CO2 reduction intermediates with in-situ SFG spectroelectrochemistry
Gaia Neri a, Paul Donaldson b, Gilberto Teobaldi b, Alexander J Cowan a
a Department of Chemistry, University of Liverpool, Crown Street, Liverpool, Liverpool, United Kingdom
b Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, OX11 0QX
Poster, Gaia Neri, 006
Publication date: 7th June 2020

Research into new, efficient catalysts for the electrochemical reduction of CO to fuels is a major challenge in the field of renewable energy. Study of the mechanisms of electrocatalysis is key in order to rationally modify catalysts to improve their performance, however the complicated nature of the double layer and the surface interactions involved during catalysis make these studies challenging.

Vibrational sum frequency generation (VSFG) spectroscopy is a powerful technique, as it is intrinsically surface specific, and allows detection of surface species in submonolayer concentrations. We have successfully applied this technique to the study of a few well-known group 6 and 7 molecular catalysts for electrochemical CO2 reduction.

Mo(bpy)(CO)4 is an efficient CO2 reduction homogeneous electrocatalyst.1,2 It has been found that the onset for catalysis is highly dependent on the working electrode material, with CO2 reduction on Au occurring ca. 300 mV earlier than on Pt and GCE. We have investigated the mechanism of CO2 reduction by Mo(bpy)(CO)4 on Au and Pt electrodes using in situ VSFG spectroelectrochemistry (SEC-VSFG).3 The technique is highly surface selective, allowing the identification of species forming at the electrochemical interface during CV measurements. Our results indicate that on Au the active catalyst is formed via a second pathway following the formation of the intermediate [Mo(bpy)(CO)4]•-, and that the degree of interaction of [Mo(bpy)(CO)4]•- and the electrode material is the controlling factor for enabling the lower energy pathway. Our study demonstrates the viability of Mo(bpy)(CO)4 and analogue group 6 complexes as efficient CO2 reduction catalysts, by careful modification of the reaction conditions such as electrode material, solvent and electrolyte salt.

Mn(bpy)(CO)3Br and its derivatives is one of the most widely studied class of catalysts due to their high selectivity for CO, high turnover frequency, ease of synthesis and low cost of the metal centre. Most studies involving these type of complexes use aprotic solvents with the addition of an acid.

The mechanism of Mn(bpy)(CO)3Br has been studied both experimentally and computationally, and two main pathways have been identified, however some of the key intermediates have not been experimentally observed. We have used SEC-VSFG to study the catalyst under operating conditions. We have studied the catalyst with a range of added acids and were able to: 1)rationalize the high selectivity of Mn(bpy)(CO)3Br towards CO, 2)observe a previously undetected reaction intermediate,4 and 3)find evidence for the much debated “dimer mechanism”.5

We would like to thank the  EPSRC (EP/K006851/1) and the STFC for their financial support.

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