The Role of Central Metal Atom and Ligand in Transition Metal Based Metal Organic Frameworks for Selective Electrochemical Reduction of CO2 to Value-Added Chemicals

Abstract

Considering the rapid decline of the cost of renewable electrons (wind and solar), electrochemical conversion of carbon dioxide (CO2) to energy-dense or value-added chemicals with high selectivity (Faradaic efficiency >80%) is an increasing economic imperative. Despite the recent optimization efforts on noble, alkali, alkaline-earth and transition metal (TM) based electrocatalysts for efficient CO2 reduction, the rising cost of these metals (esp. noble metals) hinders large-scale commercialization. Recently, research into the electrocatalytic reduction of CO2 has focused on efficient and cost-effective catalysts such as metal-free, organometallic, hetero-atom doped or conducting polymers (1). Alternatively, electrocatalysts containing pyridinium derivatives have been proposed to avoid the overpotentials required for activating of carbon dioxide (via a high energy intermediate radical of CO2 -) and to promote CO2 reduction through successive proton-hydrate transfers (PT-HT) (2-4). To this end, Metal-Organic Framework (MOF) catalysts with central (TM based) heteroatom and surrounding pyridinic or pyrrolic ligands have been prepared and electrochemically characterized for selective CO2 reduction to methanol or carboxylic acids. In this study, the effect of electrolyte pH on reaction selectivity and reaction kinetics via Tafel analysis of the electrocatalysts were determined. Additional variables such as reactant’s partial pressure and phase, and electrolyzer temperature for optimum electrochemical reduction of CO2 will be also be discussed. This presentation will showcase our efforts to tailor electrocatalyst for value added chemicals such as methanol and formic acid. We will present electrochemical data such as Tafel kinetics and Faradaic efficiency in close concert with spectroscopy such as in situ Raman and Synchrotron X-ray Absorption. Acknowledgements: The authors gratefully acknowledge the financial support from arpa.e under the auspices of the REFUELS initiative. This grant lead by Sustainable Innovation (grant # DE-AR0000810) involves the participation of Northeastern University Center for Renewable Energy Technology as a catalyst partner. The authors also acknowledge instrumental support from Thermo Fisher Corp., and access to synchrotron based facility for x-ray absorption spectroscopy at National Synchrotron Light Source-II (NSLS-II) situated in Brookhaven National Laboratory (BNL), Upton, NY, under grant # DE-SC0012704.