Theoretical modeling of NO electrochemical reduction on multifunctional layer electrode by alternating/direct current electrolysis Xi Wang, Yixiang Shi *, Ningsheng Cai Key laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering, Tsinghua University, Beijing 100084, China A R T I C L E I N F O Article history: Received 13 October 2014 Received in revised form 14 November 2014 Accepted 19 November 2014 Available online xxx Keywords: solid oxide electrolysis cell nitrogen oxide electrochemical reduction alternative current electrolysis direct current electrolysis modeling A B S T R A C T A one-dimensional symmetric model on NO electrochemical reduction in solid oxide electrolysis cell (SOEC) considering gas transport, electronic conduction, ionic conduction, and electrochemical process based on multifunctional layer electrode is developed. The simulation results agree well with the experimental results both in the direct current(DC) and alternative current(AC) electrolysis. The distributions of the NO concentration in the electrode are predicted in both DC and AC electrolysis. The effects of temperature, voltage, and O 2 concentration were investigated on NO alternative current electrolysis and direct current electrolysis processes. The modeling results show that the optimal frequency of 0.3 Hz is corresponded to the maximum NO decomposition rate in different temperatures and voltages. The NO decomposition increases with increasing temperature and decreasing O 2 concentration in most cases. At 450  C, the NO decomposition presents first increased and then decreased trend with different voltages at the frequency of 0.3 Hz. This is similar to the effects of O 2 concentration at 450  C and 475  C at the same frequency. ã 2014 Elsevier Ltd. All rights reserved. 1. Introduction Electrochemical reduction of NO in solid oxide electrolysis cell (SOEC) was first proposed by Pancharatnam et al. [1] and was later demonstrated by Huggins [2] in experiments by using Pt, Au electrode, etc. Extensive researches have been focused on different electrode materials and structures [3–8] for electrochemical removal of NO x . The electrochemical rection of NO has the advantages in reducing the complicated reducing agents storage system and in avoiding the secondary pollutions due to he leak of the reducing agents compared with the conventional NO purification technologies such as selective catalytic reduction (SCR) method [9,10]. The improvement of NO reduction selectivity and conversion are significantly important for improving NO reduction efficiency. Researches has been focused on applying multifunctional layer electrode [11–15] or adding the adsorbents as the NO storage layer [16–20] in which NO can be enriched and stored by adsorption in the adsorption layer in the excess O 2 gas. Hansen et al. [20] reported a high NO reduction conversion of 82% at 500  C under the polarization of -1.25 V in an electrochemi- cal cell with an K/Pt/Al 2 O 3 adsorption layer. This indicated that K/ Pt/Al 2 O 3 can improve the NO conversion and current efficiency. Peden [18] studied the effects of K loading in K/Pt/Al 2 O 3 adsorption layer on the NO reduction characteristic. Hibino [21,22] has studied the alternating current(AC) electrolysis for NO reduction on Au, Pd, Pt and Rh electrodes with frequencies ranging from 0.01 Hz to 10 3 Hz. The direct current (DC) electrolysis was less durable than AC electrolysis though a higher conversion below the voltage of 3 V. Hamamoto [23] used K/Pt/Al 2 O 3 as the NO adsorption layer and YSZ as the covering layer to prevent the O 2 molecules from diffusing to the inner electrode. Electrochemical reduction of NO in AC electrolysis was more stable than DC electrolysis and also had a higher decomposition rate. In the other application area, Hibino [24,25] found that AC electrolysis was superior to DC electrolysis in the electrochemical oxidation of CH 4 and benzene. Numerical simulation is an essential tool to understand the behavior of the NO reduction performance on an adsorption layer, and to predict the optimal operating conditions such as Abbreviation: SOEC, Solid oxide electrolysis cell; AC, Alternative current; DC, Direct current; SCR, Selective catalytic reduction; YSZ, Yttrium stabilized zirconium; FM, Fick’s model; SMM, Stefan-Maxwell model; DGM, Dust Gas model; EFM, Extended Fick’s model. * Corresponding author. Tel.: +86 10 62789955; fax: +86 10 62789955. E-mail address: shyx@tsinghua.edu.cn (Y. Shi). http://dx.doi.org/10.1016/j.electacta.2014.11.125 0013-4686/ ã 2014 Elsevier Ltd. All rights reserved. Electrochimica Acta xxx (2015) 202–215 Contents lists available at ScienceDirect Electrochimica Acta journal homepa ge: www.elsev ier.com/locate/electacta