Large-area freestanding 2D Ni/Co vertical heterostructures with strong interfacial coupling for efficient oxygen evolution reaction

Designing vertical heterostructures from 2D ultrathin nanosheets provides an effective pathway to improve energy conversion performance by maximizing the density of accessible catalytic sites, enabling efficient interfacial charge migration and inducing favorable electronic band alignment. Such electronic and structural modifications collectively regulate the adsorption energies of key intermediates, thereby reducing the energy barriers governing the oxygen evolution reaction (OER). Achieving anisotropic crystal growth by disrupting lattice symmetry remains a key challenge for non-layered systems. For transition metal hydroxides, it is crucial to tackle issues such as disordered stacking, synthesis complexity, structural fragility, and insufficient interfacial integration. Herein, we synthesized ultrathin 2D nickel/cobalt hydroxide vertical heterostructures through a wet-chemical synthesis approach. The obtained free-standing vertical heterostructures were subsequently utilized as an active electrocatalyst for the OER. The electrocatalyst delivered an overpotential (η) of 364 mV (vs. RHE) at 10 mA cm^-2, along with a Tafel slope of 70 mV dec^-1, reflecting efficient reaction kinetics. DFT analysis indicates that interfacial interaction between the layers is the key parameter for OER activity. This combined experimental and theoretical work demonstrates an effective approach for designing 2D heterointerface-based electrocatalysts with enhanced performance and maximized material utilization.