Nitrogen-Doped Carbon Nanotube-Supported Pd Catalyst for Improved Electrocatalytic Performance toward Ethanol Electrooxidation

High-Dispersive Pd Nanoparticles on Hierarchical N-Doped Carbon Nanocages to Boost Electrochemical CO2 Reduction to Formate at Low Potential

Electrochemical CO2 reduction reaction (CO2 RR) to value-added chemicals/fuels is an effective strategy to achieve the carbon neutral. Palladium is the only metal to selectively produce formate via CO2 RR at near-zero potentials. To reduce cost and improve activity, the high-dispersive Pd nanoparticles on hierarchical N-doped carbon nanocages (Pd/hNCNCs) are constructed by regulating pH in microwave-assisted ethylene glycol reduction. The optimal catalyst exhibits high formate Faradaic efficiency of >95% within -0.05-0.30 V and delivers an ultrahigh formate partial current density of 10.3 mA cm-2 at the low potential of -0.25 V. The high performance of Pd/hNCNCs is attributed to the small size of uniform Pd nanoparticles, the optimized intermediates adsorption/desorption on modified Pd by N-doped support, and the promoted mass/charge transfer kinetics arising from the hierarchical structure of hNCNCs. This study sheds light on the rational design of high-efficient electrocatalysts for advanced energy conversion.

CoP/RGO-Pd Hybrids with Heterointerfaces as Highly Active Catalysts for Ethanol Electrooxidation

The ethanol oxidation reaction is of critical importance to the commercial viability of direct ethanol fuel cell technology. However, owing to the poor C-C bond cleavage capability, almost all ethanol oxidation is incomplete and suffers from low selectivity toward the C1 pathway. Herein, under the support of theoretical calculations that the heterointerfaces between CoP and Pd can reduce the energy barrier of C-C bond cleavage, rich heterointerfaces in CoP/RGO-Pd hybrids were designed to improve ethanol electrooxidation performance through enhancing the selectivity toward the C1 pathway. The experimental results show that the faradaic efficiency of the C1 pathway of CoP/RGO-Pd hybrids is as high as 27.6%, surpassing most reported catalysts in the literature. As a result of this enhancement, CoP/RGO-Pd10 exhibits mass activity as high as 4597 mA·mg_Pd^-1 and specific activity as high as 10 mA·cm^-2, which are much higher than those of other Pd-based electrocatalysts.

Molecular Sieve Based on a PMMA/ZIF-8 Bilayer for a CO-Tolerable H2 Sensor with Superior Sensing Performance

Semiconductor sensors equipped with Pd catalysts are promising candidates as low-powered and miniaturized surveillance devices that are used to detect flammable hydrogen (H₂) gas. However, the following issues remain unresolved: (i) a sluggish sensing speed at room temperature and (ii) deterioration of sensing performance caused by interfering gases, particularly, carbon monoxide (CO). Herein, a bilayer comprising poly(methyl methacrylate) (PMMA) and zeolitic imidazolate framework-8 (ZIF-8) is utilized as a molecular sieve for diode-type H₂ sensors based on a Pd-decorated indium-gallium-zinc oxide film on a p-type silicon substrate. While the PMMA effectively blocks the penetration of CO gas molecules into the sensing entity, the ZIF-8 improves sensing performances by modifying the catalytic activity of Pd, which is preferable for splitting H₂ and O₂ molecules. Consequently, the bilayer-covered sensor achieves outstanding CO tolerance with superior sensing figures of merit (response/recovery times of <10 s and sensing response of >5000% at 1% H₂).

Charge Engineering of Mo2C@Defect-Rich N-Doped Carbon Nanosheets for Efficient Electrocatalytic H2 Evolution

Charge engineering of carbon materials with many defects shows great potential in electrocatalysis, and molybdenum carbide (Mo2C) is one of the noble-metal-free electrocatalysts with the most potential. Herein, we study the Mo2C on pyridinic nitrogen-doped defective carbon sheets (MoNCs) as catalysts for the hydrogen evolution reaction. Theoretical calculations imply that the introduction of Mo2C produces a graphene wave structure, which in some senses behaves like N doping to form localized charges. Being an active electrocatalyst, MoNCs demonstrate a Tafel slope as low as 60.6 mV dec-1 and high durability of up to 10 h in acidic media. Besides charge engineering, plentiful defects and hierarchical morphology also contribute to good performance. This work underlines the importance of charge engineering to boost catalytic performance.

