## 3 Results and Discussion  
It was found that Ni atoms are octahedrally coordinated by six O atoms, and the resulting pseudo-octahedra are interconnected to form a metal layer. The adjacent Ni layers are separated by terephthalatic acids, with an interlayer distance of 3.5 A on the (200) facet. Meanwhile, Co adopts a regular [CoN\({}_{4}\)] tetrahedral geometry to form ZIF-L, which contains a large zero-dimensional pore (cavity) well-suited for accommodating CO\({}_{2}\) molecules. Powder X-ray diffraction (PXRD) analysis (scan range: 5-70\({}^{\circ}\), step size: 5\({}^{\circ}\)/min) confirms that the pure Ni-MOF nanoarray shares an identical crystalline structure with the previously reported monoclinic Ni\({}_{2}\)(OH)\({}_{2}\)BDC MOF [40] As shown in Figure 2a, the four diffraction peaks can be indexed to the (200) and (001) crystallographic planes. After growing ZIF-L onto Ni-MOF, additional peaks corresponding to the (112), (220), and (004) lattice planes of ZIF-L appear in the heterojunction, further demonstrating the high crystallinity of both Ni-MOF and ZIF-L [41]. TEM images reveal that the Ni-MOF nanoarray is grown vertically on carbon paper, with a thickness of \(\sim\)10 nm and a diameter of \(\sim\)1.2 \(\upmu\)m (not mm). As shown in Figure 2b, rod-like ZIF-L with a diameter of \(\sim\)50 nm is grown on the Ni-MOF surface, forming the Ni-MOF@ZIF-L heterojunction. The ZIF-L grows preferentially along the (001) direction on the (200) plane of Ni-MOF, consistent with the XRD results. The hierarchical structure, composed of sheet-like Ni-MOF and rod-like ZIF-L, is clearly visible in the TEM image (Figure 2c). High-resolution TEM further reveals distinct lattice fringes corresponding to the Ni-MOF (001) plane and the ZIF-L (004) plane, with a sharp interface between them [42; 43]. Elemental mapping analysis shows homogeneous distributions of Ni and O in the Ni-MOF core and Co and N in the ZIF-L shell, confirming the uniform coating of ZIF-L on the Ni-MOF surface (Figure 2d). Energy-dispersive EDS and inductively coupled plasma optical emission spectrometry (ICP-OES) reveal a Ni:Co atomic ratio of \(\sim\)3:2, further verifying the successful formation of the Ni-MOF@ZIF-L heterojunction. The porous structure of the heterojunction was evaluated by N\({}_{2}\) adsorption-desorption measurements. As shown in Figure 2e, N\({}_{2}\) adsorption-desorption tests indicate that the excellent porous properties of ZIF-L itself (with a BET-specific surface area of 231.5 cm\({}^{3}\) g\({}^{-1}\)) are inherited by the heterojunction (the BET-specific surface area of Ni-MOF@ZIF-L is 185.7 cm\({}^{3}\) g\({}^{-1}\)). The pore-size distributions are predominantly in the range of 2-4 nm (Figure 2d, inset), further confirming the hierarchically micro- and mesoporous structure of the heterojunction, which provides ample storage spaces and active contact sites for CO\({}_{2}\). The soft cushion-type cavities in the ZIF-L shell can adaptively accommodate CO\({}_{2}\) molecules, and the strong interactions (such as hydrogen bonds) between 2-methylimidazole ligands and CO\({}_{2}\) can \"anchor\" CO\({}_{2}\) to increase its concentration near the catalyst. Meanwhile, the heterojunction interface formed by Ni-MOF and ZIF-L generates a synergistic effect, optimizing active sites and promoting adsorption from multiple dimensions. As shown in Figure 2f, due to the highly dense metal layer structure, Ni-MOF has almost no porosity, resulting in low CO\({}_{2}\) adsorption capacity, which significantly limits CO\({}_{2}\) adsorption. In contrast, Ni-MOF@ZIF-L achieves more efficient CO\({}_{2}\) adsorption and enrichment than Ni-MOF by virtue of its porous structure, shell function, and interfacial synergy. Figure 2g shows a typical photograph of carbon paper and these MOF arrays. It was found that ZIF-L and Ni-MOF@ZIF-L possess hydrophobic properties with external water contact angles of 138.7 and 132.3\({}^{\circ}\), while the hydrophilic Ni-MOF shows a contact angle of only 26.3\({}^{\circ}\).