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Publications
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Direct Solar Charging of an Organic–Inorganic, Stable, and Aqueous Alkaline Redox Flow Battery with a Hematite Photoanode
Communication- K. Wedege J. Azevedo A. Khataee A. Bentien A. Mendes
DOI: 10.1002/anie.201602451
First published online: 6 May 2016PDFSourceThe intermittent nature of the sunlight and its increasing contribution to electricity generation is fostering the
energy storage research. Direct solar charging of an auspicious type of redox flow battery could make solar energy directly and efficiently dispatchable. The first solar aqueous alkaline redox flow battery using low cost and environmentally safe materials is demonstrated. The electrolytes consist of the redox couples
ferrocyanide and anthraquinone-2,7-disulphonate in sodium hydroxide solution, yielding a standard cell potential of 0.74 V. Photovoltage enhancement strategies are demonstrated for the ferrocyanide-hematite junction by employing an annealing treatment and growing a layer of a conductive polyaniline polymer on the electrode surface, which decreases electron–hole recombination. -
Laser assisted glass-glass encapsulation for perovskite solar cells
Presentation- S. Emami I. Mesquita J. Pinto L. Andrade A. Mendes
First published online: 4 Mar 2016PDF -
Extremely stable bare hematite photoanode for solar water splitting
Paper in international journal with revision- P. Dias A. Vilanova T. Lopes L. Andrade A. Mendes
DOI: 10.1016/j.nanoen.2016.03.008
First published online: 10 Mar 2016PDFSourcePhotoelectrodes that are efficient, highly stable,made from low cost materials and easily prepared using
inexpensive techniques are required for commercially viable solar photoelectrochemical (PEC) water-
splitting technology. Hematite is one of few materials that is being considered for this application. In this
work, bare hematite thin films prepared by spray pyrolysis were systematically optimized following a
design of experiments approach. Are sponse surface methodology was applied to factors:(i) sprayed
volume of solution; (ii) temperature of the glass substrate during the deposition; and (iii) time gap
between sprays and the optimized operating conditions obtained were v¼ 42 mL, T¼425 °C and t¼35 s.
The optimized hematite photoelectrode showed a photocurrent density of ca. 0.94mAcm2 at 1.45VRHE,
without dopants orco-catalysts, which is remarkable for a thin film of ca. 19nm. The stability of this
photoelectrode was assessed over 1000h of PEC operation under1 -sun of simulated sunlight. Are cord-
breaking result was obtained with no evidences of hematite film degradation neither of current density
loss. These results open the door to turn PECcells into a competitive technology in the solar fuel
economy. -
Unbiased solar energy storage: Photoelectrochemical redox flow battery
Paper in international journal with revision- J. Azevedo T. Seipp J. Burfeind C. Sousa A. Bentien J. Araújo A. Mendes
DOI: 10.1016/j.nanoen.2016.02.029
First published online: 22 Feb 2016PDFSourceElectricity from renewable energy sources is craving for efficient storage technologies,in particular
solar industry,to enable practica small-scale solutions for residential and offices use.The best estationary technology is probably the redox flow batteries.This article proposes the direct conversion of sunlight into electrochemical energy store in a redox flow battery. A photoelec-ctrochemical cell is used to charge a vanadium redox flow cell (CdS(s)|V3+, VO2+||V3+, V2+|Carbon Felt(s), E0=0.6 VNHE). ACdSthin film photoelectrode is prepared to directly charge the cell, pairs V3+/VO2+. CdS photoanode exhibits competitive photo currents,when compared to other photo-electrochemical devices,and yields enough photovoltage to charge the vanadium battery up to 75% with no external bias. An over layer of CdSe improves the performance of CdS with current densities up to ca.1.4mAcm2. Finally,a tandem configuration is tested using a dye-sensitized solar cell and a CdS photoanoade creating 1.3 V of photovoltage. This tandem arrangement proves to charge conventional all vanadium redox cell(DSC/CdS(s)|VO2+, VO2
+||V3+, V2+|Carbon Felt(s), E0=1.2 VNHE) without external bias. -
N-doped carbon quantum dots/TiO2 composite with improved photocatalytic activity
