Electrocatalytic Hotspots in Hierarchical Structures with Ion-Pump Effect Enable High-Selectivity Synthesis of...

The catalytic hotspot effect is a well-documented phenomenon in photocatalysis, referring to regions with higher catalytic activity at the mesoscale. Whether analogous effect exists in electrocatalysis presents an intriguing question worthy of exploration. In this work, hierarchical NiCo₂O₄ catalysts with needle-like, rod-like, sheet-like, and bulk-like morphologies were synthesized and used to explore the hotspot effect in electrocatalysis. The needle-like hierarchical catalyst demonstrated optimal performance, achieving a 93% yield of 2,5-furandicarboxylic acid (FDCA) from 5-hydroxymethylfurfural in neutral electrolyte, comparable to alkaline conditions, while other morphologies yielded less than 40%. In situ Raman spectroscopy revealed that the exceptional catalytic performance stems from a localized high-pH environment on the surface of the needle-like catalyst. Finite element simulations reveal that the high pH environment is related to high density of corner sites where the electric field is highly concentrated, resulting in formation of catalytic hotspots. These hotspots can play a role of ion pumps by attracting anions ions which subsequently diffuse into the surrounding regions. The ion pump effect establishes an alkaline local microenvironment which greatly boosts FDCA yield. This work demonstrates that the surface microenvironment of heterogeneous electrocatalysts can be modulated by hotspot engineering, and thus offers a new strategy for catalyst design.