Three-dimensional Inkjet Printed Solid Oxide Electrochemical Reactors. I. Yttria-stabilized zirconia Electrolyte

Solid oxide fuel cell (SOFC) and electrolyser (SOE) performances can be enhanced significantly by increasing the densities of (electrode | electrolyte | pore) triple phase boundaries and improving geometric reproducibility and control over composite electrode | electrolyte microstructures, thereby also aiding predictive performance modelling. We developed stable aqueous colloidal dispersions of yttria-stabilized zirconia (YSZ), a common SOFC electrolyte material, and used them to fabricate 2D planar and highly-customisable 3D microstructures by inkjet printing. The effects of solids fraction, particle size, and binder concentration on structures were investigated, and crack-free, non-porous electrolyte planes were obtained by tailoring particle size and minimising binder concentration. Micro-pillar arrays and square lattices were printed with the optimised ink composition, and a minimum feature size of 35 μm was achieved in sintered structures, the smallest published to-date. YSZ particles were printed and sintered to a 23 μm thick planar electrolyte in a Ni-YSZ|YSZ|YSZ-LSM|LSM electrolyser for CO2 splitting; a feed of 9:1 CO2:CO mixture at 1.5 V and 809 °C produced a current density of −0.78 A cm−2 even without more complex 3D electrode | electrolyte geometries

Solid oxide electrochemical reactors and processes for carbon dioxide and water splitting

The increasing contributions of renewable energy sources into the electricity grid necessitates large-scale energy storage to balance supply and demand due to their inherent intermittency. Storing electrical energy in chemical bonds by electrolysis of CO2 and / or H2O is one option. The aims of this project were to develop and characterise (micro)-tubular solid oxide electrolysers for the reduction of CO2 and/or steam at temperatures of 700–800 °C. Micro-tubular hollow fibre reactors were fabricated by phase inversion. Ni(O) – yttria stabilised zirconia (YSZ) cermet electrodes (electrolysis cathode) and YSZ electrolyte (15-50 μm) were simultaneously co-extruded and sintered, followed by the application of a lanthanum strontium doped manganite (LSM) – YSZ|LSM electrode (electrolysis anode) onto the outer surface, which was subsequently sintered. At 800 °C, current densities of up to -1.0 A cm-2 were achieved at ca. 1.8 V for CO2 electrolysis with a silver wire and silver conductive paste cathodic lumen current collector. Replacing the silver wire with nickel and removing any paste additives resulted in a 50 % increase in current density. Electrode polarization for steam and co-electrolysis (H2O/CO2 co-feed) was 62-382 % lower compared to CO2 electrolysis, with the extent depending on the current collector design; the silver paste had a greater detrimental effect on the electrode performance of the SOE operating with CO2. Evidence supporting dual-step co-electrolysis with electro-generation of hydrogen preceding the heterogeneous chemical reaction of H2 with CO2 included electrochemical performance, adsorption modelling, diffusion considerations, and response to silver paste. However, isotopic studies to differentiate between (electro)chemical processes using labelled C18O2 and H216O were inconclusive due to oxygen-18 exchange occurring between C18O2 and H216O, within the alumina feed tube, despite the absence of a Ni-YSZ cathode acting as a catalyst. To further characterize the intrinsic CO2 reduction mechanism, the surface exchange kinetics of C18O2 on YSZ and oxide diffusion coefficients, without electrochemical polarization, were determined using secondary ion mass spectrometry. These results facilitated the analyses of SOE experiments using oxygen-18 tracers that compared the effect of applied current on oxide ion transport rates within the hollow fibre reactors. Techno-economical evaluation of intra-day energy storage using the micro-tubular reactors cyclically in electrolyser and fuel cell operational mode resulted in an electricity storage cost of £0.016 per kWh, considering capital and operating costs (assuming £0.1 per kWh electricity costs), which is lower than current pumped hydroelectric storage (£0.05 per kWh).Open Acces

Accelerated Benders Decomposition for Variable-Height Transport Packaging Optimisation

This paper tackles the problem of finding optimal variable-height transport packaging. The goal is to reduce the empty space left in a box when shipping goods to customers, thereby saving on filler and reducing waste. We cast this problem as a large-scale mixed integer problem (with over seven billion variables) and demonstrate various acceleration techniques to solve it efficiently in about three hours on a laptop. We present a KD-Tree algorithm to avoid exhaustive grid evaluation of the 3D-bin-packing, provide analytical transformations to accelerate the Benders decomposition, and an efficient implementation of the Benders sub problem for significant memory savings and a three order of magnitude runtime speedup

