Nitrate Reduction by NiFe-LDH/CeO2: Understanding the Synergistic Effect between Dual-Metal Sites and Dual Adsorption

Sulfur Defect Tuning of CuS/BiVO4 and Understanding the Function of Hydrogen Radicals for Photoelectrochemical Ammonia Production

Photoelectrochemical nitrate reduction has been a promising method for ammonia (NH3) production under normal temperatures and neutral conditions. However, hydrogenation is a key process in the selective production of NH3 during nitrate reduction; therefore, inducing the active hydrogen for nitrate hydrogenation and inhibiting hydrogen production are a noteworthy problem. In this study, BiVO4/CuS (BVO/CS) heterostructure has been constructed for a photoelectrochemical nitrate reduction reaction (PEC NIRR). The introduction of CuS optimizes the electron-transfer ability and enhances the surface catalytic kinetics of BVO/CS. At the same time, the presence of sulfur vacancies on the surface promotes the adsorption and activation of nitrate, realizes the splitting of H2O, and successfully generates abundant hydrogen radicals (H*). The generated H* is effectively utilized in the hydrogenation of NIRR. The NH3 yield and selectivity of optimal BVO/CS reach 30.55 μg h-1 cm-2 and 43.8%, respectively, which are 2.65 and 2.39 times that of bare BVO. Therefore, this work determines the key role of H* for nitrate hydrogenation, providing a novel strategy for boosting PEC NIRR. CuS/BiVO4 was successfully fabricated for photoelectrochemical nitrate reduction. Sulfur defects enabled the generation of hydrogen radicals, which effectively promoted nitrate hydrogenation and NH3 production.

Synergism of Hydrogen-Induced Interstitial Effect and Gold-Induced Alloying Effect in PdAuH Metallene for Urea Electrosynthesis from Nitrate and Carbon Dioxide

Urea is a common agricultural fertilizer and industrial raw material, but at present, the traditional industrial production of urea is energy-and pollution-intensive. Electrocatalytic coupling of CO2 and ubiquitous nitrogen sources to synthesize urea is considered as a promising alternative method but requiring high-performance catalysts to boost the C-N coupling electrocatalysis process. Herein, hydrogen-intercalated Pd-Au bimetallene (PdAuHene) was prepared by a three-step method and used for electrosynthesis of urea from NO3- and CO2, deriving an optimum urea Faradaic efficiency of 33.88% and yield rate of 6.68 mmol g-1 h-1 at an applied potential of -0.6 V vs RHE. Detailed material characterizations and electrochemical studies reveal that the metallene structure with ultrathin thickness could improve atomic utilization of precious metal atoms, and the introduction of Au and H atoms could adjust the electronic structure of Pd atoms, regulate the evolution pathway of key N-/C-intermediates, and promote the C-N coupling to form urea.

Rapid Fabrication of N-, Cu-, and Co-Doped Electrodes with Strong Electronic Coupling by Cold Plasma for Electrocatalytic Reduction of Nitrate to Ammonia

Electrochemical NOx- reduction (NOxRR) is a sustainable technology for ammonia synthesis. The development of a simple, fast, and economical catalytic electrode preparation technique is crucial for large-scale ammonia synthesis. Herein, we propose a plate-to-plate DBD plasma strategy to synthesize the catalytic electrodes M-N/CP (M = Cu, Co, Ni, CuCo, and CuNi), achieving in suit codoping of N and bimetals on carbon paper (CP) at room temperature within 3 h. N-doping improves the metal loading and the NOxRR performance by forming N-M bonds. The electronic coupling and synergistic effect of Cu and Co sites facilitate the relay conversion of NO3- to NO2- to NH3. Notably, the NO3- removal efficiency of CuCo-N/CP reaches 82%, with NH3 yield rate of 346 μg h-1 cm-2, and the faradaic efficiency is as high as 86% at -0.58 V vs RHE, which remains competitive in terms of NOxRR performance. Importantly, wet flue gas denitrification and desulfurization coupled with electrocatalytic reduction can convert NOx and SO2 to (NH4)2SO4, Additionally, the maneuverability of plasma technology offers the potential for batch preparation of CuCo-N/CP electrodes for electrochemically driven wet denitrification wastewater valorization.

Polyoxometalate-Intercalated Tremella-Like CoNi-LDH Nanocomposites for Electrocatalytic Nitrite-Ammonia Conversion

The electrocatalytic reduction of NO2- (NO2RR) holds promise as a sustainable pathway to both promoting the development of emerging NH3 economies and allowing the closing of the NOx loop. Highly efficient electrocatalysts that could facilitate this complex six-electron transfer process are urgently desired. Herein, tremella-like CoNi-LDH intercalated by cyclic polyoxometalate (POM) anion P8W48 (P8W48/CoNi-LDH) prepared by a simple two-step hydrothermal-exfoliation assembly method is proposed as an effective electrocatalyst for NO2- to NH3 conversion. The introduction of POM with excellent redox ability tremendously increased the electrocatalytic performance of CoNi-LDH in the NO2RR process, causing P8W48/CoNi-LDH to exhibit large NH3 yield of 0.369 mmol h-1 mgcat-1 and exceptionally high Faradic efficiency of 97.0% at -1.3 V vs the Ag/AgCl reference electrode in 0.1 M phosphate buffer saline (PBS, pH = 7) containing 0.1 M NO2-. Furthermore, P8W48/CoNi-LDH demonstrated excellent durability during cyclic electrolysis. This work provides a new reference for the application of POM-based nanocomposites in the electrochemical reduction of NO2- to obtain value-added NH3.