Limited overall efficiency and excessive complexity can hinder the competitiveness of biomass gasifier solid oxide fuel cell micro combined heat and power systems. To overcome these problems, hydrocarbons direct internal reforming is analysed as a strategy to increase efficiency and reduce system complexity. To the same end, two biosyngas heating-up strategies are compared: catalytic partial oxidation and afterburner off gases utilization. A comprehensive approach combining thermodynamic equilibrium calculations, experimental measurements, and system modelling was used. The gas cleaning unit should operate at 400 °C to decrease H₂S and HCl below 1 ppmv. A tar amount of 120–130 g Nm⁻³ dry biosyngas for woodchips and 190 g Nm⁻³ for straw pellets was measured and 2-methoxyphenol, hydroxyacetic acid and hydroxyacetone were selected as representative compounds. With direct internal reforming the cathode air flow rate decreases from approximately 90 kg h⁻¹ to 60 kg h⁻¹. This leads to an increase of around 1% point in electrical efficiency and of even 5–6% points in thermal efficiency. Direct internal tar reforming seems therefore an advantageous strategy. The catalytic partial oxidation unit increases the system overall efficiency but reduces the electric efficiency from roughly 38%–30% and is therefore not advised.

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High temperature biosyngas cleaning is more efficient when the end user operates at elevated temperature, as in biomass gasifier solid oxide fuel cell systems. However, there is not much experience with this technology and low temperature gas cleaning is usually adopted. This paper advances current knowledge by presenting the results from the investigation of side reactions catalysed by commercially available sorbents involving biosyngas main components, and the results obtained with the pilot plant developed within the Horizon2020 project “Flexifuel-SOFC”. K₂CO₃, used for HCl removal, appeared catalytically active towards the water gas shift reaction. Under conditions representative of a real system, the residence time was not sufficient for the gas composition to reach thermodynamic equilibrium. ZnO–CuO, used for H₂S removal, showed a catalytic activity significantly higher. Both sorbents seemed not active towards the methanation reaction. The pilot plant tests confirmed the occurrence of the WGS reaction in the HCl removal reactor. The sorbents decreased H₂S and HCl below the target value of 1 ppmv for H₂S and 5 ppmv for HCl. The catalytic activity of sorbents and the heat released by these reactions should be carefully considered in the design phase of high temperature gas cleaning units.

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Contaminants as particulate matter, sulfur, chlorine and tar should be removed from biosyngas to avoid damaging solid oxide fuel cells. However, there is no sufficient information on tar effect since they might be potentially used as a fuel, or they might cause performance losses and irreversible damages. Therefore, this study aims to assess whether tar can be reformed inside the SOFC and used as fuel. Short-duration experiments were conducted on Ni-GDC cells operating with simulated biosyngas containing different concentrations of representative tar compounds from biomass gasification. While benzene and ethylbenzene could be regarded as additional fuels even at concentrations as high as 15 g/Nm³, naphthalene and phenanthrene act as contaminants for the SOFC electrochemical and catalytic reactions, even at concentrations of 0.3 and 0.05 g/Nm³. However, the effect on these reactions appeared almost completely reversible. Solid carbon deposited on the SOFC ceramic housing in proximity of the inlet. Post-mortem analysis should be performed to asses the tar effect on the cell anode.

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Tar compounds have been defined as Achilles’ heel in biomass gasification. Catalytic reforming solves problems caused by tar by converting them into H₂ and CO. Most of the research has focused on secondary and tertiary tar reforming while some information on primary tar can be derived from bio-oil reforming. However, these studies use humidified N₂, Ar or He as gas carrier. Therefore, in this work, three catalysts are compared for reforming 40 g/Nm³ acetic acid as main primary tar compound from biomass updraft gasification using simulated biosyngas as gas carrier. The catalysts were tested over a 72 h period between 680 and 750 °C with a gas composition of 35.0 vol% H₂O, 2.3 vol% CO, 19.5 vol% CO₂, 3.6 vol% CH₄, 24.0 vol% H₂ and 15.6 vol% N₂. Olivine completely converted acetic acid, but a considerable amount of carbonaceous deposits was found on the catalyst and the catalytic activity decreased over time with 0.2 g/Nm³ hydroxyacetone measured in the last day of testing. Dolomite showed promising performances by completely converting acetic acid and accumulating carbonaceous deposits only in the low temperature part of the catalyst bed. The carbonaceous deposits could be suppressed increasing the steam content to 50.1 vol% and the temperature to 900 °C. However, the catalyst became excessively brittle. The metal-based catalyst out-performed the naturally-occurring catalysts by completely converting acetic acid with almost no carbonaceous deposits accumulation. These results are expected to help the further development of tar reformers, and the commercialisation of biomass updraft gasifiers based systems.

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Integrated biomass gasifier solid oxide fuel cell systems are an alternative to fossil-fuel-based combined heat and power generators. However, biosyngas contaminants represent a bottleneck for small-scale systems. In this work, we present the results of experiments on the effects of H₂S, HCl, and acetic acid as model primary tar on Ni-GDC SOFC. First, the effects of 17-128 g/Nm³ dry basis acetic acid were studied. On a second cell, 0.8 and 1.3 ppm(v) H₂S were added to the simulated biosyngas anode flow. After a full recovery, the cell was exposed to 42 g/Nm³ acetic acid and 0.8 ppm(v) H₂S. On a third cell, 3.4, 20, and 50 ppm(v) HCl were tested and, after a recovery period, 42 g/Nm³ acetic acid and HCl were added. Even 0.8 ppm(v) H₂S caused an immediate voltage drop. H₂S affected CH₄ reforming and water-gas shift reaction. Differently, even 50 ppm(v) HCl appeared not to significantly affect these reactions. Acetic acid increased the cell voltage but caused carbon deposition at the cell inlet. The voltage increase seemed not to be affected by H₂S or HCl, and no acetic acid was measured at the cell outlet, indicating that these contaminants do not affect the primary tar conversion.

