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High-loaded oxygen reduction reaction (ORR) Pt intermetallic compounds with high performance expression under PEMFC operating conditions are prerequisite for practical application. Nevertheless, high metal-loading would lead to the severe agglomeration...

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Developing highly efficient and durable electrocatalysts for the oxygen reduction reaction (ORR) is essential for commercializing renewable and clean energy, but this remains a challenge. Herein, we design an electrocatalyst by confining Pt nanoparticles on a conjugated nitrogen-rich covalent organic framework (COF) and demonstrate its ORR activity in an acid electrolyte. In the catalyst, multiple pyridinic nitrogens act as nucleation sites for controllably growing Pt in a layer over the COF’s surface and the pore channel, resulting in uniform Pt distribution and more accessible Pt active sites. The catalyst exhibits ultrahigh ORR activity with an onset potential of 1.05 V versus reversible hydrogen electrode and a half-wave potential of 0.89 V, which are more positive than those of commercial Pt/C and other reported catalysts. This strategy offers a new way to fabricate electrocatalysts with atomically definite active sites and high-performance catalytic activities for clean energy storage and conversion.

A strategy for scaffold-free self-assembly of multiple oligomeric enzymes was developed by exploiting enzyme oligomerization and protein-protein interaction properties, and was tested both in vitro and in vivo. Octameric leucine dehydrogenase and dimeric formate dehydrogenase were fused to a PDZ (PSD95/Dlg1/zo-1) domain and its ligand, respectively. The fusion proteins self-assembled into extended supramolecular interaction networks. Scanning-electron and atomic-force microscopy showed that the assemblies assumed two-dimensional layer-like structures. A fluorescence complementation assay indicated that the assemblies were localized to the poles of cells. Moreover, both in vitro and in vivo assemblies showed higher NAD(H) recycling efficiency and structural stability than did unassembled structures when applied to a coenzyme recycling system. This work provides a novel method for developing artificial multienzyme supramolecular devices and for compartmentalizing metabolic enzyme cascades in living cells.

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Single-atom catalysts (SACs) are getting more attention in the field of electrochemical energy storage and conversation, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), due to their welldefined active centers, tunable electron structure, maximum atom-utilization efficiency, and excellent durability. [1] Pyrolysis of metal-containing precursors is one of the most frequent approaches for SACs preparation. [2] With the atomic dispersion of catalysts, however, the increasing surface free energy results in atom aggregation to form metal clusters or nanoparticles in the thermal treatment. [3] Therefore, it is a challenge to obtain SACs with a high loading rate of metal via pyrolysis. Wei et al. synthesized atomic Zn (9.3 wt%) by adopting a low annealing rate method. [4a] Jiang et al. reported a high loading Zn atoms (11.3 wt%) supported on the N-doped hollow carbon derived from ZIF-8 covered polystyrene nanospheres. [4b] Additionally, Wan et al. developed a cascade anchoring strategy to obtain SACs with a 12.1 wt% metal loading rate [4c] and Huang et al. fabricated Co atoms (15.3 wt%) on graphenelike carbons by a salt-template method. [3c] However, developing a high atomic density is still under further exploration. Compared with the solo single-atom sites, dual-metal active sites have been demonstrated to have higher catalytic activity and selectivity for ORR. [5] Nevertheless, it is difficult to build the interaction between the dual-metal sites even on the same carbon support, because the low-density distribution of metal atoms resulted in the long distance between each other, and thus trended into isolated sites rather than synergistic sites. Therefore, developing carbon supports with highly dense atom distribution is the potential to provide a template to construct dual-metal active sites with synergistic roles.

Here, we report a universal single-atom coating (SAC) strategy by taking advantage of the rich chemistry of tannic acid (TA). TA units not only selfassemble into a cross-linked porous polyphenolic framework, but also can grip on different substates via multiple binding modes. Benefiting from the diverse chelating ability of TA, a series of mono-, and bimetallic SACs can be formed on substrates of different materials (e. g., carbon, SiO 2 , TiO 2 , MoS 2 ), dimensions (0D-3D) and sizes (50 nm-5 cm). By contrast, uniform SAC cannot be achieved using common approaches such as pyrolysis of metal-dopamine complexes or metal-organic frameworks. As a proof-of-concept demonstration, two Co SACs immobilized on graphene and TiO 2 were prepared. The former one shows six-fold higher mass activity than Pt/C toward oxygen reduction. The latter one displays outstanding photocatalytic activity owing to the high activity of the single atoms and the formation of the single-atom coating-TiO 2 heterojunction.