Disclosing CO2 Activation Mechanism by Hydroxyl-Induced Crystalline Structure Transformation in Electrocatalytic Process

The activation of CO2 on the electrocatalyst surface is regarded as the rate-determining step in electrocatalytic CO2 reduction (ECR), and it is therefore highly important to find out its adsorption and activation mechanism. Herein, we develop the OH--coordinated metal-organic framework (NNU-15) to simulate the surface state of catalyst in alkaline environment of ECR and then further explore its activation mechanism to CO2. NNU-15 shows high faradic efficiency for CO (FECO) reaching up to 99.2% at -0.6 V versus RHE along with long-term stability (110 h) and surpassing 96% over a wide potential range from -0.6 to -0.9 V. In the ECR process, single-crystal to single-crystal transformation between NNU-15 and NNU-15-CO2 demonstrates that coordinated OH- can activate the CO2 into HCO3-, which will chelate to the metal center. Theoretical calculations validate that both O-adsorbed and C-adsorbed initial geometries are inclined to result in the formation of HCO3- during the ECR process.