B, N Co-Doping Sequence: An Efficient Electronic Modulation of the Pd/MXene Interface with Enhanced Electrocatalytic Properties for Ethanol Electrooxidation

Improving the electrocatalytic properties by regulating the surface electronic structure of supported metals has always been a hot issue in electrocatalysis. Herein, two novel catalysts Pd/B-N-Ti₃C₂ and Pd/N-B-Ti₃C₂ are used as the models to explore the effect of the B and N co-doping sequence on the surface electronic structure of metals, together with the electrocatalytic properties of ethanol oxidation reaction. The two catalysts exhibit obviously stratified morphology, and the Pd nanoparticles having the same amount are both uniformly distributed on the surface. However, the electron binding energy of Ti and Pd elements of Pd/B-N-Ti₃C₂ is smaller than that of Pd/N-B-Ti₃C₂. By exploring the electrocatalytic properties for EOR, it can be seen that all the electrochemical surface area, maximum peak current density, and antitoxicity of the Pd/B-N-Ti₃C₂ catalyst are much better than its counterpart. Such different properties of the catalysts can be attributed to the various doping species of B and N introduced by the doping sequence, which significantly affect the surface electronic structure and size distribution of supported metal Pd. Density functional theory calculations demonstrate that different B-doped species can offer sites for the H atom from CH₃CH₂OH of dehydrogenation in Pd/B-N-Ti₃C₂, thereby facilitating the progress of the EOR to a favorable pathway. This work provides a new insight into synthesizing the high-performance anode materials for ethanol fuel cells by regulating the supported metal catalyst with multielement doping.

Bio-synthesis of palladium nanocubes and their electrocatalytic properties

The bio-synthesis of palladium nanocubes (PdNCs) was realised using pine needle extract as the reducing agent and cetyl trimethyl ammonium bromide as the capping agent. As an eco-friendly and readily available biomass, pine needle extract avoided the use of highly polluting chemical reducing agents. The growth process of PdNCs was analysed using ultraviolet-vis and Fourier transform infrared spectroscopy. Flavonoids, esters, terpenoids and polyhydric alcohols, which contain reductive groups, were mainly responsible for the transition of Pd2+ ions to PdNCs. The morphology and structure of PdNCs were characterised using transmission electron microscopy (TEM), high-resolution TEM, selected area electron diffraction and X-ray diffraction. It was indicated that the as-prepared PdNCs displayed a relatively high purity and good crystallinity with a face-centred cubic structure and exhibited sizes ranging from 6.11 to 29.51 nm with an average particle size of 11.18 nm. In the methanol electro-oxidation reaction, the PdNCs enclosed by {100} facets exhibited superior electro-catalytic activity to commercial Pd/C, which was rarely reported in other bio-synthesis processes for Pd catalysts. Meanwhile, the PdNCs showed excellent anti-poisoning ability and long-term stability. This study reveals the possibility of preparing shape-controlled PdNCs with a specific structure and excellent electro-catalytic activity.

Construction and Application of a Non-Enzyme Hydrogen Peroxide Electrochemical Sensor Based on Eucalyptus Porous Carbon

Natural eucalyptus biomorphic porous carbon (EPC) materials with unidirectional ordered pores have been successfully prepared by carbonization in an inert atmosphere. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) were employed to characterize the phase identification, microstructure and morphology analysis. The carbon materials were used to fabricate electrochemical sensors to detect hydrogen peroxide (H₂O₂) without any assistance of enzymes because of their satisfying electrocatalytic properties. It was immobilized on a glassy carbon electrode (GCE) with chitosan (CHIT) to fabricate a new kind of electrochemical sensor, EPC/CHIT/GCE, which showed excellent electrocatalytic activity in the reduction of H₂O₂. Meanwhile, EPC could also promote electron transfer with the help of hydroquinone. The simple and low-cost electrochemical sensor exhibited high sensitivity, and good operational and long-term stability.

