A new strategy of building covalently MOF–COF core–shell heterostructure with MOFs without –NH ₂ group for improved photocatalytic hydrogen evolution under visible light irradiation.

Highly active and earth-abundant catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) play vital roles in developing efficient water splitting to produce hydrogen fuels. Here, we reported an effective strategy to fabricate a completely new nitrogen-doped MoS₂/COF-C₄N vertical heterojunction (N-MoS₂/COF-C₄N) as precious-metal-free bifunctional electrocatalysts for both HER and OER. Compared with MoS₂ and COF-C₄N, the obtained vertical N-MoS₂/COF-C₄N catalyst showed enhanced HER with a low overpotential of 106 mV at 10 mA cm⁻², which is six times lower than MoS₂. The superior acidic HER activity, molecular mechanism, and charge transfer characteristic of this vertical N-MoS₂/COF-C₄N were investigated experimentally and theoretically in detail. Its basic OER activity is almost equal to that of COF-C₄N with an overpotential of 349 mV at 10 mA cm⁻², which showed that the in-situ growing method maintains the exposure of the C active sites to the greatest extent. The preparation and investigation for vertical N-MoS₂/COF-C₄N provide ideas and a research basis for us to further explore promising overall water-splitting electrocatalysts.