Galvanic deposition of Rh and Ru on randomly structured Ti felts for the electrochemical NH3 synthesis

Abstract

Nowadays NH₃ is exclusively synthesized by the Haber process. Unfortunately, the energy demand and the CO₂ emissions due to H₂ production are high. Hydrogen production utilizes precious carbon sources such as coal and natural gas. In the past we proposed an alternative process concept using a membrane electrode assembly in an electrochemical membrane reactor (ecMR). At the anode H₂O is oxidized at an IrMMO catalyst to form protons. By applying an external potential to the ecMR N₂ is reduced to NH₃ at the cathode. Just recently Rh and Ru were identified as possible cathodic electrocatalysts by DFT calculations. We present an easy and highly efficient method for galvanic coatings of Rh and Ru on randomly structured Ti felts to be used in a membrane electrode assembly. Linear sweep voltammetry measurements give a slightly higher activity of Ru for the liquid phase electrochemical NH₃ synthesis. The NH₄⁺ concentration reached is 8 times higher for Ru than for Rh. From an economical point of view, Ru is also more feasible for an electrochemical NH₃ synthesis process. Such electrodes can now be evaluated in an ecMR in comparison to recently demonstrated Ti-based electrodes.