Engineering Double Perovskite Oxynitrides for Electrocatalytic Nitrogen Activation

Ohio State University, The, Columbus OH

Investigators

Abstract

Ammonia is the key chemical for the mass production of fertilizers to feed the World’s growing population. The current conventional route for manufacturing ammonia (NH3) is the Haber-Bosch (HB) process, which involves converting nitrogen and hydrogen through a thermo-catalytic reaction path at high temperatures and pressures. Being the exclusive route for producing one of the most crucial chemicals worldwide, HB consumes almost 2% of the World’s total energy supply and releases significant amounts of the primary greenhouse gas, carbon dioxide (CO2). Therefore, for a sustainable future, alternative NH3 production processes need to be developed. To that end, the project investigates an alternative electrochemical process for scalable and on-site ammonia production from readily available nitrogen (N2) and water (H2O), thus providing a less energy-intensive, more economically feasible, and environmentally friendlier path compared to the conventional Haber-Bosch process. Beyond the technical aspects, the project includes STEM related activities at the high-school and undergraduate levels. The project investigates double perovskite oxynitride-type materials as electrocatalysts for potential application in solid oxide nitrogen reduction reaction (e-NRR) electrochemical cells (SOECs) operating at atmospheric pressure and an intermediate-temperature range (450-600°C). These materials show a large diversity of features that can be tuned using strategies such as doping and optimizing nitridation parameters. The cathode development efforts will concentrate on maximizing lattice nitrogen amount and maintaining the co-presence of nitrogen and oxygen vacancies while preserving their crystallinity and cationic/anionic ordering. Although the double perovskite oxynitrides are potentially very promising materials to be used in electrocatalytic nitrogen fixation/activation, they have been scarcely investigated and, to the best of the investigators’ knowledge, the study is the first to consider these materials as an alternative cathode catalyst in an e-NRR process. The project will undertake a systematic design and ex-situ/in-situ/operando characterization of novel iron-based double perovskite oxynitride-type electrocatalytic materials. The study fundamentally investigates properties of the double perovskite oxynitrides at the electronic, atomic, and molecular levels. The carefully formulated and engineered double perovskite oxynitrides will be evaluated in the e-NRR process to elucidate a relationship between the structure/(electro)-chemical/physical properties of iron-based double perovskite oxynitrides and their e-NRR activity. Considering the fact that even the reaction mechanism of the thermal ammonolysis - which is the main route to synthesize oxynitride materials - is not yet fully understood, the present study can be considered as an important first step to gain insights into (i) the engineering and synthesis of oxynitride-type electrocatalysts, (ii) the effect of ammonolysis parameters on their catalytic performance, (iii) anionic order and O/N distribution in the crystalline structure, (iv) preferential sites for the nitride ions, and (v) maintaining the co-presence of nitrogen and oxygen vacancies. The ultimate goal is to understand how these properties affect the electrocatalytic activity of the oxynitrides towards nitrogen fixation/activation using H2O as the H2 (proton) source. The project benefits from access to state-of-the-art characterization tools within the PIs’ laboratories as well as those at the Oak Ridge and Brookhaven National Laboratories and the Stanford Synchrotron Radiation Lightsource. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.