Solid Oxide Electrochemical Cells for Nitrogen and Oxygen Production

Abstract

Nitrogen and oxygen are both very important commodities with a wide variety of applications in industries, such as chemical, food and metallurgical plants as well as in the medical sector. Nowadays most of the nitrogen and oxygen are produced via air separation technologies such as cryogenic distillation (ASU) or pressure swing adsorption (PSA). Both ASU and PSA offer economical and mature ways for nitrogen and oxygen production at large (>100 ton/day) or medium scales (20-100 tons/day). If one can develop a technology for providing these gases in an energy efficient and cost effective way also at small scale, preferably driven by electricity only, this would enable new applications of the gases. Such a technology would match characteristics of the future green electricity system relying on small scale (few MWs) power generation and fluctuating production..In this work we present an efficient electrochemical process for N2 and O2 production based on a solid oxide electrochemical cell technology by oxygen extraction from air. Cells with a 53 × 53 mm2 size were produced by a conventional tape casting method. They consist of a ca.10 μm CGO (Ce0.9Gd0.1O2-δ) electrolyte sandwiched between composite electrodes made from either LSCF (La0.6Sr0.4Co0.2Fe0.8O3-δ) - CGO, or LSF (La0.6Sr0.4FeO3-δ) - CGO. To boost performance at low temperature, the electrodes were infiltrated with Pr-oxide. The electrochemical performance with the different supports were characterized by obtaining current-voltage (iV) characteristics at different temperatures as well as through electrochemical impedance spectroscopy(EIS) with or without infiltration. For characterization, air was used as feed stock to the cathode compartment and air, or oxygen was used as sweep gas to the anode compartment. A voltage below 200 mV is needed to drive a current of 1 A/cm2 through the cell, which can provide a purity of 90% of N2 out at an operation temperature of 650 °C (see Figure 1a). The cells were demonstrated to operate for producing a 98% pure N2 stream without degradation over a 1500 h period (see Figure 1b).Further analysis show that the specific power consumption calculated based on the power input and outlet gas flow rate for 90% N2 production is ca. 0.1 kWh/m3 and the specific power consumption for 96% and 98% N2 production is 0.21 and 0.31 kWh/m3, respectively. A 3-fold increase in required power is observed when going from a N2 purity from 90% to 98%.Detailed electrochemical analysis and the electrochemical performance comparison between LSCF and LSF based mixed ionic electronic conductor (MIEC) electrodes will be presented. Factors limiting cell performance will as well as analysis of optimal point of operation in terms of energy consumption and reliability will also be discussed. Acknowledgment This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 862482. Figure 1