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The outdoor operation of an up scaled thermally photovoltaic electrolyzer PV EC , constructed using a heat exchanger HE made of low cost materials, compared to its nonintegrated counterpart to quantify heat transfer and its effects, is studied. Thermal coupling of the PV and EC can reduce the difference between their temperatures, benefitting device performance. Such devices can produce hydrogen at rooftop installations of small to medium sized nonindustrial buildings. The devices are tested outdoors using automated real time monitoring. Under amp; 8776;880 amp; 8201;W amp; 8201;m amp; 8722;2 peak irradiance, they produced hydrogen at amp; 8776;120 and amp; 8776;110 amp; 8201;mL amp; 8201;min amp; 8722;1 rate with and without HE, respectively, corresponding to about 8.5 and 7.8 solar to hydrogen efficiencies. During about 700 amp; 8201;h of testing, the HE is beneficial at over amp; 8776;500 amp; 8201;W amp; 8201;m amp; 8722;2 due to cyclic device operation. Under lower irradiance levels, pumping previously heated electrolyte through the HE increases the PV and reduces the electrolyte temperature, reducing the device performance. The HE increases the cumulative hydrogen production amp; 8776;800 amp; 8201;L from both devices , so even relatively modest heat transfer rates can improve the PV EC operation. Improving the HE should further increase the benefits, but additional measures may be needed to maximize the hydrogen production

Direct solar hydrogen generation via a combination of photovoltaics PV and water electrolysis can potentially ensure a sustainable energy supply while minimizing greenhouse emissions. The PECSYS project aims at demonstrating a solar driven electrochemical hydrogen generation system with an area gt;10 amp; 8201;m2 with high efficiency and at reasonable cost. Thermally integrated PV electrolyzers ECs using thin film silicon, undoped, and silver doped Cu In,Ga Se2 and silicon heterojunction PV combined with alkaline electrolysis to form one unit are developed on a prototype level with solar collection areas in the range from 64 to 2600 amp; 8201;cm2 with the solar to hydrogen StH efficiency ranging from amp; 8776;4 to 13 . Electrical direct coupling of PV modules to a proton exchange membrane EC to test the effects of bifaciality 730 amp; 8201;cm2 solar collection area and to study the long term operation under outdoor conditions 10 amp; 8201;m2 collection area is also investigated. In both cases, StH efficiencies exceeding 10 can be maintained over the test periods used. All the StH efficiencies reported are based on measured gas outflow using mass flow meters

An integrated photovoltaic electrolyser with a solar collection area of 294 cm2 was constructed and its performance, represented by the solar to hydrogen STH conversion efficiency and hydrogen production rate mH2 in various outdoor and indoor conditions, was investigated by measurements of the product gas streams. The device was composed of silicon heterojunction photovoltaic cells integrated with an electrolysis cell using nickel foam electrodes coated with nickel iron oxide and nickel molybdenum on the anode and cathode side, respectively, with 1.0 M KOH electrolyte. Depending on the operating conditions, the STH efficiency was typically 3.4 10 and typical mH2 of 30 60 mg h amp; 8722;1, approximately corresponding to 1 2 W output power. When considering non concentrating devices, the STH efficiency is one of the best for solar collection areas exceeding 100 cm2 and the hydrogen production rate the highest reported for devices smaller than 1 m2. The efficiency seems to depend mainly on the temperature, and less on the irradiance, reducing at a rate of about 0.35 absolute per 1 C increase in ambient temperature, significantly steeper than the efficiency of the used photovoltaic cells, making it a possible concern for practical hydrogen generation

We study the Cu(In,Ga)Se2 absorber fabrication by fast atmospheric pressure selenization of metal precursor films utilizing elemental selenium vapor from independent sources. We find that a high Se supply during selenization leads to the generally observed Ga accumulation at the back contact, while a reduced Se supply leads to a more homogeneous Ga distribution within the absorber. By optimizing the precursor as well as the Ga in‐depth distribution in the CIGSe layer, a conversion efficiency of 15.5% was achieved.

