Click to edit Master title style Natalia Garcia Rey and Dana D. Dlott University of Illinois at Urbana-Champaign International Symposium on Molecular Spectroscopy 70 th Meeting, Champaign-Urbana Vibrational Sum Frequency Spectroscopy study of the CO 2 electroreduction mediated by ionic liquid-water on Ag

Electrolyzer Energy CO 2 Filter Air H2H2 H2H2 Filtere d Air Fuel Water electrolyser Synthesi s Energ y Efficient CO 2 electroreduction: Recycling CO 2 Production of hydrocarbon fuels CO 2 CO Artificial Photosynthesis o Efficient systems for CO 2 reduction serve a vital role in the renewal fuel generation

CO 2 electroreduction at low-overpotential o Ionic liquid mediated the CO 2 electroreduction into CO at low-overpotential 1,2. o Water increases Faradaic efficiency. H2H2 CO 2 Ionic liquid: EMIM-BF 4 Ag CO H2OH2O (1) Rosen, B. A. et al., Science 2011, 334, 643; (2) Rosen, B. A. et al., J. Electroch. So. 2013, 160, H138.

Vibrational sum frequency spectroscopy synchronized with cell potential allowed us to… o CO produced in the cell from the CO 2. CO adsorbs on Ag but not poisons the electrode  CO stretching mode at IR 2100 cm -1. o The ionic liquid-water-Ag interface controls the CO 2 electroreduction  nonresonant sum frequency at IR 2600 cm -1. o Water concentration shifts the structural orientation to lower potentials  nonresonant sum frequency at IR 2600 cm -1.

Vibrational Sum Frequency Spectroscopy on electrified surfaces  IR  VIS  VSFS resonant E DC VSFS sensitive and selective! OCOC OCOC OCOC OCOC

polarization analyzer lens Ti:sapphire Laser 120 fs 800 nm kHz Rep. rate Ti:sapphire Laser 120 fs 800 nm kHz Rep. rate optical parametric amplifier (OPA) 2.5–16 µm 5µm optical parametric amplifier (OPA) 2.5–16 µm 5µm delay stage 60° Fabry-Perot étalon short-pass filter (738 nm) Ge filter grating slit potentiostat counter electrode reference electrode spectro- graph BBIR NBvis VSFS CC D computer potentiostat computer trigger Pt CO 2 Luggin cappilary Ag/AgCl VSFS-CV setup

onset of CO 2 reduction Ag working electrode negative potential CaF 2 window O C O BF O C O + BF 4 - EMIM + BF4 - O C O inner region diffuse region double layer 25  m electrolyte BF O C O O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H + BF CO 2 electroreduction in situ on cathode mediated by room temperature ionic liquid (RTIL) EMIM- BF 4

onset of CO 2 reduction Ag working electrode negative potential CaF 2 window O C O BF O C O + BF 4 - EMIM + BF4 - O C O inner region diffuse region double layer 25  m electrolyte BF O C O O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H + BF CO 2 electroreduction in situ on cathode mediated by room temperature ionic liquid (RTIL) EMIM- BF 4 OCOC OCOC OCOC OCOC OCOC OCOC OCOC OCOC OCOC OCOC OCOC OCOC Ar CO 2

Resonant VSFS vs Cell Potential CO 2 electroreduction in EMIM-BF 4 / 0.3% H 2 0 / Ag CO stretching mode 22 cm -1 /V *mol% of water

Resonant VSFS vs Cell Potential CO 2 electroreduction in EMIM-BF 4 / 0.3% H 2 0 / Ag CO stretching mode 22 cm -1 /V *mol% of water

Nonresonant VSFS vs Cell Potential CO 2 electroreduction EMIM-BF 4 / 0.3% H 2 0 / Ag Potential vs Ag/AgCl / V OCOC OCOC OCOC  IR  VIS  VSFS

Nonresonant SF vs cell potential: CO 2 electroreduction in EMIM-BF 4 / 0.3% H 2 0 / Ag

Addition of water 130 mV Neat EMIM-BF 4 adding mol % by mol of water cell potential (V)

Click to edit Master title style Take home message o CO 2 electroreduction into CO was observed. A minimum in the nonresonant SF was found at the same potential, -1.33V. o CO was the specie mainly produced, not poisoning the Ag electrode o The structural transition of the water-EMIM-BF 4 on Ag, the double layer, mediated the CO 2 electroreduction. o Increase in water concentration shifts the EMIM-BF 4 on Ag structural transition to a lower cell potentials.

Click to edit Master title style Acknowledgments Prof. Dana D. Dlott Dlott’s group Thank you all for your attention! Any questions?