Revealing the structure–activity relationship of two Cu-porphyrin-based metal–organic frameworks for the electrochemical CO2-to-HCOOH transformation

Abstract

The eCO₂RR activity is correlated to the internal structural character of the catalyst. We employed two types of structural models of porphyrin-based MOFs of PCN-222(Cu) and PCN-224(Cu) into heterogeneous catalysis to illustrate the effect of structural factors on the eCO₂RR performance. The composite catalyst PCN-222(Cu)/C displays better activity and selectivity (η = 450 mV, FE_HCOOH = 44.3%, j = 3.2 mA cm⁻²) than PCN-224(Cu)/C (η = 450 mV, FE_HCOOH = 34.1%, j = 2.4 mA cm⁻²) for the CO₂ reduction to HCOOH in the range of −0.7–−0.9 V (vs. RHE) due to its higher BET surface area, CO₂ uptake, and a larger pore diameter. It is interesting that PCN-224(Cu)/C displays better performance in the range of −0.4–−0.6 V (vs. RHE) due to its greater heat of adsorption, Q_st and a higher affinity for CO₂ molecule, which could promote the capture of CO₂ onto the exposed active sites. As a result, PCN-224(Cu)/C exhibits better stability for the long-term electrolysis.