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A simple strategy is developed for synthesis of PdCu nanoplates as efficient ORR electrocatalysts with simultaneously highly methanol tolerance. [Display omitted] The methanol-poisoning of electrocatalysts at the cathodic part of direct methanol fuel cells (DMFCs) can severely degrade the overall efficiency. Therefore, engineering cathodic catalysts with outstanding oxygen reduction activity, and simultaneously, superior methanol tolerance is greatly desired. Herein, bimetallic palladium-copper (PdCu) nanoplates with the optimized d-band center are designed as promising cathodic catalysts for DMFCs. It shows outstanding oxygen reduction activity with a mass activity (MA) of 0.522 A mg Pd −1 in alkaline electrolyte, overwhelming the benchmarked commercial Pt/C and Pd/C. Meanwhile, it has prominent stability with only 4.0 % loss in MA after continuous 20 K cycles. More importantly, the PdCu nanoplates are almost inert toward methanol oxidation and show excellent anti-methanol capability. The theoretical calculations reveal that the downshift of d-band center in PdCu nanoplates and the electronic interaction between Pd and Cu atoms could effectively lower the methanol adsorption energy, thus leading to enhanced methanol tolerance. This work highlights the important role of tuning the electronic structure and optimized geometry of electrocatalysts to simultaneously boost their oxygen reduction activity, stability, and methanol tolerance for their future application in DMFCs. [ABSTRACT FROM AUTHOR]

A simple guest molecule-directed approach to transforming COFs into carbon materials with high content N dopants and defects for ORR is reported. [Display omitted] • A guest molecule-directed method to obtain COF-derived carbon material is reported. • The optimized carbon material is provided with high content defects and N dopants. • The defective N-doped carbon material exhibits high ORR activity and stability. • The synergistic effect between carbon defect and N dopant is theoretically proved. Creating intrinsic defects and N dopants in metal-free carbon matrix has proven to be an effective approach for enhancing their electroactivity toward oxygen reduction (ORR), though it is still a big challenge. Herein, metal-free carbon materials with tunable contents of defects and N dopants were prepared through the guest molecule-directed conversion of covalent organic framework (COFs). Due to the corrosion of guest molecules and subsequent substitution by ammonia (NH 3) during the pyrolysis, the optimal carbon catalyst is provided with high content of N dopants (8.22 at%) and carbon defects (I D /I G , 1.41). It delivers remarkable ORR activity, with a half-wave potential (E 1/2) of 0.863 V versus reversible hydrogen electrode (vs. RHE) and impressive durability, with a 10.9 % current loss over 40 h. Moreover, the optimal carbon catalyst-assembled Zn-air battery achieves a maximum power density of 107.1 mW cm−2, demonstrating its potential in practical devices. Theoretical calculations reveal that the synergistic effect between carbon defects and heteroatom N dopants is responsible for the enhancement of ORR activity. This work might inspire the development of highly efficient metal-free carbon catalysts for various energy conversion applications. [ABSTRACT FROM AUTHOR]

