A Honeycomb-Like Porous Crystalline Hetero-Electrocatalyst for Efficient Electrocatalytic CO₂ Reduction.

Abstract

Porous heterostructured electrocatalysts with multifunctionality and synergistic effect have much benefit for efficient electrocatalytic CO₂ reduction reaction (CO₂ RR), yet it still remains a daunting challenge to explore heterostructures based on covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) in this field. Here, a series of honeycomb-like porous crystalline hetero-electrocatalysts (MCH-X, X = 1-4, X stands for the numbered sample obtained from different MOF doses in the synthesis of the MCH) are synthesized, and these are successfully applied in electrocatalytic CO₂ RR. The specially designed heterostructures with integrated porous MOF-template and ultrathin COF-coating enable efficient CO₂ adsorption/activation and conversion into CH₄ . The best of them, MCH-3, shows greatly inhibited H₂ evolution, excellent current density (-398.1 mA cm^-2 ), and superior <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics> <mrow><msub><mtext>FE</mtext> <msub><mtext>CH</mtext> <mn>4</mn></msub> </msub> </mrow> <annotation>${\rm{F}}{{\rm{E}}_{{\rm{C}}{{\rm{H}}_4}}}$</annotation></semantics> </math> (76.7%) to the physical mixture (38.0%), the MOF@COF without the honeycomb-like morphology (47.7%), and the bare COF (37.5%) and MOF (15.9%) at -1.0 V. Based on the density functional theory calculations and various characterizations, the vital roles of the MOF in facilitating CO₂ adsorption/activation, stabilizing intermediates, and conquering the energy barrier of rate-determining step are intensively studied.