Local Proton Source Enhanced Nitrogen Reduction on a Combined Cobalt-Molybdenum Catalyst for Electrochemical Ammonia Synthesis.

Electrochemical nitrogen reduction reaction (NRR) under ambient conditions has attracted considerable scientific and engineering interest as a green alternative route for NH3 production. Molybdenum is a promising candidate as an electrocatalyst for NRR as it has a suitable binding strength with N species. However, the design of an efficient Mo-based catalyst remains elusive. To enhance the selectivity of NRR toward NH3 , we have developed a carbon nanofiber catalyst embedded with molybdenum and cobalt (Co-Mo-CNF). Co with a strong ability to dissociate water enhances local proton source near Mo, where the hydrogenation step of the NRR occurs. A NH3 formation rate of 72.72 µg h-1 mg-1 and a Faradaic efficiency of 34.5 % were obtained at -0.5 V vs. RHE. We also attempted to provide a mechanistic understanding of the NRR via in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and isotopic labeling experiments using 15 N2 and D2 O.

Green ammonia synthesis using CeO2/RuO2 nanolayers on vertical graphene catalyst via electrochemical route in alkaline electrolyte.

The electrochemical synthesis of ammonia at ambient temperature and pressure has the potential to replace the conventional process for the production of ammonia. However, the low ammonia yield and poor long-term stability of catalysts for the synthesis of ammonia hinders the application of this technology. Herein, we endeavored to tackle this challenge by synthesizing 3-D vertical graphene (VG) on Ni foam via a one-step, low-temperature plasma process, which offered high conductivity and large surface area. Subsequently, the vertical graphene on Ni foam was loaded with nanolayers of ruthenium oxide (RuO2, ∼2 nm) and cerium oxide (CeO2, <20 nm) nanoparticles via magnetron sputtering. The incorporation of nanoparticle layers (RuO2 and CeO2/RuO2) on VG significantly increased the NH3 yield in KOH electrolyte. Finally, the performance and long-term stability of this composite material were successfully demonstrated by the addition of CeO2/RuO2 nanolayers on the VG electrocatalyst. The catalyst achieved an excellent performance with a high ammonia synthesis yield of 50.56 µg mgtotal cat.-1 h-1 (1.11 × 10-10 mol cm-2 s-1) during the performance evaluation period of 36 h. This observation was also verified by density functional theory calculation, where CeO2 exhibited the best catalytic performance compared to RuO2 and pristine graphene.

Comparison between Fe2O3/C and Fe3C/Fe2O3/Fe/C Electrocatalysts for N2 Reduction in an Alkaline Electrolyte.

Cost-effective and nonprecious iron-based catalysts were synthesized, evaluated, and compared for electrocatalytic N2 reduction reaction (NRR) under alkaline conditions in the potential range from -0.4 to 0.1 V [vs reversible hydrogen electrode (RHE)] at low temperature (≤60 °C) and atmospheric pressure. The tested H-type cell was separated by an anion exchange membrane in 6 M KOH alkaline electrolyte (pH = over 14) in order to minimize hydrogen evolution reaction and to directly form NH3 gas. The amount of ammonia synthesized was quantified using an indophenol blue method and cross-checked with 1H nuclear magnetic resonance spectroscopy and ion chromatography using both 14N2 and 15N2 gases. Because of the synergistic effect between the Fe3C, Fe2O3, and Fe composites in the NRR, both the ammonia formation rate and faradaic efficiency in Fe3C/Fe2O3/Fe/C were approximately fourfold higher than those in Fe2O3/C at 60 °C and 0.1 V (vs RHE). These results can provide insights into designing Fe-based electrocatalysts for NRR at atmospheric pressure.

Insights into Nitrogenase Bioelectrocatalysis for Green Ammonia Production.

There is a growing interest in using ammonia as a liquid carrier of hydrogen for energy applications. Currently, ammonia is produced industrially by the Haber-Bosch process, which requires high temperature and high pressure. In contrast, bacteria have naturally evolved an enzyme known as nitrogenase, that is capable of producing ammonia and hydrogen at ambient temperature and pressure. Therefore, nitrogenases are attractive as a potentially more efficient means to produce ammonia via harnessing the unique properties of this enzyme. In recent years, exciting progress has been made in bioelectrocatalysis using nitrogenases to produce ammonia. Here, the prospects for developing biological ammonia production are outlined, key advances in bioelectrocatalysis by nitrogenases are highlighted, and possible solutions to the obstacles faced in realising this goal are discussed.

Engineering a solid-state metalloprotein hydrogen evolution catalyst.

Hydrogen has the potential to play an important role in decarbonising our energy systems. Crucial to achieving this is the ability to produce clean sources of hydrogen using renewable energy sources. Currently platinum is commonly used as a hydrogen evolution catalyst, however, the scarcity and expense of platinum is driving the need to develop non-platinum-based catalysts. Here we report a protein-based hydrogen evolution catalyst based on a recombinant silk protein from honeybees and a metal macrocycle, cobalt protoporphyrin (CoPPIX). We enhanced the hydrogen evolution activity three fold compared to the unmodified silk protein by varying the coordinating ligands to the metal centre. Finally, to demonstrate the use of our biological catalyst, we built a proton exchange membrane (PEM) water electrolysis cell using CoPPIX-silk as the hydrogen evolution catalyst that is able to produce hydrogen with a 98% Faradaic efficiency. This represents an exciting advance towards allowing protein-based catalysts to be used in electrolysis cells.

A high-performing nanostructured TiO2 filter for volatile organic compounds using atomic layer deposition.

Novel nanostructured gas filtering systems with TiO(2) thin films using atomic layer deposition (ALD) were developed for volatile organic compounds. A superior toluene adsorption efficiency was found for the nanostructured TiO(2) thin films.