Fully exposed edge/corner active sites in Fe substituted-Ni(OH)2 tube-in-tube arrays for efficient electrocatalytic oxygen evolution

• The am -Ni(OH) 2 can be transformed into so -Fe-Ni(OH) 2 , which contains abundant active edge/corner sites. • The special so -Fe-Ni(OH) 2 tube-in-tube arrays (TTAs) can accelerate the reaction kinetics of OER. • The so -Fe-Ni(OH) 2 TTAs can facilitate the formation of O radicals, which is crucial for efficient OER. • The so -Fe-Ni(OH) 2 TTAs show excellent OER electrocatalytic performance. The tremendous works focusing on long-range ordered hydroxides have ignored the investigation of the edge/corner sites in hydroxides, which is recently believed to be crucial for electrocatalytic activity enhancement of oxygen evolution reaction (OER). In this study, by anodic galvanostatic treatment in (NH 4 ) 2 Fe(SO 4 ) 2 solution, the amorphous Ni(OH) 2 ( am -Ni(OH) 2 ) is transformed into a short-range ordered Fe substituted-Ni(OH) 2 ( so -Fe-Ni(OH) 2 ), which contains abundant electroactive edge/corner sites. To further enhance surface area, the special tube-in-tube arrays (TTAs) are fabricated for so -Fe-Ni(OH) 2 to accelerate the reaction kinetics of OER. From DFT calculation, the low-coordinated defect sites with Fe-Ni-Fe units caused by the short-range ordered structure of so -Fe-Ni(OH) 2 TTAs facilitate the formation of adsorbed oxygen, which is rate-determining step for efficient OER. The so-Fe-Ni(OH) 2 TTAs show higher OER performance than long-range ordered Fe substituted-Ni(OH) 2 ( lo -Fe-Ni(OH) 2 ). This study will provide a new strategy for electroactive edge/corner-site engineering of hydroxide-based electrocatalysts for efficient OER.