Semihydrogenation of trace acetylene in an ethylene gas stream is a vital step for the industrial production of polyethylene, in which Pd single-site catalysts (SSCs) have great potential. Herein, two Pd SSCs with different coordination structures are prepared on hierarchical nitrogen-doped carbon nanocages (hNCNC) by regulating the nitrogen species with or without using dicyandiamide. With using dicyandiamide, the obtained Pd₁-N_dicy/hNCNC SSC features the coordinated Pd by two pyridinic N and two pyrrolic N ( ${\text{PdN}}_{\text{2}}^{\text{py}}{\text{N}}_{\text{2}}^{\text{pr}}$). Without using dicyandiamide, the obtained Pd₁/hNCNC SSC features the coordinated Pd by pyridinic N and C ( ${\text{PdN}}_x^{\text{py}}{\text{C}}_{\text{4}-x}$, x = 1–4). The former exhibits an 18-fold increase in catalytic activity compared to the latter. Theoretical results reveal the abundant unoccupied orbital states above the Fermi level of ${\text{PdN}}_{\text{2}}^{\text{py}}{\text{N}}_{\text{2}}^{\text{pr}}$ moiety, which can facilitate the activation of substrate molecules and dynamics of acetylene hydrogenation as supported by the combined theoretical and experimental results. In addition, the ${\text{PdN}}_{\text{2}}^{\text{py}}{\text{N}}_{\text{2}}^{\text{pr}}$ moiety presents a favorable desorption of ethylene. Consequently, the Pd₁-N_dicy/hNCNC SSC exhibits high C₂H₂ conversion (99%) and C₂H₄ selectivity (87%) at 160 °C. This study demonstrates the impact of Pd single-site coordination structure on catalytic performance, which is significant for the rational design of advanced Pd SSCs on carbon-based supports.

Glycerol is an alternative sustainable fuel for fuel cells, and efficient electrocatalyst is crucial for glycerol oxidation reaction (GOR). The promising Pt catalysts are subject to the inadequate capability of C–C bond cleavage and the susceptibility to poisoning. Herein, Pt-Sn alloyed nanoparticles are immobilized on hierarchical nitrogen-doped carbon nanocages (hNCNCs) by convenient ethylene glycol reduction and subsequent thermal reduction. The optimal Pt₃Sn/hNCNC catalyst exhibits excellent GOR performance with a high mass activity (5.9 A·mg_Pt⁻¹), which is 2.7 and 5.4 times higher than that of Pt/hNCNC and commercial Pt/C, respectively. Such an enhancement can be mainly ascribed to the increased anti-poisoning and C–C bond cleavage capability due to the Pt₃Sn alloying effect and Sn-enriched surface, the high dispersion of Pt₃Sn active species due to N-participation, as well as the high accessibility of Pt₃Sn active species due to the three-dimensional (3D) hierarchical architecture of hNCNC. This study provides an effective GOR electrocatalyst and convenient approach for catalyst preparation.

The cathode of lithium-oxygen (Li-O₂) batteries should have large space for high Li₂O₂ uptake and superior electrocatalytic activity to oxygen evolution/reduction for long lifespan. Herein, a high-performance MnO_x/hCNC cathode was constructed by the defect-induced deposition of manganese oxide (MnO_x) nanoparticles on hierarchical carbon nanocages (hCNC). The corresponding Li-O₂ battery (MnO_x/hCNC@Li-O₂) exhibited excellent electrocatalytic activity with the low overpotential of 0.73‒0.99 V in the current density range of 0.1‒1.0 A·g^–1. The full discharge capacity and cycling life of MnO_x/hCNC@Li-O₂ were increased by ~86.7% and ~91%, respectively, compared with the hCNC@Li-O₂ counterpart. The superior performance of MnO_x/hCNC cathode was ascribed to (i) the highly dispersed MnO_x nanoparticles for boosting the reversibility of oxygen evolution/reduction reactions, (ii) the interconnecting pore structure for increasing Li₂O₂ accommodation and facilitating charge/mass transfer, and (iii) the concealed surface defects of hCNC for suppressing side reactions. This study demonstrated an effective strategy to improve the performance of Li-O₂ batteries by constructing cathodes with highly dispersed catalytic sites and hierarchical porous structure.

Novel hierarchical carbon nanocages (hCNCs) are proposed as high-rate anodes for Li- and Na-ion batteries. The unique structure of the porous network for hCNCs greatly favors electrolyte penetration, ion diffusion, electron conduction, and structural stability, resulting in high rate capability and excellent cyclability. For lithium storage, the corresponding electrode stores a steady reversible capacity of 970 mAh·g^-1 at a rate of 0.1 A·g^-1 after 10 cycles, and stabilizes at 229 mAh·g^-1 after 10, 000 cycles at a high rate of 25 A·g^-1 (33 s for full-charging) while delivering a large specific power of 37 kW∙kg_electrode^–1 and specific energy of 339 Wh∙k_gelectrode^–1. For sodium storage, the hCNC reaches a high discharge capacity of ~50 mAh·g^-1 even at a high rate of 10 A·g^-1.