Paper in international journal with revision- N. Martins J. Ângelo A. Violeta Girão T. Trindade L. Andrade A. Mendes
DOI: 10.1016/j.apcatb.2016.04.016
First published online: 11 Apr 2016PDFSourceA new composite of TiO2(P25) and N-doped carbon quantum dots (P25/NCQD) was prepared by ahydrothermal method and was used for the first time as catalyst of the photo-oxidation of NO underUV and visible light irradiation. P25/NCQD composite exhibited a NO conversion (27.0%) more than twotimes higher of that observed for P25 (10%) under visible light and the selectivity of the process wasincreased from 37.4% to 49.3%. The composite also showed better photocatalytic performance than P25in the UV region with increases of 36.3% on NO conversion and 16.8% on selectivity. Moreover, com-pared with P25, the photodegradation ratio of methylene blue was enhanced from 68% to 91% after UVirradiation for 1 h. NCQD played a crucial role on the photocatalytic activity improvement of P25/NCQD,increasing visible light absorption, slowing the recombination and improving the charge transfer. -
Role of temperature in the recombination reaction on dye-sensitized solar cells
Paper in international journal with revision- J. Maçaira I. Mesquita L. Andrade A. Mendes
DOI: 10.1039/C5CP02942B
First published online: 28 Jul 2015PDFSourceThe DSC recombination kinetics was studied up to 100 °C without electrolyte leakage or external contamination using a unique laser assisted glass sealing process. In addition to temperature having a strong influence on the recombination reaction rate, the energy of the exited electrons was found to be critical for determining the recombination activation energy. -
Tailoring the Ti surface via electropolishing nanopatterning as a route to obtain highly ordered TiO2 nanotubes
Paper in international journal with revision- A. Apolinário C. T. Sousa J. Ventura L. Andrade A. M. Mendes J. P. Araújo
DOI: 10.1088/0957-4484/25/48/485301
First published online: 7 Nov 2014PDFHighly ordered TiO2 nanotubes (NTs) were synthesized by the electrochemical anodization of Ti foils subjected to electropolishing (EP) pre-treatment. We found that the Ti surface roughness plays an important role in the onset of pore nucleation in enhancing the local focusing effect of the electrical field. Additionally, EP induces the formation of dimple structures on the metal surface, which can work as a pre-pattern prior to anodization. These shallow ripples lead to a preferentially ordered pore nucleation, offering an organizational improvement of the anodic oxide NTs. We found that, depending on the EP applied potential, the roughness and the spatial period of the ripple-like structures varies from 8–2 nm and from 122–30 nm, respectively. -
Transparent graphene-based counter-electrodes for iodide/triiodide mediated dye-sensitized solar cells
Paper in international journal with revision- R. Cruz
- J. P. Araújo
- L. Andrade
- A. Mendes
DOI: 10.1039/C3TA14593J
First published online: 10 Dec 2013PDFA new highly transparent and low cost counter-electrode for dye-sensitized solar cells was fabricated, comprised of a structured graphene film over nickel nanoparticles. Annealed nickel particles induced an enhanced restoration of graphene double bonds, which led to cells with energy conversion efficiencies similar to those using a conventional platinum electrode.
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Modeling, simulation and design of dye sensitized solar cells
Paper in International Journals with Revision- J. Maçaira
- L. Andrade
- A. Mendes
DOI: 10.1039/C3RA46295A
First published online: 22 Nov 2013PDFIt is well known that recombination and transport rule the performance of dye sensitized solar cells (DSC's); although, the influence that these two phenomena have in their performance, particularly on the open circuit-potential (Voc) and on the short circuit current (Jsc), is not fully understood. In this paper a phenomenological model is used to describe the quantitative effect that transport and recombination have on the performance of the solar cell and their influence on its optimal design. The model is used to predict the influence of the recombination reaction rate constant (kr) and diffusion coefficient (Deff) on the Voc and on the Jsc, whether a linear or non-linear recombination kinetic is considered.