Carbon- and Binder-Free Core-Shell Nanowire Arrays for Efficient Ethanol Electro-Oxidation in Alkaline Medium

To achieve high electrochemical surface area (ECSA) and avoid carbon support and binder in the anode catalyst of direct ethanol fuel cell, herein, we design freestanding core-shell nickel@palladium-nickel nanowire arrays (Ni@Pd-Ni NAs) without carbon support and binder for high-efficiency ethanol electro-oxidation. Bare Ni nanowire arrays (Ni NAs) are first prepared using the facile template-assistant electrodeposition method. Subsequently, the Ni@Pd-Ni NAs are formed using one-step solution-based alloying reaction. The optimized Ni@Pd-Ni NA electrode with a high ECSA of 64.4 m² g^-1_Pd exhibits excellent electrochemical performance (peak current density: 622 A g^-1_Pd) and cycling stability for ethanol electro-oxidation. The facilely obtained yet high-efficiency core-shell Ni@Pd-Ni NA electrode is a promising electrocatalyst, which can be utilized for oxygen reduction reaction, urea, hydrazine hydrate, and hydrogen peroxide electro-oxidation, not limited to the ethanol electro-oxidation.

Self-assembly of highly conductive self-n-doped fullerene ammonium halides and their application in the in situ solution-processable fabrication of working electrodes for alcohol electrooxidation

Self-assembled highly conductive fullerene ammonium halides are potential support of metal-based nanoparticles toward alcohol electrooxidation.

Novel Co3O4 Nanoparticles/Nitrogen-Doped Carbon Composites with Extraordinary Catalytic Activity for Oxygen Evolution Reaction (OER)

Herein, Co₃O₄ nanoparticles/nitrogen-doped carbon (Co₃O₄/NPC) composites with different structures were prepared via a facile method. Structure control was achieved by the rational morphology design of ZIF-67 precursors, which were then pyrolyzed in air to obtain Co₃O₄/NPC composites. When applied as catalysts for the oxygen evolution reaction (OER), the M-Co₃O₄/NPC composites derived from the flower-like ZIF-67 showed superior catalytic activities than those derived from the rhombic dodecahedron and hollow spherical ZIF-67. The former M-Co₃O₄/NPC composite displayed a small over-potential of 0.3 V, low onset potential of 1.41 V, small Tafel slope of 83 mV dec^-1, and a desirable stability. (94.7% OER activity was retained after 10 h.) The excellent performance of the flower-like M-Co₃O₄/NPC composite in the OER was attributed to its favorable structure.

Pd supported on carbon containing nickel, nitrogen and sulfur for ethanol electrooxidation

Carbon material containing nickel, nitrogen and sulfur (Ni-NSC) has been synthesized using metal-organic frameworks (MOFs) as precursor by annealing treatment with a size from 200 to 300 nm. Pd nanoparticles supported on the Ni-NSC (Pd/Ni-NSC) are used as electrocatalysts for ethanol oxidation in alkaline media. Due to the synergistic effect between Pd and Ni, S, N, free OH radicals can form on the surface of Ni, N and S atoms at lower potentials, which react with CH₃CO intermediate species on the Pd surface to produce CH₃COO⁻ and release the active sites. On the other hand, the stronger binding force between Pd and co-doped N and S is responsible for enhancing dispersion and preventing agglomeration of the Pd nanoparticles. The Pd(20 wt%)/Ni-NSC shows better electrochemical performance of ethanol oxidation than the traditional commercial Pd(20 wt%)/C catalyst. Onset potential on the Pd(20 wt%)/Ni-NSC electrode is 36 mV more negative compared with that on the commercial Pd(20 wt%)/C electrode. The Pd(20 wt%)/Ni-NSC in this paper demonstrates to have excellent electrocatalytic properties and is considered as a promising catalyst in alkaline direct ethanol fuel cells.

Radiation-induced synthesis of nanoscale Co- and Ni-based electro-catalysts on carbon for the oxygen reduction reaction

A facile synthesis of 3d-metal based electro-catalysts directly incorporated into a carbon support was carried out by γ-radiation.