(730b) Exploring Peptide-Bound Catalysts for Electrochemical Ammonia Generation

Authors: 
Renner, J. N., Case Western Reserve University
Loney, C., Case Western Reserve University
Acharya, P., University of Arkansas
Suttmiller, D., University of Arkansas
Wiles, L., Proton OnSite
Ayers, K., Proton OnSite
Gellett, W., Proton OnSite
Greenlee, L. F., University of Arkansas
Today, most ammonia (NH3) manufacturing occurs via the Haber-Bosch process. This process consumes hydrogen from fossil fuels, and as a result NH3 contributes the highest amount of greenhouse gas emissions out of the top 18 large-volume chemicals made globally. Because the process is high temperature (400°–500°C) and pressure (150–300 atm) with a low (15%) single-pass conversion efficiency, the plants have to be very large to be economical. This means that ammonia is shipped from centralized locations, further increasing greenhouse gas emissions because of the fuel consumed in transportation. Additionally, their large size makes it difficult to integrate with renewable sources of hydrogen, such as electrolysis.

One promising alternative approach for NH3 manufacturing is to use electricity to drive the reaction, decreasing the need for high pressure and heat. This electrochemically driven process would be compatible with intermittent operation and enable utilization of renewable electricity, eliminating greenhouse gas emissions. Because electrochemical technologies are highly scalable, electrochemical ammonia production would enable distributed, near-point-of-use manufacturing. As megawatt (MW)-scale electrolysis systems are already being sold by companies such as Proton OnSite, localized ammonia production at relevant scales is feasible. There is also a natural synergy in using distributed wind power for fertilizer production. In the Plains and Upper Midwest, excess wind production capacity, transmission limitations, and high regional demand for nitrogen based fertilizers combine to create excellent economic drivers for this technology. Ammonia also has many other uses, including in chemical synthesis, refrigeration, or even has a fuel. It also features a high energy storage density. This flexibility in use makes ammonia an attractive renewable energy storage option.

While electrochemical ammonia generation is promising, the low-temperature and low-pressure testing to date has shown low efficiencies (<1%), highlighting the need for creative catalyst approaches. An ideal catalyst would facilitate the reduction of nitrogen to NH3 without undesired hydrogen evolution occurring. Meanwhile, the enzyme nitrogenase which reduces nitrogen in nature, operates at mild temperatures and pressures with high efficiency (75%). To address the need for efficient catalysts in electrochemical ammonia generation, Case Western Reserve University, the University of Arkansas, and Proton OnSite are collaborating to develop manufacturable, peptide-bound electrocatalysts inspired by the enzyme nitrogenase. Proton OnSite and their collaborators have spent the past few years developing an anion exchange membrane (AEM)-based technology, which is ideal for ammonia synthesis because the alkaline configuration allows the utilization of a wider array of low-cost catalysts. In this work, peptide-functionalized catalysts are developed, characterized and tested in and AEM-based system. The novel materials show promise compared to conventional catalyst approaches.