Metal-organic-frameworks passivated CuBi2O4 photocathodes boost CO2 reduction kinetics

Photoelectrochemical reduction of CO₂ to produce CO with metal-organic frameworks (MOFs) is recognized as a desirable technology to mitigate CO₂ emission and generate sustainable energy. To achieve highly efficient electrocatalyst, it is essential to design a new material interface and uncover new reaction mechanisms or kinetics. Herein, we developed two metal-organic Cu-MOF and Bi-MOF layers using benzene tricarboxylic acid (H₃BTC) ligands on CuBi₂O₄ photocathodes. Both MOF layers drastically improved the photoelectrochemical stability by suppressing the photo-corrosion through conformal surface passivation. The Cu-MOF modified CuBi₂O₄ showed more significant charge separation and transfer efficiencies than the Bi-MOF modified control. Based on the transient photocurrent curves under the applied potential of 0.6 V vs. RHE, the rate-law analysis showed the CO₂ photoreduction took place through a first-order reaction. Further, the photoelectrochemical impedance spectra (PEIS) revealed this reaction order, representing an “operando” analysis. Moreover, the reaction rate constant on Cu-MOF modified sample was higher than that on Bi-MOF modified one and bare CuBi₂O₄. Combined with the density functional theory calculation, the surface absorption of CO₂ and CO molecules and the higher energy barrier for ∗COOH intermediates could significantly determine the first order reaction.