NSF-DFG Echem: Electrochemically enhanced low-temperature catalytic ammonia synthesis

Colorado School Of Mines, Golden CO

Investigators

Abstract

As the nation and the world move toward carbon-free energy economies, ammonia will likely play significant roles as a hydrogen carrier. Today, essentially all ammonia is produced in high pressure Haber-Bosch plants at very large scale. There is a growing need for smaller scale, geographically distributed, ammonia synthesis using renewable resources. However, because of inherent thermodynamic and kinetic limitations, typical catalyst-based thermal processes (e.g., Haber-Bosch) are not economic at smaller scale. The present project seeks to enable distributed ammonia synthesis using electrochemical interactions that significantly reduce activation barriers. The research relies on the combined, complementary, and unique expertise of the partners in the context of materials synthesis, characterization and process demonstration (KIT) and physically based modeling of the electrochemistry, charged-defect transport, and catalysis (CSM). This joint project addresses significant scientific challenges in transitioning to environmentally friendly ammonia production as an energy carrier and commodity chemical. The project’s objective is to develop and demonstrate electrochemical enhancement that enables low-temperature and low-pressure ammonia synthesis. Nanophase Ru is dispersed on a proton-conducting BCZY support (BaCe1-x-yZrxYyO3-δ). Directly polarizing the catalyst structure with an electric field decreases the kinetically limiting barrier for N2 activation. Although the proposed research is scientifically fundamental, it has excellent technology potential for cost-effective distributed production of ammonia. The research focuses on postulating, modeling, and validating proposed chemical behaviors. The electrical field is expected to reduce rate-limiting N2 dissociation barriers via two synergistic mechanisms: 1. Electrical fields affect the proton-conducting BCZY support, enabling H2 dissociation to form protons that can activate gas-phase N2, directly forming desired surface adsorbates such as NH on the BCZY support. 2. Fields in the range of 0.1 to1.0 V/Å on dispersed nano-Ru also reduce the nitrogen activation barrier. The energy barrier for nitrogen activation Ru varies between 30-42 kJ mol-1. Based on our validated reaction mechanisms for Ba-promoted Ru/YSZ, simulations show that reducing the N2 dissociation energy by 10 kJ mol-1 will increase the ammonia formation rate by an order of magnitude. This research was funded under the NSF-DFG Lead Agency Activity in Electrosynthesis and Electrocatalysis (NSF-DFG EChem) opportunity NSF 20-578. 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.