Ammonia Electrochemical Synthesis Using Platinum Ruthenium Alloy at Ambient Pressure and Low Temperature

Abstract

Large scale energy storage from renewable is a critical step for development of CO2 free modern society. Electrical energy conversion to chemical compound is one of the preferred alternatives for grid leveling, photovoltaic and windmills storage applications. Nitrogen (N2) reduction to ammonia (NH3) is being offered as an interesting approach of chemical energy storage solution, due to the properties of ammonia which includes high energy density, liquefaction at relative low pressures (10 bars at room temperature) and availability N2 from air. Nevertheless, the slow electrochemical reduction of N2 to NH3 and low coulombic efficiency are the main herders in promoting nitrogen to ammonia technology. Ammonia was electrochemically produced from nitrogen and water using a ruthenium-platinum (RuPt) alloy catalyst cathode and a nickel anode under ambient pressure and room temperature. The rate of ammonia formation was 5.1×10-9 gNH3 s-1cm-2 with a 13.2% faradaic efficiency at an applied potential of 0.123 V vs. RHE and it reached 1.1×10-8 gNH3 s-1cm-2 at 0.023 V. Ammonia formation reaction was investigated under selected potentials and temperatures and analyzed. Real-time direct electrochemical mass spectrometry (DEMS) analysis of the evolved gases measured at various applied potentials detected only the mass signals of hydrogen and ammonia, which exhibit intensities increase with overpotentials, with no trace of a hydrazine signal at the full potential range. Compared to metallic ruthenium and platinum catalysts, RuPt showed a an improved kinetic indicating a synergistic effect in the reduction of N2, attributed to proximity of Pt-H and Ru-N sites acting in a co-catalysis mechanism (figure 1). An analysis of these processes and comparison to FeOx based stat of the art catalysts are discussed. Figure 1. Proposed Cooperative Reaction Mechanism for N2 reduction to NH3 on RuPt Figure 1