Orderly Coating of Bilayer Polymer to Tailor Microenvironment for Efficient C-N Coupling Toward Highly Selective Urea Electrosynthesis.

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 CO2 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 CO2 at the same time. Polyaniline with abundant basic amino groups is capable of triggering chemical interaction with acidic CO2 molecules, so that is used as the underlying polymer to serve as CO2 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.

Triggering Heteroatom Ensemble Effect over RuFe Alloy to Promote Nitrogen Chemisorption for Efficient Ammonia Electrosynthesis at Ambient Conditions.

Ammonia (NH3) electrosynthesis from nitrogen (N2) provides a promising strategy for carbon neutrality, circumventing the energy-intensive and carbon-emitting Haber-Bosch process. However, the current system still presents unsatisfactory performance, and the bottleneck lies in the rational synthesis of catalytic centers with efficient N2 chemisorption ability. Herein, a heteroatom ensemble effect is deliberately triggered over RuFe alloy with spatial proximity of metal sites to promote electrocatalytic nitrogen reduction. The heteronuclear RuFe ensemble with increased surface polarization and modulated electronic structure offers the feasibility to optimize the adsorption configuration of electroactive substances and facilitate chemical bond scission. The promotion of N2 chemisorption and the following hydrogenation are demonstrated by the in situ Fourier transform infrared spectroscopy characterizations. The catalyst thus permits significantly enhanced conversion of N2 to NH3 in a 0.1 M HCl environment, with a maximum ammonia yield rate of 75.45 µg h-1 mg-1 and a high Faradaic efficiency of 35.49%.

Built-In Positive Valence Space Shifting the Chemical Equilibrium Forward for Nitrate Reduction to Ammonia.

The electrochemical conversion of nitrate pollutants into value-added ammonia (NH3) is an appealing alternative synthetic route for sustainable NH3 production. However, the development of the electrocatalytic nitrate-to-ammonia reduction reaction (NO3RR) has been hampered by unruly reactants and products at the interface and the accompanied sluggish kinetic rate. In this work, a built-in positive valence space is successfully constructed over FeCu nanocrystals to rationally regulate interfacial component concentrations and positively shift the chemical equilibrium. With positive valence Cu optimizing the active surface, the space between the stern and shear layers becomes positive, which is able to continuously attract the negatively charged NO3- reactant and repulse the positively charged NH4+ product even under high current density, thus significantly boosting the NO3RR kinetics. The system with a built-in positive valence space affords an ampere-level NO3RR performance with the highest NH3 yield rate of 150.27 mg h-1 mg-1 at -1.3 V versus RHE with an outstanding NH3 current density of 189.53 mA cm-2, as well as a superior Faradaic efficiency (FE) of 97.26% at -1.2 V versus RHE. The strategy proposed here underscores the importance of interfacial concentration regulation and can find wider applicability in other electrochemical syntheses suffering from sluggish kinetics.

Rare-Earth Lanthanum-Evoked Amorphization and Optimization to Boost Ambient Nitrogen Fixation over Single-Atom Catalysts.

Single-atom catalysts (SACs) have been widely studied in a variety of electrocatalysis. However, its application in the electrocatalytic nitrogen reduction reaction (NRR) field still suffers from unsatisfactory performance, due to the sluggish mass transfer and significant kinetic barriers. Herein, a novel rare-earth-lanthanum-evoked optimization strategy is proposed to boost ambient NRR over SACs. The incorporation of La with a large atomic radius tends to break the atomic long-range order and trigger the amorphization of SACs, endowing a greater density of dangling bonds that could modify affinity for reactants and adsorbates. Moreover, with unique 5d16s2 valence-electron configurations, its presence could further enrich the electron density and enhance the intrinsic activity of single-metal center via the valence orbital coupling. As expected, the La-modified catalyst presents excellent activity toward the electrochemical NRR, delivering a maximum ammonia yield rate of 33.91 µg h-1 mg-1 and a remarkable Faradaic efficiency of 53.82%.

Molecular Imprinting Technology Enables Proactive Capture of Nitrogen for Boosted Ammonia Synthesis under Ambient Conditions.

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.