Electrochemical nitrogen reduction reaction (NRR) is a burgeoning field for green and sustainable ammonia production, in which numerous potential catalysts emerge endlessly. However, satisfactory performances are still not realized under practical applications due to the limited solubility and sluggish diffusion of nitrogen at the interface. Herein, molecular imprinting technology is adopted to construct an adlayer with abundant nitrogen imprints on the electrocatalyst, which is capable of selectively recognizing and proactively aggregating high-concentrated nitrogen at the interface while hindering the access of overwhelming water simultaneously. With this favorable microenvironment, nitrogen can preferentially occupy the active surface, and the NRR equilibrium can be positively shifted to facilitate the reaction kinetics. Approximately threefold improvements in both ammonia production rate (185.7 µg h-1 mg-1 ) and Faradaic efficiency (72.9%) are achieved by a metal-free catalyst compared with the bare one. It is believed that the molecular imprinting strategy should be a general method to find further applicability in numerous catalysts or even other reactions facing similar challenges.
Electrochemical nitrate reduction reaction (NO3RR) stands out as a promising route for sustainable ammonia synthesis, in which active hydrogen (*H) plays a crucial role in both the deoxygenation and hydrogenation steps. However, the regulation of surface *H is still overlooked, and without intervention, the competing hydrogen evolution reaction is kinetically more favored over the NO3RR, leaving the current system as far from satisfactory. Herein, based on reverse utilization of the Sabatier principle, a series of FexNiy substitutional solid-solution alloys (SSAs) are synthesized to manipulate *H behavior for enhanced NO3RR. Upon precise optimization of the alloy composition, the d-band center of HER-active Ni shifts toward the Fermi level, endowing the catalyst with strong interaction to *H and greatly prolonging its lifetime, which enables abundant supply to facilitate the NO3RR. As expected, a maximum NH3 yield rate of 31.46 mmol h-1 mg-1 is delivered over the optimized Fe3Ni1-SSA, which is considerably higher than most of the extensively reported works. Several in situ characterizations are combined to gain in-depth insight. Especially, in situ Fourier transform infrared spectroscopy in internal reflection mode directly observes *H enrichment on the catalyst surface, while the accompanied facilitation of the NO3RR process is verified by external reflection mode.
Abstract Electrosynthesis of urea from co‐reduction of carbon dioxide and nitrate is a promising alternative to the industrial process. However, the overwhelming existence of proton and nitrate as well as the insufficient supply of CO 2 at the reaction interface usually result in complex product distributions from individual nitrate reduction or hydrogen evolution, instead of C−N coupling. In this work, we systematically optimize this microenvironment through orderly coating of bilayer polymer to specifically tackle the above challenges. Polymer of intrinsic microporosity is chosen as the upper polymer to achieve physical sieving, realizing low water diffusivity for suppressing hydrogen evolution and high gas permeability for smooth mass transfer of CO 2 at the same time. Polyaniline with abundant basic amino groups is capable of triggering chemical interaction with acidic CO 2 molecules, so that is used as the underlying polymer to serve as CO 2 concentrator and facilitate the carbon source supply for C−N coupling. Within this tailored microenvironment, a maximum urea generation yield rate of 1671.6 μg h −1 mg −1 and a high Faradaic efficiency of 75.3 % are delivered once coupled with efficient electrocatalyst with neighboring active sites, which is among the most efficient system of urea electrosynthesis.
Abstract: Direct ammonia fuel cells (DAFCs) have drawn great attention recently with the recognition that liquid ammonia (NH3), as a carbon-free hydrogen storage medium, is easy to store, transport, and distribute. However, its practical application is significantly limited by the anodic ammonia oxidation reaction (AOR), which not only is kinetically sluggish, but also suffers from competitive adsorption of oxidizing agent, OH–. Herein, we tackle the above challenges simultaneously by alloying the highly active platinum with electron-deficient tungsten. The W sites with low electronegativity would preferentially adsorb *OH to serve as the reservoir and supply for the dehydrogenation of NH3. The Pt sites are thus liberated and free for the targeting adsorption of NH3. Moreover, density functional theory calculations suggest that, with the pre-adsorption of *OH, the d band center of PtW alloy experiences a positive shift toward the Fermi level, which would contribute to stronger adsorption of the reaction intermediates and thus benefit the whole AOR process. As expected, the synthesized alloy with the optimum ratio exhibits a low onset potential of 0.46 V versus reversible hydrogen electrode and a large peak current density of 11.70 mA cm-2, ranking at the top of the state-of-the-arts. When subjected to practical application, the DAFCs assembled with such electrocatalyst deliver an excellent peak power density of 11.75 mW cm-2, indicating its potential feasibility in the next-generation energy devices.
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