Amorphous CoFe(OH)x hollow hierarchical structure: an efficient and durable electrocatalyst for oxygen evolution reaction

Developing novel earth-abundant electrocatalysts with highly efficient and durable activity for oxygen evolution reaction (OER) is in great demand in the clean hydrogen production. Herein, an amorphous mixed cobalt-iron hydroxide (CoFe(OH)x) with uniform hollow hierarchical structure is exploited and applied in OER. The amorphous structure can supply abundant defects and reaction sites, and the hollow hierarchical microspheres with numerous vertically grown nanosheets on the shell can provide sufficient contact between electrolyte and active species, thus exposing abundant accessible active sites for electrocatalysis. As a result, the as-prepared CoFe(OH)x exhibits a superior electrocatalytic OER activity in alkaline medium with a low overpotential of 293 mV at current density of 10 mA cm-2 and a small Tafel slope of 67.4 mV dec-1. The CoFe(OH)x also shows significantly enhanced OER activity compared to Co(OH)2 owing to the optimized electronic structure and conductivity tuned by the introduction of Fe. The turnover frequency of CoFe(OH)x (55.7×10-3 s-1) is 8.8 times larger than that of Co(OH)2 (6.3×10-3 s-1). This work paves a way for rational design of hollow structured bimetal hydroxides with enhanced electrocatalytic performance.