Enhanced and Facet-specific Electrocatalytic Properties of Ag/Bi2Fe4O9 Composite Nanoparticles

Ag/Bi₂Fe₄O₉ nanoparticles (BFO NPs) have been synthesized using a two-step approach involving glycine combustion and visible light irradiation. Their structures were characterized in detail using X-ray diffraction, transmission electron microscope, scanning electron microscopy, and scanning transmission electron microscopy techniques. Their electrocatalytic properties were studied through enzymatic glucose detection with an amperometric biosensor. The Ag deposited on selective crystal facets of BFO NPs significantly enhanced their electrocatalytic activity. To gain insights into the origin of the enhanced electrocatalytic activities, we have carried out studies of Ag⁺ reduction and Mn²⁺ oxidation reaction at the {200} and {001} facets, respectively. The results suggest effective charge separation on the BFO NP surfaces, which is likely responsible for the enhanced electrocatalytic properties. Furthermore, enhanced ferromagnetism was observed after the Ag deposition on BFO NPs, which may be related to the improved electrocatalytic properties through spin-dependent charge transport. The facet-specific electrocatalytic properties are highly interesting and desired for chemical reactions. This study demonstrates that Ag/BFO NPs are potentially useful for electrocatalytic applications including biosensing and chemical synthesis with high product selectivity.

From two-dimensional graphene oxide to three-dimensional honeycomb-like Ni3S2@graphene oxide composite: insight into structure and electrocatalytic properties

Three-dimensional (3D) graphene composites have drawn increasing attention in energy storage/conversion applications due to their unique structures and properties. Herein, we synthesized 3D honeycomb-like Ni₃S₂@graphene oxide composite (3D honeycomb-like Ni₃S₂@GO) by a one-pot hydrothermal method. We found that positive charges of Ni²⁺ and negative charges of NO₃^- in Ni(NO₃)₂ induced a transformation of graphene oxide with smooth surface into graphene oxide with wrinkled surface (w-GO). The w-GO in the mixing solution of Ni(NO₃)₂/thioacetamide/H₂O evolved into 3D honeycomb-like Ni₃S₂@GO in solvothermal process. The GO effectively inhibited the aggregation of Ni₃S₂ nanoparticles. Photoelectrochemical cells based on 3D Ni₃S₂@GO synthesized at 60 mM l^-1 Ni(NO₃)₂ exhibited the best energy conversion efficiency. 3D Ni₃S₂@GO had smaller charge transfer resistance and larger exchange current density than pure Ni₃S₂ for iodine reduction reaction. The cyclic stability of 3D honeycomb-like Ni₃S₂@GO was good in the iodine electrolyte. Results are of great interest for fundamental research and practical applications of 3D GO and its composites in solar water-splitting, artificial photoelectrochemical cells, electrocatalysts and Li-S or Na-S batteries.

One-Pot Synthesis of Penta-twinned Palladium Nanowires and Their Enhanced Electrocatalytic Properties

This article reports the design and successful implementation of a one-pot, polyol method for the synthesis of penta-twinned Pd nanowires with diameters below 8 nm and aspect ratios up to 100. The key to the success of this protocol is the controlled reduction of Na₂PdCl₄ by diethylene glycol and ascorbic acid through the introduction of NaI and HCl. The I^- and H⁺ ions can slow the reduction kinetics by forming PdI₄^2- and inhibiting the dissociation of ascorbic acid, respectively. When the initial reduction rate is tuned into the proper regime, Pd decahedral seeds with a penta-twinned structure appear during nucleation. In the presence of I^- ions as a selective capping agent toward the Pd(100) surface, the decahedral seeds can be directed to grow axially into penta-twinned nanorods and then nanowires. The Pd nanowires are found to evolve into multiply twinned particles if the reaction time is extended beyond 1.5 h, owing to the involvement of oxidative etching. When supported on carbon, the Pd nanowires show greatly enhanced specific electrocatalytic activities, more than five times the value for commercial Pd/C toward formic acid oxidation and three times the value for Pt/C toward oxygen reduction under an alkaline condition. In addition, the carbon-supported Pd nanowires exhibit greatly enhanced electrocatalytic durability toward both reactions. Furthermore, we demonstrate that the Pd nanowires can serve as sacrificial templates for the conformal deposition of Pt atoms to generate Pd@Pt core-sheath nanowires and then Pd-Pt nanotubes with a well-defined surface structure.