A highly stable bifunctional catalyst based on 3D Co(OH)₂@NCNTs@NF towards overall water-splitting

Electrocatalysts with low overpotential and high stability are highly demanded in water-splitting system. The efficiency of water-splitting is largely restricted by the oxygen evolution reaction (OER). Here, we developed a two-step method to prepare 3D porous material through chemical vapor deposition and electrodeposition combined with the first-principles calculations. Ultrathin α-Co(OH)₂ nanosheets grown on the combined substrate of N-doped carbon nanotubes (NCNTs) and nickel foam were fabricated to investigate their electrochemical behaviour. Because of the characteristics of the ultrathin, microporous α-Co(OH)₂ and its derivatives, the 3D Co(OH)₂@NCNTs@NF exhibits outstanding performance as a bifunctional catalyst for water-splitting. The overpotentials to achieve 10 mA cm⁻² current density in 1 M KOH for OER and hydrogen evolution reaction (HER) are 270 mV and 170 mV, respectively. The as-prepared material exhibits superior stability, which generate 10 mA cm⁻² current density in overall water-splitting over 600 h without obvious degradation in 1 M KOH at voltage of 1.72 V vs. RHE. The first-principles calculations reveal that the N-doping not only can effectively enhance the interaction between the substrate and active material (CoOOH), but also modulate the electronic structure of CoOOH to speed up the O₂ releasing during the OER.