Ni and Co containing precursor derived ceramics (ceramers) were prepared from a polysiloxane based preparation route. All catalysts were characterised by BET, XRD and TEM as well as water and heptane adsorption and tested for CO2-methanation and Fischer-Tropsch synthesis. Different pyrolysis temperature between 400 and 600 °C were used to get catalysts with different surface hydrophilicities. With increasing synthesis temperature less organic groups remain on the surface resulting in a more hydrophilic catalyst. For all Ni containing ceramers, well dispersed particles in the range of 3 nm were formed with comparable surface areas. The catalysts with the lowest tendency towards water adsorption showed the highest activity for CO2-methanation. From the cobalt containing synthesis route, different material properties were observed. In contrast to the Ni catalysts, the Co particle formation depends on the pyrolysis temperature. While no metallic particles were formed above 400 °C, smallest particles were obtained using a pyrolysis temperature of 500 °C with particle sizes in the range of ~5 nm. With increasing pyrolysis temperature to 600 °C, particle size increases to ~10 nm. Nevertheless, first tests for CO2-methantion and Fischer-Tropsch reaction were successful and the catalysts with less hydrophilic surface showed higher activity and a higher selectivity towards C5+-products.

Ammonia is globally produced on an industrial scale, with 142 Mt in 2019 [1]. Most of it is used as nitrogen fertiliser (USA, 88 %, [1]), demonstrating the indispensability for modern agriculture. Ammonia is also considered as a future carbon free, energy dense liquid fuel with high volumetric hydrogen content. Today, the production via the long-established Haber-Bosch process is energy intensive and ill-suited for scaling down, which is important for intermittent, decentralised use. Thus, an electrochemical production of green ammonia directly from water and nitrogen using renewable electricity is of high research interest. Electrochemical ammonia synthesis (EAS) is an emerging technology. It suffers to date from fundamental limitations of known catalyst materials for the nitrogen reduction reaction (NRR). The NRR is assumed to follow an associative Heyrovský mechanism at room temperature. Simulative evaluations of metal catalysts confirmed that weakly nitrogen binding materials adsorb nitrogen insufficiently, while too strong nitrogen binding impedes consecutive reduction of surface bound NHx species, also known as Sabatier principle. As a consequence high overpotentials for an appreciable production rate are required with low reaction selectivity towards ammonia.[2] In conclusion, novel catalyst materials are needed. Theoretical catalyst screening by Abghoui and Skuláson of the NRR via a Mars-van-Krevelen (MvK) mechanism on transition metal nitrides has identified certain ones as potentially active, selective and stable for the EAS. Among these promising candidates are vanadium, niobium, chromium and zirconium.[3] Some of these have been investigated already to some extent, with partially opposing results [4-6]. There is yet no fundamental link between material properties and catalytic activity for the EAS as with established catalyst materials like platinum. Proving the electrochemical activity of catalyst materials requires the quantitative determination of produced ammonia. This can generally prove challenging due to low production rate and several possible sources of advantageous contaminations. [7, 8]In this work chromium and zirconium nitride nanoparticles have been successfully synthesised via a pyrolytic conversion of a suitable metallic precursor in presence of urea as a nitrogen source [9]. Additionally, commercially available chromium and zirconium nitride powders were purchased for comparison. The main focus in this work will be on chromium nitride. These materials were physically characterised in regards to elemental composition, phase composition, physical surface area, thermal decomposition and particle size. Electrochemical characterisation was implemented in a commercial measurement cell for gas diffusion electrodes (GDE). GDEs were spray coated by hand, allowing for fast, flexible processing. Activity and selectivity of the catalyst material for the EAS were determined by quantitative measurement of the electrochemically produced ammonia. Ammonia was collected by acid trap in form of ammoni...