Confining N-Doped Carbon Dots into PtNi Aerogels Skeleton for Robust Electrocatalytic Methanol Oxidation and Oxygen Reduction.

Noble metallic aerogels with the self-supported hierarchical structure and remarkable activity are promising for methanol fuel cells, but are limited by the severe poisoning and degradation of active sites during electrocatalysis. Herein, the highly stable electrocatalyst of N-doped carbon dots-PtNi (NCDs-PtNi) aerogels is proposed by confining NCDs with alloyed PtNi for methanol oxidation and oxygen reduction reactions. Comprehensive electrocatalytic measurements and theoretical investigations suggest the improvement in structure stability and regulation in electronic structure for better electrocatalytic durability when confining NCDs with PtNi aerogels. Notably, the NCDs-PtNi aerogels perform 12-fold higher activity than that of Pt/C and maintain 52% of their initial activity after 5000 cycles toward acidic methanol oxidation. The enhanced stability and activity of NCDs-PtNi aerogels are also evident for oxygen reduction reactions in different electrolytes. These results highlight the effectiveness of stabilizing metallic aerogels with NCDs, offering a feasible pathway to develop robust electrocatalysts for fuel cells.

Monodispersed Molecular Phthalocyanine with Sulfur-Driven Electron Delocalization for Enhanced Electrochemical Biosensing.

Heterogenizing the molecular catalysts on conductive scaffolds to achieve the isolated molecular dispersion and expected coordination structures is significant yet still challenging. Herein, a sulfur-driving strategy to anchor monodispersed cobalt phthalocyanine on nitrogen and sulfur co-doped graphene (NSG-CoPc) is demonstrated. Experimental and theoretical analysis prove that the incorporation of S dramatically improves the adsorption capability of NSG and evokes the monodispersion of the CoPc molecule, promoting the axial Co─N coordination and the electron delocalization of the Co catalytic center. Benefiting from the reduced activation energy barrier and boosted electron transfer, as well as the maximized active site utilization, NSG-CoPc exhibits outstanding H2 O2 oxidization and sensing performance (used as a representative reaction). Moreover, the usage of NSG as a substrate can be readily extended to other metal (Ni, Cu, and Fe) phthalocyanine molecules with molecular-level dispersion. This work clarifies the mechanism of heteroatoms decoration and provides a new paradigm in devising monodispersed molecular catalysts with modulated chemical surroundings for broad applications.

Superhydrophilicity Regulation of Carbon Nanotubes Boosting Electrochemical Biosensing for Real-time Monitoring of H2O2 Released from Living Cells.

Dynamic and accurate monitoring of cell-released electroactive signaling biomolecules through electrochemical techniques has drawn significant research interest for clinical applications. Herein, the functionalized carbon nanotubes (f-CNTs) featuring with gradient surface wettability from hydrophobicity to hydrophilicity, and even to superhydrophilicity, were regulated by thermolysis of an ionic liquid for exploration of the dependence of surface wettability on electrochemical biosensing performance to a cell secretion model of hydrogen peroxide (H2O2). The superhydrophilic f-CNTs demonstrated boosting electrocatalytic reduction activity for H2O2. Additionally, the molecular dynamic (MD) simulations confirmed the more cumulative number density distribution of H2O2 molecules closer to the superhydrophilic surface (0.20 vs 0.37 nm), which would provide a faster diffusional channel compared with the hydrophobic surface. Thereafter, a superhydrophilic biosensing platform with a lower detectable limit reduced by 200 times (0.5 vs 100 µM) and a higher sensitivity over 56 times (0.112 vs 0.002 µA µM cm-2) than that of the hydrophobic one was achieved. Given its excellent cytocompatibility, the superhydrophilic f-CNTs was successfully applied to determine H2O2 released from HeLa cells which were maintained alive after a 30 min real-time monitoring test. The surface hydrophilicity regulation of electrode materials presents a facile approach for real-time monitoring of H2O2 released from living cells and would provide new insights for other electroactive signaling targets at the cellular level.

Untangling the Effects of Doping Carbon with Diverse Heteroatoms on the Bioelectrochemistry of Glucose Oxidase.

Great enthusiasm for doping carbon materials with nonmetallic heteroatoms for promoting electrical contact of redox enzymes with electrodes in bioelectronics has been aroused. However, systematic studies of different heteroatoms on enzyme activities are still lacking. Herein, choosing glucose oxidase (GOD) as a model enzyme, carbon nanotubes (CNTs) are used as electron carriers to evaluate the effects of heteroatoms' species on the direct electron transfer and catalytic activities of GOD. Experimental data demonstrate that phosphorus (P)-doped CNTs provide the most intimate electrical contact with GOD compared to other elements (B, N, and S) doping, delivering a 3-fold increase in rate constant (ks, 2.1 s-1) and an enhanced turnover rate (kcat, 2.74 × 10-9 M cm-2 s-1) in comparison with CNTs. Meanwhile, theoretical modeling clarifies that the active center of GOD interacts more strongly with P-doped CNTs and maintains their conformation well compared to other CNTs. This study will help to understand the mechanism of heteroatom doping of carbon on the enzymatic electron transfer and shed light on the design of efficient bioelectrocatalytic interfaces.

