Single-atom catalysts supported on solid substrates have inspired extensive interest, but the rational design of high-efficiency single-atom catalysts is still plagued by ambiguous structure determination of active sites and its local support effect. Here, we report hybrid single-atom catalysts by an axial coordination linkage of molecular cobalt phthalocyanine with carbon nanotubes for selective oxygen reduction reaction by screening from a series of metal phthalocyanines via preferential density-functional theory calculations. Different from conventional heterogeneous single-atom catalysts, the hybrid single-atom catalysts are proven to facilitate rational screening of target catalysts as well as understanding of its underlying oxygen reduction reaction mechanism due to its well-defined active site structure and clear coordination linkage in the hybrid single-atom catalysts. Consequently, the optimized Co hybrid single-atom catalysts exhibit improved 2e− oxygen reduction reaction performance compared to the corresponding homogeneous molecular catalyst in terms of activity and selectivity. When prepared as an air cathode in an air-breathing flow cell device, the optimized hybrid catalysts enable the oxygen reduction reaction at 300 mA cm−2 exhibiting a stable Faradaic efficiency exceeding 90% for 25 h.

Pollutants in wastewater, such as Cr(VI) is a continuous threat to our ecological system and human well-being because of its high noxiousness and latent carcinogenicity. Photocatalytic Cr(VI) reduction is the most suitable and eco-friendly way to convert the toxic Cr(VI) to environmentally friendly Cr(III). Porous metal−organic frameworks (MOFs) based nanocomposites are emerging green photocatalysts for Cr(VI) reduction due to their unique characteristics such as high photoconductivity, large surface area, and suitable porous structure. Herein, the preparation of ultrathin BiOCl sheets over UiO-66-NH 2 is reported for the first time at room temperature via a simplistic in situ synthetic process to yield a series of UiO-66-NH 2 @BiOCl-UTN's heterogeneous nano composites. The activity toward Cr(VI) reduction was tested under visible-light. UiO-66-NH 2 @BiOCl-UTN's heterogeneous nanocomposites exhibited better performance as equated to individual BiOCl and UiO-66-NH 2 , particularly the composite with Bi 3+ mole ratio of 5 mM surpassed other composites for photocatalytic Cr(VI) reduction. Furthermore, boosted visible-light absorption (λ > 420 nm) was observed in the presence of −NH 2 moiety on the organic linker. The excellent photocatalytic activity was attributed to the synergistic effect between BiOCl and UiO-66-NH 2 for the effective separation of photogenerated electron−hole suppressing their recombination. Through active species trapping experiments, electron spin resonance measurements, and electrochemical analysis, the reliable mechanism was predicted and confirmed. Moreover, heterogeneous nanomaterial retained its structure and activity for four consecutive cycles demonstrating its superior stability.