The built-in electric field at the heterogeneous interface makes FeCoNi LDH in p–n heterojunction FeCoNi LDH/CuO more positively charged, which is more favorable for the adsorption of OH⁻, leading to the promoted OER activity in the alkaline media.

The electrons transfer from Cu ₂ O to NiCo ₂ O ₄ with the formation of Cu–O bonds at the interface of the NiCo ₂ O ₄ /Cu _x O, making parts of the relatively inert Cu( i ) into the active Cu( ii ) and introducing abundant new active sites.

The effectiveness of the tandem catalysts was verified by a combination of Co ₉₈ Ce ₂ for low temperature reactions and Co ₁₅ Ce ₈₅ for high temperature reactions.