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Removing biosyngas contaminants is crucial for the efficient and safe operation of biomass gasifier solid oxide fuel cells systems. Among the contaminants, tar might be considered an additional fuel if converted into H₂ and CO in a reformer or directly in the SOFC. However, no sufficient information is available on direct internal tar reforming. The knowledge gained during the 4-years project FlexiFuel-SOFC is presented. The aim of these studies was to determine the possibility to directly reform tar in the SOFC, and to assess the influence that other biosyngas contaminants (i.e., H₂S and HCl) can have on the process. Benzene can be regarded as fuel, while naphthalene as a contaminant. Also toluene can be reformed inside the SOFC, but HCl seems to affect the process. Acetic acid is completely converted inside SOFCs and its conversion appears not affected by H₂S. However, it causes carbon deposition, mainly in the inlet pipelines.

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Charge carrier-selective contacts transform a light-absorbing semiconductor into a photovoltaic device. Current record efficiency solar cells nearly all use advanced heterojunction contacts that simultaneously provide carrier selectivity and contact passivation. One remaining challenge with heterojunction contacts is the tradeoff between better carrier selectivity/contact passivation (thicker layers) and better carrier extraction (thinner layers). Here we demonstrate that the nanowire geometry can remove this tradeoff by utilizing a permanent local gate (molybdenum oxide surface layer) to control the carrier selectivity of an adjacent ohmic metal contact. We show an open-circuit voltage increase for single indium phosphide nanowire solar cells by up to 335 mV, ultimately reaching 835 mV, and a reduction in open-circuit voltage spread from 303 to 105 mV after application of the surface gate. Importantly, reference experiments show that the carriers are not extracted via the molybdenum oxide but the ohmic metal contacts at the wire ends.

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The diffusion of photovoltaic systems is deterred by the struggle in combining high efficiency and low cost. Nanowire devices have been demonstrated to hold great promise to solve this predicament, but the substrate cost is still an unavoidable obstacle. Repeated nanowire growth on a single substrate is demonstrated by embedding InP nanowires in a polymer layer and removing them from the substrate. Our approach promises cost reduction by using the substrate multiple times. In addition, it provides a pathway to increase the open-circuit voltage by placing a mirror at the backside of the cell.

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Integrated Biomass Gasifier Solid Oxide Fuel Cell Systems represent an alternative to fossil fuel based power plants, and direct internal tar reforming allows achieving high efficiency and decreasing system complexity. However, at present, tar is removed or reformed externally since there is not yet general agreement on the fate of these compounds in the anode chamber, and no information is available on the combined effects of tar and other biosyngas contaminants. In this paper, we present the results of short-term experiments on the cross-influence of HCl and tar on Ni-GDC Solid Oxide Fuel Cell anode and on direct internal tar reforming. Initially, the cell was fed with humidified hydrogen and an increasing concentration of HCl (8, 42 and 82 ppmv) and toluene (2.5, 4.2 and 8.4 g/Nm3) separately. Successively, 8.4 g/Nm3 of toluene and an increasing concentration of HCl were fed to the cell. We used polarisation and power density curves, and outlet gas composition analysis to evaluate the contaminants effects. The presence of HCl and toluene caused only a marginal increase in the cell Area Specific Resistance (around 1.5% when the cell was operated at Open Circuit), and the Area Specific Resistance remained then constant during the exposure time. However, HCl affects tar reforming decreasing the concentration of CO2 and CO at the cell outlet. The results indicate the feasibility of direct internal toluene reforming and suggest the revision of currently used tolerance limits based on contaminants cross-influence effects. Extensive research on this topic is still required.@en

A summary of research activities and on-going multiple projects at Delft University of Technology aimed at the development of Solid Oxide Fuel Cells (SOFCs) integrated waste to energy systems are presented in this paper. A wide range of studies ranging from pattern cell impedance analysis to integrated system development is also presented. Cleaning the gas to match constraints of SOFCs requires complex approaches. A brief discussion on the achievable system efficiencies with SOFC integrated waste to energy systems is presented and novel concepts such as gasifier-Reversible SOFC integrated power production cum energy storage systems are discussed. Additionally, an overview of a wide range of national, European and international projects that helped or currently helping us to carry out the above mentioned research activities are presented.@en

The functionality of semiconductor devices is determined by the incorporation of dopants at concentrations down to the parts per million (ppm) level and below. Optimization of intentional and unintentional impurity doping relies on methods to detect and map the level of impurities. Detecting such low concentrations of impurities in nanostructures is however challenging to date as on the one hand methods used for macroscopic samples cannot be applied due to the inherent small volumes or faceted surfaces and on the other hand conventional microscopic analysis techniques are not sufficiently sensitive. Here, we show that we can detect and map impurities at the ppm level in semiconductor nanowires using atom probe tomography. We develop a method applicable to a wide variety of nanowires relevant for electronic and optical devices. We expect that it will contribute significantly to the further optimization of the synthesis of nanowires, nanostructures and devices based on these structures.@en