Surface Hydrophobicity Engineering of Pt-Based Noble Metal Aerogels by Ionic Liquids toward Enhanced Electrocatalytic Oxygen Reduction.

Modulating the surface properties of electrocatalysts with ligands could effectively regulate their catalytic properties, while limited in-depth understanding of the surface ligands restricted their rational combination. Herein, ionic liquids (ILs) with different lengths of hydrophobic side chains were employed to regulate the surface hydrophobicity of noble metal aerogels, for comprehending the relationship between surface hydrophobicity and oxygen reduction reaction (ORR) activity and enhancing electrocatalytic ORR. The volcano-like trends between the hydrophobicity and the ORR activity for various Pt-based aerogels indicated that a suitable hydrophobic surface constructed by ILs was most favorable for contacting with oxygen molecules and the desorption of oxygen intermediates. Typically, the PtPd aerogel modified by ILs (PtPd aer-[MTBD][PFSI]) exhibited an inspiring ORR activity, with a 70 mV increase in half-wave potential and a 7.1-fold mass activity compared to the commercial Pt/C. Therefore, the regularity between the surface hydrophobicity and ORR activity of noble metal aerogels was uncovered and will facilitate the modulation of electrocatalysts for practical applications.

Insights into the Surface Oxygen Functional Group-Driven Fast and Stable Sodium Adsorption on Carbon.

Engineering the oxygen functional groups (OFGs) is a dynamic strategy to tune the surface chemistry and electrochemical properties of carbon-based materials. In this paper, the species and contents of OFGs on the surface of ordered mesoporous carbon (OMC) and their effects on the sodium storage performance are systematically investigated without the interference of interlayer distance variation, extrinsic defects, other heteroatoms (e.g., N, S), etc. Theoretical calculations performed on various OFGs demonstrate that quinones and carboxylic anhydride groups possess two C═O bonds with stable configurations, good electronic conductivity, and strong sodium adsorption capability, contributing greatly to the Na+ storage capacity compared to the carboxylic acid groups. The ex situ techniques disclose the evolution of the OFGs and manifest the stable coordination of Na+ with C═O bonds even after long cycles. The optimized OFGs boost the Na+ redox reaction kinetics and enhance the surface capacitance contribution, achieving a capacity enhancement of 64.7% compared to the pristine OMC. This work would present implications in rational designing of oxygen-functionalized carbon materials for energy storage fields.

Defect formation-induced tunable evolution of oxygen functional groups for sodium storage in porous graphene.

The coinciding effects of carbon defects and oxygen functional groups in porous graphene were demonstrated in this work. The species and distributions of oxygen functional groups evolved with the types of defects, especially those containing C[double bond, length as m-dash]O bonds mainly distributed along the edge of ring defects, and enhanced Na+ storage.

High gravimetric and volumetric sodium storage in a functionalized coal-based microcrystal/CNT binder-free electrode.

Abundant oxygen functional groups in coal-based microcrystals, especially for carboxylic anhydrides and quinone groups with two Na+ storage sites, provide plentiful active sites to adsorb Na+. The carboxyl groups serve as the binder connecting active material with a current collector. High gravimetric and volumetric sodium storage was achieved in this binder-free electrode.

Pseudocapacitive Na+ Insertion in Ti-O-C Channels of TiO2-C Nanofibers with High Rate and Ultrastable Performance.

Ti-O-C channels for ultrafast sodium storage were constructed in N/S-co-doped TiO2-C nanofibers, which deliver a high rate performance of 181.9 mAh g-1 at 5 A g-1 after 3000 cycles. The existence of Ti-O-C bonds at the interface of TiO2-C phases was revealed by synchrotron radiation X-ray absorption spectra. Based on this, first-principles calculations further verified the low energy barrier for Na+ insertion/extraction in the Ti-O-C channels formed by the intimately integrated graphite layer with TiO2 near the surface. In addition, surface defects induced by heteroatoms accelerate the Na+ mass transfer through the pathway from the carbon surface to the Ti-O-C channel.

Enhanced sodium storage via the hetero-interface effect in BiOCl/TiO2 p-n junctions.

This work introduces a new alternative way to improve the sodium storage of TiO2, which can play a joint role in common techniques like carbon coating and heteroatom doping. The hetero-interface between BiOCl and TiO2 provides extra sodium storage sites and more importantly, a built-in electric field accelerates electron and ion diffusion.