Electrochemically shape-controlled synthesis of great stellated dodecahedral Au nanocrystals with high-index facets for nitrogen reduction to ammonia

Nanomaterials Synthesis Discovery via Parallel Electrochemical Deposition

Electrodeposition of nanoparticles is investigated with a multichannel potentiostat in electrochemical and chemical arrays. De novo deposition and shape control of palladium nanoparticles are explored in arrays with a two-stage strategy. Initial conditions for electrodeposition of materials are discovered in a first stage and then used in a second stage to logically expand chemical and electrochemical parameters. Shape control is analyzed primarily with scanning electron microscopy. Using this approach, optimized conditions for the electrodeposition of cubic palladium nanoparticles were identified from a set of previously untested electrodeposition conditions. The parameters discovered through the array format were then successfully extrapolated to a traditional bulk three-electrode electrochemical cell. Electrochemical arrays were also used to explore electrodeposition parameters reported in previous bulk studies, further demonstrating the correspondence between the array and bulk systems. These results broadly highlight opportunities for electrochemical arrays, both for discovery and for further investigations of electrodeposition in nanomaterials synthesis.

Oxygen vacancy modulation in interfacial engineering Fe3O4 over carbon nanofiber boosting ambient electrocatalytic N2 reduction

The oxygen vacancy modulation of interface-engineered Fe3O4 nanograins over carbon nanofiber (Fe@CNF) was achieved to improve electrocatalytic nitrogen reduction reaction (NRR) activity and stability via facile electrospinning and tuning thermal procedure. The optimal catalyst calcined at 800 ℃ (Fe@CNF-800) was endowed with abundant nanograin boundaries and optimized oxygen vacancy (Vo) concentration of iron oxides, thereby affording 37.1 μg h-1 mgcat.-1 (-0.2 V vs. reversible hydrogen electrode (RHE)) NH3 yield and rational Faraday efficiency (10.2%), with 13.6 times atomic activity enhancement compared to of that commercial Fe3O4. The interfacial effect of assembled nanograins in particles correlated with the formation of Vo and more intrinsic active sites, which is conducive to the trapping and activation of nitrogen (N2). The in-situ X-ray photoelectron spectroscopy (XPS) measurement revealed the real consumption of adsorbed oxygen when introducing N2 by the trapping effect of Vo. Density-Functional-Theory (DFT) calculation validates the promotive hydrogenation effect and elimination of hydrogen intermediate (H*) interacted with N2 transferring toward oxygen of the support. The optimal catalyst shows a lasting NRR activity at least 90 h, outperforming most reported Fe-based NRR catalysts.

Nitrogen Electrocatalysis: Electrolyte Engineering Strategies to Boost Faradaic Efficiency

The electrochemical activation of dinitrogen at ambient temperature and pressure for the synthesis of ammonia has drawn increasing attention. The faradaic efficiency (FE) as well as ammonia yield in the electrochemical synthesis is far from reaching the requirement of industrial-scale production. In aqueous electrolytes, the competing electron-consuming hydrogen evolution reaction (HER) and poor solubility of nitrogen are the two major bottlenecks. As the electrochemical reduction of nitrogen involves proton-coupled electron transfer reaction, rationally engineered electrolytes are required to boost FE and ammonia yield. In this Review, we comprehensively summarize various electrolyte engineering strategies to boost the FE in aqueous and non-aqueous medium and suggest possible approaches to further improve the performance. In aqueous medium, the performance can be improved by altering the electrolyte pH, transport velocity of protons, and water activity. Other strategies involve the use of hybrid and water-in-salt electrolytes, ionic liquids, and non-aqueous electrolytes. Existing aqueous electrolytes are not ideal for industrial-scale production. Suppression of HER and enhanced nitrogen solubility have been observed with hybrid and non-aqueous electrolytes. The engineered electrolytes are very promising though the electrochemical activation has several challenges. The outcome of lithium-mediated nitrogen reduction reaction with engineered non-aqueous electrolyte is highly encouraging.

Electrodeposition: An efficient method to fabricate self-supported electrodes for electrochemical energy conversion systems

The development of electrocatalysts for energy conversion systems is essential for alleviating environmental problems and producing useful energy sources as alternatives to fossil fuels. Improving the catalytic performance and stability of electrocatalysts is a major challenge in the development of energy conversion systems. Moreover, understanding their electrode structure is important for enhancing the energy efficiency. Recently, binder-free self-supported electrodes have been investigated because the seamless contact between the electrocatalyst and substrate minimizes the contact resistance as well as facilitates fast charge transfer at the catalyst/substrate interface and high catalyst utilization. Electrodeposition is an effective and facile method for fabricating self-supported electrodes in aqueous solutions under mild conditions. Facile fabrication without a polymer binder and controlability of the compositional and morphological properties of the electrocatalyst make electrodeposition methods suitable for enhancing the performance of energy conversion systems. Herein, we summarize recent research on self-supported electrodes fabricated by electrodeposition for energy conversion reactions, particularly focusing on cathodic reactions of electrolyzer system such as hydrogen evolution, electrochemical CO2 reduction, and electrochemical N2 reduction reactions. The deposition conditions, morphological and compositional properties, and catalytic performance of the electrocatalyst are reviewed. Finally, the prospective directions of electrocatalyst development for energy conversion systems are discussed.

Regeneration of porous Fe3O4 nanosheets from deep eutectic solvent for high-performance electrocatalytic nitrogen reduction

The production of ammonia through electrocatalytic nitrogen reduction reaction (NRR) is environmentally friendly and energy-saving, but it still suffers from the low NH₃ yield rate and poor selectivity. Herein, enlightened by the unique solubility of Fe₃O₄ in deep eutectic solvent (DES), we, for the first time, reported a DES-based regeneration strategy to fabricate porous Fe₃O₄ nanosheets utilizing commercial Fe₃O₄ powder as raw materials. The as-regenerated porous Fe₃O₄ nanosheets exhibited satisfactory electrocatalytic performance toward NRR, affording a NH₃ yield rate of 12.09 μg h^-1 mg^-1_cat along with an outstanding Faradaic efficiency (FE) of 34.38% at -0.1 V versus reversible hydrogen electrode (RHE), in the 0.1 M Na₂SO₄ electrolyte. The superior electrocatalytic activity of the as-regenerated Fe₃O₄ nanosheets mainly resulted from their unique sheet-like morphology with large active surface area, high porosity, and abundant oxygen vacancies. Our proposed DES-based regeneration strategy opens a new avenue for the construction of high-performance electrocatalyst from commercial raw materials, holding great promise in NRR.