Efficient multifunctional electrocatalyst based on 2D semiconductive bimetallic metal-organic framework toward non-Pt methanol oxidation and overall water splitting

As the efficient approaches for obtaining clean H₂ energy, methanol oxidation (MOR) and water over slitting reactions have been increasingly essential. A series of novel semiconductive CoNi bimetal–organic framework (CoₓNi₃₋ₓ(HAB)₂ MOF) have been prepared using hexaaminobenzene (HAB) as an organic linker. The obtained series of CoₓNi₃₋ₓ(HAB)₂ MOFs were then explored as efficient multifunctional electrocatalysts for the non-Pt MOR and overall water splitting in alkaline medium. The basic characterizations of CoₓNi₃₋ₓ(HAB)₂ MOFs revealed that they comprised multiple metal valence states (Co⁰/Co²⁺/Co³⁺ and Ni²⁺/Ni³⁺) and graphene-like nanostructures embedded with abundant CoNi alloy nanoparticles. Compared with the sole-metal MOFs (Co₃(HAB)₂ MOF and Ni₃(HAB)₂ MOF), the CoₓNi₃₋ₓ(HAB)₂ MOF with a mass ratio of Co:Ni = 1:3 (CoₓNi₃₋ₓ(HAB)₂ MOF-2) exhibited superior electrocatalytic performance for MOR. It gave a high current density of 92.8 mA cm⁻² at 1.6 V vs. reversible hydrogen electrode (RHE) for MOR, along with the low overpotentials at the current density of 10 mV cm⁻² (η₁₀) and Tafel slopes toward hydrogen evolution reaction (η₁₀ = 119 mV, Tafel slope = 46 mV dec⁻¹) and oxygen evolution reaction (η₁₀ = 1.35 V, Tafel slope = 26 mV dec⁻¹). The analysis on the catalysis mechanism of MOR and water splitting in alkaline medium was also proposed. The voltages applied to the three- and two-electrode systems based on the bifunctional CoₓNi₃₋ₓ(HAB)₂ MOF-2 catalyst for overall water splitting are 1.52 V vs. RHE and 1.45 V vs. silver/silver chloride (Ag/AgCl), respectively. This work provides a novel strategy for investigating the applications of promising two-dimensional semiconductive MOF as multifunctional electrocatalysts with boosted electrocatalytic activities in energy fields.