Sustainable removal of nitrite waste to value-added ammonia on Cu@Cu2O core-shell nanostructures by pulsed laser technique.

The biochemical reduction of nitrite (NO2-) ions to ammonia (NH3) requires six electrons and is catalyzed by the cytochrome c NO2- reductase enzyme. This biological reaction inspired scientists to explore the reduction of nitrogen oxyanions, such as nitrate (NO3-) and NO2- in wastewater, to produce the more valuable NH3 product. It is widely known that copper (Cu)-based nanoparticles (NPs) are selective for the NO3- reduction reaction (NO3-RR), but the NO2-RR has not been well explored. Therefore, we attempted to address the electrocatalytic conversion of NO2- to NH3 using Cu@Cu2O core-shell NPs to simultaneously treat wastewater by removing NO2- and producing valuable NH3. The Cu@Cu2O core-shell NPs were constructed using the pulsed laser ablation of Cu sheet metal in water. The core-shell nanostructure of these particles was confirmed by various characterization techniques. Subsequently, the removal of NO2- and the ammonium (NH4+)-N yield rate were estimated using the Griess and indophenol blue methods, respectively. Impressively, the Cu@Cu2O core-shell NPs exhibited outstanding NO2-RR activity, demonstrating a maximum NO2- removal efficiency of approximately 94% and a high NH4+-N yield rate of approximately 0.03 mmol h-1.cm-2 at -1.6 V vs. a silver/silver chloride reference electrode under optimal conditions. The proposed NO2-RR mechanism revealed that the (111) facet of Cu favors the selective conversion of NO2- to NH3 via a six-electron transfer. This investigation may offer a new insight for the rational design and detailed mechanistic understanding of electrocatalyst architecture for the effective conversion of NO2- to NH4+.

On the electrochemical deposition and dissolution of divalent metal ions.

The deposition of Cu(2+) and Zn(2+) from aqueous solution has been investigated by a combination of classical molecular dynamics, density functional theory, and a theory developed by the authors. For both cases, the reaction proceeds through two one-electron steps. The monovalent ions can get close to the electrode surface without losing hydration energy, while the divalent ions, which have a stronger solvation sheath, cannot. The 4s orbital of Cu interacts strongly with the sp band and more weakly with the d band of the copper surface, while the Zn 4s orbital couples only to the sp band of Zn. At the equilibrium potential for the overall reaction, the energy of the intermediate Cu(+) ion is only a little higher than that of the divalent ion, so that the first electron transfer can occur in an outer-sphere mode. In contrast, the energy of the Zn(+) ion lies too high for a simple outer-sphere reaction to be favorable; in accord with experimental data this suggests that this step is affected by anions.

Electrochemical adsorption of OH on Pt(111) in alkaline solutions: combining DFT and molecular dynamics.

The adsorption of OH on Pt(111) in alkaline solution has been investigated by a method that combines density functional theory, molecular dynamics, and quantum statistical mechanics. In particular, we have calculated the free energy surface for the reaction. A physisorbed hydroxide ion in a metastable state and a stable adsorbed uncharged OH group are observed. The energy of activation at equilibrium is comparatively low, so that the reaction is fast.

Why silver deposition is so fast: solving the enigma of metal deposition.

A perfect match: Silver deposition is one of the fastest electrochemical reactions, even though the Ag(+) ion loses more than 5 eV solvation energy in the process. This phenomenon, an example of the enigma of metal deposition, was investigated by a combination of MD simulations, DFT, and specially developed theory. At the surface, the Ag(+) ion experiences a strong interaction with the sp band of silver, which catalyzes the reaction.

Non-noble metal (Ni, Cu)-carbon composite derived from porous organic polymers for high-performance seawater electrolysis.

The hydrothermal preparation of o-dianisidine and triazine interlinked porous organic polymer and its successive derivatisation via metal infusion (Ni, Cu) under hydrothermal and calcination conditions (700 °C) to yield pristine (ANIPOP-700) and Ni/Cu decorated porous carbon are described here (Ni-ANIPOP-700 and Cu-ANIPOP-700). To confirm their chemical and morphological properties, the as-prepared materials were methodically analyzed using solid state 13C and 15N NMR, X-ray diffraction, Raman spectroscopy, field emission scanning and high resolution transmission electron microscopic techniques, and x-ray photoelectron spectroscopy. Furthermore, the electrocatalytic activities of these electrocatalysts were thoroughly investigated under standard oxygen evolution (OER) and hydrogen evolution reaction (HER) conditions. The results show that all of the materials demonstrated significant activity in water splitting as well as displayed excellent stability (22 h) in both acidic (HER) and basic conditions (OER). Among the electrocatalysts reported in this study, Ni-ANIPOP-700 exhibited a lower overpotential η10 of 300 mV in basic medium (OER) and 150 mV in acidic medium (HER), as well as a lower Tafel slope of 69 mV/dec (OER) and 181 mV/dec (HER), indicating 30% lower energy requirement for overall water splitting. Gas chromatography was used to examine the electrolyzed products.