Unveiling the Electrooxidation of Urea: Intramolecular Coupling of the N−N Bond

Abstract

The nitrogenous nucleophile electrooxidation reaction (NOR) plays a vital role in the degradation and transformation of available nitrogen. Focusing on the NOR mediated by the β‐Ni(OH)2 electrode, we decipher the transformation mechanism of the nitrogenous nucleophile. For the two‐step NOR, proton‐coupled electron transfer (PCET) is the bridge between electrocatalytic dehydrogenation from β‐Ni(OH)2 to β‐Ni(OH)O, and the spontaneous nucleophile dehydrogenative oxidation reaction. This theory can give a good explanation for hydrazine and primary amine oxidation reactions, but is insufficient for the urea oxidation reaction (UOR). Through operando tracing of bond rupture and formation processes during the UOR, as well as theoretical calculations, we propose a possible UOR mechanism whereby intramolecular coupling of the N−N bond, accompanied by PCET, hydration and rearrangement processes, results in high performance and ca. 100 % N2 selectivity. These discoveries clarify the evolution of nitrogenous molecules during the NOR, and they elucidate fundamental aspects of electrocatalysis involving nitrogen‐containing species.

Intertwined Signaling Pathways Governing Tooth Development: A Give-and-Take Between Canonical Wnt and Shh

“…While the Wnt/β-catenin pathway is activated in the epithelium of the dental placode, Wnt antagonists are upregulated in the dental mesenchyme, and mesenchymal Wnt/β-catenin activity is accordingly reduced (Sarkar and Sharpe, 1999;Järvinen et al, 2018), suggesting that this downregulation is needed for proper odontogenesis. In line, constitutively active β-catenin in dental mesenchyme impairs tooth germ morphogenesis (Chen et al, 2019), and elevated β-catenin activation in vitro in incisor re-aggregates of dissociated primary dental epithelial and mesenchymal cells is detrimental to tooth formation (Liu et al, 2013). However, full deletion of β-catenin in the dental mesenchyme also arrests tooth development in the bud stage (Chen et al, 2009;Fujimori et al, 2010), and constitutively active β-catenin in palatal mesenchyme induces ectopic tooth bud-like invaginations (Chen et al, 2009).…”

“…A consequence of deficient mesenchymal BMP4 signaling is a decrease in Shh expression in the adjacent dental epithelium, suggesting that BMP4 is necessary for the maintenance of Shh expression (Zhang et al, 2000;Fujimori et al, 2010). Along the same line, constitutive activation of mesenchymal β-catenin results in increased expression of the BMP antagonist noggin in the dental epithelium resulting in reduced epithelial Shh expression (Chen et al, 2019). A similar effect was observed in Bmp4-deficient mice, or in ex vivo tooth germ explants exposed to noggin-soaked beads (Fujimori et al, 2010;Munne et al, 2010).…”

Unraveling the role of oxygen vacancy in the electrooxidation of 5-hydroxymethyfurfural on Co3O4

“…The R p and R ct represented the resistance of the electrode inner oxidation and interface oxidation, respectively. 21,42,43 For Vo-Co 3 O 4 , in Fig. 4c, the R p dropped when the potential reached 1.1 V RHE , suggesting the structural evolution of catalysts.…”

“…41 The high-frequency region (10 1 Hz-10 5 Hz) is associated with the oxidation of the electrode inner, and the oxidation of Vo-Co 3 O 4 and Co 3 O 4 electrodes occurred in this region. 42 The low-frequency region (10 -1 Hz-10 1 Hz) is related to the nonhomogeneous charge distribution, namely the appearance of oxidation species at the electrode interface. 10 In Fig.…”

Accelerating Hydrogen Evolution by Anodic Electrosynthesis of Value‐Added Chemicals in Water over Non‐Precious Metal Electrocatalysts

“…In order to explore the versatility of this innovative approach, the addition of organic solutions, which are miscible with water, may facilitate the homogeneity of the reaction environment [60,61] . 2) In situ characterization techniques, such as Raman, Fourier‐transform infrared and sum frequency generation vibrational spectroscopy, and theoretical simulation are needed to monitor and predict the interaction between the elecrocatalysts and reactants in the electrochemical oxidation process, respectively, which could contribute to the rational design of multi‐metal or composite electrocatalyst for the consturction of energy‐saving and stable water splitting system [62–64] . 3) Alkaline conditions could make for the organic dehydrogenation reactions, so this strategy usually works smoothly in the strong alkaline conditions.…”