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Laser Assisted Dye-sensitized Solar Cell Sealing: from small to large cells areas
Paper in International Journals with Revision- F. Ribeiro
- J. Maçaira
- I. Mesquita
- J. Gabriel
- L. Andrade
- A. Mendes
DOI: 10.1063/1.4865948
First published online: 12 Feb 2014PDFDye sensitized solar cells (DSCs) modules are an emergent photovoltaic technology but still present some weaknesses in terms of long-term stability: sealing is presently the Achilles' heel of DSCs, which is currently preventing their commercialization. Thermoplastic sealants are normally used to bond the two glass substrates of a DSC. However, these thermoplastic sealants, such as Surlyn®, are permeable towards ambient water vapor, UV sensitive, and they cannot be used above 60 °C. Laser assisted glass-frit sealing is a very interesting alternative sealing technique as it has been demonstrated on microelectromechanical systems assembly.
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Dye sensitized solar cells – paving the way to commercialization
Invited Lecture- L. Andrade
- A. Mendes
First published online: 8 May 2014PDF -
Recent developments on dye-sensitized solar cells to pave the way for commercialization
Invited Lecture- L. Andrade
- A. Mendes
First published online: 5 Jun 2013PDFThe electric power produced by photovoltaic panels is already very close to the electricity market price. Photovoltaics have the ability to produce electricity where it is consumed, using builds as support. New technologies are emerging with the ability to merge into buildings’ structure. Dye sensitized solar cells (DSC) belong to the so-called third generation of photovoltaic cells and are front positioned to lead the building-integrated photovoltaic (BIPV) market. DSCs are very aesthetic, with various patterns and colors, and show a unique ability to harvest efficiently the diffuse sunlight, making them suitable for façades. -
Photovoltaic dye sensitized solar cells: paving the way to commercialization
Invited Lecture- L. Andrade
- A. Mendes
First published online: 12 Nov 2013PDF -
Photoelectrochemical cells: from water splitting to electrochemical energy storage
Invited Lecture- A. Mendes
- L. Andrade
- A. Bentien
First published online: 12 Feb 2014PDFElectricity produced from solar and wind energy sources have limited or no dispatchability, making storage of energy a hot research topic. Pumped-storage hydroelectricity has several advantages, namely high capacity, reasonable response time, high cycle efficiency and low costs. However, for countries of limited hydraulic energy resources and for local storage, other approaches should be considered. -
The end of Pt counter-electrodes: Transparent graphene-based cathodes for iodine and cobalt-based liquid-junction (electrolytes in) DSCs
Poster Presentation- R. Cruz
- L. Andrade
- A. Mendes
First published online: 11 May 2014PDFDye-sensitized solar cells (DSCs) are a promising technology among the so-called third generation of photovoltaic cells, based on the idea of using nanotechnology and fairly abundant/environmentally friendly raw materials for lowering production costs and increase sustainability. The DSCs technology is now emerging due to its superior performance under more demanding atmospheric conditions and semi-transparency properties. -
Optimization of photoelectrode features in Cobalt (II/III) based electrolyte DSCs
Poster Presentation- J. Maçaira
- I. Mesquita
- L. Andrade
- A. Mendes
First published online: 11 May 2014PDFFrom the 1.7 × 105 TW of solar energy that strikes continuously the earth, a practical terrestrial solar energy conversion potential value is estimated to be about 600 TW. The way of taking advantage of all this energy is, undoubtedly, using solar cells. The photovoltaic cells made from silicon, although showing efficiencies of 15-25 %, present high-manufacturing costs and toxic chemicals in their fabrication process. On the other hand, dye sensitized solar cells (DSCs) are environmentally friendly and have a low-cost production. The current and voltage outputs determining the DSC’s efficiency are recombination limited and result from a balance between charge generation and recombination fluxes. -
Dye sensitized solar cells – how far are we from a commercial product?