Photoelectrochemical systems have the potential to contribute to de-carbonation of the energy system because solar energy can be directly converted to hydrogen which can be burnt without the release of greenhouse gases. However, meaningful deployment of photoelectrochemical (PEC) technology in the global energy system, even when highly efficient scaled up devices become available, shall only be a reality when their safe and reliable operation can be guaranteed over serveral years of service life. The first part of the review discusses the importance of hermetic sealing of up scaled PEC device provided by the casing and sealing joints from a reliability and risk perspective. The second part of the review presents a survey of fully functional devices and early demonstrators and uses this to establish the extent to which the state of the art in PEC device design address the issue of hermetic sealing. The survey revealed that current material choices and sealing techniques are still unsuitable for scale –up and commercialization. Accordingly, we examined possible synergies with related photovoltaic and electrochemical devices that have been commericalised and derived therefrom, recommendations for future research routes that could accelerate the development of hermetic sealings of PEC devices.

We present transmission electron microscope (TEM) tomography investigations of ruthenium-based fuel cell catalyst materials as employed in direct methanol fuel cells (DMFC). The digital three-dimensional representation of the samples not only enables detailed studies on number, size, and shape but also on the local orientation of the ruthenium particles to their support and their freely accessible surface area. The shape analysis shows the ruthenium particles deviate significantly from spherical symmetry which increases their surface to volume ratio. The morphological studies help to understand the structure formation mechanisms during the fabrication as well as the high effectiveness of these catalysts in the oxygen reduction reaction at the cathode side of fuel cells.

A structural model of selenium-modified ruthenium nanoparticles was derived from anomalous small-angle X-ray scattering (ASAXS) and small-angle neutron scattering (SANS) experiments and further approved and supported by TEM, XRD, and extended X-ray adsorption fine-structure (EXAFS) analysis. Carbon-supported ruthenium nanoparticles modified with selenium (RuSex/C) have been suggested as highly active and Pt-free cathode catalysts for the oxygen reduction reaction in PEM fuel cells. However, so far no definite conclusion regarding the nature of the catalytically active surface could be drawn. ASAXS and SANS experiments now revealed that the surface of Se modified Ru nanoparticles after reductive catalyst activation at elevated temperatures is not completely covered by Se. The Se rather forms patches on the Ru surface while the rest of the surface is covered by oxygen. It could be demonstrated that the different scattering contributions of the carbon black carrier and various metallic constituents of the su...

Kurzfassung Zur Optimierung moderner Katalysatoren für Brennstoffzellen werden diese elektronen-tomografisch charakterisiert. Die Elektronentomografie ermöglicht einzigartige Einblicke in die Nanometer-Strukturen der metallischen Katalysatorpartikel, die auf einem elektrisch leitenden, inerten Kohlenstoffträger abgeschieden werden. Die dreidimensional bildgebende Methode ermöglicht über qualitative Untersuchungen hinaus detaillierte quantitative Form- und Strukturanalysen der Katalysatormaterialien. So werden beispielsweise die Positionen der Katalysatorpartikel relativ zum Trägermaterial analysiert. Ihre Form und Einbettung in den Träger, welche die für die katalytische Reaktion maßgebliche „freie Oberfläche“ definieren, werden bestimmt. Die Elektronentomografie ermöglicht somit quantitative Vergleiche zwischen verschiedenen Katalysatormaterialien und Herstellungsverfahren. Sie erweitert die Möglichkeiten der Korrelation gewünschter elektrochemischer Eigenschaften mit der Nanostruktur dieser Materialien und macht so weitere Optimierungen der Katalysatormaterialien möglich.

In contrast to still inefficient and expensive technical proton-conducting membranes, which rely on sulfonic acid activity, biology has solved its energy-related proton-conduction problems by evolving protein-bordered channels exposing amino acids for proton conduction (bacteriorhodopsin, CF0-channel of ATP-synthase, cytochrome oxidase complex). In this contribution, amino acids (l-lysine, aspartic acid, methionin) were attached to silica nanoparticles, which were incorporated into narrow (100−400 nm) channels produced in proton-inactive membranes (polyethlyene terephthalate, polycarbonate) forming nanowire structures for protons. The amino acid-modified porous membranes were shown to function in a real fuel cell setup with energy conversion efficiencies, corrected for the pore densities, approaching those of state-of-the-art fuel cell membranes. The dependence of proton-conduction properties of these channels on different parameters was studied. Further development of proton-conduction channels lined or ...

