Diamond-based materials for the photoelectrocatalytic reduction of molecular nitrogen

• Applicants: Professor Dr.-Ing. Elias Klemm; Professorin Dr. Anke Krüger; Dr. Marcel Risch
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 501932605

Diamond has become a widely available material that is being produced on industrial scale by high-temperature and high-pressure synthesis for particles and chemical vapor deposition for extended thin films on substrates up to m2 scale. Diamond is chemically inert, has a high overpotential for the hydrogen evolution reaction, and in doped form possesses a high mobility for electrons and holes. Furthermore, engineered diamond materials offer a unique opportunity to adjust and control the properties of bulk diamond for the photoelectrochemical nitrogen reduction reaction (N2RR). Namely the negative electron affinity of diamond enables the emission of highly reductive electrons from the conduction band. However, the large bandgap currently requires deep UV excitation to achieve this. Doping, thermal annealing, surface termination/modification, and nanostructuration are means of knowledge-based engineering of the bandgap and charge transfer for visible light driven N2RR as well as of the conductivity and the surface for enhanced electrochemical N2RR. At first, the design and synthesis of modified diamond materials will aim at adjusting and understanding structure-activity relationships separately for electrocatalytic and photocatalytic N2RR. Therefore, a thorough characterization of these materials is necessary, especially an ex situ and in situ characterization by X-ray absorption and emission spectroscopy (XAS-XES) to map the density of states near the Fermi level which can be populated by electrical polarization or light irradiation. Since the local concentrations of N2 and of the proton donor (pH, pKa) play a crucial role in electrochemical N2RR, different cell and electrode designs will be investigated in order to enhance N2RR and suppress hydrogen evolution reaction, which is the main Faradaic side reaction. For the photocatalytic N2RR, reactor designs using nanoparticles suspensions or nanoparticle coated surfaces will be investigated. With this experimental approach at hand, structure-activity relationships can be identified and rationalized. Finally, synergistic effects in combining electrical polarization and light irradiation will be explored to establish a photoelectrochemical approach to direct nitrogen reduction to ammonia under very mild and sustainable conditions.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2370: Interlinking catalysts, mechanisms and reactor concepts for the conversion of dinitrogen by electrocatalytic, photocatalytic and photoelectrocatalytic methods (“Nitroconversion”)