Decoding Short‐Range Order in Amorphous Two‐Dimensional Nanosheets for Efficient and Durable Ampere‐Level Seawater Electrolysis: A Case Study of Amorphous Ni(OH)2

ABSTRACT Amorphous nanomaterials, once considered structurally disordered, are now recognized for exceptional catalytic performance, yet their atomic‐scale origins remain elusive. Here, we combine atom probe tomography (APT), theoretical simulation, and operando spectroscopy to reveal the hidden architecture of amorphous Ni(OH) 2 nanosheets (a‐Ni(OH) 2 NSs)—a highly active and durable catalyst for alkaline seawater electrolysis. As cathodes in anion exchange membrane water electrolyzers, a‐Ni(OH) 2 NSs deliver a remarkably low cell voltage of 1.89 V at 1.0 A cm − 2 , outperforming crystalline Ni(OH) 2 (2.53 V) and commercial Pt/C (2.39 V), while sustaining over 1000 h of stable operation with negligible decay (<0.02 mV h −1 ). APT enables 3D, atom‐by‐atom mapping—including hydrogen—revealing four distinct short‐range order (SRO) motifs with thickness‐dependent distributions. These motifs act synergistically: surface O–Ni–OH SROs promote water dissociation, interior Ni–OH SROs optimize proton reduction, and bridging O–Ni–O and Ni–OH 2 SROs accelerate proton transport via hydrogen‐bond networks. This coordinated motif network fully accounts for the exceptional performance, transforming the view of amorphous materials from “black boxes” to atomically designable systems. Our findings establish APT as a transformative platform for uncovering functional motifs in amorphous catalysts, paving the way for rational design of next‐generation materials for sustainable energy conversion.