Enhanced Activity of Small Pt Nanoparticles Decorated with High-Loading Single Fe─N4 for Methanol Oxidation and Oxygen Reduction via the Assistive Active Sites Strategy.

Decorating platinum (Pt) with a single atom offers a promising approach to tailoring their catalytic activity. In this study, for the first time, an innovative assistive active sites (AAS) strategy is proposed to construct high-loading (3.46wt.%) single Fe─N4 as AAS, which are further hybridized with small Pt nanoparticles to enhance both oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) activities. For ORR, the target catalyst (Pt/HFeSA-HCS) exhibits a higher mass activity (MA) of 0.98 A mgPt -1 and specific activity (SA) of 1.39 mA cmPt -2 at 0.90 V versus RHE. As for MOR, Pt/HFeSA-HCS shows exceptional MA (3.21 A mgPt -1) and SA (4.27 mA cmPt -2) at peak values, surpassing commercial Pt/C by 15.3 and 11.5 times, respectively. The underlying mechanism behind this AAS strategy is to find that in MOR, Fe─N4 promotes water dissociation, generating more *OH to accelerate the conversion of *CO to CO2. Meanwhile, in ORR, Fe─N4 acts as a competitor to adsorb *OH, weakening Pt─OH bonding and facilitating desorption of *OH on the Pt surface. Constructing AAS that can enhance dual functionality simultaneously can be seen as a successful "kill two birds with one stone" strategy.

A facile strategy to prepare FeNx decorated PtFe intermetallic with excellent acidic oxygen reduction reaction activity and stability.

The construction of low-Pt-content intermetallic on carbon supports has been verified as a promising method to promote the activity of the oxygen reduction reaction (ORR). In this study, we have developed a simple and effective strategy to obtain a well-designed CNT-PtFe-PPy precursor. This precursor contains modulated Pt- and Fe-based content dispersed in polypyrrole (PPy) chain segments, which are in-situ generated on the templates of carbon nanotubes (CNTs). Subsequent pyrolysis of the CNT-PtFe-PPy precursor produces a CNT-PtFe@FeNC catalyst, which contains both Fe-Nx and PtFe intermetallic active sites. Due to the highly efficient dispersion of active species, the CNT-PtFe@FeNC electrocatalyst displays a 9.5 times higher specific activity (SA) and 8.5 times higher mass activity (MA) than those of a commercial Pt/C catalyst in a 0.1 M HClO4 solution. Additionally, these results, combined with excellent durability (the SA and MA maintained 94 % and 91 % of initial activity after a 10-k cycle accelerated durability test), represent among the best performance achieved so far for Pt-based ORR electrocatalysts. Furthermore, density functional theory (DFT) calculations revealed that the presence of Fe-N4 species reduces the adsorption energy between the PtFe intermetallic compound and OH*, accelerating the ORR process.

Atomically Dispersed Ni-N4 Sites Assist Pt3 Ni Nanocages with Pt Skin to Synergistically Enhance Oxygen Reduction Activity and Stability.

Currently, the rarity and high cost of platinum (Pt)-based electrocatalysts seriously limit their commercial application in fuel cells cathode. Decorating Pt with atomically dispersed metal-nitrogen sites possibly offers an effective pathway to synergy tailor their catalytic activity and stability. Here active and stable oxygen reduction reaction (ORR) electrocatalysts (Pt3 Ni@Ni-N4 -C) by in situ loading Pt3 Ni nanocages with Pt skin on single-atom nickel-nitrogen (Ni-N4 ) embedded carbon supports are designed and constructed. The Pt3 Ni@Ni-N4 -C exhibits excellent mass activity (MA) of 1.92 A mgPt -1 and specific activity of 2.65 mA cmPt -2 , together with superior durability of 10 mV decay in half-wave potential and only 2.1% loss in MA after 30 000 cycles. Theoretical calculations demonstrate that Ni-N4 sites significant redistribute of electrons and make them transfer from both the adjacent carbon and Pt atoms to the Ni-N4 . The resultant electron accumulation region successfully anchored Pt3 Ni, that not only improves structural stability of the Pt3 Ni, but importantly makes the surface Pt more positive to weaken the adsorption of *OH to enhance ORR activity. This strategy lays the groundwork for the development of super effective and durable Pt-based ORR catalysts.

C-DeepTrust: A Context-Aware Deep Trust Prediction Model in Online Social Networks.

Trust prediction provides valuable support for decision making, information dissemination, and product promotion in online social networks. As a complex concept in the social network community, trust relationships among people can be established virtually based on: 1) their interaction behaviors, e.g., the ratings and comments that they provided; 2) the contextual information associated with their interactions, e.g., location and culture; and 3) the relative temporal features of interactions and the time periods when the trust relationships hold. Most of the existing works only focus on some aspects of trust, and there is not a comprehensive study of user trust development that considers and incorporates 1)-3) in trust prediction. In this article, we propose a context-aware deep trust prediction model C-DeepTrust to fill this gap. First, we conduct user feature modeling to obtain the user's static and dynamic preference features in each context. Static user preference features are obtained from all the ratings and reviews that a user provided, while dynamic user preference features are obtained from the items rated/reviewed by the user in time series. The obtained context-aware user features are then combined and fed into the multilayer projection structure to further mine the context-aware latent features. Finally, the context-aware trust relationships between users are calculated by their context-aware feature vector cosine similarities according to the social homophily theory, which shows a pervasive property of social networks that trust relationships are more likely to be developed among similar people. Extensive experiments conducted on two real-world datasets show the superior performance of our approach compared with the representative baseline methods.

A Combination of "Push Effect" Strategy with "Triple-Phase-Boundary Engineering" on Iron Porphyrin-Based MOFs: Enhanced Selectivity and Activity for Oxygen Reduction.

Herein, the "push effect" strategy combined with "triple-phase-boundary" (TPB) engineering was innovatively employed to target the single Fe-N4 sites in an iron porphyrin-based metal-organic framework, with axially coordinated 4-octylpyridine groups on Fe-N4 (named as PCN-224 (Fe)-1). The amphiphilic 4-octylpyridine groups donate sufficient electrons toward Fe-N4 by the Fe-N(pyridine) coordination bond and simultaneously provide effective TBP reactive sites by the hydrophobic octyl terminals, resulting in enhanced ORR activity of the PCN-224 (Fe)-1 in hydrophobic octyl terminals, with an E1/2 of 0.81 V and complete 4-electron selectivity. Furthermore, TPB engineering is utilized to construct the PCN-224 (Fe)-1-based Zn-air battery with a maximum power density of 98 mW cm-2, demonstrating great practical application potential for molecule-based ORR catalysts. Meanwhile, the "push effect" mechanism on ORR is revealed by electron paramagnetic resonance, in situ UV-vis spectroelectrochemical analysis, and density functional theory.