An electrocatalytic system that utilizes tungsten oxide modified carbon-supported RuSex nanoparticles is developed and characterized here using transmission electron microscopy and such electrochemical diagnostic techniques as cyclic voltammetry and rotating ring-disk voltammetry, as well as upon its introduction (as cathode) to the low-temperature hydrogen–oxygen fuel cell. After the modification of RuSex catalytic centers with ultra-thin films of WO3, the potential of oxygen reduction in 0.5 mol dm−3 H2SO4 (in the absence and presence of methanol) is shifted ca. 70 mV (under rotating disk voltammetric conditions) towards more positive values, and the percent formation (at ring) of the undesirable hydrogen peroxide has decreased approximately twice when compared to the WO3-free system. Relative to bare electrocatalyst, an increase of power density from 75 to 100 mW cm−2 (at 300 mA cm−2) has been observed upon utilization of WO3-modified RuSex in polymer electrolyte membrane fuel cell at 80 °C. In comparison to Vulcan-supported Pt nanoparticles, the overall electrocatalytic performance of tungsten oxide modified carbon-supported RuSex nanoparticles is lower, but the latter system is practically insensitive to the presence of methanol even at 0.5 mol dm−3 level.

Introduction of carbon-supported RuSex nanoparticles or cobalt protoporphyrin into ultra-thin WO3 matrices results in the enhancement of their electroctalytic properties towards electroreduction of dioxygen in acidic medium (0.5 mol dm-3 H2SO4). The enhancement effects are evidenced from the positive shifts of the O2 reduction potentials (ca 150 mV and 200mV, respectively). An important issue is that the mixed-valent tungsten (VI, V) oxide support is characterized by good electronic and protonic conductivities. Further, not only RuSex and/or cobalt protoporphyrin are catalytic but also the tungsten oxide matrix is reactive: it provides protons and is capable of promoting the reduction of hydrogen peroxide intermediate.

Ruthenium catalysts modified by selenium are of interest as a methanol insensitive oxygen reduction catalyst in a polymer electrolyte membrane fuel cell for mobile application. To elucidate the structural and chemical features of unsupported and carbon supported ruthenium nanoparticles prepared by thermolysis of Ru3(CO)12 in an organic solvent with and without the presence of dissolved selenium, different bulk and surface sensitive methods such as transmission electron microscopy, X-ray diffractometry, thermogravimetry coupled with mass spectrometry, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure analysis were performed. It was found that the as-grown catalytic particles prepared without Se and handled under ambient conditions are distinguished by a ruthenium core of 4 nm size, the surface of which is covered by an amorphous ruthenium oxide/hydroxide and metal organic residues from the process of synthesis. In the presence of Se, Ru−Se and Se−O bondings have additionally be...

Ruthenium catalysts were prepared employing aqueous solutions of ruthenium salts as precursors to obtain 2 nm sized metal particles homogeneously dispersed on a CO2-activated carbon support after annealing in hydrogen at 200 {degree sign}C. Selenium treatment was performed pouring the reduced product into a H2SeO3 or a SeCl4 solution prior to reduction in hydrogen at 300 {degree sign}C and 800 {degree sign}C. RuSex clusters have been formed which convert into a RuSexOy cluster after exposure to air. The presence of selenium in the cluster surface leads to a significant stabilisa-tion against oxidation of the metallic core and enables a highly selective catalytic activity towards the oxygen reduction reaction. Varying metal loading, PTFE and NAFION content in the cathode layer of a DMFC-MEA structure, best results were obtained using a metal loading of 1 mg/cm2 obtaining power densities of 20 mW/cm2 at a cell voltage of 0.4 V in a single cell.

Carbon supported ruthenium-based catalysts (Ru/C) for the oxygen reduction in acid electrolytes were investigated. A treatment of Ru/C catalysts with selenious acid had a beneficial effect on catalytic activity but no influence on intrinsic kinetic properties, like Tafel slope and hydrogen peroxide generation. Reasons for the increased activity of RuSex/C catalysts are discussed. Potential step measurements suggest that at potentials around 0.8 V (NHE) a selenium or selenium-oxygen species protects the catalyst from formation of inactive RuO2-films. This protective effect leads to an enhanced activity of RuSex/C compared to Ru/C. No evidence was found for a catalytically active stoichiometric selenium compound. The active phase may be described as a ruthenium suboxide RuOx (x

