Boosting Oxygen Reduction Reaction Kinetics by Designing Rich Vacancy Coupling Pentagons in the Defective Carbon.

In the energy conversion context, the design and synthesis of high-performance metal-free carbon nanomaterials with topological defects for the oxygen reduction reaction (ORR) are essential. Herein, we first report a template-assisted strategy to fabricate carbon defect electrocatalysts with rich vacancy coupling pentagons (VP) as active sites in two-dimensional (2D) carbon nanosheets (VP/CNs). Experimental characterizations verify the presence of abundant VP active sites in the VP/CNs electrocatalyst, and the ORR activity is linearly related to the amounts of VP active sites. In situ spectroscopic results identify that the VP/CNs can catalyze direct O-O bond cleavage, bypassing the formation of traditional *OOH intermediates, resulting in the fast kinetics of ORR via a dissociative pathway. The as-prepared VP/CNs show outstanding intrinsic activity for alkaline ORR (half-wave potential of 0.86 V vs reversible hydrogen electrode) with an almost 99% efficiency for four-electron selectivity, outperforming that using the benchmark of Pt/C. Density functional theory calculations further reveal that the cooperative effect between carbon vacancy and adjacent pentagons significantly increases the charge transfer and achieves a lower ORR reaction energy barrier compared with the counterpart of adjacent pentagons or single pentagon. The well-designed carbon defects pave a new avenue for the rational design of metal-free electrocatalysts with high efficiency.

Identifying Luminol Electrochemiluminescence at the Cathode via Single-Atom Catalysts Tuned Oxygen Reduction Reaction.

Luminol-based electrochemiluminescence (ECL) can be readily excited by various reactive oxygen species (ROS) electrogenerated with an oxygen reduction reaction (ORR). However, the multiple active intermediates involved in the ORR catalyzed with complex nanomaterials lead to recognizing the role of ROS still elusive. Moreover, suffering from the absence of the direct electrochemical oxidation of luminol at the cathode and poor transformation efficiency of O2 to ROS, the weak cathodic ECL emission of luminol is often neglected. Herein, owing to the tunable coordination environment and structure-dependent catalytic feature, single-atom catalysts (SACs) are employed to uncover the relationship between the intrinsic ORR activity and ECL behavior. Interestingly, the traditionally negligible cathodic ECL of luminol is first boosted (ca. 70-fold) owing to the combination of electrochemical ORR catalyzed via SACs and chemical oxidation of luminol. The boosted cathodic ECL emission exhibits electron-transfer pathway-dependent response by adjusting the surrounding environment of the center metal atoms in a controlled way to selectively produce different active intermediates. This work bridges the relationship between ORR performance and ECL behavior, which will guide the development of an amplified sensing platform through rational tailoring of the ORR activity of SACs and potential-resolved ECL assays based on the high-efficiency cathodic ECL reported.

Facile Uniaxial Electrospinning Strategy To Embed CsPbBr3 Nanocrystals with Enhanced Water/Thermal Stabilities for Reversible Fluorescence Switches.

All-inorganic halide perovskite nanocrystals with their fascinating optical properties have drawn increasing attention as promising nanoemitters. However, due to the intrinsic poor colloidal stability against the external environment, the practical applications are greatly limited. Herein, a facile and effective strategy for the in situ encapsulation of CsPbBr3 NCs into highly dense multichannel polyacrylonitrile (PAN) nanofibers via a uniaxial electrospinning strategy is presented. Such a facile uniaxial electrospinning strategy enables the in situ formation of CsPbBr3 NCs in PAN nanofibers without the introduction of stabilizers. Significantly, the obtained CsPbBr3 nanofibers not only display intense fluorescence with a high quantum yield (≈48%) but also present high stability when exposed to water and air owing to the peripheral protecting matrix of PAN. After immersing CsPbBr3@PAN nanofiber films in water for 100 days, the quantum yield of CsPbBr3@PAN nanofibers maintained 87.5% of the original value, which was much higher than that using CsPbBr3 NCs. Furthermore, based on the spectral overlap between the electrochromic material of ruthenium purple and fluorescence of CsPbBr3@PAN nanofiber films with excellent water stability, a reversible fluorescence switch is constructed with good fatigue resistance, suggesting their promising applications.

Supramolecular Anchoring Strategy for Facile Production of Ruthenium Nanoparticles Embedded in N-Doped Mesoporous Carbon Nanospheres for Efficient Hydrogen Generation.

Because of the favorable mass transport and increased available active sites, the rational design and preparation of porous carbon structures are essential but still challenging. Herein, a novel and facile supramolecular anchoring strategy was developed to achieve the embedding of ruthenium (Ru) nanoparticles in N-doped mesoporous carbon nanospheres through pyrolyzing the precursor formed by coordination assembly between metal ions and zinc gluconate (G(Zn)). Featuring rich hydroxyl groups, the G(Zn) can effectively chelate Ru3+ via metal-oxygen bonds to form 3D supramolecular nanospheres, and meanwhile, mesopores in carbon nanospheres were expanded after subsequent pyrolysis thanks to the volatilization of zincic species at high temperature. As a demonstration, the best-performing catalyst displayed extraordinary activity for the hydrogen evolution reaction (HER) with a small overpotential of 43 mV versus reversible hydrogen electrode (vs RHE) at 10 mA/cm2 and a Tafel slope of 39 mV/dec, which was superior to that of commercial Pt/C in alkaline medium. Theoretical calculations revealed that the catalytic activity was significantly promoted by the strong electronic coupling between Ru nanoparticles and N-doped porous carbon, which increased the electron transfer capability and facilitated the adsorption and dissociation of H2O to realize an efficient HER.

A General Method for Transition Metal Single Atoms Anchored on Honeycomb-Like Nitrogen-Doped Carbon Nanosheets.

Excavating and developing highly efficient and cost-effective nonnoble metal single-atom catalysts for electrocatalytic reactions is of paramount significance but still in its infancy. Herein, reported is a general NaCl template-assisted strategy for rationally designing and preparing a series of isolated transition metal single atoms (Fe/Co/Ni) anchored on honeycomb-like nitrogen-doped carbon matrix (M1 -HNC-T1 -T2 , M = Fe/Co/Ni, T1 = 500 °C, T2 = 850 °C). The resulting M1 -HNC-500-850 with M-N4 active sites exhibits superior capability for oxygen reduction reaction (ORR) with the half-wave potential order of Fe1 -HNC-500-850 > Co1 -HNC-500-850 > Ni1 -HNC-500-850, in which Fe1 -HNC-500-850 shows better performance than commercial Pt/C. Density functional theory calculations reveal a choice strategy that the strong p-d-coupled spatial charge separation results the Fe-N4 effectively merges active electrons for elevating d-band activity in a van-Hove singularity like character. This essentially generalizes an optimal electronic exchange-and-transfer (ExT) capability for boosting sluggish alkaline ORR activity. This work not only presents a universal strategy for preparing single-atom electrocatalyst to accelerate the kinetics of cathodic ORR but also provides an insight into the relationship between the electronic structure and the electrocatalytical activity.