Periodic Reporting for period 1 - CILCat (Nanocarbon-Ionic Liquid-Interfaces for Catalytic Activation of Nitrogen)
Reporting period: 2022-10-01 to 2025-03-31
A cornerstone of the ongoing green transformation is the electrification and decentralization of chemical processes which are currently based on fossil fuels-based energy supply and reactands. One of these processes causing immense energy consumption and carbon dioxide emissions is the synthesis of ammonia. Ammonia is one of the most important chemicals and finds wide application in fertilizers and other nitrogen-containing compounds of the chemical industry. Its production from the elements hydrogen and nitrogen takes place in large reactors within centralized production schemes at high temperatures and extremely high pressures. The hydrogen most often comes from steam reforming of natural gas. For that reason, ammonia synthesis is responsible for 1-2% of the annual global carbon dioxide emissions. A possible alternative towards decentralized production schemes which can operate under milder conditions is the electrocatalytic reduction of nitrogen (eNRR) at ambient conditions. eNRR is driven with electricity as energy source and can be operated at relatively low temperatures and moderate pressures. The necessary protons and electrons (instead of elemental hydrogen) can be for instance produced by electrochemical water splitting. This half-reaction can be coupled with the reduction of nitrogen to ammonia within one and the same electrochemical cell. However, just like the established chemocatalytic process, also eNRR suffers from the difficulty to activate the very stable chemical triple bond in nitrogen for reaction with protons and electrons. In addition, the low solubility of nitrogen in typical electrolytes and the competing hydrogen evolution reaction are major drawbacks of this approach lowering the possible yield of ammonia and hindering its technological implementation. From this starting point, the ERC project CILCat aims to establish a new disruptive principle that holds holistic perspectives for the activation of dinitrogen and other small molecules such as carbon dioxide and nitrate. By confining ionic liquids into charged porous carbon materials, an interface will be created, that as a whole serves as catalytic area. CILCat will contribute to a fundamental understanding of the physicochemical principles of sorption upon confinement in pores. Targeted catalyst development will follow and the possibility of using the principle for catalytic activation of small molecules will be explored in technically relevant electrochemical cells.
The following executive report describes the main achievements of the project so far and is written in general language:
In the initial phase of CILCat, a library of model carbon materials with gradually adjusted chemical architecture (i.e. different amounts of different heteroatoms) and varying pore sizes has been established by templating approaches and chemical activation. Other approaches are based on hybrid materials connecting porous carbons with nitrogen-rich porous carbons. The materials systems serve as a basis for the investigation of the impact of ionic liquid loading on the sorption properties of gases such as nitrogen, carbon dioxide and water vapor. Such measurements of gas adsorption in liquids are still rare which gives the approach a high intrinsic novelty. A main achievement which can already be seen is that the ionic liquids allow for a nearly step-less adjustment of the pore sizes and surface chemistry properties of porous carbon materials. Comparable to the concept of porous liquids, free space is left when ions are confined into pores. This allows for adjustable sorption properties (e.g. gas uptakes or heat of adsorption) of the IL-carbon interface for small molecules. This is a promising starting point for the transfer to the application of such interfaces in eNNR.
Secondly, a catalytic setup for eNRR with advanced gas cleaning procedures and various operation modes has been established for the further work packages in CILCat. It has been found with the prepared model catalysts, that eNRR in aqueous electrolytes is feasible under the application of a strict protocol, however the amounts of produced ammonia remain in the ppm-level. Improvement of the specific currents and ammonia production rates is expected when the materials are filled with ionic liquids to form catalytically active interface structures. These materials are currently tested in different electrochemical cells including flow cells and zero-gap electrolyzers.
Finally, in collaborative projects the synthesized materials or the established characterization methods have also been applied to investigate the properties of synthesized materials in electrocatalytic applications (oxygen reduction reaction) and the confined state structures of ionic liquids within metal-organic framework materials. These collaborative projects are first examples for the expansion of the CILCat concept and materials into related applications connected to electrochemistry and materials science.
