Ammonia is synthesized directly from water and N at room temperature and atmospheric pressure in a flow electrochemical cell operating in gas phase (half-cell for the NH synthesis). Iron supported on carbon nanotubes (CNTs) was used as the electrocatalyst in this half-cell. A rate of ammonia formation of 2.2×10 gNH3  m h was obtained at room temperature and atmospheric pressure in a flow of N , with stable behavior for at least 60 h of reaction, under an applied potential of -2.0 V. This value is higher than the rate of ammonia formation obtained using noble metals (Ru/C) under comparable reaction conditions. Furthermore, hydrogen gas with a total Faraday efficiency as high as 95.1 % was obtained. Data also indicate that the active sites in NH electrocatalytic synthesis may be associated to specific carbon sites formed at the interface between iron particles and CNT and able to activate N , making it more reactive towards hydrogenation.

Fe 2 O 3 -CNT samples are studied for the roomtemperature electrocatalytic synthesis of NH 3 from H 2 O and N 2 in a gas−liquid−solid three-phase reactor. A 30 wt % iron-oxide loading was found to be optimal. The performances greatly depend on the cell design, where the possibility of ammonia crossover through the membrane has to be inhibited. The reaction conditions also play a significant role. The effect of electrolyte (type, pH, concentration) was investigated in terms of current density, rate of ammonia formation, and Faradaic efficiency in continuous tests up to 24 h of time on stream. A complex effect of the applied voltage was observed. An excellent stability was found for an applied voltage of −1.0 V vs Ag/AgCl. At higher negative applied voltages, the ammonia formation rate and Faradaic selectivity are higher, but with a change of the catalytic performances, although the current densities remain constant for at least 24 h. This effect is interpreted in terms of reduction of the iron-oxide species above a negative voltage threshold, which enhances the side reaction of H + /e − recombination to generate H 2 rather than their use to reduce activated N 2 species, possibly located at the interface between iron-oxide and functionalized CNTs.

Ammonia is synthesized directly from water and N2 at room temperature and atmospheric pressure in a flow electrochemical cell operating in gas phase (half‐cell for the NH3 synthesis). Iron supported on carbon nanotubes (CNTs) was used as the electrocatalyst in this half‐cell. A rate of ammonia formation of 2.2×10−3 gNH3  m−2 h−1 was obtained at room temperature and atmospheric pressure in a flow of N2, with stable behavior for at least 60 h of reaction, under an applied potential of −2.0 V. This value is higher than the rate of ammonia formation obtained using noble metals (Ru/C) under comparable reaction conditions. Furthermore, hydrogen gas with a total Faraday efficiency as high as 95.1 % was obtained. Data also indicate that the active sites in NH3 electrocatalytic synthesis may be associated to specific carbon sites formed at the interface between iron particles and CNT and able to activate N2, making it more reactive towards hydrogenation.

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Advantages of hydrotalcite-like precursors and the synergistic effect of bimetallic Ni–Fe alloys are combined and the most appropriate amount of Fe identified with respect to activity, selectivity and stability.

Composite oxide supported Ni-based catalysts were prepared by a wet impregnation technique and applied to the methanation of carbon dioxide. The composite oxide supports were prepared by an impregnation−precipitation method using commercial γ-Al 2 O 3 powder as a host with variation of the percentage of loading of ZrO 2 , TiO 2 , and CeO 2 promoters from their respective salt precursors. NH 4 OH was used as the precipitating agent. The as-prepared catalysts were characterized by Brunauer−Emmet−Teller surface area analysis, atomic absorption spectroscopy, X-ray diffraction, temperature-programmed reduction by H 2 (H 2 -TPR), and CO chemisorption. Catalytic activity of the newly synthesized catalysts was investigated toward hydrogenation of CO 2 at atmospheric pressure by varying reaction temperature between 250 and 400 °C (with increasing step equal to 25 °C). Experimental results revealed that the composite oxide supported Ni-based catalysts showed performance superior to that of the γ-Al 2 O 3 only supported Ni-based catalyst (which was synthesized using the same procedure for comparison). Among the investigated catalysts, the Ni/C15 catalyst with composite oxide support (55% of γ-Al 2 O 3 loading and 15% equivalent loading of ZrO 2 , TiO 2 , and CeO 2 ) showed the best activity: 81.4% conversion of CO 2 to CH 4 at 300 °C. Better performance of the composite oxide supported Ni-based catalysts was achieved because of the improvements in the reducibility nature of the catalysts (investigated using H 2 -TPR).

Renewable H 2 production by water electrolysis has attracted much attention due to its numerous advantages. However, the energy consumption of conventional water electrolysis is high and mainly driven by the kinetically inert anodic oxygen evolution reaction. An alternative approach is the coupling of different half-cell reactions and the use of redox mediators. In this review, we, therefore, summarize the latest findings on innovative electrochemical strategies for H 2 production. First, we address redox mediators utilized in water splitting, including soluble and insoluble species, and the corresponding cell concepts. Second, we discuss alternative anodic reactions involving organic and inorganic chemical transformations. Then, electrochemical H 2 production at both the cathode and anode, or even H 2 production together with electricity generation, is presented. Finally, the remaining challenges and prospects for the future development of this research field are highlighted.