Controlled electrodeposition of silver onto glassy carbon, gold and indium tin oxide-coated glass substrates has been achieved from three room temperature protic ionic liquids (PILs), ethylammonium ...nitrate, triethylammonium methylsulfonate, and bis(2-methoxyethyl)ammonium acetate. Cyclic voltammetric, chronoamperometric, together with microscopic and X-ray techniques reveal that micro/nanostructured Ag thin films of controlled morphology, size, density, and uniformity can be achieved by tuning the electrodeposition parameters such as potential, time, types of PILs, substrate materials, and ionic liquid viscosity by altering the water content. Chronoamperometric results provide direct evidence that electrodeposition of Ag in protic ionic liquids takes place through a progressive nucleation and diffusion-controlled 3D growth mechanism. The as prepared Ag micro/nanoparticles have been employed as electrocatalysts for oxygen reduction reaction and exhibit excellent catalytic activity. The study provides promise for using protic ionic liquids as alternative electrolytes to conventional aprotic ionic liquids for electrodeposition of metals and nanostructured electrocatalysts.
Multiwall carbon nanotubes (MWCNTs) have been applied extensively in various aspects of advanced materials development. However, the purification of multi-walled carbon nanotubes and the removal of ...internally confined metal impurities, without compromising the CNT structural integrity, have proved to be a great challenge. The presence of inherent metal impurities has increased the complexity and health risks associated with the use of MWCNTs. In this study, we developed a low-cost purification strategy to effectively remove encapsulated metal impurities. MWCNTs synthesized by Ni-catalyzed chemical vapor deposition (CVD), were annealed in the presence of melamine under Ar-atmosphere protection at 1000 °C. Electron microscopy indicated that the pyrolysis of MWCNTs in the presence of melamine induces the leaching of encapsulated Ni particles via the tube open-end or the defect sites found along the MWCNTs. With this method, the leached impurities were shown to be more susceptible and accessible to acid purification. Upon acid treatment, ultrapure MWCNTs with trace amounts of metallic impurities (<0.01 wt%) can be achieved. Alternatively, the leached metal nanoparticles could serve as highly efficient electrocatalytically active sites for oxygen evolution reactions with a turn over frequency (TOF) of 0.61 s −1 .
Renewable energy-driven ammonia electrosynthesis by N2 reduction reaction (NRR) at ambient conditions is vital for sustainability of both the global population and energy demand. However, NRR under ...ambient conditions to date has been plagued with a low yield rate and selectivity (<10%) due to the more favorable hydrogen evolution reaction (HER) in aqueous media. Herein, surface area enhanced α-Fe nanorods grown on carbon fiber paper were used as NRR cathodes in an aprotic fluorinated solvent–ionic liquid mixture. Through this design, significantly enhanced NRR activity with an NH3 yield rate of ∼2.35 × 10–11 mol s–1 cmGSA –2, (3.71 × 10–13 mol s–1 cmECSA –2) and selectivity of ∼32% has been achieved under ambient conditions. This study reveals that the use of hydrophobic fluorinated aprotic electrolyte effectively limits the availability of protons and thus suppresses the competing HER. Therefore, electrode–electrolyte engineering is essential in advancing the NH3 electrosynthesis technology.
A highly efficient porous NiCu-phosphide (NiCu-P) electrode is reported for a hydrogen evolution reaction (HER) in acidic, neutral, and basic electrolytes. The NiCu-P electrode was prepared via ...hydrogen bubbles dynamic templated electrodeposition of NiCu alloy onto nickel mesh, followed by phosphidation. Due to the synergistic interaction in NiCu-P, the material exhibits excellent HER activity in a wide pH range from 0.3–14. Current density of −10 mA cm–2 was achieved at low overpotentials of −226, −250, and −175 mV in 0.5 M H2SO4, 1 M phosphate buffer solution, and 1 M KOH, respectively. The fabricated NiCu-P electrode also shows an outstanding electrochemical stability, regardless of electrolyte pH. The NiCu-P has a slope value of −53 mV dec–1, indicating that HER at NiCu-P follows the Heyrovsky mechanism in 1 M KOH.
The electrochemical N2 reduction reaction (NRR) offers a direct pathway to produce NH3 from renewable energy. However, aqueous NRR suffers from both low Faradaic efficiency (FE) and low yield rate. ...The main reason is the more favored H+ reduction to H2 in aqueous electrolytes. Here we demonstrate a highly selective Ru/MoS2 NRR catalyst on which the MoS2 polymorphs can be controlled to suppress H+ reduction. A NRR FE as high as 17.6% and NH3 yield rate of 1.14 × 10–10 mol cm–2 s–1 are demonstrated at 50 °C. Theoretical evidence supports a hypothesis that the high NRR activity originates from the synergistic interplay between the Ru clusters as N2 binding sites and nearby isolated S-vacancies on the 2H-MoS2 as centers for hydrogenation; this supports formation of NH3 at the Ru/2H-MoS2 interface.