In the initial phase of CILCat, a library of model carbon materials with gradually adjusted chemical architecture (i.e. different amounts of different heteroatoms) and varying pore sizes has been established by templating approaches and chemical activation. Other approaches are based on hybrid materials connecting porous carbons with nitrogen-rich porous carbons. The materials systems serve as a basis for the investigation of the impact of ionic liquid loading on the sorption properties of gases such as nitrogen, carbon dioxide and water vapor. Such measurements of gas adsorption in liquids are still rare which gives the approach a high intrinsic novelty. A main achievement which can already be seen is that the ionic liquids allow for a nearly step-less adjustment of the pore sizes and surface chemistry properties of porous carbon materials. Comparable to the concept of porous liquids, free space is left when ions are confined into pores. This allows for adjustable sorption properties (e.g. gas uptakes or heat of adsorption) of the IL-carbon interface for small molecules. This is a promising starting point for the transfer to the application of such interfaces in eNNR.
Secondly, a catalytic setup for eNRR with advanced gas cleaning procedures and various operation modes has been established for the further work packages in CILCat. It has been found with the prepared model catalysts, that eNRR in aqueous electrolytes is feasible under the application of a strict protocol, however the amounts of produced ammonia remain in the ppm-level. Improvement of the specific currents and ammonia production rates is expected when the materials are filled with ionic liquids to form catalytically active interface structures. These materials are currently tested in different electrochemical cells including flow cells and zero-gap electrolyzers.
Finally, in collaborative projects the synthesized materials or the established characterization methods have also been applied to investigate the properties of synthesized materials in electrocatalytic applications (oxygen reduction reaction) and the confined state structures of ionic liquids within metal-organic framework materials. These collaborative projects are first examples for the expansion of the CILCat concept and materials into related applications connected to electrochemistry and materials science.
The results concerning the effect of confined ionic liquid ions on the gas sorption properties of porous carbon materials are expected to achieve high impact. The concept to adjust pore architectures and surface chemistries by addition of a low vapor pressure liquid film instead of by the synthetic procedure of the carbon materials themselves promises a way towards precise adjustment of sorption properties. Alone the approach followed in CILCat to measure the properties of confined ionic liquids and resulting pore structures by volumetric sorption devices, thermal response measurements, and differential scanning calorimetry is a toolbox which goes beyond the state of the art.
The technological implementation of the CILCat concept into electrochemically-driven conversion of small molecules will need more research and demonstration in the second phase of CILCat. Combining sorption and catalytic properties of materials with electrodes, coupled electrochemical processes, and product separation/analytics is not at all a trivial task and requires the combination of various expertise from the fields of chemistry, materials science, engineering. The project team is currently working on the implementation of this task of CILCat. At the present state, the existence of a advanced laboratory-scale electrochemical setup for the characterization of eNRR in different electrolyte systems which provides reliable and reproduceable data can be seen as a major contribution to the field. Over the last years, eNRR (especially in aqueous electrolytes) became a topic of intense discussion in the scientific community due to differing results obtained between different research laboratories. CILCat is currently making a noteworthy contribution here to resolve these issues and to clarify the origin of ammonia but also to investigate possible degradation pathways of actually formed ammonia under electrochemical conditions.
The technological implementation of the CILCat concept into electrochemically-driven conversion of small molecules will need more research and demonstration in the second phase of CILCat. Combining sorption and catalytic properties of materials with electrodes, coupled electrochemical processes, and product separation/analytics is not at all a trivial task and requires the combination of various expertise from the fields of chemistry, materials science, engineering. The project team is currently working on the implementation of this task of CILCat. At the present state, the existence of a advanced laboratory-scale electrochemical setup for the characterization of eNRR in different electrolyte systems which provides reliable and reproduceable data can be seen as a major contribution to the field. Over the last years, eNRR (especially in aqueous electrolytes) became a topic of intense discussion in the scientific community due to differing results obtained between different research laboratories. CILCat is currently making a noteworthy contribution here to resolve these issues and to clarify the origin of ammonia but also to investigate possible degradation pathways of actually formed ammonia under electrochemical conditions.