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High-Temperature Electrocatalysis

     

      Various applications in high temperature electrocatalysis are being studied, including sulfur- and coke-resistant solid oxide fuel cells,  reduction of carbon dioxide and water to produce syngas, and oxidative dehydrogenation of lower alkanes to olefins. Reaction experiments are performed using an electrocatalytic cell, which is sealed onto a reaction chamber, and heated to temperatures between 500-850 °C. Challenges in this research include the reactor design and sealing procedure, development of the catalysts which make up the cell’s electrodes, and characterization of the electrocatalysts.


  • Reduction of Carbon Dioxide and Water to Syngas

      Due to the detrimental effect of CO2 as a greenhouse gas, its capture and storage has become an active area of research. One promising way of converting CO2 into value added products is through high temperature co-electrolysis of steam and CO2 in a solid oxide electrolysis cell (SOEC) to produce syngas, which can subsequently be turned into liquid fuels by Fischer-Tropsch synthesis. Reduction of CO2 is possible at low temperature also, but requires the usage of highly active and costly noble metal catalysts for achieving suitable kinetics. At a high temperature, voltage requirement for electrolysis decreases and a faster reaction rate can be achieved.

      In an SOEC, H2O and CO2 simultaneously get reduced at the cathode and produce oxide ions; these ions then travel through an oxygen ion conducting electrolyte to the anode where they combine to form molecular oxygen. The main challenge in the construction of an efficient SOEC lies in the development of a suitable cathode catalyst. A cathode catalyst should be coke resistant, thermally stable and have high electrical and ionic conductivity. Ni-YSZ, which is commonly employed as cathode in SOECs, suffers from material degradation in oxidative environments. Perovskite oxides of the form ABO3 (typically containing an alkaline earth, alkali, or rare earth metal at the A-site and a transition metal at the B-site) are being studied for this application due to their stability at high temperatures, and ability to conduct both oxygen ions and electrons.

Schematic design of solid oxide electrolysis cell and TEM image of LSNF perovskite with exsoluted Ni particle
 

  • Oxidative Dehydrogenation of Lower Alkanes to Olefins

      Olefins are major chemical building blocks, which are used to produce nearly all consumer products. Oxidative dehydrogenation (ODH) is a method of producing light olefins like ethylene and propylene from widely available hydrocarbon sources such as ethane and propane. Typically, olefins are produced through steam cracking in petrochemical facilities. However, one of the shortcomings of traditional ODH is the limited ability to prevent the further oxidation of the formed olefins to carbon oxides, in addition to being dependent on fossil fuels. 

Novel reactors using an oxide ion-conducting membrane offer a potential solution to control the selectivity to the desired olefins by regulating the availability of oxygen to the alkane, and make use of a cheap hydrocarbon source, which is becoming more widely available as natural gas is developed. These reactors are also similar to the setup of solid oxide fuel cells, but instead of generating power, an external voltage/ current is applied to control the oxygen supply to the alkane. The external current pushes oxygen ions through the cell so that they may react with the alkane at the anode. In this scenario, the cell is operating in ion pump mode. This can potentially help regulate the extent of alkane conversion and enhance the selectivity towards partial oxidation products. Because the ODH reaction occurs on the anode electrocatalyst’s surface, that component is of highest interest. Perovskite oxide catalysts are also being considered for this application.

      


  • Electrochemical Ammonia Synthesis from water and nitrogen

      We aim to develop a strategy for electrochemical production of NH3 at atmospheric pressure that could replace or reduce the need for the energy-intensive Haber-Bosch process. An active electrocatalyst is the key to creating a widely available and environmentally-friendly ammonia synthesis process. This project focuses on ammonia synthesis at intermediate to high temperatures in a solid oxide electrolyte system. We are targeting the use of N2 and H2O as the reactants, so that ammonia can be produced directly from air. 

      We investigate nitrides, oxynitrides, perovskites, and a combination thereof for catalytic activity. Ammonia production rates will be measured in our high-temperature reactor system. In addition, characterization techniques including XRD, Raman, TPD/TPRxn with mass spectroscopy, XPS, XANES, and DRIFTS. Few research groups have explored the possibility of using nitrogen and water from the air to produce ammonia electrochemically. Eliminating methane reforming and hydrogen purification steps would greatly improve the implementation of this technology. Also, using a composite perovskite-nitride catalyst is a unique strategy, to the best of our knowledge.