Exploring metal-free, highly active and durable electrocatalysts with tunable selectivity toward oxygen reduction reaction (ORR) still remains a standing challenge. Herein, porous carbon nanotubes derived from a self-supporting hyper-cross-linked polymer with tailored selectivity for efficient ORR are reported. The sulfur-containing tubular polymer provides a versatile platform to fabricate diverse heteroatom doped porous carbon nanotubes. Attributed to the porous tubular morphology, abundant dopants and defects, the N-doped porous carbon nanotubes through pyrolysis under Ar-NH 3 show excellent 4e− ORR performance with a half-wave potential (E 1/2) of 0.85 V. It also has superior stability and methanol tolerance. Meanwhile, the O, S co-doped porous carbon nanotubes through oxygen plasma treatment show enhanced 2e− ORR performance with a selectivity up to 85.4%, which is probably ascribed to the more C=O and COOH species introduced in the carbon matrix. This work not only provides a useful strategy to design and prepare efficient ORR catalysts, but also paves the avenue for the facile tailoring of selectivity in ORR process. Diverse porous carbon nanotubes derived from a self-supporting hyper-cross-linked polymer with tailored selectivity for efficient electrocatalytic oxygen reduction reaction is reported. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] A novel strategy is developed for controlled synthesis of hyper-dendritic PdZn nanocrystals as efficient bifunctional electrocatalysts toward ORR and EOR. • A novel strategy is developed for synthesis of hyper-dendritic PdZn nanocrystals. • The HD-PdZn NCs have ample pores, hyper-dendritic morphology and electron effect. • The HD-PdZn NCs exhibit enhanced ORR and EOR activity and durability. • DFT calculation proved that the reduction of OOH* to OH* is accelerated during ORR. Although attentions have been devoted to developing Pd-based bimetallic nanocrystals towards the electrocatalytic oxygen reduction reaction (ORR) and ethanol oxidation reaction (EOR), the engineering of efficient bifunctional electrocatalysts with high atomic utilization still faces big challenges. Herein, we reported a facile one-pot template-free route to fabricate three-dimension hyper-dendritic PdZn nanocrystals (HD-PdZn NCs) that regulated by gas mixtures of carbon monoxide and hydrogen. The developed catalysts acted as robust bifunctional electrocatalysts for cathodic ORR and anodic EOR. Specifically, the engineered HD-PdZn NCs not only displayed superior mass activity (MA, 0.461 A mg Pd -1) and specific activity (SA, 0.393 mA cm−2) at 0.9 V, which were 5.2 and 5.0 times of commercial Pt/C, respectively, but also showed enhanced stability with only 3% loss of MA after 10,000 cycles for ORR. Density functional theory (DFT) calculations revealed the Zn implantation could facilitate the reduction of OOH* to OH* on the surface of Pd during the ORR process. Moreover, HD-PdZn NCs exhibited the highest EOR mass activity with a value of 3.45 A mg Pd −1 among benchmarked catalysts in alkaline solution. The advantageous structural features and electron effects are proposed to be responsible for the remarkable bifunctional activities. This work illustrates a facile method to fabricate highly efficient bifunctional electrocatalyst for energy conversation application. [ABSTRACT FROM AUTHOR]

Palladium-based catalyst represents one of the most promising candidates among all non-platinum oxygen reduction reaction (ORR) catalysts. However, it is still challenging to precisely engineering their morphology and composition. Herein, highly branched core-shell PdCu@Pd nanocrystals have been fabricated via a simple one-pot synthesis that co-directed by hydrogen gas and halide ions. Such unique PdCu@Pd nanocrystals exhibit prominent ORR activity, durability and methanol-tolerance in alkaline media owing to their core-shell composition, highly-branched structure and defect-rich surface. This work elucidates a facile strategy to design highly branched core-shell nanomaterials, shedding light on the exploration and optimization of novel non-platinum ORR catalysts. A facile method for one-pot synthesis of Defect-rich PdCu@Pd Core-shell Nanobranches is developed. The as-made catalyst shows superior activity, durability and methanol-tolerance towards oxygen reduction reaction. Image 1 [ABSTRACT FROM AUTHOR]

A novel strategy to prepare COF-derived carbon materials mediated by volatile guest molecule for efficient electrocatalytic oxygen reduction reaction is reported. [Display omitted] Covalent organic framework (COF) derived metal-free carbon materials have emerged as promising electrocatalysts for the oxygen reduction reaction (ORR). Herein, a volatile guest molecule mediated-pyrolysis strategy was explored on a designed thiophene-rich and imine-linked COF. Through the modulation of guest mediators (iodine and sulfur), the properties of the as-obtained carbon materials can be well regulated. The optimized nitrogen and sulfur dual-doped carbon electrocatalyst demonstrates remarkable ORR activity with a half-wave potential of 0.87 V and impressive durability, with only an 8% current loss over 21 h. The corresponding assembled zinc-air battery has a comparable power density (60 mW cm−2) to that of the commercial Pt/C. It is proposed that the coexistence of the guest mediators iodine and sulfur in the channels of COFs could prevent the loss of N species. The enhanced N content and N/S ratio are assumed to be responsible for the ORR performance. This study puts forward a novel strategy to prepare COF-derived carbon materials mediated by volatile guest molecules, which may provide new insights into the development of metal-free ORR catalysts. [ABSTRACT FROM AUTHOR]