Poster Presentation- L. Andrade
- Adélio Mendes
First published online: 11 May 2014PDFDye-sensitized solar cells (DSSCs) were first proposed by Michael Grätzel in 1991. Since then the scientific knowledge and performance of these devices observed a tremendous evolution; still, these devices are mostly not commercial. The number one reason is the stability of DSCs, which has never been properly addressed by the research community. Other reasons are related to target market for these devices that was never clearly defined, besides other technological aspects related to their fabrication. Indeed, the research community has been so far deeply fascinated in developing and testing new materials targeting more efficient devices, neglecting other important objectives towards the development of DSCs. -
Laser sealed DSCs: Efficiency and long term stability analysis
Poster Presentation- J. Maçaira
- F. Ribeiro
- I. Mesquita
- J. Gabriel
- L. Andrade
- A. Mendes
First published online: 5 May 2013PDFThe environmental pollution arising from oil spills and the climatic consequences of the greenhouse effect caused by fossil fuels combustion fostered the development of several alternatives for energy production. Solar energy is the fastest growing segment of renewable energy sources, which in the non-OECD countries is expected to grow annually 22.8 % until 2035. The forecasts for 2015 put total installed photovoltaic (PV) capacity in the world between 131 GW and 196 GW. -
Temperature Influence in the Recombination Reaction of Dye-Sensitized Solar Cells
Presentation- J. Maçaira L. Andrade A. Mendes
First published online: 11 Sep 2014PDF -
Novel Photocatalytic Paint towards NO Deep Oxidation
Poster presentation- J. Ângelo P. Magalhães L. Madeira L. Andrade A. Mendes
First published online: 10 Sep 2014PDF -
Synthesis and Assessment of a Graphene-based Composite Photocatalyst
Presentation- P. Magalhães J. Ângelo V. M. Sousa
- O. Nunes L. Andrade
- A. Mendes
First published online: 10 Sep 2014PDF -
Effect of Doping On The Photocatalytic Activity of TiO2 Nanowires Prepared By the Hydrothermal Method
Poster Presentation- M. Honório R. Moreira
- A. Mendes L. Andrade
First published online: 10 Sep 2014PDF -
Predicting activation energies for the recombination reaction in dye-sensitized solar cells
Poster Presentation- J. Maçaira
- I. Mesquita
- L. Andrade
- A. Mendes
First published online: 8 Jul 2014PDFDye-sensitized solar cells (DSSCs) have been considered an effective alternative to conventional p-n junction devices. Their low production cost, ability to harvest diffuse light and versatile applications, makes them a very interesting PV technology. However, for the DSSC technology become a competitive alternative, higher efficiencies are required. Up to now the major drawback in increasing the DSSCs efficiency is the voltage loss during the dyeregeneration reaction; the use of iodide/triiodide redox electrolyte limits the open-circuit potential to 0.8 V. With the current state-of-art sensitizers, such as N719, and high surface area TiO2, I-/I3 electrolytes achieve an efficiency maximum of 11.1 %. However, replacing I-/I3 by cobalt based redox couples new opportunities for higher efficiency DSSCs have been unlocked. -
Highly efficient and stable transparent cuprous oxide photocathode for photoelectrochemical cells
Presentation- P. Dias M. Mayer J. Azevedo L. Andrade A. Mendes M. Graetzel S. D. Tilley
First published online: 31 Jul 2014PDF -
Preparation and optimization of transparent cuprous oxide photocathodes for allowing efficient solar water splitting
Presentation- P. Dias M. Mayer J. Azevedo L. Andrade A. Mendes M. Graetzel S. D. Tilley
First published online: 10 Sep 2014PDF
