The rational design of the catalysts with easily-accessible surface and high intrinsic activity is desirable for electrocatalytic hydrogen evolution reaction (HER). Here, we reported the construction of two-dimensional (2D) Co-Mo nitrides based heterojunctional catalyst for efficient HER based on a “mediated molecular” assisted route. The 2D Co(OH)₂ sheet reacted partially with the “mediated molecular” (2-methylimidazole (2-MIM)) to form zeolitic imidazolate framework (ZIF)-67 at surface, giving ZIF-67/Co(OH)₂ sheets. The ZIF-67 combines with [PMo₁₂O₄₀]³⁻ cluster (PMo₁₂) due to the interaction of mediated molecular with PMo₁₂, producing 2D Mo-Co-2MIM/Co(OH)₂ bimetallic precursor. After controlled nitriding, the Mo₂N islands dispersed on 2D porous Co-based sheets were formed. A series of characterizations and density functional theory (DFT) calculation indicated the formation of a close contact interface, which promotes the electron transfer between Mo and Co components, enhances the electron migration/redistribution and redistribution and down-shift of d-band center and thus gives a high intrinsic activity. The 2D characteristics make the catalyst more accessible contact sites, which is favourable to promot the HER. The tests showed that the optimized catalyst exhibits an onset potential of 0 mV and an overpotential of 10 mA·cm⁻² at 35.0 mV, which is quite close to that of Pt/C catalyst. It also exhibits an activity superior to Pt/C at high current density (> 100 mA·cm⁻²). A good stability of the catalyst was achieved with no significant decay for 100 h of continuous operation. The electrolytic cell composed of optimized catalyst and P-NiFe-layered double hydroxide (LDH) can be driven by low voltage (only 1.47 V) to reach a current density of 10 mA·cm⁻².

Development of cost-effective and highly-efficient bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts is crucial for overall water splitting in practical utilization. Herein, we proposed a novel non-noble metal bifunctional HER/OER electrocatalyst by synergistically coupling a dual-active Co-based heterojunction (Co-CoO) with high conductive and stable two-dimensional Ti₃C₂-MXene (defined as Co-CoO/Ti₃C₂-MXene). A series of characterizations and theoretical calculations verify that the synergistic effect of metallic Co with HER activity and CoO with OER performance leads to superb bifunctional catalytic performance, and Ti₃C₂-MXene can enhance electrical conductivity and prevent the aggregation of the Co-based catalysts, thereby improving both the activity and stability. Co-CoO/Ti₃C₂-MXene presents low onset potential (η_onset) of 8 mV and Tafel slope of 47 mV·dec⁻¹ for HER (close to that of Pt/C) and η_onset of 196 mV and Tafel slope of 47 mV·dec⁻¹ for OER (superior to that of RuO₂). Assembled as an electrolyzer, Co-CoO/Ti₃C₂-MXene shows a low voltage of 1.55 V at 10 mA·cm⁻², high Faradaic efficiency and remarkable stability. It can be driven by a solar cell of ~ 1.55 V for consecutive production of hydrogen and oxygen gases.