Sulfidation and NaOH etching in CoFeAl LDH evolved catalysts for an efficient overall water splitting in an alkaline solution.

In this study, a hierarchical interconnected porous metal sulfide heterostructure was synthesized from CoFeAl layered double hydroxides (LDHs) by a two-step hydrothermal process (sulfidation and a NaOH etching process). Among the as-made samples, the CoFeAl-T-NaOH electrode exhibited excellent oxygen and hydrogen evolution reaction catalytic activities with overpotentials of 344 mV and 197 mV at the current density of 100 mA cm, respectively. Meanwhile, small Tafel slopes of 57.7 mV dec and 106.5 mV dec for water oxidation and hydrogen evolution were observed for the CoFeAl-T-NaOH, respectively. Serving as both the cathode and anode for overall water splitting, the CoFeAl-T-NaOH electrode reached a current density of 10 mA cm at a cell voltage of 1.65 V with excellent stability. The enhanced electrocatalytic activity could be attributed to: the hierarchical interconnected nanosheet structure facilitating mass transport; the porous structure promoting electrolyte infiltration and reactant transfer; the heterojunction accelerating charge transfer; and the synergistic effect between them. This study offered a new clue for synthesizing porous transition-metal based heterojunction electrocatalysts with a careful tuning of the sequence of sulfuration and alkaline etching to enhance the electrocatalytic performance.