Household occupancy monitoring using electricity meters

Occupancy monitoring (i.e. sensing whether a building or room is currently occupied) is required by many building au-tomation systems. An automatic heating system may, for ex-ample, use occupancy data to regulate the indoor temperature. Occupancy data is often obtained through dedicated hardware such as passive infrared sensors and magnetic reed switches. In this paper, we derive occupancy information from elec-tric load curves measured by off-the-shelf smart electricity meters. Using the publicly available ECO dataset, we show that supervised machine learning algorithms can extract occu-pancy information with an accuracy between 83 % and 94%. To this end we use a comprehensive feature set containing 35 features. Thereby we found that the inclusion of features that capture changes in the activation state of appliances provides the best occupancy detection accuracy

A novel spatiotemporal home heating controller design: system emulation and field testing

We have developed a spatiotemporal heating control algorithm for use in homes. This system utilises a combination of relatively low-tech hardware interfaced with electric heating systems and a smartphone interface to this hardware, and a central server that progressively learns users’ room-specific presence profiles and thermal preferences. This paper describes the associated spatiotemporal heating control algorithm, its evaluation utilising the dynamic building performance simulation software EnergyPlus, and a longitudinal deployment of the algorithm controlling a quasi-autonomous spatiotemporal home heating system in three domestic homes. In this we focus on the prediction of occupants’ presence and preferred set-point temperature as well as on the calculation of optimum start time and the utilisation of user-scheduled absences; this for two comfort strategies: to maximise comfort and to minimise discomfort. The former aims to deliver conditions equating to a ‘neutral’ thermal sensation, whereas the latter targets a ‘slightly cool’ sensation with corresponding heating energy savings. Simulation results confirmed that the algorithm functions as intended and that it is capable of reducing energy demand by a factor of seven compared with EnergyStar recommended settings for programmable thermostats. Field study results align with these findings and highlight the possibility to reduce energy under the minimise discomfort strategy without compromising on occupants’ thermal comfort

Syngas (CO-H₂) production using high temperature micro-tubular solid oxide electrolysers

AbstractCO2 and/or H2O were reduced to CO/H2 in micro-tubular solid oxide electrolysers with yttria-stabilized zirconia (YSZ) electrolyte, Ni-YSZ cermet cathode and strontium(II)-doped lanthanum manganite (LSM) oxygen-evolving anode. At 822°C, the kinetics of CO2 reduction were slower (ca. −0.49Acm−2 at 1.8V) than H2O reduction or co-reduction of CO2 and H2O, which were comparable (ca. −0.83 to −0.77Acm−2 at 1.8V). Performances were improved (−0.85 and −1.1Acm−2 for CO2 and H2O electrolysis, respectively) by substituting the silver current collector with nickel and avoiding blockage of entrances to pores on the inner lumen of micro-tubes induced by silver paste applied previously to decrease contact losses. The change in current collector materials increased ohmic potential losses due to substituting the lower resistance Ag with Ni wire, but decreased electrode polarization losses by 80–93%. For co-electrolysis of CO2 and H2O, isotopically-labelled C18O2 was used to try to distinguish between direct cathodic reduction of CO2 and its Ni-catalysed chemical reaction with hydrogen from reduction of steam. Unfortunately, oxygen was exchanged between C18O2 and H216O, enriching oxygen-18 in the steam and substituting oxygen-16 in the carbon dioxide, so the anode off-gas isotopic fractions were meaningless. This occurred even in alumina and YSZ tubes without the micro-tubular reactor, i.e. in the absence of Ni catalyst, though not in quartz tubes. Unfortunately, larger differences between the thermal expansion coefficients of quartz and YSZ precluded using a quartz tube to house the micro-tubular reactor. However, the kinetic results, CO/H2 yields from off-gas analysis, diffusional considerations and model predictions of reactant and product gas adsorption on Ni suggested that syngas should be produced by electrochemical reduction of steam to H2, followed by its Ni-catalysed chemical reaction with CO2

Highly-robust solid oxide fuel cell (SOFC): simultaneous greenhouse gas treatment and clean energy generation

Herein, results of combined greenhouse gas treatment with clean energy conversion is reported for the first time. Multi-channel tubular SOFCs were operated with N2O instead of air as the oxidant leading to a 50% increase in power density. Techno-economic evaluation suggested the feasibility of the combined approach eliminating the cost penalty for N2O abatement