Electrocatalytic oxidation of ammonia is an appealing, low‐temperature process for the sustainable production of nitrites and nitrates that avoids the formation of pernicious N2O and can be fully ...powered by renewable electricity. Currently, however, the number of known efficient catalysts for such a reaction is limited. The present work demonstrates that copper‐based electrodes exhibit high electrocatalytic activity and selectivity for the NH3 oxidation to NO2− and NO3− in alkaline solutions. Systematic investigation of the effects of pH and potential on the kinetics of the reaction using voltammetric analysis andin situ Raman spectroscopy suggest that ammonia electrooxidation on copper occurrs via two primary catalytic mechanisms. In the first pathway, NH3 is converted to NO2− via a homogeneous electrocatalytic process mediated by redox transformations of aqueous Cu(OH)4−/2− species, which dissolve from the electrode. The second pathway is the heterogeneous catalytic oxidation of NH3 on the electrode surface favoring the formation of NO3−. By virtue of its nature, the homogeneous‐mediated pathway enables higher selectivity and was less affected by electrode poisoning with the strongly adsorbed “N” intermediates that have plagued the electrocatalytic ammonia oxidation field. Thus, the selectivity of the Cu‐catalyzed NH3 oxidation towards either nitrite or nitrate can be achieved through balancing the kinetics of the two mechanisms by adjusting the pH of the electrolyte medium and potential.
Switch it up: Electrooxidation of ammonia can become a sustainable technology for the synthesis of nitrates but requires efficient, stable, and selective catalysts. The present work shows that copper can act as such catalyst and explores the underlying electrocatalytic mechanisms, the interplay of which defines the selectivity towards either nitrite or nitrate. By adjusting the reaction conditions, the reaction pathway can be switched towards the desired product.
Taking advantage of a continuous-flow apparatus, the iridium(III)-containing polytungstate cluster K12Na2H2Ir2Cl8P2W20O72·37H2O (1) was obtained in a reasonable yield (13% based on IrCl3·H2O). ...Compound 1 was characterized by Fourier transform IR, UV–visible, 31P NMR, electrospray ionization mass spectrometry (ESI-MS), and thermogravimetric analysis measurements. 31P NMR, ESI-MS, and elemental analysis all indicated 1 was a new polytungstate cluster compared with the reported K14(IrCl4)KP2W20O72 compound. Intriguingly, the successful isolation of 1 relied on the custom-built flow apparatus, demonstrating the uniqueness of continuous-flow chemistry to achieve crystalline materials. The catalytic properties of 1 were assessed by investigating the activity on catalyzing the electro-oxidation of ruthenium tris-2,2′-bipyridine Ru(bpy)32+/3+. The voltammetric behavior suggested a coupled catalytic behavior between Ru(bpy)33+/2+ and 1. Furthermore, on the highly oriented pyrolytic graphite surface, 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) was used as the two-dimensional host network to coassemble cluster 1; the surface morphology was observed by scanning tunneling microscope technique. “S”-shape of 1 was observed, indicating that the cluster could be accommodated in the cavity formed by two TCDB host molecules, leading to a TCDB/cluster binary structure.
A Roadmap to the Ammonia Economy MacFarlane, Douglas R.; Cherepanov, Pavel V.; Choi, Jaecheol ...
Joule,
06/2020, Volume:
4, Issue:
6
Journal Article
Peer reviewed
Open access
Ammonia is increasingly recognized as an important, sustainable fuel for global use in the future. Applications of ammonia in heavy transport, power generation, and distributed energy storage are ...being actively developed. Produced at scale, ammonia could replace a substantial fraction of current-day liquid fuel consumption. This ammonia-based economy will emerge through multiple generations of technology development and scale-up. The pathways forward in regard to current-day technology (generation 1) and immediate future approaches (generation 2) that rely on Haber-Bosch process are discussed. Generation 3 technology breaks this nexus with the Haber-Bosch process and enables direct reduction of dinitrogen to ammonia electrochemically. However, the roadmap toward scale in this technology has become obscured by recent research missteps. Nevertheless, alternative generation 3 approaches are becoming viable. We conclude with perspectives on the broader scale sustainability of an ammonia economy and the need for further understanding of the planetary nitrogen cycles of which ammonia is an important part.
It is increasingly clear that there is massive global potential to generate renewable energy at costs already competitive with fossil fuels. However, a means of storing and transporting this energy at a very large scale is a roadblock to further development and investment. Ammonia produced from renewables is widely seen as viable liquid fuel replacement for many current-day uses of fossil fuels, including as a shipping bunker fuel, as a diesel substitute in transportation, as a replacement fuel in power turbines, and even as a potential jet fuel. The global transportation of ammonia by pipeline and bulk carrier is already a well-developed technology.
In this roadmap, we envisage renewable ammonia being produced in the future at a scale that is significant in terms of global fossil fuel use. This will emerge via three overlapping technology generations. Generation 1 is based on an expansion of current-day Haber-Bosch ammonia production using CO2 sequestration or offsets. Generation 2 moves the Haber-Bosch process to renewable sources of hydrogen, while generation 3 avoids the need for the Haber-Bosch process entirely by direct electrochemical conversion of N2 to NH3. One of the attractive features of generation 3 technology is that it can be implemented at any level of scale, from kW to GW, and in a highly distributed fashion.
Ammonia produced sustainably and at sufficient scale could become one of the important liquid fuels and energy stores of the future. This roadmap article surveys the state of development of the production technologies and the many developing modes of direct use of ammonia as a liquid fuel, including as a shipping bunker fuel, as a diesel substitute in transportation, as a replacement fuel in power turbines, and even as a potential jet fuel. Economic, safety, and sustainability factors impacting on this roadmap are also discussed.
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