NiCo-Layered Double Hydroxides as Tunable Electrocatalysts for Efficient Alkaline Oxygen Evolution Electrocatalysis

The oxygen evolution reaction (OER) is a major kinetic bottleneck in alkaline water electrolysis, motivating the development of efficient, durable, and cost-effective electrocatalysts. This review critically examines NiCo layered double hydroxides (NiCo-LDHs) as earth-abundant OER precatalysts, emphasizing how synthesis, structural modification, and operando reconstruction govern catalytic performance. Reported design strategies are evaluated according to the key limitations they address, including insufficient active-site accessibility, suboptimal intrinsic activity, poor electrical conductivity, restricted mass transport, uncontrolled reconstruction, and limited scalability. The crystal chemistry, interlayer structure, and anodically induced transformation of NiCo-LDHs into catalytically active Ni/Co oxyhydroxide-like phases are discussed as a basis for understanding structure-activity relationships. Major synthesis and modification approaches, including morphology control, heteroatom doping, defect engineering, conductive-support integration, interface engineering, and heterostructure formation, are critically compared in terms of activity, transport, durability, fabrication complexity, and structural stability. Particular emphasis is placed on post-OER, in situ, and operando characterization for identifying working-state structures. Finally, challenges in electrochemical benchmarking, metal dissolution, substrate effects, long-term stability, and scalable fabrication are assessed, providing design principles for advancing NiCo-LDH-based electrodes toward practical alkaline water electrolysis.