Selenium phosphorus co-doped cobalt oxide nanosheets anchored on Co foil: A self-supported and stable bifunctional electrode for efficient electrochemical water splitting

The design of inexpensive, efficient, durable and self-supported bifunctional electrodes for simultaneously catalyzing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the same electrolyte is essential for renewable energy conversion processes and future sustainable development, however, it still remains a challenging issue. Reported herein is the first example of selenium phosphorus co-doped cobalt oxide nanosheets on highly conductive Co foil collector (CoOSeP@Co foil), fabricated by successively selenylation and phosphorization of a pre-oxidized Co foil, as a novel bifunctional electrode for water electrolysis. Due to the improved intrinsic catalytic activity of cobalt oxide derived from doping and the strong interaction between active CoOSeP nanosheets and highly conductive Co foil collector, the designed CoOSeP@Co foil integrated electrode displays favorable catalytic activities towards both HER and OER in strongly alkaline media, achieving an electrocatalytic current density of 10 mA cm⁻² at a low overpotential of 155 mV for HER and 347 mV for OER, respectively. Beyond that, the electrode could keep working and maintain its catalytic activity for at least 30 h. Furthermore, an alkaline electrolyzer constructed by employing CoOSeP@Co foil as an integrated bifunctional electrode in both the cathode and anode can generate 10 mA cm⁻² at a cell voltage of 1.74 V and shows good long-term stability of more than 30 h. This work not only opens a new avenue to improve the intrinsic catalytic activity of materials by co-doping with heteroatoms, but also brings us a new idea for designing other cost-effective, self-supported, efficient and robust overall water splitting electrodes.