Structure and stability of an iron-based catalyst for the oxygen reduction reaction, prepared by heat treatment of carbon-supported iron(III) tetramethoxyphenylporphyrin chloride (FeTMPP−Cl), were investigated. The oxygen reduction in acid electrolyte was examined with the rotating (ring) disk electrode. The measurements confirmed that H2O2 is generated as a byproduct of the oxygen reduction. The structural elucidation of the catalyst showed that the porphyrin decomposes during heat treatment. Nitrogen atoms of the heat-treated porphyrin become bonded at the edge of graphene layers as pyridine- and pyrrole-type nitrogen. Two Fe3+ components as well as metallic, carbidic and oxidic iron were detected by Mossbauer spectroscopy. An electrochemical longevity test and two degradation experiments with sulfuric acid and H2O2 showed that H2O2 causes the degradation of active sites. A 6-fold coordinated Fe3+ compound seems to be responsible for the catalytic activity. Only 8% of the primary iron content is present...

Experience gained during efforts towards optimization of noble metal free electrocatalysts for oxygen reduction is simultaneously used to understand the chemical and morphological necessities for inducing efficient multielectron transfer catalysis. The analysis of many preparative experimental steps between the moderately performing metal porphyrines and the highly efficient transition metal and sulfur containing pyrolised catalyst material contributes to the following model of the catalyst 1. The metals function enclosed in nitrogen or graphitic environment where they are shielded against oxidation. 2. The metals can be exchanged but are not identical in their efficiency. 3. Higher efficiency is only achieved, when the function of a binary reaction center is warranted. 4. The carbonization of the environment is critical and provides intercalated metal centers and attached metal complexes in graphite environment for interaction with the nitrogen chelated partner center in the simultaneously obtained graphene layers. Experimental support for these models from EXAFS, RAMAN, Mössbauer and X ray spectroscopy is given and a parallel is drawn with the cytochrome oxidase oxygen reduction catalysis, which is proposed to proceed according to roughly the same mechanism. A special effort is made to discuss strategies for shielding and protecting catalytically active abundant transition metals against chemical reaction with oxygen or hydrogen peroxide.

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Understanding the oxygen evolution reaction (OER) activity and stability of the NiFe-based materials is important for achieving low-cost and highly efficient electrocatalysts for practical water splitting. Here, we report the roles of Ni and Fe on the OER activity and stability of metallic NiFe and pure Ni thin films in alkaline electrolyte. Our results support that the Ni(OH)2/NiOOH does not contribute to the OER directly, but it serves as an ideal host for Fe incorporation, which is essential for obtaining high OER activity. Furthermore, the availability of Fe in the electrolyte is found to be important and necessary for both NiFe and pure Ni thin films to maintain enhanced OER performance, while the presence of Ni is detrimental to the OER kinetics. The impacts of Fe and Ni species present in KOH on the OER activity are consistent with the dissolution/re-deposition mechanism we proposed. Stability studies show that the OER activity will degrade under prolonged continuous operation. Satisfactory stability can, however, be achieved with intermittent OER operation in which the electrocatalyst is cycled between a degraded and recovered state. Accordingly, two important ranges, i.e., the recovery range and the degradation range, are proposed. Compared to intermittent OER operation, prolonged continuous OER operation (i.e. in the degradation range) generates a higher NiOOH content in the electrocatalyst, which is likely related to the OER deactivation. If the electrode works in the recovery range for a certain period, i.e., at a sufficiently low reduction potential, where the Ni3+ is reduced to Ni2+, the OER activity can be maintained and even improved, if also Fe is present in the electrolyte.

Pyrolysis of chloroiron-tetramethoxyphenyl-porphyrin (FeTMPP-Cl) in the presence of iron oxalate ({plus minus} sulphur) leads to the formation of higly porous and active catalysts for the oxygen reduction reaction (ORR). In order to clarify the influence of sulphur the pyrolysis process is analyzed by thermogravimetry (TG) and by high-temperature X-ray diffraction (HT-XRD). In the absence of sulphur iron carbide (FexC) is formed which catalyses the proceeding graphitisation of the pyrolysis products. As a result catalytic active centres are decomposed by this reaction. This can be avoided by the addition of sulphur because iron monosulphide (FeS; troilite) is formed instead of FexC. Furthermore, FeS can easily be removed in a successive etching step so that nearly all inactive by-products can be removed. The results are in accordance with the higher electrochemical performance of the sulphur containing catalysts.