Mohsine Zahid

Syngas production via high-temperature steam/CO2 co-electrolysis: an economic assessment

Although it is not yet technologically mature, the high-temperature steam/CO2 co-electrolysis process offers potentially a feasible and environmentally benign way to convert carbon-free or low-carbon electrical energy into chemical energy stored in syngas with a desired H2 to CO ratio for further processing. An attractive application is to convert the as-produced syngas further into synthetic liquid fuels through the Fischer–Tropsch (F-T) process. The synfuel can be used as alternative fuels in the transportation sector while keeping the existing infrastructure and motor engine technology unchanged. The combination of the high-temperature steam/CO2 co-electrolysis process and the F-T process thus offers an efficient way to store electricity in transportation fuels. The implementation of such a quasi carbon-neutral process depends on its economic competitiveness. In the present paper, an economic assessment of this process is performed through process modelling and sensitivity analysis. As an energy-intensive process, the availability of cost-effective electricity is crucial for its economic competitiveness. Preferred electricity sources are probably nuclear power and surplus wind power, with which synthetic fuels could be produced at a cost comparable to BTL (Biomass to Liquid) process. The present process is biomass-independent, and can also be located in regions where solar energy is abundant.

Electronic Conduction of Yttria-Stabilized Zirconia Electrolyte in Solid Oxide Cells Operated in High Temperature Water Electrolysis

Anode-supported solid oxide fuel cells with yttria-stabilized zirconia (YSZ) electrolytes, both commercial and research, are used at 800-900°C as solid oxide H 2 O electrolyzer cells (SOECs). When the operation is extended to current densities j corresponding to a steam-conversion rate above 100%, or when the steam supply is interrupted under constant current conditions, cell voltages saturate at ~ 1.9 V at 810°C. A cell survives 64 h polarization at j = -0.34 A cm -2 without any steam supply. The mechanism limiting the cell voltage is attributed to electronic conduction in the YSZ electrolyte. No indications are found for electrolyte decomposition. Because the saturation voltage exceeds typical operation voltages by several hundred millivolts, electrolyte conduction in the normal SOEC mode remains predominantly ionic. The rise in the cell voltage to the value determined by electronic conduction occurs when steam transport in the hydrogen/steam electrode becomes limiting. As a consequence of H 2 O back-diffusion from the cell exhaust in the used unsealed test configuration, the rise occurs at nonzero current density under zero steam supply. Impedance spectroscopic data are compared with and without steam supply and are qualitatively interpreted with an equivalent circuit model.

Optimization of SOFC interconnect design using Multiphysic computation

Abstract The aim of this work is to optimize an interconnect design. A three-dimensional model have been developed in order to investigate the effect of interconnect design on electrical performance and degradation process. Oxygen concentration, potential, current density and temperature distribution in interconnect and SOFC cathode have been calculated. Cathode degradation has been supposed to be due to temperature gradient non-uniformity. Our studies have demonstrated the impact of cathode/interconnect contact on thermal and electrical behavior. Thus, an optimization of the cathode/interconnect contact using COMSOL Multiphysics ® software has been investigated. In this investigation, the effects of the two geometrical parameters are considered. This paper presents the modification of cathode/interconnect contact area and electrical collecting pins size. Simulations show a decreasing power density and a reduction of temperature gradient for an increasing contact area. With a decreasing size of collecting pins, better temperature homogeneity and power density are recorded.

Electrical Interaction Model of Planar SOFC Stack Fed with Natural Gas

Solid oxide fuel cells (SOFC) are energy conversion devices thatproduce electricity and heat directly from a fuel such asnatural gas. Little attention has been paid to the electricalbehaviour of a SOFC stack. This paper presents an electricalinteraction model of a planar anode supported intermediatetemperature SOFC stack with direct internal reforming. The SOFCstack model is built up of multiple single repeat units stackedon top of each other and takes into account, amongst otherparameters, contact resistances and gas flow. This assembly issandwiched between two end plates. A combined model with mass,charge and heat balances has been developed with a specialattention to the description of electrical behavior. Such anapproach can provide a picture of the two dimensionaldistribution of potential, current density, and temperature.Simulations are performed to analyse the impact of changes inmaterial conductivities, electrical configuration and operation conditions.