a less flexible molecule. Moreover, the results evidence that intermolecular bonding disruption along the fusion transition is more extensive for phenylamine derivatives. Due to the asymmetric nonplanar structure, mCP is characterized by a ratio of {T g/T m ≈ 3/4} while the more symmetric CBP and TCB molecules display ratios closer to {T g/T m ≈ 2/3}. Vapor-deposited thin films of mCP, CBP, and TCB are amorphous and their morphology is highly dependent on the substrate roughness. The lower flexibility of nonplanar phenylcarbazoles induces the formation of a glassy state due to the harder packing mechanism leading to the lower ability of the crystallization process.

PffBT4T-2OD Based Solar Cells with Aryl-Substituted N-Methyl-Fulleropyrrolidine Acceptors.

Novel C60 and C70 N-methyl-fulleropyrrolidine derivatives, containing both electron withdrawing and electron donating substituent groups, were synthesized by the well-known Prato reaction. The corresponding highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy levels were determined by cyclic voltammetry, from the onset oxidation and reduction potentials, respectively. Some of the novel fullerenes have higher LUMO levels than the standards PC61BM and PC71BM. When tested in PffBT4T-2OD based polymer solar cells, with the standard architecture ITO/PEDOT:PSS/Active-Layer/Ca/Al, these fullerenes do not bring about any efficiency improvements compared to the standard PC71BM system, however they show how the electronic nature of the different substituents strongly affects the efficiency of the corresponding organic photovoltaic (OPV) devices. The functionalization of C70 yields a mixture of regioisomers and density functional theory (DFT) calculations show that these have systematically different electronic properties. This electronic inhomogeneity is likely responsible for the lower performance observed in devices containing C70 derivatives. These results help to understand how new fullerene acceptors can affect the performance of OPV devices.

Double-walled iron oxide nanotubes via selective chemical etching and Kirkendall process.

Double-walled oxide nanotube structures are interesting for a wide range of applications, from photocatalysis to drug delivery. In this work, a progressive oxidation method to fabricate double-walled nanotube structures is reported in detail. The approach is based on the electrodeposition of metallic iron nanowires, in porous alumina templates, followed by a selective chemical etching, nanoscale Kirkendall effect, a fast oxidation and out-diffusion of the metallic core structure during thermal annealing. To validate the formation mechanism of such core-shell structure, chemical composition and atomic structure were assessed. The resulting hematite nanotubes have a high degree of uniformity, along several microns, and a nanoscopic double-walled structure.

Temperature Impact on Perovskite Solar Cells Under Operation.

Perovskite solar cells (PSC) have emerged as a promising substitute for conventional silicon panels, showing the fastest power conversion efficiency evolution within the photovoltaic field, going from 3.8 % to 23.7 % in a few years. However, PSC thermal stability is still an obstacle to their commercialization. In this study, the temperature effect on mesoporous triple-cation perovskite solar cells with two different hole extraction materials-2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA)-is assessed. The cells are exposed to thermal stress between -5 °C and 80 °C and their photovoltaic performance is monitored in situ to reproduce real operating conditions. At low temperatures, the devices present very stable values (average loss <5 %), but as the temperature increases significant decreases in the open circuit potential and short-circuit current are observed. X-ray diffraction shows no change in the perovskite crystal structure with temperature. However, electron scanning microscopy and X-ray photoelectron spectroscopy indicate that temperature has a great impact on the hole extraction layer. The cell performance loss is attributed to the evaporation of additives added to the hole extraction layer to enhance its conductivity. Although the decrease in power conversion efficiency at 80 °C is slightly higher for PTAA cells, spiro-OMeTAD cells present a higher irreversible loss of (21.6±2.3) % after thermal stress tests, whereas PTAA devices showed only a loss of (8.2±1.6) %.