Nanoscale hetero-structured Co−Co(OH)2 composite/amorphous carbon core/shell bi-functional electrocatalysts electrochemically evolved from metastable hexagonal-phase cobalt for overall water splitting

Bi-functional electrocatalysts suited to alkaline water splitting systems are highly pursued, towards the most realistic application enabled by simplified electrolyzer design and cost-effective operation. Herein, a novel nanocomposite Co−Co(OH)2/C electrocatalyst with nanoscale hetero-structured metastable hexagonal-phase Co (H-Co) crystallites and Co(OH)2 crystallites encapsulated by amorphous carbon shells is developed. We employ a mild thermal decomposition route coupled with in-situ carbon deposition performed at 400 °C to prepare H-Co/C core/shell structured precursor. In a following controllable electrochemical transformation at room temperature the partial conversion of the metastable H-Co to Co(OH)2 leads to the mutual embedding of nanoscale crystalline H-Co and Co(OH)2 confined in the amorphous carbon shells. Taking advantage of the nanowire array morphology, carbon coated core/shell structure, nanoscale size, and the synergistic H-Co and Co(OH)2 bi-components, an outstanding bi-functional electrocatalytic performance for overall water splitting is attained with proved small overpotentials (93 mV for hydrogen evolution reaction, 264 mV for oxygen evolution reaction at 10 mA cm−2).