A CO2 adsorption-enhanced semiconductor/metal-complex hybrid photoelectrocatalytic interface for efficient formate production

Abstract

In photoelectrochemical CO₂ conversion, the concentration of fixed CO₂ on the photocathode surface is of primary concern. Herein, a CO₂ adsorption-enhanced semiconductor/metal-complex hybrid photoelectrocatalytic interface was established by utilizing a carbon aerogel as the CO₂ fixation substrate. In CO₂ reduction photoelectrocatalysis, Co₃O₄ was employed as the light harvester, and Ru(bpy)₂dppz was utilized as the electron transfer mediator and CO₂ activator. The CO₂ surface concentration exhibited a 380-fold increase on this hybrid interface than that on Co₃O₄/FTO. The CO₂ conversion to formate occurred at an onset potential of −0.45 V (vs. normal hydrogen electrode, NHE) under photoelectrochemical conditions, 160 mV more positive than its thermodynamic redox potential. At an applied potential of −0.60 V (vs. NHE), the selectivity of the formate yield reached 99.95%, with a production rate of approximately 110 μmol cm⁻² h⁻¹ and a Faradaic efficiency of 86%. Such a conversion has an electron transfer rate of 2.94 × 10⁻³ cm s⁻¹. The CO₂ conversion to formate was confirmed to be an instantaneous proton-coupled electron transfer process, originating from the rapid photoelectrochemical activation of bpy and dppz in Ru(bpy)₂dppz as well as the synergic effect of the promoted CO₂ adsorption and the applied molecular catalysis.