Mn-Incorporation-Induced Phase Transition in Bottom-Up Synthesized Colloidal Sub-1-nm Ni(OH)2 Nanosheets for Enhanced Oxygen Evolution Catalysis

Sub-1-nm structures are attractive for diverse applications owing to their unique properties compared to those of conventional nanomaterials. Transition-metal hydroxides are promising catalysts for oxygen evolution reaction (OER), yet there remains difficulty in directly fabricating these materials within the sub-1-nm regime, and the realization of their composition and phase tuning is even more challenging. Here we define a binary-soft-template-mediated colloidal synthesis of phase-selective Ni(OH)₂ ultrathin nanosheets (UNSs) with 0.9 nm thickness induced by Mn incorporation. The synergistic interplay between binary components of the soft template is crucial to their formation. The unsaturated coordination environment and favorable electronic structures of these UNSs, together with in situ phase transition and active site evolution confined by the ultrathin framework, enable efficient and robust OER electrocatalysis. They exhibit a low overpotential of 309 mV at 100 mA cm^-2 as well as remarkable long-term stability, representing one of the most high-performance noble-metal-free catalysts.